Patent ID: 7265503

Claim:
A power supply circuit for powering a load, comprising: a half-bridge comprising a pair of high-side and low-side switching devices arranged in series between a high-side supply circuit and a common return circuit; a connection point between said switching devices providing a switched output for powering said load; and an integrated circuit, including a high-side driver and a low-side driver for respectively providing drive signals to control terminals of said high- and low-side switching devices, said high- and low-side drivers being controlled by an oscillator and timing and logic elements in the integrated circuit; said IC having a current sense pin connected to said half-bridge, said current sense pin receiving from said half-bridge a current signal representative of a current in said half-bridge, and said IC having an internal shut-down circuit operative to shut down said drive signals in response to said current signal indicating an overcurrent in said half-bridge; further comprising a dimming circuit connected to said current sense pin and having components for generating a waveform, setting a variable duty cycle of said waveform, and applying said waveform separately from said current signal from said half-bridge to said current sense pin of said IC, thereby to periodically shut down said IC independently of said current signal from said half-bridge so as to vary the duty cycle at said load.