Design and realization of high-performance LED drivers for automotive lighting applications

• Main Author: Qu, Yong
• Other Authors: Chang Joseph Sylvester
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Integrated circuits; DRNTU::Engineering::Electrical and electronic engineering::Power electronics
• Online Access: https://hdl.handle.net/10356/82740; http://hdl.handle.net/10220/46654
• Institution: Nanyang Technological University

This Ph.D. program pertains to the design and monolithic realization of Light Emitting Diode (LED) drivers for automotive lighting where the imperative parameters are high power-efficiency and high reliability. The grand objectives thereto are substantial improved specifications over the state-of-the-art, including power-efficiency, reliability, current driving capability, and dimming range. To achieve the said grand objectives, the specific objectives are to decouple, and hence mitigate the following two major design trade-offs that limit the performance of contemporary automotive LED drivers. The first trade-off is between high reliability and high current driving capability, and applies to both single-phase and multi-phase LED drivers. Specifically, to achieve high current driving capability, the contemporary single-phase LED driver typically suffers from low reliability arising from large current ripples. On the other hand, the multi-phase LED driver is highly advantageous to provide high current driving capability, but suffers from low reliability because of the ensuing subharmonic oscillation. To decouple this limiting trade-off, we propose the design and monolithic realization of a novel Pulse-Width-Modulation (PWM)-based dual-phase LED driver in Global Foundries (GF) 130nm BCDLite process. To achieve high current driving capability, we adopt a dual-phase power stage. To achieve high reliability, we propose an Average Current Control to eliminate the subharmonic oscillation by considering the complete inductor-current profile vis-à-vis peak current adopted/reported elsewhere. To further improve the reliability, we propose an accuracy-enhanced current sensor to ascertain good current balance in the adopted dual-phase power stage. With measurements on our prototype LED driver ICs embodying our aforesaid adoption and proposed circuits, we demonstrate, to the best of our knowledge, for the first time that the trade-off between high reliability and high current driving capability is decoupled, i.e., an LED driver uniquely featuring high reliability, yet high current driving capability. The second trade-off is between high power-efficiency and wide dimming range. Specifically, a wide dimming range is derived by means of high switching frequency, hence the ensuing reduced settling time of the LED current. This, however, in turn leads to a degradation of the power-efficiency due to increased switching losses. To decouple this limiting trade-off, we propose the design and monolithic realization of a novel fully soft-switched LED driver in GF 130nm BCDLite process. We achieve wide dimming range by operating at high switching frequencies, but the high switching does not compromise the power-efficiency. Using a fully soft-switching approach, the ensuing switching losses are negligible. This is achieved by a proposed Hysteretic SoftSwitching Controller (HSSC) and proposed circuitries, i.e., a voltage detector, current sensor, and a level shifter. The HSSC enables complete soft-switching, including zerovoltage switching and zero-current switching, by means of turning on/off power switches when their voltage/current is zero. The proposed voltage detector and current sensor, featuring low power, monitor the voltage and current of the power switches. The proposed level shifter, featuring ultra-fast speed, serves to quickly transmit the monitored signal from the said voltage detector and current sensor to the HSSC. With measurements on our prototype LED driver ICs embodying our proposed HSSC and proposed circuits, we demonstrate, to the best of our knowledge, for the first time that the trade-off between high power-efficiency and wide dimming range is decoupled, i.e., an LED driver uniquely featuring wide dimming range, yet high power-efficiency.