TL431 Calculator

This TL431 calculator will help you calculate:

Output Voltage based on resistor divider.
Optionally calculate R1 or R2 if you fix output voltage then.
Use internal reference voltage = 2.5V (default for TL431).

TL431 regulates like this:

Vout = Vref × (1 + R1 / R2)

Where:

• Vref = 2.5V (internal reference of TL431)
• R1 = Top resistor (from OUT to REF)
• R2 = Bottom resistor (from REF to GND)
• Vout = Output voltage (between OUT and GND)

Tips on Using TL431:

Connect R1 between OUT and REF,

Connect R2 between REF and GND,

Vout is taken from OUT pin,

TL431 will adjust its cathode voltage to make REF = 2.5V.