I'm trying to convert a broken halogen lamp to LED using a commonly available G4 bulb.

I have a lot of orphaned universal power supplies from various electronic accessories. Can I use a 100-240V => 12VDC (switching?) power supply to power an LED bulb?

[update] The specs on the bulb says driver: constant current. Is constant current incompatible with switching power supplies?

  • \$\begingroup\$ You should add some more information, for example the specification of the bulb and the specifications of the power supply. In general you can run a 12V bulb from a 12V power supply, but obviously it depends on the current ratings, the stiffness of the power supply, and how much ripple current the LED lamp makes. \$\endgroup\$
    – james
    Jan 26, 2019 at 12:13

1 Answer 1


Can I use a 100-240V => 12VDC (switching?) power supply to power an LED bulb?

Maybe. Yes with the correct LED(s).

NOTE: An LED is not a "bulb". You cannot look at an LED as a little incandescent light bulb, they are very different.

Is constant current incompatible with switching power supplies?

No. A constant current supply can be a switching power supply. Power supplies can be constant voltage or constant current. For you it is probably best to use a typical constant voltage power supply and a resistor to limit the current.

It is best to use a voltage just over the LED's forward voltage.

Example: A 12V power supply would work well for a 12V Cree XHP50.2 LED
You may be able to find one (or similar) mounted to a "star" PCB. Try searching for "flashlight LED PCB".

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These LEDs get very hot so I would start out trying for for about 11V and 350 mA and see if it gets too hot. Temperature should not burn you. You should be able to touch the PCB for at least a few seconds.

For this Cree LED, try a 1 W, 3 Ω resistor. This should be plenty bright. It would be better to use multiple LEDs at a lower current (higher resistance) to keep the temperate low rather than run this LED at a higher current/temperature. If you need it brighter or it gets too hot.

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