Thermo-Electric Controllers (TEC)

Thermo-electric coolers are relatively inefficient and require a significant amount of power if it is very large. Linear regulation is also horrendously inefficient. PWM is very efficient for controlling large loads. You could look for application notes on most any micro-controller (Microchip, Inc.) website as most microcontrollers these days include PWM circuits for the control of motor but it would not be a big deal to adapt to control heating/cooling devices. You will probably want to incorporate a PID algorithm into your regulator due to the long thermal time constants not uncommon to thermal devices. You can also find info on that on the web.

Either you are talking about Thermo Electric Coolers or Temperature Controllers, the answer is the same: Efficiency.

If you use a linear controller in a 100W system, at 20% power, you will dissipate 80W in the control electronics...20% efficient.

A PWM system shall be better than 90% efficient. Losses are due to the transient resistance and the ON resistance of the electronics (tipically very low)

Up until 5 years ago, PWM or swiching controllers were not available for Thermo Electric Coolers. As they do not behave as purely resistive elements during the switching transients, only the volume demand of the telecom industry prompted their developpement.

PWM control is also used in many power electronics applications such as variable cordless drills and computer power supplies. Linear control would make these devices somewhar bulky and a lot less popular...