Patent ID: 9118255
Filing Date: 2015-08-25
Classification: H02M,Y02B

Abstract:
1. A flyback power converter, suitable for a synchronous rectification, transforming an input voltage received into an output voltage, comprising: a transformer, having a primary side and a secondary side, wherein both ends of a magnetizing inductance are coupled to a winding on the primary side of the transformer; a main switch, having a control end for receiving a main switch switching signal to control the main switch to be switched on or off, and a drain of the main switch is coupled to the winding on the primary side of the transformer, and a source of the main switch is coupled to a first ground voltage; a synchronous rectification switch, coupled to a winding on the secondary side of the transformer, and a drain and a source of the synchronous rectification switch are respectively coupled to a cathode and an anode of a body diode, and a signal of a drain-to-source voltage of the synchronous rectification switch is equal to a main switch switching signal; a synchronous rectification control circuit, transmitting a control signal to the control end of the synchronous rectification switch according to a sensing signal received, wherein the sensing signal is generated by a voltage-dividing circuit according to a switch cut-off pulse signal and a signal of the drain-to-source voltage of the synchronous rectification switch; a sampling circuit, coupled to the drain of the synchronous rectification switch so as to generate a first logic signal and a second logic signal; and an operation circuit, coupled to the sampling circuit, receiving the first logic signal and the second logic signal and accordingly executing timing for charging/discharging, further outputting the switch cut-off pulse signal to the voltage-dividing circuit, wherein if a voltage of the sensing signal is lower than a predetermined threshold voltage, the synchronous rectification switch enters into a cut-off state according to the control signal, and when the synchronous rectification switch is cut off, the body diode is switched on to provide a current path for the magnetizing inductance to release energy, wherein when the first logic signal or the second logic signal is a low level voltage, the operation circuit executes timing for discharging; when the first logic signal or the second logic signal is a high level voltage, the operation circuit executes timing for charging, wherein the first logic signal and the second logic signal are complementary logically.