一般而言，連接於直流匯流排之DC/DC轉換器，其閉迴路系統應具有良好的性能與穩定度。然而，為了避免直流匯流排的雜訊，干擾C/DC轉換器之正常操作，及避免DC/DC轉換器所產生的切換頻率諧波雜訊，汚染直流匯流排，故需要在DC/DC轉換器與匯流排之間，加入輸入EMI濾波器，以濾除雜訊。然而，加入輸入EMI濾波器卻可能影響DC/DC轉換器之閉迴路系統的性能與穩定度。因此，為了克服此問題，輸入EMI濾波器之輸出阻抗 ，必須滿足某些設計條件。
本論文中，吾人分別求出在電壓及電流控制時，DC/DC轉換器的小訊號控制方塊圖。並應用EET理論，分別推導DC/DC轉換器在電壓及電流控制時，輸入EMI濾波器的輸出阻抗 之設計條件。依此條件，即可設計具有抑制高頻雜訊功能的輸入濾波器。
若輸入EMI濾波器為 低通電路，則必須加入阻尼電阻，以抑制輸入濾波器之輸出阻抗 的共振峰值，才能滿足設計條件。此外，輸入EMI濾波器對直流匯流排汚染DC/DC轉換器之雜訊，及DC/DC轉換器汚染直流匯流排之雜訊，具有相同的濾波能力，符合互易定理。
最後，吾人實現一組輸入電壓 、輸出電壓 及輸出功率 之降壓型轉換器，應用三種不同元件值的輸入濾波器，分別加入DC/DC轉換器中，並以輸入電壓變動及負載變動，驗證輸入濾波器，對DC/DC轉換器閉迴路系統之性能與穩定度的影響。

In general, the closed-loop system of a DC/DC converter, connected to DC bus, is well designed with good performance and stability. However, an input EMI filter is needed between the DC/DC converter and DC bus to eliminate the high frequency noise. The noise on the DC bus is kept away from disturbing the operation of the DC/DC converter, and the switching frequency harmonics noise of the DC/DC converter is prevented from polluting the DC bus. However, the performance and stability of the closed-loop system of a DC/DC converter may be affected by an adding input EMI filter. To overcome this problem, the output impedance of the input EMI filter must comply with some design criteria.
The small-signal block diagram of a DC/DC converter for the voltage or current feedback control is derived individually in the thesis. Applying Extra Element Theorem (EET) to the block diagram, the design criteria for output impedance of input EMI filter is thereby obtained separately for voltage or current feedback control. An input EMI filter based on the design criteria is then constructed to suppress the high frequency noise.
If the input EMI filter is an lowpass circuit, a damping resistor is required to pull down the resonant peak of the output impedance to meet the design criteria. In addition, the capabilities of input EMI filter prevent noise on the DC bus from disturbing the operation of the DC/DC converter, and also prevent noise on the DC/DC converter from reducing DC bus quality. The noise suppression capabilities of the input EMI filter conform with Reciprocity Theorem.
Finally, for input and output, a prototype of the buck converter is established. Then three input EMI filters of the DC/DC converters are investigated. The effects on the performance and stability of the closed-loop system of a DC/DC converter with input EMI filter are verified by the experimental results in the presence of the variations of input voltage and load resistance.

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