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Does the output of a 120 volt AC to 12 volt DC LED driver differ depending on whether it receives forward-phase AC input or reverse-phase AC input from a dimmer?

I’m curious because I have some LED lamps that are failing prematurely and some that are not.

The ones that seem happier are those that came with a universal driver that’s advertised as accepting either forward or reverse phase, but preferring forward-phase.

The ones failing prematurely (of course, the much more $$$ ones) came with a universal driver that’s advertised as accepting either forward or reverse phase, but preferring reverse-phase.

Definition of forward-phase and reverse-phase linked here.

Any ideas about why the DC output of the LED driver depends on the AC phased input? Should the AC signal not be rectified and thus the same?

Glorfindel
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Edward Ocampo-Gooding
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    Depends on the LED driver. Most will be happy with either but the devil is in the details. Check the datasheet. – winny Oct 28 '22 at 19:26
  • Seems like you answered your own question: the ones that say prefer forward-phase prefer forward-phase, and the others don't. I presume the dimmer is forward-phase. – user253751 Nov 17 '22 at 12:59
  • Do you know why the output of an LED driver is different depending on the input being reverse or forward phase? That’s what I’m after. I wonder why the output isn’t the same DC voltage signal. – Edward Ocampo-Gooding Nov 17 '22 at 19:22

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I can see that forward phase dimming might cause higher stress because of the fast rise time where voltage is suddenly applied, whereas reverse phase applies power at zero crossing. It might help to add an inductor to reduce the dV/dt of the forward phase waveform.

Edward Ocampo-Gooding
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PStechPaul
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  • Thanks for the definition link! I’ve merged it into the question. – Edward Ocampo-Gooding Nov 17 '22 at 19:26
  • “reduce the dV/dt of the forward phase waveform” – interesting! How could I measure this? Why would the voltage change if it’s being rectified (presumably) by the LED driver? Maybe that’s a misplaced assumption on my part? – Edward Ocampo-Gooding Nov 17 '22 at 19:28
  • @EdwardOcampo-Gooding If you turn on the voltage at the zero crossing it charges the power supply capacitors gradually. If you turn on at full power much higher peak current rushes into the power supply to charge up the capacitors. – user1850479 Nov 17 '22 at 20:20