MOSFET Question

Stratcat 21 years ago

Hi guys -

First time posting here.

I'm doing some PC overclocking & have been finding my cpu pwr FETs are really sizzlin'! I don't have the equipment to get a temp reading, but several ppl on an overclocking forum I'm a member of, have already lost some motherboards due to blowing a FET. We're overclocking 1st generation Intel P4 Prescott cpu's, and they extremely power hungry. Some peeps have resorted to adding heat sinks to their FETs, with varying success.

I don't have the PN or datasheet handy; Sorry. They're 3P (S-G-D) power MOSFETS w/a high impedance gate.

I was wondering: Since the gate is a very high impedance, can MOSFETs be 'paralleled up' if they are identical components? IOW, I'm considering simply soldering an identical FET to the legs of the original FETs, in a pin-to-pin manner. This would be an attempt to loadshare using additional FETs.

It would seem to me the only concern would be if the device driving the gates can provide enough gate current for the original & additional FET, in each instance.

Anyone have any opinions???

TIA

Strat

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Darknot 21 years ago

Two fets probably wont share the current equally, one will hog 80% the other

20%, and you will still have to heat sink them both. (you can get them to share current more evenly by adding series resistance, but that leads to voltage drop and frequency loss.) If you can hold your finger on the part, it is less than 140 F. Which should be OK. If not, then it needs more heat sink. If they are sunk on the board, you should be able to use a stand up one, and heat sink the back, the board is a poor heat sink. You could put in a faster fet too. [But, why overclock, is 20% faster noticeable?}

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w_tom 21 years ago

FETs generally become less conductive when hotter. Different from bipolar that become more conductive when hotter. To parallel bipolar, put resistors on each emitter. Check datasheet for the FET. If it gets less conductive when it gets hotter, then paralleling should be OK. But don't expect to get 200% out of two paralleled FETs. The more conductive FET may fail first - causing the second to fail.

Ballpark - its not too hot until it blisters (severely burns) sk> I'm doing some PC overclocking & have been finding my cpu pwr FETs are

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