A switching power supply includes a switch and a controller for dimming control of the switching power supply. The controller includes a phase angle measurement block and a drive logic block. The phase angle measurement block is coupled to receive an input sense signal. The phase angle measurement block generates a phase angle signal representative of a phase angle of an input voltage of the power supply in response to the input sense signal. The drive logic block is coupled to control switching of the switch. The drive logic block controls the switch in a closed loop dimming control when the phase angle is less than or equal to a phase threshold and in a open loop dimming control when the phase angle is greater than the phase threshold.