| 摘要 |
PURPOSE:To secure a dielectric strength without lowering a current amplification factor, by connecting a backward diode between the base and the emitter of the first transistor out of two high-dielectric strength transistors of the Darlington constitution of a DC constant voltage circuit. CONSTITUTION:An AC two-wire contactless switch has two terminals which connect a load and an AC power source in series, and a switching element 2 is connected to two terminals through a rectifying circuit 1, and the element 2 is turned on and off in accordance with the detection operation of a detecting circuit 5. Power is supplied to the circuit 5 through a DC constant voltage circuit. The DC constant voltage circuit consists of high-dielectric strength transistors 7 and 10 of the Darlington constitution, a high resistance 8 connected between the base of the transistor 7 and commonly connected collectors of transistors 7 and 10, a diode 12 connected backward between the base and the emitter of the transistor 7, and a constant voltage diode 9 connected to the base of the transistor 7 and the power supply line. Lowering of the dielectric strength due to the leakage current of the collector junction of the transistor 10 is prevented without lowering the high current amplification factor due to the Darlington connection of the transistor 10 by the diode 12. |
