What is LM317T? Positive Adjustible Voltage Regulator

What is LM317T?

This is a popular adjustable voltage regulator integrated circuit (IC) that is widely used in electronic circuits for its versatile functionality. It is designed to provide a stable and adjustable output voltage, making it ideal for use in power supplies, battery chargers, and other applications where precise voltage regulation is required.

Part Number: LM317T

Function: Three-terminal adjustible output positive voltage regulator

Package: TO-220 type

Manufacturer: Motorola


LM317T voltage regulator


The LM317T is an adjustable 3–terminal positive voltage regulator capable of supplying in excess of 1.5 A over an output voltage range of 1.2 V to 37 V.

This voltage regulator is exceptionally easy to use and requires only two external resistors to set the output voltage. Further, it employs internal current limiting, thermal shutdown and safe area compensation, making it essentially blow–out proof.

The LM317 serves a wide variety of applications including local, on card regulation. This device can also be used to make a programmable output regulator, or by connecting a fixed resistor between the adjustment and output, the LM317 can be used as a precision current regulator.


LM317T datasheet


1. Output Current in Excess of 1.5 A
2. Output Adjustable between 1.2 V and 37 V
3. Internal Thermal Overload Protection
4. Internal Short Circuit Current Limiting Constant with Temperature
5. Output Transistor Safe–Area Compensation
6. Floating Operation for High Voltage Applications
7. Available in Surface Mount D2PAK, and Standard 3–Lead Transistor Package
8. Eliminates Stocking many Fixed Voltages

LM317T Circuit

LM317T Circuit

Advantages Vs Disadvantages


1. Versatile: can be used in a wide range of applications
2. Precise voltage regulation: allows for accurate and stable output voltage
3. Adjustable output voltage: can be set to meet specific requirements
4. Wide input voltage range: can handle a variety of input voltages
5. Overload and thermal protection: ensures the circuit remains safe even under adverse conditions


1. Heat dissipation: Generate significant heat when regulating voltage, requiring additional heat sinks or cooling systems in some applications

2. Limited output current: It is not designed to handle high output currents and may require additional components to handle larger loads

3. Higher cost: It is more expensive than other voltage regulators, especially fixed regulators



1. How do I calculate the output voltage of an LM317T circuit?

The output voltage of an LM317T circuit can be calculated using the formula: Vout = Vref (1 + R2/R1), where Vref is the reference voltage (usually 1.25V), R1 is the resistor between the ADJ and OUT pins, and R2 is the resistor between the OUT and GND pins.

2. Can this IC be used as a current regulator?

Yes, It can be used as a current regulator by using a sense resistor in series with the load to limit the output current to a desired level. The output voltage will then adjust automatically to maintain the current level.


LM317T Datasheet PDF Download

LM317T pdf

Other data sheets are available within the file: LM317, LM317BD2T, LM317BT, LM317D2T

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