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flyback voltage

hpfiend

Feb 20, 2013
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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:

hpfiend

Feb 20, 2013
31
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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:

Laplace

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

attachment.php


Can you see why this won't work? :(
 

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hpfiend

Feb 20, 2013
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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
 

davenn

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Sep 5, 2009
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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
 

hpfiend

Feb 20, 2013
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Laplace-

What software did you use to make that nice diagram?

Thanks!
 

Laplace

Apr 4, 2010
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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.
 

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hpfiend

Feb 20, 2013
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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!
 

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Laplace

Apr 4, 2010
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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.

attachment.php


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.
 

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