#360 TL431 Shunt Regulator

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

Notes

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:

Construction

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

• TL431 datasheet
• ..as mentioned on my blog