The effect of pulse width modulation (PWM) frequency on the reliability of thermoelectric modules

Pulse-width-modulation (PWM) control has many benefits when used to control power to thermoelectric modules (TEM's). This scheme allows the use of smaller, lighter circuitry that dissipates less heat than a comparable linear controller. However, abruptly turning power on and off to a TEM has been known to cause thermal cycling which reduces the reliability of the module. This thermal cycling fatigues the solder junctions causing an increase in the module's electrical resistance. As a result, some system designers have been reluctant to use PWM controllers in their cooling equipment. This paper quantifies the effect of PWM control on the reliability of TEM. TEM's are powered with PWM signals of various frequencies from 0.1 Hz to 10 kHz. The electrical resistance of these modules is then tracked throughout the duration of the test. These changes in electrical resistances are used to directly correlate the frequency of PWM control with TEM reliability.