... any chance you share the whole schematic ? Including the tap switcher if you mind ... is that with adjustable current too ?
Tricky situation. It was 1 of many contract designs ... then got sacked after several years :-) (long story) .... never paid for R+D or other "trades" ...
With all that, I don't want to risk any more animosity ... circuit operation theory, though, is common knowledge -
Run a small dual 5-8VAC, say 50mA transformer to power logic, REF 0V, and an isolated 6-12V high side FET driver rail
Use a small micro, with A/Ds to monitor AC V and I, and DC V and I. Then depending on Vop, switch in the respective winding, using the bridge type FETs.
Have this pre-regulator on a separate PCB, with it's OWN storage caps. Then, IF you want to get fancy, "active feed" the MAIN storage cap that supplies the
regulator PCB. At low current, it doesn't matter if Vin_Reg is a bit higher, as power dissipation will be low. Keeping the Vreg cap at an ideal, low ripple voltage
is the "tricky" part :-) .. but then, working that out, is the challenge :-) In one 10A design, I believe I got ~97% efficiency .. not bad for linear (-Trx).
I can see you're still using that venerable LT4320 there.
Ahhh yeah, didn't I send you a couple boards way back? Did you ever use them? Useful? It's a DAMN fine IC !!