| bushing washer screw for to-247 package - Click HERE for Original Thread |
| rwagter |
Arggggh,
just been thru the digikey catalog again but I cannot seem to find a isolationkit for to-247 (like the IRFP240).
Does somebody know where to find these ???? I already have bergquist silpads (from digikey)
Ralph |
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| rwagter |
Probably found it myself :xeye:
3103K-ND 0.187 inch long 0.145 wide combined with a m3 screw this should work
Ralph |
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| grataku |
| I don't understand what you need exactly, once you have the silpad all you need is a screw, washer and lock washer, if you don't thread the heatsink you may need the bolt too, but you need not to mess with plastic washers and other ****. That's the beauty of the plastic cases. I would buy nice SS screws, the ones that come with the isolation kit are abysmal. |
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| rwagter |
Oops,
forgot the p from plastic. Only worked with metal casings so far.
Ralph |
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| halojoy |
| quote: | Originally posted by rwagter
Oops,
forgot the p from plastic. Only worked with metal casings so far.
Ralph |
ALWAYS not PUT TOO much stress on the transistor
but 247 can take a lot |
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| BrianL |
You should be able to fine an ap-note on the ON Semi
or International Rectifier web sites that have proper
hardware and torques for mounting these device. |
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| rwagter |
Brain,
that what I thought. But it's nowhere to be found.
Halojoy,
not to much pressure is a little vague. Do you use a torque (adjustable) screwdriver. I ask because to little pressure is also not recomended |
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| Elso Kwak |
Hi BrianL,
The problem with these socalled Belleville washers (concave washers) is that I can find them NOWHERE!:bawling: |
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| rwagter |
Elso,
zoek op schotelveer in google (zo heet zo'n ding in het nederlands.)
Excuse me for the dutch but had to translate belleville washer.
Ralph |
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| rwagter |
Belleville washer is a washer which complies to:
DIN 2093 (good google searchstring :) )
Ralph |
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| Joe Berry |
McMaster-Carr (http://www.mcmaster.com) has these, and the correct choice for a 6-32 screw is catalog # 90127A007.
The IR datasheet for TO247 devices like IRFP140/240 specifies a mounting torque of 10 in-lbs, but slightly less than this "feels" better to me, and I get away with it (so far!). When using belleville washers, a workable rule of thumb is to apply enough torque to fully compress the washer, but no more. |
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| BrianL |
Joe,
One of the supposed advantages to Belleville washers
is that the compression is relatively independent of
amount of compression.
So, I'd say apply enough torque to ALMOST fully
compress the washer. |
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| Joe Berry |
Brian, you raise a good point. I was thinking in terms of when the washer *appears* to be just fully compressed. In my estimation, this happens before the washer actually becomes fully compressed, but others may find this advice rather vague. Yet in that case, I'm not sure that "almost fully compress" would offer sufficient clarity.
It may be helpful here to refer to the fuller description of the situation available at http://www.bellevillesprings.com/di...cteristics.html. This description includes a graph which plots deflection against force, and shows that the relationship becoming nonlinear as the spring washer compresses and becomes stiffer. Because of this, the text suggests that deflection be limited to 75% of maximum.
This is something that may be more accurately judged by the number of turns applied, rather than visually. So, for example, if it takes one full turn to fully compress the washer from the point where the driver becomes harder to turn, apply 3/4 of a turn rather than the full turn. |
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