Analysis of Wide Voltage Variation in LLC Converters Using Variable Transformers

One of the most important applications of power converters nowadays are Battery chargers in which the gain of the converter requires a wide range and high efficiency, the LLC resonant converter has become one of the most used topologies in this area. The most used approach for varying the output voltage is by changing its switching frequency. However, when the applications require wide variations of the output voltage it is necessary to perform wide frequency variations. This paper compares two methods to achieve wide voltage variations, the first one the previously mentioned technique of increasing the frequency and the second one the implementation of variable magnetics. The trade-offs of both techniques are presented and simulated.