LM317 Calculator

The LM317 is one of the most widely used adjustable voltage regulators in electronics. It provides a stable output voltage from a higher input voltage, making it ideal for powering sensitive electronic components. Whether you are building a custom power supply or powering devices that require a specific voltage, the LM317 is a versatile and reliable choice.

LM317 Voltage Regulator

The LM317 is an adjustable linear voltage regulator. It can output a range of voltages between 1.25V and 37V, depending on the resistors used in the circuit. It has three main pins:

• Input pin (Vin): The pin where the unregulated input voltage is supplied.
• Output pin (Vout): The pin that provides the regulated output voltage.
• Adjust pin: This pin is used to set the output voltage via external resistors.

LM317 Regulator Working

The LM317 works by using a reference voltage of 1.25V at the adjust pin. To achieve the desired output voltage, the regulator uses two external resistors (R1 and R2) to form a voltage divider, which sets the output voltage according to the following formula:

Vout = Vref x (1 + R2 / R1)

Where:

• Vout is the desired output voltage.
• Vref is the reference voltage (1.25V for LM317).
• R1 and R2 are the external resistors connected to the LM317.

The formula indicates that by adjusting the values of R1 and R2, you can vary the output voltage, which allows you to use the LM317 in a wide range of applications.

Key Features of the LM317

• Adjustable Output Voltage: You can set the output voltage anywhere between 1.25V and 37V.
• Current Limiting: The LM317 includes current limiting, thermal overload protection, and safe operating area (SOA) protection to prevent damage to the regulator and connected components.
• Easy to Use: It is widely available, inexpensive, and easy to implement into a project with just a few external components.

How to Use LM317 Calculator?

Above you have a simple LM317 Voltage Regulator Calculator. This tool allows users to calculate either the output voltage (Vout) or the necessary resistor values (R1 and R2) based on user input. The calculator works by performing real-time calculations when you enter values for R1, R2, and Vout.

1. Enter Resistor Values (R1 and R2):

If you already know R1 and R2, simply input their values into the respective fields. The calculator will then compute the output voltage using the formula:

Vout = 1.25V x (1 + R2 / R1)

Example: If R1 = 240Ω and R2 = 720Ω, the output voltage would be:

Vout = 1.25V x (1 + 720 / 240) = 1.25V x 4 = 5V

The calculator would show Vout = 5V.

2. Enter Desired Output Voltage (Vout):

If you know the desired output voltage (Vout) and want to calculate the resistor values, you can input the value of Vout into the input field. The calculator will automatically compute R2 based on the following formula:

R2 = ((Vout / Vref) - 1) x R1

Example: If you want a Vout = 5V and have chosen R1 = 240Ω, the calculator will calculate R2 as follows:

R2 = ((5 / 1.25) - 1) x 240 = 720Ω

Example: Designing a 9V Regulator with LM317

Let’s say we want to design a 9V regulator using the LM317, and we have R1 = 240Ω.

Vout = 1.25V x (1 + R2 / R1)

Set Vout = 9V, solve for R2:

9 = 1.25 x (1 + R2 / 240)
R2 = 1488Ω

So, to design a 9V regulator with R1 = 240Ω, you would need R2 = 1488Ω. You could use the calculator to verify or adjust these values for your specific needs.

Common Applications of LM317

• Powering LED Strips: Regulates voltage for consistent brightness and long life.
• Battery Chargers: Creates charging circuits for various battery types.
• DIY Power Supplies: Ideal for hobbyists building custom power supplies.

Conclusion

The LM317 is a versatile and reliable voltage regulator that offers adjustable output voltage, making it ideal for a wide variety of applications. By using the LM317 Voltage Regulator Calculator, you can quickly calculate the required resistor values or the output voltage based on your design needs. With a basic understanding of the formulas involved, you can confidently build your own power supply circuits and modify existing ones to meet specific voltage requirements.