Circuits and methods for reducing output voltage overshoot of switch mode power supply

A three-terminal device for controlling a switching mode power supply (SMPS), comprising

• a first terminal for coupling to the output of the switching mode power supply;
• a second terminal for coupling to a secondary side ground of the SMPS;
• a third terminal for coupling to a secondary winding of the SMPS;
• a discharge control circuit coupled to the first terminal, the discharge control circuit being configured to issue a discharge signal to cause a voltage at the first terminal to discharge to the second terminal when the voltage at the first terminal is higher than a first overvoltage reference voltage;
• wherein the discharge control circuit includes a comparator having a negative input coupled to the second reference voltage and a positive input coupled to a third reference voltage that is lower than the second reference voltage, the comparator also having a power supply terminal coupled to the output voltage of the SMPS.

A method of controlling the output of a switching mode power supply (SMPS), the SMPS including a transformer having a primary winding coupled to a power switch, a secondary winding for providing an output, and an auxiliary winding, the method comprising:

• on the primary side of the transformer, regulating the output of the SMPS by controlling the power switch in response to a feedback voltage signal that is representative of an output of the SMPS;
• and
• on the secondary side of the transformer, causing the output voltage of the SMPS to discharge when the output voltage of the SMPS is higher than a first overvoltage reference voltage;
• generating a pulsed discharge signal to cause the discharge;
• wherein generating the pulsed discharge signal comprises detection when the output voltage of the SMPS is higher than the first overvoltage reference voltage and combining the result of the detection with a delay signal and a clock signal.