POWER SUPPLY FOR LED LAMP WITH TRIAC DIMMER

摘要

A bleeder circuit is provided in a switched mode power supply (SMPS) that provides a compensation current when the loop current drops below the holding current of the TRIAC to alleviate light flickering problem. Further, automatic power factor correction is also provided in embodiments of the invention, which enables the output current to be in phase with the input voltage. The power factor correction not only improves the efficiency of the power supply, it can also reduce the compensation current and the duration in which compensation current flows, thereby reducing the power loss in the bleeder circuit.

主权项

1. A power supply for an LED (light-emitting diode) lighting system with a TRIAC (Triode for Alternating Current) dimmer, the power supply comprising:
a rectifier circuit for coupling to an AC input voltage through a TRIAC dimmer, the TRIAC dimmer being characterized by a holding current, the rectifier circuit having a first output terminal and a second output terminal; a transformer coupled to the first output terminal of the rectifier circuit for receiving a rectified DC input voltage, the transformer having a primary winding and a secondary winding; a power switch coupled to the primary winding of the transformer; a controller coupled to the power switch for controlling a current flow in the primary winding to provide a controlled output to an LED load, the controller being configured to control current pulses in the primary winding such that an envelope waveform formed by peak points of the current pulses is in phase with the AC input voltage thereby improving the power factor of the power supply; and a bleeder circuit coupled to the rectifier circuit, wherein the bleeder circuit is configured to maintain a current flow through the rectifier circuit that is equal to or greater than the holding current of the TRIAC.