US Patent 7355353 Illumination control circuit

It is an object of the invention to provide an improved illumination control circuit comprising a light emission element FL, a driving element 5 for driving the light emission element FL, and a compensation unit 8 are connected in series with respect to a power source voltage Vcc. Further, a reference unit 6 for generating a constant voltage Vz and a detecting unit 7 are connected in series with respect to the power source voltage Vcc. The detecting unit 7 is provided for detecting a differential voltage V1 between the power source voltage Vcc and the constant voltage Vz. Once there is a change in the power source voltage Vcc, the detecting unit 7 detects a voltage change of the power source voltage Vcc in accordance with the differential voltage V1, generates a detection voltage V2 formed by dividing the differential voltage V1, while the compensation unit 8 generates a compensation voltage V3 following the detection voltage V2, thereby inhibiting a change of a driving voltage Vx applied between two ends of the light emission element FL and the driving element 5, in response to a change of the power source voltage Vcc.