I m actually reading a section of a book which talks about parralleling MOSFETs. The book talk about "Power supply design". There is a sub section which describes how to design the circuit layout. It finally say : "Finally, to prevent oscillations with paralleled MOSFETs, resistors of 10 to 20 Ohm or ferrite beads should be placed in series with gate leads".

I'm surprised ! I have never seen a power MOSFET oscillates... And I actually do not understand what it means by oscillations. In which case oscillations happens ? And why when we parallelise MOSFET we increase the risk of seeing oscillatons ?

Thank you very much !

  • 3
    \$\begingroup\$ toshiba.semicon-storage.com/info/docget.jsp?did=59458 check this out \$\endgroup\$
    – C. K.
    Commented Dec 15, 2019 at 6:08
  • \$\begingroup\$ "Oscillates" means it rings when switching, so underdamped. If you scope the gate-source voltage you can see it. This can happen with single MOSFETs too. \$\endgroup\$
    – DKNguyen
    Commented Dec 15, 2019 at 20:40

1 Answer 1


Power MOSFETs have relatively large Gate-Drain capacitances.

When they are paralleled, you have a closed AC loop from common Gate to Drain1 to Drain2 back to common Gate.

What do you need for oscillation? 1) An energy source [check] 2) feedback [check]

So it’s good to insert a resistor for each gate for damping purposes.


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