A power converter circuit that includes a switch node coupled to a regulated power supply node via an inductor is configured to regulate a voltage level of a power supply node using a particular one of multiple available operating modes. In response to receiving a command to reduce the voltage level of the power supply node, the power converter circuit begins to reduce the voltage level of the power supply node, while autonomously selecting different ones of available operating modes. The power converter circuit may compare to the voltage level of the power supply node to boundary levels and select a different operating mode when the voltage level of the power supply node exceeds one of the boundaries. By switching operating modes during the negative slew of the voltage level of the power supply node, the power converter may maintain a target efficiency during the reduction in voltage.