TL431 Reference voltage regulator IC

The TL431 is a highly popular, 3-terminal programmable precision shunt regulator IC. It functions as a tunable Zener diode, offering an internal reference voltage of 2.5 V (specifically 2.495 V) that can be adjusted up to 36 V using just two external resistors.

Key Specifications & Features

·         Output Voltage: Programmable from 2.5 V to 36 V.

·         Sink Current Capability: 1 mA to 100 mA.

·         Reference Voltage Tolerance: Typically 0.5% or 1%, depending on the grade.

·         Dynamic Impedance: Very low, typically 0.22 Ω.

·         Temperature Stability: Excellent, ensuring reliable operation across wide industrial/commercial temperature ranges.

 

Pin Configuration

The TL431 is commonly found in TO-92 (through-hole) or SOT-23 (Surface Mount - SMD) packages. The three pins are:

1.    Reference: The input to the internal error amplifier used to set the output voltage.

2.    Anode: The ground or return terminal.

3.    Cathode: The output/input terminal that sinks the regulator current.

 

How It Works & Common Applications

Internally, it integrates a bandgap reference, an error amplifier, and a shunt transistor. When paired with a voltage divider, it acts as a highly accurate, temperature-compensated reference source. Because it acts as an adjustable shunt regulator, it is predominantly used in:

·         Switch-Mode Power Supplies (SMPS):

Providing isolated feedback.

 

·         Battery Chargers:

Regulating voltage and current precisely.

 

·         Zener Diode Replacements:

Offering sharper, more predictable threshold voltages.

 

Design Resources

To calculate your exact resistor values or view schematic examples, you can use the interactive resources and datasheets below:

·         Circuit Examples:

Review schematic hookups and pinouts on different websites.

 

·         Official Data Sheet:

View maximum ratings and operational curves on Texas Instruments.