Fully-Integrated LED Drivers Using Digital Control Techniques by Kichang Jang Department of Electrical and Computer Engineering The Graduate School of the University of Seoul

Fully-Integrated LED Drivers Using Digital Control Techniques by Kichang Jang A
 Ph.D. Dissertation submitted to the Department of Electrical and Computer Engineering at the Graduate School of the University of Seoul 
in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 2016 Approved by Joongho Choi Advisor

 ABSTRACTS
Most LED-lighting applications are constructed through the connection of a number of LEDs in parallel or in a series for the attainment of sufficient light. If LEDs are connected in parallel, however, an issue regarding the current-matching properties of the LEDs may arise; furthermore, if the LEDs are connected in a series, a high-voltage issue and an instability problem regarding the presence of a single open-circuit LED may also occur. Although the supply voltage varies due to the varying load condition, the current regulator maintains a constant LED current, while the employment of a switching converter can drive the LEDs for the improvement of the operating efficiency. LED drivers are still hampered by a poor operating efficiency, though, due to a voltage drop that is caused by the pass-transistor and the resistor of the current regulator. In this thesis, LED drivers that have been designed for flash-LED and LED-lighting applications are introduced; furthermore, a novel flash-LED current regulator is presented. To obtain a higher efficiency and a smaller area, the proposed regulator is operated without a resistor unlike the conventional current-regulator design. The designed flash-LED driver for which the proposed current regulator is used consists of a boost converter, an analog-to-digital converter (ADC), and a digital-to-analog converter (DAC). The boost-converter output voltage is set by an adaptive-voltage control for which the ADC and the DAC are used, and this control ensures the provision of a high-precision LED current; here, the use of the proposed LED-driver-control method provides only a 2 % current error at an LED current of 0.5 A. A higher efficiency and a smaller area are achieved through the use of a 0.13 μm-BCD process for the implementation of the flash-LED driver. A primary-side-regulated flyback converter for an LED-lighting application is also presented in this thesis. The proposed mid-current sensing circuit is introduced for the attainment of a precise outputcurrent regulation with respect to both the discontinuous-conduction mode (DCM) and the continuous-conduction mode (CCM); furthermore, a current error that is derived from an on-time propagation delay that is due to circuit imperfections is also analyzed A novel adaptive on-time-delay compensation circuit is therefore proposed for the attainment of a precise output-current regulation. The proposed compensation circuit is fully integrated for the delayerror factor; also, unlike a number of the other existing circuits, external components are not required for the proposed circuit. The LED-lighting flyback converter is implemented using a 0.35 μm- BCD process. The use of the proposed method provides only a 4 % current error regardless of the LED current that is applied
 Keywords: LED driver, adaptive voltage control, boost converter, current regulator, primary-side regulation flyback converter, mid-current sensing circuit
LINK: https://www.mediafire.com/file/c3s26xyq7fhv59w/Fully-Integrated_LED_Drivers.pdf/file