Patent ID: 7208921

Claim:
A switch mode power supply comprising: high and low side semiconductor switches; and a drive circuit for turning the high and low side semiconductor switches on and off, the drive circuit being comprised of: a variable frequency oscillator to provide a signal which determines the switching frequency for the high and low side semiconductor switches, the oscillator having a nominal frequency; an error amplifier to provide an output signal which represents departure of the power supply output from a nominal value; an adjusting circuit including a controllable current source which feeds or diverts current from an oscillator timing capacitor to determine the oscillator frequency, the adjusting circuit is responsive to departure of the power supply output from the nominal value to adjust the frequency of the oscillator to a frequency which is higher or lower than the nominal frequency according to the departure of the power supply output from the nominal value; and a clamping circuit which provides a signal defining a minimum on-time for the high-side semiconductor switch.