I'm back to working on a power supply (a forward converter), and while I think I know how to compensate the feedback loop, I did read one application note (regarding the venerable UC3845) that goes through the process the same way I would, except that they start with an equation for "control voltage (i.e., error voltage) to output voltage gain" that I'm unable to re-derive. This is on page 5 of
Adc = [(Vin-Vout)^2/VinVe](Nsec/Npri)
...which I'm interpreting as...
Adc = (Vin-Vout)^2/(Vin*Ve)*(Nsec/Npri)
with:
Adc = DC gain from "control to output" Vin = power supply input voltage, which they set as 140-200V; I figure 170V is a good nominal value Vout = output voltage, 28V in their design Ve = Ummm... they don't say... I'm guessing reference voltage, 2.5V? Nsec = number of turns on secondary, 21 Npri = number of turns on primary, 41
They calculate Adc= 13.5, but plugging in the numbers above doesn't facilitate that. The closest I could get is to take Vin=170 and Ve=4.5 -- the the equation does then work out.
But more importantly... does anyone recognize the form of this equation? And know the derivation?
I'm also interested in pointers to other application notes discussing feedback compensation for current-mode switchers. My main reference is Pressman's book, but while he goes through voltage-mode compensation thoroughly, he leaves current-mode compensation as an exercise for the reader... which, as I say, I believe I've done correctly, but it never hurts to double-check before throwing the power switch.
I probably ought to get a copy of Keith Billings' book one of these days, eh?
Thanks,
---Joel