Apparatus (6"") for providing a direct current to a load, at first and second main outputs (26, 27), the apparatus comprising: a synchronous rectifier (21"') operatively connectable to a secondary winding of a transformer whose primary winding is for carrying high-frequency alternating current, the synchronous rectifier comprising first and second rectifier outputs (22, 23) and first and second switches (61, 62) controlled by a further secondary winding of the transformer; and wherein the first and second rectifier outputs (22, 23) are connected to the first and second main outputs (26, 27) respectively, and characterised by comprising: a control circuit comprising a control port and first and second resistors (65, 66); whereby the control circuitry is connectable to the further secondary winding, the further secondary winding has a first terminal which is connectable to the gate terminal of the first switch, and has a second terminal which is connectable to the gate terminal of the second switch and the gate terminals of the first and second switches (61, 62) are also connected via said first and second resistors (65, 66), respectively, to the control port; and subcircuitry configured to provide a voltage to the control port, wherein the subcircuitry is configured to sense a voltage across the load and, in response to determining that the voltage across the load is above a predetermined level, to bias the further secondary winding to stop the direct current to the load. a synchronous rectifier (21"') operatively connectable to a secondary winding of a transformer whose primary winding is for carrying high-frequency alternating current, the synchronous rectifier comprising first and second rectifier outputs (22, 23) and first and second switches (61, 62) controlled by a further secondary winding of the transformer; and wherein the first and second rectifier outputs (22, 23) are connected to the first and second main outputs (26, 27) respectively, and characterised by comprising: a control circuit comprising a control port and first and second resistors (65, 66); whereby the control circuitry is connectable to the further secondary winding, the further secondary winding has a first terminal which is connectable to the gate terminal of the first switch, and has a second terminal which is connectable to the gate terminal of the second switch and the gate terminals of the first and second switches (61, 62) are also connected via said first and second resistors (65, 66), respectively, to the control port; and subcircuitry configured to provide a voltage to the control port, wherein the subcircuitry is configured to sense a voltage across the load and, in response to determining that the voltage across the load is above a predetermined level, to bias the further secondary winding to stop the direct current to the load. a control circuit comprising a control port and first and second resistors (65, 66); whereby the control circuitry is connectable to the further secondary winding, the further secondary winding has a first terminal which is connectable to the gate terminal of the first switch, and has a second terminal which is connectable to the gate terminal of the second switch and the gate terminals of the first and second switches (61, 62) are also connected via said first and second resistors (65, 66), respectively, to the control port; and subcircuitry configured to provide a voltage to the control port, wherein the subcircuitry is configured to sense a voltage across the load and, in response to determining that the voltage across the load is above a predetermined level, to bias the further secondary winding to stop the direct current to the load.