| 摘要 |
PROBLEM TO BE SOLVED: To prevent the outflow of charge from a capacitor on input side caused by instantaneous power failure, while contriving the suppression of a rush current and the protection of a power unit against the reverse connection of an input terminal, in a DC input type of power unit which is equipped with a capacitor for charging on input side. SOLUTION: A rush current is suppressed in condition that the on-resistance of FETs Q1 and Q2 is increased by limiting the electrical continuity of the FETs Q1 and Q2 provided in an input line by detecting the rush current with a resistor R1 thereby turning on a transistor T1 at occurrence of a rush current. In case that the input terminals are connected, with reverse polarity, to the power source line, the FETs Q1 and Q2 are biased reversely, and are turned off to function as reverse checking diodes, so they prevent the power unit from breakage. In case that instantaneous power failure occurs, this power unit detects the discharge current, which has been flowing in the reverse direction by the discharge of a capacitor C1, with the resistor R1 in a discharge preventive circuit 11, and turns on a transistor T2 and turns off the FETs Q1 and Q2 thereby checking a discharge current. |
