Switching power converter and control method thereof for suppressing radiated electromagnetic intereference and improving efficiency

A control method of a switching power converter, comprising:

• providing a switching power converter, wherein the switching power converter comprises a main switch, an auxiliary circuit electrically connected in parallel to the main switch, and a control module, the auxiliary circuit comprises an auxiliary switch and an auxiliary capacitor, and the auxiliary switch and the auxiliary capacitor are electrically connected in series;
• and
• detecting a load state of the switching power converter, wherein when the load state of the switching power converter is light, the auxiliary switch is controlled to turn off for maintaining a capacitance of a first equivalent capacitor at a first threshold, the first equivalent capacitor is between a drain and a source of the main switch, when the load state of the switching power converter is heavy, the auxiliary switch is controlled to turn on for maintaining the capacitance of the first equivalent capacitor at a second threshold, and the second threshold is higher than the first threshold;
• wherein the switching power converter is a flyback conversion circuit, and the switching power converter further comprises:
• a positive input terminal and a negative input terminal, wherein the positive input terminal and the negative input terminal are configured to receive an input power;
• a positive output terminal and a negative output terminal, wherein the positive output terminal and the negative output terminal are configured to provide an output voltage;
• a transformer comprising a primary winding and a secondary winding magnetically coupled to each other, wherein a first terminal of the primary winding is electrically connected to the positive input terminal, two terminals of the secondary winding are electrically connected to the positive output terminal and the negative output terminal respectively;
• the main switch, electrically connected between a second terminal of the primary winding of the transformer and the negative input terminal, wherein the main switch has a first parasitic capacitor;
• the auxiliary capacitor, electrically connected to the second terminal of the primary winding;
• and
• the auxiliary switch electrically connected between the auxiliary capacitor and the negative input terminal, wherein the auxiliary switch has a second parasitic capacitor,
• wherein the control module comprises a control unit, an auxiliary winding, an auxiliary diode and an extended branch circuit, the control unit comprises a first port, a second port and a third port,
• wherein the control method further comprises:
• reflecting information of the output voltage through the first port by the control unit, reflecting information of a voltage across the auxiliary winding through the second port by the control unit, and controlling an operation state of the main switch through the third port by the control unit, wherein the auxiliary winding and the auxiliary diode are electrically connected in series between the negative input terminal and the first port, the extended branch circuit comprises a first Zener diode, a first extended resistor, a second Zener diode and a second extended resistor, and the first Zener diode, the first extended resistor and the second Zener diode are electrically connected in series between the first port and the negative input terminal sequentially, the second extended resistor is electrically connected in parallel to the second Zener diode, the first extended resistor and the second Zener diode are electrically connected to a third branch connection node, and the third branch connection node is connected to the auxiliary switch for controlling the operation state of the auxiliary switch.