Drive for paralleled FETs

[John Smith]

I'm designing an H-bridge to drive a 12V DC motor. I am putting 2 FETS in
parallel for each of the 4 corners of the bridge. I will be using an IR2104
driver.

The question is, should I tie the gates of each pair together and drive them
through a common resistor, or should I provide a separate resistor for each
FET? Either way, I would appreciate knowing why that method is preferred so
that I can learn from it.

Any guidance is greatly appreciated.

John

 

[Martin Riddle]

Separate resistors, Check your gate charge. www.irf.com has some good appnotes.

cheers

 

[Fritz Schlunder]

I'm designing an H-bridge to drive a 12V DC motor. I am putting 2 FETS in
parallel for each of the 4 corners of the bridge. I will be using an IR2104
driver.

The question is, should I tie the gates of each pair together and drive them
through a common resistor, or should I provide a separate resistor for each
FET? Either way, I would appreciate knowing why that method is preferred so
that I can learn from it.

Any guidance is greatly appreciated.

John

Greetings.

For best reliability and performance it is normally recommended to use two
separate gate drive resistors. For more reading on this subject I suggest
the following:

http://www.irf.com/technical-info/appnotes/an-941.pdf

 

[John Smith]

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Any guidance is greatly appreciated.

Thanks Martin and Fritz. I will read the app note.

John

 

[Keith Buck]

You need both, as the parasitics need stoppers at each gate (these are
generally low value, i.e. 10 ohms or less depending on transistor size) Then
you need a common drive circuit with possibly 2 resistors an a diode. This
lets you adjust the rise and fall times of the gate voltage separately.
Regards Keith Buck