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Fake *******ING "MOTOROLA" Transistors
Fake *******ING "MOTOROLA" Transistors
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Old 6th February 2006, 02:07 AM   #121
clem_o is offline clem_o  Philippines
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Hey Chris,

Hahaha, would have wanted to, but no! Security was (and still is!) tight as heck. We couldn't even get dead units out of the plant - everything, as in everything - was shipped back out.

Cheers!

Clem
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Old 6th February 2006, 02:52 AM   #122
vectorplane is offline vectorplane  United States
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I guess the capacitance test should be a good screening for MOSFETs too. It's virtually impossible to get low Cgs from high powered devices and vice versa.


Quote:
Most of the heat is going down the leads, don't count on much going through the epoxy.
OK, just did a rough thermal test;

sandwiched and clamped a TO246 between 2 identical copper plates, used thermal grease, and put 30W through it.

Back plate rose by 32 deg C.
Front plate rose by 14 deg C.
With front plate removed, back rose by 38 deg C.

So, any heat removed from the epoxy side, is heat well gotten rid of, IF the mounting geometry allows the space for it.

--------------------
I'm contemplating coming to the dark side...
What kind of cookies to you have?

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Old 6th February 2006, 03:21 AM   #123
clem_o is offline clem_o  Philippines
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Hi Andy,

I'm not sure what your test proves (still thinking about it) - given that the heatsink dissipation area got reduced by having only the back heatsink.

Oh, ok... IF you can't increase the thermal efficiency of the back heatsink (due perhaps to space limitations), then what this experiment says is that you can get a bit more dissipation if you do mount a heatsink up front.

Cheers!

Clem

ps: what if you mount the Front and Back heatsinks together and mount the back of the transistor to these two combined areas? What is the temp rise then?

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Old 6th February 2006, 05:41 AM   #124
vectorplane is offline vectorplane  United States
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It doesn't prove anything.

It suggests that you can remove additional heat.

Increasing the size of the back heatsink gives diminishing returns after a point, because heat has to travel FARTHER, to reach the outer the edges of the sink. The farthest fins are not as effective as the ones closest to the chip.
Removing heat close to the source provides greatest conduction (once you get past the epoxy barrier of course).

Don't sweat it. You'll probably never need to do this. It's just a crazy idea.
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Old 6th February 2006, 04:14 PM   #125
anatech is online now anatech  Canada
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Fake *******ING "MOTOROLA" Transistors
Hi vectorplane,
Retry that experiment, but couple the front radiator to the rear heatsink instead of the package. Try aluminum blocks on each side of the device.

-Chris
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Old 6th February 2006, 11:36 PM   #126
clem_o is offline clem_o  Philippines
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Quote:
Originally posted by vectorplane
Don't sweat it. You'll probably never need to do this. It's just a crazy idea.
For the record, I don't think its a crazy idea.

OTOH there are a lot of variables involved, including the heatsink geometry. Audio people should take notice of heatsinks designed for new-generation CPUs, where 80W is concentrated on a conduction surface not much larger than 1/3"x1/3". Keeping a processor with that much power to 50 degC is no small engineering feat, given the limitations of the heatsink weight and size. Well, of course it uses a fan... :-)

Cheers!
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Old 7th February 2006, 02:32 AM   #127
anatech is online now anatech  Canada
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Fake *******ING "MOTOROLA" Transistors
Hi vectorplane,
Clem has a valid point. The packaging material makes the difference. I am thinking of amp modules mounted on those P4 heatsinks (regular mounting).

-Chris
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Old 7th February 2006, 03:25 PM   #128
vectorplane is offline vectorplane  United States
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Using CPU heatsinks in audio amps will probably provide more effective heat removal, because those HS's are engineered for a critical application, whre the CPU will die very quickly if not cooled enough.

If you leave the fan in, you'll probably end up with a very compact audio solution.

You don't need to run the fan at full speed ( noise!! ). Half or quarter speed can keep it dead quiet and still retain effectiveness.

Andy
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Old 7th February 2006, 03:27 PM   #129
anatech is online now anatech  Canada
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Hi Andy,
That was my thought. I was thinking of making a chimney structure and let convection do the work.

-Chris
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Old 7th February 2006, 04:36 PM   #130
vectorplane is offline vectorplane  United States
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Default OT

Chimney structure,
you mean 4 heat sinks enclosing a square, with the fins facing in?

I think I'm gonna start picking up all those CPU cases I often see put out with the trash...

Andy
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