Re: TO3 & HEATSINK

From: Norm Dresner (ndrez_at_att.net)
Date: 07/28/04 

Date: Wed, 28 Jul 2004 16:00:48 GMT

"exxos" <exxos@home.co.uk> wrote in message
news:4107bd61$0$6440$cc9e4d1f@news-text.dial.pipex.com...
>
> "Norm Dresner" <ndrez@att.net> wrote in message
> news:svONc.144428$OB3.71995@bgtnsc05-news.ops.worldnet.att.net...
> >
> > "Norm Dresner" <ndrez@att.net> wrote in message
> > news:_vCNc.337854$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 ?
> > > >
> > > > The transistor I have in mind is a 2N5038, a little higher wattage
> than
> > > the
> > > > 3055, I plan to have around 50watts constant disipation, it should
be
> > ok,
> > > > right ??
> > > >
> > > > Thanks
> > > > chris
> > >
> > > The actual die is mounted to the base of the package. Your scheme
> > increases
> > > the thermal resistance from the junction to the case.
> > >
> > > Norm
> > >
> >
> > After rereading your post, I see an even worse situation than poor
thermal
> > conduction (which can be alleviated with an appropriate H/S and that's
the
> > fact that the transistor case isn't at ground potential. With
traditional
> > mounting, you can get nice mica (or other material) insulators to
isolate
> > the transistor's electric potential from the H/S but not (as far as I
> know)
> > with your scheme.
> >
> > Exactly what are you trying to accomplish?
> >
> > Norm
> >
>
>
> Its not a good idea then, I was just trying to see if I could avoid
routing
> the connection wires though the finn side of the heatsink. The device I
> have found is the 2N5038, its for a audio amplifier, its about the best
gain
> and wattage I can find, The only other transistor is the TIP3055 which is
no
> problem to mount, but lower gain and wattage, perhaps someone where knows
> of a good gain transistor ? 5amps 80V 100W or there about with a good
gain,
> more there better I guess.
>

A little more expensive but good performance in the MJ150xx series of power
transformers. The complementary pair MJ15003/15004 are higher voltage than
you need but especially good for high power audio amplifiers. They're still
TO-3 but there's generally no real problem in routing wires through the heat
sink if you protect them against rubbing and overheating by installing a
gromet in the hole. The 3055 is an old workhorse, best for low frequency
designs like subwoofers.

For TO-220 packages, consider a MOSFETs instead of bipolar output stage --
there are some really good medium power units available in this package.
    Norm

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