Analysis of Diode Emulation in Light Load Condition of Synchronous Buck Converter

摘要

Light load efficiency becomes an important factor to evaluate synchronous Buck converters. Constant on-time control reduces switching frequency at light load, switching losses decreases and system efficiency increases. However, the variable switching frequency used in constant on-time control limits its application in some areas, where constant switching frequency is required. This paper investigates Diode Emulation (DE) operation in light load condition, especially from output voltage ripple, inductor current ripple, transient response, and power loss points of view. Analysis shows smaller output volt-age ripple and inductor current ripple, and less power losses in DE operation. However extra transi-tions for switching-in or -out of DE operation cause additional overshoot and undershoot on output voltage. A feasible scheme is proposed to separate DE transition from the regular load transient for reducing overshoot. Experiments have been conducted to verify the effectiveness of the analysis and the proposed scheme in this paper.