TL431 Volt ref

s this component in falstad a tl431

Ask QuestionAsked 2 days agoActive todayViewed 57 times2

I’m self studying electronics, I am now familiarizing myself with the tl431, which is pretty much a “variable zener” aparently.

I was shown the following symbol. 

I would like to simulate some circuits with it on falsad, I found this component, that looks pretty much alike and is called “SCR”, after trying some circuits, I’m no longer sure it’s the same component.

enter image description here

The question:

Is that a tl431?

If it is not, can I sumulate Tl431 in falstad?simulationscrtl431falstadShareCiteEditFollowFlagasked 2 days agoJoaquin Brandan23111 silver badge66 bronze badges

  • 1#Joaquin Brandan, I have been playing with TL431 for a couple of years, mainly as a precision voltage reference for ADC. (1) TL431 / TL432 Precision Programmable Reference Datasheet – TI 2018: ti.com/lit/ds/symlink/tl431.pdf?. TL431 is definitely not a SCR. Cheers. – tlfong01 2 days ago    
  • 1No, an SCR/thyristor is not a zener diode. – DKNguyen 57 mins ago

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2 Answers


No, it’s nothing like the same part. One is (more or less) an op-amp + reference, the other is a thyristor.

As far as I know there is no support in Falstad for adding SPICE models as in full-featured circuit simulators such as PSpice or LTspice.ShareCiteEditFollowFlaganswered 2 days agoSpehro Pefhany284k1212 gold badges239239 silver badges597597 bronze badges

  • 1Thanks, I will try out some of the web based spice simulators to see if I can find one that has this particular component then. – Joaquin Brandan 2 days ago
  • 3@JoaquinBrandan Why use web-based ones when you can just grab LTspice for free? – Hearth yesterday
  • 1Because I make online notes that I leave for my future self as reference as I study, and I like to leave links in those notes that redirect me to the simulated examples that I used to explain the material so that I can quickly click on the link, fiddle with the simulator and quickly recall what was it all about. – Joaquin Brandan yesterday 
  • 3Your future self might find these links broken or that those online simulators do not exist anymore. – Mike yesterday

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Is Falstad TL431 same as Texas Instrument TL431?


I have been playing with Texas Instrument TL431 for a couple of years, mainly as a precision voltage reference for ADC. TL431 is definitely not a SCR.


Discussion and Recommendation

I have been using Zener diode for ages, but I don’t like it. The reasons are:

  1. They are not “precise”. I usually buy a couple of a particular value, say 3.0V Zener, but found them some 3.0V, some 3.2V etc.
  2. The don’t have a “continuous” range. Eg, I can buy 3.0V Zener, but the next big step is 3.5V. In other words, it is too discrete.
  3. So as a analog voltage reference to ADC etc, I just buy special purpose, fixed factory trimmed voltage reference ICs at as 1.024V, 2.5V, at 4.096V.
  4. TL431 is good for prototyping and flexibility. However, as shunt regulators, they are a bit hard and also time consuming to “program”.


(1) TL431 / TL432 Precision Programmable Reference Datasheet – Texas Instrument 2018


Appendix A – TL431 Lab Log

tl431 1

tl431 2

kl431 3

kl431 4

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