Vehicle power-supply system

A vehicle power-supply system comprising:

• a main power-supply device mounted in a vehicle and configured to supply power to a first load unit and a second load unit;
• and
• a backup power-supply device mounted in the vehicle and configured to supply power to the second load unit while supplying no power to the first load unit when the main power-supply device is in an abnormal state, wherein
• the main power-supply device includes a first DC/DC converter configured to transform a voltage of direct-current power supplied from a power supply unit and supply the transformed direct-current power to the first load unit and the second load unit, and a first battery configured to store the direct-current power transformed by the first DC/DC converter and supply the stored direct-current power to the first load unit and the second load unit,
• the backup power-supply device includes:
• a second DC/DC converter configured to transform a voltage of the direct-current power output from the first DC/DC converter;
• a second battery configured to store the direct-current power transformed by the second DC/DC converter and supply the stored direct-current power to the second load unit;
• a first switching mechanism and a second switching mechanism configured to pass or interrupt a current;
• a first connecting wire;
• a second connecting wire;
• a third connecting wire;
• and a fourth connecting wire,
• the first connecting wire connects the first DC/DC converter and the second DC/DC converter,
• the second connecting wire connects the second DC/DC converter and the second battery,
• the third connecting wire connects a first connecting point on the first connecting wire and the second load unit,
• the fourth connecting wire connects a second connecting point on the second connecting wire and a third connecting point on the third connecting wire,
• the second switching mechanism is provided between the second connecting point and the third connecting point on the fourth connecting wire and passes or interrupts a current flowing between the second connecting point and the third connecting point,
• the first switching mechanism includes:
• a first bidirectional switch unit that includes a first semiconductor switch and a second semiconductor switch and is connected so that the first semiconductor switch and the second semiconductor switch are so positioned as to make a forward direction of a parasitic diode of the first semiconductor switch and a forward direction of a parasitic diode of the second semiconductor switch opposite to each other;
• a second bidirectional switch unit that includes a third semiconductor switch and a fourth semiconductor switch and is connected so that the third semiconductor switch and the fourth semiconductor switch are so positioned as to make a forward direction of a parasitic diode of the third semiconductor switch and a forward direction of a parasitic diode of the fourth semiconductor switch opposite to each other;
• and a unidirectional switch unit including a fifth semiconductor switch,
• the first bidirectional switch unit is provided between the first DC/DC converter and the first connecting point on the first connecting wire and passes or interrupts a current flowing between the first DC/DC converter and the first connecting point,
• the second bidirectional switch unit is provided between the first connecting point and the third connecting point on the third connecting wire and passes or interrupts a current flowing between the first connecting point and the third. connecting point, and
• the unidirectional switch unit is provided between the first connecting point and the second DC/DC converter on the first connecting wire and passes or interrupts a current flowing from the first connecting point to the second DC/DC converter.