Electronic control unit and electric power steering apparatus equipped with the same

An electronic control unit that comprises a bridge having upper-stage field-effect transistors (FETs) and lower-stage FETs and driving-controls a three-phase blushless motor, via an inverter being supplied a power supply VR, by inputting a duty signal of a pulse width modulation (PWM) calculated in a micro controller unit (MCU) into a gate driving section, comprising:

• a reverse connection protective FET which is interposed between a battery and said power supply VR and turns-ON/OFF with a switching signal from said MCU;
• a diagnostic resistor voltage-dividing circuit which is supplied said power supply VR and outputs voltage-divided voltages obtained by voltage-dividing connection point voltages of said upper-stage FETs and said lower-stage FETs;
• an FET-short detecting section which is supplied said power supply VR, and detects at least one-side short failure of said upper-stage FETs and said lower-stage FETs based on said voltage-divided voltages and outputs an error notification;
• a dark current suppressing switch which is interposed between said power supply VR and said diagnostic resistor voltage-dividing circuit and said FET-short detecting section;
• a resistor voltage-dividing circuit for power supply for level-shifting in accordance with an input range of said MCU in order to detect a voltage from said dark current suppressing switch;
• and
• a detecting-section-failure diagnostic function which inputs said error notification, is included in said MCU, and detects a failure of said FET-short detecting section,
• wherein said voltage from said dark current suppressing switch is supplied to said diagnostic resistor voltage-dividing circuit, said FET-short detecting section and said resistor voltage-dividing circuit for power supply,
• wherein said detecting-section-failure diagnostic function diagnoses said failure of said FET-short detecting section at start up and turns-OFF said upper-stage FETs and said lower-stage FETs when said failure of said FET-short detecting section is detected, and
• wherein said FET-short detecting section diagnoses said short failure of said upper-stage FETs and said lower-stage FETs when said failure of said FET-short detecting section is not detected.