I have a couple of 12V LEDs lying around, and some old 220V to DC 12V transformers. I want to build a little portable lamp.

The LEDs flicker: I guess the transformers are not delivering a constant voltage. Now, of course I could get a LED 12V driver for a couple of bucks, but that would not be sportsmanlike. Is there any common trick / simple solution, like adding a smoothing capacitor or such like?

  • \$\begingroup\$ It depends what kind of transformers or power supplies they are. Have you measured them? If they can't provide the current the LEDs need, then they can't work. \$\endgroup\$
    – Justme
    Commented Mar 12, 2023 at 18:10
  • \$\begingroup\$ What type of power supple it it? If it is a normal 12 switching power supply, it should not flicker. There are capacitors already inside. \$\endgroup\$
    – MikroPower
    Commented Mar 12, 2023 at 18:11
  • \$\begingroup\$ LED data sheet needed. \$\endgroup\$
    – Andy aka
    Commented Mar 12, 2023 at 19:37
  • \$\begingroup\$ Is it a transformer? Those output AC. They are heavy. If it is outputting DC, then it's something more complicated. It's possible it is borked, or possible you are overloading it. But if you want help with that, you'll have to describe it more accurately than "transformer". \$\endgroup\$ Commented Mar 12, 2023 at 22:51

1 Answer 1


A normal "12V white LED" is made from 3 LEDs, so the voltage drop under nominal current would be 9 Volt.

  • If you do not use a resistor to limit the current, then the internal current protection of the power supply can go in his limitation.

  • An other possibility is that the bonding wire is broken and the LED is flickering because of the thermal stress of the bonding wire.

Normally you can use a matching resistor in series to the LED to reduce the current.


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