好聽的三端子穩壓 TL431 自激 震盪 問題解決

TL431、TL432是一組很棒的並聯穩壓器，
曾經拿過LM317、78系列、RC電晶體穩壓互相比較，
雖然TL431抗雜訊能力沒有很佳，但是是裡面聲音最清晰開闊的。


曾經把DAC都用上了TL431當穩壓，但是卻發現電壓開始產生震盪，

原來是TL431的抗負載電容能力不是相當的高，於是找了相關的Datasheet，
其中包誇TI、ON Semi、DIODES，不同廠商及型號都幾乎相同，
差別最大的是DIODES，抗負載能力也是較好的。

TI、ON Semi:The areas under the curves represent conditions
that may cause the device to oscillate. For curves B, C, and D, R2 and V+
 are adjusted to establish the initial VKA and IKA conditions, with CL = 0.
VBATT and CL then are adjusted to determine the ranges of stability

DIODES:The device is stable under all conditions with a load capacitance not exceeding 50pF.
The device is stable under all conditions with a load capacitance between 5nF and 20nF.
The device is stable under all conditions with a load capacitance exceeding 300nF.
With a cathode current not exceeding 5mA, the device is stable with any load capacitance.

 比較兩者，DIODES的穩定工作範圍較大，廣泛看來只要CL只要大於7uf都是safe area，
其中高電流並聯穩壓器的負載也是要在TL431的兩端加上符合的電容器

Stability considerations The physical position of C and its value is critical to maintaining good stability. C should be located in close physical proximity to the ZXRE060 and connected to its pins with the shorted andwidest possible copper track. The value of C required to ensure stability generally ranges from about 0.1μF up to 10 μF depending on application and environment with higher gain applications generally requiring smaller values.