LM317 Adjustable Voltage Regulator DC-DC

Overview: LM317 Adjustable Voltage Regulator

The LM317 is a widely used adjustable linear voltage regulator IC designed for DC-DC applications that require precise and reliable voltage control. It provides an adjustable output range from 1.25V to 37V and can deliver up to 1.5A of output current with built-in current limiting, thermal overload protection, and safe-area compensation for dependable operation in DIY and professional circuits.

Key Features

• Adjustable output voltage: 1.25V to 37V
• Output current up to 1.5A
• Built-in current limiting and thermal protection
• High regulation and stability under varying loads
• Simple resistor-set voltage adjustment
• TO-220 package for easy mounting and heat-sinking

Specifications

• Reference voltage (Vref): 1.25V (typical)
• Output voltage range: 1.25V to 37V
• Maximum output current: 1.5A
• Typical dropout voltage: around 2-3V (depends on load)
• Adjust pin current (Iadj): typically ~50 microamps
• Package type: TO-220

Voltage Setting Formula

Set the output voltage using two resistors (R1 and R2) with the following formula:

Vout = Vref * (1 + R2 / R1) + Iadj * R2, where Vref ≈ 1.25V.

Common example: using R1 = 240 ohms gives Vout ≈ 1.25 * (1 + R2 / 240).

Typical Applications

• DIY regulated power supplies
• Battery charging circuits
• Motor speed control and small motor drivers
• LED drivers and constant-current applications (with appropriate resistor or current-limiting circuitry)
• General-purpose voltage regulation for test rigs and prototypes

Typical Circuit and Usage Tips

• Provide adequate input-to-output headroom. The input voltage should be at least 2-3V higher than the required output to account for dropout.
• Use a heatsink for sustained currents near the 1.5A limit to avoid thermal shutdown.
• Place an input bypass capacitor (0.1uF) close to the regulator input and an output capacitor (1uF or larger) for stability, especially when the regulator is located far from the supply source.
• Consider a bypass capacitor between Adj and ground (e.g., 10uF) to improve ripple rejection when needed.
• Follow safe wiring practices and observe polarity to prevent damage.

Package and Pinout

Package: TO-220. Pinout (front view, left to right): Adj, Output, Input. The metal tab is connected to the output and can be bolted to a heatsink for improved thermal performance.

Safety and Handling

• Internal thermal limiting and current limiting help protect the device, but proper heatsinking and current control are required for reliable continuous operation.
• Avoid exceeding the maximum input voltage and the device power dissipation ratings.
• Use appropriate fusing or current protection when designing battery chargers or high-current circuits.

Notes

Images are for illustration purposes only.