Optimizing the Normalized Dead-Time and Maximum Switching Frequency of a Wide-Adjustable-Range LLC Resonant Converter

Abstract

LLC resonant converter has been widely used in dc–dc converters. In this paper, optimum dead-time and maximum switching frequency of a wide-adjustable-range LLC resonant converter are investigated for realizing the zero voltage switching (ZVS) operation even under the worst-case conditions. Analyses demonstrate that these parameters depend on the converter inductance ratio and ratio of the converter resonant capacitor and the effective capacitance appeared in parallel with the drain–sources of the power MOSFETs. The necessary dead time for realizing the ZVS operation can be minimized by choosing the normalized maximum switching frequency, properly. Using the dead-time optimum value, soft switching is achieved for all power devices even under the worst-case conditions. Developed prototype of the converter has been tested under different loads (0–3 A dc) and input voltage conditions (320–370 V dc) to achieve a wide-adjustable-range output voltage (40–165 V dc). This dc–dc converter is used as an ion implanter arc power supply. The calculated optimum dead-time and maximum switching frequency are approximately equal to 184 ns and 205.7 kHz, for realizing the ZVS operation at the worst-case conditions. These parameters in the prototype are approximately equal to 195 ns and 203.5 kHz, respectively.