This digest proposes event-based sampling and periodic perturbation methods in digital PFM control. Both voltage mode and current mode PFM architectures are proposed. By suitably modulating the control signal, power spectral density (PSD) can be drastically reduced with insignificant effects in the RMS current and transient performance. A unified discrete-time (DT) large-signal model is developed, which can be used for different mode configurations of the LLC converter over the entire operating range. DT small-signal models are derived, which can be used for closed-loop stability analysis using the proposed methods. Conventional PFM and the proposed spread spectrum PFM techniques are compared. Hardware prototype of a 6.6 kW LLC converter is developed, and experimental results are presented to demonstrate EMI reduction using the proposed technique.
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