7815 regulator

Discussion in 'General Electronics Chat' started by arun230, Mar 14, 2013.

  1. arun230

    Thread Starter New Member

    Mar 12, 2013
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    HI , How to select 7815 regulator capacitor C1 and C2 value . I saw different C1&C2 value in different circuit how these value are picked.I am using 7815 regulator for 12v ,10w solar panel for 12v lead acid battery
     
    Last edited: Mar 14, 2013
  2. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    1uF for lower currents and if you already have a bulk capacitor.

    Otherwise 47uF etc. at the input and output.

    It is not critical. Preferably not using long wires or PCB traces.

    If you leave them out you may get weird oscillations at some time. Not neccessarily immediately but after some hours or days.

    You don't need 220uF or 470uF or 1000uF- overdoing it.

    Really nearly any small electrolytic cap. will work. 1uF is fine from my experience.
     
  3. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    1,393
    Here is my standard LM78xx regulator circuit. The two small caps are required. The 10 μF is highly recommended, and the 1000 μF can be anywhere from about 220 to 2200 μF depending upon how much ripple is on the input.
     
    Last edited: Mar 14, 2013
  4. takao21203

    Distinguished Member

    Apr 28, 2012
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    I use the 78l05 sometimes. 3x 1uF here. From a electronic transformer (which has a bulk capacitor already).

    Works fine not just on the margin, 32 KHz crystal osc is quite sensible. No resetting etc. during weeks 24/7.

    See it that way: Why should the tiny 78L05 have so many support parts, taking up much more space and costing much more than the 78L05 itself?

    It would be pointless to make 78L05 or 78M05.

    Sure if you want 1/2 Amp, use more than 1uF.

    But that's the advantage of 78L05- less parts than a switcher and cheaper.

    By the way 7805 was used in the SEGA MASTER board and SEGA GENESIS board. Not too sure if they had the caps set as it is often seen recommended on forums. The Genesis had a small ferrite filter on the voltage supply input.

    SEGA Master board was middle 1980s, Genesis was sold well into the 1990s.
     
  5. takao21203

    Distinguished Member

    Apr 28, 2012
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    47uF should be fine for that.

    A 10W panel will output so little current, you don't normally need to regulate it for a 12V acid battery. Have you measured actual currents in full sunlight?

    The battery is so much low-Z, almost the same as a capacitor. The panel produces DC only. 47uF is very generous, I'd say you are safe with that. Use any electrolytic caps you have around really.

    If you have long wires and some weird caps you can get oscillations maybe. Not with short wires and high-grade 1uF caps.

    If you have a long cable, 20 metres or so, install a small cap. on both ends if you want.
     
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