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