基于Boost型DC/DC变换器的电流可调的串并联白光LED驱动芯片的设计
|
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。
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.
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。
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.
引文
[1] S.P.DENBAARS. Gallium-Nitride-Based Materials for Blue to Ultraviolet Optoelectronics Devices, Proc. IEEE, 1977, Vol85, No. 10, P1740-1749.
[2] 尹长安; 赵成久等. 白光 LED 的最新进展, 发光学报,2000, 2(14) , P380-382.
[3] 李忠辉; 丁晓民等. 高亮度 InGaN 基白光 LED 特性研究.红外与毫米波学报, 2002, 21(5) , P390-392.
[4] 宋贤杰; 屠其非; 周伟; 周太明. 高亮度发光二极管及其在照明领域中的应用, 半导体光电, 2002 年第 23 卷第 5 期, P356-360.
[5] 梁秉文, 刘乃涛. 加强产业化关键技术开发促进半导体照明产业发展, 科技与经济(南京), 2004,17 (2) , P61-64.
[6] App.Note 3256:Why Drive White LEDs with Constant Current? http://www.maxim-ic.com/an3256
[7] 胡逢康. LED 驱动电路技术概述 http://www.dcdisplaytech.com/Article/Article11.htm
[8] 杨旭; 裴云庆; 王兆安. 开关电源技术, 机械工业出版社, 2002.
[9] 张占松. 开关电源的原理设计, 电子工业出版社, 2000.
[10] 杨旭; 裴云庆; 王兆安. 开关电源技术, 机械工业出版社, 2002, P20-30.
[11]R. W. Erickson ; D. Maksimovic. Fundamental of Power Electronics, Norwell, MA:Kluwer, 2001.
[12] E. Rogers. Understanding Boost Power Stages in Switch mode Power Supplies. Texas Instruments Application Report, 1999, P1-32.
[13] 罗萍; 李肇基等. PSM 开关变换器的平均模型与特性分析, 电工技术学报, 2005 年 3 月第 20 卷第 3 期, P19-23.
[14] 牛全民; 罗萍; 张波等. 基于 Boost 变换器的 PSM 建模和分析, 电力电子技术, 2005 年 8 月第 39 卷第 4 期, P109-111.
[15] 邹伯敏. 自动控制理论, 机械工业出版社, 2002, P56-66.
[16] Kranz, C. Complete digital control method for PWM DC/DC boost converter, Power Electronics Specialist Conference, 2003, IEEE 34th Annual Volume 2, P951-956.
[17] Matsuo, H.; Mimura, Y.; Nakao, Y.; Kurokawa, F.; Sasaki, M. Novel digital controller for the PWM and/or PFM controlled switchingDC-DC converters, Telecommunications Energy Conference, 1998, Twentieth International Volume , P225-230.
[18] Capponi, G; Livreri, P; Di Blasi, G.M; Marino, F. Architecture of a digital PFM controller for IC implementation, Computers in Power Electronics, 2004, P75-79.
[19]Miribel-Catala, P.L.; Puig-Vidal, M.; Samitier i Marti, J.; Goyhenetche, P.; Xuan-Quan Nguyen. An integrated digital PFM DC-DC boost converter for a power management application: a RGB backlight LED system driver, 2002, IECON 02 Volume 1, P37- 42 .
[20] Widler, R.J. New Developments in IC Voltage Regulators, IEEE J. of Solid-State Circuits, 1971,Vol 6(1) , P2-7.
[21]A. Brokaw. A Simple Three-terminal IC Bandgap Reference, IEEE J. of Solid-State Circuits, 1974, Vol 9(6), P388-393.
[22] Kuijk, K.E. A Precision Reference Voltage Source. IEEE J. of Solid-State Circuits, 1973 , Vol 8(3), P222-226.
[23]Phillip E. Allen; Douglas R. Holberg . CMOS Analog Circuit Design. Oxford University Press, Inc., 2002, P153-157.
[24] Behzad Razavi. Design of Analog CMOS Integrated Circuit, The McGraw-Hill Companies, Inc, 2001, P384-390.
[25] Pierazzi, Andrea, et al. Band-Gap Reference for near 1-V operation in standard CMOS technology, IEEE 2001 Custom Integrated Circuits Conference, P463-466.
[26] R .Jacob Baker; Harry W .Li; David E Boyce 著, 陈中建译. CMOS 电路设计、布局与仿真, 机械工业出版社,2006 第一版, P203-205.
[27]阎石主编. 数字电子技术基础, 高等教育出版社,2001 第四版, P197-199.
[28] 阎石主编. 数字电子技术基础, 高等教育出版社,2001 第四版,P240-269.
[29] Abraham I.Pressman 著; 王志强等译. 开关电源设计, 电子工业出版社 2005.09 第二版, P3-6.
[2] 尹长安; 赵成久等. 白光 LED 的最新进展, 发光学报,2000, 2(14) , P380-382.
[3] 李忠辉; 丁晓民等. 高亮度 InGaN 基白光 LED 特性研究.红外与毫米波学报, 2002, 21(5) , P390-392.
[4] 宋贤杰; 屠其非; 周伟; 周太明. 高亮度发光二极管及其在照明领域中的应用, 半导体光电, 2002 年第 23 卷第 5 期, P356-360.
[5] 梁秉文, 刘乃涛. 加强产业化关键技术开发促进半导体照明产业发展, 科技与经济(南京), 2004,17 (2) , P61-64.
[6] App.Note 3256:Why Drive White LEDs with Constant Current? http://www.maxim-ic.com/an3256
[7] 胡逢康. LED 驱动电路技术概述 http://www.dcdisplaytech.com/Article/Article11.htm
[8] 杨旭; 裴云庆; 王兆安. 开关电源技术, 机械工业出版社, 2002.
[9] 张占松. 开关电源的原理设计, 电子工业出版社, 2000.
[10] 杨旭; 裴云庆; 王兆安. 开关电源技术, 机械工业出版社, 2002, P20-30.
[11]R. W. Erickson ; D. Maksimovic. Fundamental of Power Electronics, Norwell, MA:Kluwer, 2001.
[12] E. Rogers. Understanding Boost Power Stages in Switch mode Power Supplies. Texas Instruments Application Report, 1999, P1-32.
[13] 罗萍; 李肇基等. PSM 开关变换器的平均模型与特性分析, 电工技术学报, 2005 年 3 月第 20 卷第 3 期, P19-23.
[14] 牛全民; 罗萍; 张波等. 基于 Boost 变换器的 PSM 建模和分析, 电力电子技术, 2005 年 8 月第 39 卷第 4 期, P109-111.
[15] 邹伯敏. 自动控制理论, 机械工业出版社, 2002, P56-66.
[16] Kranz, C. Complete digital control method for PWM DC/DC boost converter, Power Electronics Specialist Conference, 2003, IEEE 34th Annual Volume 2, P951-956.
[17] Matsuo, H.; Mimura, Y.; Nakao, Y.; Kurokawa, F.; Sasaki, M. Novel digital controller for the PWM and/or PFM controlled switchingDC-DC converters, Telecommunications Energy Conference, 1998, Twentieth International Volume , P225-230.
[18] Capponi, G; Livreri, P; Di Blasi, G.M; Marino, F. Architecture of a digital PFM controller for IC implementation, Computers in Power Electronics, 2004, P75-79.
[19]Miribel-Catala, P.L.; Puig-Vidal, M.; Samitier i Marti, J.; Goyhenetche, P.; Xuan-Quan Nguyen. An integrated digital PFM DC-DC boost converter for a power management application: a RGB backlight LED system driver, 2002, IECON 02 Volume 1, P37- 42 .
[20] Widler, R.J. New Developments in IC Voltage Regulators, IEEE J. of Solid-State Circuits, 1971,Vol 6(1) , P2-7.
[21]A. Brokaw. A Simple Three-terminal IC Bandgap Reference, IEEE J. of Solid-State Circuits, 1974, Vol 9(6), P388-393.
[22] Kuijk, K.E. A Precision Reference Voltage Source. IEEE J. of Solid-State Circuits, 1973 , Vol 8(3), P222-226.
[23]Phillip E. Allen; Douglas R. Holberg . CMOS Analog Circuit Design. Oxford University Press, Inc., 2002, P153-157.
[24] Behzad Razavi. Design of Analog CMOS Integrated Circuit, The McGraw-Hill Companies, Inc, 2001, P384-390.
[25] Pierazzi, Andrea, et al. Band-Gap Reference for near 1-V operation in standard CMOS technology, IEEE 2001 Custom Integrated Circuits Conference, P463-466.
[26] R .Jacob Baker; Harry W .Li; David E Boyce 著, 陈中建译. CMOS 电路设计、布局与仿真, 机械工业出版社,2006 第一版, P203-205.
[27]阎石主编. 数字电子技术基础, 高等教育出版社,2001 第四版, P197-199.
[28] 阎石主编. 数字电子技术基础, 高等教育出版社,2001 第四版,P240-269.
[29] Abraham I.Pressman 著; 王志强等译. 开关电源设计, 电子工业出版社 2005.09 第二版, P3-6.