【作者】 盛斌；

【导师】 杜国同； 常玉春；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2007， 硕士

【摘要】 随着半导体材料的发展,白光LED在照明领域有着广泛的应用,尤其是在手机、PDA等小型便携式电子产品的背光照明系统中成为不可或缺的重要元件。由于便携式应用对白光LED亮度均匀性的要求,以及白光LED自身的正向导通电压大、电学参数离散性大、容易受温度影响等特点,需要设计专门的电源管理芯片来驱动白光LED。本论文主要研究了电流可调的,采用Boost型DC/DC转换升压的串并混联的白光LED驱动芯片。首先介绍了白光LED驱动电路的各种类型,并作了分析和比较,最后确定了本论文要设计的LED驱动电路。该驱动芯片主要分为DPWM与PSM相结合调制的Boost升压模块和LED稳流模块。首先分析了Boost型变换器在CCM和DCM模式下的稳态特性,以及其反馈回路的控制模式;然后分析了Linear Regulator稳流的原理,以及芯片亮度的控制方式。在此理论分析的基础上,研究了白光LED驱动电路的主要模块,包括带隙基准电压、Digital-Ctr(DPWM控制模块)以及线性调整器,并完成了电路设计。在系统级和电路级分析、设计的基础上,利用Hspice对主要子模块和整个驱动芯片进行了仿真。仿真结果表明,本论文设计的白光LED驱动芯片达到了设计要求,具有高的转换效率,高的输出电流精度和匹配度以及低的关断电流,适合作为小型便携式电子产品的背光照明系统中白光LED的驱动电路。本芯片采用0.6um 5V/40V CMOS工艺制造。更多还原

【Abstract】 With the development of portable electronics devices, such as notebooks, cell phones and MP3, LCD Displays have been widely used. As a result, it has been an important research task to design backlight circuits for displays. Presently, white LEDs are the best choice for backlighting. Considering characteristics of white LEDs and necessity of uniform brightness in portable field, they need to be driven by special power management circuits.Nowadays, there are three kinds of white LED driver, parallel connection, series connection and series-parallel connection. The type of driver in parallel connection always uses Charge-Pump DC-DC converter to generate enough forward voltage for white LEDs. This type of driver has many advantages, such as low driver voltage, low EMI, low noise and independent brightness control for each channel. While the main disadvantage of this type is the low efficiency compared to connection in series. Moreover, it’s very important to consider different forward voltage of white LEDs. Another type of driver in series usually makes use of Boost DC-DC converter to provide enough summarized forward voltage for white LEDs. The most prominent advantage of this type is the higher efficiency compared to parallel connection, and it isn’t necessary to consider the different forward voltage of white LEDs, because these LEDs’current are same in the channel. Nevertheless, there are still some disadvantages of this type, such as high EMI, high noise and so on. And the type of series-parallel connection has both advantages of the two mentioned above.The purpose of this paper is to design a high efficiency, high reliability, Boost DC-DC converter, serial/parallel LED driver IC with current regulated. Firstly, we analyzed the theory of Boost converter. According to whether the current of the inductor is continuous, there are two modes of the Boost circuit, continuous mode (CCM) and discontinuous mode (DCM). Considering power converter was a close-loop system, we researched and analyzed the whole system, including two modes’steady state analysis, choosing control mode and stability criteria, which instructed the design of power converter. In the thesis, we used Linear Regulator to provide steady current for LEDs connected in series within each channel, so we also analyzed the basic theory of Linear Regulator. Withal, we pointed out how to change the current in LEDs by Linear Regulator. Finally, we designed the driver IC according to these analyses.In the thesis, the Boost converter worked in DCM mode. We designed a novel digital PWM controller, and we could modulate the Duty-Cycle by controlling the Up/down counter in the DPWM controller. We used DPWM and Pulse Skipping Modulation (PSM) to control the Boost circuit. Therefore, this driver IC could adapt to widely load changed.Some of the main functional modules were researched and designed in the thesis, including band-gap reference voltage, digital-ctr and linear regulator. Due to the careful designing of the reference voltage module, we acquired a high reliability, low temperature coefficient reference voltage, which improved the output current precision. On the basis of the system and circuit level design, the simulation performed in the Hspice indicated successful operation. The simulation’s results showed that this driver IC could operate in 500 KHz, with supply voltage from 2.7V to 5.5V, which was suitable for single-cell battery supply application. The maxi output voltage was about 20V, the maxi output current was 40mA. When 3 LEDs were connected in series for each channel, the output current precision was±0.5%, with two 4.7uF off-chip capacitors and a 6.8uH off-chip inductor, and the power efficiency was over 88% for 12V output voltage and 40mA load current. The results indicated that it had met the design requirements of high efficiency and high precision. The white LEDs driver IC would be fabricated with a 0.6um 5V/40V CMOS process.更多还原