A system comprising a driver circuit wherein the driver circuit comprises a converter. The system further comprises a controller operable to control a ratio between an input voltage supplied to the driver circuit and a target output voltage to be output from the driver circuit by varying a pulse width modulated signal, and by switching between operating modes of said converter. The controller is configured to determine that the driver circuit is operating in an undesired state caused by a combination of the duty cycle and the operating mode of the converter. The system further comprises a resistance adjustment circuit configured to adjust an equivalent output resistance of the driver circuit in response to the controller determining that the driver circuit is operating in an undesired state.