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LM317: How to turn on/off variable power using LM317

Grady Lee
Genius 3620 points
Part Number: LM317

Hi

The board under review is using a variable power source through LM317.

I want to turn the variable voltage ON/OFF, but I would like to ask if there is another way other than ON/OFF on the output side.

(ON/OFF control with feedback, etc.)

Please check. Thank you.

  • 0
    TI__Mastermind 48265 points

    Hi Grady,

    I have seen others use a transistor (or 2 transistors) on the input side to control whether IN gets voltage or not. Is this the kind of solution you're referring to?

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Genius 3620 points

    Hi, Nick

    Could you please let me know if there is a reference circuit on how to do it using a transistor on the input side?

    Additionally, LM317 is an LDO without an enable function. If an LDO with an enable function is applied, is on/off control possible at the input side?
    If possible, is it possible to recommend an LDO with enable function as a replacement for LM317?

    Please check. Thank you.

  • +1 in reply to Grady Lee
    TI__Mastermind 48265 points

    Hi Grady,

    I don't specifically know of a reference design, but I drew this up to show you how to achieve it. 

    Do you need the other device to be P2P with LM317? Devices that have EN can easily be controlled at the input side without this extra circuitry. If the device needs to be P2P, the options are limited because LM317 is an old device with a floating-ground architecture, which modern devices do not generally use. 

    Regards,

    Nick