| 摘要 |
PURPOSE:To reduce the current required for a transmission line, by receiving a bipolar signal and by lighting a light emitting diode by its zero cross signal. CONSTITUTION:When a bipolar signal is transmitted from a master equipment, a full-wave rectified voltage VD is obtained in the output of a diode bridge DB of a terminal equipment. This full-wave rectified voltage VD is divided by resistance R2 and R3 and is applied to the base of a transistor TRQ1 of a zero cross signal generating circuit 3. The base potential of the TRQ1 is changed to turn on and off the TRQ1. When the TRQ1 is turned off and a TRQ2 is turned on, namely, near the zero cross point of the received signal, a current is flowed to a light emitting diode 4a of a photocoupler 4. Since the light emitting diode 4a is lit by pulses of a narrow width, the power consumption of the photocoupler 4 is reduced. The output of the photocoupler 4 is given to a T type flip flop and is converted to a unipolar signal. |
