Abstract: A circuit is disclosed for charging an input filter capacitance from a source of potential before a protective circuit, e.g., a fuse, is established between the source of potential and the capacitance. If the charging circuit is connected between the potential source and the substantially discharged capacitance, a small charging current will flow through a current limiting resistance. This small current will partially charge the capacitance if no faults are present. A threshold detector circuit monitors the voltage on the capacitance and for a voltage of approximately three volts or more, in the case of a twenty-four volt potential source, activates a charging transistor. The charging transistor is controlled by feedback circuitry to provide a larger but limited charging current to complete the charging to within approximately one volt of the potential of the source of potential.