Patent ID: 9252672
Filing Date: 2016-02-02
CPC Classification: H02M,Y02B

Claim Text:
1. A method of controlling a phase-shift full-bridge (PSFB) converter in a light load operation to switch control modes by detecting magnetizing current of a transformer of the phase-shift full-bridge converter, the method comprising following steps: (a) operating the PSFB converter in an extended PSFB control mode when the magnetizing current of the transformer compared to an output choke current mapped to a primary side thereof is larger; (b) operating the PSFB converter in a modified PSFB control mode when the magnetizing current is gradually reduced until the electric charge transported by the residual magnetizing current is close to or less than or equal to a half of a DC input voltage; and (c) implementing the optimal degree of soft driving the PSFB converter to double the magnetizing current under the modified PSFB control mode, wherein in the step (a), the phase-shift full-bridge converter comprises: a full-bridge switching circuit having a first power switch, a second power switch, a third power switch, and a fourth power switch; wherein each of the power switches has a parasitic diode and a parasitic capacitance connected in parallel to the power switch; a transformer having one primary-side winding and two secondary-side windings which are a first secondary-side winding and a second secondary-side winding; wherein the primary-side winding is connected to the full-bridge switching circuit and two voltage respectively outputted at the first secondary-side winding and the second secondary-side winding according to turn ratios between the primary-side winding and the first and second secondary-side windings; and a controller producing corresponding control signals to control the first power switch, the second power switch, the third power switch, and the fourth power switch; wherein in the step (c), the switching losses of the second power switch is equal to 0.25×C×Vin2 when the PSFB converter is operated in the modified PSFB control mode, wherein the C is an equivalent capacitance and Vin is the DC input voltage.