Patent ID: 8866331

Claim:
A power supply device comprising: a first line, a second line, and a third line, each having a different electric potential from one another; a battery circuit in which a fuel cell stack and an electric storage device are connected in series; a first DC-DC converter, wherein both ends of the battery circuit are connected to the first line and the third line, a connection point of the electric storage device and the fuel cell stack of the battery circuit is connected to the second line, a primary side of the first DC-DC converter is connected to the second line and the third line, a secondary side of the first DC-DC converter is connected to the first line and the third line, electric power is outputted from the first line and the third line, and at least two operating modes are provided, comprising a first mode in which electric power is supplied to a load under a condition in which a discharge current of a battery is greater than an electric generation current of the fuel cell stack, and a second mode in which electric power is supplied to a load under a condition in which a discharge current of a battery is smaller than an electric generation current of the fuel cell stack; and a control device changes the operating modes by changing a switching duty cycle of the first DC-DC converter.