Flyback power converter and controller and driver thereof

A controller of a flyback power converter, wherein the flyback power converter includes:

• a transformer which has a primary winding, configured to operably receive an input voltage, and a secondary winding, configured to operably generate an output voltage;
• a power switch, which is coupled to the primary winding, and configured to operably control a conduction time of the primary winding;
• a driver, which is located at a primary side of the transformer, and configured to operably generate a switching signal to control the power switch;
• a synchronous rectification (SR) switch, which is coupled to the secondary winding, and configured to operably control a conduction time of the secondary winding in correspondence to a nonconductive time of the primary winding;
• the controller, which is coupled to the SR switch and located at a secondary side of the transformer, and configured to operably control the SR switch and generate an ON pulse signal and an OFF pulse signal in a normal operation mode;
• and a signal coupler circuit, which is coupled between the controller and the driver, and configured to operably convert the ON pulse signal and the OFF pulse signal to an ON trigger signal and an OFF trigger signal respectively, which are inputted to the driver;
• wherein when the output voltage reaches or exceeds a lower limit voltage, the flyback power converter operates in the normal operation mode, and in the normal operation mode, the driver generates the switching signal wherein a start conduction time point and an end conduction time point of the primary winding are determined according to the ON trigger signal and the OFF trigger signal respectively;
• the controller comprising:
• a synchronous rectification (SR) switch control signal generation circuit, configured to operably generate an SR switch control signal according to a voltage drop sense signal and/or a pulse width modulation (PWM) signal, to control the SR switch;
• a PWM signal generation circuit, which is coupled to the SR switch control signal generation circuit, and configured to operably generate the PWM signal according to a feedback signal which is related to the output voltage or related to an output current;
• and
• a pulse signal generation circuit, configured to operably generate the ON pulse signal according to a level change of the PWM signal in a first direction, and generate the OFF pulse signal according to a level change of the PWM signal in a second direction which is opposite to the first direction.

A driver of a flyback power converter, wherein the flyback power converter includes:

• a transformer, which has a primary winding, configured to operably receive an input voltage, and a secondary winding, configured to operably generate an output voltage;
• a power switch, which is coupled to the primary winding, and configured to operably control a conduction time of the primary winding;
• the driver, which is located at a primary side of the transformer, and configured to operably generate a switching signal to control the power switch;
• a synchronous rectification (SR) switch, which is coupled to the secondary winding, and configured to operably control a conduction time of the secondary winding corresponding to a nonconductive time of the primary winding;
• a controller, which is coupled to the SR switch and located at a secondary side of the transformer, and configured to operably control the SR switch and generate an ON pulse signal and an OFF pulse signal in a normal operation mode;
• and a signal coupler circuit, which is coupled between the controller and the driver, and configured to operably convert the ON pulse signal and the OFF pulse signal to an ON trigger signal and an OFF trigger signal respectively, which are inputted to the driver;
• wherein when the output voltage reaches or exceeds a lower limit voltage, the flyback power converter operates in the normal operation mode, and in the normal operation mode, the driver generates the switching signal wherein a start conduction time point and an end conduction time point of the primary winding are determined according to the ON trigger signal and the OFF trigger signal respectively;
• the driver comprising:
• a low voltage mode ON time control circuit, configured to operably determine the start conduction time point and the end conduction time point of the primary winding in the low voltage operation mode, wherein the low voltage mode ON time control circuit is disabled in the normal operation mode;
• a normal mode ON time control circuit, which is coupled to the signal coupler circuit, and configured to operably determine the start conduction time point and the end conduction time point of the primary winding in the normal operation mode;
• and
• a switching signal generation circuit, which is coupled to the low voltage mode ON time control circuit and the normal mode ON time control circuit, and configured to operably generate the switching signal for controlling the power switch.