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Thread: Need Advice on 12vdc

  1. 20th September 2005 02:27 PM #1
    mustafa56
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    Default Need Advice on 12vdc

    Good Day All

    I have a neccesity to operate 4 different circuits out of a 12vdc, 800ma wall adapter. I need to deliver to separate 6vdc and two separate 9 vdc circuits from the same single 12vdc wall transformer.

    1. One 6vdc circuit wil drive a module for two EL (electroluminiscent) strips.

    2. The other 6vdc will drive approximately 30 white LED's (all 3.3 vdc, 20ma, which have been set up in groups of 4 LED's in parallel with the respective resistor for 6vdc).

    3. One of the 9vdc circuits will drive an LED flasher board (total consumption is 9vdc, 40ma).

    4. The other 9vdc circuit will drive an LED stroboscopic board (also total consumption is 9vdc, 40ma).

    How can I divide these voltage requirements? I suppose the use of Zener diodes and voltage rectifiers may be the solution, but since my knowledge of electronics is just the good old basics, I have no idea how to create the circuit.

    Will appreciate any input, ideas, possible solutions and, of course, any diagram on how to accomplish this.

    Many Thanks.
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  2. 20th September 2005 02:47 PM #2
    stevez
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    If all of the LEDs are in parallel you'll use 600 ma of the 800 ma there. We don't know how much power #1 uses so hard to comment overall. Advise on load for #1.

    If the totals work out you could use LM317, LM7806 or similar 3 terminal regulators.

    I've only got the time to mention this but not work it out - provide multiple 6 volt or 4 volt supplies from the 12 volts to get the current requirement down. Got the picture in my mind but no way to sketch for you. Someone here will get what I mean and explain or advise that it won't work.
    stevez
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  3. 20th September 2005 04:30 PM #3
    zachtheterrible
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    Default

    Another way of doing it would be to get a transformer that has multiple voltage outputs, I found one at wallmart that would output DC 1.5v, 3v, 6v, 7.5v, 9v, and 12v if I recall correctly. Then you would take it apart and use the transformer with a bunch of different outputs. Of course to drive everything at the same time you would have to make a regulator circuit for each output.
    I'm no electronics god, i just talk too much.
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  4. 20th September 2005 08:05 PM #4
    Sebi
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    I strongly recommend to rearrange the LED-group as i drawed - so need only @200mA.
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  5. 20th September 2005 10:37 PM #5
    eblc1388
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    What is the design voltage across the 3R3 resistor?

    If it is 1.35V then PNP transistor pass 400mA. That's 40mA for each LED branch. The PNP would need to be fully turn ON to provide that. But then there is no reason to use a transistor because it has nothing to regulate.
    L.Chung
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  6. 21st September 2005 07:15 PM #6
    Sebi
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    This is a PNP current generator. On the 3R3 resistor always drop 0,7V, if the red LED forward voltage 1,4V...
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