LM317 Adjustable Positive Voltage Regulator
The LM317 is a versatile adjustable 3-terminal positive voltage regulator that gives designers the ability to set output voltage precisely between 1.25 V and 37 V using just two external resistors. It can supply up to 1.5 A of output current, making it ideal for use in regulated power supplies, battery chargers, and embedded systems.
Engineers choose the LM317 when they want more flexibility than fixed-voltage regulators like the 7805. By connecting a resistor divider between the output and adjust pins, you can control the output voltage easily and accurately. The internal reference voltage of 1.25 V ensures consistent performance.
The LM317 also integrates current limiting, thermal shutdown, and safe-area protection, which increases circuit reliability and prevents damage from overloads or overheating.
Pin Configuration (TO-220 Package)
| Pin | Name | Description |
|---|---|---|
| 1 | Adjust | Sets output voltage via external resistors |
| 2 | Output | Regulated output voltage |
| 3 | Input | Unregulated input voltage |
Key Features
Adjusts output from 1.25 V to 37 V
Supplies up to 1.5 A continuous current
Offers high line and load regulation
Maintains internal thermal overload protection
Limits current to protect against short circuits
Provides safe-area compensation
Works with minimal external components
Available in TO-220, TO-3, SOT-223, and others
Applications
Power adjustable DC circuits in labs and test setups
Build reliable voltage regulators for microcontrollers
Design variable bench power supplies
Regulate output for battery chargers
Use in DIY audio amplifier power rails
Drive LED strips or sensors with exact voltage
Step down from 12V or 24V for sensitive components
Interface with analog circuits that need custom supply levels
Provide post-regulation after a switching supply
Protect sensitive circuits with current-limited rails
Specifications Table
| Parameter | Value |
|---|---|
| Output Voltage Range | 1.25 V to 37 V |
| Output Current (max) | 1.5 A |
| Line Regulation | 0.01%/V (typical) |
| Load Regulation | 0.1% (typical) |
| Reference Voltage | 1.25 V ± 1% |
| Input Voltage (max) | 40 V |
| Dropout Voltage | 2–3 V ‘ |
| Thermal Overload Protection | Yes |
| Short Circuit Protection | Yes |
| Package Types | TO-220, TO-3, SOT-223 |
| Operating Temperature Range | 0 °C to +125 °C |
