Parallel Current Sharing Design Of High Frequency And High Efficiency Transformer Applied To Half Bridge LLC Converter

Nowadays,power supplies are developing towards high efficiency,high frequency and high power density.As a common circuit topology,LLC converter has attracted attention due to the simpler topology,less components,and high efficiency by operating in Zero Voltage Switch(ZVS)conditions over the entire load range.For planar transformers,which is one of the most important components of LLC converter,the parallel windings cannot naturally share the current evenly.The uneven current sharing may cause additional power loss,which enhance with frequency,and may affect the performance of the circuit.In response to the above problems,the influence of factors such as winding structure and insulation layer thickness on the parallel current sharing has been analyzed,and the correctness of the analysis through simulation is verified.The most suitable winding structure for current sharing is clarified,and the relationship of the thickness of the insulating layer when the current sharing is optimal is given.When the copper thickness is thin,the loss caused by leakage inductance dominates,and when the copper thickness is thicker,the loss caused by current sharing dominates.On this basis,a current sharing optimization transformer using magnetic integration and staggered port technology is proposed,and the current of this structure is more balanced.Then,a simple LLC converter is proposed,and the previously designed transformer is applied to the LLC converter.Finally,the LLC converter prototype was evaluated.The simulation and test results show that the proposed planar transformer has a high transformation ratio of 8 : 1,and can stably transmit 136 W power at the frequency of 1.1 MHz～1.3MHz,the output current can reach up to 38.37 A,and the efficiency can reach 97.6 %.The current difference of each layer is less than 11.25%,the current distribution is uniform,and the overall temperature does not exceed 64.4 ℃.