Patent ID: 7791326

Claim:
A pulse width modulation-based dimming circuit for adjusting DC constant current from a phase-controlled, AC power source to at least one light source, the circuit comprising: a phase-angle detection circuit that senses input voltage from the AC power source and provides a DC pulse signal when the sensed input voltage exceeds a predetermined threshold voltage; a power stage that is electrically coupled to the at least one light source and that is adapted to control delivery of power to the at least one light source; a dv/dt filter that is electrically coupled to the AC power source and to the power stage and that is adapted to filter out voltage transients and to prevent reverse current ring back; a controller power supply that provides power to the power stage; and a controller that is adapted to establish a first pulse width modulation (PWM) switching frequency; to adjust a duty cycle of a second PWM signal; and to adjust a peak level of the current during the duty cycle, based on the DC pulse signals from the phase-angle detection circuit and on sensed current levels from the at least one light source.