Patent ID: 7420295

Claim:
A power unit for conveyance comprising: a main power source and a standby power source, wherein a thermal battery is provided as the standby power source, a backup power source connected to the main power source through a power supply wire; a thermal battery ignition circuit for activating the thermal battery by electric power from the backup power source; a voltage conversion circuit connected to the power supply wire, for allowing selectively either the voltage of the main power source to increase and to be supplied to the backup power source side, or the voltage of the backup power source side to decrease and to be supplied to the main power source; a thermal battery ignition control circuit connected to the power supply wire between the main power source and the voltage conversion circuit to activate the thermal battery during operation, by controlling the thermal battery ignition circuit in response to voltage decrease of the main power source which operates by electric power from the power supply wire; a diagnosis circuit to diagnose for activation of the thermal battery, which is connected to the power supply wire between the main power source and the voltage conversion circuit and operates by electric power from the power supply wire; a disconnection detection circuit which has a connection point between the main power source and the voltage conversion circuit, to detect disconnection of the power supply wire between the connection point and the main power source; a voltage increase/decrease control circuit controlled by the disconnection detection circuit, for allowing the voltage conversion circuit to increase the voltage of the main power source side to supply to the backup power source side in a state such that disconnection of the power supply wire is not detected, and for allowing the voltage conversion circuit to decrease the voltage of the backup power source side to supply to the main power source side in a state such that disconnection of the power supply wire is detected; and an operation stop control circuit to stop operation of the diagnosis circuit in response to detection of the power supply wire disconnection by the disconnection detection circuit.