Power supply device for vehicle

A power supply device for vehicle comprising:

• a capacitor;
• a DC/DC convertor connected to said capacitor;
• a battery connected to said DC/DC convertor;
• a load connected to said battery;
• and
• a power supply control circuit that monitors a voltage of said capacitor and battery and controls operation of said DC/DC convertor, and is provided with a first operational mode, a second operational mode, and a third operational mode,
• wherein said power supply control circuit is configured to operate in the first operational mode and control so that an electric power having been stored in said capacitor is supplied to said load in response to the voltage of said capacitor being not less than a predetermined voltage for a first predetermined time period T1 after operation of a vehicle engine has been stopped, to operate in the second operational mode immediately after the first predetermined time period T1 lapses and control so that the electric power having been stored in said capacitor is supplied to said battery in response to the vehicle engine remaining stopped and the voltage of said capacitor remaining not less than the predetermined voltage for a second predetermined time period T2, and to operate in the third operational mode immediately after the second predetermined time period T2 lapses and control so as to force the capacitor to discharge the stored electric power, for a third predetermined time period T3, in response to the vehicle engine being stopped and the voltage of the capacitor being not less than the predetermined voltage, and
• wherein the power supply control circuit includes:
• a capacitor voltage detection circuit configured to detect the voltage of the capacitor;
• a battery voltage detection circuit configured to detect a battery voltage;
• a state of charge (SOC) calculation circuit configured to calculate a charged state of the battery;
• and
• a DC/DC convertor control circuit configured to control the DC/DC convertor in response to a signal from the capacitor voltage detection circuit, battery voltage detection circuit and SOC calculation circuit.