Calling All Engineers - ELI5 SCR vs FET in Dimmers

[HimuraMOdo]

Correct, when MOSFET is on, it acts like a resistor. But the on resistance is low, in tens or hundreds of mOhm at typical gate voltage (usually spec’ed at 10V or so.). MOSFET on resistance will drop even more if gate-source voltage is higher (In this case, the gate-source will increase with the phase of the AC voltage which will help I think).
As for SRC, it’s a minimum drop regardless of the load current. And it gets even higher with higher load current. So as far as voltage drop’s concern, I think MOSFET is still a better choice assuming a properly spec’ed MOSFET can be sourced.

[apwelsh]

@Eric_Inovelli

This is what I was told last night:

I’m not entirely sure what it means, but it may possibly answer your statement?

This is saying that when you are dimming a fluorescent bulb or LED, you are not adding resistance to lower the output voltage, you are manipulating the sine wave. The driver voltage from the dimmer at 100% brightness is a perfect sine wave. At 50%, voltage is not a sine wave, it is more of a shark-fin looking wave. For the first half of the sine wave, the output voltage is still at 0v, then it shoots up to 110VAC, and rolls back down. Dimming is achieved by modifying the shape of the wave.

With FETs (Field Effect Transistors), you have the freedom to handle dimming using a better technique. It is actually something you can control.

ELV dimming is the solution to eliminate LED bulb buzzing.

It looks like this:

[jkister]

@Eric_Inovelli

@jtronicus

The benefit is that you could theoretically write firmware that allows you to switch between Leading edge or Trailing edge dimming (ELV or MLV).

Well this is certainly interesting. I’d love to understand this more from the engineers as maybe it would help with better bulb compatibility.

wondering, @Eric_Inovelli have you put any time into looking into a firmware change/update in red series that would let us select leading vs trailing dimming ?