Patent ID: 11870361
Assignee: STMICROELECTRONICS S.R.L.
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H  Y | IPC H

Claim 7:
8. A device, comprising:
a control circuit; and
a flyback converter, that includes:
first and second input terminals for receiving an input voltage;
first and second output terminals for providing an output voltage;
a transformer having primary and secondary windings and a leakage inductance;
a first electronic switch coupled with the primary winding between the first and second input terminals;
a phase node between the first electronic switch and the primary winding;
a capacitance associated with the phase node;
an active clamp coupled to the primary winding and including a connection of a clamp capacitor and a second electronic switch, and a third electronic switch coupled with the secondary winding between the first and second output terminals, the control circuit being configured to:

during a first time interval of a switching cycle, close the first electronic switch and open the second and third electronic switches, wherein the closed first electronic switch during the first time interval couples the primary winding to the input voltage and causes a current flowing through the primary winding to increase, to store energy in the transformer;
during a subsequent second time interval of the switching cycle, open the first electronic switch, and keep open the second and third electronic switches, whereby the current flowing through the primary winding charges the capacitance associated with the phase node;
during a subsequent third time interval of the switching cycle, keep open the first electronic switch and close both of the second and third electronic switches, which couples the clamp capacitor with the primary winding and the current flowing through the primary winding charges also the clamp capacitor, wherein the third time interval ends when the current flowing through the primary winding reaches zero;
during a subsequent fourth time interval of the switching cycle, keep open the first electronic switch, keep closed the third electronic switch, and open the second electronic switch, whereby the current flowing through the primary winding is zero and the energy stored in the transformer is released via a current flowing through the secondary winding; and
during a subsequent fifth time interval of the switching cycle, keep open the first electronic switch, close the second electronic switch, and keep closed the third electronic switch, whereby the clamp capacitor is coupled in parallel with the primary winding, whereby the clamp capacitor and the leakage inductance form a resonant circuit having a given resonance period, and wherein the fifth time interval ends after one or more half-periods of the resonance period.