Circuitry for resetting magnetic field of transformer

A reset circuitry for resetting an internal magnetizing field of a transformer of a power converter when a main switch of the power converter is turned off, the reset circuit comprising:

• a first capacitor connected in series with a winding of the transformer;
• a rectifier connected in parallel with a series circuit comprising the first capacitor and the winding of the transformer;
• a second capacitor;
• an auxiliary switch connected in series with the second capacitor to form a series circuit to be connected in parallel with the rectifier;
• and
• a switch control circuit configured to control the main switch and the auxiliary switch to prevent the main switch and the auxiliary switch from turning on simultaneously;
• wherein the switch control circuit is configured to turn on the main switch and turn off the auxiliary switch instantaneously so as to store magnetizing energy in a magnetizing inductor, and turn on the auxiliary switch and turning off the main switch after a short period of time so as to transmit the magnetizing energy in the magnetizing inductor to the second capacitor, and charge the magnetizing inductor and the first capacitor by the second capacitor after the magnetizing energy of the magnetizing inductor is fully discharged.

A power converter comprising:

• a main switch;
• a transformer having at least a primary winding and a secondary winding, the primary winding is connected in series with the main switch for receiving an input DC voltage and inducing an AC voltage on the secondary winding according to anon/off state of the main switch;
• a switch control circuit;
• and
• a reset circuitry for resetting an internal magnetizing field of the transformer;
• wherein the transformer comprises a magnetizing inductor, and the switch control circuit is configured to output a pulse signal to turn on the main switch and turn off the reset circuitry instantaneously so as to store magnetizing energy in a magnetizing inductor of the transformer, and output another pulse signal to turn on the reset circuitry and turn off the main switch instantaneously so as to transmit magnetizing energy stored in the magnetizing inductor to the reset circuitry.