Originally Posted By: mlord
Originally Posted By: tfabris
What you're hearing is the transformer.


I haven't disassembled an LED bulb to look, but it's really doubtful they use such expensive (copper) and space consuming tech. More likely a simple diode or similar.

The cheapest/simplest way I can imagine to build an LED bulb from scratch, would be to just insert a power diode in series with about 80 LEDs (120V operation), assuming each LED drops 1.5V from input to output. Adjust the quantity if the drop is different.

EDIT: actually, the power diode isn't needed, since each LED is a diode already!

Now that bulb will flicker at 60HZ, so it could be improved with a full-wave rectifier, aka. four diodes instead of one, so that it flickers at 120HZ instead. Add a nice capacitor or two to blur the flicker to imperceptible levels.

Commercial bulbs are undoubtedly fancier than that. I really should sacrifice one to the gods of curiosity some day soon!


The two most common versions I've seen are
1) proper switchmode supply (controller chip and inductor) operating at a much higher frequency than the mains.
2) series inline capacitive dropper limiting the current like a resistor, but with an almost 90 degree phase angle between voltage and current to avoid much real power lost,followed by rectifier bridge and smoothing cap. Resistors to limit inrush current and to discharge caps - mainly in the cheap Chinese ones.

For looks inside various LED bulbs I can recommend BigClivedotcom on youtube

Edit: He just posted on dimming LEDs with mains dimmers - https://www.youtube.com/watch?v=fWh2obSY0dQ


Edited by mtempsch (29/09/2016 16:49)
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/Michael