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Re: Flyback Converter
From: Bill Lemieux[SMTP:gomez-at-netherworld-dot-com]
Sent: Friday, January 09, 1998 12:38 PM
To: Tesla List
Subject: Re: Flyback Converter
Roderick Maxwell wrote:
> The transistors came in Monday! I now have six IRF440 power mosfets
> in parallel.They are all mounted on a large common heatsink. I am making
> the sink do double duty because the transistors are not isolated from
> the sink by mica insulators(case is drain). This enables me to use the
> sink as a buss for all the transistor drains. This also gives better
> heat transfer between the transistor case and the heatsink.
You used either heat sink grease or silpad or equivalent between the
sink and the xistor cases, right? Otherwise, you won't get as good
thermal transfer as you're expecting. To be honest, isolation using
mica washers and good silicone grease only increases your thermal
resistance about 0.1 degrees C per watt, if it's done right. But if
it's more convenient to use the heatsink as a bus, fine. But don't omit
the heatsink compound- it fills in all the little gaps and surface
imperfections which impede heat xfer between the case and sink
(theta cs)
-Gomez
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