混合電源中線性穩壓器噪聲的理解

　　在許多應用中，工程師團隊的開關DC-DC電壓轉換器（“開關穩壓器”）與低輟學線性穩壓器（LDO）。這樣的混合電源是一個很好的方法，以最大限度地提高電池壽命，同時保持無噪聲電壓供應適合電池供電的產品與敏感的模擬電路。

　　然而，“無噪音”只是相對而言的，因為即使是最好的LDO產生一些噪聲。許多工程師認為在LDO的輸出噪聲是一個簡單的電源抑制比（PSRR）功能。當使用一個開關穩壓器系列，PSRR的確是一個很好的衡量LDO處理電壓和電流紋波的開關穩壓器的輸出–但比不應該是唯一的標準時，LDO的選擇。

　　The LDO has several sources of internal noise generated from its internal components and， worse still， some of this is frequency dependent. It is this combination of PSRR and internal noise that determines the stability of the LDO’s output.

　　This article explains how combining a switching regulator with an LDO can be a good solution for connected， wireless portable products， then leads on to explain why it is important that an engineer analyze the LDO’s datasheet to ensure that its overall noise from the power supply remains within the end-product specification.