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VReg Turn-Off Delay

Discussion in 'General Electronics Discussion' started by sall, Jul 8, 2011.

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  1. sall


    Jan 29, 2010
    I am looking for a way to delay the turn off of a voltage regulator. So, that once power source is turned off the regulator stays on for 5-15 seconds. Thanks in advance!:D
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Where will the power come from for that 5 to 15 seconds?

    Do you want the regulator to power the equipment even though it is receiving no power?

    That calls for very large capacitors (cf with what you would normally have) or some form of battery backup.
  3. poor mystic

    poor mystic

    Apr 8, 2011
    Please tell us what kind of equipment needs the turn-off delay, and why it would be better for turn-off to be delayed. These details can go a long way in helping us to visualise a solution.
    Please include all the details - make & model, usage... and we'll be able to give it some thought.
  4. sall


    Jan 29, 2010
    This 12v Vreg is being used to regulate voltage to the touchscreen display in my vehicle. The reason for the regulator is the monitor can only handle 14v and my vehicle regularly charges at above 15v in cold weather (normal for my vehicle). I would like to have the 5-15 second delay in turning off so that whenever the ignition goes from OFF to ACC to RUN or from OFF to RUN to START, etc, etc. There is not much today about going off during cranking (different issue).

    The laptop is setup so when loses power from DC-DC adapter the system goes into hibernate utilizing the internal battery. During this hibernate sequence I would like to be able view the screen to make sure it hibernates gracefully as well.

    Is it better to use a relay in this situation before the vreg and use a cap to keep the relay on after relay loses trigger input? I was trying to keep the circuit to a minimum space constraint as space is very limited.

    I apologize for not thoroughly explaining in the beginning.
  5. MagicMatt


    Jun 15, 2011
    Do you have a wattage for the touchscreen display? They're quite power hungry aren't they? I'm guessing around 10-15watts.

    I'm no expert though, so this really is just an idea that maybe you or somebody more experienced could take further...

    Not sure what your vehicle is like, but mine has a feed that stays live all the time (one to the inside lights is like that for example). I think I'd use one of the always-live feeds as main power, controlled by a relay. I'd have a 555 timer, driving a transistor to switch the relay off 15 seconds after the ignition is turned off, and maybe chuck a big cap in there just to control any brief power dip during vehicle start.
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