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Using an LED with 220V AC

Discussion in 'Microcontrollers' started by haxan, Jun 11, 2010.

  1. haxan

    haxan New Member

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    Hi, can anyone suggest a simple circuit which lights up an LED with 220V AC. I am trying to make something without the use of transformers.

    Maybe a bridge rectifier and a resistance connected with LED.
    What should be the resistance value (is 1M enough) ?
     
    Last edited: Jun 11, 2010
  2. cobra1

    cobra1 New Member

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    what are the specs of the led???
     
  3. SYE

    SYE Member

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    Most LED's don't like being reversed biased by more than a few volts so you will need to add some diodes to protect your LED.
     

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  4. dave

    Dave New Member

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  5. haxan

    haxan New Member

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    Why so many diodes, cant i just use a simple bridge with resistor in series ? :)
     
  6. cobra1

    cobra1 New Member

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    ok lets see

    220 v AC rectified will give you about 300v DC

    since you didnt put the specs of your led lets assume your led is red..2.4v @ 20ma

    this works out that you need a resistor rated at 15k ohm @ 6watts

    Thats a big resistor, it will just gets hot and use far more power than the led uses.
    Simply put its impractical.

    What do you intend using this for as there is more than likely a better way to do this
     
  7. haxan

    haxan New Member

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    I want to attach an LED in a switch board which should glow when electricity is coming in that board and should not glow when not.

    I actually made a circuit earlier for a Fan dimmer which had 220V AC come in, connected to a bridge and went directly into NPN-Optocoupler for Zero crossing detection. which gave pulses to microcontroller when ever a zero - crossing went by. For this reason i thought that it would be easy to do this.

    Also a few years ago i saw a small night light made from one LED (green) which plugged directly into 220V Mains. It didnt have any transformer.
     
  8. Kryten

    Kryten New Member

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    You culd also put diodes in oposites directions without rectifiing ( you know they will turn off and on @ 50Hz) ;)
     
  9. haxan

    haxan New Member

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  10. csaba911

    csaba911 Member

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  11. haxan

    haxan New Member

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    It is saying "Invalid Attachment specified. If you followed a valid link, please notify the administrator"
     
  12. yash gupta

    yash gupta New Member

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    It is the only solution that i know. you will have to use a circuit as shown by the above post.
    The impendence of the cap is used here instead of a resistor to limit the current.
    The benefit is that a cap doesn't heat up, as the current ans voltage are 90deg out of phase.
    You can use a simple formula for the impendence of a cap.
    Z=1/(2*pi*50*C)
    Generally, as it is shown, 180-220 nF is fine for a 5mm red led.
    And dont forget to use a diode to prevent high reverse voltages.
    A 1n4007 in opposite dir in parallel to the LED will do.
    Make sure that the voltage rating of the cap is 400V or so.

    But, this type of supply is not recommended if you plan to use it for serious circuits.
    Use a limiting cap,a fuse,a full wave bridge rectifier, a zener and a filter electrolytic cap to create a useful power supply without transformer.
    Limiting caps with values ranging upto 2.2uf 400v are small enough to be used as a cheaper and smaller alternative to transformers.

    But, don't think of using transformerless supply for expensive circuits. They can blow anytime.
     
  13. haxan

    haxan New Member

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    I found an even simpler circuit.

    The only problem is that the LED is not very bright. Can anyone suggest how to make it a little bright.? I am using standard green LED.
     

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    Last edited: Jun 12, 2010
  14. haxan

    haxan New Member

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    If the capacitor blows up, it will stop the LED to glow right? Also i hope these capacitors have a good life so that i dont have to change it after a few days.
     
  15. yash gupta

    yash gupta New Member

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    Sorry for late reply.
    That 1k is not really required.
    Use 4007 instead of 4148 and 380nf or near about.
     
  16. colin55

    colin55 Well-Known Member

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    The circuit is halfwave and you will get 25Hz flicker, which is noticeable. 100n caps will only deliver 10mA in full wave or 5mA in your situation, so a few 100n in parallel is required. They need to X2 caps or at least 400v.
    You really need a full wave rectifier at the front end for better results.
     
  17. Diver300

    Diver300 Well-Known Member

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    The 1k is useful, as it reduces the surge when you turn the circuit on. Without the 1k, you are trying to charge the capacitor almost instantaneously.
     

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