The LM317 is an adjustable 3-terminal positive voltage regulator capable of supplying in excess of 1.5A over an output voltage range of 1.2V to 37V. Unlike fixed regulators like the 7805, the LM317 requires only two external resistors to set the output voltage. It is exceptionally easy to use and features internal current limiting, thermal shutdown, and safe-area compensation, making it nearly blowout-proof. It is the preferred choice for designers building variable lab power supplies, battery chargers, and constant current sources due to its excellent line and load regulation performance.
LM317 Pinout (TO-220)
In the standard TO-220 package, with the metal tab at the back and pins pointing downward, the pinout differs significantly from the 78xx series.
| Pin | Terminal | Function |
| 1 | Adjust (ADJ) | Used to set the output voltage via a resistive divider |
| 2 | Output (OUT) | Regulated DC output; also tied to the metal tab |
| 3 | Input (IN) | Unregulated DC voltage input |
Technical Specifications
- Output Voltage Range: 1.25V to 37V
- Output Current: 1.5A (Minimum)
- Input-Output Voltage Differential: 40V (Maximum)
- Line Regulation: 0.01% (Typical)
- Load Regulation: 0.1% (Typical)
- Operating Temperature: 0°C to 125°C
- Reference Voltage (VREF): 1.2V to 1.3V
Key Features & Benefits
- Adjustable Output: Provides maximum flexibility for non-standard voltage requirements.
- Excellent Regulation: Offers much tighter voltage control than most fixed regulators.
- Current Limiting: Protects the IC and the load from overcurrent conditions.
- High Ripple Rejection: Ensures a very clean DC output, even with noisy inputs.
Common Applications
- Variable Power Supplies: Creating adjustable bench power supplies for testing.
- Constant Current Regulators: Driving LEDs or charging NiCd/NiMH batteries.
- On-Card Regulation: Providing specific voltages for sensitive analog sub-circuits.
- Programmable Output: Can be digitally controlled using a digital-to-analog converter (DAC).
LM317 Equivalent & Substitutes
- LM338 (Higher current version – 5A)
- LM350 (Higher current version – 3A)
- LT1085 (Low dropout version)
- NTE956 (Standard replacement)
Related Tutorials on ElxHub
- Basics: Learn more in Integrated Circuits – Basics and Working
- Selection Guide: Compare power options in our Ultimate IC Selection Guide
Conclusion
The LM317 remains the gold standard for adjustable linear regulation. Its combination of simplicity, high performance, and ruggedness ensures it stays in the toolkit of every electronics enthusiast. Whether you are building a precision reference or a heavy-duty power supply, the LM317 delivers the stability your project demands.
Download the IC’s Datasheet pdf
Yoast SEO Settings: focus keyword: LM317 Voltage Regulator Datasheet seo title: LM317 Adjustable Voltage Regulator Datasheet & Pinout slug: lm317-adjustable-regulator-datasheet meta description: Complete LM317 datasheet. Features 1.2V to 37V adjustable output, 1.5A current, TO-220 pinout, and variable power supply circuit examples.