| 摘要 |
PURPOSE: To block throw-in of AC main power supply by providing means for opening a switch when the DC output voltage from a DC power supply does not exceed a predetermined level thereby detecting short circuit at DC section before the AC main power supply is thrown in. CONSTITUTION: When erroneous wiring is not present, a charging current flows from the DC power supply 17 of an erroneous wiring detector 19 through a route L1 to smoothing capacitors 6, 8 to raise the charging voltage VC. The forward drop voltage VP of a diode DP, the voltage V2 across a resistor 3, and the base-emitter voltage VB of a transistor Q7 are then subtracted from the charging voltage VC. When the difference exceeds the break voltage VZ of a constant voltage diode Zd, a base current is fed to the transistor Q7 and the emitter-collector thereof is conducted to feed the coil of an electromagnetic relay 18 with a current through a current limit resistor R1. Consequently, the contacts of the electromagnetic relay 18 are closed to produce an interlock signal for an electromagnetic switch 2. |
