Patent ID: 8964415
Filing Date: 2015-02-24
Classification: H02M,Y02B

Abstract:
1. A switch mode power supply (SMPS) system, comprising: a rectifying device configured for converting a periodically varying input AC (alternating current) voltage into a DC (direct current) voltage; a transformer including a primary winding, a secondary winding, and an auxiliary winding, the primary winding being coupled to the rectifying device; an input capacitor having a first terminal and a second terminal, the first terminal coupled to the rectifying device and the primary winding of the transformer; a first power switch coupled to the second terminal of the input capacitor and a primary side ground; and a control circuit coupled to the first power switch and the input AC voltage, the control circuit being configured to control the first power switch based on a phase or amplitude of the input AC voltage, wherein the control circuit is configured to: turn on the first power switch when the AC input voltage is near a zero crossing of its waveform to cause the input capacitor to discharge to the primary winding; and turn off the first power switch to prevent the input capacitor from discharging when the input AC voltage is near a peak or a valley of its waveform; whereby power is provided to the primary winding during a longer portion of the AC input voltage cycle, allowing the rectifier device to have a larger conduction angle to increase a power factor (PF).