Chapter 5 Measurement Results
5.3 The Measure Result of BSBR Technique
The chip containing the boost converter and BSBR technique was fabricated in a 0.25µm BCD process and Figure 54 shows a die micrograph of the implement with the die area is 4.03mm2 which the BSBR controller only occupies 0.072 mm2. The maximum allowable voltages for drain-source voltage and gate-source voltage are 40V and 12V, respectively. The developed prototype is shown inFigure 55. Table III summarizes the design parameters and the measurement results.
Figure 54. Chip micrograph.
Figure 55. The prototype for testing the RGB LED driver with the BSBR technique.
Table III: Chip Features of BSBR Technique
Fabrication Process 0.25µm BCD 40V 1P5M
(Maximum VDS = 40 V and VGS = 12 V)
Maximum Efficiency of Charge Recycling 94%
Maximum Efficiency of Boost Converter 94.5%
Reference Tracking Speed 20 µs for 9.3V→12.4V with ILoad=100mA
10 µs for 12.4V→9.3V with ILoad=100mA The prototype working with input voltage ranging from 3.3~6 V is applied to the RGB LED backlight module with FCS technique and thus the boost converter steps up the output voltage to 9.3 V for 4 series R-LED and 12.4 V for 4 series G- or B-LEDs. The values of the inductors L and LBSBR are both chosen as 10µH. The values of the capacitors CLoad and CBSBR
are chosen as 1 µF and 10 µF in this proposal. Besides, the voltage VBSBR is regulated around 3.8 V to turn on white-LED implemented on the flashlight of the portable device. However, the capacitor CBSBR can be chosen to be any types of capacitors according to different applications. The frequency of the FCS technique usually utilizes the 60 Hz or 50 Hz switching frequency to switch different color LEDs. Nevertheless, in order to ensure the functionality and reliability of the developed prototype, a higher switching frequency (3 kHz) is utilized to test the performance and observe the response of the reference tracking procedure as shown in Figure 56. The output voltage is dynamically stepped up to 9.3 V and 12.4 V according to the digital signal Eref from the FCS technique when the load current is 100mA. For reference down-tracking response, the output voltage without BSBR technique drops slowly and causes large power consumption on the constant current generator. However,
the output voltage with BSBR technique can transfer extra charge to the capacitor CBSBR so that the period of reference down-tracking is smaller than 10 µs and 5X faster than that of the traditional converter when load current is 100mA. Furthermore, extra charge stored on the capacitor CBSBR is more efficient than prior art [18], [40], and [42]. Therefore, the voltage VBSBR is raised from 3.8 V to 4.09 V under no-load situation when the boost converter changes the output voltage level to turn on the R-LEDs. On the contrary, when the output voltage is raised from 9.3 V to 12.4 V, the boost-restore technique is enabled to transfer the stored charge back to the capacitor Cload. Until the voltage VBSBR is smaller than 3.8 V, the boost-restore technique is disabled. In succession, the boost converter continues to step up the output voltage to the desired voltage, 12.4V. As shown inFigure 56, the output voltage has two different rising slopes when the output voltage is stepping up from 9.3V to 12.4V. The first slope is controlled by the BSBR technique and the second one is by the boost converter.
Since the BSBR technique uses the smaller transforming current for reducing the power consumption, the first slope is smaller than the second one. However, the up-tracking response is smaller than 20 µs and fast enough for the FCS technique. Furthermore, the maximum efficiency of the extra charge recycling can be up to 94%.
Figure 57 shows the measured waveforms of the BSBR power stage with 80mA load current. Because the forwarding voltage of white-LED is close to 3.5V, the voltage VBSBR
must be set above 3.7V. Therefore, the PFM control and BSBR techniques are used to regulate VBSBR to be 3.8V in this application. When the output voltage drops from 12.4V to 9.3V, the BSBR technique is enabled to transfer the extra charge and thus the voltage VBSBR is instantly increased owing to buck-store technique. When the buck-store technique is disabled, the PFM control technique continues to regulate the voltage VBSBR. However, when the output voltage rises from 9.3V to 12.4V, the boost restore technique is still enabled at first. As mentioned before, the technique is disabled when the voltage VBSBR is lower than 3.8V and
Figure 56. Measured waveforms for reference tracking response with/without BSBR technique.
then the BSBR power stage is controlled by the PFM operation. Figure 58 shows the measured efficiency of boost converter under different load current with and without BSBR technique when input voltage is 5V. The effective efficiency of LED backlight driver composed of boost converter and constant current generator is calculated as (42).
_
LED LED driver boost
out
V
η =η ×V (42))
The VLED is the total voltage of the string LED and the Vout is the output voltage of the boost converter as illustrated in Figure 7. The ηLED_drver indicates the efficiency of the LED driver. In addition, the ηboost indicates the efficiency of the boost converter. Thus, the efficiency of LED backlight module with BSBR technique can be improved by 8%.Figure 59 (a) and (b) show the measured efficiency the boost converter versus load current under different input voltages when output voltages are 9.3V and 12.4V, respectively. The efficiency
measurement is setup by the power supply and electron load. When the electron load is connected with the prototype, the power supply would show the input voltage and input power. The input power Pin can be calculated by multiplying the input current and input voltage. And the electron load also show the output current and output voltage. The output power Pout also can be calculated by the output current and output voltage. Thus, the efficiency of boost converter can be measured through output power Pout divided input power Pin. The charge recycling efficiency is calculated by the transmission ratio. The output of CR power stage should be pulled up about 5 V. The measured result is about 4.5 V. The efficiency of CR technique is about 90%. And the output of BSBR power stage should be pulled up 310 mV and measured result are about 290 mV. Thus, the efficiency is about 94%.
Moreover, the BSBR power stage not only can operate the buck-store and boost-restore techniques for reference tracking performance but also can supply the regulated voltage VBSBR by the PFM operation technique.
Figure 57. Measured waveforms showing the BSBR power stage with 80mA load current (IBSBR) for forwarding white-LED. The PFM control and BSBR techniques are used to maintain the voltage VBSBR above 3.8V.
Effi c ie n c y (% )
Figure 58. Measured efficiency of the boost converter with and without BSBR technique enabled under different load current when input voltage is 5V.
(a)
(b)
Figure 59. Measured efficiency of the boost converter versus load current under different input voltages are illustrated (a) when output voltage is 9.3V and (b) when output voltage is 12.4V.
.
Chapter 6
Conclusions and Future Works
6.1 Conclusions
The prior arts of the LED drivers such as the PCC and HCC methods have shown a trade-off between efficiency and accuracy. In this thesis, the LED driver with the SAR-controlled adaptive off-time technique is proposed to achieve high accuracy and efficiency at the same time. According to the operation of this technique, the average inductor current can be adjusted to a constant value. The on-chip low-side current sensing method and the active diode can greatly improve efficiency. Thus, this topology achieves 94% efficiency and 98% accuracy. The power efficiency is increased to about 8%~15% compared to the HCC method and to about 5%~8% compared to the PCC method. The SAR-controlled adaptive off-time technique can be widely used in LED lighting systems with PWM dimming control.
Moreover, the constant current regulator for the RGB backlight module requires the DC-DC converter with fast reference tracking technique. A RGB LED backlight driver is proposed for rapidly switching between driving 6-series R (about 16V) and 6-series G/B LED (about 21V). Owing to voltage difference about 5V between driving series-R and series-G/B LEDs, the FRT technique is presented to enhance line and load regulations. Besides, the CR technique stores extra energy on the re-cycling capacitor at the transition from high-suuplying voltage (21V) to low-supplying voltage (16V). On other hand, it can restore the energy back to output node to speed up the raising of voltage back to 21V at the stage of driving G/B LEDs. Both the transient response time and efficiency are enhanced. The proposed LED
driver with the FRT and CR techniques was implemented in 0.25µm TSMC BCD 40V technology. Experimental results show that the load transition time can be reduced within 10µs and the line transient response time can be reduced within 10µs. It demonstrates the fast reference tracking performance achieved by the proposed FRT technique. The power consumption of the backlight module in the implementation of the field color sequential (FCS) algorithm is smaller than 3W. Furthermore, the power loss due to the LED driver can be effectively reduced to about 24% of the LED driver without CR and FRT techniques. The proposed LED driver with the FRT and CR techniques can improve the reference tracking performance and reduce the power loss.
In addition, another innovative control mechanism, the BSBR technique, is proposed to enhance the reference-tracking response and reduce the power consumption of the LED backlight module. The proposed BSBR technique can store extra charge on the output capacitor to the recycling capacitor when the output voltage transits from high-supplying voltage (12.4V) to low-supplying voltage (9.3V). As a result, the power dissipation on constant current generator can be considerably improved. On the other hand, when the output voltage level is changed from low- to high-supplying voltage, the charge stored on the recycling capacitor can be used for raising the output voltage back to the high-supplying voltage level. Therefore, extra charge can be recycled and the overall power consumption of the backlight module can also be reduced. In addition, the regulated voltage can be utilized to implement other applications such as turning on white-LED on the portable devices.
6.2 Future Works
The proposed charge-recycling (CR) and buck-store/boost-restore (BSBR) technique can store extra charge on the output capacitor to the recycling capacitor when the output voltage transits from high-supplying voltage for turning on the G- B-LED to low-supplying voltage
for turning on the R-LEDs. As a result, the power dissipation on constant current generator can be considerably improved. In addition, these techniques also can reduce the numbers of output component to improve the PCB area. However, these two techniques still require the external large capacitor and inductor to achieve the performance of fast reference tracking. In order to have future works on the reference tracking, furthermore simplify the driving module and reduce more power consumption of the FCS-LCD backlight module can be continuously studied. The BSBR and CR technique can be based on a synchronous boost DC-DC converter.
In addition, there are many challenges on the studies of reference tracking technique. Such as that the new control algorithm for reducing chip area and power consumption, the fast transient technique for stepping load transition, a new controlling error amplifier or compensator for improving the load\line regulation.
References
[1] Yi-Fu Chen, Che-Chin Chen, and Ke-Horng Chen, “Mixed Color Sequential Technique for Reducing Color Breakup and Motion Blur Effects,” IEEE/OSA Journal of Display Technology, pp. 377-385, Dec. 2007.
[2] T. Shirai, S. Shimizukawa, T. .Shiga, S. Mikoshiba, and K. Kalantar, “RGB-LED Backlights for LCD-TVs with 0D, 1D, and 2D Adaptive Dimming,” Society of Information Display, 2006 Dig. 44.4, pp. 1520–1523.
[3] K. Käläntär, T. Kishimoto, K. Sekiya, T. Miyashita, and T. Uchida, “Spatio-Temporal Scanning Backlight for Color-Field Sequential Optically Compensated Bend Liquid-Crystal Display,” Society of Information Display, 2005 Dig. 36.3, pp.
1316–1319.
[4] A. Yohso and K. Ukai, “How Color Break-up Occurs in the Human Visual System:
Mechanism of Color Break-up Phenomenon,” Society of Information Display, 2006 Dig.
25.2, pp. 1223–1228.
[5] R. Van Dijk and J. A. Shimizu, “A System and Method for Motion Compensation Image Planes in Color Sequential Displays,” U.S. Patent 6 831 948, Dec. 14, 2004.
[6] Datasheet “3508 White SMD LED,” Light House Technology Co., LTD.
[7] Datasheet “MAX16807/MAX16808: Integrated 8-Channel LED Drivers with Switch-Mode Boost and SEPIC Controller,” Maxim Integrated Products, Inc.
[8] O. Ronat, P. Green and S. Ragona, “Accurate Current Control to Drive High Power LED Strings,” IEEE Applied Power Electronics Conference, 2006, pp.376-380.
[9] Doshi, Montu, Zane, and Regan, “Digital Architecture for Driving Large LED Arrays with Dynamic Bus Voltage Regulation and Phase Shifted PWM” IEEE Applied Power Electronics Conference, 2007, pp.287-393.
[10] C.-C. Chen, C.-Y. Wu and T.-F. Wu, “LED Back-Light Driving System for LCD Panels,” in Proc. IEEE Applied Power Electronics Conference, 2006, pp.381-385.
[11] Yogesh K. Ramadass and Anantha P. Chandrakasan, “Minimum Energy Tracking Loop with Embedded DC-DC Converter Enabling Ultra-Low-Voltage Operation Down to 250 mV in 65 nm CMOS,” IEEE Journal of Solid-State Circuits, vol. 43, no. 1,pp.
256-265, January 2008.
[12] Datasheet “1206 RGB SMD LED,” Light House Technology Co., LTD.
[13] Baddela, S.M., and Zinger, D.S, “Parallel Connected LED Operated at High Frequency to Improve Current Sharing,” IEEE Industrial Application Society, 2004, vol. 3, pp.1677- 1681.
[14] In-Hwan Oh, “A Single-Stage Power Converter for a Large Screen LCD Back-Lighting,” in Proc. IEEE Applied Power Electronics Conference, 2006, pp.1058-1063.
[15] Huang-Jen Chiu and Shih-Jen Cheng, “LED Backlight Driving System for Large-Scale LCD Panels,” IEEE Transaction on Industrial Electronics, vol. 54, pp. 2751-2760. Oct.
2007
[16] Heinz van der Broect, Georg Sauerlander, and Matthias Went, ”Power Driver Topologies and Control Schemes for LEDs,” IEEE Applied Power Electronics Conference, 2007, pp. 1319~1325
[17] Man Siu, Philip K.T. Mok, Ka Nang Leung, Yat-Hei Lam, and Wing-Hung Ki, “A Voltage-Mode PWM Buck Regulator with End-Point Prediction,” IEEE Transaction on Circuits and Systems II, vol. 53, no. 4, pp. 294-298, April 2006.
[18] Feng Su, Wing-Hung Ki, and Chi-Ying Tsui, “Ultra Fast Fixed-Frequency Hysteretic Buck Converter with Maximum Charging Current Control and Adaptive Delay Compensation for DVS Application”, IEEE Journal of Solid-State Circuits, pp. 805-814, Apr. 2008
[19] Datasheet ”DD311: High Constant Current LED Driver,” Silicon touch technology inc [20] Application Note “EL7801: Powering LED Strings and Arrays in Backlight
Applications,” Intersil Corp.
[21] Application Note “TLC5940: PWM Dimming Provides Superiorcolor Quality in LED video displays,” Texas Instruments Incorporated.
[22] R. D. Middlebrook, “Modeling Current-Programmed Buck and Boost Regulators,”
IEEE Transaction on Power Electronics, vol. 4, pp. 36-52, Jan. 1989.
[23] Chi Yat Leung, P. K. T. Mok, and Ka Nang Leung, “A 1-V Integrated Current-Mode Boost Converter in Standard 3.3/5-V CMOS Technologies,” IEEE Journal of Solid-State Circuits, pp. 2265-2274, Nov. 2005.
[24] Guangbin Zhang, Sooping Saw, Jin Liu, Scott Sterrantino, David K. Johnson, and Sungyong Jung, “An Accurate Current Source With On-Chip Self-Calibration Circuits for Low-Voltage Current-Mode Differential Drivers” IEEE Transaction on Circuits and System I, vol. 53, pp. 40-47, Jan. 2006.
[25] Kihyuk Sung and Lee-Sup Kim, “A High-Resolution Synchronous Mirror Delay Using Successive Approximation Register,” IEEE Journal of Solid-State Circuits, pp.
1997-2004, Nov. 2004.
[26] Application Note “Buck-Based LED Drivers Using the HV9910B,” Supertex Inc.
[27] Chun-Yu Hsieh, Shih-Jung Wang; Yu-Huei Lee, and Ke-Horng Chen, “LED Drivers with PPD Compensation for Achieving Fast Transient Response” IEEE International Symposium on Circuits and Systems, 2008, pp.2202-2205.
[28] Michel D. Mulligan, Bill Broach, Thomas H. Lee “A 3MHz Low-Voltage Buck Converter with Improved Light Load Efficiency” IEEE Solid-State Circuits Conference, 2007, pp. 528-529.
[29] Chun-Yu Hsieh and Ke-Horng Chen, “Boost DC-DC Converter with Charge-Recycling (CR) and Fast Reference Tracking (FRT) Techniques for High-Efficiency and Low-cost LED Driver” IEEE European Solid-State Circuits Conference, pp.358-361. 2008.
[30] Hong-Wei Huang, Ke-Horng Chen, and Sy-Yen Kuo, “Dithering Skip Modulation, Width and Dead Time Controllers in Highly Efficient DC-DC Converters for System-on-chip Applications,” IEEE Journal of Solid-State Circuits, pp. 2451-2465, Nov. 2007.
[31] Werner Hollinger, Manfred Punzenberger, “An Asynchronous 1.8MHz DC/DC Boost Converter Implemented in the Current Domain for Cellular Phone Lighting Management,” IEEE European Solid-State Circuits Conference, 2006, pp. 528-531.
[32] Ke-Horng Chen, Hong-Wei Huang, and Sy-Yen Kuo, “Fast Transient DC-DC Converter with On-Chip Compensated Error Amplifier,” IEEE Transaction on Circuits and Systems II, pp. 1150-1154, Dec. 2007.
[33] Robert W. Erickson and Dragon Maksimovié, Fundamentals of Power Electronics, 2nd ed. Noirwell, MA: Kluwer, 2000.
[34] Ke-Horng Chen, Chia-Jung Chang, and Ter-Hsing Liu, “Bidirectional Current-Mode Capacitor Multipliers for On-Chip Compensation,” in IEEE Transaction on Power Electronics, pp. 180-188, Jan. 2008.
[37] Qiang Bian, Zushu Yan, Yuanfu Zhao, and Suge Yue, “Analysis and Design of Voltage Controlled Current Source for LDO Frequency Compensation”, IEEE Conference on Electron Devices and Solid-State Circuits, 2005, pp.363-366.
[38] Hong-Wei Huang, Chun-Yu Hsieh, Ke-Horng Chen, and Sy-Yen Kuo, “Adaptive Frequency Control Technique for Enhancing Transient Performance of DC-DC Converters,” IEEE European Solid-State Circuits Conference, Sep. 2007, pp. 174-177.
[39] Hong-Wei Huang, Chun-Yu Hsieh, and Ke-Horng Chen, “A 1V 16.9ppm/°C 250nA Switched-Capacitor CMOS Voltage Reference” IEEE Solid-State Circuits Conference, 2008, pp. 438-439.
[40] Patrick Y. Wu and Philip K. T. Mok, “A Monolithic Buck Converter With Near-Optimum Reference Tracking Response Using Adaptive-Output-Feedback,” IEEE Journal of Solid-State Circuits, vol. 42, no. 11,pp. 2441-2450, November 2007.
[41] Chun-Yu Hsieh and Ke-Horng Chen, “Adaptive Pole-Zero Position (APZP) Technique of Regulated Power Supply for Improving SNR,” in IEEE Transaction on Power Electronics, pp. 2949-2963, Nov. 2008.
[42] Osama Abdel-Rahman and Issa Batarseh, “Transient Response Improvement in DC-DC Converters Using Output Current for Faster Transient Detection,” IEEE Annual Power Electronics Specialists Conference, 2007, pp. 157-160.
Published Paper
International Journal Paper： ： ： ：
2010
1. (SCI) Chia-Hsiang Lin, Chun-Yu Hsieh, and Ke-Horng Chen, “A Li-Ion Battery Charger with Smooth Control Circuit (SCC) and Built-in Resistance Compensator (BRC) for Achieving Stable and Fast Charging,” in IEEE Transaction on Circuit and System I, pp. 506-517, Feb., 2010.
2. (SCI) Chao-Hsuan Liu, Chun-Yu Hsieh, Yu-Chiao Hsieh, Ting-Jung Tai, and Ke-Horng Chen, “SAR-controlled Adaptive Off-time Technique without Sensing Resistor for Achieving High Efficiency and Accuracy LED Lighting System,” in IEEE Transaction on Circuit and System I, pp. 1384-1394, June, 2010.
3. (SCI) Chun-Yu Hsieh, Chih-Yu Yang, and Ke-Horng Chen, “A Low-Dropout Regulator with Smooth Peak Current Control (SPCC) Topology for Over-Current Protection,” in IEEE Transaction on Power Electronics, pp. 1386-1394, June, 2010.
4. (SCI) Chun-Yu Hsieh, Hong-wei Huang, and Ke-Horng Chen, “A 1 -V, 16.9 ppm/
°C, 250 nA Switched-Capacitor CMOS Voltage Reference,” in IEEE Transaction on Very Large Scale Integration System, accept to be published.
2009
5. (SCI) Chun Yu Hsieh and Ke Horng Chen, “Boost DC-DC Converter With Fast Reference Tracking (FRT) and Charge-Recycling (CR) Techniques for High-Efficiency and Low-Cost LED Driver”, IEEE Journal of Solid-State Circuits, pp. 2568-2580, Sep., 2009.
6. (SCI) Chun-Yu Hsieh, Chih-Yu Yang, and Ke-Horng Chen, “A Charge-Recycling Buck-store and Boost-Restore (BSBR) Technique with Dual Outputs for RGB LED Backlight and Flashlight Module,” in IEEE Transaction on Power Electronics, pp.
1914-1925, Aug., 2009.
2008
7. (SCI) Chun-Yu Hsieh and Ke-Horng Chen, “Adaptive Pole-Zero Position (APZP) Technique of Regulated Power Supply for Improving SNR,” in IEEE Transaction on Power Electronics, pp. 2949-2963, Nov. 2008.
International Conference Paper： ： ： ：
2010
1. Chen-Li Chu, Chun-Yu Hsieh, Da-Liang Chiu, and Ke-Horng Chen,
“Multi-LC/BL Algorithmic Technique in Field Color Sequential LCD for Color Breakup Suppression,” Society for Information Display, 2010 Digest 12.3, pp 159-162.
2. Chun-Yu Hsieh, Chih-Yu Yang, Fu-Kuei Feng, and Ke-Horng Chen, “A Photovoltaic System with an Analog Maximum Power Point Tracking Technique for 97.3% High Effectiveness,” Society for Information Display, 2009 Digest 43.2, pp640-643.
2009
3. Chun-Yu Hsieh, Chih-Yu Yang, Ming-Hsin Huang, Don-Hwan Li, Chi-Lin Chen, and Ke-Horng Chen, “A Charge-Reservoir with Buck-Store and Boost-Restore
3. Chun-Yu Hsieh, Chih-Yu Yang, Ming-Hsin Huang, Don-Hwan Li, Chi-Lin Chen, and Ke-Horng Chen, “A Charge-Reservoir with Buck-Store and Boost-Restore