Patent ID: 8766671

Claim:
A load driving apparatus for driving a load with a constant current, the load driving apparatus comprising: a shunt resistor through which a shunt current corresponding to the constant current flows; a driver circuit connected to a first end of the shunt resistor to supply the constant current corresponding to the shunt current to the load, the driver circuit including a reference voltage source for generating a predetermined reference voltage, wherein the driver circuit adjusts the magnitude of the constant current by performing a feedback-control of the magnitude of the shunt current in such a manner that a first voltage corresponding to the reference voltage and a second voltage corresponding to a voltage at the first end of the shunt resistor become equal to each other, the driver circuit further includes an operational amplifier and a first switching element, the first voltage is applied to a first terminal of the operational amplifier, the second voltage is applied to a second terminal of the operational amplifier, the first switching element is switched by an output of the operational amplifier, and the operational amplifier keeps the magnitude of the shunt current at a constant value by switching the first switching element in such a manner that the first voltage and the second voltage become equal to each other; and a second switching element connected to the load and having a higher current capability than the first switching element, wherein the first end of the shunt resistor is connected to the driver circuit and the second switching element so that the shunt current is supplied as the constant current to the load through the second switching element, the first switching element and the second switching element are connected in a Darlington configuration in such a manner that the second switching element is driven by the first switching element and that a first current flowing though the first switching element is added to a second current flowing through the second switching element to form the constant current, and the driver circuit performs the feedback-control of the magnitude of the shunt current by driving the second switching element by driving the first switching element in such a manner that the first voltage and the second voltage become equal to each other.