PWM system for ECM motor

A pulse width modulation control system for an electronically commutated motor (ECM) adapted to be energized from a DC power source includes a power switching system coupled in circuit with each winding stage terminal of the ECM for selectively coupling each terminal to the DC power source for applying a DC voltage to selected ones of the winding stages of the ECM in a preselected sequence to effect energization of the ECM. The control system includes signal processing circuitry for generating switching signals for identifying selected power switching devices for energization in order to connect each terminal of the ECM to the power source in the preselected sequence. A pulse width modulation (PWM) circuit generates PWM enables signals for energizing the selected power switching devices and includes a clock for generating periodic clock signals defining sequential clock intervals of predetermined duration. A logic circuit is coupled to the PWM circuit for limiting the cycling of the PWM enable signal to once per clock interval.