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LM317 Datasheet, Circuit Schematic, Pinouts and Sources

LM317 Datasheet and Circuit Schematic Overview

LM317 is the standard part number for an integrated three-terminal adjustable linear voltage regulator. LM317 is a positive voltage regulator supporting input voltage of 3V to 40V and output voltage between 1.25V and 37V

LM317 Datasheet PDF Download LM317 Pinout

LM317 Price Check

The LM317 Regulator Technical Capabilities

LM317 is the standard part number for an integrated three-terminal adjustable linear voltage regulator. LM317 is a positive voltage regulator supporting input voltage of 3V to 40V and output voltage between 1.25V and 37V. A typical current rating is 1.5A although several lower and higher current models are available. Variable output voltage is achieved by using a potentiometer or a variable voltage from another source to apply a control voltage to the control terminal. LM317 also has a built-in current limiter to prevent the output current from exceeding the rated current, and LM317 will automatically reduce its output current if an overheat condition occurs under load. LM317 is manufactured by many companies, including National Semiconductor, Fairchild Semiconductor, and STMicroelectronics.

Although LM317 is an adjustable regulator, it is sometimes preferred for high-precision fixed voltage applications instead of the similar LM78xx devices because the LM317 is designed with superior output tolerances. For a fixed voltage application, the control pin will typically be biased with a fixed resistor network, a Zener diode network, or a fixed control voltage from another source. Manufacturer datasheets provide standard configurations for achieving various design applications, including the use of a pass transistor to achieve regulated output currents in excess of what the LM317 alone can provide.

LM317 is available in a wide range of package forms for different applications including heatsink mounting and surface-mount applications. Common form factors for high-current applications include TO-220 with part number LM317T and TO-3 with part number LM317K. LM317 is capable of dissipating a large amount of heat at medium to high current loads and the use of a heatsink is recommended to maximize the lifespan and power-handling capability.

LM337 is the negative voltage complement to LM317 and the specifications and function are essentially identical, except that the regulator must receive a control voltage and act on an input voltage that are below the ground reference point instead of above it.


Voltage Regulator: LM317 Datasheets

Texas Instruments LM317 Datasheets

TI LM317L Datasheets LM317L Datasheet PDF
TI LM317M Datasheets TI LM317M Datasheet PDF

National Semiconductor LM317 Datasheets

National Semiconductor LM317 Datasheets National LM317 Datasheet PDF

Fairchild LM317 Datasheets

Fairchild LM317 Datasheets Fairchild LM317 Datasheet PDF
Fairchild LM317L Datasheets Fairchild LM317L Datasheet PDF
Fairchild LM317AHV Datasheets Fairchild LM317AHV Datasheet PDF

On Semiconductor LM317 Datasheets

On Semi LM317 Datasheets On Semi LM317 Datasheet PDF

STMicroelectronics LM317 Datasheets

STMicro LM317 Datasheets ST Micro LM317 Datasheet PDF

LM317 Circuit Schematic

lm317 circuit schematic


LM317 Pinout

LM317 Pinouts


LM317 Specifications

Vout range 1.25V - 37V
Vin - Vout difference 3V - 40V
Operation ambient temperature 0 - 125°C
Output Imax <1.5A
Minimum Load Currentmax 10mA

Cross Reference LM317 vs 7805 Voltage Regulators

For a regulated 5V supply, is there any reason to use a LM317 circuit rather than the 7805 regulator?

  • If it's for digital, consider a switching power supply; they're far more efficient.
  • If it's for linear, you really need a linear supply.

The 7805 and LM317 ICs have been around for a long time, and they still work. However, they have a minimum Vdrop of about 1.7V across them, which means they consume power and generate heat.  "Low dropout voltage" it means that the difference between the input and output voltage is lower than the typical 1.7V. Those regulators use a more efficient scheme to pass current through than traditional linear regulators.


LM317 Output Voltage Formula

LM317 Pinouts and Formula


LM317 Packaging Options

LM317 Packaging Options


LM317 Models and Manufacturers

Manufacturers Models/Types
National Semiconductors LM317/LM317A/LM317HV/LM317L
ON Semiconductor LM317
Texas Instruments LM317/LM317L/LM317M/LM317MQ
STMicro LM317
Fairchild Semiconductors LM317/LM317AHV/LM317L

LM317 Application Notes: LED Constant Current Source Scheme

(Excerpt) The LM317L wants to see 1.25 V between its VOUT pin and the Vadj pin, and it will do whatever it can to keep that voltage differential between them.

But what if a series/parallel combination of LEDs is wanted in the LM317 circuit? The following circuit works fine, assuming that there are not large variations in the forward voltage drop of the LEDs. There could be a problem however if one of the strings opens up for some reason. The LEDs that remain would have 50% more current flowing through them, which could cause them to be driven too hard and fail. So how does one get around this problem? Download LM317 Application Note from On Semi.


Excepts from the STMicro Datasheet

The LM117/LM217/LM317 are monolithic integrated circuit in TO-220, TO-220FP, TO-3 and D2PAK packages intended for use as positive adjustable voltage regulators. They are designed to supply more than 1.5 A of load current with an output voltage adjustable over a 1.2 to 37 V range. The nominal output voltage is selected by means of only a resistive divider, making the device exceptionally easy to use and eliminating the stocking of many fixed regulators.


Project: Solar Battery Charger Using the LM317

A small solar panel makes an excellent battery charger for AA and AAA rechargeable batteries. Only a few components are required and construction is very simple making this a perfect first renewable energy project.

Rechargeable AA and AAA batteries have a voltage of around 1.2 Volts when fully charged. Therefore 2 in series gives a total of 2.4 Volts, 4 in series 4.8 Volts. Common solar panel output voltages are 3 Volts

In this example we will make a solar charger using a 6 Volt 250ma Solar Panel to charge four 800mah AAA batteries. The batteries can be put into a couple of 2 x AAA battery holders and wired in series (link the positive output from one battery holder to the negative of the other).

This gives us 4 x 1.2 = 4.8 Volts with a capacity of 800mah - therefore we want a charging current of around 80ma. According to the table above, a 15 Ohm resistor gives a fixed current of 83.3 milliamps which will be perfect.

The power loss in the resistor is again given by Ohm's Law as I * I * R = 0.0833 * 0.0833 * 15 = 0.10 Watts, therefore we can safely use a standard 0.25 Watt 15 Ohm resistor.

Provided by:

Solar Battery Charger with LM317T

Automatic LED Emergency Light


This is the circuit diagram of a low cost emergency light based on white LED.The white LED provide very bright light which turns on when the mains supply is not there.The circuit has an automatic charger which stops charging when the battery is fully charged.

The IC LM 317 produces a regulated 7 V for the charging of Battery.Transistor BD 140 drives the out put.Transistor BC 548 and Zener diode controls the charging of the battery.


It is always better to connect a heat sink with BD 140.Before using the circuit out put of LM317 must be set to 7V by adjusting the potentiometer. Original article:



LM317T Voltage Regulator with Pass Transistor

The LM317T output current can be increased by using an additional power transistor to share a portion of the total current. The amount of current sharing is established with a resistor placed in series with the 317 input and a resistor placed in series with the emitter of the pass transistor. In the figure below, the pass transistor will start conducting when the LM317 current reaches about 1 amp, due to the voltage drop across the 0.7 ohm resistor. Current limiting occurs at about 2 amps for the LM317 which will drop about 1.4 volts across the 0.7 ohm resistor and produce a 700 millivolt drop across the 0.3 ohm emitter resistor. Thus the total current is limited to about 2+ (.7/.3) = 4.3 amps. The input voltage will need to be about 5.5 volts greater than the output at full load and heat dissipation at full load would be about 23 watts, so a fairly large heat sink may be needed for both the regulator and pass transistor. The filter capacitor size can be approximated from C=IT/E where I is the current, T is the half cycle time (8.33 mS at 60 Hertz), and E is the fall in voltage that will occur during one half cycle. To keep the ripple voltage below 1 volt at 4.3 amps, a 36,000 uF or greater filter capacitor is needed. The power transformer should be large enough so that the peak input voltage to the regulator remains 5.5 volts above the output at full load, or 17.5 volts for a 12 volt output. This allows for a 3 volt drop across the regulator, plus a 1.5 volt drop across the series resistor (0.7 ohm), and 1 volt of ripple produced by the filter capacitor. A larger filter capacitor will reduce the input requirements, but not much.



LM317T Variable Voltage Regulator

The LM317T is a adjustable 3 terminal positive voltage regulator capable of supplying in excess of 1.5 amps over an output range of 1.25 to 37 volts. The device also has built in current limiting and thermal shutdown which makes it essentially blow-out proof.

Output voltage is set by two resistors R1 and R2 connected as shown below. The voltage across R1 is a constant 1.25 volts and the adjustment terminal current is less than 100uA. The output voltage can be closely approximated from Vout=1.25 * (1+(R2/R1)) which ignores the adjustment terminal current ``but will be close if the current through R1 and R2 is many times greater. A minimum load of about 10mA is required, so the value for R1 can be selected to drop 1.25 volts at 10mA or 120 ohms. Something less than 120 ohms can be used to insure the minimum current is greater than 10mA. The example below shows a LM317 used as 13.6 volt regulator. The 988 ohm resistor for R2 can be obtained with a standard 910 and 75 ohm in series.

When power is shut off to the regulator the output voltage should fall faster than the input. In case it doesn't, a diode can be connected across the input/output terminals to protect the regulator from possible reverse voltages. A 1uF tantalum or 25uF electrolytic capacitor across the output improves transient response and a small 0.1uF tantalum capacitor is recommended across the input if the regulator is located an appreciable distance from the power supply filter. The power transformer should be large enough so that the regulator input voltage remains 3 volts above the output at full load, or 16.6 volts for a 13.6 volt output.



Project: LM317 Variable Power Supply

A truly timeless circuit. LM317 is a versatile and highly efficient 1.2-37V voltage regulator that can provide up to 1.5A of current with a large heat sink. It's ideal for just about any application. This was my first workbench power supply and I still use it. Since LM317 is protected against short-circuit, no fuse is necessary. Thanks to automatic thermal shutdown, it will turn off if heating excessively. All in all, a very powerful (and affordable!) package, indeed. Although LM317 is capable of delivering up to 37V, the circuit pictured here is limited to 25V for the sake of safety and simplicity. Any higher output voltage would require additional components and a larger heat sink. Make sure that the input voltage is at least a couple of Volts higher than the desired output. It's ok to use a trimmer if you're building a fixed-voltage supply.

LM317 power supply


Project: Battery Charger Circuit using LM317

Here is a simple but effective battery charger circuit using IC LM 317. The circuit can be used to charge 12V lead acid batteries.The circuit is very simple and can be easily assembled on a general purpose PCB.

The heart of the circuit is IC LM317, which is an adjustable voltage regulator IC.The pin 1 of the IC is the control pin which is used to control the charging voltage.The pin 2 is the output pin at which the charging voltage appears.The pin 3 is the input pin to which the regulated DC supply is given.

The charging voltage and current is controlled by the Transistor Q1, resistor R1 and POT R5.  When the battery is first connected to the charging terminals, the current through R1 increases.This in turn increases the current and voltage from LM317. When the battery is fully charged the charger reduces the charging current and the battery will be charged in the trickle charging mode.  Source: CircuitsToday.

LM317 Battery Charger Circuit


  • The input voltage to the circuit must be at least 3V higher than the expected output voltage.  LM 317 dissipates around 3V during its operation.  Here I used 18V DC as the input.
  • The charging voltage can be set by using the POT R5.
  • The LM 317 must be mounted on a heat sink.
  • All capacitors must be rated at least 25V.
  • You can use crocodile clips for connecting the battery to the charger.

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LM317 Datasheet and Circuit Schematic Overview

LM317 is the standard part number for an integrated three-terminal adjustable linear voltage regulator. LM317 is a positive voltage regulator supporting input voltage of 3V to 40V and output voltage between 1.25V and 37V

LM317 Datasheet PDF Download LM317 Pinout

LM317 Price Check


LM317 Datasheet and Circuit Schematic Overview

LM317 is the standard part number for an integrated three-terminal adjustable linear voltage regulator. LM317 is a positive voltage regulator supporting input voltage of 3V to 40V and output voltage between 1.25V and 37V

LM317 Datasheet PDF Download LM317 Pinout

LM317 Price Check