| 摘要 |
PURPOSE:To obtain a subscriber circuit reducing power consumption on the whole by varying the value of the reference voltage with a monitor output and turning on and off a feeding circuit by the monitor output. CONSTITUTION:When a resistance having smaller than a specific resistance value is connected between circuit connection terminals 8-a and 8-b, the output of an operational amplifier 30 exceeds a reference voltage and the output of a comparator 37 drops to a low level to turn on transistors (TRs)50 and TR60. Therefore, feeding circuits 1 and 2 operate to obtain a specific DC feeding impedance value, supplying currents to circuits (a) and (b). Then, the feeding impedance is switched from high impedance by resistance 80 and 90 to low impedance by the feeding circuits 1 and 2. Then, the voltage between the terminals 8-a and 8-b rises and the output of the amplifier 30 drops. Consequently, the subscriber circuit detects the resistance values of the circuits; the feeding circuits are turned off when the resistance values are larger than a specific value or turned on when the values are smaller than the specific value. |
