voltage control to 555

Discussion in 'The Projects Forum' started by oopsSmoke, Apr 20, 2010.

  1. oopsSmoke

    Thread Starter Member

    Jun 16, 2009
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    0
    Hi all,

    I'm still working on that PWM problem from last year and it has gone through many changes. However, what it seems I need to do now is regulate the voltage to my 555 and at the same time give the motor unregulated voltage. The circuit by itself, without a voltage regulator, seems to work great except for the mosfet getting really hot. But I haven't had any luck trying to add a 7805 to it. Quite honestly, I don't even know where to put it. I've tried the Vin, but I think I've just been grasping a straws.

    If anyone could help, that would be fantastic! I'll attach a copy of my fritzing generated schematic after work.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    The MOSFET gets hot? There may be a problem there. We'll wait for the schematic.
     
  3. oopsSmoke

    Thread Starter Member

    Jun 16, 2009
    23
    0
    Ok, here it is without the 7805.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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  5. SgtWookie

    Expert

    Jul 17, 2007
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    That can't possibly work the way you have it wired.

    What is the "Power Plug" you show? I hope that's not to mains power! 12v-14v DC, perhaps?

    You show a P-channel MOSFET, but it's oriented upside-down. You appear to be switching power to both the 555 timer and the motor. That's not going to work.

    You show no values for your resistors, capacitors, or part numbers for the diodes. Please fill them in.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    A 555 at 12 V will drive a MOSFET just fine by itself. A MOSFET should have a gate resistor.

    You can cover the basics at the link I gave.
     
  7. oopsSmoke

    Thread Starter Member

    Jun 16, 2009
    23
    0
    I apologize for the lack of labels on the diagram, I'll take care of that tonight. From the way it sounds though, I should take this back to formula. With that said, I did find this on the parallax forums and it seems to do something very similar to what I am trying:

    http://forums.parallax.com/forums/default.aspx?f=36&m=369913
     
  8. oopsSmoke

    Thread Starter Member

    Jun 16, 2009
    23
    0
    I've been trying for the last few days to partially breadboard the diagram in my previous post, but I'm not quite sure how to breadboard the ground. Does this just go back to the negative end of my power source?
     
  9. oopsSmoke

    Thread Starter Member

    Jun 16, 2009
    23
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    I think I found my answer, it is the return path. So, in this example it would be the negative terminal of the power source, right?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Yes. All "grounds" should be connected together, and collectively connected to the negative terminal of your power source.
     
  11. der_fisherman

    New Member

    Aug 9, 2008
    2
    1
    In your original schematic, in addition to the errors already noted, the diode appears to be the wrong way around, it will conduct all the time.....
     
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