A flyback circuit providing synchronized control includes a pulse width modulation (PWM) unit, a synchronized control unit and an ON period limiting unit. The PWM unit generates a driving signal to control a switch ON period of a primary winding and provides a synchronized signal prior to the generation of the driving signal that has output time series ahead the driving signal. The synchronized control unit receives the synchronized signal through an induction winding to set off a synchronized commutation switch. The ON period limiting unit starts a period limiting time series after the synchronized commutation switch has been set on. After the synchronized commutation switch is set off by the synchronized signal the ON period limiting unit is reset to an initial condition. The synchronized commutation switch maintains an ON condition until the period limiting time series end, then the ON period limiting unit generates a forced ending signal to set off the synchronized commutation switch so that the flyback circuit maintains operation at a minimum duty frequency.