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LM317T by XBLW

The LM317T is a versatile, widely used three-terminal positive adjustable voltage regulator capable of supplying output voltages ranging from 1.25V to 37V, with an output current capacity of up to 1.5A. Manufactured by various semiconductor companies including Texas Instruments, ON Semiconductor, and STMicroelectronics, the LM317T is part of the LM317 family and is designed for use in a variety of regulated power supply applications.


Key Features

  • Adjustable Output Voltage: 1.25V to 37V

  • Output Current: Up to 1.5A (with proper heat sinking)

  • Line Regulation: Typically 0.01%/V

  • Load Regulation: Typically 0.1%

  • Thermal Overload Protection

  • Short-Circuit Current Limiting

  • Safe Area Compensation

  • Package Type: TO-220 (standard for LM317T)

Functional Description

The LM317T functions by maintaining a constant reference voltage of 1.25V between its output and adjustment (ADJ) terminal. By configuring the regulator with an external voltage divider (two resistors), the output voltage is set according to the following formula:

VOUT=VREF(1+R2R1)+IADJR2

VOUT​=VREF​(1+R1​R2​​)+IADJ​⋅R2​

  • VREF1.25VVREF​≈1.25V

  • R1R1​ and R2R2​ are external resistors

  • IADJIADJ​ is the adjustment pin current (typically ~50µA, usually negligible in most designs)


Application Circuit

A typical application includes:

  • R1 & R2: Set the output voltage using the formula

    VOUT=1.25(1+R2R1)

    VOUT​=1.25(1+R1R2​)

  • C1_in: Input capacitor (e.g., 0.1µF to 1µF) — stabilizes input voltage.

  • C2_out: Output capacitor (e.g., 1µF to 10µF) — improves transient response.



  • Thermal and Protection Features

    • Thermal Overload Protection: Shuts down the regulator if the junction temperature exceeds safe levels (~125–150°C).

    • Current Limiting: Internal circuitry limits the output current to protect the regulator and connected components.

    • Safe Area Protection: Prevents operation outside the safe operating region of the power transistor.


    Applications

    • Adjustable power supplies

    • Battery chargers

    • Constant current sources

    • Precision current regulators

    • Post-regulation for switching power supplies


    Notes on Use

    • Proper heat sinking is essential for full 1.5A operation; the TO-220 package can dissipate significant power if mounted correctly.

    • A minimum load current (~10mA) is often required for proper regulation.

    • When used in high-output voltage configurations, the differential voltage between IN and OUT should be managed to avoid excessive power dissipation.

    +1.2 to 37V 1.5A Variable Voltage Regulator TO-220 17L

    XBLW
    LM317T
      Delivery time:1-5 Days
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