Dissertation/Thesis Abstract

Power control architectures for cold cathode fluorescent lamp and light emitting diode based light sources
by Doshi, Montu V., Ph.D., University of Colorado at Boulder, 2010, 220; 3404046
Abstract (Summary)

In this dissertation, two different energy efficient power supply topologies are introduced for controlling cold cathode fluorescent lamp (CCFL) and high-brightness light emitting diode (HBLED) based lighting modules. A low-frequency architecture is developed to power cold cathode fluorescent lamp (CCFLs) based LCD backlight modules. In contrast to the conventional high frequency inverter power supply modules, the proposed lowfrequency architecture is capable of driving a large number of parallel connected lamps using a single DC-DC converter circuit with independent lamp current regulation. The architecture relies on the concept of capacitive coupling based lamp ignition, resulting in reliable, simultaneous ignition of parallel lamps at a lamp terminal voltage near the steady-state operating voltage. Equal lamp electrode degradation and reduction in ac coupling losses is achieved by performing low-frequency square-wave switching operation. The efficiency improvements when using the proposed low frequency architecture are demonstrated for a prototype system consisting of 4 parallel connected 250 mm length lamps.

A digital power supply architecture is developed for controlling a large array of series-parallel connected HBLEDs using the multiphase pulse width modulation (MPWM) dimming technique. The proposed MPWM technique operates by uniformly time shifting the individual on/off LED string current pulses, thus avoiding large current transients. The dimming operation results in a reduced risk of visible flicker perception and associated health hazards, reduced magnitude of audible noise, smaller power stage output capacitance and improved EMI performance. A digital reconfigurable and fault tolerant modulator (RFTM) architecture is developed to implement the MPWM technique and meet the design requirements of different types of solid state lamps. Based on the number of parallel HBLED strings present in the lamp and their power rating, the proposed modulator circuit can be configured to generate a desired number of uniformly phase-shifted control signals. Further, the modulator circuit is capable of detecting fault conditions and performing recovery procedures in order to maintain the total light luminance and improve lamp reliability. Along with MPWM dimming, the concept of dynamic voltage scaling is introduced to further reduce the losses in the current regulator circuit and to improve the efficiency of the system. The operation of the proposed architecture, using MPWM dimming and dynamic voltage scaling technique is verified using a prototype lamp consisting of a 64 HBLED array and a 27 W Boost converter that is digitally controlled using an FPGA.

Indexing (document details)
Advisor: Zane, Regan
Commitee: Erickson, Robert, Fornberg, Bengt, Maksimovic, Dragan, Park, Wounjhang
School: University of Colorado at Boulder
Department: Electrical Engineering
School Location: United States -- Colorado
Source: DAI-B 71/06, Dissertation Abstracts International
Subjects: Electrical engineering
Keywords: Capacitive ignition, Cold cathode fluorescent lamps, Dynamic bus voltage scaling, LED dimming, Light-emitting diodes, Low frequency square waves, Power control
Publication Number: 3404046
ISBN: 978-1-109-78224-0
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