Discussion of the Capacitor Effect with Equivalent Series Resistance and Inductance in Switching Mode Power Supplies

• Main Authors: Yu-Hsun Wang, 王御旬
• Other Authors: 陳政裕
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/au8rnh

碩士 === 國立虎尾科技大學 === 電機工程系碩士班 === 105 === The output capacitor has a great effect on the output ripple voltage of switching mode dc-dc converters. In this thesis, switch mode power supply circuits are classified into two types: continuous current through output capacitor and discontinuous current through output capacitor. Furthermore, the effects of equivalent series resistance (ESR) and equivalent series inductance (ESL) of the capacitor on output ripple voltage are studied. The output ripple voltage is dominated by ESR when the switching frequency of the converter at 100kHz. In order to get low output ripple voltage, the converter must use low ESR capacitor, but such low ESR capacitor will reduce the stability of the converter. When the output capacitor has continuous current, and output ripple voltage is affected obviously by the ESL as the switching frequency increases. In addition, when the current through output capacitor is discontinuous, the instantaneous change of ESL current will result in serious spike appearing in the output voltage. Two methods are proposed to reduce effectively the output voltage spike. Then, a buck converter is implemented with voltage-mode control. For frequency response of the output ripple voltage, different switching frequencies which are 100kHz to 1MHz are simulated. The output ripple voltage of ESL possesses 56% of the total output ripple voltage when the converter switching frequency is 700kHz. The output ripple voltage is affected by the ESL when the converter increases switching frequency gradually. Also, a flyback converter is implemented with peak-current-mode control. The proposed method can reduce almost 97% the total output voltage spike. As a result, the output capacitor is selected according to the output ripple voltage with 1.5% and the phase margin with at least 50 degrees. Last but not least, we used different kinds of network analyzer, including Agilent 4395A, Mathcad and Simplis to draw Bode plot and referred to the results of the implementation and simulation to prove the correctness of selecting output capacitor methods.