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flyback voltage

Discussion in 'General Electronics Discussion' started by hpfiend, Oct 24, 2013.

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  1. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    Hey all-

    Hi there- If I use two schottky diodes in parallel in opposite orientations will that protect my circuit from flyback and allow current in both directions? Right now I have just two LED to absorb it but feel that this should be improved on.

    Thanks!

    Here is a ASCII diagram

    -----INDUCTOR--------
    |00000000000000000|
    Resistor0000000Resistor
    |00000000000000000|
    |------+ LED - -----------|
    |----- - LED + -----------|
    |00000000000000000|
    |00000000000000000|
    ----- + Battery - --------

    0's are for blank space.
     
    Last edited: Oct 24, 2013
  2. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    Specifically.....

    Can anyone tell me what the circuit sees differently between two of these schottky diodes:
    http://www.mouser.com/ProductDetail...60R3sKQeCok7Vbb2br0wRu30VEk3xqlFeN/ISPuzLMxbI

    installed in alternate orientations as in the circuit above

    VS

    two white LED's also installed in alternate orientations as in the circuit above?

    Do they have a different resistance once voltage is applied? Both read 0 ohm with my multimeter.

    Thanks!
     
    Last edited: Oct 24, 2013
  3. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    I believe this is the schematic translation of the ASCII diagram:

    [​IMG]

    Can you see why this won't work? :(
     

    Attached Files:

  4. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    Yes, that is it, thank you!
     
  5. davenn

    davenn Moderator

    13,894
    1,969
    Sep 5, 2009
    but did you read Laplace's question ?


    Dave
     
  6. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    I did read his question. I figured he was restating it for me as if I knew why it wouldn't work, I wouldn't have asked in the first place?

    I am confused
     
  7. davenn

    davenn Moderator

    13,894
    1,969
    Sep 5, 2009
    OK forgetting the 2 resistors and the inductor exist for a moment

    can you understand the problem with 2 diodes in parallel across the battery

    Hint: even if there was only 1 diode and in a particular orientation you would have the problem.
    Do you see what that problem is ?

    Dave
     
  8. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    oh- its a short to the battery...


    Thanks!
     
  9. davenn

    davenn Moderator

    13,894
    1,969
    Sep 5, 2009
    thats it :)

    and what Laplace was hinting at

    Dave
     
  10. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    Laplace-

    What software did you use to make that nice diagram?

    Thanks!
     
  11. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    I used LibreOffice Draw to create the schematic, and used GIMP to finalize the graphics .png file, both running on Linux. I think there may be versions that run on Windows (don't really know and don't care).

    Have attached a copy of the Draw .odg file with your schematic on the second slide. On the first slide are basic components that I create as I need them. It is a work in progress. Of course, I do have more professional tools I could use to produce circuit diagrams but this is an experiment to see if free, open-source software can produce acceptable results.
     

    Attached Files:

  12. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    Ok- I downloaded libredraw and with your components file I made this! Thanks!

    Will this work as flyback emf protection?

    I have a positive 10 volts on one side of the source and a -14 volts on the other for a net -4 volts.

    It still looks like a short to the battery but I can't figure out any other way to do it but to absorb the pulse with a bunch of LEDs

    Thanks again!
     

    Attached Files:

  13. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    When the loop is closed current (blue) from the battery flows through the resistors and inductor. Note that the diode is reverse-biased. When the switch suddenly opens, current through the inductor does not suddenly stop, rather the inductor generates a flyback voltage as high as necessary to find a path for the current. In this case the inductive kick forward biases the diode and current flows until the magnetic field collapses.

    [​IMG]

    Two, possibly too subtle, points regarding use of Libre Draw. 1: Alignment is easier with snap-to-grid turned on. Component symbols are constructed so that when placing the symbol the reference point snaps to a grid point and any symbol connection points will also be located at a grid point for easy connection of a line. 2: Junction points at the beginning or end of a line are a property of the line itself. Select a line and edit the line properties for arrow styles - select the 'circle' and check the 'center' box.
     

    Attached Files:

  14. hpfiend

    hpfiend

    31
    0
    Feb 20, 2013
    Thank you Laplace!
     
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