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What efficiency? Did you not understand the part where it just conducts through the MOSFET body diodes while the rest of the MOSFET does nothing? The circuit behaves the same if you removed the resistors and zeners and just left the gates floating. Hell, it's behaviour doesnt change if you removed the entire MOSFET as long as you left the parasitic diode there.
The circuit is not doing the equivalent function of a diode-bridge, It IS a diode bridge with a bunch of superfluous components. Those MOSFETs are not operating as ideal diodes.
EDIT: Oh wait, after staring at it a few more times, they are. nvm.
Hmm, question. Q43 has a negative charge on the source (Ac1) which would pull -100v below the gate. I suspect that'll be a problem, sorted if I use an opticoupler instead with a resistor to drain the gain.
If the opticoupler goes between pin 3 and 1 I'll need one with the collector-emitter breakdown to work at 100V?
I could keep the MIC5019's for the low side FET driving but it probably makes more sense economically to go with a 4 channel opticoupler.
And final question, regarding the 4N25, the LED creates a current at the base which allows the collector to flow. I'd expected the LED to create a voltage between pin 4 and 5 but the use of a transistor indicates otherwise?
My PIC power source isn't tightly regulated, swinging from 2.4-5V and this has an effect on the opto's performance. I'm thinking about using the PIC's PWM's to keep the current constant. What do you think?