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LM431 Adjustable Shunt Regulator: Pinout, Circuit, Datasheet [Video]

  • Contents

 

In today's blog, I'll introduce LM431 systematically from pinout, features, to its manufacturer, datasheet, and so on.

The LM431 is a 3-terminal adjustable shunt regulator with ensured temperature stability over the entire temperature range of operation. The output voltage may be set at any level greater than 2.5 V (VREF) up to 36 V merely by selecting two external resistors that act as a voltage divided network. Due to the sharp turnon characteristics, this device is an excellent replacement for many Zener diode applications. The LM431 is available in space-saving SOIC-8, SOT-23, and TO-92  packages.

LM431 adj precision zener shunt regulator component wired as low 9V battery indicator circuit

Catalog

LM431 Pin Configuration and Function

LM431 Features

LM431 Alternatives

LM431 Functional Equivalents

LM431 Package Outline

LM431 Applications

How to Use LM431

LM431 Manufacturer

Component Datasheet

FAQ

Ordering & Quantity

LM431 Pin Configuration and Function

LM431 Pin

LM431 pin function


LM431 Features

  • Average Temperature Coefficient of 50 ppm/°C

  • Temperature Compensated for Operation Over the Full Temperature Range

  • Programmable Output Voltage

  • Fast Turnon Response

  • Low-Output Noise

  • Low-Dynamic Output Impedance

  • Available in Space-Saving SOIC-8.  SOT-23, and TO-92  Packages

LM431 Alternatives

LM432, NJM2820, NJM2821, NJM2822, ZXRE060


LM431 Functional Equivalents

Part Number

Description

Manufacturer

LM431BIZPOWER CIRCUITS

1-OUTPUT TWO TERM VOLTAGE REFERENCE, 2.495V, PBCY3, PLASTIC, TO-92, 3 PIN

Texas Instruments

LM431AIZXAPOWER CIRCUITS

Two Terminal Voltage Reference, 1 Output, 2.5V, Trim/Adjustable, PBCY3, TO-92, 3 PIN

Rochester Electronics LLC

LM431BIZXAPOWER CIRCUITS

Two Terminal Voltage Reference, 1 Output, 2.495V, Trim/Adjustable, PBCY3, TO-92, 3 PIN

Rochester Electronics LLC

LM431BCZXAPOWER CIRCUITS

Adjustable/2.5 V, 1% Tolerance Shunt Regulator, 3 LD, TO92, MOLDED 0.200 IN LINE SPACING LD FORM, 2000/AMMO

Fairchild Semiconductor Corporation

LM431ACZPOWER CIRCUITS

IC 1-OUTPUT TWO TERM VOLTAGE REFERENCE, 2.495 V, PBCY3, PLASTIC, TO-92, 3 PIN, Voltage Reference

National Semiconductor Corporation

LM431AIZPOWER CIRCUITS

Adjustable/2.5 V, 2% Tolerance Shunt Regulator, 3LD, TO92, JEDEC TO-92 COMPLIANT STRAIGHT LEAD CONFIGURATION (OLD TO92AM3), 10000/BULK

Fairchild Semiconductor Corporation

LM431AIZ/NOPBPOWER CIRCUITS

2%, 1%, or 0.5% accuracy, adjustable precision Zener shunt regulator 3-TO-92 -40 to 85

Texas Instruments

LM431CCZPOWER CIRCUITS

IC 1-OUTPUT TWO TERM VOLTAGE REFERENCE, 2.5 V, PBCY3, PLASTIC, TO-92, 3 PIN, Voltage Reference

National Semiconductor Corporation

LM431ACZ/NOPBPOWER CIRCUITS

2%, 1%, or 0.5% accuracy, adjustable precision Zener shunt regulator 3-TO-92 0 to 70

Texas Instruments

LM431CIZ/LFT1POWER CIRCUITS

Adjustable Precision Zener Shunt Regulator 3-TO-92

Texas Instruments


LM431 Package Outline

  • SOIC-8

LM431(SOIC-8 Package)

LM431(SOIC-8 Package)LM431(SOIC-8 Package)

LM431(SOIC-8 Package)

  • SOT-23

LM431 in SOT-23 Package

LM431(SOT-23 Package)

LM431(SOT-23 Package)

LM431(SOT-23 Package)

LM431(SOT-23 Package)

  • TO-92

LM431 in TO-92 PackageLM431(TO-92 Package)

LM431(TO-92 Package)

LM431(TO-92 Package)

LM431(TO-92 Package)


LM431 Applications

  • Adjustable Voltage or Current Linear and Switching Power Supplies

  • Voltage Monitoring

  • Current Sourse and Sink Circuits

  • Circuits Requiring Precision References

  • Zener Diode Replacements


How to Use LM431?

Before going for the application circuit of LM431, let us first understand the internal working of the device and for that consider the functional diagram of the device as shown below.

LM431 Block Diagram  LM431 Symbol

 

In the LM431 functional diagram, we have three main devices namely Op-amp, NPN transistor, and +2.5V voltage source. Based on the working of the op-amp, the output voltage Vo/p will be positive only when Vref >+2.5V because the voltage at inverting terminal of the op-amp is +2.5V.

 

Now let us consider a simple application circuit for the device as shown below:

LM431 Application Circuit

Here reference voltage (Vref) is the voltage at the non-inverting terminal of the op-amp and this voltage determines whether the op-amp outputs positive voltage or not. Also, Vref is the voltage at the midpoint voltage divider network formed by the two resistors R2 and R3. Based on the concept of voltage division we have Vref = Vo(R3/R2+R3). By exchanging terms we have Vo = Vref(R2+R3/R3) = Vref(1+R2/R3) = 2.5(1+R2/R3). Based on the equation you can adjust two resistor values in the circuit to get the desired output voltage.

Working Principle of the Circuit: 

The op-amp here keeps comparing the voltage at the non-inverting terminal which is Vref (which is directly related to output voltage) with +2.5V (the voltage connected to inverting terminal by default) and depending on the result the op-amp triggers the transistor to draw current from the source V1. Whenever the output crosses the threshold (threshold is the value determined by R2 and R3 value) the op-amp get feedback via Vref and it drives the transistor ON. When the transistor turns ON the device draws current and because of this current drawing a voltage drop appears across R1 resistor which is in series with voltage source V1.

Because of this drop, we have Vo = V1 – (R1) * (Ic). Here Ic is the current drawn by the transistor. Also, the current draw by op-amp and resistor network is neglected for easy explanation.

The op-amp turns ON transistor up to a point where it’s current drawing leads to lowering Vo (by R1 voltage drop) from V1 to Vref(1+R2/R3).

So in the final result, Vo will always be adjusted to float near the measured value by op-amp setup (or LM431).  In a similar way, we can setup other application circuits.


LM431 Manufacturer

Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog chips and embedded processors, which account for more than 80% of its revenue. TI also produces TI digital light processing technology and education technology products including calculators, microcontrollers and multi-core processors. The company holds 45,000 patents worldwide as of 2016.


Component Datasheet

LM431 Datasheet


FAQ

  • What is the LM431?

3 terminal adjustable shunt regulator.

 

  • What is the output voltage of the LM431?

2.5 V (VREF) up to 36 V

 

  • What are the derivatives of LM431?

TL432, ATL431, KA431, LM431, TS431, 142ЕН19 and others.

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