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. enter image description here

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?

  • 1
    \$\begingroup\$ #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. \$\endgroup\$
    – tlfong01
    Mar 27, 2021 at 2:51
  • 2
    \$\begingroup\$ No, an SCR/thyristor is not a zener diode. \$\endgroup\$
    – DKNguyen
    Mar 29, 2021 at 2:10

2 Answers 2


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.

  • 1
    \$\begingroup\$ Thanks, I will try out some of the web based spice simulators to see if I can find one that has this particular component then. \$\endgroup\$ Mar 27, 2021 at 2:22
  • 4
    \$\begingroup\$ @JoaquinBrandan Why use web-based ones when you can just grab LTspice for free? \$\endgroup\$
    – Hearth
    Mar 27, 2021 at 3:23
  • 1
    \$\begingroup\$ Because 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. \$\endgroup\$ Mar 27, 2021 at 3:29
  • 6
    \$\begingroup\$ Your future self might find these links broken or that those online simulators do not exist anymore. \$\endgroup\$
    – Mike
    Mar 27, 2021 at 8:34


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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