| 摘要 |
PURPOSE:To execute a test accurately even for a subscriber line test, by providing a compensating circuit for preventing a thrysistor from beaking down owing to the voltage drop and the overcurrent when thyristors are used in the link and trunk of a switchboard. CONSTITUTION:When a current flows through a channel 5 as shown by the arrow L, the voltage at a point A is applied to one terminal of an operational amplifier 8 and a voltage which is lower than that voltage at the point A by a level corresponding to one thyristor switch is applied to a point B. A voltage obtained by dividing the potential difference between points B and C, i.e. a correcting voltages VS through resistances (R1)10 and (R2)11 is applied to the plus terminal of the operational amplifier 8. The operational amplifier 8 outputs a base current to a transistor (TR)7 corresponding to the difference in input voltage between the minus and plus terminals and the collector- emitter current of the TR7 flows corresponding to the base current. Consequently, a voltage drop is caused across a resistance 9 and the voltage between the points B and C is held at the voltage which is the potential difference obtained by subtracting the voltage drop across the resistance 9 from the voltage of an additional source 13 for compensation to reduce the potential difference between the minus and plus terminals of the operational amplifier 8 to zero. |
