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Multiple LL N-Channel MOSFET's in Series
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TheDood:
Hey guys, I was wondering if is it possible to reduce power dissipation by using multiple LL MOSFET's (VDSmax ~55V) in series to replace a single higher ΩDSon power MOSFET (VDSmax ~200V)?  Are there special considerations to design for or take into account?

As an example:
(4) IRLZ44N : total RDSon 0.088Ω

(1) IRF640N : total RDSon 0.150Ω

Thanks!
nigelwright7557:

--- Quote from: TheDood on August 03, 2019, 05:47:09 pm ---Hey guys, I was wondering if is it possible to reduce power dissipation by using multiple LL MOSFET's (VDSmax ~55V) in series to replace a single higher ΩDSon power MOSFET (VDSmax ~200V)?  Are there special considerations to design for or take into account?

As an example:
(4) IRLZ44N : total RDSon 0.088Ω

(1) IRF640N : total RDSon 0.150Ω

Thanks!

--- End quote ---
You could put the mosfets in parallel to reduce power in each  but together they would still generate same amount of heat.
If its just a switching mosfet application why not use a lower RDSon mosfet ?

Circlotron:
If it is a fast switching application like in a power supply then the total energy stored in the drain-source capacitance and dissipated every switching cycle might be a whole lot greater with series low voltage mosfets. Driving all the non ground referenced gates will be a nuisance. So will making sure the max voltage across each mosfet is not exceeded. IRF640 is not a modern mosfet. There are much better ones available today.
digsys:
Without taking into account as to what it is used for - the answer is YES of course - BUT there are considerations to address, some have been pointed out -
IF it is just a switch, and you're worried about losses, and multiple parallel is not an option (which it is) - then you have 2 major questions -
1/ Protection of each FET, should one FET go O/C or short, leaving the other(s) with too high voltage
2/ Extra complexity of drive circuits, as these are all at different levels and protection for 1/
Whales:
> 2/ Extra complexity of drive circuits

This would be my main point here.  The lower mosfet can be driven normally, but the upper mosfet must be driven relative to its source pin.  This requires much more complex driving circuitry.

If at all possible: try and get a better mosfet, it will make things a lot simpler.  Are there any reasons you would prefer to do otherwise?
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