I've just purchased some 12V LED MR-16 bulbs, intending to use them to replace the existing 12V Halogen MR-16 bulbs in my bathroom. I have found, much to my chagrin, that the LED bulbs seem to have different supply requirements.

What do I need to do in order to replace the halogen bulbs with the LED bulbs I've purchased?

The circuit to which the bulbs connect is 12V. Mains voltage is 240V here. To the best of my knowledge the LED bulbs are driver-less. Do I need to install a driver between each socket and the bulb, or does it just need to be somewhere on the 12V circuit? I do not have access to the 240V-12V transformer, even if I felt comfortable manipulating it.

I have tried the following configurations for the 4 sockets in my bathroom:

  • 4 Halogen
  • 2 Halogen, 2 LED
  • 4 LED
  • 1 LED

In each case the halogens act as would be expected: on when I switch the power on, off when I switch the power off.

When I switch on the power: The LEDs flash on, then go off and stay off.

When I switch off the power: LEDS stay off.

  • 2
    Please don't cross post to several Stack Exchange sites simultaneously - electronics.stackexchange.com/questions/14219/… - if you get the wrong site, or the question hasn't got the necessary attention after a few days, it can be migrated for you.
    – ChrisF
    Commented May 12, 2011 at 13:14

1 Answer 1


Key difference:

  • Halogen lights generally run from AC so this is what your transformer outputs.

  • LED's require DC so generally yes, you will need a rectified output from your transformer.

I am guessing the transformer is providing enough forward voltage on initial switch-on, but not thereafter.

You may be able to add a rectifier circuit at each bulb location to cope with this.

  • Yup- Agreed on that- Halogen runs on Alternating Current (AC) - You will need to change the transformers to DC12Volt. To be hones I would stick with the halogens- better light. but the LED's don't give off heat I suppose and last longer.
    – Piotr Kula
    Commented Jun 22, 2011 at 14:53

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