Electronics > Projects, Designs, and Technical Stuff
Thermal INSULATOR Pad to Reduce Housing Temperature? (Desperate!)
KaneTW:
GaN FETs get pretty cheap, depending on what you need. https://www.digikey.com/products/en/discrete-semiconductor-products/transistors-fets-mosfets-arrays/289?FV=ffe00121%2Cfffc0395&quantity=0&ColumnSort=1000011&page=1&pageSize=25
2 N-channel GaN in one package, 100V, 1.7A continuous for $0.75/pc @ 2500pc. Lots of other offerings too.
jbb:
Hi Tim
You’re welcome. Some quick replies:
- the idea on the heat pipe was to distribute the heat load from the inductor all the way along the aluminium part. This would mean a warm stripe rather than a hot spot. No need to try to bond the inductor to the heat pipe and heat sink too, this would make assembly annoying. Simply glue the heat pipe to the hestsink next to the inductor and see what happens. Beware that thermal fillers tend to degrade mechanical strength, so don’t just get the thermal epoxy with lowest thermal resistance; you need to survive vibration and drops.
- what I meant with surface coating is that the standard might say “maximum X degrees if metal and Y degrees if plastic,” which might let you get away with a higher spot temperature
- looks like you’ve done he hard work on the inductor
- SiC Schottky diodes are great :-)
- SiC and GaN devices do carry a cost premium, which you have to recover by total system design. Given you’re using TO-220 devices, the package inductance is such that a TO-220 SiC device might not do much better than a Si one.
I had a further thought. It’s really hackey. Can you make a 0.5 - 1.0mm deep indent in the OUTSIDE of the enclosure (keep electrical safety and drop resistance in mind) and use a neoprene (or other foam) label to cover the hot spot? You might be able to argue that even if the spot is touched, the heat flux through neoprene is limited. Could have trouble with porosity and sanitary control, though.
TimNJ:
--- Quote from: jbb on August 15, 2019, 10:46:18 pm ---Hi Tim
You’re welcome. Some quick replies:
- the idea on the heat pipe was to distribute the heat load from the inductor all the way along the aluminium part. This would mean a warm stripe rather than a hot spot. No need to try to bond the inductor to the heat pipe and heat sink too, this would make assembly annoying. Simply glue the heat pipe to the hestsink next to the inductor and see what happens. Beware that thermal fillers tend to degrade mechanical strength, so don’t just get the thermal epoxy with lowest thermal resistance; you need to survive vibration and drops.
- what I meant with surface coating is that the standard might say “maximum X degrees if metal and Y degrees if plastic,” which might let you get away with a higher spot temperature
- looks like you’ve done he hard work on the inductor
- SiC Schottky diodes are great :-)
- SiC and GaN devices do carry a cost premium, which you have to recover by total system design. Given you’re using TO-220 devices, the package inductance is such that a TO-220 SiC device might not do much better than a Si one.
I had a further thought. It’s really hackey. Can you make a 0.5 - 1.0mm deep indent in the OUTSIDE of the enclosure (keep electrical safety and drop resistance in mind) and use a neoprene (or other foam) label to cover the hot spot? You might be able to argue that even if the spot is touched, the heat flux through neoprene is limited. Could have trouble with porosity and sanitary control, though.
--- End quote ---
Thanks for the ideas/clarification about the heatpipe. I think I'll ask our mechanical guys what they think about it.
Do you think there would be any benefit of dropping in an SiC MOSFET without changing switching frequency, inductor redesign, etc? Unfortunately, trying to think of a quick way out here.
To my knowledge, plastic materials are allowed to be the hottest per medical safety standards, and I think a foam might fall under that category, though I can't be sure. If the enclosure was metal, then yes, for sure, we could put something plastic on those areas and get an additional 10-15C. The enclosure does need to be wiped down/sanitized, so I'm not sure how the porous foam would go over. :-\
Thanks.
TimNJ:
--- Quote from: KaneTW on August 15, 2019, 10:13:38 pm ---GaN FETs get pretty cheap, depending on what you need. https://www.digikey.com/products/en/discrete-semiconductor-products/transistors-fets-mosfets-arrays/289?FV=ffe00121%2Cfffc0395&quantity=0&ColumnSort=1000011&page=1&pageSize=25
2 N-channel GaN in one package, 100V, 1.7A continuous for $0.75/pc @ 2500pc. Lots of other offerings too.
--- End quote ---
Thanks. I am looking for 600-800V MOSFETs unfortunately!
thermistor-guy:
--- Quote from: TimNJ on August 15, 2019, 06:33:52 pm ---...
Our issue is on the top of the housing. There is a small gap, maybe 1 or 2mm, between the top heatsink and the plastic housing. We've tried filling that with thermal RTV among other things. But now, at my wits end, I'm wondering if perhaps a thermal insulator on the hotspot could get us the reduction in temperature we need.
...
Any other suggestions on how to make this work?
--- End quote ---
You could try adding adhesive-backed metallic sheet (copper or aluminium foil) to the top of the housing (inside surface). The sheet reflects infra-red radiation away from the top of the housing, spreads the heat a little via conduction, plus the adhesive provides a small amount of thermal insulation. Together, these small improvements may provide just enough hotspot reduction.
Since you have 1mm to work with, you could also add a thin insulating layer between the foil and housing. This would be a cheap solution if it works. Once you get a working prototype, Parker Chomerics (http://www.chomerics.com/) may be able to help you with a professional production-ready solution.
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