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MOSFET and VRM temperatures

post #1 of 9
Thread Starter 
Hey,

I ran a thermal diode to my motherboard to check out the MOSFET and VRM temperatures. Here's what I got:
VRM (ferrite chokes): 52C (aftermarket heatsink installed)
MOSFETs: 72C
CPU Vcore: 1.45v
Motherboard: Asus M4N68-M

So... What is too hot for a MOSFET? The VRMs look okay.
Edited by test tube - 1/5/11 at 6:38pm
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post #2 of 9
It depends on what the MOSFET specifically is in terms of serial number.

The problem with "safe" temps is that a MOSFET will start supplying irregular inconsistent power before it cooks. They are at a risk of thermal runaway. That is that once a MOSFET starts getting hot, it gets unstable and start producing more heat, making it more unstable and so on.

Chokes are just inductors, temps don't matter that much. MOSFETs are power gates, that are timed and controlled by a PWM chip. BTW- the term "VRM", applies to the entire array of MOSFETs/chokes/capacitors/PWM clock that drives the CPU. The VRM is not just the chokes.
Edited by Skripka - 1/5/11 at 6:42pm
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post #3 of 9
Are your mosfets bare?

That's pretty hot. I'd recommend some small mosfet heatsinks, it may prolong the life of your motherboard and aid your overclock.
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post #4 of 9
Quote:
Originally Posted by BlackHoleSon View Post
Are your mosfets bare?

That's pretty hot. I'd recommend some small mosfet heatsinks, it may prolong the life of your motherboard and aid your overclock.
Some MOFETs are rated for up to 160C from what I've read. Again it depends on the specific MOFET though.
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post #5 of 9
The 790X-UD4P has a very good power phase/mosfets, that came with heatsinks by default. Perhaps the heatsink isn't stuck on properly. Usually for me the mosfets load at the same temp as CPU (though this is going by the sensor in HWMonitor, not an actual diode).
post #6 of 9
Quote:
Originally Posted by Skripka View Post
Some MOFETs are rated for up to 160C from what I've read. Again it depends on the specific MOFET though.
Yeah I know, and how many there are. But $15-20 is pretty justified to ensure that they are much cooler. You never know how high quality your particular mosfets are, so it's just a good idea.
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post #7 of 9
Thread Starter 
Quote:
Originally Posted by Skripka View Post
It depends on what the MOSFET specifically is in terms of serial number.

The problem with "safe" temps is that a MOSFET will start supplying irregular inconsistent power before it cooks. They are at a risk of thermal runaway. That is that once a MOSFET starts getting hot, it gets unstable and start producing more heat, making it more unstable and so on.

Chokes are just inductors, temps don't matter that much. MOSFETs are power gates, that are timed and controlled by a PWM chip. BTW- the term "VRM", applies to the entire array of MOSFETs/chokes/capacitors/PWM clock that drives the CPU. The VRM is not just the chokes.
Right, I found that out now...

Quote:
Are your mosfets bare?

That's pretty hot. I'd recommend some small mosfet heatsinks, it may prolong the life of your motherboard and aid your overclock.
Yep, they're bare
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post #8 of 9
Thread Starter 
Quote:
Originally Posted by xd_1771 View Post
The 790X-UD4P has a very good power phase/mosfets, that came with heatsinks by default. Perhaps the heatsink isn't stuck on properly. Usually for me the mosfets load at the same temp as CPU (though this is going by the sensor in HWMonitor, not an actual diode).
It's not the board in the sigrig, it's my HTPC which is an asus M4N68-M

I guess I'll order a few more heatsinks from dealextreme and slap em on the mosfets too, they're only $3 for 8
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post #9 of 9
Quote:
Originally Posted by BlackHoleSon View Post
Yeah I know, and how many there are. But $15-20 is pretty justified to ensure that they are much cooler. You never know how high quality your particular mosfets are, so it's just a good idea.
Yup. Cooler is better. MOSFETs are DC-DC convertors. The power supply for your CPU. And just like your PSU, you don't want those MOSFETs getting hot.
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