A power conversion apparatus including a flyback power conversion circuit, a control chip and a detection auxiliary circuit is provided. The flyback power conversion circuit converts an input voltage into a direct current (DC) output voltage. The control chip generates a pulse width modulation (PWM) signal for controlling operations of the flyback power conversion circuit. The detection auxiliary circuit assists the control chip in obtaining a first detection voltage via a multi-function detection pin of the control chip within an enabling period of the PWM signal, so as to execute an over current detection according to the first detection voltage. Besides, the detection auxiliary circuit assists the control chip in obtaining a second detection voltage via the multi-function detection pin within a disabling period of the PWM signal, so as to execute a valley voltage detection according to the second detection voltage.