Fault detection apparatus of direct-current motor drive bridge circuit

A fault detection apparatus of a direct-current motor drive bridge circuit, comprising a direct-current motor drive bridge circuit structured such that a pair of forward rotation switching elements and a pair of reverse rotation switching elements are alternately connected annularly, a direct-current motor interposed between first diagonal node points in one side, and a portion between second diagonal node points in another side via the existing resistance receives an applied power source voltage, and

• a fault detection means for detecting an electric potential of the one first node point to which the power source voltage is applied via the existing resistance and for detecting a short circuit fault of the switching elements on the basis of a fluctuation of the electric potential, said fault detection means interposed between the second diagonal node points,
• at least one field effect transistor being utilized in the fault detection, wherein,
• during normal forward rotation drive, the electric potential VB of a node point r being determined by the relationship
• VB=VO(RF+RM+RF)/(RO+RF+RM+RF)=VO(RM+2RF)/(RO+RM+2RF)
• where VB is approximately equal to VO
• and when a reverse rotation field effect transistor generates a closed-circuit fault, the electric potential VB of the node point r being determined by the relationship
• VB=VO(RF+RF)/(RO+RF+RF)=VO(2RF)/(RO+2RF)
• where VB is approximately equal to (⅔)VO, and where VB is the electric potential of a node point, VO is the electric voltage of the battery power source, RO is the resistance of the battery power source, RM is the resistance of the motor, and RF is the on-resistance of each field effect transistor.