Flyback power converter and control method thereof

A control method for a flyback power converter, the control method comprising steps of:

• (a) providing the flyback power converter, wherein the flyback power converter comprises a transformer, a voltage clamping circuit, a main switch element and a control circuit, the voltage clamping circuit comprises a first capacitor and a clamping switch element, a first terminal of the first capacitor is electrically connected with a first terminal of a primary winding of the transformer, a first terminal of the clamping switch element is electrically connected with a second terminal of the primary winding, a second terminal of the clamping switch element is electrically connected with a second terminal of the first capacitor, and a first terminal of the main switch element and the first terminal of the clamping switch element are electrically connected with the second terminal of the primary winding;
• (b) the control circuit detecting a capacitor voltage between the second terminal and the first terminal of the first capacitor and detecting a current flowing through the clamping switch element, wherein the first terminal of the first capacitor is a negative terminal, the second terminal of the first capacitor is a positive terminal, and a direction of the current flowing from the first terminal of the clamping switch element to the second terminal of the clamping switch element is defined as a forward direction;
• (c) the control circuit determining whether the capacitor voltage is greater than a reference voltage, wherein when the capacitor voltage is greater than the reference voltage, the clamping switch element is turned on, and then a step (d) is conducted, wherein when the capacitor voltage is not greater than the reference voltage, the control method returns to conduct the step (b) again;
• (d) the control circuit determining whether the capacitor voltage is lower than or equal to the reference voltage, wherein when the capacitor voltage is lower than or equal to the reference voltage, a step (e) is conducted, wherein when the capacitor voltage is greater than the reference voltage, the step (d) is conducted again;
• (e) the control circuit determining whether the current flowing through the clamping switch element is lower than a reference current value, wherein when the current flowing through the clamping switch element is lower than the reference current value, a step (f) is conducted, wherein when the current flowing through the clamping switch element is not lower than the reference current value, the control method returns to conduct the step (d) again;
• and
• (f) turning off the clamping switch element under control of the control circuit.