[HELP!!] Will these LED be okay in this circuit? (Circuit diagram included)

Discussion in 'The Projects Forum' started by ABaruwal, Apr 23, 2011.

Will the LEDs be okay as the way they are?

  1. Yes

    0 vote(s)
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  2. No

    2 vote(s)
    100.0%
  1. ABaruwal

    Thread Starter New Member

    Jan 28, 2011
    15
    0
    Hello
    I'm making a wake up light which will gradually turn on when a power is turned on.

    The power source of this circuit is 9-12V, and each of the leds have standard (330ohms) resistors before them.

    So my question is; Will the LEDs be okay and not burn out?

    Because when i breadboarded the led to check its brightness by slowly turning the power up with a standard resistor before it, it burnt out when it reached about 3V.

    Thank you
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    I'm betting you has a wiring error, and did not have the resistors in series with the LEDs as shown. LEDs must have resistors, it is not optional.

    According to my off the cuff math, you would have had 30ma going through each LED. This is a bit high, I usually go for 20ma, but it would not have burned the LEDs out quickly. Slowly maybe, in a matter of weeks or months, but not minutes. Without knowing exactly what LEDs you used this is a educated guess, but it is a good one.

    Care to show a digital picture of your breadboard? Where you got the LEDs and their type would also be helpful.

    I'm not going to answer the poll due to lack of data.

    Rereading your post, you did not say it was the LEDs that burned out. Was it?
     
  3. ABaruwal

    Thread Starter New Member

    Jan 28, 2011
    15
    0
    Unfortunately, i didn't take the picture of the breadboard.
    The LEDs i used were:
    Blue LED 5mm Ultra Bright (9000mcd)
    Lenses Type : Crystal Clear
    Case Style : Round 5mm
    Brightness : 9000mcd (Ultra Bright)
    Forward Voltage : 3.2v – 3.8v
    Forward Current : 20mA (Typical) 30mA (Max)

    And yes, the leds burnt out rather quickly within few seconds.
    This was the first time I was breadboarding and maybe i got the series and parallel wrong..?

    Thank you
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your schematic had the darlington transistors connected wrong. Your right side transistor was doing nothing.
     
    ABaruwal and RogerTango like this.
  5. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    If the LEDs were connected backwards to the power you could have burned them out. While LEDs are diodes they can only take 5V PIV (reversed voltage) max, especially blue types LEDs. They would not have burned out quickly with 30ma (adjust for the revised specs it would be 25ma), which puts it further away from the realm of possibility.

    They are static electricity sensitive, but it wouldn't hit them all equally if that were the case.

    LEDs are very predictable, and I know them well.

    This is a tutorial I've written for beginners, LEDs is chapter 1.

    LEDs, 555s, Flashers, and Light Chasers
     
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