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Last updated: September 22, 2025

Programmable Zener Diode Circuit Using LM431 Adjustable IC

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LM431 Voltage Regulator

LM431 Voltage Regulator

A programmable shunt voltage regulator that provides an adjustable output voltage (typically 2.5V to 36V), used for precision voltage reference and regulation in power supplies and control circuits.

10K Fixed Resistor

10K Variable Resistor

Adjustable resistor with 10,000 ohm resistance

1K Fixed Resistor 1/4W

1K Fixed Resistor 1/4W

A 1,000-ohm resistor rated for 0.25 watts

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Programmable Zener Diode

Create a programmable zener diode using LM431 to provide an adjustable reference voltage. Ideal for DIY voltage regulation, hobby electronics, and precision circuits.

adjustable zener diode project

LM431 is a programmable zener diode that can be used as a voltage reference. Simple voltage regulation and control of an IC can be done by connecting a resistor divider to the IC.

LM431 programmable zener

The Programmable Zener Diode with LM431 enables you to make a variable reference voltage for a range of uses in electronics. LM431 is a shunt regulator IC that acts as a zener diode with a fixed adjustable voltage output. With the addition of a voltage divider (resistors) between the output and reference pin, the output voltage can be adjusted between 2.5 V and all the way to the supply voltage. The circuit has broad applications in fine voltage regulation, variable power supply, and in hobby electronics projects. It may substitute fixed zener diodes in case a certain voltage is needed. Stability and low ripple are achieved by proper selection of resistors and capacitors. The LM431 has the capability of moderate current, and a further transistor may be added to increase the current capacity. This arrangement is small, economical, and would suitably suit students and electronics hobbyists who would experiment with voltage references.

Work / Installation (Inputs → Outputs)

  • Input Supply → Provide DC voltage slightly higher than desired output.
  • LM431 IC → Acts as adjustable shunt regulator.
  • Voltage Divider → Resistors between output and reference pin set output voltage.
  • Optional Capacitors → Filter output for stability.
  • Output → Provides precise programmable reference voltage.
  • Installation → Assemble on PCB, connect input, resistors, and load; test output voltage and adjust resistors to set desired voltage.

Testing & Final Adjustments

Once it is assembled, input the voltage and test the output on a multimeter. Tilt the values of resistors in the voltage divider to obtain the desired voltage. LM431 is heat-sinked on the heat sink side when used at higher currents. Check stability with the output with and without the load. To get more current output, a transistor may be connected in parallel with the shunt regulator. The voltage is kept constant by testing different loads to ensure that it is functioning properly. The circuit is a safe, adjustable, and accurate voltage reference for hobby electronics, an adjustable power supply, and other low-power precision applications.

Frequently Asked Questions - Programmable Zener Diode:

What is LM431?

LM431 is an adjustable shunt voltage regulator IC.

Can it replace a zener diode?

Yes, it acts like a programmable zener diode.

What voltage range is possible?

From 2.5V up to the supply voltage, adjustable via resistors.

Do I need resistors?

Yes, a voltage divider sets the output voltage.

Can it handle high current?

Moderate current; use an external transistor for higher loads.

Is it stable?

Yes, with proper capacitors and resistor selection.

Applications?

Voltage reference, adjustable power supply, hobby projects.

Is it beginner-friendly?

Yes, simple assembly with basic electronics knowledge.

Do I need a heat sink?

Recommended for higher currents to prevent overheating.

Can it be used with LEDs?

Yes, for precise voltage regulation in LED circuits.

Rojony Khatun

Rojony Khatun

CalculatorToolsProject

Rojony Khatun is the creator of a free online tools website designed to simplify everyday and engineering-related calculations for students, professionals, and hobbyists. The platform offers a wide variety of basic and advanced calculators across key categories, including Electrical Calculators, Electronic Calculators, and Time & Date Calculators, helping users solve problems quickly and accurately.