| 摘要 |
PURPOSE:To prevent malfunction at an abnormal voltage by connecting a collector of an NPN transistor (TR) to a start pulse supply circuit of a silicon control rectifier element and connecting a base to a cathode of the silicon controlled rectifier element via a resistor. CONSTITUTION:Since a DC input voltage B1, a DC output voltage B2 and a Zener voltage EZ of a Zener diode 40 have a relation of B1-B2<EZ at normal state, when the base voltage of an NPNTR43 is selected near the DC output voltage B2, the NPNTR43 is turned off. When the DC input voltage is abnormally high due to the effect of an induced lightening, the relation changes to B1- B2>EZ. Thus, the Zener diode 40 of a start pulse supply circuit 26 is turned on, a voltage B3 of a cross point 42 has a relation of B1-EZ=B3>B2, the NPN TR43 is turned on immediately and the voltage B3 is lowered below the DC output voltage B2. Thus, the silicon controlled rectifier element 13 is not malfunctioned and a horizontal outut circuit is not destroyed. |
