| 摘要 |
PURPOSE:To protect a load circuit from the overvoltage and reduced voltage of supply voltage by inserting a reduced-voltage load circuit between a DC power circuit and the load circuit. CONSTITUTION:A capacitor C2 is connected in series between an anode electrode A1 for a PUTQ1 in a reduced-voltage detector P1'' and a gate electrode G1 and a constant voltage element ZD3 with a constant current element Z1 between the anode electrode A1 and a + terminal. The capacitor C2 and the constant voltage element ZD3 are connected, thus preventing the malfunction of the reduced-voltage detector generated when a power circuit is turned ON-OFF. Capacitors C3 and C4 and resistors R5 and R6 are added as countermeasures limiting gate currents at the time of the trigger of the PUT and an SCR, and a circuit positively protecting the load circuit side is shaped. Accordingly, the load circuit is protected by bringing the load circuit side to the state of a short circuit even when supply voltage is lowered due to the layer short circuit of a flyback transformer, etc., on the load circuit by using the reduced-voltage detector, thus ensuring safety.
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