A controller and controlling method is disclosed for a boost converter. The controller includes a first node for receiving an output sense signal indicative of an output DC voltage, a second node for receiving a boost current sense signal indicative of current through an inductor of the boost converter, a first combiner which provides an error signal based on a difference between the output sense signal and a reference signal, an integrator which integrates the error signal and which provides a compensation signal indicative thereof, and a pulse controller which provides a pulse control signal for controlling the power switch to operate the boost converter in DCM. The pulse controller develops pulse control signal based on comparing the compensation signal with a ramp signal and further adjusts the pulse control signal over a cycle of a rectified AC input voltage based on the boost current sense signal.