| Summary: | 碩士 === 國立臺灣大學 === 電機工程學研究所 === 103 === The constant on-time (COT) controller for DC converters has received much attention recently for the reason of its unique feature of high conversion efficiency under both the heavy-load and light-load conditions. However, most of the published papers on this subject have been focused on the buck converters. In this thesis, a boost converter using the current-mode COT controller is considered. It finds applications in hand-held mobile devices.
The focus of the efforts is to establish a small-signal control model for the current-mode constant on-time (CMCOT) controlled boost converter. Since the conventional low-frequency average model cannot be applied in a COT control scheme, a describing function model is developed. Both the resistive load and the current load are considered in the modeling to adapt to different applications. From the model, control loop gain functions are used for the investigation of the converter control stability. In addition, the output impedance model is also developed. From the complicated model, a simplified version is obtained by mathematical approximations from which the output step-load response can be estimated. Based on the model, a compensation design procedure is developed to achieve desired stability margin and step-load transient response. Simulations and experimental results are given to confirm the proposed model.
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