Patent ID: 7504815

Claim:
A switch mode power supply controller employing a combination of pulse frequency modulation and pulse width modulation to control a power switching device, the controller having: an input to receive an output voltage dependent feedback signal; an output for driving said power switching device; and a control system to provide a switching control signal to said output responsive to said feedback signal from said input, said switching control signal having a switching cycle including an ON portion for switching on said power switching device, and wherein said control system is configured to select one of a plurality of discrete pulse widths for said ON portion of said switching cycle using at least one stored pulse width, and to vary a duration of said switching cycle responsive to said feedback signal; and wherein the control system is configured to determine said switching cycle duration and to select one of said at least one stored pulse width responsive to said determined duration; and wherein said control system has a plurality of operating power ranges each defining a range of average power transferred per switching cycle by said power switching device, each said range being defined by a combination of one of said at least one stored pulse width and a range of durations of said switching cycle, adjacent ones of said operating power ranges overlapping across a range of power levels.