LM317P: Overview,parameter,Main uses,Features,application fields,working principle and alternative models


LM317P Detailed Introduction:


The LM317P is an adjustable three-terminal positive voltage regulator IC commonly used to generate stable and adjustable output voltages. It is a versatile component in electronic circuits due to its ability to provide precise output voltage regulation.



  • Output Voltage Range: Typically adjustable from 1.25V to 37V.
  • Output Current: The maximum current the regulator can source.
  • Input Voltage Range: Maximum and minimum input voltages supported.
  • Load Regulation: Ability to maintain output voltage stability under varying load conditions.
  • Line Regulation: Capability to maintain output voltage stability with changing input voltages.
  • DataSheet

    LM317P PDF

Main Uses:

  • Voltage Regulation: Offers stable voltage output for various applications.
  • Power Supply Design: Commonly used in linear power supply circuits.
  • Voltage Reference: Provides a stable reference voltage for other components.
  • Battery Chargers: Regulating charging voltages for batteries.


  • Adjustable Output: Output voltage can be set using external resistors.
  • Thermal Regulation: Includes thermal overload protection.
  • Short Circuit Protection: Safeguards against excessive current draw.
  • Low Dropout Voltage: Can regulate output voltage close to the input voltage.
  • High Ripple Rejection: Ability to filter out AC noise on the input.

Application Fields:

  • Linear Power Supplies: Used in various voltage regulation circuits.
  • Test and Measurement: Providing stable reference voltages.
  • Audio Equipment: Powering analog and audio circuits.
  • Battery-Powered Devices: Regulating charging voltages and providing stable power.

Working Principle:

  • Reference Voltage: The internal voltage reference establishes a fixed voltage at the output.
  • Adjustment Resistors: External resistors connected to the ADJ pin set the desired output voltage.
  • Error Amplifier: Compares the reference voltage to the output voltage and adjusts the regulator accordingly.
  • Pass Transistor: Controls the flow of current to maintain the set output voltage.

Alternative Models:

  • LM317T: Standard through-hole version of the LM317.
  • LM337: Adjustable negative voltage regulator, complementary to the LM317.
  • LM1117: Low dropout voltage regulator with fixed output voltage options.

The LM317P is a widely-used voltage regulator known for its adjustable output voltage, robust features, and stability. It finds applications in various fields including power supply design, voltage reference circuits, and battery chargers. Alternative models like the LM317T, LM337, and LM1117 offer different specifications and features for specific voltage regulation requirements. Review datasheets and specifications to select the most suitable regulator for your application.