LM317 Voltage Regulator: Features, Uses, and Specifications
The LM317 is a popular and versatile adjustable linear voltage regulator used in a wide range of electronic applications. With its ability to output a variable voltage from 1.25V to 37V and handle up to 1.5A of current, the LM317 is ideal for DIY power supplies, battery chargers, LED drivers, and voltage regulation circuits.
In this article, we’ll explore the key features, specifications,
and common uses of the LM317 to help you understand why it remains a favorite
among hobbyists and engineers alike.
What is LM317?
The LM317 is a 3-terminal adjustable positive voltage regulator
designed to provide a stable output voltage that can be adjusted using two
external resistors. It offers superior line and load regulation and includes
built-in protection features like thermal overload protection, current
limiting, and safe area compensation.
Key Features of LM317
·
Adjustable Output Voltage: 1.25V to 37V
·
Output Current: Up to 1.5A
·
High Regulation Accuracy: Typically ±1% output voltage tolerance
·
Thermal Overload Protection
·
Current Limiting and Short-Circuit Protection
·
Safe Operating Area Compensation
·
Simple to Use: Requires only two resistors to set output voltage
·
Available Packages: TO-220, TO-3, and surface-mount packages
LM317 Specifications
Parameter Value
Output Voltage Range
1.25V to 37V
Output Current
Up to 1.5A
Line Regulation
0.01% / V
typical
Load Regulation
0.1% typical
Reference Voltage
1.25V
Input Voltage
Up to 40V
Dropout Voltage
Typically 2V to
3V
Operating Temperature Range
0°C to +125°C
Package Types
TO-220, TO-3,
TO-263, SOT-223
LM317 Voltage Calculation Formula
To set the output voltage of the LM317, you use the following
formula:
Vout = 1.25V × (1 + R2 / R1) + Iadj × R2
Where:
- Vout = Output Voltage
- R1 and R2 = External resistors
- Iadj = Adjustment pin current (typically very small and often
neglected)
For most practical applications, R1 is chosen as 240Ω, and R2 is
adjusted to get the desired voltage.
Common Applications of LM317
1. Variable Power Supply
- Used in benchtop power
supplies where adjustable output is needed.
2. Battery Chargers
- Can be configured to
safely charge batteries by regulating voltage and current.
3. LED Drivers
- Provides a constant
current source for powering LEDs, ensuring brightness consistency.
4. Post-Regulation in SMPS
- Used after a switching
regulator to provide clean and stable output.
5. Current Regulator
- Configured to provide a
fixed current output in constant-current mode.
6. Powering Embedded Systems
- Used to step down
voltages for microcontrollers and sensors.
Typical LM317 Circuit (Voltage Regulator)
Place capacitors at the input and output for better stability:
0.1µF (input), 1µF or larger (output).
Advantages of Using LM317
·
Simple and flexible design
·
Easily available and cost-effective
·
Built-in protection features ensure safety
·
Works with a wide range of voltages
·
Can be used in both voltage and current regulation configurations
The LM317 adjustable voltage regulator is a powerful and
easy-to-use component that remains a staple in electronics design. Whether
you're building a variable power supply, a battery charger, or an LED
controller, the LM317 offers the flexibility, protection, and reliability you
need.
Its popularity and vast community support make it a must-know part
for electronics hobbyists, students, and engineers.
For video tutorial
No comments