IN-VEHICLE POWER SUPPLY DEVICE

摘要

PROBLEM TO BE SOLVED: To provide an in-vehicle power supply device achieved in sufficient cost reduction by eliminating a DC-DC converter which has been indispensable hitherto.SOLUTION: The in-vehicle power supply device comprises a lead battery electrically connected to an alternator, and a lithium battery (second battery) connected to the lead accumulator in parallel therewith, and sets the opening voltages and internal resistances of both the batteries so that the following conditions (a) to (c) are satisfied: condition (a): there is a point VdS at which the opening voltage V0 (Pb) of the lead battery and the opening voltage V0 (Li) of the lithium battery coincide with each other in an SOC use range W1 of the lead battery and an SOC use range W2 of the lithium battery exists; condition (b): an expression of V0(Li)>V0(Pb) is satisfied at the upper limit side of the coincident point VdS in the SOC use range W2; and condition (c): a terminal voltage Vc (Li) at the time when a maximum charging current flows to the lithium battery is lowered to a constant voltage Vreg (set voltage) generated by a regulator or lower.