Patent ID: 7986109

Claim:
A load driving circuit that supplies an electric current to a load formed of one or more light emission diodes to drive the load, comprising: a step-up circuit that has a step-up ratio changeable according to an input control signal and supplies electric power to the load; a current setting circuit configured to set a value of the electric current to be supplied to the load according to a load current setting signal input from outside; a constant current circuit configured to generate and supply a constant electric current having the value set by the current setting circuit; a determination circuit configured to determine whether the constant current circuit is able to supply the constant electric current; and a control circuit configured to control the step-up ratio of the step-up circuit according to determination results of the determination circuit; wherein when the load current setting signal used for changing the setting value of the electric current is input, the current setting circuit sets the value of the electric current to be maximum, and decreases the setting value of the electric current step by step down to a predetermined value, and each time the current setting circuit decreases the setting value of the electric current by one step, the control circuit changes the step-up ratio of the step-up circuit according to the determination results of the determination circuit until the constant current circuit supplies the electric current having the current value set by the current setting circuit.