Abstract
LLC techniques have been popular solutions for high density power converters due to the benefits of soft switching and no reverse recovery losses. But the need of switching frequency control for output voltage regulation is always a considerable challenge for practical design. This letter proposes a simple and low-cost scheme to suppress the frequency variation for LLC resonant converters with wide range operation. An auxiliary circuit, which only deals with a relatively lower current, is utilized to regulate the output voltage by providing an adaptive current injection for the resonant capacitor. Then, by taking the benefit of controllable current injection, adjustment of the energy transferring time for the power transformer is achievable without the need of switching frequency variation, and soft switching of the power switches is still maintained. In addition to detailed theoretical analysis, experimental results verify the feasibility and effectiveness of the proposed concept.
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