Theoretical and Experimental Analyses of Dynamic Performance of Three-Level Buck Converters in Discontinuous Conduction Mode for Standby Mode Power Supply

A three-level buck converter in the discontinuous conduction mode (DCM), where the output power is typically less than 1 W and the output current is less than several hundreds of mA, is a key circuit for integrated voltage regulators to achieve high efficiency at a light load in the standby mode operation of microprocessors. In this study, the fundamental circuit characteristics including the conversion ratio and transfer function are analytically derived for the first time. The derived transfer function is verified via time-domain small-signal-injection simulation as well as experimental measurements using a prototype of the three-level buck converter in the DCM with off-the-shelf ICs. Similar to conventional two-level buck converters in the DCM, three-level buck converters have a first-order lag transfer function, while those in the continuous conduction mode (CCM) have a second-order lag transfer function. A compensator design for the three-level buck converters in DCM and CCM in low-power application is discussed.

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