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5volt regulator added to circuit not working? — Parallax Forums

5volt regulator added to circuit not working?

metron9metron9 Posts: 1,100
edited 2004-11-02 20:04 in General Discussion
I am making a simple emitter-detector switch
It works on 5 volts

I want to use the 24 volt supply in the project

Can I just add the 5volt regulator like I show it in the drawing?

I tried a adjustable voltage regulator (its all I had on hand) but even though the led lights up showing I have power to the ir led
the transistor wont trigger the relay. Oh and i forgot to show the diode across the relay fot the inductance spike.

In case the attachment thing isn't working: http://www.dowvideofutures.com/images/question1.jpg
question1.jpg
900 x 814 - 87K

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-11-02 15:53
    If memory serves, the LM7805 can handle 30V on the input side (As Jon says, always check your datasheet!), so yes, you could connect like your diagram, but remember, regulating from 24V down to 5V will dissapate most of the lost power through the regulator in the form of heat, so you should get a nice heat sink on there.· The actual size will depend on your current requirements, but from the looks of your schematic, it's not going to be a problem.



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    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
  • ellizardellizard Posts: 106
    edited 2004-11-02 18:18
    HI metron9



    for what I can see there is a mistake in the connection of the relay, it should be connected betwen the·+ 5 V·and the collector (that you call drain) of the transistor.

    NOT TO THE COLLECTOR AND THE EMITTER, this way when the base of the transistor is positive, the collector will go low energizing the relay.

    In your way, the relay, will sink current from the resistor that beeing of 1Kohm, will not allow the relay to move because of the 0,005 A current TOO LOW.

    Ohm's Law will tell you everithing in this case.

    best regards
  • metron9metron9 Posts: 1,100
    edited 2004-11-02 18:44
    oops yes you are correct, it was 3 am when I drew that. It is connected to the +5 volts

    I will redo a schematic showing how I put the variable voltage regulator in and see if you can figure out why its not working.
    As this schematic was drawn by someone else and I added the voltage regulator, I need to understand what I did wrong.
    Thank's
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-11-02 20:04
    Hey I can't believe *I* missed that!

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
    ·
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