Re: Flyback Converter

From: 	RODERICK MAXWELL[SMTP:tank-at-mail.magnolia-dot-net]
Reply To: 	tank-at-mail.magnolia-dot-net
Sent: 	Friday, January 09, 1998 8:32 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

   Thanks for your reply! Yes I did use silicone grease. The heatsink is
bare aluminum made by AAVID. They have a very nice heatsink selection
program at their website in case anyone is interested.


  The sink part number I'm using is 60055. It comes in a 4' bar. I only
used about 9" though.

                                 Frankensteins Helper