Power supply device

A power supply device, comprising:

• a power supply line for supplying power from an external power supply to a load device;
• and
• a battery unit connected to the power supply line and connected in parallel with the external power supply, wherein
• the battery unit includes:
• a battery pack including a first battery pack and a second battery pack of which each charge voltage is higher than a voltage of the external power supply and which are connected to the power supply line in parallel with each other;
• a step-up/down circuit for stepping up the voltage of the external power supply to the charge voltage;
• a first charge circuit for charging the first battery pack at the charge voltage;
• a second charge circuit for charging the second battery pack at the charge voltage;
• a first discharge circuit for detecting a voltage drop of the external power supply and discharging from the first battery pack to the load device through the power supply line;
• and
• a second discharge circuit for detecting a voltage drop of the external power supply and discharging from the second battery pack to the load device through the power supply line;
• and
• a control circuit that controls the first charge circuit, the first discharge circuit, the second charge circuit and the second discharge circuit, wherein
• the first discharge circuit includes a first discharge switch and a second discharge switch connected in series between the first battery pack and the power supply line, the first discharge switch is switched to on/off by receiving a switching signal from the control circuit, and the second discharge switch is directly switched to on/off based on the voltage of the external power supply without via the control circuit,
• the first discharge circuit includes a third discharge switch and a fourth discharge switch connected in series between the second battery pack and the power supply line, the third discharge switch is switched to on/off by receiving a switching signal from the control circuit, and the fourth discharge switch is directly switched to on/off based on the voltage of the external power supply without via the control circuit,
• the first discharge circuit and the second discharge circuit are connected to the power supply line in parallel with each other and include a first voltage drop circuit and a second voltage drop circuit, respectively, for dropping the output voltage of the first battery pack and the second battery pack by a predetermined voltage to output the voltage to the power supply line,
• the first voltage drop circuit is connected between the power supply line and the second discharge switch, and
• the second voltage drop circuit is connected between the power supply line and the fourth discharge switch.