CIRCUIT FOR LIMITING RUSH CURRENT

PURPOSE:To reduce the scale of a circuit for limiting a rush current, by configuring with active elements the switching means for cutting-off substantially a line between front and rear stages when the generation of the rush current is sensed through a sensing means and for switching the state of the line to a conduction state when the value of the current flowing through the line is the one of its stationary state. CONSTITUTION:When a DC power supply circuit 1 is in its operated state and a DC/DC converter 2 is in its unoperated state, if the power supply switch of the converter 2 is closed, just thereafter, a rush current I begins quickly to flow from the circuit 1 into a capacitive load C. But, when the voltage drop of a resistor R1 by the rush current I reaches the ON-voltage of a transistor (Tr) Q1, the Tr Q1 is turned on and a current flows from a terminal X1 to the base of a Tr Q2 via the Tr Q1 to a resistor R2. As a result, the Tr Q2 is turned on, and its collector voltage VQ2 is lowered to the voltage nearly equal to the one of a terminal X2, and further, a MOS FET Q3 is turned off from its ON-state. Therefore, the line between the terminal X1 and a terminal Y1 is brought into a nearly cut-off state, and substantially, the rush current I is suppressed from flowing into the capacitor C.