Voltage-impressed current measuring apparatus and current buffers with switches used therefor

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.