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Old 14th May 2013, 07:11 AM   #1
tnargs is offline tnargs  Australia
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Default Insulator for LM3886T

Hi all, what is the correct insulator for my LM3886T chips? The datasheet says TO-220 package, but that can't be right, the chip is much wider than a TO-220 insulator!
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Old 14th May 2013, 07:48 AM   #2
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Hi,
You can try the TO247. It is 20mm 26mm.
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Old 14th May 2013, 11:29 AM   #3
AndrewT is offline AndrewT  Scotland
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What about a strip of "Selotape"?
If the chip never gets hot, the Selotape will never degrade.
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Old 14th May 2013, 11:49 AM   #4
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If you hunt on E-bay you will find something suitable.

MT-200 Transistor Mica Insulator,Insulation sheet, x 50 | eBay

I wouldn't recommend the sellotape as it tears very easily.
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Old 14th May 2013, 02:06 PM   #5
AndrewT is offline AndrewT  Scotland
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The clamps squeeze it.
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Old 14th May 2013, 02:07 PM   #6
AndrewT is offline AndrewT  Scotland
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I don't recommend Selotape either.
But I have used it, short term during testing, and sometimes to quite high sink temperatures.
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Old 14th May 2013, 02:37 PM   #7
macboy is offline macboy  Canada
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Quote:
Originally Posted by AndrewT View Post
What about a strip of "Selotape"?
If the chip never gets hot, the Selotape will never degrade.
You are joking right?!
The point is to get electrical insulation and excellent thermal conductivity. I don't think a strip of sellotape (aka "scotch tape" for Americans) will provide good thermal performance. And the electrical isolation is iffy too. As it gets hot, and it will due to bad thermal conductivity, it will probably melt and could allow the chip's tab (at -Vcc) to contact the heatsink (usually at gnd). Boom!
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Old 14th May 2013, 06:12 PM   #8
AndrewT is offline AndrewT  Scotland
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I am not joking.
I recognise that sticky tape for fixing parcel wrapping is not a recommended Thermally conductive and Electrically insulative and Temperature tolerant interface material.
But in the short term for OBSERVED testing it works and it works well.
Try it.
It is a good Electrical insulator for typical SS amplifiers, i.e <100Vdc
It is a good Thermal conductor compared to real tapes. Not as good as thin mica, but certainly better than 6thou Kapton and 5thou mica.
It does tolerate the lower temperatures of warm to very warm heatsinks. I would not use it for a too hot to touch heatsink.
I would not use it for hidden use long term inside a chassis.
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Old 14th May 2013, 07:23 PM   #9
M Gregg is offline M Gregg  United Kingdom
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Well,

Its a lot for just a few pieces..You would have to check the thickness its just an example...

Kapton Tape Polyimide High Temperature Roll 10mm X 33m: Amazon.co.uk: DIY & Tools

Heat Sinks


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Last edited by M Gregg; 14th May 2013 at 07:28 PM.
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Old 15th May 2013, 02:21 AM   #10
tnargs is offline tnargs  Australia
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Thanks for the tips guys.

TO-247 looks like a good idea. I don't care that it is over-sized. I have done a bit of digging and it seems a TO-218 washer will work on a TO-247 chip, so it should also be usable.

AndrewT, I am looking for a permanent installation, so sellotape is not my best solution, but thanks for the tip!

I am looking for a 'proper' solution that is big enough, has its hole in a usable location with LM3886T, and can be purchased.

Does anyone know why the TI datasheet says the LM3886 is a TO-220 package? It seems misleading. (I actually bought a bunch of TO-220 insulation washers to use with my LM3886 purchase, based on the TI datasheet, and only saw their inadequate size once I got them).
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