Patent ID: 9601987
Date: 2017-03-21
CPC Classifications: G01R,G05F,H02M

Claim:
1. A power supply apparatus comprising: an input terminal adapted to be connected to an input power source; an output terminal adapted to be connected to a load; a power transmission circuit configured to transmit electric power in a direction from the input terminal to the output terminal and capable of adjusting the transmitted power; a detection circuit configured to detect an output voltage of the output terminal in a predetermined detection ratio; a reference voltage generation circuit configured to generate a reference voltage; a control circuit configured to control the transmitted electric power so that the voltage detected by the detection circuit can be equal to the reference voltage; a monitor circuit, to which the output voltage is applied, configured to output a voltage reduction signal when the output voltage decreases below a predetermined threshold voltage; a change circuit configured to change at least one of the detection ratio and the reference voltage so that the output voltage can transition between a target voltage higher than the threshold voltage and a middle voltage lower than the threshold voltage, the middle voltage being larger than a minimum operation voltage of the monitor circuit; and a determination circuit configured to perform an abnormality determination process, when the output voltage is equal to the target voltage, by supplying a change command to the change circuit, wherein the change circuit changes at least one of the detection ratio and the reference voltage in response to the change command so that the output voltage can transition from the target voltage toward the middle voltage only during a predetermined time period, when the output voltage is decreased to the middle voltage during the abnormality determination process, the control circuit controls the power transmission circuit so that the output voltage remains at or above the middle voltage thereby preventing the output voltage from decreasing below the minimum operation voltage of the monitor circuit, when the monitor circuit outputs the voltage reduction signal in the abnormality determination process, the determination circuit determines that a capacitance connected to the output terminal or a load current flowing through the load is abnormal, the predetermined time period is given by K·(CL·ΔV/IL), K is a positive coefficient less than one, CL is a predetermined value of the capacitance, IL is a predetermined value of the load current, and ΔV is a difference between the target voltage and the threshold voltage.