Hello,
As you know, such an SMPS, (for class D supply) must be able to go from no load to full load very quickly.
(This smps is isolated and uses an optocoupler in the feedback loop.)
When you are in no load, how do you stop the opto transistor from saturating?.....as its this saturation which makes the amplifier slow when coming out of no load, and causes overshoot.
A schematic helps!!!
If the optocoupler is saturation then the design has problems. (possibly) Where did you get the SMPS?
Many SMPSs do not work well with no load.
So your opto saturates and you don't like it. I noticed that the base of Q1 is 1.5 volts bellow 5V reference. So the opto should have about 0.9 volts across C to E. If you have 0.5 volts (or less) cross it then Q1-C must be above 2.5V that U1 is looking for. Why? Probably when the supply went form full load to no load the error amplifier is too slow and did not get the duty cycle reduced in time and the voltage over shot. (got too high). This causes the error amplifier to overcompensate and go to zero duty cycle for a while.
Does your supply "ring" when going from no load to full load and to no load?
Please tell if there are downsides to this cascoding...because i see no downside....other than a bit of extra cost...howcome nobody does this cascode thing?...optos are a nightmare, and cascoding takes away that nitemare
stability is as easy as when getting stability for a non isolated supply
Assuming this is all about you designing a SMPSU for a class-D amplifier?, then you're not making a very good job of it!
...I dont think anybody is making a good job of it.....you can tell, because every <600W guitar amplifier on the market has a 50Hz mains transformer for a power supply.....and none of these <600W guitar amplifiers have a PFC stage (as you can tell from the fact they use 50Hz trafo's)....i have written confirmation from the biggest guitar amplifier maker in the world that none of their guitar amplifiers have power factor correction.
I don't see any issues with cascoding..........I actually think it is a great idea for an optocoupler......keeping its Vce constant should prevent some of the issues associated wit an optocoupler in the feedback path.
As to how come guitar amplifier manufacturers don't use PFC? I sincerely don't know, but I suspect that they are traditionalists with respect to circuit design.
...I dont think anybody is making a good job of it.....you can tell, because every <600W guitar amplifier on the market has a 50Hz mains transformer for a power supply.....and none of these <600W guitar amplifiers have a PFC stage (as you can tell from the fact they use 50Hz trafo's)....i have written confirmation from the biggest guitar amplifier maker in the world that none of their guitar amplifiers have power factor correction.
Without PFC current is only pulled from the power line at very peak of the sign wave. In my house the sine wave is very flat on top because of all the electronics. PFC lowers the peak current greatly.
The noise on the power line, in the audio range, drops when current is pulled in a sign wave.
Without PFC the wires in walls heat more.
The power company likes 'resistive' loads. PFC looks like a resistive load.
Many countries there are PFC requirements on large loads.
Breakers and fuses like sing wave current not sharp spikes of current.
....whomsoever knows how to get away with non-PFC'd SMPS's for guitar amplifiers, will make a tidy sum. Mains transformer PSU's dont need PFC, and so thats how guitar amp manufacturers get away with not using it at the moment.
....whomsoever knows how to get away with non-PFC'd SMPS's for guitar amplifiers, will make a tidy sum. Mains transformer PSU's dont need PFC, and so thats how guitar amp manufacturers get away with not using it at the moment.