Design Of White LED Driving IC (Front-end)

With the development of semiconductor materials, white LEDs are main selection of illuminating devices. Considering characteristics of white LEDs and necessity of uniform brightness in portable field, they need to be driven by special power management circuits.In this paper, we analyzed basic theories of several kinds of white LED driver. Purpose of this project is studying a kind of driver with constant output voltage called DC-DC converter, and designing all the analog circuits of it. Having analyzed theory of switched-capacitor DC-DC converters, we need to design a charge-pump and its control circuits to realize them at least. In the conventional converters, there is a voltage doubler. Applying a doubler to a converter, transformation efficiency of power is pretty low. So we proposed a DC-DC converter with new structure comprised by a fractional charge-pump.In this paper block diagram of the circuit is given, then the working theory and the working principle are showed. All the sub-circuits are designed and simulated, which answer the requirements. Fractional charge-pump is used to boost the supply power, and to drive white LEDs. It is the core of the circuit. Voltage reference circuit is used to supply invariable voltage. Oscillator gives switch signal to the fractional charge-pump and control the frequency. Voltage comparator compares the voltage reference and the feedback voltage. Over thermal protect circuit can protect the whole circuit from being destroyed by over thermal. Control circuit is used to control the fractional charge-pump's working condition.At last the synthetic circuit is simulated, and the results of simulation meet the function requirement.