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TL431 – Programmable Reference Voltage

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The TL431 is a regulator diode whose output voltage can be programmed by changing the value of resistors connected to it. It acts almost like a Zener diode except for that the voltage rating of this IC is programmable. It is commonly used to provide negative or positive voltage references.


Pin Configuration

Pin Number

Pin Name




This pin sets the voltage rating of the Zener diode.



Anode of the equivalent Zener diode



Cathode of the equivalent Zener diode



  • Programmable Zener diode
  • Output voltage: 2.5V to 36V
  • Output Current: 1mA to 100mA (sink current)
  • Output voltage tolerance: ±4%
  • Output Impedance: 0.22 ohms
  • Available in To-92(3-pin) and PDIP,SOIC (8-pin) Package


Note: Complete Technical Details can be found at the TL431 datasheet given at the end of this page.


TL431 Alternative

Zener diodes



TLV431, TS431LI, LM431


TL431 Overview

The TL431 is a programmable shunt regulator which can provide both positive and negative reference voltages. It is a Zener diode whose voltage rating can be adjusted based on the value of resistors connected to the reference pin. It is commonly used as a low cost reference voltage provider in isolated power supply circuits.

TL431 Internal Circuit Diagram

From the internal circuit diagram of the IC shown above we can notice that it consists of a NPN transistor with an op-amp that has a precise voltage of 2.5V on the non-inverting terminal.  The collector and emitter pin of the transistor forms the cathode and the anode terminal of the IC respectively.  Now you can think of the IC as a comparator with one side of the comparator having a precise 2.5V and the other side can be set using the reference pin.

This property comes in very handy for switching power supplies where the TL431 can used to compare the output voltage with desired voltage and provide a feedback to control switching frequency. Normally an Optocoupler is used along with this set-up to isolate the high voltage side. Apart from this the IC finds applications in many circuits where a Zener diode can be used few of them are listed below.



  • Switch mode Power supplies
  • Isolated Power supply circuits
  • Voltage comparators
  • Current Regulation circuits


2D model (TO-92)

The IC is also available in 8-pin package. The dimensions of TO-92 package is shown below

TL431 Dimensions

Component Datasheet