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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

About LEAP#360 PowerRegulatorReference
Project Source on GitHub Return to the LEAP Catalog

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

LEAP is my personal collection of electronics projects, 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 (IMHO!).

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Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.