Power supply

A power supply is described having a current measurement circuit connected between a supply voltage terminal and an output voltage terminal of the power supply. The current measurement circuit comprises a set of two or more sense resistors in a parallel configuration, first and second ones of the sense resistors having different impedances. Switching circuitry is provided, which is responsive to a control signal to connect one or more of the sense resistors between the supply voltage terminal and the output voltage terminal. A controller is operable to generate the control signal in dependence on a measured current level across the set of sense resistors. In this way, by switching the resistors in and out of the circuit, the voltage drop across the measurement circuit can be kept to a desired range.