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Light Bulb

Discussion in 'LEDs and Optoelectronics' started by Glenn Wilson, Apr 5, 2015.

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  1. Glenn Wilson

    Glenn Wilson

    Apr 5, 2015
    Hello Members,

    Could someone please help me, I have a 240volt LED light that I only want to come on when mains voltage is reached in the UK that's 240 v AC, but what is happening, is when a lower voltage is applied say 190 volts AC the bulb is coming on but dimmer than when 240 is applied

    Can some one tell me how to prevent the light coming on when voltages less than 240 V are applied, so what I don't want is the bulb coming on when lower voltages than 240 v are applied and when 240 is applied the bulb switches on at full brightness

    Many Thanks

  2. alex Chiu

    alex Chiu

    Apr 1, 2015
  3. Glenn Wilson

    Glenn Wilson

    Apr 5, 2015
    Hello Alec

    Thanks for your reply I have had a look at what you suggested they are to expensive they cost about £70.00 is there another way that is cheaper


  4. ramussons


    Jun 10, 2014
    Well, you need a voltage sensor that disables the LED from switching ON below a certain voltage. That's what
    alex Chiu said.
    You can make one or buy one. Making one will be <<< £70.00.
  5. Glenn Wilson

    Glenn Wilson

    Apr 5, 2015
    Thanks for your reply

    Do you know of a kit I could buy for this purpose that I could build myself as new to electronics
  6. duke37


    Jan 9, 2011
    I would use a wall wart with AC output.
    Rectify this to give a power supply for the circuit with a suitable time constant.
    Compare this supply with a reference and drive a relay.
    You will only be dealing with low voltage in the circuit so safe for a beginner.
  7. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    Firstly you need to get an old CFL and remove the 3003 transistor.
  8. Gryd3


    Jun 25, 2014
    That would be a great learning process. but sounds like it requires a second power supply.
    If this is learned and understood there is no reason an almost identical circuit could be built into the light build or light fixture.
    Regardless of the method used though, you MUST have some kind of circuit to detect the current voltage level and switch on when it has reached a set point. They can be bought or built, but great care should be taken when dealing with mains voltages.

    Perhaps Colin can elaborate on his 3003 proposal. We wouldn't want you to begin hacking apart fluorescent light bulbs if this solution is not acceptable to you
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