BSEE types: Cascade versus Parallel MOSFET design?

[zaphod_phil]

If you're trying to regulate a power supply, then you would parallel the MOSFETs together to increase the current handling, and as you suggested, also introduce a safety factor. I can't think of how you could use cascaded MOSFETs in any way in such an application, as the idea of cascading is usually to increase gain, which is an irrelevant concept here.

[markh]

WHen you say 'cascaded' do you mean in series, or hooked up Darlington-style?

The former would be useful for lowering voltage stress on the parts, and also dividing up the power dissipation in a predictable manner (parallel devices are somewhat random in how they divide up power, since no two devices are identical).

The latter makes no sense, as Phil said.

--mark h

[zaphod_phil]

I just asked my wife, who has a PhD in power supply design. She says you can run MOSFETs in parallel with no problem, as their characteristics are very close with quite tight tolerances. She says you can stack them to share the voltage handling as well (I guess that's what was meant by "series"). The main problem you have to deal with is their quite high gate capacitances.