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Prepare circuit of Automatic Emergency Light using IC- LM317 on bread board. Make circuit
on PCB.
Battery, Transformer, Resistors, Capacitors, LED, IC- LM317, Transistor, Diodes
Here is a white-LED-based emergency light that offers the following advantages:
1. It is highly bright due to the use of white LEDs.
2. The light turns on automatically when mains supply fails, and turns off when
mains power resumes.
3. It has its own battery charger. When the battery is fully charged, charging stops
The circuit comprises two sections: charger power supply and LED driver.

The charger power supply section is built around 3-terminal adjustable regulator IC
LM317 (IC1), while the LED driver section is built around transistor BD140 (T2).
In the charger power supply section, input AC mains is stepped down by
transformer X1 to deliver 9V, 500 mA to the bridge rectifier, which comprises
diodes D1 through D4. Filter capacitor C1 eliminates ripples. Unregulated DC
voltage is fed to input pin 3 of IC1 and provides charging current through diode D5
and limiting resistor R16. By adjusting preset VR1, the output voltage can be
adjusted to deliver the required charging current.

When the battery gets charged to 6.8V, zener diode ZD1 conducts and charging
current from regulator IC1 finds a path through transistor T1 to ground and it stops
charging of the battery.

The LED driver section uses a total of twelve 10mm white LEDs. All the LEDs are
connected in parallel with a 100-ohm resistor in series with each. The common-
anode junction of all the twelve LEDs is connected to the collector of pnp transistor
T2 and the emitter of transistor T2 is directly connected to the positive terminal of
6V battery. The unregulated DC voltage, produced at the cathode junction of diodes
D1 and D3, is fed to the base of transistor T2 through a 1- kilo-ohm resistor.

When mains power is available, the base of transistor T2 remains high and
T2 does not conduct. Thus LEDs are off. On the other hand, when main fails, the
base of transistor T2 becomes low and it conducts. This makes all the LEDs (LED1
through LED12) glow.

The mains power supply, when available, charges the battery and keeps the LEDs
off as transistor T2 remains cut-off.
During mains failure, the charging section stops working and the battery supply
makes the LEDs glow. Assemble the circuit on a general-purpose PCB and enclose
in a cabinet with enough space for battery and switches. Mount the LEDs on the
cabinet such that they light up the room. A hole in the cabinet should be drilled to
connect 230V AC input for the primary of the transformer.
1.Collect all the components and fix them(excluding-transformer and re-chargeable
battery) in the bread board according to the circuit diagram.
2.Now check the circuit using battery (6-9v non- rechargable) by connecting its
+ve and ve terminals across D2 and D3 respectively.
3. Adjust/rotate the variable resistance simultaneously.If the bulb glows we can say
that all the connections are proper.
4. Now solder the whole circuit in PCB and join transformer and rechargable
battery to the circuit in the respective poistion.
5. When we connect the circuit to 230v power supply the LED (near the BC 548)
glows inculding that the battery is geeting charged..
6. After the battery is fully charged remove it from the socket and switch ON the
circuit. The LEDs starts glowing,