Circuit and method for driving led lamp with a dimmer

A system for driving an LED (light-emitting diode) lamp, comprising:

• a dimmer circuit coupled to a line input voltage for varying a magnitude of an input voltage;
• a transformer having a primary winding, a secondary winding, and one or more auxiliary windings, the primary winding coupled to the dimmer circuit;
• an output rectifying circuit coupled to the secondary winding for providing an output current to the LED lamp;
• a power switch coupled to the primary winding for controlling a current flow in the primary winding;
• 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 coupled to the capacitor, the ratio being related to the average input voltage signal from the dimmer circuit.

A driver circuit for an LED (light-emitting diode) lamp, comprising:

• a transformer having a primary winding, a secondary winding, and one or more auxiliary windings;
• a dimmer circuit coupled to a power source and the primary winding;
• an output rectifying circuit coupled to the secondary winding for providing an output current to the LED lamp;
• a controller coupled to the dimmer circuit to receive an average input voltage from the dimmer circuit (DIM), the controller being configured to vary the output current according to the average output voltage.