In some examples, a circuit includes a state machine. The state machine is configured to operate in a buck state in which the state machine is configured to control a power converter to operate in a buck mode of operation at a first frequency. The state machine is configured to determine that a switch time of the power converter has decreased to within a threshold amount of a minimum switch time for the power converter. The state machine is configured to, responsive to the switch time of the power converter having decreased to within the threshold amount of the minimum switch time for the power converter, transition from the buck state to a reduced frequency buck state in which the state machine is configured to control the power converter to operate in the buck mode of operation at a second frequency that is less than the first frequency.