Patent ID: 9054592
Filing Date: 2015-06-09
Classification: H02M,Y02B

Abstract:
1. A synchronous rectifying control method for an isolated switching power supply, the method comprising: a) generating a ramp voltage comprising generating a charging current corresponding to a power terminal voltage and using said charging current to charge a capacitor, wherein said power terminal voltage comprises a voltage between first and second power terminals of a synchronous rectifier in said isolated switching power supply, wherein a voltage across said capacitor is configured as said ramp voltage, and wherein said charging current is in direct proportion to a difference between said power terminal voltage and an output voltage of said isolated switching power supply; b) determining whether said power terminal voltage starts declining, wherein said ramp voltage continues to rise when said power terminal voltage is rising; c) comparing said ramp voltage to a threshold voltage when said power terminal voltage starts to decline, wherein said threshold voltage is in direct proportion to said output voltage of said isolated switching power supply and a minimum conduction time of said synchronous rectifier, and in inverse proportion to a capacitance value of said capacitor; d) reducing said ramp voltage and controlling said synchronous rectifier in an off state when said ramp voltage is lower than said threshold voltage; and e) reducing said ramp voltage and controlling said synchronous rectifier in on state when said ramp voltage is higher than said threshold voltage.