555 Auto Shut Off Power Circuit

Discussion in 'Digital Circuit Design' started by Zfensler, Sep 27, 2016.

  1. Zfensler

    Thread Starter New Member

    May 28, 2014
    10
    0
    Hello All,

    I am currently designing a mobile sound device that needs auto off functionality. It consists of a sound module, and audio amp, speaker, and battery. The sound module goes high (3.3V) when it is done playing. I would like the entire circuit to shut off after about 2 minutes of not being played. My idea is a 555 that is triggered by this signal, and after two minutes will kill all power through a transistor. Does this seem correct? If so how do I go about choosing the correct transistor? My initial thought was a darlington PNP BJT, but I would like to keep power dissipation down, so I am learning towards a mosfet, but don't know really how to choose one correctly. Appreciate any suggestions, thanks!
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,019
    3,235
    You left out a critical bit of info.
    What it the Vbat voltage?

    This should actually be in the a different forum, such as Analog & Mixed-Signal Design, since there's nothing really digital in your design (except the on/off of the power).
     
  3. Zfensler

    Thread Starter New Member

    May 28, 2014
    10
    0
    Vbat is most likely 4.5 The soundboard does not have a 3.3V power rail either.

    As far as the forum, I agree its not a digital design, I just saw 555 timer in the quotations. Sorry about that.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,019
    3,235
    Then just about any logic-level P-MOSFET [Rds(on) of ≤100mΩ specified at a Vgs of 5V or less] should work for you.

    It's okay to post in the Digital forum if you like, but you are likely to get more responses if you post in a forum more appropriate to your question type. ;)
     
  5. Zfensler

    Thread Starter New Member

    May 28, 2014
    10
    0
    Awesome thanks!
     
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