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Thread: How to make a PWM circuit

  1. #1
    Senior Member HID KING
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    How to make a PWM circuit

    Here is all you need to know to build a PWM circuit. Thanks to XERO for finding this site.

    http://www.doctronics.co.uk/555.htm

    Here is the rest of what he mentioned about it:

    "basically, if you can't figure it out from that, you prolly shouldn't be attempting it.

    That is the model I'm using for mine, works like a charm, just hook the output pin up to the signal pin on a transistor to activate the LEDs.

    That will get you flashing, atleast. (There's a link for a nifty dowloadable timer calculator so you can figure out values of resistors and capacitors needed)

    The way mine is set up is, I have diodes on the 2 positive(+) inputs, and I flash the LEDs at half their rated voltage. When flashign at half voltage, it's as dim as it should be, when the brake light constant comes on (also at half voltage) it brightens up very noticeably, and a constant half voltage is bright enough in the day time for brake lights.

    There wasn't a significant enough change to just "stop" the flashing, also I couldn't figure out how to do it, that's why I'm doing it this way.

    anyway, just noticed alot more PWM questions, so thought I'd share (and to think, before I got here, I didn't know jack, lol)"


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  2. #2
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    Does the ouput of thoes create a full power source? ex. can I hook up as many LED's (in parrell/ series) that I need?

  3. #3
    Senior Member HID Nut
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    the output source is the same as the input source, I think they're 1.5amps, though. I'd suggest some transistors, unless you're not drawing that much. Don't quote me on the amperage, though.

  4. #4
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    I am still trying to put this all together but this schematic from Ledcar.com
    It should help a bunch


  5. #5
    Senior Member HID Nut
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    I looked at that a while back and got all confused,

  6. #6
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    I was thinking, do you even need a PWM circuit if you have stock input for your tail lights, ground, parking and stop/signal? I mean cant you just run differnt voltages off of thoes to get the desired out put?

  7. #7
    Senior Member HID Rookie
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    It's possible to use different resistor values to dim the LEDs if you are using standard LEDs. One brand of LED bulb uses a resistor bridge or voltage bridge, or something like that. Basically, it uses multiple relays in series and taps different points of the series for the two appropriate voltages.

    However, it is more desireable to use a PWM. Also, with superflux I believe it's the only option. I don't think they can be dimmed by limiting voltage the way normal LEDs can.


    EDIT: Thanks a lot for posting this! I was going to ask if you couldn't just run a straight line to the LEDs for brake lights (with resistor, of course), but I suppose that goes back to the fact that you went with superflux. It's good to know that even with half power it shows up well enough. I'd still like to know how to go full power, since my "brake" LEDs are going to be used for strobes also.

  8. #8
    Senior Member HID Nut
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    you need a circuit that makes it so when the flash from the strobe is sent, it doesn't allow the other voltages to get to the LEDs

    a flip-flop may work, do a google search for "flip-flip", might come up with what you need.

  9. #9
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    Oh, really? I didn't realize it would cause a problem. I just assumed if I put on the brakes it would essentially over-ride the strobe output since it would just be solid power straight to the LEDs. I guess I could put a relay inline with the brake light output so that when I activate the LED strobes, it closes the relay and takes the brake signal off. Honestly, it would be nice if I COULD maintain brake lights at the same time, though. I do plan on running the LED strobes on the way to calls and need to retain the use of my brake lights so people don't run into me.

  10. #10
    Senior Member HID KING
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    This is why I prefer to not use the same LED's for brake and driving lights.


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