PLEASE HELP! Insulating Transistors Electrically from Heat Sink

Do It Yourself · 8th November 2009, 04:38 AM

I want to mount all of my power transistors (TO-264 and TO-126(also called SOT-32) on a single heat sink but this would cause all the collectors to short out.

pictures of the cases:
http://media.digikey.com/photos/Pana...tos/TO-126.jpg
http://media.digikey.com/photos/On%2...488-TO-264.jpg

audi0 · 8th November 2009, 06:08 AM

Wouldn't you just buy suitable silicone or mica insulators?

MJL21193 · 8th November 2009, 12:43 PM

Hi,
Most TO-126 are insulated package - no isolator required.
The TO-264 need a silpad or mica washer (as mentioned above). It can be difficult to locate mica washers for the TO-264 but you can use washers for TO-3 and cut them to size. Use a hole punch to make a new hole.

Do It Yourself · 8th November 2009, 04:34 PM

i just thought about cutting some wax paper/parchment paper to do the job. anyone know if that will work?

SY · 8th November 2009, 05:11 PM

Bad idea. Lousy insulation, hygroscopic, mechanically weak, lousy thermal conductivity... A proper insulator costs maybe a quarter and can be gotten as easily as transistors.

nad · 8th November 2009, 06:21 PM

Couldn't you use some 'heat sink compound'?
It comes in a syringe of around 10ml and is available from most PC accessory stores.

powerflux · 8th November 2009, 06:32 PM

Quote:

Originally Posted by nad

Couldn't you use some 'heat sink compound'?
It comes in a syringe of around 10ml and is available from most PC accessory stores.

this does not guarantee electrical isolation.. i'd even say it conducts!

nad · 8th November 2009, 06:56 PM

Quote:

Originally Posted by powerflux

this does not guarantee electrical isolation.. i'd even say it conducts!

Silly me, my mistake, sorry.

Face · 8th November 2009, 07:23 PM

Quote:

Originally Posted by powerflux

this does not guarantee electrical isolation.. i'd even say it conducts!

Some do, some don't. I believe Arctic Silver Ceramique Thermal Compound is safe.

MJL21193 · 8th November 2009, 07:58 PM

Quote:

Originally Posted by Do It Yourself

i just thought about cutting some wax paper/parchment paper to do the job. anyone know if that will work?

I used regular white printer paper once (long ago) when I didn't have anything else. Smeared it with heatsink compound and it seemed to hold up pretty good, although I didn't leave it for long - just to test the circuit.
Truly, you would be better off with proper insulators. As Sy pointed out, they are a lot cheaper than the devices they are isolating.

8th November 2009, 04:38 AM	#1
Do It Yourself diyAudio Member Join Date: Nov 2009	PLEASE HELP! Insulating Transistors Electrically from Heat Sink I want to mount all of my power transistors (TO-264 and TO-126(also called SOT-32) on a single heat sink but this would cause all the collectors to short out. pictures of the cases: http://media.digikey.com/photos/Pana...tos/TO-126.jpg http://media.digikey.com/photos/On%2...488-TO-264.jpg

8th November 2009, 06:08 AM	#2
audi0 diyAudio Member Join Date: May 2009 Location: 37.34 degrees South Blog Entries: 5	Insulating kits? Wouldn't you just buy suitable silicone or mica insulators?

8th November 2009, 05:11 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Bad idea. Lousy insulation, hygroscopic, mechanically weak, lousy thermal conductivity... A proper insulator costs maybe a quarter and can be gotten as easily as transistors. __________________ "...we stumble and get up, we are sad, confident, insecure, feel loneliness and joy and love. There is nothing more; but I want nothing more.” - Christopher Hitchens 1949-2011

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8th November 2009, 12:43 PM	#3
MJL21193 Account disabled at member's request Join Date: Mar 2007	Hi, Most TO-126 are insulated package - no isolator required. The TO-264 need a silpad or mica washer (as mentioned above). It can be difficult to locate mica washers for the TO-264 but you can use washers for TO-3 and cut them to size. Use a hole punch to make a new hole.

8th November 2009, 04:34 PM	#4
Do It Yourself diyAudio Member Join Date: Nov 2009	i just thought about cutting some wax paper/parchment paper to do the job. anyone know if that will work?

8th November 2009, 06:21 PM	#6
nad diyAudio Member Join Date: Oct 2009	Couldn't you use some 'heat sink compound'? It comes in a syringe of around 10ml and is available from most PC accessory stores.

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