Adjustable Regulator 1.5A LM317T

The LM317T is one of the most popular and widely used adjustable three-terminal positive voltage regulators in the electronics industry. Since its introduction by National Semiconductor (now Texas Instruments), it has become a go-to solution for designers who need a simple, reliable, and flexible voltage regulation in their circuits. Unlike fixed regulators such as the 7805 or 7812, which provide only a single output voltage, the LM317T allows users to set any output voltage from 1.2V to 37V by using just two external resistors to form a voltage divider. This adjustability makes it exceptionally useful for designers, hobbyists, and engineers who no longer need to stock multiple fixed voltage regulators for different applications. The device is housed in the widely recognized TO-220 package, which features a metal tab for heat sinking to handle higher power dissipation. Despite its simplicity, the LM317T includes several built-in protection features that make it extremely robust: internal current limiting, thermal overload protection, and safe operating area (SOA) protection, all of which work together to prevent damage from short circuits, overheating, and excessive current draw. The regulator provides impressive performance specifications, including load regulation of 0.1% and line regulation of 0.01%, ensuring a clean and stable output voltage even with varying input voltage or load conditions. With a maximum output current capability of over 1.5A and operating over a wide temperature range, the LM317T is suitable for countless applications ranging from laboratory power supplies and battery chargers to LED drivers, motor speed controllers, and audio amplifiers.

Specifications

• Product Name: LM317T Adjustable Voltage Regulator
• Model Series: LM317T
• Regulator Type: Linear, 3-terminal, positive adjustable
• Package Type: TO-220
• Mounting Type: Through-hole
• Number of Outputs: 1
• Output Type: Adjustable
• Polarity: Positive
• Input Voltage Range: 3V to 40V DC
• Output Voltage Range: 1.2V to 37V DC
• Maximum Output Current: 1.5A (higher with proper heatsink)
• Reference Voltage (Vref): 1.25V (typical)
• Load Regulation: 0.1%
• Line Regulation: 0.01%
• Operating Temperature Range: 0°C to +125°C
• Dropout Voltage: ~3V (typical)
• Adjustment Pin Current: 50 µA (typical)
• Ripple Rejection: 80 dB (typical)
• Short-Circuit Protection: Yes (built-in)
• Thermal Overload Protection: Yes (built-in)
• Dimensions: 10 × 4.5 × 1 mm (approximate)
• Weight: Approximately 1 gram

Pin Configuration (TO-220 Package)

• Pin 1 (ADJ): Adjustment pin — connects to the voltage divider.
• Pin 2 (OUTPUT): Regulated output voltage.
• Pin 3 (INPUT): Unregulated input voltage.

Output Voltage Formula

Vout = 1.25 × (1 + R2/R1) + (IADJ × R2)

Where R1 and R2 form the external voltage divider.

Applications

• Used in variable laboratory power supplies for electronics testing.
• Essential in battery charger circuits with controlled voltage output.
• Employed in DIY electronics projects requiring custom voltage levels.
• Used in LED drivers to provide constant current for LED strips.
• Applied in motor speed controllers for DC motors.
• Common in Arduino and microcontroller power supplies for stable voltage.
• Used in audio amplifier circuits for clean, regulated power.
• Found in voltage regulators for prototyping and breadboard experiments.
• Employed in solar charge controllers and renewable energy systems.
• Used in automotive electronics for 12V to custom voltage conversion.
• Applied in guitar effect pedals and musical electronics.
• Common in adjustable bench power supplies.
• Used in linear voltage-regulated amplifiers.
• Found in sensor and transducer power circuits.
• Employed in signal conditioning circuits requiring stable reference voltages.
• Used in electroplating and electrolysis experiments.
• Applied in RC car and drone battery chargers.
• Common in step-down voltage conversions from higher to lower voltage.
• Used in thermoelectric cooler (TEC) controllers.
• Found in educational electronics kits for teaching voltage regulation.