Charging-Discharging Capacitor

Discussion in 'General Electronics Chat' started by aacbh, Feb 9, 2018.

  1. aacbh

    Thread Starter New Member

    Feb 9, 2018
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    0
    I have an application where I charge up a capacitor from a DC source.
    I only want the capacitor to discharge into a load if the DC source charging the capacitor increases and then goes to zero. I have considered just using an upper threshold for the source voltage and trigger off that, but since the DC + source can vary I wanted to add the condition that the source go to zero to activate the mosfet. Both conditions need to be true.
    I do not have another power source Circuit.jpg available to power ICs, such as a comparitor, so it needs to be done with diodes, caps, etc

    Any suggestions for a circuit? The capacitor will discharge to the load thru a mosfet so I would like to supervise the discharge from the mosfet. This is only a very short duartion discharge of the capacitor into the coil of a latching relay.

    Thanks for all the help!
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
    5,951
    1,120
    hi aa,
    Welcome to AAC.
    What you are asking can easily be achieved are you able to build circuits.?
    E
     
  3. aacbh

    Thread Starter New Member

    Feb 9, 2018
    4
    0
    Yes.
     
  4. ericgibbs

    Moderator

    Jan 29, 2010
    5,951
    1,120
    OK,
    Give me some details of the working voltage and the relay coil resistance.
    Also some idea of the pulse width you want from the relay drive.

    Any other information about the project will help.
    E
     
  5. aacbh

    Thread Starter New Member

    Feb 9, 2018
    4
    0
    The working voltage will be approx 0 to 5V.
    The latching relay coils are about 64 ohm. I have not settled on all the components yet. Just looking for the methodology on how to accomplish this. The capaitor will need to store enough energy to drive the latching relay coil. This is a minature signal latching relay. The DC+ source that charges the capacitor will be available for plenty of time prior to the action requested.

    THX
     
  6. ericgibbs

    Moderator

    Jan 29, 2010
    5,951
    1,120
    OK,
    5V/64R is approx 80mA.
    A 2N2222 transistor will be suitable.
    How do you plan to start the pulse, is it a push switch or a micro controller output pin.?

    E
     
  7. ericgibbs

    Moderator

    Jan 29, 2010
    5,951
    1,120
    hi,
    This typical circuit would be a starting point.
    E
     
  8. aacbh

    Thread Starter New Member

    Feb 9, 2018
    4
    0
    Your .gif file causes an error. I do not have an external way to trigger the mosfet. I want to trigger it when the source DC+ rises and then goes to zero after that. THX
     
  9. ericgibbs

    Moderator

    Jan 29, 2010
    5,951
    1,120
    hi,
    Changed the file type to jpg, can you open that.?
    Will look at some options regarding the trigger.
    E
     
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