Abstract: A circuit (10) and method for detecting a fault in a recirculation diode (13) in a switched power supply. The power supply has a switching transistor (12) that is turned on and off by a power supply control device (31), switchably applying a supply voltage (15) to an output (14). The recirculation diode (13) is connected between the output (14) and a reference potential (16). The circuit includes a sense resistor (11) in series between the supply voltage (15) and the switching transistor (12). A biasing element (25) is connected to clamp a current control element of the switching transistor (12) to the reference potential (16) when the switching transistor (12) is switched off so that a fault in the recirculation diode (13) results in a current flowing in the switching transistor (12). An amplifier (33) is connected across the sense resistor (11).