Electrical – Average power dissipation in radar

Cooling is a vital part of most computer system design.

Air at room temperature is the usual coolant, because it's available everywhere* and you can move it easily with a small fan.

Some enthusiasts and large systems are liquid cooled. All the plumbing and pumping systems can't be miniaturized, and add cost, so this is usually done only on "tower" size systems: http://www.pcworld.com/article/227964/pc_liquid_cooling_system_do_it_yourself.html

The extreme is liquid nitrogen cooling: http://www.corsair.com/blog/setting-up-your-pc-for-liquid-nitrogen-overclocking/ , which is even more expensive and impractical. It's nearly always easier to stick with conventional cooling and buy more computers to achieve the same computational throughput.

(There are also issues with hold timing when running extremely cold - signals may arrive too early if the chip has not been designed to run at that temperature. If you move the minimum design temperature down to -200 that may force you to move the maximum temperature down as well, leaving you with a product that requires a liquid air supply and thus a very limited market)

• Except in space, where ultimately all your cooling must be radiative

When one MOSFET is heating up more than the other, it is usually one of two items:

1. Higher resistance in one leg.

It appears that you have included a 0.5ohm resistor in one leg, therefore, most of the current will go the low resistance route - the other leg.

2. In switching applications, the diode of one MOSFET is being used instead of simply turning it on during that portion of the cycle.

The diode has ~0.7V drop at the same current whereas if you simply turned on the MOSFET, this would drop to a much lower value, dissipating less power. This is why there are synchronous power supplies.