A FAST RESPONSE ZERO-VOLTAGE-TRANSITION PULSE-WIDTH MODULATION BOOST CONVERTER USING A VARIABLE GAIN CONTROL TECHNIQUE Yuk-Ming Lai, Siew-Chong Tan, and Sze-Nok Chan Department of Electronic and Information Engineering The Hong Kong Polytechnic University Hong Kong, China email: enymlai@polyu.edu.hk ABSTRACT This paper describes the design of a fast response zero- voltage-transition (ZVT) pulse-wdith modulation (PWM) boost converter. The techniques employed in the design in- clude a combination of a PWM variable gain control and zero-voltage switching (ZVS), to improve the switching speed and efficiency of the converter for high frequency op- eration. A prototype was built to verify the design and to compare the proposed variable gain controller and the con- ventional controller using PWM. It is shown that with the proposed controller, the ZVT boost converter has a much faster response than the conventional PWM control. More- over, the proposed controller is easily realized with simple analogue circuitries. Keywords: Zero-voltage-transition, variable gain control, pulse-width modulation, boost converter. 1. INTRODUCTION To accommodate the ever increasing demand for light weight, small size, fast response, and high efficiency power supplies, the switching frequency of DC/DC converters has been increased significantly over the last two decades. How- ever, the increase in switching frequency causes the prob- lems of higher switching losses and electromagnetic inter- ference (EMI). To alleviate these problems, different soft- switching techniques were proposed [1]–[8]. Among the proposed techniques, the ZVT-PWM technique is deemed desirable because of its constant switching frequency na- ture and its ability to reduce the switching voltage/current stresses on the main switch and also the conduction and switching power losses [3]–[5]. This technique was subse- quently further improved by utilizing the body diode of the auxiliary switch to achieve soft-switching in both the main and auxiliary switches [6]–[8]. However, the majority of these development efforts have been focused on the steady state operation analysis and de- sign considerations of using snubber cells in the ZVT PWM converters. So far, very few researches that offer improved feedback control have been reported [9], [11]. In view of this, we propose a variable gain feedback controller that is suitable to be used in the ZVT PWM converters in this pa- per. As seen in the experimental results, the proposed con- troller not only reduces load transient response time, but can also attain the same high efficiency of those employed con- ventional PWM control. This paper is organized as follow. Section 2 first gives a brief description on the ZVT PWM boost converter that was used in the prototype circuit [6]. Then, the design of the variable gain feedback controller is described. Section 3 gives the prototype design and its implementation. An experimental evaluation of the prototype system is also pre- sented in this section. Finally, Section 4 summarizes the findings of the paper. 2. THE PROPOSED PROTOTYPE CIRCUIT In the following sub-sections, the operation of a ZVT PWM boost converter with active snubber is first briefly described. And, subsequently, a variable gain feedback controller is designed and analyzed. 2.1. The ZVT PWM boost converter Fig. 1 shows the circuit diagram of a ZVT PWM boost con- verter with an active snubber. In the circuit, the auxiliary switch (S 2 ), the resonant parasitic junction capacitor (C r ), the resonant inductor (L r ), and the fast recovery diodes (D 3 ) form a resonant path to obtain zero voltage switch- ing. A snubber cell which consists of two diodes (D 1 , D 2 ), and the capacitor (C B ) is incorporated in the circuit to re- duce the switching losses due to (1) the turn-off of the main switch, and (2) the turn-on and -off of the auxiliary switch (S 2 ). To facilitate the description of the circuit operation of the ZVT PWM boost converter, the input filter inductance (L) and the output filter capacitance (C) are chosen to be sufficiently large so that they can be considered as an ideal 978-1-4244-1706-3/08/$25.00 ©2008 IEEE.