Abstract: A controller for controlling the frequency of an oscillator associated with establishing the switching frequency of a PWM power supply. Each one of a plurality of PWM power supplies are connected through a common bus to a bi-directional connection on the controller. The controller has an internal comparator which compares its associated oscillator frequency with the frequency on the common bus. If the frequency of its associated oscillator is lower than the frequency on the bus then the controller increases its associated oscillator frequency to the the bus frequency. If the frequency on the bus is less than the frequency of its associated oscillator then the controller elevates the bus frequency to its associated oscillator frequency. In this manner, the power supply associated with the oscillator having the highest frequency establishes the master frequency and all other oscillators are slaves. The controller can be either capacitively or DC coupled to its associated oscillator.