Circuit for preventing electromagnetic interference (EMI) for electric control unit mounted in vehicle

摘要

The circuit has a small signal earth line (52) connected to an earth side of a vehicle battery (72), through which a small current flows. A large signal earth line (55) is connected to the earth side of the battery (72) independent of the small signal line. A larger current flows through this line. A first earth structure (57) is formed in a printed circuit board (56) and is earthed to the vehicle chassis (62) via a metal housing (60) containing the circuit board. The large signal earth line (55) is connected to the first earth structure (57) via a first EMI capacitor (65). A second earth structure (58) is formed in the pcb (56) electrically independent of the first structure and is connected to the first structure via a second EMI capacitor (63). The small signal line (52) is connected directly with the second earth structure (58) without an intermediate capacitor so as to prevent fluctuation of an earth potential of the second structure when that of the first structure fluctuates.