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Series RC circuit for LED

Discussion in 'LEDs and Optoelectronics' started by rajat, Sep 12, 2013.

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  1. rajat

    rajat

    16
    0
    Jun 3, 2012
    Hello All,

    Just an easy question probably, I have got Series RC circuit, i.e.

    9v --(connected to) --Reistor (330 Ohm)--- Capacitor (220 microfarads)

    This charged capicitor to approx 6 v.

    NOW

    Resistor (330 Ohm)---Capicitor(220 microfarads)--LED

    But LED will not light??
    Can anyone explain please explain why as for my understanding,I have got enough volt of 6 v where as LED needs only 1.7 v.

    I am not sure on current. I am assuming as I am using 9 v @1.5 amp battery to charge the capicitor, the current should also be approx to 1.5 amp.

    Sorry if it is very simple questions...i have spent hours trying to understand but could not come to any conclusion.
     
  2. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Have you tried lighting the LED directly from the battery to make sure it is working?

    Are you sure you have the correct polarity?

    I tried this and I get quite a flash, diminishing over about 2 seconds.

    Bob
     
  3. GonzoEngineer

    GonzoEngineer

    321
    2
    Dec 2, 2011
    You dumped 220 mF into an LED without a series resistor in between?
    I am afraid you might have blown the LED!
     
  4. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Gonzo,

    He has a resistor.

    Bob
     
  5. GonzoEngineer

    GonzoEngineer

    321
    2
    Dec 2, 2011
    But, his pseudo-diagram doesn't show it in series with the LED.
     
  6. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    yeah that's what I was thinking ... he's dumping the cap directly into the LED

    Dave
     
    Last edited: Sep 14, 2013
  7. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Since the diagram does not show a circuit, I guess it is ambiguous. He should have seen a flash though, at least once!.

    Bob
     
  8. rajat

    rajat

    16
    0
    Jun 3, 2012
    Sorry guys for late reply.

    As they say picture says thousand words...so I have clicked pictures to make it easier

    I am a beginner in electronics.To answer your queries..LED is working fine. I tried to load pic but they exceeded size limitation of the site. Hence i have to use picassa


    Pic 1: Shows all led are working
    https://picasaweb.google.com/lh/photo/ZmtWVNyDKBG1pJIHIwpS1tMTjNZETYmyPJy0liipFm0?feat=directlink

    Pic 2: Size of Capicitor 22 uf @ 25 V sufficient for 9v battery used.
    https://picasaweb.google.com/lh/photo/niEtrbvftk7ddVbiIyZTdtMTjNZETYmyPJy0liipFm0?feat=directlink

    Pic 3: Capcitor charged to approx 6 V using 9V battery
    https://picasaweb.google.com/lh/photo/qojoXr2aVCDGz4EaKiFtH9MTjNZETYmyPJy0liipFm0?feat=directlink

    Pic 4: Battery removed but charged capicitor will not light the LED.
    https://picasaweb.google.com/lh/photo/UIMpk1IiGRdRvrvPBK2D5NMTjNZETYmyPJy0liipFm0?feat=directlink

    I used Series RC circuit to charge capicitor as shown in Pic 3 but still no light to LED in Pic 4.

    Please advise.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
    2,780
    Jan 21, 2010
    The reason is that your last circuit isn't a circuit.

    Here's what you can try.

    1) connect the resistor and the capacitor on the breadboard so that the capacitor charges. I think you are doing this correctly.

    2) remove the battery

    3) connect a LED in the place of the battery

    What you are doing at present has a non circuit going X---RESISTOR---CAPACITOR----LED---X. Nothing will happen until you join the X's together. Note that the LED must be oriented correctly or it won't work.
     
  10. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    So the diagram was not ambiguous after all -- there was no circuit.

    Bob
     
  11. rajat

    rajat

    16
    0
    Jun 3, 2012
    Thanks you guys for all your replies. It worked like a charm and I got LED lighted for 2 sec.
     
  12. Jibby

    Jibby

    15
    0
    Sep 12, 2013
    Because of the capacitor the voltage across the LED is much more than its tolerance level so it is actually failing and it is giving an impression that it is not working.
     
  13. BobK

    BobK

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    1,686
    Jan 5, 2010
    Jibby,

    You should read the entire thread before responding. The issue was already resolved.

    Bob
     
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