Disclosed is a controller for controlling a string of N LEDs connected in series and each having a current bypass switch in parallel therewith and configured to be supplied from a current source connected in series with the string of LEDs and being supplied by a supply voltage, the controller comprising: a respective bypass switch controller for each bypass switch and configured to control the respective bypass switch such that the respective LED has an on-period and an off-period, according to a common duty cycle; a phase control unit configured to set a respective timing of each of the bypass switches such that the fraction of LEDs not bypassed corresponds to the duty cycle; and a duty cycle adjustor configured to adjust the duty cycle, in dependence on the supply voltage. Associated methods and circuits are also disclosed.