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Can I protect VDS of MOSFET with TVS diode ?

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anotherbrick

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hello dear forum,

I drive 24 V brush DC motor with H bridge - frequency is 10 Khz

the current can raise to 50 amperes

the VDS voltage rating of mosfets is 40 V

my question;

can I protect the mosfet from voltage peaks occuring during cutoff of Mosfet
with TVS diode parallel to Drain Source pins ?

thank you
 

You should not need any additional protection at the individual mosfet level as in an H-bridge the motor back EMF will re-circulate via the embedded mosfet diodes. Of course this can cause bus-pumping so you may need some means of preventing your 24V rail becoming excessive.
 

Doing this will add drain capacitance and possibly
add to ringing (and ground noise) short of breakdown.

What the FET breakdown "is", is a stupid thing to try
and stick to. Better to go with a FET that doesn't need
protection, which will be cheaper than the sum of a
wimp FET and a TVS big enough to protect it (and, you
hope, fast enough as well).

A snubber that's tuned right would probably do the job
that really wants done, anyhow (if the FET is not -that-
under-spec'd).

If the H-bridge is tuned right then the current would be
handed off from FET to FET with only a small nonoverlap
interval, such that a snubber can suffice to "svck it up".
 

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