| 摘要 |
PURPOSE:To make it possible to constitute a relay driving circuit suitable for LSI by using an NPN type transistor as a transistor for relay driving to drive a relay, and providing a saturation preventive means to prevent saturation of the NPN type transistor. CONSTITUTION:Since a transistor Q4 becomes ON when call control signal SD is 0, transistors Q3 and Q4 become ON, and driving currents flow to a relay winding RL1. When a diode D2 for saturation prevention is connected to between the collector of the transistor Q4 and the collector of Q2, the potential at A point of the diode D2 is 2Vbe (Vbe is voltage between the base and the emitter of the transistor and is about 0.7V), and the potential at B point, that is, Vce is restrained to about 0.7V which is lower by the voltage drop of the diode D2. On the other hand, since Vce at the time of the transistor Q2 saturation is about 0.3V, this transistor does not become saturated condition, and leakage current is prevented from flowing, and a relay driving circuit suitable for LSI can be constituted. |
