Patent ID: 8610409

Claim:
A controller for use in a power supply, the controller comprising: a zero crossing detection (ZCD) circuit coupled to generate a ZCD signal that pulses each zero-crossing of an ac input voltage of the power supply; a threshold detection circuit coupled to receive and compare a signal representative of an output of the power supply with a threshold reference; a punctuated switching control circuit coupled to the ZCD circuit and to the threshold detection circuit to generate a switching signal to control a switch to regulate the output of the power supply, wherein, the punctuated switching control circuit generates the switching signal having intervals of switching and intervals of no switching, wherein an ac input current of the power supply flows during the intervals of switching and not during the intervals of no switching, each interval of switching begins responsive to the threshold detection circuit indicating that the output of the power supply has dropped below the threshold reference, each interval of no switching begins responsive to the threshold detection circuit indicating that the output of the power supply has risen above the threshold reference, and each interval of switching and each interval of no switching has a beginning that is synchronized with a pulse of the ZCD signal.