A method may include detecting an output voltage of the output smoothing capacitor in the bridgeless interleaved power factor correction circuit of a critical mode, comparing the detected output voltage with a reference voltage, controlling the first and the second half-bridge circuits included in the bridgeless interleaved power factor correction circuit of the critical mode to be on and off based on an error signal between the output voltage and the predetermined reference voltage, measuring ON time of a synchronous rectification switch operation of the first half-bridge circuit by measuring a time period between OFF timing of an active switch of the first half-bridge circuit and output of a differentiation signal generated by a differentiation circuit included in the bridgeless interleaved power factor correction circuit of the critical mode; and assigning the measured time to next ON time of the synchronous rectification switch operation of the second half-bridge circuit.