A circuit comprising a controller (2) for controlling a pulse width modulated input signal, and a driver (4) configured to supply current to a load (6) based on the input signal, wherein over the on time of each pulse width modulation period the driver (4) supplies current to the load (6) with a second frequency that is greater than the first frequency. The controller (2) is configured to control the duty cycle to set the output of the load (6) to a desired output level, and to dither the duty cycle about a point corresponding to the desired output level.