探討電容之等效串聯電阻及電感對切換式電源供應器的影響

由於切換式直流電源供應器的輸出電容對其輸出電壓的漣波影響甚大，為探討此問題，本論文將切換式電源電路分成輸出電容為連續電流與輸出電容為不連續電流兩大類，更進一步分析輸出電容之等效串聯電阻(ESR)與等效串聯電感(ESL)對切換式電源供應器的影響。在目前常用的開關頻率範圍，由於輸出電容之等效串聯電阻為造成輸出漣波電壓之主要因素，若要得到低的輸出漣波電壓就必須選用低等效串聯電阻之輸出電容，但若使用低內阻電容將會導致電源電路系統穩定度的降低。首先，在屬於輸出電容為連續電流的轉換器中，隨著開關頻率工作的提升，輸出漣波電壓明顯感受到輸出電容之等效串聯電感所造成的影響。另外，我們發現在屬於輸出電容為不連續電流的轉換器中，由於輸出電容之等效串聯電感因通過的電流瞬間變化較大而導致輸出電壓產生相當大的突波，本論文將提出兩種有效降低輸出電壓突波的方式。最後使用電壓模式控制於降壓型轉換器，並模擬開關頻率工作於100kHz至1MHz時之輸出漣波電壓，當開關工作頻率達到700kHz時，輸出電容之等效串聯電感漣波電壓已佔總輸出漣波電壓之56%，此等效串聯電感對輸出漣波電壓之影響，明顯受到開關工作頻率提升的影響。再使用峰值電流模式控制返馳式轉換器，得到所提供之降低輸出電壓突波之方法，最多可減少總輸出電壓突波之97%。本論文設計降壓型轉換器與返馳式轉換器之輸出漣波電壓百分比為1.5%，且相位裕度至少需50°以上，根據此條件選用符合規格之電容。最後，使用網路分析儀Agilent 4395A、Mathcad與Simplis繪製波德圖，並根據模擬與實測驗證選用輸出電容方法的正確性。

關鍵字

輸出電容；輸出電壓突波；等效串聯電阻；輸出漣波電壓；相位裕度；穩定度

並列摘要

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.

並列關鍵字

Output capacitor ； Output voltage spike ； Equivalent series resistance (ESR) ； Output ripple voltage ； Phase margin (PM) ； Stability

參考文獻

[24] 施承德，“返馳式電源供應器之研究” 國立台北科技大學電資學院電資碩士班碩士學位論文，中華民國九十七年七月。

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探討電容之等效串聯電阻及電感對切換式電源供應器的影響

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