Referring also back to FIG. 2, logic circuit 136 can include OR-gate circuit or1, RS flip-flop 136a, and pulse-width modulation (PWM) generation circuit 136b. An input terminal of OR-gate circuit or1 can receive turn-on trigger signal set1 and phase overlap trigger signal ext1 generated by phase overlap trigger circuit 139′, and thus RS flip-flop 136a can be set when turn-on trigger signal set1 and/or phase overlap trigger signal ext1 is active, thereby controlling PWM generation circuit 136b to generate active switching control signal TG1 and inactive switching control signal BG1 to control power switch Q1 to be turned on, and to control rectifier switch Q2 to be turned off. Similarly, logic circuit 137 can generate active switching control signal TG2 and inactive switching control signal BG2 when turn-on trigger signal set2 and/or phase overlap trigger signal ext2 generated by phase overlap trigger circuit 139 is active, thereby controlling power switch Q3 to be turned on, and controlling rectifier switch Q4 to be turned off. Logic circuit 137 can include OR circuit or2, RS flip-flop 137a, and PWM generation circuit 137b. Also, logic circuit 137 may have substantially the same circuit structure and operation as logic circuit 136.