Circuit and method for driving LED lamp with a dimmer

摘要

A system for driving an LED (light-emitting diode) lamp includes a dimmer circuit coupled to a line input voltage for varying a magnitude of an input voltage and a transformer having a primary winding, a secondary winding, and one or more auxiliary windings, the primary winding coupled to the dimmer circuit. The system also includes an output rectifying circuit coupled to the secondary winding for providing an output current to the LED lamp and a power switch coupled to the primary winding for controlling a current flow in the primary winding. The system further includes a controller having a comparator and a capacitor for providing a control signal to control the power switch for regulating the output current. The controller coupled to the dimmer circuit for receiving an average input voltage signal from the dimmer circuit, wherein the control signal is characterized by a duty cycle that is determined by a ratio of a charging current to a discharging current of the capacitor, and the ratio is related to the average input voltage signal from the dimmer circuit.

主权项

1. A control circuit for providing a pulsed control signal, the control circuit comprises:
an input terminal for receiving an input voltage; an output terminal for providing a pulsed control signal; a capacitor; and a comparator; wherein the pulsed control signal is characterized by a duty cycle that is determined by a charging current and a discharging current coupled to the capacitor, the charging current and the discharging current being related to the input voltage.