Patent ID: 7352193

Claim:
A voltage-impressed current measuring apparatus which impresses a prescribed voltage and measures a current flowing in a load apparatus, comprising: a current-range switching portion having a plurality of series connections, each comprising a current buffer with a switch connected in series with a current measurement resistance, wherein the respective series connections are connected in parallel to each other, each of the current buffers with switches has an output stage capable of being electrically connected or disconnected and a pre-stage portion controlling the output stage in its connected or disconnected state in response to a control signal supplied thereto and capable of acting as a current buffer, the current measurement resistances have different resistance values, one end of a measurement resistance connects to the output stage of its respective current buffer with a switch and the other end connects to the output side of the respective series connection connected to the load apparatus, and the control signal selects any one of the plurality of series connections to switch the current measurement range so that the output stage of the current buffer with a switch of the selected series connection is taken to be in its connected state; a direct-current power supply portion, connected to input ends of the pre-stage portions as input sides of the respective series connections and supplying the prescribed direct-current voltage to the load apparatus through the selected series connection; and a potential difference measuring means, measuring, as a value corresponding to the current flowing in the load apparatus due to the impression of the direct-current voltage on the load apparatus, a potential difference between the input side and the output side of the selected series connection due to the current which flows from the current buffer with a switch of the selected series connection to the load apparatus.