Shunt Regulators

Architectures

• Two-pin shunt regulators
• Three-pin shunt regulators

Three-Pin Shunt Regulators

A three-pin shunt voltage regulator is typically drawn as a Zener diode with a third pin coming from the middle and out to the side.

The schematic symbol for a three-pin shunt voltage regulator, with the pin names also shown.

This can be confusing, as a three-pin shunt regulator is an IC (integrated circuit) that typically contains an op-amp and a BJT along with a precision voltage reference! This is also reflected by the U IC designator prefix which is commonly used for these devices. The following image shows what actually is inside one of these devices:

The internal functional diagram of a three-pin shunt regulator. Note that there is much more to one of these than just a simple Zener diode! Image from the LM431 datasheet.¹

Manufacturer Part Numbers

• 431: Very common shunt regulator.
• LM431: Shunt regulator from Texas Instruments based on the 431 series.

See Also

• Linear Regulators: The series-pass counterpart to the shunt regulator.

Footnotes

1. Texas Instruments. LM431 Adjustable Precision Zener Shunt Regulator [datasheet]. Retrieved 2021-01-26, from https://www.ti.com/lit/ds/symlink/lm431.pdf. ↩