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Project Notes

#360 TL431 Shunt Regulator

Testing a TL431 voltage reference (regulator) circuit with manual coarse and fine trim.



The TL431 Precision Programmable Reference is a cheap and easily adjustable shunt regulator. The standard grade offers a reasonable 2% reference voltage tolerance.

In this mini-circuit I am testing the common application as a shunt regulator/reference voltage e.g. for use in power supplies. This just requires a voltage divider (R1, R2) across Vref (2.5V). The output voltage will then be:

Vout = (1 + R1/R2) * Vref

For adjustment, I’m using two variable pots to provide course and fine grained control:

R1 Range R2 Trim Range
Min: 0Ω 105kΩ - 110kΩ
Max: 100kΩ 5kΩ - 10kΩ


See the schematic in EasyEDA.


First testing on a breadboard:


I put the circuit on some protoboard to improve the stability:



Under test. Set to 4.00V, remains stable as long as input voltage is > Vout.


Here’s a very unexciting demonstration of a quick test:


Credits and References

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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.