Dimmable LED power supply with power factor control

摘要

A dimmable LED power supply circuit arrangement is disclosed. The circuit arrangement includes a flyback converter coupled between an input for receiving a rectified alternating line voltage and an output providing power for at least one LED device. The flyback converter includes a transformer and a semiconductor switch for switching a primary current of the transformer. A current sensing unit provides a current sense signal dependent on the primary current. A control unit controls the switching operation of the semiconductor switch dependent on the rectified alternating line voltage and the current sense signal such that the flyback converter operates in a quasi-resonant mode of operation, whereby the current sense signal is compared with a time-varying reference signal representing the rectified alternating line voltage and whereby a switch-off time of the semiconductor switch is determined dependent on the comparison.

主权项

1. A power supply circuit comprising:
a control unit configured to be coupled to a semiconductor switch connected to a primary winding of a transformer, wherein the control unit is configured to
control a switching operation of the semiconductor switch dependent on a rectified alternating line voltage and a current sense signal dependent on a current of the primary winding of the transformer,compare the current sense signal with a time-varying reference signal representing the rectified alternating line voltage,determine a switch-off instant of the semiconductor switch dependent on the comparing the current sense signal with the time-varying reference signal, anddrive the semiconductor switch such that a short-term average of the current of the primary winding follows the rectified alternating line voltage to provide a power factor correction.