Design of a 1 MHz LLC resonant converter based on a DSP-driven SOI half-bridge power MOS module

Abstract

In this paper, the design of a 1MHz LLC resonant converter prototype is presented. Aiming to provide an integrated solution of the resonant converter, a half-bridge power MOS module employing Silicon-On-Insulator (SOI) technology has been designed. Such a technology, which is suitable for high-voltage and high-frequency applications, allows enabling HB power MOSFET modules operating up to 3MHz with a rated voltage of 400V. The power device integrates the driving stages of the high-side and low-side switch along with a latch circuit used to implement over-voltage/over-current protection. The module has been designed to be driven by a DSP device, which has been adopted to perform frequency modulation of the resonant converter. By this way, output voltage regulation against variations of the load conditions has been achieved. The issues related to the transformer design of the LLC resonant converter are discussed, too. Owing to the high switching frequency experienced by the converter, 3F4 ferrite cores have been selected for their low magnetic power losses between 0.5 and 3MHz and core temperatures up to 120°C. The resonant converter has been designed to operate in an input voltage range of 300–400V with an output voltage of 12V and a maximum output power of 120W. Within these design specifications, a performance analysis of the LLC converter has been conducted, showing the results obtained at the switching frequencies of 650kHz and 1.4MHz. A model of the LLC resonant converter has been developed to aid the prototype design.