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What insulator type can I use for mosfet/case insulation?

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Dissipation Problem

I have an IRFP350 commuting 340V to a 71Ohms load. The Mosfet need dissipate 28W. If I fix the transistor to the case, this quantity of power can be dissipated, but the problem is that this case is accessible by the operator (the case is electrically connected to the earth terminal).
Any body can tell me what kind of insulator can I use in order to insulate the mosfet from case and this insulator must to be a good thermal conductor?. I have not enough space to use an extruded dissipater into the case.

Thanks a lot
 

Dissipation Problem

Add a fan?
 

Re: Dissipation Problem

It's difficult because generally good thermal conductors are good electrical conductors, I know an specialist in materials and I'll answer if he know a good and easy to buy material with this characteristic ...

leomecma
 

Re: Dissipation Problem

Use mica washer with thermal compound and plastic bushes.
(see attached table on thermal properties of selected materials)
More info you can find here:
**broken link removed**
Regards,
IanP
 

Re: Dissipation Problem

I need to know that is safety to use a mica insulator between an active part (using 340V) and accessible part (with a protection earth connection) to the operator.
The mica has dielectric constant of 160MV/m; using a 0.1 mm mica film obtains 16000V of insulation. This solution is in concordance with some international standard?.

Thanks in advance
 

Re: Dissipation Problem

In guideline on safety use of electricity typical test voltage in 300V circuits is ≈3000VRMS for 1second or 2500VRMS for 60seconds.
In this case mica insulator of 0.1mm can easily withstand this test voltage ..
Regards,
IanP
 

Re: Dissipation Problem

First of all, is the power dissipation as high as 28W? If you are only applying power to the load statically, the power should be much lower.

Other materials that can be used are the Sil-Pad from Bergquist. They also make tubes. so you can put the device in one of these tubes and attach it to the heatsink not with a screw, but with a clamp. That way the device is enclosed. www.bergquistcompany.com/tm_sil_pad_list.cfm

However, in the situation you describe, I think an insulating wall that would separate the hazardous area from the operator-accessible area should be considered.
 

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