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Camera flash style circuit - help!

Discussion in 'General Electronics Discussion' started by tabs, Oct 14, 2010.

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  1. tabs


    Oct 14, 2010
    Hi guys,

    I've been looking for a knowledgeable electronics forum for a while, where I can go to ask the stupid questions that I usually get stuck on. I've stumbled across your site and think that it might be the right place for me. I hope you don't mind me jumping right in, but I'm trying to put together a fairly simple circuit and need some guidance;

    I have a number of 1W LED spots, running at either 350mA or 700mA depending on which transformer I use (I have two). I'd like to wire these up so that they work like a camera flash - I.E once they are triggered they'll produce a couple of seconds worth of light, before fading to off. Quantity of LEDs is flexible, up to a max of four. Basically whatever works. The whole thing will be UK mains powered (230V @ 50Hz). The transformers I have step down to 24V.

    I *think* that I want to be using capacitors, but am unsure of the quantity, type or position in the circuit. I'd really appreciate any help that you could give me to get this sorted!


  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    What colour are the ones running at 700mA? I hope they're red or yellow.

    It sounds like you have some downlight replacement LED "bulbs". These have their own controller in them, so you can just hook them up to an existing downlight system and off they go...

    If you were using bare LEDs, then it would be possible (although not trivial) to create a circuit to do what you want.

    If they are as I suspect, it may be much harder.

    It might be possible to switch power to the LEDs using PWM, but it may not work, and it may even damage the drivers.
  3. tabs


    Oct 14, 2010
    You're kinda right, they're small architectural spotlights. They already have their own transformer, so can indeed be wired straight into an existing lighting circuit. The problem is that this isn't what I want to be doing :)

    All I want is a schematic like this;
    mains > transformer > capacitor> trigger > light(s)

    The problem is that I don't know what kind of capacitor I need. Can anyone talk me through it?

    They're cool white by the way!
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