A power conversion apparatus including a transformer, a synchronous rectification (SR) transistor and an SR control circuit is provided. A first terminal of a primary side of the transformer receives an input voltage, and a first terminal of a secondary side outputs a DC voltage. A drain terminal of the SR transistor is coupled to a second terminal of the secondary side of the transformer. A source terminal of the SR transistor is coupled to a ground terminal. The SR control circuit receives a signal of the drain terminal of the SR transistor to serve it as a detection signal and generate a duty cycle signal. The SR control circuit converts the duty signal into a charging current and a discharging current so as to charge and discharge an energy-storage device and generate a first voltage. The SR control circuit turns off the SR transistor according to the first voltage.