An example controller for a power supply includes a first circuit and a drive signal generator. The first circuit receives a first signal representative of a switch current flowing through a switch of the power supply and then generates a second signal in response the switch current not reaching a current threshold within an amount of time. The second signal indicates when a dimming circuit at an input of the power supply is utilized. The drive signal generator generates a drive signal to control switching of the switch in response to the second signal, where energy is transferred across an energy transfer element of the power supply in response to the switching of the switch.