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Old 31st July 2012, 02:26 PM   #1
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Default Heatsink with 'thread gutter'

I was looking at some heatsinks and came across extruded heatsinks with a M3 'thread gutter' for mounting. At first I thought it was for mounting it to a chassis, but I also found some pictures of components bolt to the chassis using this 'thread gutter'.

Radiatory serii SK125, SK125-50SA, SK125-84SA

That picture can only be for illustration purposes, as all tabs are probably shortcircuited. So, can it really be used this way? And would want limit the dissipation on the TOxxx body (because part of the body is not in contact with the heatsink)?

many thanks for your replies! Erik
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Old 31st July 2012, 03:07 PM   #2
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Looking at the heatsink again I think the thread gutter is indeed meant to be used that way, as the TO220 'feet' just go nicely through a possible PCB attached to the bottom of the heatsink (and held in place with other M3 screws to the other thread gutter on the heatsink).

And what about insulating pads? Do you think there will be additional stress on them due to the 'gutter'? Shall it be possible to use silpads without them tearing?
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Old 31st July 2012, 04:28 PM   #3
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This will not limit dissipation by any appreciable amount. The heat is concentrated under the body of the part, not at the end of the tab.

Sometimes it is OK to short out the tabs. In the case of four diodes (presumably configured into a bridge recitifer) as pictured, it is not OK. But the picture is for illustration only, and any insulating washers would obscure the view of the heatsink.
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Old 31st July 2012, 04:52 PM   #4
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Good! I also thought that the heat will not concentrate on the tab, as it is there only for mounting purposes. Also heat will spread well over a metalic surface, so the tab won't be 'very hot' even if it is not completely in contact with heatsink material.

yes, you are right, sometimes shorted tabs are indeed needed. It is just that these four diodes (I think) on the example don't make sense.

All with all, many thanks!
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Old 5th August 2012, 03:46 PM   #5
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See this semi-relevant AN from IRF that popped up here a few months ago:

http://www.irf.com/technical-info/appnotes/an-1000.pdf

For the 'super-220' package they propose a clip that presses on the body of the device, in lieu of the regular bolted-tab mounting.


ON has something similar to say in their AN:

http://www.onsemi.com/pub_link/Collateral/AN1040-D.PDF

Last edited by discrete; 5th August 2012 at 03:49 PM.
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