RUSH CURRENT CONTROL CIRCUIT OF CAPACITOR

PURPOSE:To set the rush current of an input capacitor at a constant level at all times regardless of the variations of the power supply voltage, by controlling a current control element in response to the difference between the signal that has detected the changing amount of the both-terminal voltage of the input capacitor and a reference signal. CONSTITUTION:A transistor Q works at first in a linear area when the power supply voltage is applied. Therefore the input signal keeps balance at the input side of an operational amplifier A, and dE2/dt=Vr/C.R is satisfied (Vr: reference voltage). Thus the rate of change of the voltage E2 of an input capacitor Ci is fixed. While the current supplied from the capacitor Ci is obtained from Iin=Ci.dE2/dt, and therefore Iin=Ci.Vr/C.R is obtained. That is, the current flowing to the capacitor Ci is fixed regardless of the power supply voltage Vcc. Such an action is carried out within a linear active period and ends as soon as the Q is saturated.