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LF: MOSFET gate resistors question

To: [email protected]
Subject: LF: MOSFET gate resistors question
From: Chris Wilson <[email protected]>
Date: Sun, 2 Jun 2019 14:39:29 +0100
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Reply-to: [email protected]
Sender: [email protected]
Hi all,

My pal G6ECH and myself are battling poor drain waveforms in Class D
470 kHz push pull amps. We have two main initial questions. Some
circuits show a gate pull down resistor used, some do not. Is one
needed? How do you ascertain a suitable value? Given a 475 kHz amp
would a pull down of say 47k on the gate be a ball park figure? Do
some FET drivers have this internally?

Similarly the series gate resistor. Current limiting and also a slow
down function? 10 Ohms seems the common value, how do you know if
higher or lower resistance might be better?

Maybe our issue is noise on the INPUT to the FET driver IC's, so would
a small pF cap to ground be prudent? Say 30pF at these frequencies, or
not required?

Finally  is  it  worth  delving  into  "exotic" FET's and drivers that
utilize  a  negative  gate  turn  off  voltage  and  hence need a dual
polarity supply? FET's like the Cree Wolfspeed C3M0065090D



Best regards,
 Chris                          mailto:[email protected]

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