I saw this press release where DCM was listed as a feature for a new Infineon driver chip.

enter image description here
Source: led-professional.com

I'm involved in LED driver design for Horticulture where DCM is undesirable.

In what case would DCM be desirable for any LED lighting application?

Or is DCM in reference to something other than the output to the LED? Still, if so, why is DCM desirable in any LED driver?

UPDATE: Why DCM is used in the power stage was answered in the comments. I still wonder if DCM is ever desirable in the output to the LEDs? This secondary question is not related to the linked AC powered LED driver.

Datasheet defines operating modes on Page 11 and has an appendix with definitions of related terminology.

Section Other PFC Protections, mentions CCM.
Section 3.2 Flyback Controller Features, mentions DCM.

Datasheet: XDPL8221 Digital PFC+Flyback Controller IC

enter image description here

  • \$\begingroup\$ DCM is a common thing in switching power supplies. They switch to DCM when the output load is too low for the PWM regulation to keep the output voltage steady. I don't know why that would be a bad thing for your grow lights. \$\endgroup\$ – JRE Mar 18 at 21:49
  • \$\begingroup\$ @JRE research has found any type of lighting strobe effect will adversely affect growth. This is why I am unfamiliar with DCM. And I always use a DC-DC buck driver or an off the shelf Mean Well CC driver. \$\endgroup\$ – Misunderstood Mar 18 at 21:50
  • \$\begingroup\$ @JRE The output to the LEDs can be CCM or DCM. I assumed that DCM was a cost saving measure for cheap LED drivers, e.g. driving an LED with an FET and PWM. \$\endgroup\$ – Misunderstood Mar 18 at 21:59
  • \$\begingroup\$ You've linked to a switching regulator. It varies the on time to control the the output voltage or current. DCM is used when the regular switching frequency (at the lowest on time) is still too much for the attached load \$\endgroup\$ – JRE Mar 18 at 22:05
  • \$\begingroup\$ @JRE if you look at the schematic you will see the output marked as LED+ and LED-. And the press release was on led-professional.com. I assumed the DCM in this release is related to the power stage, but I have always wondered if DCM was ever desirable in the LED output as well. \$\endgroup\$ – Misunderstood Mar 18 at 22:10

A SMPS in DCM will not give lighting strobe effect.

Discontinuous Conduction Mode is an operational mode of a switching power supply in which the current starts and returns to zero.

This applies to the current through the inductor/transformer, not to the current through the load.
The load current will have a non-zero mean value.

EDIT: additional clarification
Another 'proof' DCM will not give lighting strobe effect: check the grey shaded features of this driver in led-professional.com

Target Applications:
Flicker-free LED driver for indoor or outdoor applications


The IC supports so to say two SMPS, the PFC and the flyback. The following applies:

  1. DCM in the PFC stage (power stage) is to support light load conditions and ensure efficient operation.
  2. DCM in the flyback is to support light load conditions and ensure efficient operation.

So, DCM is used in both SMPS for exactly the same reason.

Depending on the actual situation, the built-in digital control (of the flyback converter) selects the best mode of operation. It can switch between

  • QRM: quasi-resonant (when e.g. 100 LED's are connected)
  • DCM: discontinuous conduction (when e.g. 10 LED's are connected)
  • ABM: active burst modes. (when e.g. 1 LED is connected)

(Number of LED's is illustrative of course)

Why would Discontinuous Conduction Mode be desirable for an LED driver?
To have freedom to connect 1 LED one time and 100 LED's the other time, using the same LED driver having high efficiency for every type of load.

  • \$\begingroup\$ And why is that desirable? \$\endgroup\$ – Harry Svensson Mar 18 at 23:09
  • \$\begingroup\$ Because otherwise you can't serve light (medium in this case) loads without getting an overvoltage. It's a must have rather than a desire. \$\endgroup\$ – Huisman Mar 18 at 23:16
  • \$\begingroup\$ Check @JRE 's first remark \$\endgroup\$ – Huisman Mar 18 at 23:23
  • \$\begingroup\$ I now understand the reason for DCM in an SMPS as stated in my update. DCM and CCM does apply to "the current through the load". Many LED driver chips require that the output to the LEDs operate in CCM. Some datasheet state they can be operated in DCM. I never understood why anyone would want the LED load run in DCM. \$\endgroup\$ – Misunderstood Mar 19 at 6:59
  • 1
    \$\begingroup\$ @Misunderstood Please read the addition to the answer. I hope it becomes clearer now. \$\endgroup\$ – Huisman Mar 19 at 8:17

Your Answer

