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Topic: Quick 3 phase question (Read 618 times) previous topic - next topic

nali2001

I have been looking into 3phase setups and one thing I wonder is, is it possible to have the 3 lower mosfets on the same heat sink hence tying them electrically together (sine the heatsink is conductive)? I know all the 3 top mosfets can be on the same heat sink. But I wonder if that also applies to the 3 lower.


Thanks!

CrossRoads

Well, you have PNP/NPN type transistors drawn instead of P-channel/N-channel MOSFETs.

But anyway, the answer could be yes, as long as you select parts that have the 'tab' on the correct pin; and if not, yes if you use mica insulator/nylon spacer to insulate the tab from the heat sink.
See this as example, found thru a search at digikey.
http://www.keyelco.com/pdfs/M55p103.pdf
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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nali2001

#2
Nov 01, 2011, 03:24 pm Last Edit: Nov 01, 2011, 03:28 pm by nali2001 Reason: 1
Hi,
All should be NPN
I want to use irfp250n http://www.hestore.hu/files/irfp250n.pdf
The metal heat sink back part is on the Drain. So I guess on the high side all 3 mosfets can be electrically connected and it won't be a problem. But I wonder if all 3 low side fets can be on one heatsink as well.
So having 1 heatsink for the high side fets and 1 heatsink for the low side fets.

Grumpy_Mike

No you can't do that, the drain will be on the load not the supply.
You have to use insulated washers.

nali2001

Thanks all,
I indeed see now.

At least the low side fets need to be all isolated.
Thanks!

Grumpy_Mike

and the high side ones, if they are P-channel then it will be the source at the +ve supply.
If they are N-channel then they will only work as a source follower and do you want that configuration?

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