## Saturday, May 13, 2023

LM317 – Circuit for variable voltage regulator

LM317 – Introduction

The LM317 is a dimmable power supply. In this tutorial you will learn how to set up your circuit to design a voltage source. The LM317 regulator has different configuration circuits. In this tutorial we will see the LM317 circuit to configure it as a variable source from 1.25V to 30V. At the end of the tutorial you will find the LM317 datasheet. It should also be noted that it is one of the most used regulators because it is variable.

The LM317 regulator has different configurations or circuits according to the application. For example, it can be a voltage regulator from 0 to 30V or from 1.25 to 30V. Its variability is controlled by different arrangements.

The LM317 circuit is also shown to design an adjustable source from 1.25V. For this circuit only 2 components are required, a 1kohm resistor and a 20Kohm potentiometer.

What is a voltage source

A voltage source is a circuit like this that can provide a constant voltage and current. For this purpose the LM317 circuit requires an input voltage source. For example, the difference between the input and the output of the LM317 regulator should be a minimum of 3V and a maximum of 40V.

The LM317 voltage regulator has the feature of having a variable setting. This adjustable source is controlled via a variable resistor.

The main function of a voltage source is to supply the power that the load needs. For example, a 4.5V DC motor at 1A will require at least a source that can supply 4.5W continuously. Remember that P = VI. The following image shows an example of a dimmable power supply.

Pinout or pins of the LM317

The LM317 regulator has 3 connection pins. Basically they are the Adjustment pin, the regulated output pin and the input pin. These pins connect to the various configuration circuits. In Figure-1, a diagram of the TO-220 packaging is shown.

LM317 regulator and its main features

A voltage input is necessary for the voltage regulator. In this case the LM317 circuit can be fed with an input voltage that is at least 3V different from the desired output voltage. That is, if you want to regulate from 1.25 to 5 volts, a minimum 8V input source is required. This source can be the regulated voltage from a transformer or an external 9V/12V regulator.

output current. For the regulator the output current depends on the voltage difference between the output and the input voltage. There are two important ranges:

From 1.5A to 2.5A when the difference is less than 15V.

From 0.15A to 0.4A for when the difference between the regulator and its input is up to 40V and up to 15V.

Despite this, the recommended rated output current is 0.01A to 1.5A.

Input voltage. There must be a minimum difference of 3V between the input and the regulated output.

3V to 40V.

Output voltage.

From 1.25V to 37V.

LM317 circuit

The LM317 Circuit has different configurations to regulate the voltage. For example, the most used configuration is the variable regulator from 1.5V to 37V. To achieve this dimmable power supply, the following circuit is required to be connected. For this source, a 1kOhm resistor and a 20k potentiometer are required. Then, two of the potentiometer's terminals will be connected together (one in the center and one on the edge). These connections will be attached to the terminal of the resistor and the adjustment pin of the regulator. Also the other terminal of the potentiometer is connected to ground as well as the ground of the input source. The output of the regulated voltage (the center pin), is connected to the terminal of the 1k resistor. Finally, the positive of the input source is connected to pin 3. The following figure shows the resulting circuit.

Precautions to consider when using the LM317

The precautions to consider when using the LM317 are mainly related to heat dissipation. For example, if we have a 5V regulated output and we have a load that requires a constant 1A, we would be having an output power P = 5V*1A = 5W. So we have to have a way to dissipate the heat that this load is generating in the regulator. It is then very important to have a heatsink that can disperse the heat generated. A heatsink can be a piece of aluminum that is attached to one face of the voltage regulator.

LM317 – Circuit for variable voltage regulator

LM317 – Introduction

The LM317 is a dimmable power supply. In this tutorial you will learn how to set up your circuit to design a voltage source. The LM317 regulator has different configuration circuits. In this tutorial we will see the LM317 circuit to configure it as a variable source from 1.25V to 30V. At the end of the tutorial you will find the LM317 datasheet. It should also be noted that it is one of the most used regulators because it is variable.

The LM317 regulator has different configurations or circuits according to the application. For example, it can be a voltage regulator from 0 to 30V or from 1.25 to 30V. Its variability is controlled by different arrangements.

The LM317 circuit is also shown to design an adjustable source from 1.25V. For this circuit only 2 components are required, a 1kohm resistor and a 20Kohm potentiometer.

What is a voltage source

A voltage source is a circuit like this that can provide a constant voltage and current. For this purpose the LM317 circuit requires an input voltage source. For example, the difference between the input and the output of the LM317 regulator should be a minimum of 3V and a maximum of 40V.

The LM317 voltage regulator has the feature of having a variable setting. This adjustable source is controlled via a variable resistor.

The main function of a voltage source is to supply the power that the load needs. For example, a 4.5V DC motor at 1A will require at least a source that can supply 4.5W continuously. Remember that P = VI. The following image shows an example of a dimmable power supply.

Pinout or pins of the LM317

The LM317 regulator has 3 connection pins. Basically they are the Adjustment pin, the regulated output pin and the input pin. These pins connect to the various configuration circuits. In Figure-1, a diagram of the TO-220 packaging is shown.

LM317 regulator and its main features

A voltage input is necessary for the voltage regulator. In this case the LM317 circuit can be fed with an input voltage that is at least 3V different from the desired output voltage. That is, if you want to regulate from 1.25 to 5 volts, a minimum 8V input source is required. This source can be the regulated voltage from a transformer or an external 9V/12V regulator.

output current. For the regulator the output current depends on the voltage difference between the output and the input voltage. There are two important ranges:

From 1.5A to 2.5A when the difference is less than 15V.

From 0.15A to 0.4A for when the difference between the regulator and its input is up to 40V and up to 15V.

Despite this, the recommended rated output current is 0.01A to 1.5A.

Input voltage. There must be a minimum difference of 3V between the input and the regulated output.

3V to 40V.

Output voltage.

From 1.25V to 37V.

LM317 circuit

The LM317 Circuit has different configurations to regulate the voltage. For example, the most used configuration is the variable regulator from 1.5V to 37V. To achieve this dimmable power supply, the following circuit is required to be connected. For this source, a 1kOhm resistor and a 20k potentiometer are required. Then, two of the potentiometer's terminals will be connected together (one in the center and one on the edge). These connections will be attached to the terminal of the resistor and the adjustment pin of the regulator. Also the other terminal of the potentiometer is connected to ground as well as the ground of the input source. The output of the regulated voltage (the center pin), is connected to the terminal of the 1k resistor. Finally, the positive of the input source is connected to pin 3. The following figure shows the resulting circuit.

Precautions to consider when using the LM317

The precautions to consider when using the LM317 are mainly related to heat dissipation. For example, if we have a 5V regulated output and we have a load that requires a constant 1A, we would be having an output power P = 5V*1A = 5W. So we have to have a way to dissipate the heat that this load is generating in the regulator. It is then very important to have a heatsink that can disperse the heat generated. A heatsink can be a piece of aluminum that is attached to one face of the voltage regulator.