TL431 Voltage Reference Calculator

Input Voltage (V): Resistor R1 (kΩ): Resistor R2 (kΩ):

Calculate Reference Voltage

Reset

Formula and Usage Instructions

Formula for TL431 Output Voltage:

The output voltage (Vout​) of a TL431 shunt voltage regulator is determined by the following formula:

Vout=Vref×(1+R1/R2)

Where:

• Vref​ is the reference voltage of the TL431, which is typically 2.495V.
• R1​ is the first resistor (in kΩ) connected between the reference pin and cathode pin of the TL431.
• R2​ is the second resistor (in kΩ) connected between the reference pin and anode pin of the TL431 (negative rail).

This formula calculates the output voltage based on the resistor values provided by the user. The TL431 regulates the output voltage by adjusting the ratio of the resistors R1 and R2 to set the desired voltage.

How to Use the Calculator:

1. Input Voltage (Vin):
   • Enter the input voltage (in volts) that your circuit will be using. This value does not directly affect the TL431’s output voltage, but it’s typically the operating voltage of the system you’re working with.
   • Note: The TL431 works with input voltages between 2.5V and 36V. If the input voltage is outside this range, the calculator will display an error message.
2. Resistor R1 (kΩ):
   • Enter the value of the first resistor (R1​) in kilo-ohms (kΩ).
   • This resistor is connected between the reference pin and cathode pin of the TL431.
3. Resistor R2 (kΩ):
   • Enter the value of the second resistor (R2​) in kilo-ohms (kΩ).
   • This resistor is connected between the reference pin and anode pin of the TL431 (negative rail).
4. Calculate the Output Voltage:
   • Once you have entered all the values, click on the Calculate button.
   • The calculator will then compute the output voltage based on the formula and display the result below.
5. Reset the Calculator:
   • If you need to reset the inputs and results, click on the Reset button. This will clear all fields and hide the results, allowing you to start over with new values.

Important Notes:

• TL431 Voltage Range: The TL431 operates correctly with input voltages between 2.5V and 36V. If the input voltage exceeds or falls below this range, it may lead to unpredictable behavior or damage the TL431 IC.
• Resistor Selection: Make sure the resistor values you choose for R1​ and R2​ are within practical limits. Typically, resistors are selected in the range of kΩ (1kΩ to 100kΩ), but the exact values will depend on your desired output voltage. Resistor Rseries doesn’t have any role in reference voltage but being in series it limits the current to keep the TL431 current within maximum operating limit.

By using this calculator, you can easily determine the required resistor values to set your desired output voltage with the TL431 reference IC.