AC powered LED light

Discussion in 'The Projects Forum' started by bosoko, Feb 16, 2013.

  1. bosoko

    Thread Starter New Member

    Feb 10, 2013
    3
    0
    Hello, I bought some bright powerful LED's peak-rated at 2W each and I want to run them off a safe 50 VAC power supply. I decided against regulator circuits because of the cost and/or complexity (if I were to build one) so I thought of another design using caps for limiting current but yet using both halves of the wave.

    Here's the basic circuit:
    [​IMG]

    As safety precautions I plan to add a fuse before the circuit and MOhm-rated resistors in parallel with caps so there's no residual voltage. The anti-parallel diode is there just in case any reverse voltage goes over

    I haven't built it yet (it works in simulations) and I would be happy to receive criticism and warnings before I do build it and it melts my face.

    One concern I have that the simulation shows is the possible sudden current peak when it's turned on.
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,659
    632
    You should be concerned about the peak current at turn-on. In some tests on some 240VAC AC powered LED luminaires, failure rates were very high when a series current limiting resistor was bypassed. Ten ohms gets you a safe peak current of 7.5 amps.

    Another, more common topology for the capacitor limited power supply is to put a capacitor and series resistor in series with the AC source and then drive the AC input of a full wave bridge with that. The output of the full wave bridge is...full wave! Remember the bleeder.
     
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  3. #12

    Expert

    Nov 30, 2010
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    Your schematic makes my eyes cross...and besides, I think you have parts that aren't doing anything helpful. Try this. Add a surge limiter if you want.
     
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  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Microchip may still have some app notes online discussing similar schemes to get a few milliamps to run a tiny micro controller. While not directly applicable they do discuss capacitor type and ratings.

    #12 adds another diode I do not see the need for. I also do not see the need for your C4, just one series cap should suffice.

    Expect this thread to be closed ASAP as it violates the TOS.
     
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  5. #12

    Expert

    Nov 30, 2010
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    OP was careful to say, "safe 50V AC supply".

    ps, the 5th diode is an LED. This circuit will not light up an LED if you do not attach one.
     
  6. bosoko

    Thread Starter New Member

    Feb 10, 2013
    3
    0
    Ah, of course, I had thought about using a full-wave rectifier with 4 diodes but decided that it wouldn't work as I imagined the cap to be in series with the LED. It never occured to me that I could put it before the rectifier, thanks guys! Diodes are cheaper than caps anyway.

    ErnieM: I found Microchip's notes, they do have some helpful details, thank you.
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    OP is probably fibbing about his source, and 50V should be considered dangerous.

    I've been working a long week (can't remember the last day off but it was before the storm Nemo) so I'm seeing things. But the circuit still needs less not more diodes:

    [​IMG]
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,348
    Hello,

    Here is my idea for a 50 Volts 50 Hz led light.
    I am assuming standard 20 mA leds.

    [​IMG]

    Bertus
     
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  9. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    But!!! A transformer is mandatory for such circuits on AAC, lest the thread disappear. It is not your life you are risking (though that is also true) but those who may come after and not know what you have done.

    Personally I don't have a problem with discussing the subject, but it is important for people to understand the risks. Don't try LEDs to mains at home!!!
     
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