Boosting the input potential which possesses

摘要

PROBLEM TO BE SOLVED: To rapidly carry out capacity calculation of a back up capacitor even when a DC-DC converter is downsized.;SOLUTION: The capacity calculation circuit comprises a by-passing energization passage 12 connecting an input side and an output side of the DC-DC converter 4, a resistance 13 and a resistance switching element 14 and a resistance charging circuit 15 for resistance-charging is provided on the back up capacitor 11. A control part 16 outputs a control signal for resistance charging making switching elements 8 and 9 for first and second coils to the off state and the resistance switching element 14 to the on state at the initial state after throwing the battery power source 1. During the control signal is outputted and a current from the battery power source 1 is fed to the back up capacitor 11 through the by-passing energization passage 12, the capacitor of the back up capacitor 11 is calculated based on the detection voltage of an input voltage detection means 17 and a capacitor voltage detection means 18.;COPYRIGHT: (C)2005,JPO&NCIPI