Electronics question

topic posted Thu, September 24, 2009 - 10:48 AM by  ALLAH God of...
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I have never been an electronics guy. The math made my eyes go off in different directions.
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  • Re: Electronics question

    Fri, September 25, 2009 - 1:40 AM
    Try this:
    led.linear1.org/led.wiz

    > Resistors are supposed to be cheap

    The one you have selected is a big one (5W), I don't think you need one this powerful.
    In general, for common parts, Radio Shack is way cheaper than DigiKey.

    > I should have thought the Resistor would need to be on the + terminal of the LED and not the - terminal.

    It should be the same
    • Re: Electronics question

      Fri, September 25, 2009 - 11:34 AM
      *************It should be the same ***************

      Same as what? The negative terminal or the positive?
      Or does it matter?
      • Re: Electronics question

        Fri, September 25, 2009 - 11:27 PM
        It doesn't matter....
        You can put the resistor on the + or on the - terminal
        • Re: Electronics question

          Sat, September 26, 2009 - 6:11 AM
          I forgoe the peak voltage too. It's the square root of 2 times the base voltage.

          I think I'll use the transformers and a bridge rectifier.

          I think a capacitor will smooth out the current but I don't know which kind.
          I understand start and run capacitors just fine and I know that bigger is always better so the down stream cascade doesn't make 'em burst but this is different isn't it?
          I need a different capacitor but the words I know: reservoir capacitor don't get a response when I plug it into any electronics supply house search protocols.

          I figure a 6 LED string Of about 2 VDC draw (each LED) powered by a 24 Volt Transformer will need a 1.2 kΩ 1/2 W resistor which would would give a bit less than 20 mA . A little Cap on that circuit would make smooth the flow out.

          I still don't full understand the power consumption issue. I figure I'll build a board and add Serial strings of LEDs (6 in Parallel) until the power draw. starts to make 'em dimmer.
          • Re: Electronics question

            Sat, September 26, 2009 - 1:04 PM
            > I think a capacitor will smooth out the current but I don't know which kind.

            Electrolytic: en.wikipedia.org/wiki/Elec...capacitor.
            The bigger the better. Use a voltage higher that the rectified AC.
            Electrolytic capacitors have polarity, if you reverse them they can (often will) explode.Nothing dangerous though.

            > A little Cap on that circuit would make smooth the flow out.

            Yes, but rectified/filtered DC will have a slightly higher voltage than the transformer output (don't remember the constant...)

            > I still don't full understand the power consumption issue.

            Unless you are building something really big, any small transformer will have plenty of juice. I wouldn't worry about it.

            For the capacitor, I would desolder one form some old electronics. Elecrolytic can get expensive.

            This is a nice doc on the subject:
            www.st.com/stonline/boo...docs/1707.pdf

            If you really want to get fancy, you can decide to add a voltage regulator (see Fig 16-18) the 78XX and 79XX (XX is your output voltage) are very simple to use.


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