Motor current detector on the high side of the voltage

摘要

A high-side type motor current detecting circuit for controlling an electric motor such as employed in a motor-driven power steering system of a motor vehicle is capable of detecting with high accuracy and reliability a voltage making appearance across a shunt resistor (Rs) upon flowing of a motor current. The shunt resistor (Rs) is inserted at a side of a power-supply voltage (VB) of a H-bridge circuit (4) for driving the motor (M). The shunt voltage (V1) appearing across the shunt resistor (Rs) upon turning-on of relevant FETs constituting the H-bridge circuit (4) is held by a sample-and-hold circuit (61), and a hold voltage (V2) is amplified to an amplified voltage (V3) serving as a reference power-supply voltage by means of a differential amplifier (11) incorporated in an amplifier circuit (10). A negative voltage power-supply circuit (20) is provided for stabilizing the power-supply voltage and a first ground level (Gnd1) for the differential amplifier with reference to the power-supply voltage (VB) to thereby shift the level of the amplified voltage to a detection voltage (Vo) with reference to a second ground level (Gnd2) by means of a constant current circuit incorporated in the amplifier circuit. IMAGE