Solid-Duty-Control Technique for Alleviating the Right-Half-Plane Zero Effect in Continuous Conduction Mode Boost Converters

This paper proposes a solid-duty-control (SDC) technique for application in boost converters to maintain a constant duty value and reduce dip voltage during load transient periods. Fast transient response was also achieved because of the variable transient enhancement controller. The proposed SDC technique can provide a stable and regulated output for edge-lit light-emitting diode backlight systems. This converter was used in a 0.25-μm CMOS process. Experimental results show that compared with a conventional design without a fast transient technique, the proposed approach yields about 30% and 80% improvement in undershoot voltage and recovery time, respectively, as load current changes from 50 to 250 mA.

I. Introduction

The current trend in the development of current liquid crystal display (LCD) panels is geared toward weightlessness and thinness. In this regard, edge-lit light-emitting diode (LED) backlight configuration has become a popular technique applied to medium- and small-size LCDs [1]–[3]. Fig. 1(a) illustrates a conventional block diagram of an LCD TV with edge-lit LED backlight units containing three LED colors. To obtain perfect image quality, light guides in the edge-lit LED backlight are designed to prevent total internal reflection and uniformly distribute light emitted from the LED sources across the light-guide surface [4]–[7]. Furthermore, the LED backlight driver, which is composed of boost converters, must be able to handle the requirements of fast transience, high stability, power efficiency, and space minimization to handle large instant load variations without sacrificing image quality and increasing motion blur effects [8]–[10]. The conventional current-mode boost converter contains one dominant pole and two zeros, the right-half-plane (RHP) and left-half-plane (LHP) zero. However, the RHP zero results in a tradeoff between fast transient response and system stability in the boost converters, which operate in (CCM) [11], [12]. Fig. 1.

(a) Conventional current-mode boost converter. (b) Proposed boost converter with SDC controller containing the AHW and VTE controllers. (c) Selection of the RHP zero can simultaneously ensure transient response and system stability.