1. Pulse Width Modulation
Pulse width modulation (PWM) is a power conversion technique that converts the AC line voltage to a lower voltage DC signal. Pulse width modulation essentially controls the duty cycle as well as the frequency of the power applied to the TEC.
To prevent thermal cycling, most PWM circuits filter the DC output to provide a "smooth" DC component to the TEC. The frequency of the PWM can be as low as possible to maintain a continuous, smooth output voltage.