In-vehicle backup circuit and in-vehicle backup device

An in-vehicle backup circuit for use in an in-vehicle power supply system including:

• a power supply portion-side conductive path serving as a path to which power is supplied from a power supply portion;
• a first load-side conductive path serving as a path for supplying power to a first power supply target;
• a second load-side conductive path serving as a path for supplying power to a second power supply target;
• and
• an electricity storage portion serving as a power supply source different from the power supply portion,
• wherein, when supply of power performed from the power supply portion via the power supply portion-side conductive path is in a predetermined normal state, power is supplied to the first power supply target from the power supply portion via the power supply portion-side conductive path and the first load-side conductive path, and power is supplied to the second power supply target from the power supply portion via the power supply portion-side conductive path and the second load-side conductive path, the in-vehicle backup circuit comprising:
• an electricity storage portion-side conductive path electrically connected to the electricity storage portion;
• a predetermined intermediate conductive path;
• a first voltage conversion portion configured to perform a first operation of stepping down or stepping up a voltage applied to the power supply portion-side conductive path to apply an output voltage to the electricity storage portion-side conductive path, and a second operation of stepping down or stepping up a voltage applied to the electricity storage portion-side conductive path to apply an output voltage to the power supply portion-side conductive path;
• a resistive portion provided in parallel with the first voltage conversion portion between the power supply portion-side conductive path and the electricity storage portion-side conductive path;
• a second voltage conversion portion configured to perform a voltage conversion operation of stepping up or stepping down a voltage applied to the electricity storage portion-side conductive path to apply an output voltage to the intermediate conductive path;
• an element portion that is provided between the intermediate conductive path and the second load-side conductive path, and is configured to allow flow of current from the intermediate conductive path to the second load-side conductive path when the backup circuit is in a first state in which a potential of the intermediate conductive path is higher than a potential of the second load-side conductive path by a predetermined potential difference or more, and to limit flow of current from the intermediate conductive path to the second load-side conductive path when the backup circuit is in a second state in which the first state has been cancelled;
• and
• a control unit configured to control operations of the first voltage conversion portion and the second voltage conversion portion,
• wherein the control unit is configured to:
• cause the first voltage conversion portion to start the first operation in response to satisfaction of a predetermined charge start condition, and to stop the first operation in response to a predetermined charge stop condition having been satisfied during the first operation;
• cause the second voltage conversion portion to perform the voltage conversion operation in response to satisfaction of a predetermined first backup condition;
• and
• cause the first voltage conversion portion to perform the second operation in response to a predetermined second backup condition having been satisfied when the control unit is causing the second voltage conversion portion to perform the voltage conversion operation, and
• the power supply portion-side conductive path and the electricity storage portion-side conductive path are configured to be electrically connected via the resistive portion when the control unit is causing the second voltage conversion portion to perform the voltage conversion operation.