ZVS control circuit for use in a flyback power converter

A zero voltage switching (ZVS) control circuit, configured to operably control a flyback power converter, the ZVS control circuit comprising:

• a primary side controller circuit, configured to operably generate a switching signal which controls a power transformer through a power transistor to generate an output voltage;
• a secondary side controller circuit, configured to operably generate an SR control signal and a PWM synchronous signal, wherein the SR control signal controls a synchronous rectifier transistor, wherein the SR control signal includes an SR-control pulse and an SR-ZVS pulse, wherein the SR-control pulse controls the synchronous rectifier transistor to be ON for an SR time period;
• and
• a pulse transformer, configured to operably couple the PWM synchronous signal from the secondary side controller circuit to the primary side controller circuit to generate the switching signal;
• wherein before the PWM synchronous signal delivers a synchronous pulse, the synchronous rectifier transistor is turned ON for a predetermined ZVS time period by the SR-ZVS pulse;
• wherein when the synchronous rectifier transistor is turned OFF at the end of the SR-ZVS pulse, the PWM synchronous signal is generated to trigger the power transistor to be turned ON, to achieve zero voltage switching;
• wherein the SR-ZVS pulse controls the synchronous rectifier transistor to be ON for the predetermined ZVS time period when a voltage of a drain terminal of the synchronous rectifier transistor is lower than a low-voltage threshold.

A zero voltage switching (ZVS) control circuit, configured to operably control a flyback power converter, the ZVS control circuit comprising:

• a primary side controller circuit, configured to operably generate a switching signal and an SR synchronous signal, wherein the switching signal controls a power transformer through a power transistor to generate an output voltage;
• a secondary side controller circuit, configured to operably generate an SR control signal for controlling a synchronous rectifier transistor at a secondary side of the power transformer, wherein the SR control signal includes an SR-control pulse and an SR-ZVS pulse, wherein the SR-control pulse controls the synchronous rectifier transistor to be ON for an SR time period;
• and
• a pulse transformer, configured to couple the SR synchronous signal from the primary side controller circuit to the secondary side controller circuit to generate the SR control signal;
• wherein the SR control signal is triggered to generate the SR-ZVS pulse according to the SR synchronous signal, and the synchronous rectifier transistor is turned ON for a predetermined ZVS time period by the SR-ZVS pulse;
• wherein when the synchronous rectifier transistor is turned OFF at an end of the SR-ZVS pulse, the power transistor is turned ON, to achieve zero voltage switching;
• wherein after the synchronous rectifier transistor is turned OFF at the end of the SR-ZVS pulse, the power transistor is turned ON after a predetermined ZVS delay time period from a turned-OFF timing of the synchronous rectifier transistor;
• wherein after the synchronous rectifier transistor is turned OFF at the end of the SR-ZVS pulse, the ZVS delay time period is started when a voltage of an auxiliary winding of the power transformer is lower than a primary-side-winding threshold, wherein the auxiliary winding is coupled to the primary side controller circuit.