| 摘要 |
PURPOSE:To prevent generation of a dynamic current when an overcurrent is shut off by connecting two photocouplers in parallel, and connecting two parallel diodes opposingly to each other to load and an AC power supply, and employing a transistor(TR) for a switch part. CONSTITUTION:A switch 4 is turned on to turn on parallel connected photocouplers 171, 172 to conduct photodetectors 171b, 172b thereby supplying an AC (i) from an AC power supply 8 to the load 7. TRs T51, T52 are turned on and the current is discriminated by the 1st and 2nd current discrimination sections 181, 182. If the current (i) becomes an overcurrent, the voltage V1, V2 are increased and when the voltage across the resistors R81, R82 exceeds the base-emitter voltage of the TRs T31, T32, the TRs 31, 32 are turned on and the base potential of the TRs T41, T42 rises. Then the TRs T41, T51 and T42, T52 are turned off sequentially and no current (i) flows. Thus, the dynamic current turned off due to overcurrent is made zero quickly to prevent surely circuit components from baking. |
