Quasi-resonant (QR) flyback converter with zero-voltage detection and improved digital control

摘要

The present invention relates to a quasi-resonant (QR) flyback converter that includes a transformer circuit having a primary winding configured to receive an input voltage from the AC input, a secondary winding configured to provide an output voltage to the DC output, and an auxiliary winding connected to a primary side zero crossing detection circuit for detecting at least one zero voltage condition in the auxiliary winding and the timing thereof. A primary-side control circuit is configured to control a switching element to turn on and off the input voltage across the primary winding. Furthermore, a secondary-side control circuit is configured to detect the level of the output voltage and/or the level of an output current supplied to the DC output and to transmit and/or display the detected output voltage level and/or the detected output current level in a second response signal to the primary-side control circuit. The primary-side control circuitry is configured to set the OFF-duration to a pre-configured amount of time in accordance with the output voltage level and/or the output current and input voltage levels for a subsequent cycle, regardless of the OFF-duration of the current cycle, until the input voltage is switched back on again. respectively received in the second response signal.