I have seen reverse voltage protection circuits that use a pmos instead of a diode so that there is minimal power loss and voltage drop in that sector of the circuit.

I want to make a charge pump for logic level MOSFETs, but if I only have 5v as a supply, my charge pump will only charge the capacitor to around 4.3v. Is a pmos suitable for fast switching applications in a charge pump?

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  • \$\begingroup\$ Using a Schottky diode instead of a normal silicon junction diode will improve the conversion efficiency a bit without adding any complexity. \$\endgroup\$ – mkeith Dec 20 '19 at 23:16

No, you will need a more complicated circuit hanging off the gate of the PMOS. The simple PMOS "diode" circuit, unlike a real diode, is able to conduct in both directions if it's on. What determines whether it is on is if the "cathode" voltage is positive relative to the gate terminal.

That's not a problem if what is on the cathode end is something like a resistor which can only develop a voltage drop if there is a power source connected to the "anode". But it's a problem if what is on your output end has its own energy supply like a charge pump since it can maintain that voltage that keeps the PMOS on in the absence of a supply on the "anode" end. It can push current back the other way.

  • \$\begingroup\$ Hmm... perhaps that is why I haven’t seen this approach before. Many thanks. \$\endgroup\$ – Judson Hudson Dec 20 '19 at 22:45
  • \$\begingroup\$ @JudsonHudson Sorry, had to walk away for work. THere is a circuit that would work. It looks like a PMOS circuit with two matched PNP BJTs hanging off of it. It's somewhere on this website under ideal diode or something like that. \$\endgroup\$ – DKNguyen Dec 21 '19 at 0:15

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