| 摘要 |
PURPOSE:To sufficiently improve the reliability of transmission by providing a diode connected in series with an NPN and a PNP transistor (TR) of a transmission circuit of push-pull circuit constitution. CONSTITUTION:Since diodes 22, 23 are biased forward in sending a control signal, the transmission circuit 20 acts like a conventional equipment and outputs a signal with a low impedance. On the other hand, if a signal of s large amplitude is superimposed on a lighting line 1 at the non-transmission of the signal, the diodes 22, 23 are biased backward and the input impedance characteristic of the circuit 20 has no effect different from a conventiona equipment. That is, a high impedance load is connected to a primary winding 4 of a transformer T equivalently and the input impedance is always kept to a high impedance.
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