I need help with pulse width modulator with constant 12volt output

Discussion in 'The Projects Forum' started by ron roberts, Sep 7, 2010.

  1. ron roberts

    Thread Starter Active Member

    May 7, 2008
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    I need help with pulse width modulator with constant 12volt output

    Hi all hope some one can help with this.
    I need to build a circuit that will allow a constant 12volt until it’s activated, when it’s activated it needs to pulse the output just like a pulse width modulator, when switch off it must go back to a constant 12volt until it’s activated again.

    The output needs to supply a +12volt rail to drive an array of bulbs.

    I’ve tried to show more details what I need in a diagram

    [​IMG]
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Do you have any preferences on what type of components you use? Are you seeking to master the use of a certain element(say transistors, or relays)?

    Next question- how fast does the modulation need to be? Faster than human eye response? Meaning it will simply appear to 'dim' the bulbs, or do you want the modulation to be visible, as in a flashing/dancing light display?

    How much power( amps) are available from the 12v supply? More than enough for driving multiple relay coils, or just barely enough to light up 64 lights?

    Are the lights incandescent, or LED? I'm assuming incandescent because of the 12 volt supply. Are you aware of the amount of power 64 bulbs will require?

    Lots of questions here. It would help if you fleshed out your plans a little more. Details, details, details. The more the merrier so to speak.

    See attachment for a solid state relay which handles up to 4 amps/20VDC which you could leave on steady, or pulse. Response time is a max. 5 msec on, and 0.5 msec off. You would probably need 4 of these to handle 64 bulbs, so control circuits would be minimal.
     
    Last edited: Sep 7, 2010
  3. ron roberts

    Thread Starter Active Member

    May 7, 2008
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    0
    Q: Do you have any preferences on what type of components you use? Are you seeking to master the use of a certain element (say transistors, or relays)?
    A: Transistors or mosfets would be best for me.

    Q: Next question- how fast does the modulation need to be? Faster than human eye response? Meaning it will simply appear to 'dim' the bulbs, or do you want the modulation to be visible, as in a flashing/dancing light display?

    A: Sorry I would like to be able to adjust with some kind of pot.

    Q: How much power( amps) are available from the 12v supply? More than enough for driving multiple relay coils, or just barely enough to light up 64 lights?

    A: there will never be all on at once maybe 10 pushing it at 15.
    As the Control board users UNL2803’s for all out puts. it will be one of this outputs that will be used to switch the circuit in and out.


    Q: Are the lights incandescent, or LED? I'm assuming incandescent because of the 12 volt supply. Are you aware of the amount of power 64 bulbs will require?

    A: This display is all ready built and running for some time, just want to modify it. The display users 60 incandescent bulbs but will be change at some point, it users MIDI files to flash the light. A keyboard can also used.


    thanks for your reply.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    A: This display is all ready built and running for some time, just want to modify it. The display users 60 incandescent bulbs but will be change at some point, it users MIDI files to flash the light. A keyboard can also used.

    If you just want to make them flash and the board is already built and in use then how about this.

    break the inputs lines to the 2803's and send them to a series of AND gates which output into the 2803's. For the other input to the AND gates use a 555 timer or equiv. and use an RC network to set freq. using a pot for the R part, so yo can set the flash rate. Only the lights being sent an "on" signal would flash done this way. The addition of an 'OR' gate on the original 2803 inputs tied to the timer input of the AND gates, controlled by a switch, would give you the option of turning on all the lights in a 'strobe' like effect.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    I thought that seemed to easy. You have 12volts going into those 2803's don't you!

    Damn, scratch that idea. logic gates won't do you any good with that voltage level.

    Let me think awhile on it, I'll try to come up with something else
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Okay, I think you can still use the 555 timer and pot for 'blink' freq control, but instead of messing with the 2803's, you'll need to use some NchFETs on the lamps. Between the lamp and ground.

    Here's my idea. The timer will feed the gates on ALL of the FET's and you'll keep the pot turned all the way for a 99%+ duty cycle for normal operation. (may have to buffer the output from the 555 through some opamps to feed all 64, maybe not though since FET gates don't use much current, if any. The number of lines and their length might require some additional drive though.) Upon turning down the pot you'll get flickering of the lights at a high freq and getting slower the farther down you go with the control pot. This would require minimal extra juice, hardly any in fact. Even though you are switching on all the FET's at once, only those lamps getting drive voltage from the 2803's would be lighting up.
     
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