LM317

From Wikipedia, the free encyclopedia

A current-limiting circuit constructed with LM317

LM317 is the standard part number for an integrated three-terminal adjustable linear voltage regulator. LM317 is a positive voltage regulator supporting input voltage of 3V to 40V and output voltage between 1.25V and 37V. A typical current rating is 1.5A although several lower and higher current models are available. Variable output voltage is achieved by using a potentiometer or a variable voltage from another source to apply a control voltage to the control terminal. LM317 also has a built-in current limiter to prevent the output current from exceeding the rated current, and LM317 will automatically reduce its output current if an overheat condition occurs under load. LM317 is manufactured by many companies, including National Semiconductor, Fairchild Semiconductor, and STMicroelectronics.

Although LM317 is an adjustable regulator, it is sometimes preferred for high-precision fixed voltage applications instead of the similar LM78xx devices because the LM317 is designed with superior output tolerances. For a fixed voltage application, the control pin will typically be biased with a fixed resistor network, a Zener diode network, or a fixed control voltage from another source. Manufacturer datasheets provide standard configurations for achieving various design applications, including the use of a pass transistor to achieve regulated output currents in excess of what the LM317 alone can provide.

LM317 is available in a wide range of package forms for different applications including heatsink mounting and surface-mount applications. Common form factors for high-current applications include TO-220 and TO-3. LM317 is capable of dissipating a large amount of heat at medium to high current loads and the use of a heatsink is recommended to maximize the lifespan and power-handling capability.

LM337 is the negative voltage complement to LM317 and the specifications and function are essentially identical, except that the regulator must receive a control voltage and act on an input voltage that are below the ground reference point instead of above it.