Another type of convection cooling requires forced-air flow, via fans that direct the air across the power devices, with or without heatsinks. Many power supplies come with a built-in fan to provide this forced-air type of convection cooling. Other types of power devices specify the amount of air flow that must pass through or around the unit, in cubic or linear feet-per-minute (CFM or LFM), in order for the device to provide its maximum rated output power.
Radiant cooling: This is the transfer of heat by means of electromagnetic radiation (energy waves) that flows from a hot object (e.g., power device) to a cooler object. True radiant heat transfer can take place in a vacuum and does not require air. For example, our Sun not only emits light waves, but, also infrared heat waves through great distances in space, which results in our Earth having daylight and various degrees of warmth.
Other Cooling Technologies
Thermoelectric coolers: Peltier coolers, also known as thermoelectric coolers (TEC), are solid-state devices that function similar to heat pumps. TECs require an external DC power source to operate them. The power device to be cooled is mounted on one side of the TEC with an appropriate thermal grease or thermal pad. When a voltage is applied to the TEC, the heat is pulled away from the power device and pumped to the opposite side that has a heatsink and sometimes a fan to dissipate the heat. Thermoelectric coolers are effective, but have low efficiencies and are more expensive than heatsinks and/or fans. However, they are used to cool laser diodes, ultra-fast microprocessors, and laboratory instruments.
Liquid cooled cold plates: In some applications where multiple electronic power devices are employed or where there is a concentrated heat load in a confined area, it may be necessary to consider the use of liquid cooled cold plates. As the name implies, these are usually comprised of aluminum or copper plates on which the power devices are mounted that contain parallel ducts or serpentine tubes through which a liquid coolant is pumped and then routed to an external heat exchanger where the liquid is cooled; then it is recycled through the pump in a continuous closed loop. This type of cooling is very effective, but also one of the most expensive techniques to employ. Nonetheless, liquid cooled cold plates are used extensively in many military, aerospace, RF amplifier, medical, industrial, and telecom applications.