RE: Flyback Converter (fwd)

To: tesla-at-pupman-dot-com
Subject: RE: Flyback Converter (fwd)
From: Tesla List <mod1-at-pupman-dot-com>
Date: Mon, 12 Jan 1998 11:48:13 -0700 (MST)
Approved: mod1-at-pupman-dot-com


---------- Forwarded message ----------
Date: Mon, 12 Jan 1998 08:55:40 -0500
From: "Thornton, Russ #CSR2000" <ThorntoR-at-rc.pafb.af.mil>
To: 'Tesla discussion Group' <tesla-at-pupman-dot-com>
Subject: RE: Flyback Converter

Be careful about the compound you use if you are wanting electrical
connections between the case and the sink.  We had some very high power
transistors(half a pound each) that we need not only thermal but
electrical conducting compound.  I don't remember what we actually wound
up using but most of the traditional brands we had available were of the
insulating type.  Don't assume!
Just a caution.

Russ Thornton
CSR 2040, 
Building 989, Rm.  A1-N20
Phone: (407) 494-6430 
Email: thorntor-at-rc.pafb.af.mil


>----------
>From: 	Tesla List[SMTP:tesla-at-pupman-dot-com]
>Sent: 	Friday, January 09, 1998 6:28 PM
>To: 	'Tesla List'
>Subject: 	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
>
>-- 
>.......................................................................
>.                personal email: gomez-at-netherworld-dot-com                .
>.          personal web page: http://www-dot-netherworld-dot-com/~gomez       .
>.......................................................................
>
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