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Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
I am really looking to water cool my future project that uses discrete igbts. I don't want to pay for the sot227 package or some modules so I am looking at packages like the to247 that have isolated metal tabs on the back. The reson is to reduce thermal resistance and to cool the igbt with water directly on its surface. To do this I require the igbt to be completely isolated. I have looked at packages from Fairchild and have seen that the to3p and to3pf are both isolated(or just forget to mention the connection to their tabs if they even have metal on the back). Can anyone think of some off the top of their head so I can get a good idea of where to start?
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
True isolated-tab packages are horrendously expensive, since they have internal ceramic insulation. And if you're using a plastic-tabbed transistor, you might as well use a TO-247, some sil-pad, and a waterblock. If you're going immersion cooled it might be a good idea to use deionized water anyway.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The isolated tabs have considerably higher thermal resistance too, because of the internal insulator which isn't really that much better than a high performance Sil-pad. Plain TO247 or Super-247 (same form factor minus the mounting hole) is hard to beat for thermal performance.
However, I and many others have used the SOT-227 "miniblocks", which are isolated, with great results. You can think of them as a TO247 with a high performance Sil-pad and copper heat spreader already assembled for you. Of course you pay for the convenience.
PS: Cheap isolated packages just mould the plastic over the heat transfer surface. The thermal conductivity is lousy. These devices are not suitable for a high performance Tesla coil.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
how would i distill the water to remove the necessary ions? more specifically, what ions are responsible most for creating conductivity in h2o? i would like to run tap water through the system and have a filter to de-ionize the water so i don't have to add new liquid every time i want to use it, but i need to know what kind of filter to use.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
ben123324 wrote ...
how would i distill the water to remove the necessary ions? more specifically, what ions are responsible most for creating conductivity in h2o? i would like to run tap water through the system and have a filter to de-ionize the water so i don't have to add new liquid every time i want to use it, but i need to know what kind of filter to use.
You'd buy a purpose biult de-ionising unit, and incorporate in into the loop.
(you could make one, but as you are asking this question, I assume you won't consider constructing your own)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
If you're going for a closed-loop system with a radiator, you might as well use mineral oil instead of water. The only drawback is that you may need a different pump, because oil is more viscous than water.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
just my observation, but the isolated tab devices vary wildly, some are worse at heat conductivity than the sill pad route and still more expensive and can have lower electrical ratings than its non isolated tab peer.
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Isolated tabs
