Multiple-Output LLC Resonant Converter with Magnetic Control

Multiple-output DC/DC converters are favored in various industrial applications due to its characteristics of high power density and low cost. However, cross regulation is an important issue that requires to be solved. As one of the most popular isolated DC/DC converters, LLC resonant converter has been adopted for multiple-output application. In this paper, a magnetically controlled multiple-output LLC resonant converter with input voltage feedforward is proposed. The variable resonant inductor is adopted to regulate the output voltage of each channel, so the independent control is achieved and there is no cross regulation issue. However, due to the magnetic material limitation and power loss consideration, a wide variable resonant inductance range is both impractical and lossy. Therefore, the input voltage feedforward control is introduced to minimize the influence of input voltage. Since the input voltage has the same influence on each output channel, the switching frequency of the primary switch can be adjusted according to the input voltage. Moreover, the proposed control strategy is suitable for more than two outputs application and it has no limitation on the number of output channels. To validate the effectiveness of the proposed multiple-output LLC resonant converter, a 200 W laboratory prototype was built, and the circuit parameters are selected based on the design considerations discussed in this paper. Both the steady state and dynamic response experimental waveforms are presented and analyzed.