| 摘要 |
PROBLEM TO BE SOLVED: To provide a reverse voltage preventive circuit capable of lowering the level of voltage falling reversely upon a power source line at abnormality. SOLUTION: The reverse voltage preventive circuit in a device using + and - power sources is equipped with switch elements Q1 and Q2 connected between a power cable and an earth, and circuits R1-R4 which control the switch elements Q1 and Q2 so that the switch elements Q1 and Q2 may be turned on in the case when the power voltage is not applied to the power cable and that the switching elements Q1 and Q2 may be turned off in the case when the power voltage is applied normally to the power cable. As the switching elements Q1 and Q2, a transistor or a normally on type of FET is used. According to this, the absolute value of the voltage of the power cable can be clamped to the maximum rating of the load or under at abnormality of one power source. |
