Patent ID: 6940246

Claim:
A power-window jamming preventing apparatus, comprising; a current sensing circuit, which senses a motor current flowing through a motor for driving a window glass; a current limiting circuit, which increases and decreases the motor current based on a current-limitation control signal outputted from the current sensing circuit when an amount of increase of the motor current exceeds a predetermined vale; and a jamming determining circuit, which determines a jamming of a foreign matter in the window glass based on increase of the motor current to reverse a rotation of the motor, wherein the current sensing circuit includes; a shunt resistor, on which the motor current is flown; a reference resistor, which has a resistance value that is n times the shunt resistor; and a current following circuit, which increases and decreases a reference current that flows through the reference resistor and is 1/n of the motor current, based on a voltage applied to the shunt resistor; wherein the current following circuit includes: a reference current controlling circuit, which controls increase/decrease of the reference current, and generates a first reference voltage which is lowered according to increase of the motor current, and a second reference voltage which is higher than the first reference voltage, based on the reference current; a first comparator, which has a first input terminal to which the first reference voltage is applied; and a charging/discharging circuit, which generates a third reference voltage in compliance with a charge/discharge controlling signal outputted from the first comparator and outputs the third reference voltage to a second input terminal of the first comparator, the third reference voltage indicating an average value of the first reference voltage, and the charge/discharge controlling signal being shifted alternately to two voltage levels, and the apparatus, further comprising a potential difference generating circuit, which monitors a power source voltage supplied to the current sensing circuit and the power window motor, and which clamps the third reference voltage so as to drop a constant voltage from the third reference when the power source is low, such that a potential difference between the second reference voltage and the third reference voltage is kept greater than a predetermined voltage.