Study On White LED Drivers And The Sub-circuits Design

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 four 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 main 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 supplied by lithium ion battery with voltage of 2.7V to5.5V, transformation efficiency of power is pretty low. So we proposed a DC-DC converters with new structure comprised by a fractional charge pump, ADC, comparator and other circuits. New structure has two feedback paths to sample input voltage and output voltage respectively instead of only one paths to feedback output.We have completed the tasks as showed hereafter.a) Analyzed theories of fractional charge pump thoroughly, designed a fractional charge pump with 14 MOS transistors that can achieve 7 gains.b) Simplified the charge pump to new one with 4 MOS transistors. To make charge pump work properly, designed a bulk voltage generator that supply to bulk of PMOSs used in charge pump. All MOSs used in charge pump is with a large value of W/L. In order to get more efficient area and more robutness of charge pump, we designed them as bent-gate MOSs. A 3-bit ADC and a comparator were also designed. All these circuits were taped out in CSMC Technologies Corporation. And we got satisfying testing results.c) Designed some other analog circuits needed in DC-DC converter. Proposed a design flow of digital control circuit and sampling ways of input and output voltages.