Fault detection circuit

A fault detection circuit for detecting a fault in an inverter that outputs a three-phase pulse width modulated signal that becomes a three-phase alternating-current signal for driving a motor, the fault detection circuit comprising:

• a rectangular pulse comparison circuit configured to generate, for each combination of the pulse width modulated signals, a detection signal indicating a difference component between pulse widths of two of the pulse width modulated signals having phases adjacent to each other;
• a fault diagnosis unit configured to detect a fault in the inverter based on a shift in a combination of logic levels of a plurality of the detection signals output by the rectangular pulse comparison circuit from a preset determination value, wherein
• the fault diagnosis unit uses the preset determination value that is different for each motor rotation angle assuming in advance that two alternating-current signals having phases adjacent to each other among the three-phase alternating-current signals have the same voltage;
• and
• a rotation angle acquisition unit configured to acquire the motor rotation angle from an angle sensor for detecting the motor rotation angle and transmit the acquired motor rotation angle to the fault diagnosis unit.