Pulse Width Modulation (PWM) modules are commonly used in many applications to provide an inexpensive control output method that uses only a few external components. The PWM signal can be used directly as a digital signal to drive switches in a power conversion circuit. Or it can be filtered using external components to produce an averaged ‘analog’ signal with an output level that is proportional to the duty cycle. Either way, the duty cycle of the PWM signal determines the level of system output while the frequency remains fixed. The typical PICmicro PWM module (CCP/ECCP) is ideally designed to support these common types of applications providing high duty cycle resolution for a given fixed frequency.

In this application note, a simple technique is illustrated that allows all PICMicro PWM modules to support a different class of applications, including several lighting applications, where the duty cycle is required to be constant and it is the output frequency that changes in small increments.