Re: Gate drive resistor question.

On Jan 24, 9:30 am, seegoo...@xxxxxxxxx wrote:
On Jan 24, 4:58 am, Mark <makol...@xxxxxxxxx> wrote:





On Jan 23, 4:32 am, seegoo...@xxxxxxxxx wrote:

Hi to all.
I have been asked to look into a SMPS that is experiencing a higher
than wanted failure
rate in the field.Something that I've come across is ringing a bell.
The controller chip (NCP1207)
is driving a fet(IRFBE30) via a 47R resistor. The resistor is an 0805
smt package.
Somewhere on this group in the past I've read something about gate
resistors failing because
they are under sized.(power wise)
Is this possible in this case with such a small package. If the gate
resistor goes high impedance
it would obviously cause catastrophic failure of the FET and then
surrounding components.
Which is what we are seeing.

Could this be an issue?
Cheers
Rob

test your theory by shorting the gate to ground so you overstress the
gate resistor....run it like that for a day or two and see if you can
cause the resistor to blow open the way you think....if a few samples
don't open with a 10x or similar overtest like this, then I would look
elsewhere for your problem.

How much margin do you have in the FET dissipation and voltage and
current ratings, how hot does it get?

Mark- Hide quoted text -

- Show quoted text -

Thanks for all the tips guys.
I'll try running the resistor into a short for a while and see what
happens. The fet is not getting to hot at all. 50deg c at full load.- Hide quoted text -

- Show quoted text -

OK,

how about the Drain Souce voltage derating?
gate voltage derating?
Drain current derating?


.

Relevant Pages

  • Re: Gate drive resistor question.
    ... than wanted failure ... is driving a fetvia a 47R resistor. ... Somewhere on this group in the past I've read something about gate ... if its a DCM smps, check it has a soft-start, as DCM supplies ALWAYS power up in CCM until the output cap is charged. ...
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  • Re: Gate drive resistor question.
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  • Re: Gate drive resistor question.
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  • Re: Gate drive resistor question.
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  • Re: Gate drive resistor question.
    ... than wanted failure ... is driving a fetvia a 47R resistor. ... Somewhere on this group in the past I've read something about gate ... it would obviously cause catastrophic failure of the FET and then ...
    (sci.electronics.design)