摘要 |
<p>PURPOSE:To sufficiently and preventively maintain a photocoupling circuit by intentionally forming the increase in the leakage current and the deterioration in the current transfer in the circuit which cntains a transistor when a circuit having a power source, a limiting resistor and a light emitting diode is arranged opposed to a circuit having a power source, a load resistor, a comparator and a phototransistor as the photocoupling circuit. CONSTITUTION:A circuit having a light emitting diode PD is composed of an external input contact SW, an external input power source VE, and a light emitting diode limiting resistor RE. A circuit having a phototransistor PT is composed of a load resistor R, a comparator CP, a control power source VC and a reference boltage setting power source Vth, and they are opposed to each other. In this structure, a current transfer rate deterioration checking resistor RC is connected through a checking switch S1 to the comparison input terminal a of a comparator CP while connecting it in parallel with a resistor R, and a leakage current checking resistor RL is connected via a checking switch S2 in parallel with the collector and the emitter of the transistor PT.</p> |