LM317T Adjustable Voltage Regulator (TO-220)

LM317T Adjustable Voltage Regulator (TO-220) – Technical Specifications:

Module Type – Adjustable Linear Voltage Regulator
Output Voltage – 1.25V to 37V DC (Adjustable)
Input Voltage – Up to 40V DC (Maximum)
Output Current – Up to 1.5A (with proper heatsinking)
Voltage Dropout – ~2V to 3V (typical)
Reference Voltage – 1.25V
Regulation Type – Positive Adjustable Regulator
Package Type – TO-220
Load Regulation – ~0.1% (typical)
Line Regulation – ~0.01% (typical)
Protection Features – Thermal Shutdown, Current Limiting, Safe Area Protection
Operating Temperature – 0°C to +125°C (junction)
Mounting Type – Through-Hole
Pin Configuration – ADJ (Adjust), OUT (Output), IN (Input)
Adjustment Method – External Resistors (Voltage Set via Divider)
Series – LM317 Adjustable Regulator Family
Compatible Applications – Variable power supplies, battery chargers, LED drivers, prototyping, DIY electronics

Handy Tips for Using the LM317T Adjustable Regulator:

1: The LM317T allows you to set any output voltage between 1.25V and 37V using just two external resistors. A common configuration uses:

• R1 = 240Ω
• R2 = variable resistor (potentiometer) to adjust output voltage

2: The regulator requires the input voltage to be at least ~2–3V higher than the desired output voltage. For example, to get 12V output, supply at least 14–15V input.

3: As a linear regulator, the LM317 dissipates excess voltage as heat. At higher currents or large voltage drops, it will generate significant heat — always use a heatsink when needed.

4: This regulator is ideal for building adjustable power supplies, battery chargers, LED drivers, and prototyping circuits where variable voltage is required.

5: For stable performance, always include capacitors:

• Input: ~0.1µF
• Output: ~1µF
• Optional: Add a capacitor on the ADJ pin (~10µF) for improved ripple rejection

6: Built-in thermal shutdown and current limiting protect the device, but proper thermal design is still essential for long-term reliability.

7: The LM317 can also be used as a current regulator (constant current source), making it useful for LED driving or battery charging applications with a simple resistor configuration.

8: If efficiency is important (e.g., solar or battery systems), consider using a switch-mode (buck) converter, as linear regulators waste power as heat when stepping down voltage.