| 摘要 |
<p>A current device comprises a constant d.c. voltage power supply circuit (500) which is fed with a current flowing in one direction and outputs a positive potantial, a medium potential and a negative potantial at a positive output terminal (5a), a medium output terminal (5c) and a negative output terminal (5d), respectively, a current sensing resistive element (40) connected in series to the power circuit (500), a differential amplifier circuit (60) which is fed with power from the output of the power supply circuit (500), and converts the voltage drop across the current sensing resistive element (40) proportional to the one-direction current into an output signal based on the medium potential between the positive potential and the negative potential of the output of the power supply circuit (500),and a switching circuit (121); a control circuit (70) which is fed with power from the power supply circuit (500) and receives the output signal of the differential amplifier circuit (60) proportional to the one-direction current to control the closing operation of a switching circuit signalling device (81) which is activated by the closure of the switching circuit (121) to emit light or produce a warning sound; and a switching operation prohibitive circuit (50) which is connected to prevent the switching circuit (121) from being closed improperly when the output voltage of the power supply circuit (500) is not enough to operate the differential amplifier (60) or the control circuit (70) properly.</p> |
