混合電源中線性穩(wěn)壓器噪聲的理解

　　在許多應(yīng)用中，工程師團(tuán)隊(duì)的開(kāi)關(guān)DC-DC電壓轉(zhuǎn)換器（“開(kāi)關(guān)穩(wěn)壓器”）與低輟學(xué)線性穩(wěn)壓器（LDO）。這樣的混合電源是一個(gè)很好的方法，以最大限度地提高電池壽命，同時(shí)保持無(wú)噪聲電壓供應(yīng)適合電池供電的產(chǎn)品與敏感的模擬電路。

　　然而，“無(wú)噪音”只是相對(duì)而言的，因?yàn)榧词故亲詈玫腖DO產(chǎn)生一些噪聲。許多工程師認(rèn)為在LDO的輸出噪聲是一個(gè)簡(jiǎn)單的電源抑制比（PSRR）功能。當(dāng)使用一個(gè)開(kāi)關(guān)穩(wěn)壓器系列，PSRR的確是一個(gè)很好的衡量LDO處理電壓和電流紋波的開(kāi)關(guān)穩(wěn)壓器的輸出–但比不應(yīng)該是唯一的標(biāo)準(zhǔn)時(shí)，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.