Power control method during input line voltage fluctuation

Abstract

A resonant power converter as disclosed herein, e.g., an LED driver, comprises first and second switches in a half-bridge arrangement and responsive at an operating frequency to controlled drive signals. A resonant circuit is coupled between the switch output and an isolation transformer. A negative feedback control loop provides an error signal for regulation of the output current. A reference control circuit is added to the feedback control loop, and configured to sense when the error signal exceeds a threshold value, and further configured in response to control a feedback reference signal wherein the error signal is reset to a value below the threshold value. By resetting the feedback control reference value, loop runaway may be prevented, e.g., for enough time that the LED load may warm up or otherwise stabilize. As a result the LED driver will always maintain negative current closed loop control, and restore normal operating mode.