Modeling of 3-level buck converters in discontinuous conduction mode for stand-by mode power supply

A 3-level buck converter in the discontinuous conduction mode (DCM) is a key circuit for integrated voltage regulators to achieve high efficiency at a light load in the stand-by mode operation of microprocessors. In this paper, fundamental circuit characteristics including the conversion ratio and transfer function are derived for the first time, enabling the design of controllers for 3-level buck converters in the DCM. The derived transfer function is verified by time-domain small-signal-injection simulation. Similar to conventional 2-level buck converters, 3-level buck converters in the DCM have a flrst-order lag transfer function, while 3-level buck converters in the continuous conduction mode (CCM) have a second-order lag transfer function, suggesting that different controllers are required for the DCM and CCM.

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