Automotive 12vdc powering microcontroller circuit

Discussion in 'The Projects Forum' started by Spragmatic, Apr 1, 2010.

  1. Spragmatic

    Thread Starter New Member

    Mar 30, 2010
    6
    0
    Hello-

    I have designed and built a Parallax SX28 microcontrolled circuit to drive a relay board for a project I'm doing. I've got everything installed and working in the truck. The SX28 protoboard I'm using has a voltage regulator circuit that suggests 6-9vdc input (specs say 6-30vdc). With that being said I hooked directly to the ignition source in the truck. It works, but at higher voltages(13-14.5vdc) I get some random glitches. I want to build a 9vdc(using a L7809CV) regulated power supply to power the board with constant voltage. Current is at 300ma max when circuit is fully loaded.

    My questions are--

    1- What is the best way to build the voltage regulator circuit?

    2- Should I or can I use a diode bridge on the DC input voltage?

    3- Do I just use the diagram that is in the L7809CV datasheet?

    Thanks!!
    Greg
     
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    1 -- refer to data sheet, and use good lot of cap on input, perhaps add a ferrite bead if noise is really high frequency.
    2-- no diode bridge, one diode if you fear you will connect your circuit backwards.
    3 -- pertty much, but read the text as well.
     
  3. Spragmatic

    Thread Starter New Member

    Mar 30, 2010
    6
    0
    Thanks!! That's what I was thinking! :)
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Automotive environments are pretty brutal.

    You might want to use some extra filtering on the front end of it.
     
  5. Spragmatic

    Thread Starter New Member

    Mar 30, 2010
    6
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    SgtWookie-

    What kind of filtering would you suggest? I haven't really ever had to add filtering to my projects. Thanks!!
    Greg
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    This works pretty well in simulation:

    [​IMG]

    V1 and V2 are simulations of a range of input voltages you might see, but with a lot of noise on it.

    L1 and L2 represent inductors that you can find at any Radio Shack; catalog number 273-102 "RF Choke"

    The 5 Ohm resistor really knocks down the noise quite a bit. It will also take some of the heat dissipation load away from your regulator. It should be rated for at least 1W. You could use a couple of 10 Ohm resistors wired in parallel to get 5 Ohms.

    R2 simply represents your 300mA load.

    I used an LM317 in the simulation, as I didn't have a 7809 regulator model available.
     
  7. Spragmatic

    Thread Starter New Member

    Mar 30, 2010
    6
    0
    Great Service SgtWookie!! I'm going to give this a shot and see how it does. Thanks for the quick response. I'll let you know how it works out.

    Greg
     
  8. Spragmatic

    Thread Starter New Member

    Mar 30, 2010
    6
    0
    SgtWookie-

    I have finally built the circuit and I have a question. Do I connect the ground side of my load between R3 and R4 in the above schematic? Thanks!!

    Greg
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Your load takes the place of R2.

    All of the ground symbols in the schematic are connected together, and would be connected to the negative (ground) terminal of your vehicle's electrical system.

    If you are using a 7809, then R3 and R4 would not be used, and the GND terminal of the 7809 would be connected to ground. If you were using an LM317, then you would need R3 and R4 connected as shown.
     
  10. Spragmatic

    Thread Starter New Member

    Mar 30, 2010
    6
    0
    Thank you Sir!! I'm going to test it now!
     
  11. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    SgtWookie,
    Do you have any objection to me showing your diagram/simmulation to the Picaxe forum. Some of thier members run into problems with Picaxe automative applications and may benefit from your expertise.

    Thanks

    pilko
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I don't mind a bit.

    Please reference "AllaboutCircuits.com" when you post it.

    Note that it is not an ideal solution; but it will help quite a bit to reduce transient spikes using commonly available components.
     
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