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Hello,

We have a light fitting with G4 bulbs and I am attempting to replace with LEDs. The main part of the light fitting has a transformer to convert the mains down to 12v. However I think it does not have a rectifier as the LEDs exhibit a pronounced 50HZ flicker when fitted.

I guess that normal G4 bulbs do not care if the supply is AC or DC but clearly AC is no good for LEDs.

Does anyone know of any G4 LEDs that contain a built-in rectifier or will I have to install a rectifier in the light fitting?

Any help on this issue is greatly appreciated. We really like this light and do not want to get rid of it but with normal bulbs it uses 130 watts which seems rather wasteful.

Regards, Matt

What you have assumed is correct. You would be better off taking out the transformer and installing a 12v DC power supply.
It may also be just as easy to bypass the transformer and use a "remote" 12v DC power supply and mount it in the ceiling above the light.(That is what is done with most "down lights")

LED lights are a package with rectifier, driver etc built in, not just a LED. Yes the LED its self is DC, but the package in the bulb could be either, it is unlikely any human can detect 50 Hz flicker, flies can, but not human, the flicker is likely less than 50 Hz caused by an interaction between two switch mode controllers.

Switch mode means instead of controlling the voltage spot on, if supplies an average voltage by switching on/off/on very quickly, the power supply turns AC to DC charges a capacitor then turns it back to AC in kHz range then it can use a very small transformer due to high frequency, and then it samples average output and changes the mark/space ratio making the kHz supply to correct average voltage, then this is feed to the bulb which likely also has a switch mode or pulse width modulated current controller but the two together are upsetting each other, so two ways to cure, one use a toroidal transformer to drop to 12 volt AC at 50 Hz not in kHz range or use a smoothed DC supply, either will work.

I note some G5.3 lamps are actually marked 50 Hz, not sure if they will work with DC, one way to control current is to use a capacitor at a set frequency a capacitor will pass a set current, but will not allow any DC to flow, I know this is used with 230 volt but don't know if used with 12 volt, more likely a simple resistor, but to say use 12 volt DC or AC without reading the spec is nothing more than a guess. So I would lean towards the toroidal transformer.