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placement of diode — Parallax Forums

placement of diode

CogburnCogburn Posts: 62
edited 2005-09-16 10:55 in BASIC Stamp
I am trying to switch a small 12 volt motor on and off·with the basic stamp and a switching transistor.· I am using the diagram that Scott Edwards suggested in his Nuts and Volts of Basic Stamps column page 54.· I have the circuit working if I place an LED as the load but before I connect my electric motor in place of the LED, I·want to be sure·where to place the diode to prevent transient currents from damaging my stamp.· The instructions seem vague as they say " Just add a common rectifier diode like a 1N4002 with its banded end to the + connection of the relay or motor."·· Is it in series or parallel? Where does the other end of the diode belong?· I would appreciate a diagram of the proper placement of the diode.

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Comments

  • doggiedocdoggiedoc Posts: 2,245
    edited 2005-09-15 20:07
    ....snip....


    Having said that - You probably will need a Darlington Array or a MOSFET type H-bridge or half-bridge to drive the motor - the Stamp can't source or sink enough current for DC motor.

    There is another Nuts and Volts article that covers that nicely.
    Jon Williams posted this link in a similar thread covering a similar problem. It should help.

    LINK:
    www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf

    Doc

    Post Edited (doggiedoc) : 9/16/2005 2:38:19 AM GMT
  • CogburnCogburn Posts: 62
    edited 2005-09-15 20:13
    That is the same article that I am referring to.·

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    Showing up to school doesn't·mean you are a student any more than crawling up in an oven means that·you are a biscuit.
  • allanlane5allanlane5 Posts: 3,815
    edited 2005-09-15 20:14
    The diode goes in parallel with the motor leads 'reverse biased' (Anode (little arrow) to minus, Cathode to plus -- "pointing up" in other words). This does assume you only want to run the motor in one direction.

    What happens is, when you energize the motor, a magnetic field is built up, which runs the motor. When you cut off the voltage, that magnetic field collapses -- this generates current, which runs in the same direction as the current you were using to run the motor.

    So, you need to have somewhere for that current to go. A diode going from Negative to Positive on the motor gives that current somewhere to go.

    Oh, and if you have the transistor in the circuit, transients would damage the transistor, not the BS2.· Not that you want to damage either, of course.



    Post Edited (allanlane5) : 9/15/2005 8:14:31 PM GMT
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2005-09-15 20:18
    The diode goes in parallel see page 58 of...

    http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf


    See also...

    http://forums.parallax.com/attachment.php?attachmentid=37701

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • doggiedocdoggiedoc Posts: 2,245
    edited 2005-09-16 00:23
    Cogburn said...
    That is the same article that I am referring to.

    blush.gif ooops... I suppose I should have read a little further....


    .... just trying to help.
  • CogburnCogburn Posts: 62
    edited 2005-09-16 10:55
    I appreciate all the help I can get doggie doc and to all I say thanks.· The forum has saved my bacon many times now.·

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    Showing up to school doesn't·mean you are a student any more than crawling up in an oven means that·you are a biscuit.
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