High Frequency LLC Resonant Converter with Magnetic Shunt Integrated Planar Transformer

LLC resonant converter has been proved as an excellent candidate to achieve high efficiency and power density. To achieve smaller size of passive components, the resonant inductor in LLC converter is usually integrated into the transformer by utilizing its leakage inductance. However, leakage inductance of transformer is usually insufficient and thus the LLC converter has to be operated in a limited frequency range, otherwise the power efficiency will drop dramatically. Therefore, a larger resonant inductance in LLC converter is expected to operate in a wider input voltage range. This paper proposes a new method to create a larger resonant inductance by using a magnetic shunt integrated into planar windings. Accurate leakage inductance modelling, calculation and optimal design guideline for LLC transformer are presented. A 280-380V input and output 48V-100W half bridge LLC resonant converter with 1 MHz resonant frequency is built to verify the design methodology. A comparison is made between the converter with magnetic shunt integrated transformer and the other with traditional planar transformer without magnetic shunt. Experimental results show the proposed converter with magnetic shunt can greatly narrow switching frequency range and thus achieve high efficiency under a wider input range