Re: TO3 & HEATSINK

From: CWatters (colin.watters_at_pandoraBOX.be)
Date: 07/28/04 

Date: Wed, 28 Jul 2004 12:57:55 GMT

"Norm Dresner" <ndrez@att.net> wrote in message
news:_vCNc.337854$Gx4.89883@bgtnsc04-news.ops.worldnet.att.net...
> "exxos" <exxos@home.co.uk> wrote in message
> news:4106d62f$0$6451$cc9e4d1f@news-text.dial.pipex.com...
> > Hi all,
> >
> > Instead of mounting the TO3 transistor ont he flat part (bottom) onto
the
> > heatsink, do you lot recon I could drill a large hole in a heatsink and
> > mount the can side into it, and put heatpaste around the can and screw
it
> > down from the top ? does anyone have any thoughts if this would work as
> good
> > or worse than the bottom just being bolted to the heatsink ?

It will be worse. You are increasing the thermal resistance between the die
and heatsink quite a lot - the die is on the center of the base plate
normally only 1 or 2 mm away from the heatsink. Try this.. build it or a
test rig as you describe. Power it up and measure the temperature in the
middle of the T03 base plate. Then calculate the die junction temperature
(Tj) using....

Tj = (WxR)+Tc

where

R= Thermal res of the case = 1.25 C/W for a 2N5038 in a T03
W= power in watts = 50
Tc= Temp of case measured in the center of the base.

The calculated value of Tj must be below 200 C according to the data and
150C would give it longer life.

It's impossible to calculate how big a heatsink you will need because the
case res R is specified from the die junction to center of the base not the
mounting holes.

Relevant Pages

  • TO3 & HEATSINK
    ... Instead of mounting the TO3 transistor ont he flat part (bottom) onto the ... heatsink, do you lot recon I could drill a large hole in a heatsink and ...
    (sci.electronics.misc)
  • Re: TO3 & HEATSINK
    ... > heatsink, do you lot recon I could drill a large hole in a heatsink and ... > mount the can side into it, and put heatpaste around the can and screw it ...
    (sci.electronics.misc)