Zero-Voltage and Zero-Current-Switching Half Bridge DC/DC Converter Vencislav Valchev, Dimitre Yudov, Jeliazko Batchvarov Department of Electronics, Technical University of Varna, Studenska Str.1, Varna, Bulgaria vencivalchev@hotmail.com Alex Van den Bossche, Jan Melkebeek Department of Electrical Energy, Systems and Automation, Ghent University, Sint-Pietersnieuwstraat 41, Gent, Belgium, Tel.+32-9-2643419 fax. 32-9-2643582, alex.vandenbossche@rug.ac.be Abstract: This paper introduces an improved zero-voltage and zero-current-switching half bridge (ZV-ZCS HB) DC/DC converter for medium and high-power applications. The soft switching is obtained by adding only small capacitors. The operation principle and design procedure are presented together with an analysis of the total losses in the switch. By using the proposed operation principle and design procedure zero-voltage- zero-current switching and high efficiency operation for full load range are provided. The operation and design considerations are illustrated and verified on a 6-kW prototype, which has been simulated (PSPICE) and successfully tested at 20 kHz operating frequency. The obtained efficiency is above 97% for full load. Increasing the operating frequency above 50kHz is possible, which contributes to a decrease of the losses in the transformer and to a reduction the size and weight. The simple topology, high efficiency and low cost make the proposed converter attractive for medium and high power applications. Keywords—Soft Switching, Zero-Voltage-Zero-Current Switching I. INTRODUCTION Recent developments in high-frequency power conversion have shown an increased utilization of soft switching techniques. These techniques can be classified into four families [1]: resonant [2,3,4], quasi-resonant [5,6], multi- resonant [7] and PWM converters with soft switching [8,9,10]. All these circuits and techniques can be regarded as resonant and soft switching PWM techniques. For resonant-type techniques the main drawbacks are significantly higher voltage and/or current stresses on semiconductors (compared with those in the conventional PMW technique) and variable- frequency control. The distinctive features of soft-switching PWM techniques are constant-frequency duty-ratio control with simultaneous reduction of switching losses for the same, or only slightly increased current and voltage stresses on the semiconductors. But those topologies usually require auxiliary passive and/or active components. Depending on the specific application, different topologies could be used according to the specific requirements. In some applications the voltage control is not needed or can be realized in another part of the total circuit. This paper presents an improved zero-voltage and zero-current-switching half bridge (ZV-ZCS HB) DC/DC converter suitable for such conditions. A simultaneous zero- current and zero-voltage switching is obtained for full load range without any additional drawbacks. The converter is applicable with benefits in medium and high-power applications because of its high efficiency and optimal switching conditions. II. PRINCIPLE OF OPERATION The proposed converter (fig.1) consists of a half bridge inverter and a half bridge rectifier. The combined circuit is a high efficiency DC/DC converter with simultaneous zero- voltage and zero-current switching conditions. The features of the ZV-ZCS HB DC/DC converter have been achieved by adding only small capacitors in parallel to the switches and by a specific operation principle and components dimensioning. The zero-current turn-on and turn-off are obtained by a series resonant circuit consisting of the capacitors C d1 ,C d2 of the voltage divider and the leakage inductance of the transformer. The zero-voltage turn-on is achieved by discharging the capacitors C k1 ,C k2 with a sufficient magnetizing current. These specific operation conditions are accomplished in the proposed design procedure. An additional advantage of the circuit is its low series impedance due to the series resonance between the transformer leakage inductance and the capacitors C d1 ,C d2 , resulting in a low variation of the ratio U out /U in . i in i out U in S2 D2 C k2 C k1 S1 D1 C d1 D3 C O1 C o2 C d2 D4 C f Fig.1. Zero-Voltage and Zero-Current-Switching Half Bridge (ZV-ZCS HB) DC/DC Converter. i L1 i L2 R out U out 2327 0-7803-7420-7/02/$17.00 © 2002 IEEE