on October 15th 143

LM317 Voltage Regulator : Pinout, Circuit, Comparison with LM7805, and Datasheet Overview

The LM317 adjustable voltage regulator is a widely used component in power supply design. It is known for its ability to provide stable output voltages between 1.25V and 37V, with a current capacity of up to 1.5A. Its versatility in industrial applications and features like thermal overload protection, current limiting, and wide voltage adjustment range make it a staple in many electronics projects. This article explores the key features of the LM317, compares it with alternative regulators like the LM7805 and LT3080, and examines its various practical applications, from power supply design to battery chargers and LED drivers.

Catalog

Overview of LM317

The LM317 represents a highly adaptable three-terminal voltage regulator, crafted by several renowned Integrated Circuit (IC) manufacturers. This component enjoys widespread usage in DC-regulated power supply circuits because of its aptitude for delivering adjustable and stable voltage levels.

The LM317 can deliver an output voltage that varies from 1.25 V to 37 V and adapts to different current requirements, enhancing its application range. It can supply more than 1.5 A of current to the load, promoting its use in various projects.

Internal current limiting balances load fluctuations. Thermal shutdown prevents overheating, promoting longevity. Safe area compensation ensures stable operation under diverse conditions. Stability under fluctuating input conditions maintains consistent performance. In actual scenarios, the LM317 is embraced in a diverse array of electronic ventures and commercial uses. You can utilize its adjustability for custom voltage needs in DIY kits, prototyping, and industrial designs. Specifically, it is frequently used in bench power supplies, battery chargers, and LED drivers.

LM317 Pin Configuration

Pin Number	Pin Name	Description
1	Adjust	These pins adjust the output voltage
2	Output Voltage (Vout)	The regulated output voltage set by the adjust pin can be obtained from this pin
3	Input Voltage (Vin)	The input voltage which has to be regulated is given to this pin

Specifications of LM317

Here is the table content for the ON Semiconductor LM317T.

Type	Parameter	Details
Lifecycle Status		Obsolete
Last Shipments	(Last Updated: 3 days ago)
Contact Plating		Tin
Mount		Through Hole
Mounting Type		Through Hole
Package / Case		TO-220-3
Number of Pins		3
Weight		1.214012g
Operating Temperature		0°C~125°C
Packaging		Tube
Published		2004
JESD-609 Code		e3
Pbfree Code		Yes
Part Status		Obsolete
Moisture Sensitivity Level (MSL)		1 (Unlimited)
Number of Terminations		3
ECCN Code		EAR99
Power Rating		20W
Packing Method		RAIL
Max Power Dissipation		20W
Terminal Position		SINGLE
Peak Reflow Temperature (°C)		235
Number of Functions		1
Terminal Pitch		2.54mm
Time @ Peak Reflow Temperature-Max (s)		30
Base Part Number		LM317
Pin Count		3
Number of Outputs		1
Voltage - Input (Max)		40V
Output Voltage		37V
Max Output Current		1.5A
Output Configuration		Positive
Max Output Voltage		37V
Number of Regulators		1
Min Input Voltage		4.2V
Protection Features		Over Temperature, Short Circuit
PSRR		75dB ~ 60dB (120Hz)
Reference Voltage		1.3V
Dropout Voltage		2V
Dropout Voltage1-Nom		3V
Min Output Voltage		1.2V
Power Supply Rejection Ratio (PSRR)		60dB
Min Current Limit		1.5A
Load Regulation-Max (%)		5.80%
Height		9.15mm
Length		10.4mm
Width		4.6mm
REACH SVHC		No SVHC
Radiation Hardening		No
RoHS Status		RoHS Compliant
Lead Free		Lead Free

CAD Models for LM317

Symbol

Footprints

3D Models

Key Features of the LM317

Feature	Description
Adjustable Output Voltage Range	Adjustable from 1.25V to 37V
Maximum Output Current	Greater than 1.5A
Internal Short-Circuit Protection	Built-in current limiting to prevent damage
Thermal Overload Protection	Prevents overheating by shutting down the regulator
Output Safe-Area Compensation	Ensures safe operation within the specified limits

Applications of LM317

The LM317 finds its place in a myriad of applications due to its versatility and reliability. These uses range from positive voltage regulation to protecting circuits from reverse polarity and controlling motors.

Positive Voltage Regulation

In the realm of positive voltage regulation, the LM317 excels in delivering a consistent output voltage amidst fluctuations in input voltage or load conditions. You can turn to this regulator to stabilize voltage supplies for microprocessors and serious electronic components. The steady performance it ensures is basic for the optimal functioning of power-sensitive devices, thereby enhancing their performance and lifespan.

Variable Power Supplies

The LM317 shines in variable power supplies, admired for its capability to finely adjust output voltage through resistance variation. This flexibility is especially valued in experimental environments demanding diverse voltages for testing electronic components. You can regularly rely on the LM317 for providing adjustable power levels during prototyping or repair projects, making it a staple in their toolkits.

Current Limiting Circuits

In current limiting circuits, the LM317 guards sensitive components from overcurrent scenarios by setting precise current limits. This protection is dominant in applications like battery charging circuits, where controlling the charging currents is used to avoid battery degradation. By preventing excessive current flows, the LM317 contributes significantly to prolonging the lifespan of various devices.

Reverse Polarity Protection

Reverse polarity can wreak havoc on electronic circuits, but the LM317 paired with auxiliary components acts as a shield against such mishaps. This safeguard proves invaluable in automotive electronics and other power systems prone to accidental polarity reversals. The regulator’s role in these configurations underlines its importance in fortifying the robustness of power supply systems.

Motor Control

In motor control applications, the LM317 plays a key role by managing the voltage supplied to motors, directly influencing their speed and torque. This control is active in fields like industrial automation and robotics, where precise motor operation is required. Even in projects, such as remote-controlled vehicles, the LM317's robust performance is highly beneficial.

Consumer Electronics

The LM317 is omnipresent in consumer electronics, including desktop PCs and DVDs, where it maintains voltage levels within specified ranges. This consistency ensures reliable device performance and prevents functional anomalies, thereby improving your experience. Its widespread use in consumer devices attests to its effectiveness and reliability.

Alternatives to LM317

• LM7805

• LM7806

• LM7809

• LM7812

• LM7905

• LM7912

Implementing LM317

Using the LM317 as a variable voltage regulator involves a meticulous setup to maintain precise control over the output voltage. The procedure includes connecting the input voltage to the VIN pin and finely tuning the voltage at the ADJ pin using a resistor network. This configuration enables the desired output voltage at VOUT. Including a potentiometer in this potential divider circuit permits dynamic adjustments to the output voltage as needed.

To utilize the LM317 effectively, the output voltage (VOUT) can be determined with the equation

VOUT = 1.25 ×l(1 +(R2/R1))

Here, (R1) and (R2) are resistive components in the circuit, with (R2) often being a potentiometer. For example, if (R1) is 1kΩ and (R2) is a 10kΩ potentiometer, the output voltage can range from 1.25V to 10V.

The practical use of the LM317 goes beyond notional calculations. Fine-tuning the resistor values, especially using a potentiometer, requires insightful considerations for optimizing performance. Understanding load conditions and managing thermal aspects are required to ensure the stability and reliability of the regulator in diverse environments. Heat dissipation is a considerable factor affecting the LM317's performance. Applying proper heat sinking techniques can prevent overheating, which could otherwise lead to voltage regulation issues or damage to the component. The LM317's behavior under different load conditions impacts the overall output stability. Testing the regulator circuit under multiple load scenarios provides valuable insights into how load fluctuations influence the output voltage.

LM317 vs. LM7805

Adjustable vs. Fixed Output Voltage

The LM317 and LM7805 serve distinct roles due to their differing output capabilities, each bringing its unique appeal to the table. The LM317 caters to those craving flexibility with an adjustable output voltage ranging from 1.25V to 37V, a feature that's cherished in applications where variable voltage levels enhance performance. Conversely, the LM7805 stands out with its steadfast nature, delivering a fixed 5V output, earning its place in systems that thrive on stability and uniformity.

Current Output Capabilities

A notable benefit of the LM317 is its ability to support higher current outputs. This is mostly advantageous for scenarios demanding robust power delivery, offering reliability for more intensive projects. On the other hand, the LM7805, with its more straightforward design, generally manages lower current outputs. While this might seem limiting, it often perfectly suits fewer demanding applications, providing a simple yet effective solution.

Component Requirements

Using the LM317 for voltage adjustment requires additional components, such as resistors or potentiometers. This added complexity injects a layer of flexibility into the voltage regulation process but does necessitate a more thoughtful approach to design. In stark contrast, the LM7805's fixed output considerably streamlines circuit design. Minimizing the need for external components, enables quicker and more straightforward implementation, sparking a sense of ease and efficiency in the design process.

Comparable Parts

Part Number	Manufacturer	Package / Case	Number of Pins	Number of Outputs	Max Output Current	Min Input Voltage	Max Input Voltage	Min Output Voltage	Max Output Voltage	Dropout Voltage	View Compare
LM317T	ON Semiconductor	TO-220-3	3	1	1.5 A	4.2 V	40 V	1.2 V	37 V	2 V	LM317T VS LM317KCS
LM317KCS	Texas Instruments	TO-220-3	3	1	1.5 A	4.2 V	40 V	1.25 V	37 V	2 V	LM317T VS LM317KCS
LM317T	STMicroelectronics	TO-220-3	3	1	1.5 A	4.2 V	40 V	1.2 V	37 V	-	LM317T VS LM317T
LM217T	STMicroelectronics	TO-220-3	3	1	1.5 A	4.2 V	40 V	1.2 V	37 V	-	LM317T VS LM217T
LM317KCT	Texas Instruments	TO-220-3	3	1	1.5 A	4.2 V	40 V	1.25 V	37 V	2 V	LM317T VS LM317KCT

Datasheet PDF

LM317T Datasheets:

TO220B03 Pkg Drawing.pdf

KA317,LM317.pdf

LM317, NCV317 Datasheet.pdf

LM317, NCV317 Datasheet.pdf

LM317KCS Datasheets:

LM317KCE3.pdf

LM317T Datasheets:

LM217, LM317.pdf

LM217T Datasheets:

LM217, LM317.pdf

Frequently Asked Questions [FAQ]

1. How does LM317 work?

The LM317 operates as an adjustable linear voltage regulator, providing meticulous control over output voltage via a feedback mechanism that employs a voltage divider composed of two external resistors. By altering the resistance values, the feedback voltage varies, consequently adjusting the regulator's output voltage. This approach is routinely utilized in electronics to derive different voltage levels from a single power supply, catering to applications ranging from microcontroller projects to industrial power systems. In practical scenarios, you may witness this during the design phase of electronic devices, where precise voltage regulation ensures reliable operation and mitigates unforeseen issues—emphasizing how serious accuracy and stability are in electronic circuits.

2. What is a LM317 used for?

The LM317 can be utilized for providing a stable output voltage, ensuring constant current regulation, facilitating battery charger designs, and acting as a major component in variable power supplies. Its ability to supply adjustable voltage is especially useful in various contexts. You can leverage it to power different sections of a circuit requiring variable voltage levels, ensuring compatibility and operational efficiency. Within these diverse practical setups, the LM317 demonstrates its versatility, reflecting its adaptability in myriad electrical environments.

3. What is the maximum input voltage of a LM317?

The LM317 supports a maximum input voltage of 40V and operates efficiently with an input-output voltage differential ranging from 3V to 40V. This characteristic broadens its applicability in various power supply setups, catering to both high and low-voltage demands. For example, this attribute proves to be invaluable when designing resilient power supply units where substantial input voltage variations may occur, enhancing design flexibility and ensuring dependable performance in actual applications.

4. What is the output voltage of an LM317?

The LM317 offers a flexible output voltage range from 1.25V to 37V, with a current delivery capability of up to 1.5A. This flexibility makes it a useful tool for customizing power solutions to meet specific requirements, from small-scale projects to large industrial applications. By utilizing its adjustable output, you can tailor the voltage supply to align with various electronic components' demands, optimizing performance and enhancing the longevity of electronic systems. Often in laboratory settings, the ability to precisely control voltage is paramount for achieving experimental accuracy and ensuring safety, showcasing the regulator's invaluable utility.