To provide a compact vehicle power supply unit capable of reducing burdens on a main power supply.
The vehicle power supply unit comprises a starter 15 connected to the main power supply 11, and a load 19 connected to the main power supply 11 via a power storage device 17. The power storage device 17 includes: a power storage section 27; a charge circuit 31 that is connected between the main power supply 11 and the power storage section 27 and charges the power storage section 27 to a predetermined full-charge voltage Vcf; a selection switch 37 for connecting one of the power storage section 27 and the main power supply 11 to the load 19; a charge switch 29 connected between the power storage section 27 and the output of the charge circuit 31; a change-over switch 47 for connecting the power storage section 27 to one of the main power supply 11 and the ground; and a control circuit 55 for exerting control to set the selection switch 37 to the side of the main power supply 11 and the change-over switch 47 to the ground side and turn on the charge switch 29 successively when charging the power storage section 27, and for exerting control to turn off the charge switch 29, and set the change-over switch 47 to the side of the main power supply 11, and the selection switch 37 to the side of the power storage section 27 successively when driving the starter 15.
MITANI YASUSUKE
Hiroki Naito
Daisuke Nagano