Patent ID: 8148934

Claim:
A voltage step-up/down converter comprising: a coil; a first switch having one end connected to one end of the coil and the other end grounded; a first rectifier connected in parallel to the first switch to allow current flow only from the other end to the one end of the first switch; a second switch having one end connected to a junction between the coil and the first switch; a second rectifier connected in parallel to the second switch to allow current flow only from the one end to the other end of the second switch; a first capacitor having one end connected to the other end of the coil and the other end grounded for smoothing a DC voltage outputted to the other end of the coil; a second capacitor having one end connected to the other end of the second switch and the other end grounded for maintaining a DC voltage outputted to the other end of the second switch; a third switch having one end connected to a circuit power source and the other end connected to a junction among the coil, the first switch and the second switch; and a control circuit configured to turn on and off the first switch in a voltage step-up operation, in which the DC voltage at the other end of the coil is stepped up and outputted from the other end of the second switch, and the control circuit configured to turn on and off the second switch in a voltage step-down operation, in which the DC voltage at the other end of the second switch is stepped down and outputted from the other end of the coil, wherein the control circuit is further configured to check whether the second switch is normal or abnormal based on voltages of the first capacitor and the second capacitor, by turning on the third switch while turning on the first switch, then turning off the third switch and then turning on the first switch.