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Description: This is the LM317TG voltage regulator, a three-terminal positive regulator with a 1.2V to 37V adjustable output voltage. This adjustable regulator provides a local regulation, internal current limiting, thermal shut-down control, and safe area protection for your project. Did we mention that this guy is easy to use? It only requires two external resistors to set the output voltage. Each one of these voltage regulators can output a max current of 1.5A.

Features:

  • Output Voltage: 1.2V - 37V Adjustable
  • Output Current: 1.5A
  • Thermal Overload Protection
  • Short Circuit Protection
  • Output Transistor Safe
  • Floating Operation for High Voltage Applications

Documents:

Comments 13 comments

  • The data sheet gives a minimum current draw to maintain regulation. Does anyone know what behavior to expect if this current isn’t being drawn? I’m picturing some disaster like having it power an Arduino that is temporarily turned off, and then when it’s turned on, awaking to 40 volts.

    • Now that would be a wake up call - TADA! 40V right in the input!

      I’d imagine when you design your circuit - you’d design it so that no load connected to the supply, you pull at least the minimum draw somehow - lights, resistor, etc?

  • I know the ‘LM317 Calculator’ is a third party site, not run by SparkFun.
    but this calculator only lets you input R1 and R1 and get output voltage, whereas I needed to input VOUT and R1, to get R2
    Could I recommend this link?
    http://www.reuk.co.uk/LM317-Voltage-Calculator.htm
    The site isnt as pretty as the existing one, but has two calculators depending on your needs :)

  • If I wanted this to be able to supply 9 volts, for when I have a dc jack and 9V battery connected, would it still supply 9V if I removed the jack?

    • No the input voltage must be 1.5v higher then the output voltage therefore you would not get 9 volts with a 9 volt battery the most you would get is 7.5 volts. Also if you wanted 9 volts from a wall wart you would need a 10.5 volt one but a 12 volt would be the best

  • Shouldn’t you carry the LM337, as well, so you provide a regulator that can be used for negative voltage power supplies?

  • The data sheet says that the Vout is the top metal piece and then the middle pin. Whats the top piece for? I always thought it was just a screw hole.

    • The top piece serves 3 functions: * It provides a way to secure the IC * It is a heat sink * It is also connected to the output. The reason it’s connected to the output is so it can do the best job possible of removing heat from the actual chip. If you are mounting this chip to something metal, using the screw hole, you should be sure to use a T-220 mounting kit or a mica insulator, especially if the piece of metal is grounded or electrically connected to any other part of the circuit.

  •  Can anyone suggest the bare minimum beside the two resistors to give me a 1 amp max output current?
    
     To charge an LI battery at 4.2V, the calculator shows me I should use R2=570 ohms.  But how can I determine how much current this will pass to the batteries? Specs on this list a 1.5A output current. I need to limit charge current to 1.0 Amps for safety, as per standard lithium ion safe practices.
    

    Would it be simple as calculating the correct RsubS value shown under load regulation on page 8 of the spec sheet? Is there an equation or calculator to determine RsubS? I’m severely limited on space too, no larger than what the Sparkfun Lipoly USB basic charger takes up, and no taller than a 2.1mm barrer connector. tia, Barry, bike light designer at Barry Beams Bicycle Lights

  • Uh… datasheet says output is adjustable from 1.25 volts to 37 volts, not 25.

    • Just because it can go up to 37V doesn’t mean you should use that much, especially without a heatsink.


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