Rectifier circuits, synchronous rectifier circuits, and related electric devices

A power converter, comprising:

• a transformer with a primary winding and a secondary winding;
• a power switch, connected in series with the primary winding between two input power lines;
• a synchronous rectifier circuit connected to the secondary winding, the synchronous rectifier circuit comprising:
• a rectifier switch, electrically connected between one of two output power lines and the secondary winding;
• an auxiliary switch, electrically coupled to the rectifier switch;
• a synchronous rectifier controller, for detecting a demagnetization time of the transformer to control the rectifier and auxiliary switches, wherein the demagnetization time includes a charge time and a rectification time;
• and
• an operating power capacitor, across which is an operating power voltage, for supplying power to the synchronous rectifier controller;
• wherein, during the charge time, the synchronous rectifier controller turns OFF the auxiliary switch, and the synchronous rectifier circuit directs a secondary-side current from the secondary winding to charge the operating power capacitor;
• and
• during the rectification time, the synchronous rectifier controller turns ON the rectifier and auxiliary switches, and the synchronous rectifier circuit directs the secondary-side current to go through the rectifier switch without charging the operating power capacitor.

A control method in use of a power converter supplying an output power voltage across two output power lines, wherein the power converter comprises a transformer with a primary winding and a secondary winding, and a synchronous rectifier circuit connected to the secondary winding, the synchronous rectifier circuit comprises a rectifier switch and an auxiliary switch electrically coupled to each other, and the rectifier switch is electrically connected between the secondary winding and one of two output power lines, the control method comprising:

• detecting a demagnetization time of the transformer to control the rectifier and auxiliary switches, wherein the demagnetization time comprises a charge time and a rectification time;
• during the charge time, turning OFF the auxiliary switch, so as to direct a secondary-side current from the secondary winding to charge an operating power capacitor that supplies power to a synchronous rectifier controller controlling the rectifier and auxiliary switches;
• and
• during the rectification time, turning ON both the rectifier and auxiliary switches, so as to direct the secondary-side current from the secondary winding to build up the output power voltage and not charge the operating power capacitor.