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Thermal conductivity of IHLP series inductor core?

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Flyback

Well-Known Member
Hello,
We are designing a sync Buck converter with..
Vin = 28V
Vout = 1V5
Iout = 17.1 A
F(sw) = 200kHz

There are eight of these with outputs all paralleled.

The inductor is 1uH and is the IHLP5050CE-01 type (datasheet below). This SMPS is in a totally sealed enclosure with the internal ambient at 70degC. There is however, a cold plate, which is gap-padded to the inductors and FETs. The FETs are BSC027N04 (datasheet below). Obviously we are heatsinking the FETs wrong because these FETs are designed to put heat into the PCB via their heat pad, and not meant to conduct heat to a heatsink up through their plastic bodies.

The problem is that the inductor datasheet does not give the thermal conductivity for the iron powder material that it is made of. Therefore, we are not sure how much hotter the inductor will be than the cold plate in parts of the inductor which are away from the cold plate. Also, each inductor has 1.7W of loss in its windings, and 0.4W of loss in its core. Therefore, we really need to know the thermal conductivity of the inductor core because then we can have some idea of how much of the winding heat will conduct through the core and from there to the cold plate via the gap pad.

If the core is quite thermally insulative then the windings heat will just conduct mostly into the PCB and heat that up, which will heat up the FETs even more.
So do you know what is the thermal conductivity of the IHLP material of the inductor?

The below has thermal conductivity of a different iron powder than IHLP material as being at least ten times less than that of aluminium…that’s not good..what’s it like for IHLP material?…

Page 5 shows general iron powder thermal conductivity…
http://www.micrometals.com/appnotes/appnotedownloads/desguide.pdf

BSC027N04 FET datasheet:-
http://www.infineon.com/dgdl/Infine...n.pdf?fileId=db3a30431689f4420116c4323646080c

IHLP5050CE-01 inductor datasheet:-
http://www.vishay.com/docs/34105/ihlp50c1.pdf
 

ChrisP58

Well-Known Member
Most Helpful Member
I expect the the IHLP inductor is ferrite, not powdered iron. Which, according to the info in your micrometals link, is about 1/45th that of aluminum.

I don't know if there is anything similar that fits your geometery, but I use this of a heatsink to get heat up out of the PCB for a SMT device.
http://www.aavid.com/products/standard/573300d00010g
 

Flyback

Well-Known Member
thanks ChrisP58, -so you stuff gap pad under the "arch" thing so that the gap pad closes the gap between the dpak body and the heatsink?
IHLP series inductors are actually powdered iron, i looked up the material spec on vishay site.
 

ChrisP58

Well-Known Member
Most Helpful Member
No, the 'feet' of the heatsink is soldered to the PCB on each side of the mosfet, so that it carries heat up from the same copper that the mosfet is pushing heat into. This gives you a continuous metal heat path.

In your case, I would look for something similar that could provide a metal heat path from the PCB up to the gap pad touching your cold plate. That would give you a much lower thermal resistance from the device to the cold plate.
 

Flyback

Well-Known Member
thanks, i see, thats the way to go, but it looks to me that the whole thing could be helped by shoving gap pad between the "arch" and the dpak body aswell...though you are right to point out that the dpak is primarily pushing its heat into the pcb so that is the first place to go for it...just looking at dpak body RTH(jc) via the body and it is not given.
 
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