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MOSFET Heat Sink Guide
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Editor's Preface : Power Regulation & MOSFETs

MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor. It is the most important component of the motherboard's switching voltage regulator.

As you all know, a motherboard's voltage regulator is nothing more than several power MOSFETs and a MOSFET controller. Because the voltage regulator provides power to the processor, the number and quality of the MOSFET used directly determines the quality of the power supplied to the processor. Needless to say, better quality MOSFETs produce better voltage regulators but what about the number of MOSFETs?

The number of MOSFETs determines the number of "power phases" or "power channels" of the voltage regulator. A voltage regulator with more phases is technically superior to one with fewer power phases. The increased number of phases allows the workload to be split between an increased number of channels. This simultaneously allows the voltage regulator to run much cooler as well as provide a smoother flow of power.

Of course, a less advanced 2-phase voltage regulator can still match a 3-phase or 4-phase voltage regulator by employing larger capacitors to even out the power flow. But this would not do anything for the thermal output from the MOSFETs. In voltage regulators with fewer phases, the MOSFETs can get very hot, especially when the voltage regulator needs to supply a lot of power to the processor. Hence, the use of heat sinks on such MOSFETs.

 

MOSFET Cooling

But not all MOSFETs come with heat sinks. This is particularly true for voltage regulators with three or four power phases. The power load is split between three or four channels which reduces the load on each MOSFET. As a result, the MOSFETs produce a lot less heat.

Take my ABIT NF7-S motherboard for example. It has a 3-phase voltage regulator with six power MOSFETs and a HIP6301CB multi-phase MOSFET controller. Even with an AMD Athlon XP 1700+ running at over 1.9GHz, the MOSFETs have a peak temperature of only 38°C! That's cool enough to do away with heat sinks.

However, faster processors take up a lot more power and the voltage regulator has to keep up with the demand. With the maximum thermal output of new processors like the Intel Pentium 4 Extreme Edition at 93.9W and the AMD Athlon 64 at 84.7W, the MOSFETs will be under much greater stress. Their thermal output would definitely be more than what we have seen with my sub-40W Athlon XP.

Unfortunately, because better quality motherboards generally use voltage regulators with three or four power phases, their MOSFETs are sans heat sinks. This is unfortunate because overclockers tend to favour many of these motherboards. While my ABIT NF7-S' power MOSFETs only heated up to 38°C with my Athlon XP @ 1.9GHz, what about those who are overclocking their hotter Barton processors beyond 2.4GHz?

With that comes an interesting thought - what if we keep the MOSFETs cooler by modding some heat sinks to them? Will it improve the MOSFETs' ability to deliver clean power to the processor? How to do it?

Although it is quite impossible to tell if additional cooling will have any effect on the MOSFETs' performance with processors that are rated for the motherboard, better cooling is always a good thing... Or is it?

I'll leave you with ZuePhOk as he explains his mini-project on MOSFET heat sinks.



 
   
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