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From: "Mike Engelhardt"
Subject: Re: Two diodes in series to double PIV rating - is that a "no-no"?
Date: 20 Nov 2002 22:48:52 GMT
Reply-To: "Mike Engelhardt"
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> I have designed a low power flyback supply and I'm using a BAV74 diode for
> one of the secondary outputs.
> Trouble is that the PIV (Peak Inverse Voltage) on the diode is very close
> the allowable rating for the diode. Is it possible to connect two in
> (like the BAV99 series- two diodes on one die) to increase the PIV rating?
> Will the applied voltage split approximately equally between the diodes -
> even at fast switching?
> I would suspect that if one of the diodes has a higher reverse leakage
> current from the "get go" - then the bulk of the voltage would be
> on the other diode. But when the voltage on the other diode rises - so
> the leakage and possibly a equlibrium would exist. Anyone?
If the diodes are "avalanche grade" then you can
get away with it. An avalanche grade diode is supposed
to be able to zener instead of destrucituvely breaking
down in order to equalize the reverse drop in a diode
stack. Very high voltage diodes are a bunch of avalanche
grade diodes in series. That's why they can have a
reverse rating of several to many kilovolts but also have
a forward drop of several volts.
Every year it seems like there's fewer sources for
high voltage devices. Varo used to sell avalanche
grade diodes but went out of business about 5 years
ago. I'd check maybe Semtech.
Otherwise, take the well-placed advice of the first
two people who followed up.
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