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/Panasonic%20Photos/TO-126.jpg
http://media.digikey.com/photos/On%20Semi%20Photos/488-TO-264.jpg
pictures of the cases:
http://media.digikey.com/photos/Panasonic%20Photos/TO-126.jpg
http://media.digikey.com/photos/On%20Semi%20Photos/488-TO-264.jpg
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.
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.
i just thought about cutting some wax paper/parchment paper to do the job. anyone know if that will work?
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.
Couldn't you use some 'heat sink compound'?
It comes in a syringe of around 10ml and is available from most PC accessory stores.
It comes in a syringe of around 10ml and is available from most PC accessory stores.
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.
Look at Digikey (for example) and enter "Silpad" in the search box.
That is a brand name for a silicone insulator, made by Bergquist
For example the TO247 one ought to fit your larger transistor:
Digi-Key - BER178-ND (Manufacturer - SP900S-104)
Their part number BER178 if my link doesn't work
That is a brand name for a silicone insulator, made by Bergquist
For example the TO247 one ought to fit your larger transistor:
Digi-Key - BER178-ND (Manufacturer - SP900S-104)
Their part number BER178 if my link doesn't work
Those work very well, I've used them for years. As a bonus heat sink compound is not required with them so they are much less messy.
If you have hard anodized sinks you may not need anything more than thermal grease and isolated mounting. This has worked well for some manufacturers in the past, and creates a minimum thermal resistance interface.
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I say look on ebay, or buy from the suggested places, why build something that will just blow up, then you will be replacing the transistors that you burnt up.
What about buying the iso pad's from the source that you got the transistors from ?
J'
What about buying the iso pad's from the source that you got the transistors from ?
J'
I can second that you should not use regular Arctic Silver 5 - I tried it and sent about 180 volts through it around the mica.
I am comfortable with mica/white grease or silpads - I have used thermasil brand with good results.
I am comfortable with mica/white grease or silpads - I have used thermasil brand with good results.
Can anybody explain the pro's and con's of using silica pads over mica washers and thermal grease? Should you use thermal grease with silica pads? I have always used mica insulators with grease but latrly I have noticed pads being used and it looks like no grease. So the pads don't need grease?
The silica pads are easier to use but at least the comon ones don't transfer heat
as well as the mica. There are much more expensive silica pad type ones in the $1
each price range that do transfer heat a lot better but for a price performance standpoint mica is still hard tobeat.
as well as the mica. There are much more expensive silica pad type ones in the $1
each price range that do transfer heat a lot better but for a price performance standpoint mica is still hard tobeat.
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