Bench TalkBench Talk for Design Engineers | The Official Blog of Mouser Electronics Power Delivery Makes Circuit Protection Mandatory,Circuit Protection,Computing,ConnectorsSat, 19 Oct 2019 04:58:00 GMT<p><img alt="USB Power Delivery Makes Circuit Protection Mandatory Theme Image" src="/blog/Portals/11/Keeping_USB_circuit_protection_Theme%20Images.jpg" style="margin-left: 10px; margin-right: 10px; float: left; width: 250px; height: 167px;" title="USB Power Delivery Makes Circuit Protection Mandatory Theme Image" /></p> <p>Circuit protection is like insurance; at best, an afterthought and even when put in place, it often turns out to be insufficient. But while the cost of underinsurance can be enough to threaten the stability of a business, inadequate circuit protection could result in much worse: The loss of human lives.</p> <p>Consider the sobering example of Swissair Flight 111 flying out of JFK International Airport, New York, on September 2, 1998. The plane, a seven-year-old McDonnell Douglas MD-11 carrying 215 passengers and 14 crew members, had recently been fitted with an upgraded inflight entertainment (IFE) system. Fifty-two minutes after take-off, the crew smelled smoke and reported an emergency. Attempting to divert to Halifax, the pilots eventually lost control of the plane when a fire in the ceiling of the cockpit burned through electrical control cables. The aircraft crashed into the ocean 8km off the coast of Nova Scotia, killing all on board.</p> <p>The accident investigation determined the crash was primarily triggered when materials making up part of the IFE, which were supposed to be fire-resistant, caught alight and flames spread to critical control lines. While not definitively established, the source of the fire was believed to be arcing across wires serving the IFE. Though the wires had circuit breakers, the circuit breakers <em>were not designed to trip in response to an arc</em>. Today, such circuits are protected by arc-fault detection devices that do trip when sensing arcs (apart from those generated by normal operation such as switches flipping). Insufficient circuit protection resulted in 229 fatalities.</p> <h2>USB-PD Brings Increased Hazards</h2> <p>While the Swissair MD-11 was brought down by an electrical rather than an electronic fault, electronics engineers are increasingly designing circuits where voltages and currents are sufficient to generate arcing (and potentially life-threatening fires). One example is USB Power Delivery (<a href="" target="_blank">USB-PD</a>); this is an upgraded version of USB, which allows for higher voltages and currents, up to a maximum of 20V and 5A (for 100W maximum power). USB-PD&rsquo;s upgrade is a notable step up from, for example, USB Type-C&rsquo;s 5V and 3A (15W), dramatically increasing the likelihood of hazards.</p> <p>Apart from the risk associated with higher voltages and currents, USB-PD is used with USB Type-C connectors and cables&mdash;both of which increase the chance of accidents. This is because with just 0.5mm between pins, the USB Type-C connector features a pitch just one-fifth that of Type-A and Type-B connectors, which increases the risk that a minor twist of the connector during insertion or removal could cause a short. A build-up of detritus inside the connector could have a similar effect. Moreover, the popularity of USB Type-C has seen the development of a big supply of aftermarket cables&mdash;many of which are not up to the job of carrying 100W and yet are not marked as such. Not that such markings guarantee safety; an under-specified cable can be just as easily plugged into a USB-PD socket as a conforming one if a consumer is determined to use it.</p> <p>Arcing is not the only risk when using USB-PD at higher voltages and currents. Because of the proximity of the main bus power supply pins to other pins in the connector, a short can easily expose downstream electronics to a damage-inducing power surge&mdash;and not one just limited to 20V. The inductance of a one-meter USB cable, for example, is sufficient to generate &lsquo;ringing&rsquo; that can result in a peak voltage far higher&mdash;sometimes even double&mdash;than that of the (20V) short-circuit voltage. Depending on the application, the failure of downstream devices subject to these overvoltages could put safety at risk because some of the most vulnerable to damage are those that normally control the maximum current and voltage at which the cable should operate.</p> <h2>Comprehensive Circuit Protection</h2> <p>The risk of arcing or component damage when using USB-PD at its highest current and voltage ratings is such that paying lip service to circuit protection doesn&rsquo;t cut it. Comprehensive circuit protection in applications that regularly use USB-PD&rsquo;s highest power modes&mdash;for example, when charging the battery of a portable computer&mdash;is mandatory.</p> <p>Transient voltage suppression (TVS) diodes fitted between the USB Type-C receptacle pins and ground are a relatively simple and inexpensive start to the circuit protection task. In the event of a transient short, the TVS diodes &lsquo;clamp&rsquo; the peak voltage to a level that connected components can withstand. Unfortunately, while TVS diodes offer a good option for transients, they are not so good for sustained overvoltage events. To deal with these, additional circuitry in the shape of an overvoltage protection device paired with an n-channel MOSFET is needed. Then, during a sustained overvoltage episode, the protection device triggers the nMOSFET to disconnect the load from the input sparing downstream connected devices from overload. But TVS diodes, protection devices, and nMOSFETs still don&rsquo;t protect against all overvoltage scenarios; occasionally shorting events can occur that bypass the USB cable. In this case, receptacle inductance is very low, allowing the voltage to rise more rapidly than the protection device and nMOSFET can react. The solution lies in yet more clamping devices to hold the rise in voltage for long enough for the protection device to cut in.</p> <p>Comprehensive protection inevitably adds cost and complexity to a USB-PD application, but there are ways to rein in both by judicious selection of components. Manufacturers now offer integrated devices that incorporate TVS diodes, protection, and clamping devices into single packages (nMOSFETs typically remain as discrete chips). These monolithic chips simplify USB-PD protection design while saving money and space.</p> <div> <h2>Conclusion</h2> </div> <p>Circuit protection will never be at the glamorous end of the electronics development business. But the knowledge that suitable protection could prevent material damage, injury, or even death is certainly cause for immense satisfaction for the skilled engineer that developed the solution.</p> 1240Reinventing Overvoltage Protection,Circuit ProtectionTue, 02 Jul 2019 18:30:25 GMT<p><img alt="Reinventing Overvoltage Protection Theme Image" src="/blog/Portals/11/Bourns_Reinventing%20Overvoltage%20Protection_Theme%20Image.jpg" style="margin-left: 10px; margin-right: 10px; float: left; width: 150px; height: 109px;" title="Reinventing Overvoltage Protection Theme Image" /></p> <p>High reliability is paramount in our always on, hyper-connected world. Application downtime or failure runs the gamut from frustrating to incredibly expensive. That is why overvoltage protection remains a consistent requirement. Users expect seamless system operation so guarding them against unstable electrical service swells, switching, and lightning voltage transients just makes sense.</p> <p>In the overvoltage protection component arsenal, Metal Oxide Varistors or MOVs are popular solutions. New MOVs boast high current handling, high current absorption, and fast reaction time to protect against transient faults up to their rated limits. Power supplies, power systems, line voltage, telecom systems, white goods, and appliances are among the applications using MOVs for protection. Unfortunately, they are susceptible to degradation and failure issues in certain harsh and uncontrolled environment applications. These problems are well-documented, and UL requires extensive testing to guard against harmful failure modes. An MOV failure can occur from a thermal runaway condition, which defines the lifespan of an MOV. Thermal runaway conditions could also increase the risk of fire in an MOV, prompting designs to typically require additional thermal cutoff or fusing devices for safety.</p> <div> <h2>Bourns<sup>&reg;</sup> GMOV<sup>&trade;</sup> Overvoltage Protection Components</h2> </div> <p>Understanding the reliability and safety issues of MOVs alone, <a href="" target="_blank">Bourns</a> took an innovative approach in engineering its new <a href="" target="_blank">GMOV<sup>&trade;</sup> overvoltage protection components</a>. Developed as an enhanced protection solution, GMOV<sup>&trade;</sup> devices help overcome degradation and catastrophic failure issues that could occur in discrete MOVs that are subjected to transient surges or temporary overvoltage exceeding their maximum rated values. The hybrid design combines Bourns<sup>&reg;</sup> patented, space-saving Gas Discharge Tube (GDT) with FLAT<sup>&reg;</sup> technology with an MOV. No additional board space is needed for this compact and enhanced overvoltage protector&mdash;it is a drop-in replacement for standard 14mm and 20mm MOVs.</p> <h3>Bourns<sup>&reg;</sup> GMOV<sup>&trade;</sup> Overvoltage Protection Breakthrough Design</h3> <p>Why is this a breakthrough design? It uses the GDT to isolate the MOV from the line voltage, so it remains &ldquo;on call but not on duty,&rdquo; thereby shielding the device from transients and temporary overvoltage spikes that typically damage the MOV over time. By combining the two technologies, the GMOV<sup>&trade;</sup> device also provides ultra-low leakage (&lt;0.1&micro;A), helping to reduce damage due to watt loss heating. The result of the combination is a higher reliability protection solution with virtually zero standby energy consumption.</p> <p>And the design benefits don&rsquo;t stop there. GMOV<sup>&trade;</sup> components improve application reliability by delivering a predictable failure mode. This eliminates the need for indication circuitry and more expensive thermally protected MOV devices. Furthermore, GMOV<sup>&trade;</sup> protectors help to eliminate the need for more costly and higher performance MOVs to meet UL 1449 lost neutral tests. Another way GMOV<sup>&trade;</sup> devices offer a higher level of safety is that they are able to consistently blow fuses and breakers compared to MOVs alone, making them a superior solution for extended voltage threats.</p> <p>The lower leakage current, reduced capacitance, and robust features of Bourns<sup>&reg;</sup> GMOV<sup>&trade;</sup> devices deliver application advantages that other types of protection solutions cannot offer. In addition, GMOV<sup>&trade;</sup> components are UL 1449 Type 5 recognized, saving engineering and qualification time.</p> <div> <h2>Learn More</h2> </div> <p>For more information about the benefits Bourns<sup>&reg;</sup> GMOV<sup>&trade;</sup> devices can provide, please see the <a href="" target="_blank">Meeting Sustained Overvoltage Protection Requirements with a Hybrid Drop-In Replacement White Paper</a>.</p> 1192Keeping the Lights On: ESD and Thermal Protection for LED Lighting Systems,Circuit Protection,LightingTue, 29 Jan 2019 06:01:00 GMT<p><img alt="" src="/blog/Portals/11/Keeping%20The%20Lights%20On_Theme%20Image.jpg" style="margin-left: 10px; margin-right: 10px; float: left; width: 250px; height: 188px;" title="" />The quality of LED lighting systems has been an issue since they were invented, which is one reason they were not adopted earlier as a household lighting system. In recent years, the installation of LED lights grew at an exponential rate globally, largely due to the promises of LED lighting: long life, energy efficiency, and cost savings. The U.S. Department of Energy&rsquo;s website claims that LED light bulbs can last more than 25 times longer than traditional light bulbs. Although more than 50 million LED lights were installed in the U.S. in 2012, many LEDs failed within a few short months drawing consumers&rsquo; ire.</p> <p>In 2013, the first LED bulb received the Energy Star certification due to advancements in LED lighting system technology. An Energy Star-certified LED lightbulb means that the system has met reliability, performance, as well as energy-saving requirements&mdash;a big shift in requirements.</p> <p>How have engineers been able to meet the Energy Star certification requirements as well as overcome many of the obstacles that hindered LED systems in the past? With improvements in technology, protection devices became better able to defend against the major threats to LED lighting system&rsquo;s performance and reliability. By determining and integrating the most suitable protection devices for the application requirements into the LED design, engineers were able to counteract threats&mdash;such as Electrostatic Discharge (ESD) and thermal issues&mdash;to LED systems. Let&rsquo;s take a look at how the use of high-quality protection devices&mdash;in particular diodes, varistors, and thermistors&mdash;contribute to enhanced LED reliability, performance, energy efficiency, and cost-savings, and in turn, help LED lighting to deliver on its promises to outperform and outshine traditional light bulbs.</p> <h2>LED System Overview</h2> <p>An LED bulb&mdash;or more technically, a luminaire&mdash;is made up of three basic subsystems: an LED power supply, a power-input connection to the grid, and an LED engine. The LED engine can be further broken down into LED arrays, LED drivers, and control units.</p> <p>Over the past several years, smart LED luminaires have gained popularity due to features including remote control and maintenance. Because of this, a fourth subsystem&mdash;communication power supplies and interfaces&mdash;is often integrated into the luminaires. The design allows customers to deploy smart-networked lighting systems that maximize the efficiency and quality of lighting as well as track the status of each luminaire for maintenance purposes.</p> <h2>Factors Affecting LED Quality</h2> <p>Several factors can affect solid-state lighting, including stress, packaging-related, and component-related issues. Companies who design and manufacture LED lighting systems must take into account these factors. There are five key threats that affect the reliability of LED lighting systems:</p> <p>&nbsp;</p> <ul> <li>Electrostatic discharge (ESD) events, including lightning</li> <li>Transient overcurrent and surges</li> <li>Current and voltage spikes during hot swapping</li> <li>Reverse voltage effects</li> <li>Thermal issues such as operating at high temperatures for long periods</li> </ul> <p>&nbsp;</p> <p>For LED lighting systems to be reliable, all of the components and subsystems must be protected sufficiently against these dangers during assembly, maintenance, and operation.</p> <h2>LED Protection Solutions</h2> <p>As the LED lighting system technology matured, engineers began integrating high-quality protection devices into their LED designs to prevent high- and low-energy surges, ESD events, and thermal stress from adversely affecting LED arrays, their power supplies, and control circuits. The integration of these protection devices resulted in LED lighting systems with higher reliability, lower maintenance costs, and a longer product lifetime.</p> <p>By assessing the application requirements of the LED design, engineers can determine the most suitable protection devices to use to enhance LED performance and reliability. <strong>Figure 1</strong> shows an example of how engineers can use diodes, varistors, and thermistors in the system architecture of an LED luminaire.</p> <p>&nbsp;</p> <p><img alt="" src="/blog/Portals/11/TDK_Keeping%20the%20Lights%20On_Figure%201.jpg" style="width: 600px; height: 342px;" title="" /></p> <p><small><strong><em>Figure 1:</em></strong><em> A basic LED lighting system architecture complete with ESD and heat protection devices. (Source: TDK Corporation)</em></small></p> <h3>Diodes and Varistors</h3> <p>Diodes and voltage-dependent resistors, also known as varistors, are developed to meet unique design challenges for many applications. These solutions are often ruggedized, have a much smaller footprint, and protect against certain types of surge currents.</p> <p>The EPCOS CeraDiode&reg;&nbsp;from TDK Corporation is designed to absorb high energy at a better rate than Transient-Voltage Suppression (TVS) diodes and has a smaller footprint (<strong>Figure 2</strong>). Eighty percent of the component volume of this product is used to absorb the energy ESD events, which is superior to the thirty percent of standard TVS diodes&mdash;and it has the same performance. Because of this, non-standard parts should be considered if they can help minimize space requirements and provide an identical or improved performance. This is particularly important in applications that require miniaturization, reliable protection, and high performance.</p> <p>&nbsp;</p> <p><img alt="" src="/blog/Portals/11/TDK_Keeping%20the%20Lights%20On_Figure%202.jpg" style="width: 600px; height: 241px;" title="" /></p> <p><small><strong><em>Figure 2:</em></strong><em> An example of a specialized or non-standard component used to protect against ESD events. (Source: TDK Corporation)</em></small></p> <h3>Thermistors</h3> <p>Thermistors, or thermally sensitive resistors, are highly accurate sensors for measuring temperature. There are two types of thermistors:</p> <ul> <li>Negative Temperature Coefficient Thermistors (NTC)</li> <li>Positive Temperature Coefficient Thermistors (PTC)</li> </ul> <p>The difference between the two types of thermistors is that an NTC thermistor&rsquo;s electrical resistance decreases as temperature increases, whereas a PTC thermistor&rsquo;s electrical resistance increases as temperature increases.</p> <p>Available in surface mounted design (SMD) packages, NTC thermistors protect the LED arrays against overheating and help control their temperature profile at peak lumen efficiency. NTC thermistors provide thermal protection by automatically adjusting the current to the LEDs. Together with intelligent circuits, they enable an effective control system (<strong>Figure 3</strong>).</p> <p>&nbsp;</p> <p><img alt="" src="/blog/Portals/11/TDK_Keeping%20the%20Lights%20On_Figure%203.jpg" style="width: 300px; height: 404px;" title="" /></p> <p><small><strong><em>Figure 3</em></strong><em>: Diagram of a temperature-compensated LED driver without an IC.&nbsp;(Source:</em> <em>TDK Corporation)</em></small></p> <p>In temperature-compensated LED driver designs without integrated circuits, PTC thermistors can reduce the high temperatures of the forward current by placing them in series to the LED. In such a design, most of the LED current flows via the PTC thermistors.</p> <h2>LED Design</h2> <p>Engineers can guard against factors that adversely affect LED reliability by integrating protection devices into their design. Here are a few examples of how integrating protection devices into the LED design can counteract the major threats to LED lighting systems.</p> <h3>ESD</h3> <p>LED engines can consist of hundreds of LEDs that are normally series-connected strings, parallel-connected strings, or a combination of both. If one LED fails in a series-connected string, the entire series will fail. This is because LEDs in a series-connected string can cause an antenna effect making the array more sensitive to ESD events. Multilayer varistors can protect against such events.</p> <h3>Bidirectional Protection Against ESD and Transient Disturbances</h3> <p>Multilayer varistors are an excellent option for bidirectional protection against ESD and transient disturbances. A typical TVS diode is inherently unidirectional, making it necessary to design in two diodes. However, varistors provide bidirectional protection as a single component with the same protection. In this case, varistors will provide a size and cost advantage to the design.</p> <h3>High-energy Surges</h3> <p>Engineers realized they needed a way to prevent ESD events and high-energy surges from affecting the luminaire. These surges can cause both immediate failures&mdash;often at a junction&mdash;and an increased rate of degradation caused by latent damage. Each of the four subsystems can be exposed to events that cause this kind of damage.</p> <p>Varistors have long been a solution of choice for overvoltage protection. This is because the electrical resistance varies with the applied voltage. Engineers should select varistors that are designed to hold up to the conditions of the end application.</p> <p>Take for example the protection of power supplies. Metal oxide varistors are especially well-suited to protect the power supplies of LED lighting systems from larger energetic surges. The design may specify varistors that feature a compact design, or that provide protection against big ESD events such as lightning strikes. Due to the harsh nature of the elements and cost of maintenance, LED lighting systems designed for streetlights should meet both ANSI/IEEE&nbsp;C62.41.2 and the DOE MSSLC Model Specification for LED roadway luminaires. In these cases, surge arresters combined with varistors offer a space-saving integrated solution with exceptional performance.</p> <p>In the power input connection, a single package consisting of a disk varistor connected in series with a thermally coupled fuse is best suited to provide the protection required. In this case, if the varistor overheats, the thermal fuse&mdash;which is encapsulated in a plastic housing&mdash;disconnects the varistor from the power circuit preventing fire, safely shutting down the system.</p> <h3>Low-energy and ESD Discharges</h3> <p>TVS diodes have been used for many years to protect circuits from low-voltage ESD events below 25J (Joules). However, multilayer varistors offer significant advantages over traditional TVS diodes. These include many miniature sizes and insertion heights, more dependable performance, faster response times, and better overall operation across wide temperature ranges. Engineers can use TVS diodes to meet the absorption requirements relating to the component size.</p> <h3>Current and Voltage Spikes</h3> <p>Networks are often reconfigured, moved, replaced, and taken offline for maintenance. Consequently, hot swapping is a common practice, and hot swapping can cause ESD events and low-voltage spikes. Multilayer varistors or TVS diodes that have extremely low-parasitic capacitance are preferred for the ESD protection of data lines for the control of luminaires. Such diodes will ensure that the devices would remain fully functional for their specified lifetimes.</p> <h3>Thermal Stress</h3> <p>In most cases, sudden failures in LED lighting systems are caused by thermal stresses. The temperature of LEDs must be controlled within narrow limits to deliver an uninterrupted luminance. Thermistors provide an accurate and cost-effective way of measuring temperature.</p> <h2>Keeping the Lights On</h2> <p>As LED technology continues to mature, design engineers can increasingly prevent the high- and low-energy surges and ESD events that affect LED reliability by simply determining the most suitable protection devices that are required by the application. In addition, they can also plan for the proper temperature protection needed in their applications, thereby keeping the lights on in a very literal way.</p> <p>As a result, they will help deliver on the U.S. Department of Energy&rsquo;s claims that LEDs should last 25 times longer than traditional lighting systems.</p> 1145Pull Up Your Pins: How to Size Pull-up Resistors,Circuit ProtectionThu, 01 Nov 2018 04:50:00 GMT<p><img alt="" src="/blog/Portals/11/Parks_PullUpResistorSizing_Theme%20Image.jpg" style="margin-left: 10px; margin-right: 10px; float: left; width: 200px; height: 133px;" title="" /></p> <p>One of the first lessons many people learn when starting off learning practical, hands-on electronics is the need for pull-up resistors. Whether to prevent floating I/O pins on a microcontroller or interfacing two circuits via an open-drain design; pull-up resistors are an often necessary but rarely appreciated component. So why do we use pull-up resistors, can&rsquo;t we just connect a wire to the V<sub>cc</sub> supply of our device? What size resistor should you use?</p> <p>So why do we even need to bother with pull-up resistors to begin with? Let&rsquo;s assume we have a momentary normally open pushbutton and we don&rsquo;t want the I/O pin to float. Why not just connect a wire to the V<sub>cc&nbsp;</sub>between the I/O pin and the lead of the pushbutton? This would work to prevent the microcontroller&rsquo;s I/O pin from floating&mdash;it would need a V<sub>cc</sub> or a solid HIGH&mdash;while the button is not pressed. However, as soon as the button is pressed, a short circuit would occur between the V<sub>cc&nbsp;</sub>and ground (<strong>Figure 1</strong>). This will create a lot of heat, and if the device is battery-powered, it will drain the battery quickly. In addition to thwarting problems associated with floating microcontroller I/O pins, pull-up resistors are a necessity when using an open-drain topology. We discussed open drains at length in this <u><a href="">Bench Talk post</a></u>.</p> <p><img alt="" src="/blog/Portals/11/Parks_Figure%201.jpg" style="width: 600px; height: 190px;" title="" /></p> <p><small><strong><em>Figure 1</em></strong><em>:&nbsp; Just running a wire allows for a short circuit (Left).&nbsp;A pull-up resistor prevents floating inputs while as preventing an unwanted short circuit (Right). (Source: Author)</em></small></p> <p>&nbsp;</p> <p>So how do we select the right sized resistor? As is true with most good engineering questions, the answer depends on your application. Let&rsquo;s start by thinking about the extreme options 0Ω and let&rsquo;s say 1mΩ. The 0Ω option (small value resistors are referred to as strong pull-ups as they allow a lot of current to flow) we already discussed. Too small of a resistance value and we get too much current flow which can either be unsafe or at the very least energy inefficient. What if we go with a huge 1mΩ resistor? Won&rsquo;t that be safe? Large resistor values are referred to as weak pull-ups as they prevent too much current from flowing. The answer is yes but it comes at a cost. In this case, it&rsquo;s a trade-off between speed and power.</p> <p>Think of the microcontroller&rsquo;s I/O pin as a capacitor. Recall that the voltage across a capacitor cannot change instantaneously. Rather it charges up based on what is known as the timing constant (T) and is mathematically expressed as T=RC where R is the value of the resistor and C is the value of the capacitor. When we add a very large resistor, we are increasing the time it takes the capacitor to charge by limiting the current flow. Practically speaking that means the microcontroller will not immediately detect the pressed button as it will take some amount of time for the microcontroller to see the voltage change from what it considers a LOW/OFF state to the HIGH/ON state. This might result in unacceptable circuit performance from a user perspective. The system would appear to not respond in a timely fashion. In open-drain applications such as the I<sup>2</sup>C serial communication protocol, the large timing constant would have a negative impact on the I<sup>2</sup>C bus to achieve the desired baud rate on its Serial Data Line (SDA) and Serial Clock Line (SCL) lines.</p> <p>Mathematically speaking this is how you compute the resistor values:</p> <p>R<sub>p(min)</sub> is the smallest resistor value that is acceptable and is given by the equation:</p> <p>&nbsp;</p> <p align="center">R<sub>p(min) </sub>= (V<sub>cc</sub> - V<sub>OL(max)</sub> ) / I<sub>OL</sub>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; whereby:</p> <p>&nbsp;</p> <ul> <li>V<sub>cc</sub> is the supply voltage.</li> <li>V<sub>OL(max)</sub> is the maximum voltage that is registered as a low by the microcontroller&rsquo;s I<sup>2</sup>C pins.</li> <li>I<sub>OL</sub> is the current draw at V<sub>OL</sub></li> </ul> <p><sub>​</sub></p> <p>R<sub>p(max) </sub>is the largest resistor value that is acceptable and is given by the equation:</p> <p>&nbsp;</p> <p align="center">R<sub>p(max)</sub> =&nbsp;&nbsp; t<sub>r</sub> / (0.8473 x C<sub>b</sub>)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; whereby:</p> <p align="center">&nbsp;</p> <ul> <li><em>t<sub>r</sub> </em>is the acceptable rise time of SDA and SCL lines for the desired baud rate. Check the datasheets of the devices used in your design.</li> <li><em>C<sub>b</sub> </em>is the anticipated capacitive load that will be driven. A quick side note, the number of devices that can share an I<sup>2</sup>C bus is limited by the sum of the Printed Circuit Board (PCB) and device input capacitances. Per the I<sup>2</sup>C specification for standard and fast operating modes, this limit is 400pF. After which an I<sup>2</sup>C buffer chip is required. This usually occurs well before the theoretical addressing limit of 112 devices for 7-bit addressable I<sup>2</sup>C implementations.</li> </ul> <p>Now for a practical rule of thumb, here are the resistor values you should consider testing in your circuit to see if you get the desired performance:</p> <ul> <li>1kΩ to 10kΩ for general purposes.</li> <li>10kΩ to 100kΩ if you have a low-power use case such as a device that is battery powered.</li> </ul> <p>The last thing to consider is that many microcontrollers have internal pull-up resistors that can be turned on via code. Be sure to check the data sheets to see if the internal resistor value is appropriately sized for your application. If not, you will have to use external pull-up resistors.</p> 1123Protect Embedded Interfaces with These Clamps and Crowbars,Circuit Protection,IoTMon, 13 Aug 2018 05:01:00 GMT<p><img alt="" src="/blog/Portals/11/Bourns_Transparent%20Over-Voltage%20Protection%20Theme%20Image.JPG" style="margin-left: 10px; margin-right: 10px; float: left; width: 200px; height: 127px;" title="" /></p> <p>Embedded electronics, the Internet of Things (IoT), and machine-to-machine (M2M) connections have become widespread in diverse areas, so it is important to protect interface connections from overvoltage conditions and transient events that can cause damage (<strong>Figure 1</strong>):</p> <ul> <li>Overvoltage conditions can last seconds to minutes, or longer.</li> <li>Transient events happen in a short time&mdash;tens to a hundred microseconds during an industrial switching or lightning transient event, down to a few nanoseconds with an electrostatic discharge (ESD) transient.</li> </ul> <p><img alt="" src="/blog/Portals/11/Bourns_Transparent%20Over-Voltage%20Protection%20Figure%201.JPG" style="width: 400px; height: 249px;" title="" /></p> <p><em><small><strong>Figure 1</strong>: Protect interface connections from overvoltage conditions and transient events. (Source: Bourns)</small></em></p> <div> <h2>Protection Devices</h2> </div> <p>Several devices can be useful to protect power, signal, and communication interfaces from damage involving destructive transient voltages. Two common types of protection circuits may employ (1) clamp-circuit devices or (2) crowbar-circuit devices:</p> <ul> <li>Clamp devices are mainly useful to protect current limited power connections.</li> <li>Crowbar devices can protect current limited power lines as well as data and signal lines.</li> </ul> <p>When choosing protection devices for power and signal connections an engineer must consider the fit of the application with the various options of clamps, crowbars, silicon, and ceramic devices (<strong>Table 1</strong>). Let&rsquo;s examine these options in more detail.</p> <p><img alt="" src="/blog/Portals/11/Bourns_Transparent%20Over-Voltage%20Protection%20Table%201.JPG" style="width: 200px; height: 87px;" title="" /></p> <p><em><small><strong>Table 1</strong>: The decision to use clamps or crowbars also depends on the device materials.</small></em></p> <h3>Clamp Devices</h3> <p>Clamps will conduct enough current to maintain the voltage across it at a safe, specified value when the transient is above the conduction voltage. It receives a rating according to the power it can dissipate for a specific time. The protection device needs a rating for the power to dissipate during the transient event. The voltage across the load rises only slightly above the rated clamp voltage during the maximum surge voltage. An example is the <a href="">Bourns ChipGuard&copy; MLA μVaristor Series ESD Clamp Protectors</a> which are developed especially to protect sensitive automotive electronics from the threat of ESD up to IEC 61000-4-2 Level 4.</p> <ul> <li>The Transient Voltage Suppressor (TVS) is a silicon clamp device with breakdown voltages from 4 to 500V within various power ratings, providing different surge protection capabilities. It is a bipolar junction, similar to rectifier diodes, designed to survive a reverse breakdown. An example includes the <a href="">Bourns CDSOD323-TxxC-DSLQ AEC-Q101 TVS Diodes</a> which are transient voltage suppressor diodes for surge and ESD protection in a SOD323 package.&nbsp;</li> <li>The <a href="">Metal Oxide Varistor</a> (MOV) is a ceramic clamp device with breakdown voltages from 14 to 1400V and capable of 6.5kA in an 8/20&micro;s lightning-surge waveform.</li> </ul> <h3>Crowbar Devices</h3> <p>A crowbar device trigger occurs at a voltage above the protection voltage. The device protects by applying a low impedance across the protected load when an overvoltage condition triggers it. The device stays in the low impedance state until the current decreases below the holding current and the device returns to the high impedance state. In the low impedance state the device conducts the current that the external circuit limits. In this way, the voltage flowing across the protected device stays low. Ultimately, the crowbar protection device acts as the low impedance device on the low voltage side of a voltage divider, keeping the high voltage in the external circuit and protecting the sensitive load on the low voltage side.</p> <ul> <li><a href="">Thyristor Integrated Surge Protectors (TISP)</a> are PNPN-based silicon semiconductor crowbar devices. Their breakdown voltages can be set precisely, and they are available in many package types to dissipate various surge levels.</li> <li>Gas Discharge Tubes (GDT) are ceramic crowbar devices enclosing a spark gap that conducts a high-current arc upon the trigger of a high-voltage, high-current source, such as lightning, with an example being the <a href="">Bourns 2003 Gas Discharge Tube Surge Protector</a>.</li> </ul> <h2>Summary</h2> <p>Protecting interface connections from overvoltage conditions and transient events is more important than ever with the proliferation of embedded electronics. Bourns clamp and crowbar protection devices are effective at protecting circuit interfaces within silicon and ceramic electronic components. For more information, visit the <a href="">Bourns site at Mouser</a>.com.</p> 622Advanced Ceramic Resistors Yield Higher Power System Density,Circuit ProtectionThu, 19 Jul 2018 21:26:35 GMT<p><img alt="The Bourns model PWR247T-100 high power resistor series" src="/blog/Portals/11/Bourns%20Ceramic%20Resistor%20PWR247T-100%20AEC-Q-200%20Theme%20Image.JPG" style="margin-left: 10px; margin-right: 10px; float: left; width: 200px; height: 170px;" title="The Bourns model PWR247T-100 high power resistor series" />Shrinking product designs have one more component hero in the quest to improve power system density. Prevalent in all types of electronic applications, power resistors serve the very useful purpose of withstanding and dissipating large amounts of power in the form of electric resistance. Engineers today are asked to design applications with increasing power densities, which directly correspond to the demand for resistors. Leading manufacturers of these mighty passive components are answering current application requirements with new power resistor designs that can tolerate higher amounts of power in small and smaller form factors.</p> <p>Power resistors serve two primary functions: to absorb the inrush current caused by the switching action of a power device such as a MOSFET or IGBT, or as a shunt to measure and control current such as in a power supply. Today&rsquo;s advanced resistors are made of thick film on ceramic technology. They are constructed using a resistive paste that is a mix of metal oxides, a carrier and a binder placed on a ceramic substrate. The process continues with resistive layers that are added sequentially based on the device&rsquo;s required resistance pattern and value. The resistive pattern is printed onto the substrate at a high temperature to form a glass-like exterior that protects it from moisture or contaminants. Resistance is determined by the resistor track dimensions and the film resistivity.</p> <p>Using thick film on ceramic technology gives resistors an inherent low inductance advantage, which is quite useful in circuits where switching frequencies of 50kHz are common. Thick film resistor technology has other benefits too. It is typically lower cost, can absorb and handle large amounts of power, can provide a wider range of resistance values and is capable of withstanding high surge conditions and ESD events. These capabilities make them ideal solutions in meeting power system density improvement goals.</p> <p>An important consideration in selecting a high power thick film resistor for applications in harsh or demanding conditions is that they be AEC-Q200 compliant. AEC-Q200 is a global automotive standard for passive components to ensure temperature, pressure resistance, and safety consistency. AEC-Q200 qualified components must pass a stringent set of stress tests contained within the standard.</p> <p>What developer wouldn&rsquo;t want standards-based peace of mind in specifying components for more rugged environmental applications? Understanding this ongoing need, <a href="">Bourns</a> recently introduced its <a href="">Model PWR247T-100</a> high power resistor series. Offered in a compact TO-247 package, it is engineered with a thick film resistive element on a white alumina ceramic substrate to deliver exceptionally low inductance benefits. Because this type of element enables heat sink contact that is electrically isolated from the resistive element, Bourns&rsquo; latest resistor can absorb power up to 100W when properly mounted to a heat sink.</p> <p>Bourns offers one of the industry&#39;s broadest portfolios of AEC-Q200 compliant products consisting of resistors, magnetic and circuit protection products fully tested and qualified for the automotive market and beyond. Does your next design require the high and mighty benefits that new compact AEC-Q200 compliant high power resistors can deliver?</p> 596No Sulfur Corrosion Here: Sulfur Resistant Film Resistors,Circuit ProtectionMon, 09 Jul 2018 15:39:41 GMT<p><img alt="Bourns CRM-A &amp; CRS-A AEC-Q200 High Power Thick Film Resistors" src="/blog/Portals/11/Bourns-CRS-A_image.jpg" style="margin-left: 10px; margin-right: 10px; float: left; width: 175px; height: 117px;" title="Bourns CRM-A &amp; CRS-A AEC-Q200 High Power Thick Film Resistors" />There are plenty of hostile environments that test the reliability of electronic components. Temperature extremes, dust, humidity, and altitude are just a few conditions that designers have persevered against with rugged designs. Toxic chemicals and gases present some of the worst threats and are common conditions in many industries. In particular, high sulfur environments play havoc with everything from IT industry server farms and data/storage centers and telecommunication base stations to industrial control equipment and rubber, paper and oil manufacturing plants. For instance, sulfurous environments have a particularly negative impact on film resistors. Sulfur, when it reacts with elements such as silver, produces sulfide growth that can cause resistors to go open circuit.</p> <p>In standard film resistors, their internal silver (Ag) or silver palladium (AgPd) terminal is only protected by the epoxy passivation layer making the device very susceptible to sulfur-based gases. These gases can attack the silver in the terminal starting the corrosion process based on surrounding conditions such as temperature, humidity, and even air flow.</p> <p>Realizing how sulfur gases can affect the reliability of its film resistors, Bourns developed a specialized Palladium (Pd) layer that removes the chance for corrosion and the formation of silver sulfide. By adding the protective Palladium material over the termination and production layer of its chip resistors, it dramatically slows down the amount of sulfur penetration that can reach the internal silver layer areas of the resistor. Palladium is a highly-resistant material against sulfurous gases that also helps inhibit the growth of silver sulfide. Tests that Bourns engineers have performed demonstrate that its sulfur-resistant devices offer 20 times greater operating life compared to its standard film resistors.</p> <p>There are other solutions such as adding a gold layer or eliminating the use of silver in terminations, which can be more effective solutions to prevent sulfur corrosion damage. The downside of these approaches is they are much costlier compared to Palladium. We have found that most customers are very happy with our cost-effective Palladium solution that gives them enough protection for their applications.</p> <p>With the use of <a href="">Bourns&reg; sulfur-resistant film resistors</a>, this corrosion-related type of hard failure can be greatly reduced, resulting in improved system reliability, performance, robustness, and reduction of downtime. This is one of the most important operating factors in the IT industry where subsystems such as memory modules are used heavily in server farms and the data/storage center marketplace. If your application needs to ensure critical data transfers even in unfavorable sulfurous environments, Bourns wants to help.&nbsp;</p> <p>&nbsp;</p> 588K-SIM Improves Capacitor Datasheets and Simulates Multiple Parameters,Circuit Protection,Connectors,Industrial,Medical,Power,Student CentralMon, 30 Apr 2018 20:49:11 GMT<p>Most of us learned in school that there are two types of capacitors: Polarized and nonpolarized. The critical difference is that you should never put polarized capacitors in backwards. As we begin working with capacitors, we learn that capacitors have a much more complicated function than just serving as two electrode plates separated by a dielectric. Depending on what materials the dielectric and the electrode layers consist of, the behavior and characteristics of the capacitor can be very different.&nbsp;</p> <p>The surprise twist here is that capacitor datasheets have become notorious for not giving complete information on components. For example, often manufacturers do not publish the self-resonant frequency (SRF) for their <a name="_Hlk511147771">multilayer ceramic capacitors (MLCCs)</a>. It has become more common for capacitor manufacturers to include &ldquo;typical&rdquo; graphs for performance characteristics. Alternatively, in the case of some dielectrics, they only provide an individual chart for each parameter. While being useful information, all these approaches still require the end designer to do a bit more math.</p> <p>Before looking into the case of whether capacitor datasheets lie or not (spoiler: They do not!), let&rsquo;s first look at ceramic capacitor losses as an example.</p> <h2>Example: Ceramic Capacitor Loss Parameters</h2> <p>Ceramic capacitors are by far the most common type of capacitor used today, yet they&rsquo;re one of the least understood. Ceramic capacitors, or MLCCs, can lose capacitance for three key reasons. The first one is obvious because all passive components suffer the fate of what&rsquo;s called the <em>tolerance band</em>, and while it is possible for a device to be near the plus side of the band, this is rarely the case. Two other key issues&mdash;temperature and applied <a name="_Hlk511147867">DC voltage</a>&mdash;commonly cause a loss of capacitance in ceramic capacitors as well.</p> <h3>Temperature Loss</h3> <p>When you see a capacitor labeled as &ldquo;C0G&rdquo; or &ldquo;X7R&rdquo; you are seeing the dielectric&rsquo;s temperature coefficient. Common coefficients are C0G, U2J, X7R, and X5R. There are more than these, but these coefficients represent the more popular types. C0G and U2J are considered &ldquo;ultra-stable&rdquo; Class I dielectrics. They change very little with temperature. C0G, for example, means that the capacitor changes &plusmn;30ppm across the rated temperature range. X7R and X5R fall into Class II dielectrics. Each letter has a specific meaning, as <strong>Figure 1</strong> shows.</p> <p><img alt="" src="/blog/Portals/11/KEMET_Figure%201_1.png" style="width: 400px; height: 277px;" title="" /><img alt="" src="/Portals/11/KEMET_Figure%201_1.png" style="width: 600px; height: 415px;" title="" /></p> <p><em><small><strong>Figure 1:</strong> This table represents a ceramic capacitor&rsquo;s Class II temperature coefficients. (Source: KEMET)</small></em></p> <p>The first position is a high temperature, the second position is a low temperature, and the third position is an expected change. The X means -55&deg;C; the &quot;7&quot; means +125&deg;C; and the &quot;5&quot; means +85&deg;C. Finally, the R means &plusmn;15 percent. So X7R means between -55&deg;C and +125&deg;C with a capacitance that may vary up to 15 percent. (Hint: It rarely goes &ldquo;plus.&rdquo;). Usually, the capacitors are peaked so that at about room temperature there is no loss with a bell-shaped curve towards the extreme temperatures (<strong>Figure 2</strong>).&nbsp;</p> <p><img alt="" src="/blog/Portals/11/KEMET_Figure%202.png" style="width: 400px; height: 233px;" title="" /><img alt="" src="/Portals/11/KEMET_Figure%202_1.png" style="width: 600px; height: 350px;" title="" /></p> <p><em><small><strong>Figure <!--[if supportFields]><span style='mso-element: field-begin'></span><span style='mso-spacerun:yes'> </span>SEQ Figure \* ARABIC <span style='mso-element:field-separator'></span><![endif]-->2<!--[if supportFields]><span style='mso-no-proof: yes'><span style='mso-element:field-end'></span></span><![endif]-->: </strong>This graph represents MLCC relative permittivity change vs. temperature (Class I, II, and III). (Source: KEMET)</small></em></p> <h3>Applied DC Voltage</h3> <p>The third reason for ceramic capacitance lose has to do with a &ldquo;DC bias&rdquo; or &ldquo;voltage coefficient.&rdquo; In other words, an effective capacitance drops at the of application of a DC voltage. Paraelectric capacitor types, like C0G, do not exhibit this issue. However, all ferroelectric capacitors, like X7R and Y5V, exhibit loss at the application of a DC voltage. Several factors determine the level of loss in each capacitor type. Today, there is no commercial specification for rating this loss. Still, as a &ldquo;rule of thumb,&rdquo; the thinner a ceramic capacitor&rsquo;s dielectric layers become, the more evident this effect becomes: Which means for lower rated voltages or lower rated temperatures, the voltage coefficient will be higher.&nbsp;</p> <p>A simplified explanation for why this loss occurs is related to the electric dipoles in the dielectric material. The ceramic dielectric is composed of a crystalline structure that arranges those electric dipoles into separate domains (<strong>Figure 3</strong>). Spontaneous polarization of these domains occurs when no DC voltage is present. This polarization gives the dielectric material a high relative permittivity. (By the way, relative permittivity replaced the deprecated term &ldquo;dielectric constant.&rdquo;)</p> <p><img alt="" src="/blog/Portals/11/KEMET_Figure%203.png" style="width: 400px; height: 234px;" title="" /><img alt="" src="/Portals/11/KEMET_Figure%203_1.png" style="width: 600px; height: 351px;" title="" /></p> <p><em><small><strong>Figure <!--[if supportFields]><span style='font-size:10.0pt;mso-bidi-font-size:11.0pt;line-height:150%;font-family: "Arial",sans-serif;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman";mso-bidi-theme-font:minor-bidi; mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA'><span style='mso-element:field-begin'></span><span style='mso-spacerun:yes'> </span>SEQ Figure \* ARABIC <span style='mso-element: field-separator'></span></span><![endif]-->3<!--[if supportFields]><span style='font-size:10.0pt; mso-bidi-font-size:11.0pt;line-height:150%;font-family:"Arial",sans-serif; mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-bidi-font-family: "Times New Roman";mso-bidi-theme-font:minor-bidi;mso-ansi-language:EN-US; mso-fareast-language:EN-US;mso-bidi-language:AR-SA;mso-no-proof:yes'><span style='mso-element:field-end'></span></span><![endif]-->:</strong> This illustrates the MLCC DC voltage bias, dipole example. (Source: KEMET)</small></em></p> <p>Now, applying a DC voltage to the capacitor aligns the domains, locking them in the direction of the electric field. The higher the voltage, the more locked domains. This change reduces the permittivity of the dielectric layer, which means there is less room to store energy or, in other words, less capacitance is available.</p> <div> <h2>K-SIM Combines Parameters into a Single Graph</h2> </div> <p>As mentioned before, some capacitor vendors will provide individual graphs for each of these losses. You are probably interested in how both temperature and applied voltage might affect an MLCC; this is why&nbsp; <a href="">KEMET</a> provides a capacitor parameter simulator, called <a href="">K-SIM</a>, that combines these parameters into a single graph (<strong>Figure 4</strong>). It does not perform a Software Process Improvement and Capability dEtermination (SPICE) calculation, but it can provide a netlist for use in a PSpice<sup>&reg;</sup>.</p> <p><img alt="" src="/blog/Portals/11/KEMET_Figure%204.png" style="width: 400px; height: 211px;" title="" /><img alt="" src="/Portals/11/KEMET_Figure%204_1.png" style="width: 600px; height: 317px;" title="" /></p> <p><em><small><strong>Figure 4: </strong>This is K-SIM in action, showing multiple parameters in a single graph. (Source: KEMET)</small></em></p> <p>K-SIM can provide plots on ESR/impedance vs. frequency; capacitance change vs. frequency, ripple current calculations, S-parameters, and netlists; and for ceramics, a capacitance change vs. applied voltage (<strong>Figure 5</strong>).</p> <p><img alt="" src="/blog/Portals/11/KEMET_Figure%205.png" style="width: 600px; height: 114px;" title="" /><img alt="" src="/Portals/11/KEMET_Figure%205_1.png" style="width: 600px; height: 137px;" title="" /></p> <p><em><small><strong>Figure <!--[if supportFields]><span style='mso-element: field-begin'></span><span style='mso-spacerun:yes'> </span>SEQ Figure \* ARABIC <span style='mso-element:field-separator'></span><![endif]-->5<!--[if supportFields]><span style='mso-no-proof: yes'><span style='mso-element:field-end'></span></span><![endif]-->:</strong> K-SIM offers various controls. (Source: KEMET)</small></em></p> <p>Once a graph is selected, there are controls to allow you to enter an applied voltage and application temperature. There are various other controls also available, but these two are the most common. For some advanced comparisons, try clicking &ldquo;Compare Across Conditions,&rdquo; then you can see how a part performs, on a single graph, at -55&deg;C, 25&deg;C, and +125&deg;C.</p> <div> <h2>Conclusion</h2> </div> <p>Capacitor datasheets have become notorious for omitting performance details and, instead, include a single graph for &ldquo;typical&rdquo; performance or individual graphs for each parameter. Performance, though, isn&rsquo;t measured in a single parameter but a combination of parameters. The KEMET capacitor parameter simulator helps solves this problem by simulating combinations of variables into a single graph. The combinations include ESR/impedance vs. frequency; capacitance change vs. frequency, ripple current calculations, S-parameters, netlists; and for ceramics, capacitance change vs. applied voltage, in addition to advanced comparisons across conditions.</p> <p>&nbsp;</p> 572Protect USB Ports From Nefarious “USB Killers" Protection,Computing,Memory,PowerWed, 11 Apr 2018 18:43:09 GMT<p><img alt="" src="/blog/Portals/11/USB%20Stick%20Files%20Theme%20Image%20GettyImages-871208644.jpg" style="width: 600px; height: 420px;" title="" /></p> <p>USB ports supply both data communications and charging power to portable and wearable devices, so it&rsquo;s becoming more and more critical to protect ports against abuse.</p> <p>Any aspiring evildoer can easily find a &ldquo;USB killer&rdquo; device that can destroy almost any USB port with a power surge attack that overwhelms the standard protection circuitry. The device looks much like a standard USB flash drive but contains a boost converter that feeds a bank of capacitors. When plugged in, the control circuit charges the capacitor bank via the USB power pin, discharges it into the data pins, and repeats the charge-discharge cycle, applying a series of -200V pulses until it&rsquo;s unplugged.</p> <p>Zap&mdash;game over, in under a second! Depending on the circuitry between the USB port and the rest of the design, such a power surge can destroy anything from the USB port itself to the whole machine. Plenty of YouTube videos exist that show the havoc wreaked on various pieces of equipment, including smartphones, laptops, tablets, and even smart TVs. In fact, some people derive positive enjoyment from this activity.</p> <p>Fortunately, there are design techniques that reduce power surge risks to USB ports. USB Type-C&trade; offers a potential solution as well.</p> <div> <h2>Design Techniques that Reduce Power Surge Risks to USB Ports</h2> </div> <p>Many manufacturers offer USB protection devices, but their specifications are intended to protect against accidental events such as a finger touching an exposed USB pin&mdash;but not deliberate attempts at sabotage. The <a href="">TPD4S214</a> from <a href="">Texas Instruments</a> (<strong>Figure 1</strong>), for example, is a single-chip device that offers low-capacitance transient voltage suppression (TVS) protection and electrostatic discharge</p> <p>&nbsp;(ESD) protection for the D+ and D- data pins. The ESD protection meets the IEC 61000-4-2 Level 4 ESD protection standard and can withstand contact and air-gap ESD events up to &plusmn;15kV.</p> <p><img alt="" src="/blog/Portals/11/Pickering_USB%20Killer%20Figure%201.png" style="width: 600px; height: 286px;" title="" /></p> <p><em><strong>Figure 1: </strong>The TPD4S214 protects against expected electrical hazards, but not enemy action. (Source: <a href="">Texas Instruments</a>)</em></p> <p>Could designers include more comprehensive protection? Of course, but in the price-competitive consumer market, it&rsquo;s rarely worth adding expensive circuitry to guard against vanishingly-rare events that don&rsquo;t involve the risk of injury or death. The tradeoffs are different in higher-dollar markets, such as the medical or industrial equipment markets, that use USB ports. Designers for these products have a bigger budget and more design options to protect the USB interface.&nbsp;</p> <p>Optocouplers are relatively low-cost but aren&rsquo;t suitable for the USB bus transceivers themselves: Not only must the USB interface be bidirectional, the delay and skew of the D+ and D- signals must also be carefully matched. Both requirements are difficult to achieve with optocouplers. Careful system partitioning can accommodate optical isolation further along the signal chain&mdash;e.g., by adding it to a serial peripheral interface (SPI). Such a solution may expose the interface to attack but protects expensive downstream processors and circuitry.</p> <p>The gold standard for protection at the USB interface is galvanic isolation. Of course, given the price of gold, this option isn&rsquo;t exactly low-cost; however, it&rsquo;s a small price to pay if the alternative is risking the destruction of a $100,000 piece of equipment!</p> <p><a href="">Analog Devices</a>&rsquo; <a href="">LTP2884</a> is designed just for a USB: It&rsquo;s a USB 2.0-compatible, full-speed (12Mbps) transceiver combined with galvanic isolation that&rsquo;s rated at 2,500V<sub>RMS</sub>. The LPT2884 can supply isolated peripherals with up to 2.5W (500mA at 5V) when used with an external supply or up to 1W (200mA at 5V) from an integrated DC/DC converter.</p> <div> <h2>USB Type-C Offers a Possible Solution</h2> </div> <p>What&rsquo;s in the future? The latest revisions to the USB specifications, USB 3.0 and USB 3.1, increase the data speed to 5Gbps and 10Gbps respectively, making even isolation transformers impractical. Luckily, help is on the way. <a href="">USB Type-C</a> is the latest USB connector specification, and it&rsquo;s beginning to replace the USB 2.0. Related to the USB Type-C is a USB Power Delivery (USB PD) specification that does away with USB 2.0&rsquo;s simple 5V power delivery system. In its place, each pair of USB PD-capable devices negotiates a power transfer &ldquo;contract&rdquo; at the point of connection: The contract determines the direction of power transfers and selects the voltage and power level for use.</p> <p>The USB 3.0 Promoter Group has released an authentication specification for USB Type-C that defines a cryptographic-based authentication protocol for USB Type-C chargers (power transmitters) and devices (power receivers). With the implementation of this protocol, host systems can confirm the authenticity of a USB device or USB charger immediately once a wired connection occurs&mdash;though before inappropriate power or data can transfer. Any authentication scheme can theoretically be defeated, of course, but requiring authentication before supplying any power should certainly make life a lot more difficult for would-be USB Type-C killers.</p> <div> <h2>While You&rsquo;re Waiting, Follow These Simple Precautions</h2> </div> <p>Already-designed equipment, of course, can&rsquo;t take advantage of these products. How, then, do you keep your USB 2.0-equipped tablet or laptop safe? For maximum protection, you can store your portable data in the cloud and physically block each USB port. At its simplest (and most permanent!), this might involve a USB cover and a dollop of superglue, but a more elegant solution is a USB-closing lock: This clicks into each USB port and can&rsquo;t be removed without disassembling the case. Likewise, versions that can only be removed with a special security key are also available.</p> <p>If you must keep your USB ports easily accessible, it&rsquo;s time to fall back on a little old-school due diligence. Don&#39;t insert flash drives given to you by strangers, or those you find on the ground or otherwise abandoned. Even if you trust the person giving you the drive, make sure they&rsquo;ve used it before or purchased it from a legitimate, verified source such as <a href="">Mouser</a>. Finally, never leave your computer unattended where unauthorized persons can gain access.</p> <p>Unfortunately, there&rsquo;s no simple solution to the problem of USB-killing devices. But following a few simple precautions can ensure the safety of your laptop, tablet, or smartphone.</p> 567Will You Please Be My Heat Sink?,Circuit Protection,Computing,Dev ToolsMon, 05 Mar 2018 15:19:56 GMT<p style="text-align: center;"><img alt="" src="/blog/Portals/11/schwarz-heatsink-share.png" style="width: 650px; height: 433px;" title="" /></p> <p>I have a confession to make: I like heat sinks. Why? It&rsquo;s hard to say with certainty, but I think it&rsquo;s a combination of reasons: They have one job (to pull heat away from a source); they&rsquo;re visible and tangible; they don&rsquo;t require software or initialization; they&rsquo;re reliable; they&rsquo;re consistent, and they don&rsquo;t push back. They just sit quietly on top of (or next to) a transistor, integrated circuit (IC), or module and do their jobs as defined by their size, geometry, material, and placement, all guided by the basic principles of physics. I even have a modest collection of heat sinks I&rsquo;ve accumulated along the way (<strong>Figures 1, 2, and 3</strong>), and there are many that I simply let go by.</p> <p style="text-align: center;"><img alt="stamped heatsink" src="/blog/Portals/11/Schweber_Mar_heat-sinks_Fig1.png" style="width: 650px; height: 488px;" title="stamped heatsink" /></p> <p style="text-align: center;"><span style="font-size:x-small;">Figure 1: This simple, stamped-metal heat sink mounts on a small metal transistor as a pair of &ldquo;wings.&rdquo; (Source: Author)</span></p> <p style="text-align: center;"><img alt="Pentium II heatsink" src="/blog/Portals/11/Schweber_Mar_heat-sinks_Fig2.png" style="width: 650px; height: 564px;" title="Pentium II heatsink" /></p> <p style="text-align: center;"><span style="font-size:x-small;">Figure 2: This anodized heat sink was designed specifically for the Intel Pentium II processor and includes metal clips that snap the heat sink onto the device. (Source: Author)</span></p> <p style="text-align: center;"><img alt="large finned heatsink" src="/blog/Portals/11/Schweber_Mar_heat-sinks_Fig3.png" style="width: 650px; height: 413px;" title="large finned heatsink" /></p> <p style="text-align: center;"><span style="font-size:x-small;">Figure 3: A larger, finned heat sink is designed to cool one or two power devices that are housed in standard TO-3 packages. (Source: Author)</span></p> <p>Of course, &ldquo;heat sink&rdquo; is a term casually tossed about by many electrical engineers, especially when the real job of forcing heat out to keep things adequately cool becomes the responsibility of mechanical or packaging engineers. That&rsquo;s unfortunate because a heat sink is a &ldquo;sink&rdquo; (but only from one perspective). As it pulls heat away from the source, it must get rid of that heat, so it then becomes a heat &ldquo;source.&rdquo; In other words, one person&rsquo;s sink is another person&rsquo;s source.</p> <p>What bothers me is when designers talk about using a heat sink to cool a component and then talk as if the problem of excess heat has gone away. Sorry, but it doesn&rsquo;t work like that. Under the immutable laws of thermodynamics, heat only flows from a warmer area to a cooler one. If you don&#39;t take <a href="">steps to remove the heat</a> from a heat sink attached to your device by using&nbsp;convection, a heat pipe, forced air, or liquid, then&nbsp;it will linger and eventually create a backup-effect, similar to a pile of vehicles&nbsp;on an&nbsp;accident-blocked road. Both your device and its heat sink will just get hotter and hotter and reach thermal equilibrium at a higher temperature.</p> <p>Many of today&rsquo;s ICs are designed to eliminate the need for a heat sink attachment; this is possible when the overall system&#39;s thermal situation is&nbsp;designed right. The keyword here is &ldquo;right.&rdquo; These devices have a thermal pad underneath their package or use their leads to conduct heat towards the PC board copper. From there, the heat flows to larger copper areas, sometimes using special plated-through-hole vias between the layers of the board.</p> <p>However, this presents two problems: First, the thermal impedance of the narrow IC leads and the vias is high, so the heat flow is constricted. But let&rsquo;s assume that the thermal modeling says it will be okay, and let&rsquo;s move on to the next problem: What other components in the area are also assuming that they can push their heat into that same copper plane? I&rsquo;ve seen designs where relatively hot ICs and passives were crowded next to each other yet with each assuming it had plenty of square inches of PC copper to use for personal heat-dumping ground.</p> <p>Sorry! It doesn&rsquo;t work that way. If the cumulative heat that&rsquo;s pushed onto the copper creates a temperature close to or, perhaps, above what your components are putting out, then that heat will have nowhere to go. Sometimes the mindset of designers appears to be that they&rsquo;re all standing in a circle, pointing to the person to their right, saying, &ldquo;I&rsquo;m passing my excess heat over to this person.&rdquo; We all know such thinking doesn&rsquo;t end well.</p> <p>The real point is: Heat sinks are wonderful, but they don&rsquo;t work in a vacuum (&ldquo;pun&rdquo; intended&mdash;they don&rsquo;t work well in a real vacuum, as there is no convection, so they would have to rely on conduction alone). Any heat sink must undergo an evaluation to consider both the directional flow of the heat it expels (if the temperature differential is sufficient) and other sources that may be using the same cooling zone to expel excess heat. Ultimately, a heat sink can only do its job when you provide proper accommodations for it to release its heat, which thereby enables it to protect your device.</p> 529Don’t Ignore Current Sense Resistor TCR,Circuit Protection,PowerWed, 14 Feb 2018 16:58:38 GMT<p>It&rsquo;s not easy being a current sense resistor. So much is expected of this basic function of determining current flow by the simple measurement of voltage across a known resistance (i.e., I = V/R) then applying Ohm&rsquo;s law (<b>Figure 1</b>). What could be simpler?</p> <p style="text-align: center;"><img alt="" src="/blog/Portals/11/Schweber_resistor%20TCR_fig1.jpg" style="width: 277px; height: 400px;" title="" /><br /> <span style="font-size:x-small;"><strong>Figure 1: </strong>Current sense resistor schematic</span></p> <p>Using a resistor (&ldquo;R&rdquo;) and associated voltage drop (&ldquo;V&rdquo; from B to C) for a measurement of current flow (&ldquo;I&rdquo; from A to D) is simple in principle but has subtleties that must be acknowledged. Four-wire, high-impedance Kelvin sensing is commonly used when currents are high, and resistance is in the 100mΩ and lower range.</p> <p>Hence, it&rsquo;s not as simple as it appears. First, there is the issue of deciding on a resistor value. On one side, a larger value increases the voltage drop across the resistor, so the reading scale becomes larger for an improved signal-to-noise ratio (SNR) and resolution precision. However, a larger value wastes power, may affect loop stability as it places more idle resistance between the source and the load, and results in increased resistor self-heating. Therefore, a lower value would be better. In practice, many designers size the resistor for a maximum voltage drop of 100mV as a compromise point. Regardless of the resistance value chosen, it&rsquo;s the self-heating that is an insidious, potential problem, especially when it is carrying several amps and above. Despite their low nominal value, typically on the order of mere milliohms, it&rsquo;s unavoidable: When amps are flowing, you have watts of heat dissipation.</p> <p>This is a reality that cannot be ignored. The first problem is that self-heating degrades the resistor&rsquo;s reliability&mdash;those on/off thermal cycles are the worst. That&rsquo;s a legitimate but long-term concern. Second, and of immediate concern, is that such self-heating will shift the nominal value of the sense resistor itself, thus corrupting the perceived current-value reading.</p> <p>What to do? Unless you are in the milliamp or microamp current range, where any self-heating is acceptably small, a responsible designer must perform an analysis of resistance change using the vendor-supplied data for the temperature coefficient of resistance (TCR). Note that this may be an iterative process, considering resistance change may affect current flow (depending on what is driving the current into the load), which may (in turn) affect self-heating, which may affect resistance, which may &hellip; (it can go on and on!).</p> <p>TCR is not a small number that can be ignored. It&rsquo;s typically specified in parts per million per degree Celsius (ppm/&deg;C). An ordinary one-percent resistor has TCR on the order of several thousand parts per million per degree Celsius. Overall resistance change is a function of the materials used in the resistor element as well as the power rating and actual physical size of the component. Fortunately, vendors offer specialized, precision metal-foil resistors that have very low TCR.</p> <p>They achieve this by using various alloys composed of copper, manganese and other elements to manage TCR. For example, the Bourns<sup>&reg;</sup> Model <a href="/ProductDetail/Bourns/CRL2010-FW-R050ELF?qs=%2fha2pyFaduiMM%252bAnc5aOA1EHl4fO6jyeIXOCzjIyd8bbdzVOzXqrxA%3d%3d">CRL2010-FW-R050ELF</a> is a 50mΩ, one-percent device with a TCR of &plusmn;200ppm/&deg;C; however, devices with lower TCR are available. For the ultimate precision measurements in instrumentation applications, the lowest TCR resistors also come with fully characterized curves of their resistance versus temperature, which have a parabolic shape and are dependent on an alloy mix. It&rsquo;s a tricky alloy formulation. For example, somewhat counterintuitively, copper is added to the mix despite its extremely high TCR of 4,000ppm/&deg;C; yet, this is done to improve overall thermal dissipation and reduces self-heating of the element. The TCR of the resistor leads must also be factored into a high-precision analysis.</p> <p>Of course, some applications don&rsquo;t need high accuracy but, rather, are okay with a rough gauge. For these cases, a standard resistor may work. But many situations do need reasonable consistency and accuracy, and resistor self-heating plus TCR can easily make the presumed current value surprisingly incorrect.</p> <p>Hence, a low-TCR device should be specified on the bill of materials (BOM), but a lower-cost, higher-TCR unit should be accepted only after analysis and approval from the Design team is complete. The consequences of using a wrong current value in a system&mdash;such as an electric vehicle (EV) or hybrid electric vehicle (HEV) with a large battery pack, a photovoltaic (PV) array, or a motor driver&mdash;can range from inexplicable behavior (at first) to substandard performance and efficiency to simply dangerous.</p> 523Adopting A Functional Approach To Control Cabinet Functional Design,Circuit Protection,General,IndustrialMon, 30 Oct 2017 13:00:00 GMT<p>As more and more technology is deployed within industrial and commercial environments, there is an increasing need to safely and securely house all the various components that make up today&rsquo;s control systems. For many applications, the challenges include balancing the needs of securing crucial electronic systems, bringing order to complex systems and their associated wiring, and protecting equipment from environmental conditions such as moisture and dust.</p> <p>Planning the design of a control cabinet according to equipment functions not only makes sense from the perspectives of accessibility, maintenance, and flow, but it also helps separate any equipment that might be susceptible to interference from other components. Sturdy DIN-rail control cabinets have long been used to meet the essential requirements of production systems, accommodating everything from power, connectivity, and control. Safe and sound within a control cabinet, all the parts that make up a production control system can be laid out according to their individual functions.</p> <p>An example of a functional design approach can be found in the <a href="">Build with Confidence</a> brochure from <a href="">Phoenix Contact</a>. Providing the interconnectivity with the plant being controlled is that of the connectivity section. Tasked with making a reliable connection to cabling of all sizes, from heavy-duty electrical to small signal data switching, this section will also contain relays and isolation devices in addition to a variety of terminal blocks and connectors appropriate to the application. Emphasis needs to be placed on how each connection is made&mdash;whether by screw, crimp, or insulation displacement&mdash;and the quality of the connectors because the reliability and operation of the control system is underpinned by the connections to it.</p> <p>Safety is another key function located within the cabinet, providing further aspects of isolation, particularly that of intrinsically safe circuits. A mix of safety relays as well as configurable and distributed safety controllers will be housed within this area. Tasked with meeting occupational safety regulations such as OSHA, Phoenix Contact&rsquo;s safety controllers are configured through a simple graphical software interface.</p> <p>The next functional section is that of the core network components that are responsible for the communication, switching, and protocol conversion. This includes Ethernet/IP and process field net (PROFINET) solutions that are commonly used as the industrial network protocol of choice and also comprise the fabric of the control solution. Located above these are the networking and remote connectivity units that facilitate connectivity to the broader wired and wireless infrastructure. Typical components here include routers, firewalls, and 802.11-compliant wireless access points.</p> <p>Providing the essential control function is a variety of industrial PCs, programmable logic controllers (PLCs), and human-machine interface (HMI) controllers. Playing the pivotal role of receiving, processing and provisioning data, and using industrial network protocols such as PROFINET, EtherCAT, Modbus, and Ethernet/IP, these devices form the logical heart of the overall control solution.</p> <p>Essential to keeping everything running is that of the power reliability functional units. Incorporating the power supply units, surge, and other circuit protection devices, the management of power distribution, metering, and monitoring should also be allocated space in this area.</p> <p>A final point to consider is how the cabinet&rsquo;s various components and cables are identified. The use of equipment ID labels, cable markers, and other automated and hand tools not only helps speed the time spent configuring and commissioning a control system (making the shop floor more productive), buts also aids the ongoing maintenance of the installation. Attempting to fault-find in a cabinet without clear system diagrams and cable identification can result in considerable down-time and lost production.</p> <p>Adopting a functional layout approach to the design of your control cabinet installations will ensure they are built with confidence.</p> <p style="text-align: center;"><a href=""><img alt="Phoenix Contact Control Cabinet Design Infographic" src="/blog/Portals/11/mouser-phoenixcontact-infographic_v4-%281%29-680px.gif" style="width: 680px; height: 962px;" title="Phoenix Contact Control Cabinet Design Infographic" /></a></p> 483Bi-curious? Which Direction to Take when Dealing with a TVS ProtectionMon, 28 Sep 2015 17:00:00 GMT<p>Circuit protection is like car insurance. Some people feel like they don&rsquo;t need it if they are driving a very cheap car. I can understand that, as long as you don&rsquo;t hit a pedestrian or someone else&rsquo;s car. Car insurance is mandatory in many places for good reason. It&rsquo;s possible that nothing bad can happen, but if it does, a circuit can bring an entire system down if it doesn&rsquo;t have circuit protection.</p> <p>I was looking for circuit protection for a video device earlier today and decided on a Transient Voltage Suppressor (TVS). A TVS is pretty quick at responding to protect a circuit, so delicate circuits that can experience a lightning strike could benefit from a TVS because it would act fast enough to avoid damage. Each scenario is unique, so apply what makes sense in your application.<span>&nbsp; </span>So I knew a TVS was a good choice for my application.</p> <p>But should my TVS be &ldquo;unidirectional&rdquo; or &ldquo;bidirectional&rdquo;?<span>&nbsp; </span>I had forgotten. Had someone asked me to guess, I would&rsquo;ve thought it meant that you should apply bidirectional TVS whenever you know the voltage will go above <em>and </em>below ground. This is sort of right, and definitely applies to protecting circuits that experience AC voltage. But &ldquo;sort of right&rdquo; isn&rsquo;t something I am willing to live with, so I checked it out.</p> <p style="text-align: center;"><img alt="" style="width: 600px; height: 233px;" src="/blog/Portals/11/LynnetteReesePhotos/LR_BCTVS_01.jpg" /></p> <p style="text-align: center;"><span style="font-size: 10px;"><em>Figure 1: Unidirectional TVS from wonderful app note by On Semi: <a target="_blank" href=""></a></em></span></p> <p>&nbsp;</p> <p><span style="color: #000000;">Choosing a unidirectional or bidirectional TVS device depends on the circuit being protected. Yes, use a bidirectional TVS for AC power because it has bidirectional voltage swings. But this not <em>completely</em> right, because if I am throwing bidirectional TVS at everything &ldquo;just to be safe,&rdquo; I am missing something crucial: a bidirectional TVS assumes that going <em>below ground</em> is OK. &nbsp;This is not the case with a positive DC voltage circuit, where even though 0 to +5 volts might be ok, -5 volts could damage the circuit. This is when a <em>unidirectional </em>TVS is used, because a bi-directional 5V TVS will allow a range of -5 to +5 volts through to your circuit without regret. Choose a clamping voltage that you know will be OK for your circuit and anything downstream (as a good neighbor) to experience. The datasheets might not state what your components can withstand, and do not assume that the max voltage rating is OK. Max voltage rating on a datasheet is a tested value and may not apply perfectly to every single component every time. You need to either run a smoke test on your circuit, or assume the worst and go with the clamping voltages that you know will protect you but will not cramp the functioning of the circuit, either. If you test your circuit, keep in mind that TVS protects against transients and damage can occur that results in a delayed degradation, if not just plain failure. </span></p> <p>Thus:</p> <p>Bidirectional TVSes are used with AC circuits and with any DC circuit that is supposed to experience +/- DC Voltage. </p> <p>Unidirectional is for something that can&rsquo;t handle voltages in both directions. TVS for pretty much all ranges are available, so you can tailor it to your application. </p> <p>Choosing clamping voltages can be difficult, so being conservative isn&rsquo;t a bad idea. Place a TVS nearest to the input of where the transient is most likely to occur, such as the connector entry point on a PCB, keeping connective traces short to avoid parasitic capacitance. With high speed circuits, choose the lowest capacitance TVS you can find, because capacitance has a definite relationship with frequency and parasitic capacitance can be inadvertently generated. </p>110Don't Blame Me - I'm Only the Circuit Protection Designer! ProtectionThu, 12 Mar 2015 16:32:00 GMT<p>Seen any TV Repair Service trucks on your street lately? No? Have you ever taken a piece of electronics gear to a repair shop? Never? Really?? It's not that electronic equipment doesn't fail - it's just that the repair bill would likely exceed the cost of a replacement product. No one knows how much of the electronic trash in our landfills was put there because of technical obsolescence and how much was tossed before the end of its useful life because it failed. </p> <p> I've already expressed my view about how failures due to outside surge events (ESD, induced lightning surges or incidental power line contact) could be drastically reduced with <a target="_blank" href="">a "Surge Star" program</a>. Today I repaired a stereo amplifier that had suffered a component failure. The amplifier was less than 8 years old and had seen only light usage. What upsets me is that, as a circuit protection designer, I was powerless to prevent this one... </p> <p>The component that failed was an electrolytic capacitor. It was in a power supply circuit as a filter capacitor. The capacitor itself was 100uF and was rated at 25V. In the circuit it was in parallel with a 15V zener diode. That means that (unless the zener diode failed - which it didn't) the capacitor would never see more than 60% of its rated voltage in the forward direction and less than 1V in the reverse direction. As a circuit protection designer, I couldn't have done it better. There is no way this capacitor failed due to external circumstances! </p> <p>In the past few years, there has been a quiet revolution in most AC powered equipment. This discussion will exclude incandescent light bulbs (and they're getting harder to find...), AC motors (which are losing out to DC motors - especially in appliances) and resistance heaters (is there a less green thing to do with electricity than just converting it to heat?). Just about everything else that plugs into the AC grid has a switched mode power supply (SMPS) as its first functional block. </p> <p> In an SMPS, the line voltage is rectified directly - no power transformer is used to step the voltage down. You may have noticed "wall wart" power supplies used as USB chargers have gotten very tiny and lightweight. These are the most obvious examples of how losing the power transformer can make power supplies much smaller and lighter. </p> <p>Once rectified, the raw line voltage is then filtered by electrolytic capacitors. Any sophomore EE student will tell you that for 120VAC (RMS) inputs, this results in a 170VDC output. This is then put through a DC/DC converter to achieve the needed output voltage. But since most equipment today is rated for up to 240VAC input, 340VDC is considered the nominal voltage of the DC supply. To allow for line input voltage variation, most designers will specify 400V rated electrolytic capacitors. Conservative (high reliability) designs will call for 450V rated capacitors. </p> <p>To protect the rectifier diodes and the electrolytic capacitors, <a target="_blank" href="">MOV (Metal Oxide Varistor) devices</a> are almost always found on the AC input to clamp induced lightning and power surges. (When an AC motor shuts off, it can kick 6kV surges back onto the AC power line!) </p> <p>But in my experience, the electrolytic capacitors are still the weakest link in the SMPS design. I personally have tossed several LCD monitors and a LCD TV due to capacitor failure. <a href="">LED lighting designers are well aware that the LED's in their designs will outlast the capacitors in the driver circuits</a>.&nbsp; </p> <p>Electrolytic capacitors are big and expensive so they are an obvious target for cost and space cutting measures in the design cycle - squeezing design margins to the bare minimum. There are also a lot of inferior capacitors sold out there that probably don't meet their own ratings - I think I just pulled one out of this amplifier. </p> <p>The bottom line here is that circuit protection can't prevent every failure. Sometimes you just have to bite the bullet and either put enough margin in your design to allow for poor performance of cheap parts or pay up front for some real quality components. Just don't blame me... </p>37When to Knock Off the Knock-Offs... Protection,AllThu, 19 Feb 2015 22:41:57 GMT<p style="text-align: center;"><img alt="" style="text-align: center;" src="/blog/Portals/11/KellyCaseyPhotos/KnockOffs.jpg" />&nbsp;</p> <p style="text-align: center;">&nbsp;</p> <p>One of the duties that falls to us geek-of-the-family types is playing the role of the IT Help Desk for friends and relatives. In my case, I try to maintain my parents&rsquo; computer and connections even though they live 600 miles away. Without the ability to just show up when things go wrong, I need bullet-proof solutions. </p> <p>Last summer I installed a combination cable modem and WiFi router, as it seemed like a simple solution for what they needed. But I didn't realize that their cable company has the ability to disable the WiFi radio in their modem using remote commands. Others experiencing this same problem with this particular company and modem were discussing it on a forum where I often lurk. Apparently it&rsquo;s part of the cable company&rsquo;s periodic maintenance routine to disable WiFi on company-owned routers where the customer hadn't paid for the WiFi option. The fact that the cable company didn't own this modem didn't matter - the commands kept coming, forcing my folks to have to connect via Ethernet cable and perform a complex set of operations in the Admin screens to reset the radio. The cable company zombies on the phone denied it (it&rsquo;s not on their script) but after getting through to multiple technicians and spending a few hours at it, I determined that I would have to solve the problem without their help. </p> <p>My solution was to buy a <em>separate</em> WiFi router (one they couldn't control) and connect it to one of the LAN ports. I found a tiny router - about 4cm square that required only a USB connection for power and the LAN cable; very simple and compact (and inexpensive). I configured the router at my house and ran it for a day or two, really trying to tax it by connecting five devices and streaming some video. It was rock-solid and I knew I'd be a hero... </p> <p>Six hundred miles later, when I got to the folk's house and connected the new WiFi router, it became very unstable. One minute it was fine, the next moment it dropped the WiFi link. I could reconnect, but streaming video was impossible due to the interruptions. Can you guess the problem? I couldn't; at least not until hours later, when I realized there was one component in the system that had changed from my successful home tests... </p> <p>The USB supply for the router was a cheap knock-off cell phone charger that I'd purchased for $2 on a site that shipped direct from China. Oops. After replacing it with a name-brand charger (with the exact same form factor), the router worked perfectly. I&rsquo;m guessing that the cheap charger had either ineffective EMI filtering or poor output voltage regulation that caused the router to constantly reset. The charge was adequate for charging phones, but completely unusable as a 5V power supply. </p> <p>USB began life as serial data port but morphed into one of the most ubiquitous battery charging power standards in the world. Youngsters might not know this, but there was a time when every cell phone came with its own proprietary wall charger. If you changed from, say, Nokia to Motorola, you'd have to replace all of your home and car chargers as well. Now, every phone I have can be charged from a USB port (although the phone end of the charging cable may still be proprietary for some phones). </p> <p>Now we see USB further expanding its utility to go well beyond charging batteries. Many electronic devices now use USB for their primary power supply. However, my experience has shown that not all USB supplies are up to this new task. I've skimmed the USB 3.1 specification as well as the USB Battery Charging 1.2 specification and found no reference to any noise measurements. So I guess for now it's "buyer beware" and my advice is to stay away from the cheap knock-off devices if you need clean power to operate electronics devices... </p>36A Conversation on High Operating Voltages ProtectionTue, 09 Dec 2014 16:15:00 GMT<p>Like most professions, engineering has developed a language of its own. This is needed to convey very specific and precise information. Fuse design engineers, for instance, make a very clear distinction between an overload condition and a short-circuit condition. (Overloads are in the range of ~200% of the fuse's rating while short-circuits are 10X or more.) </p> <p>Recently, a few of us Mouser Bloggers had a discussion on the term "High Voltage". <a href="" target="_blank">Lynnette Reese</a> was asking about present-day design activity at high voltages and what techniques were used to modulate High Voltage AC signals from analog control circuits. </p> <p>The discussion pretty quickly turned to defining "High Voltage". Let the Geek Speak commence! </p> <p> I noted that to a power distribution engineer, the threshold for HV would be something like 40kV. They often refer to 25kV switchgear as "medium voltage". Littelfuse defines it this way: </p> <p> &ldquo;The terms &lsquo;Medium Voltage&rsquo; and &lsquo;High Voltage&rsquo; have been used interchangeably by many people to describe fuses operating above 600 volts. Technically speaking, medium voltage fuses are those intended for the voltage range from 2,400 to 38,000 Vac. High voltage fuses are for circuits carrying voltages greater than 38,000 Vac." (<em><a href="" target="_blank">source</a></em>) </p> <p>To a consumer electronics / communications system engineer, the threshold is probably more like 800V. Insulation and arcing take on a much more aggressive characteristic at those levels. These are typical limits of high voltage <a href=";Ntt=190359769&amp;N=1323043" target="_blank">Silicon-Controlled Rectifiers</a> (SCRs, a.k.a. thyristors) and is about the peak voltage of a 480V AC line. </p> <p><a href="" target="_blank">Mike Parks</a>, another Mouser blogger, mentions that. "In my shop, anything that can deliver more than 30V gets slapped with a warning sticker. I think that is simply a very conservative estimate, though I do believe given certain skin conditions (salinity, moisture, etc.) 50V can deliver dangerous current to a human body." </p> <p>Rudy Ramos is a Technical Project Manager at Mouser Electronics. He has experience in the support of a lot of front end wafer fab equipment for the likes of TI, National, and Hitachi, and notes that the semiconductor manufacturing process requires lots of specialized equipment that incorporate a horde of technologies including high voltage. Says Rudy: </p> <p>"A good majority of the equipment requires both high voltage and high current for either the actual manufacturing process or as a source of power to do the job, as is the case with a scanning electron microscope (SEM). The SEM requires very high voltage power supplies in order to produce the electron beam that traces the object being scanned/inspected (silicon). Ion Implanters on the other hand, are capable of ion beam energies in the range of 200KeV or higher." Another piece of equipment, plasma dry etch equipment, uses both RF and Microwave to produce the plasma used to process the silicon wafers. Both energy sources are high current and high voltage." </p> <p>In Bill Schweber's article &ldquo;<em><a href="file://localhost/%20http/">Designing at Very High Voltages: Everything Changes, Especially Your Way of Thinking</a></em>,&ldquo; he basically states that products used at high voltages of 600V - 1500V+ are typically made for specific purposes. That is, most electrical/electronics devices that operate at high voltages are not commodity-type items. Protection against high voltages associated with electrostatic discharge are much more common, but the expectation is that the extreme voltage will be very brief. However, for more commonly known applications like x-rays, MRIs, solar, electric trains/light rail, and power distribution, there are very specific custom catalog and made-to-order products. </p> <p>I would be very interested in hearing from you on the challenges you've faced in dealing with high voltage applications. How did you control the high voltages? Did you have issues with arcing or insulation? How did you maintain isolation between the HV signals and your control signals? How did you assure the safety of the people working around the equipment? And please....feel free to use Geek Speak!! </p>29Circuit Protection – Why Bother?? ProtectionThu, 25 Sep 2014 20:09:04 GMT<div><br /> </div> <p>Let&rsquo;s face it - circuit protection can be a tough sell. Here&rsquo;s why:&nbsp;</p> <p>1) Circuit protection isn&rsquo;t sexy. It doesn&rsquo;t add any &ldquo;wow factor to the product."&nbsp;</p> <p>2) In fact, it doesn&rsquo;t add any functionality to the product at all.&nbsp;</p> <p>3) Any effect circuit protection has on the function of a device is likely negative. Adding capacitance, resistance or potential non-linearity to an I/O port is rarely useful in promoting high data rates.&nbsp;</p> <p>4) It adds cost and can increase complexity.&nbsp;</p> <p>What circuit protection does do is provide some measure of reliability. It gives the end product the ability to sustain and likely survive potentially damaging electrical surges or contact with unexpectedly high voltages without exposing the user to electrical shock or becoming a fire hazard.&nbsp;</p> <p style="text-align: center;"><img alt="" src="/blog/Portals/11/KellyCaseyPhotos/whybother.jpg" style="text-align: center;" />&nbsp;</p> <p>However, protection against rather vague threats is always a challenge. <a target="_blank" href="">Mothers Against Drunk Driving (madd&reg;)</a> has undoubtedly had a positive effect on the safety of our roads, but the identities of the people whose lives their campaigns have saved cannot be determined.&nbsp;</p> <p>Circuit protection has become the norm in many types of equipment and electrical equipment is more reliable today than ever before, so when the boss tells you he doesn&rsquo;t want to pay for circuit protection, it&rsquo;s a bit like saying that seat belts aren&rsquo;t useful anymore because no one is dying in traffic accidents! I would point out that circuit protection has drastically improved the safety and reliability of all kinds of electrical equipment and its very presence is the reason for the increased safety and reliability. But that&rsquo;s hard to prove, and better circuit protection may hard to justify on a tight budget.&nbsp;</p> <p>So what is the motivation for designing circuit protection into your products? In my view, there are three kinds of circuit protection customers:&nbsp;</p> <p><strong>1) The Elite:</strong> These are companies who simply want to be the best in their markets. They are the household names &ndash; the premium brands. These companies and their customers value the enhanced reliability and longer life their designs enjoy when equipped with robust circuit protection. In a sense, they are primarily protecting their brand &ndash; their reputation. Their customers are selecting to buy their products in part due to this enhanced reputation, which allows them to price their products at a premium, thereby preserving their profit margins.&nbsp;</p> <p><strong>2) The Astute:</strong> These are companies that can justify the higher costs of designs equipped with circuit protection. Equipment that is leased or rented must have sufficient reliability to stay functional in the hands of someone that doesn&rsquo;t own it. Also, equipment sold with long warranty periods (like commercial/industrial LED lighting) must remain in service or the selling company, and not the purchaser, may be on the hook for repairs or replacement. These companies can calculate the payback on circuit protection. If the MTBF (mean time before failure) can be extended sufficiently to reduce the probability of failure &ldquo;X&rdquo; amount across all equipment sold, then they will save &ldquo;Y&rdquo; dollars in repair/replacement costs that can be used to fund the circuit protection. As a side benefit, these companies enjoy an improved reputation as well &ndash; without affecting their bottom line.&nbsp;</p> <p><strong>3) The Slackers:</strong> Let&rsquo;s face it &ndash; this is a big group. They only use sufficient circuit protection to satisfy regulatory requirements. Essentially, they only use CP components because they can&rsquo;t be in their market without it. They will search for the cheapest protection scheme that will allow them to just sneak by the regulatory tests. They aren&rsquo;t going to spend one penny more to extend the life of their products because they compete solely on price and failed product is someone else&rsquo;s problem&hellip;&nbsp;</p> <p>Into which group does your company fall? I can assure you that, as a designer, it&rsquo;s a lot more fun working in the Elite bunch! </p>30Circuit Protection without Circuit Protection Components ProtectionMon, 11 Aug 2014 21:52:48 GMT<p><span style="line-height: 1.6em;">Have you ever thought about circuit protection as analogous to fire protection? There are lots of ways to prevent fires. There are active systems (fire sprinklers, automated extinguisher systems) and passive systems (self-extinguishing materials, self-closing fire doors) and safety-by-design systems where careful selection of non-flammable and insulating materials as well as physical layout make fire propagation nearly impossible. As it turns out, circuit protection has similar options. Here is an example of circuit protection via a safety-by-design technique:&nbsp; </span></p> <p><span style="line-height: 1.6em;">When you claim to have expertise in a subject, you tend to want to measure up, so when a colleague called to ask me what I would do to protect a digital multi meter, I dove right in with my usual alacrity. But after spending at least half an hour happily conversing with myself on the dangers of under-protecting, I realized I had a conundrum on my hands. A digital multimeter (DMM)&hellip;.any test equipment, for that matter, has the responsibility of accurately measuring a signal, any signal, without complaint. 0.05mV? No problem. 120V? No problem. 1000V? &hellip;..wait a minute. How am I supposed to dispense pearls of wisdom on protecting input circuitry that has to discern truths at 0.5mV and at 1000V with the same circuit protection? Devices for circuit protection have limits, you know.&nbsp;</span><span style="line-height: 1.6em;">&nbsp;</span></p> <p><span style="line-height: 1.6em;">So the multimeter presents a tricky design issue: with this being a meter that is designed to handle such a huge range and is subject to application errors (like trying to measure the resistance of 120VAC!), it has to be sensitive enough to make it useful as a measurement device and be robust enough to withstand operator-errors and other stupid mistakes.&nbsp;</span></p> <p><span style="line-height: 1.6em;">Test equipment is not your typical embedded product that has fairly predictable inputs in its lifetime, and any circuit protection needs to retain the precision aspect. The use of traditional circuit protection components is going to be problematic, as they are highly non-linear when driven to their operational endpoint. The input to a DMM must be extremely linear for the instrument to have any hope of useful accuracy.&nbsp;</span></p> <p style="text-align: center;"><span style="line-height: 1.6em;"><img alt="" style="text-align: center;" src="/blog/Portals/11/KellyCaseyPhotos/CircuitProtectionWO.jpg" /><br /> </span></p> <p><span style="line-height: 1.6em;">There&rsquo;s no real magic to engineering anything. Engineering is just a combination of applied training, common sense, and attention to detail. The most difficult part is trying to think up all the &ldquo;corner cases&rdquo; and stuff that could happen to break whatever it is you&rsquo;re designing. Neil Armstrong said that &ldquo;Science is the study of what is. Engineering is the study of what can be.&rdquo; I might be paraphrasing, but I like it. And I could add that engineering is also the study of how to prevent things from breaking, which usually means assuming that at some point someone is going to connect a multimeter set on &ldquo;.00mV&rdquo; range to a 1000V source. At this point, I am really respecting the idiot-proofing challenges that the folks at Fluke, B&amp;K, and LeCroy have to deal with.&nbsp;</span><span style="line-height: 1.6em;">&nbsp;</span></p> <p><span style="line-height: 1.6em;">Even the cheapie &ldquo;give-away&rdquo; DMMs usually have some regulatory approval. I own one that is marked with warnings not to exceed 750VAC or 1000VDC. That means that the input circuits are designed to withstand and operate normally at those voltages. So common sense says that there is no need for overvoltage protection after the test leads (inputs) of the multimeter, because the components themselves are supposed to handle these high voltages and anything higher would violate the safety warning. It does come equipped with a fuse for fire safety.&nbsp; </span></p> <p><span style="line-height: 1.6em;">In other words, what ordinary electronics would view as hazardous voltages, a DMM considers them just another input. The safety of the input is largely inherent in the design of the switching and scaling circuits that knock those high voltages down to levels that are in range of D/A and A/D converters. Designers must carefully select these components based on worst-case scenarios. Beyond the fuse, I doubt there is much CP content - perhaps some ESD protection on the display&hellip;&nbsp; </span></p> <p><span style="line-height: 1.6em;">In my fire protection analogy, the DMM represents an inherently non-flammable design, owing to careful selection of interface components that have the inherent ability to withstand the unpredictable abuse of the DMM.</span></p>32Failure Modes Matter ProtectionTue, 01 Jul 2014 21:29:23 GMT<p>When a piece of electronics fails, the manner in which that failure occurs is important and should be included in the design specification &ndash; especially for a consumer product. Most manufacturers realize that a <a href="" target="_blank">UL</a> (or ETL or other safety lab) Listing is a minimum requirement for product safety. But those requirements are focused on preventing fires and shock hazards. A piece of gear that fails in a plume of foul-smelling toxic fog, coupled with a few sparks or even a good ol&rsquo; firecracker report invokes a visceral reaction in the consumer that will absolutely guarantee that the replacement product will be a different brand. They just don&rsquo;t want to experience that violent, scary failure again and will go out of their way to assure no repeat performances. </p> <p>On the other hand, electronic equipment that quietly just quits working will likely be replaced with the same brand &ndash; and often the same model. This avoids learning a new system or installing new software. It&rsquo;s just replace and go. A few of us have a certain piece of gear that we wish would fail (nicely) so that we have a good excuse to upgrade without having to explain the subtle or technical advantages to the household budget master! </p> <p>As a designer, I feel compelled to protect the end customer from all dangers &ndash; real or perceived. And I don&rsquo;t really want to hear about product cost issues. The protection schemes cost mere pennies. Of course we designers can always get overruled, but my bias is to design the best possible product and if management wants to cheap-out, well &ndash; I guess it&rsquo;s the boss&rsquo; prerogative&hellip; </p> <p>My two pet peeves in this area are both printed circuit board patterns. One is for overvoltage protection and the other is for overcurrent protection. </p> <p style="text-align: center;"><img alt="" src="/blog/Portals/11/KellyCaseyPhotos/Screen%20Shot%202014-07-01%20at%204.18.28%20PM.png" style="width: 596px; height: 252px;" /></p> <p> Figure 1 shows a classic &ldquo;PC Board Fuse&rdquo; &ndash; it&rsquo;s just a necked-down trace on the primary AC input. The control of the cross-sectional area of a trace like this is pretty lousy compared with the precision utilized by real fuse manufacturers. Being in contact with the PCB, the arc caused by a short circuit will usually burn a nice carbon path on the board surface that will continue to conduct power, smoke and smell until the burned region develops a large enough and rough enough surface that will allow the arc to extinguish. As long as all this happens inside the product, it will likely pass the regulatory test. </p> <p style="text-align: center;"><img alt="" src="/blog/Portals/11/KellyCaseyPhotos/Screen%20Shot%202014-07-01%20at%204.18.38%20PM.png" style="width: 601px; height: 346px;" /></p> <p>Figure 2 shows a &ldquo;Shark&rsquo;s Teeth&rdquo; overvoltage protection pattern. The theory behind this pattern is that during a voltage surge, the electric field will be concentrated at the trace points and there will be a flash over between the sets of teeth. Like the PC Board Fuse, these tend to develop a carbon path on the board that is sustained until a large area of the board is burned up. Even when they do work, the points of the trace are usually sufficiently damaged (rounded) as to render the pattern ineffective in future events. </p> <p>Both of these methods are cheap and insufficient as to be considered unethical or immoral by some. Why do this when it&rsquo;s so easy to add a legitimate solution? </p> <p>TE Connectivity has a single product that performs both the overvoltage and overcurrent function. Check out the <a href="" target="_blank">2Pro device family (LVM2P-xxxxxxxxx)</a>. They are useful in a wide variety of applications and just might be your ticket to long-lived trouble-free products. </p>31THAT Doesn’t Need Circuit Protection! ProtectionTue, 11 Feb 2014 22:43:48 GMT<p><span style="color: black;">How many times have I heard that line?&nbsp; In future I&rsquo;ll discuss the different classes of clients that circuit protection device manufacturers serve.&nbsp; But right now I&rsquo;d like to offer up a real-world example of an application that most folks would never dream would benefit from circuit protection:&nbsp; Solar-powered walkway LED lights.&nbsp; I purchased five of the lights&nbsp;for about $15 each.&nbsp;&nbsp;</span></p> <p style="text-align: center;"><span style="color: black;"><img alt="" height="384" width="512" align="middle" src="/blog/Portals/11/KellyCaseyPhotos/Blog2-Photo%201.JPG" style="text-align: center; vertical-align: middle;" /><br /> </span></p> <p><span style="color: black;"><br /> </span></p> <p><span style="color: black;">I didn&rsquo;t buy any spare units because I expected them to last a while.&nbsp; Well-constructed, they performed nicely.&nbsp; But in the third year, two of them failed &ndash; they just quit working.&nbsp; As you might imagine, losing two also makes the other three pretty useless, as my installation really needed five!&nbsp; Of course there were no matching replacements to be found.&nbsp; Time to break out the screwdriver and multi-meter!</span></p> <p style="text-align: center;"><span style="color: black;">&nbsp;<img alt="" height="384" width="512" align="middle" src="/blog/Portals/11/KellyCaseyPhotos/Blog2-Photo%202.JPG" style="text-align: center; vertical-align: middle;" /></span></p> <p><span style="color: black;">Now it doesn&rsquo;t take a genius to troubleshoot this design &ndash; the electronic bill of materials is pretty spare (see the PCB in the second photo):</span></p> <p><span style="color: black;">2 x AAA Rechargeable Cells (not pictured)</span></p> <p><span style="color: black;">3 x Solar Cells (not pictured)</span></p> <p><span style="color: black;">1 x Photocell (not pictured)</span></p> <p><span style="color: black;">1 x Resistor</span></p> <p><span style="color: black;">1 x Inductor</span></p> <p><span style="color: black;">1 x Diode</span></p> <p><span style="color: black;">1 x Switcher IC</span></p> <p><span style="color: black;">2 x LED</span></p> <p><span style="color: black;">&nbsp;</span></p> <p><span style="color: black;">The batteries were fully charged, so I ruled out the batteries and the solar cells.&nbsp; The LEDs were in parallel, so it was unlikely that both would fail.&nbsp; I focused on the switcher IC.&nbsp; After quite a bit of searching, I determined it was an oddball part and found an obscure distributor in China that would sell me 10 pcs.&nbsp; About a month after ordering the ICs, they showed up.&nbsp; I replaced the IC in the first light...</span></p> <p style="text-align: center;"><span style="color: black;"><img alt="" height="384" width="400" align="middle" src="/blog/Portals/11/KellyCaseyPhotos/Blog2-Photo%203.jpeg" style="text-align: center; vertical-align: middle;" /><br /> </span></p> <p><span style="color: black;">&nbsp;...and <em>voila!</em>- it works.&nbsp; Pretty proud of myself, I replaced the IC in the second light and&hellip;&hellip; nothing.&nbsp; Probably a bad IC, I told myself.&nbsp; Replaced it again and&hellip;.. nothing.&nbsp; A close examination of the inductor revealed serious surface cracks.&nbsp; I ordered a handful of J.W. Miller 542-77F820-RC (82uH) inductors from Mouser Electronics, they arrived quickly,</span><span style="color: black;"> and the second light was back in business.</span></p> <p style="text-align: center;"><span style="color: black;"><img alt="" height="155" width="400" align="middle" src="/blog/Portals/11/KellyCaseyPhotos/Blog2-Photo%204.jpeg" style="text-align: center; vertical-align: middle;" /><br /> </span></p> <p><span style="color: black;">&nbsp;</span></p> <p><span style="color: black;">I have to wonder how these failures occurred.&nbsp; The PC board is inside a metal housing with no attached cables &ndash; how does a surge get in?&nbsp; It must have been a surge &ndash; a pair of AAA batteries could never have damaged the inductor.&nbsp; And it must have been an induced surge from nearby lightning.&nbsp; While the metal housing offers electrostatic protection, it offers no protection from magnetic fields.&nbsp; </span></p> <p><span style="color: black;">&nbsp;</span></p> <p><span style="color: black;">From the oddball switcher IC&rsquo;s datasheet, I could see that a trio of Littelfuse P0080EA sidactor devices connected from each of the three non-grounded leads of the IC to ground would have prevented any surge damage to the IC as well as all of the other electronic components in the solar light.&nbsp; Maybe I&rsquo;ll order some of those from Mouser and add them in.&nbsp; That way my grandchildren will be able to enjoy these lights because I think they would be pretty much indestructible at that point. I just wish the OEMs had gone the extra step and added circuit protection. I&rsquo;m certain that they could have charged a premium for a long-term warranty (on everything but the easily replaceable batteries) and never have to pay a warranty claim.&nbsp; That would increase their profits, and with the right marketing, create a loyal customer base.</span></p> <p>&nbsp;</p>33