I've a fixed current source of 500mA and a variable voltage supply between 0-20V AC. I'm aware of FET Vgs but that's out of scope for this question. Generally the voltage will be somewhere in-between and I'm not using PFC below about the 3.5v mark so the comparator with it's 3.3v turn-on works well here. The AC is slow, 1-200Hz (max).
My question is on part suitability. Since active rectification is difficult and complex for low voltage my idea is to use a bridge with the diodes replaced by 2x NMOS and 2x PMOS and then the TLV1805 to prevent reverse flow by way of a 5th PMOS. I'm looking at whether the overheads are worth it the implementation. Picking 4.5v, I derived the following figures. Note I picked a 100mΩ PMOS for the reverse flow MOS which I think would be worse case I'd want to go to to allow the comparator to sense the voltage drop.
On Losses (diode v fet)
0.35v diode / 4.5v = 8% loss = 0.175W
100mΩ MOS = I^2R = 0.050W
Reverse Recovery Loss (fet)
I TRIP = V TRIP / R DS(ON) = 12 mV / 22 mΩ = 546mA = 0.006552W
12mV / 100mΩ = 120mA = 0.00144W
On the face of it there's at least a 2/3 saving for the on loss which makes the reverse loss negligible?