可調(diào)參考電壓源：Adjustable Voltage Ref

Adjustable voltage reference circuits are shown in Figures 19, 20, 21, 22. The two circuits shown have different areas of applicability. The basic difference between the two is that Figures 19, 20 illustrate a voltage source which provides a voltage greater than the reference diode while Figures 21, 22 illustrates a voltage source which provides a voltage lower than the reference diode. The figures show both positive and negative voltage sources.
High precision extended temperature applications of the circuit of Figures 19, 20 require that the range of adjustment of VOUT be restricted. When this is done, R1 may be chosen to provide optimum zener current for minimum zener T.C. Since IZ is not a function of V+, reference T.C. will be independent of V+.
The circuit of Figures 21, 22 are suited for high precision extended temperature service if V+ is reasonably constant since IZ is dependent on V+. R1, R2, R3, and R4 are chosen to provide the proper IZ for minimum T.C. and to minimize errors due to Ibias.
The circuits shown should both be compensated for unity-gain operation or, if large capacitive loads are expected, should be overcompensated. Output noise may be reduced in both circuits by bypassing the amplifier input.
The circuits shown employ a single power supply, this requires that common mode range be considered in choosing an amplifier for these applications. If the common mode range requirements are in excess of the capability of the amplifier, two power supplies may be used. The LH101 may be used with a single power supply since the common mode range is from V+ to within approximately 2 volts of V-.

可調(diào)電壓參考源的電路示于圖19、20、21、22中。圖中的兩種電路形式有著不同的應(yīng)用范圍，最基本的區(qū)別在于，圖19和20所示的電路可以提供大于電路中所使用的穩(wěn)壓二極管穩(wěn)定電壓的輸出電壓，而圖21和22中的電路的輸出電壓小于穩(wěn)壓管的穩(wěn)定電壓。在每種形式的電路中，又分別給出了正電壓和負電壓輸出的應(yīng)用電路。
由于溫度因素會影響精度，圖19、20中電路的輸出電壓范圍不能太寬。另外，由于Iz（流過穩(wěn)壓管的電流）與V+無關(guān)（僅取決于R1）， R1的取值應(yīng)該盡量使得穩(wěn)壓管的擊穿電流大小合適，借此來減小其溫度特性的影響。

圖21、22中的電路適合于要求在寬溫度范圍內(nèi)取得較好精度的情況下使用，由于Iz和V+有關(guān)，這種電路要求V+相對穩(wěn)定。R1、2、3、4應(yīng)該適當選擇，以給穩(wěn)壓管提供適當?shù)膿舸╇娏骱蜏p小其溫度特性的影響。
以上電路中的OP必須對單位增益做頻率補償，如果負載呈較大的容性，則可能需要做過補償。如果想減小輸出噪聲，可以在上述電路的輸入端采取旁路措施。
圖中的電源采用單電源供電，這就對OP的共模輸入范圍的選擇提出了要求，如果所要求的輸入電壓范圍超過共模輸入范圍，則應(yīng)該使用雙電源供電。LH101的共模電壓范圍達V+到V-之上2V，可以在單電源的情況下使用。