| 摘要 |
PURPOSE:To reduce a current at an LED side and to obtain small-sized trunk line interface by taking polarity inversion detection information out of the photocoupler bus of a serial circuit at the time of inverting the polarity of a trunk line. CONSTITUTION:Normally the contact point of a switching relay S is turned on so as to form an outgoing loop. At the time of inverting polarity, a contact point S1 is turned on the same as a normal state. The light emitting diode PC1 of the photocoupler emits light, and the polarity inversion information is transmitted to the OUT terminal of the photocoupler. The PC1 never enters a DC loop at a normal state and at the time of inverting polarity, whereby an electronic synchronization circuit at a latter stage, which satisfies the limit condition of a DC resistance viewed from L1 and L2, can be easily constituted.
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