Patent ID: 8665620

Claim:
A controller for use in a power supply, the controller comprising, a pulse width modulation (PWM) circuit to generate a drive signal to control a switch to regulate an output of the power supply in response to a switch current flowing through the switch and in response to a clock signal having a switching period; and a timing circuit coupled to the PWM circuit to provide the clock signal, wherein the timing circuit includes: a timing capacitor, where the switching period of the clock signal is based on a charging time that the timing capacitor charges to an upper reference voltage plus a discharging time that the timing capacitor discharges to a lower reference voltage; a first current source coupled to charge the timing capacitor while the timing circuit is in a normal charging mode that is when an on time of the switch is less than a threshold time; and a second current source coupled to charge the timing capacitor while the timing circuit is in an alternative charging mode that is when the on time of the switch exceeds the threshold time, wherein a magnitude of the current provided by the second current source is less than a magnitude of the current provided by the first current source such that the switching period of the clock signal is increased in response to the timing circuit entering the alternative charging mode.