Patent ID: 8159151

Claim:
A control circuit for a driving inverter for a fluorescent lamp, comprising: a reference voltage source which generates a predetermined reference voltage; a pulse modulator which receives a feedback voltage that corresponds to a current flowing through the fluorescent lamp, and generates a pulse signal having a duty ratio adjusted such that the feedback voltage approaches the reference voltage; and a driver which drives a switching circuit according to the pulse signal so as to supply a switching voltage to a transformer provided in the form of a component external to the control circuit, wherein the reference voltage source comprises: a first current source which generates a first current; a first current mirror circuit which has a plurality of output terminals, which duplicates the first current, and outputs a plurality of first duplicated currents via the plurality of output terminals; a plurality of first switches respectively provided on paths for the plurality of first duplicated currents; a converting resistor, one terminal of which is set to a fixed electric potential, and which is provided on a path for the plurality of first duplicated currents output from the first current mirror circuit; and a decoder circuit which receives a control signal from an external circuit, and controls the ON/OFF operations of the plurality of first switches according to the control signal, and wherein the control circuit outputs, as the reference voltage, a voltage that corresponds to a voltage drop that occurs at the converting resistor.