[TenTec] Is there a beefier 2N5301?

[Gary Hoffman]

That's right Jerry....and common practice.

But better practice is to seal against moisture, which is what I do.  Its
not as though there is very much moisture, nor is there any water pressure.


----- Original Message ----- 
From: "Dr. Gerald N. Johnson" <geraldj at storm.weather.net>
To: <tentec at contesting.com>
Sent: Tuesday, March 06, 2007 9:30 PM
Subject: Re: [TenTec] Is there a beefier 2N5301?


> On Tue, 2007-03-06 at 19:50 -0500, Gary Hoffman wrote:
> > It is interesting that most of us don't know how important the heat sink
> > goop is, and how much of the heat transfer takes place through it.
> >
> > The two metal surfaces (heat sink and transistor) even if machined quite
> > flat and smooth actually touch microscopically at a very few tiny
points.
> > That is the limit of the metal to metal transfer.  Even if you work
really
> > hard at it, that is the best you can do.
> >
> > The rest of the space is filled with air, and air is an excellent
insulator.
> >
> > To fix this problem, one approach is to use conventional heat sink
compound.
> > These common compounds use a passivated aluminum oxide extremely fine
powder
> > suspended in a petrochemical.  This compound fills the air gaps and the
> > aluminum oxide conducts the heat far better than the air would have.
> >
> > In extreme applications, a better heat sink compound uses extremely fine
> > silver in the place of the aluminum oxide, for many times better
results,
> > but at the expense of having the compound be electrically conductive
which
> > can cause many issues.
> >
> > So, generally we use the aluminum compound and it works really well.
> >
> > To go beyond that, you have to turn to the heat sink itself.  Make it
> > bigger.  Make it Copper.  Give it more and larger fins.  Blow air on it.
> >  Or - if you really want to do it right, use a TEC for active cooling
and
> > make that heat sink really really cold.  Just short of the dew point of
> > course.  And much more practical than liquid cooling.
>
> So today in Iowa that heat sink could be cooled to 15 F but on a warm
> summer day in Houston, the dew point might be 95 F so you would have to
> include a dew point sensor to pick the cooling point, or a moisture
> sensor on the heat sink to detect the dew...
> >
> > TECs really rock when used properly in this manner.
> >
> > 73 de Gary, AA2IZ
> >
>
> -- 
> 73, Jerry, K0CQ,
> All content copyright Dr. Gerald N. Johnson, electrical engineer
>
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