Using a TO-220 heat sink

AlN is incredible. It conducts heat almost as well as aluminum.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Mica is good because it's thin. Anodized aluminum is even thinner.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Mica and silpads require, in addition, a bolt with shoulder washer and insulating sleeve, nut, maybe washer, or nylon hardware. A 'fulpack' variant TO220 just takes a screw or rivet, or a spring clip.

The LM317 will only be powered for short periods, so it probably doesn't matter match.

--
Apparently I lack some particular perversion which today's 
employer is seeking.                 --- Ignatius J Reilly

Right, I used it as an electrical insulator. I thought because it's thin it might be better than a thicker sil pad. It wasn't.

George h.

Nice, where did you get them? and how much?

George H.

I got samples from St Gobain, but I'm having a hard time buying more.

I'm having some custom made from machinable AlN, which is actually a mix of AlN and BN, which doesn't conduct heat quite as well. They haven't come in yet.

I got one quote for pure AlN TO-220 insulators at $25 each. The custom parts will be $5 each. One Chinese source claims 80 cents.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Obviously the purpose of either of them is to reduce thermal resistance by conforming to imperfections in the two surfaces, but obviously using both would have more thermal resistance than either alone.

If you have grease, use it and throw the pad away. The pad is 10 times as thick as a layer of grease, and has 10 times the thermal resistance.

They're no better, in fact worse. Their saving grace is dieletric strength.

With all them pictures in there who knows exactly what you're getting ? Is it 5 of the finned pieces and 5 of the ones bent in a rectangle ?

Yeah, because they're not dissipating shit. There isn't enough square area there to make it even worth figuring out. I wouldn't go over about double free air with those. And if they sit down flat on a PC board that will impede the airflow.

Then you have to float the sink.

Why would that be difficult?

I've got boxes where the best place for the pass element is the back panel, which is typically grounded. (It depends on power... I'm a class A type of guy. :^)

George H.

That's if the panel is the heat sink, but for a separate hunk of metal (which is small like a TO-220) it should usually be possible to float it. I would think.

I can tell.

Well at some point the heat has to make it's way to the outside world. My first instrument at my CPoE has a bunch of floating heat sinks. I had to add a fan. As bad as sil pad is, it's better than air. (I've got dreams of redesigning my first instrument... well and all the others too. :^)

Grin, George H.

Probably isn't, but in some layouts might not be a good idea. I wonder why not just get the all plastic version.

Just so I'm getting confused, is this AC with the neutral connection going to a different panel?

Here's a floating heat sink. The drains of 32 mosfets (16 p-channel,

16 n-channel) are clamped to copper heat spreaders which are bolted to the main aluminum heat sink.

The whole thing is isolated from the chassis by big plastic blocks.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

I figured the pad is only for situations where you need electrical insulation there.

--
It's like a pair of eyes. You're looking at the umlaut, and it's 
looking at you.                             ---David St. Hubbins