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220v Lamp fade in & out in cycle Project

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by roabish, Apr 21, 2012.

  1. roabish

    roabish New Member

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    Hi Guys,

    I am busy with my son's project and need some help, at the best of times I have problems replacing the batteries in the remote so your patience is appreciated. After spending many hours on electronice forums I have afirm understanding of the technical jargon but lack the "design" experience to complete this project.

    I require a 220VAC lamp to fade in and out in a continuious cycle and be able to adjust the fade time. The "in" and "out" time must be the same, so 10 s to fade in must also be 10 s to fade out.

    I have looked at maybe using a saw tooth generator to trigger a 220V lamp dimmer circuit but it keeps blowing up, as I said before I lack the design insight, I tried to modify existing circuits to suit me needs.

    Any help would be appreciated
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Post the circuit that is giving you problems, it may just be a case of a simple modification is required.
     
  3. panic mode

    panic mode Well-Known Member

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    yes,

    of redesign is regured there are few things to consider

    unlike DC dimmers where simple PWM is used, dealing with AC is a bit more complicated.
    issue is that in AC circuit we don't use (normally) transistors because of voltage and power levels.
    device of choice is either SCR (thyristor) or triac. basic difference between the two is that
    SCR only works one way (one halfperiod of the sine, like a diode) while triac conducts both ways.

    next thing to know is that once they turn on, they stay on until AC cycle goes through zero.
    this means that proper control requires knowing when zero crossing occurs,
    then use some delay and after that delay, fire the trigger. if delay is short, we get current for most of the half period (full brightness).
    if we wait longer, smaller fraction of halfwave is used (dimmer light).

    basically this looks a lot like PWM but it is synchronized with AC.

    here is example of what current looks like when trigger is fired at different time:
    http://www.eurotherm.co.uk/EasysiteWeb/getresource.axd?AssetID=47574&type=full&servicetype=Inline

    simple dimmers use RC circuit to create adjustable phase shift or delay. to use that principle,
    one would need a hand (or motor) to keep on adjusting it to get effect you are looking for.

    the other way is use mentioned method with detecting zero crossing (and start timing at that instant)
    and when time expires fire the trigger.

    how simple or complicated this can or has to be depends on your experience level.
    for example one can use micro-controller or with few more parts do everything without programmable devices.
     
    Last edited: Apr 22, 2012
  4. dave

    Dave New Member

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  5. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Is the lamp a good old-fashioned filament type, or a compact fluorescent, or ........?
     
  6. roabish

    roabish New Member

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    its a good old-fashioned filament type, but any other lamp of the same light intensitity of a 60-80 watt filament type.

    Thanks eric, I am busy going through the circuit diagrams I download and trying to match the projects I combined to "try" and get everything to work, I feel that this might not be the right approach, a complete effecient design might be the right answer - thanks

    I understand the principle, but I struggle with the practicle, I understand what each component does but lack the technical laws governing each component, ie Triacs and transisters, forget about chips.
    I help my son build a 555 chip circuit and the other approach with 2 transisters from a diagram, but cant do that out of my head.

    I also didn't know that you can mix AC and DC in a single circuit until joining this forum.
     
    Last edited: Apr 22, 2012
  7. panic mode

    panic mode Well-Known Member

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    you can keep SCR or Triac on AC side and everything else on DC and interface the two through simple optocoupler for example
     
  8. alec_t

    alec_t Well-Known Member Most Helpful Member

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    The attached should do the job, but may need 'tweaking' to suit your exact requirements. If built, due precautions must be taken when mains voltages are present. Components subject to mains voltage must be properly rated for safety.

    6VAC is provided by a transformer and full-wave rectified by D1-D4. The result is smoothed by C1, C2 to provide a 7VDC supply.
    The AC half-cycles are applied via C4 and C5 to the inputs of an XOR gate which is used here in a pseudo-analogue mode by having its inputs biased at half the supply voltage. The gate output goes low only at the zero-crossings of the AC and discharges C6. At other times C6 voltage ramps up.
    A '555 timer IC generates a triangle wave output on cap C9. Unusually, the control input of the IC is connected via R10 to the 'Out' pin so that the internal threshold voltages of the IC are modified, resulting in a greater output swing.
    The voltages from C6, C9 and an offset voltage from pot U2 are summed via weighting resistors at the input of a non-inverting buffer comprising another XOR gate. This gate's output switches high or low according to whether the sum is above or below the gate logic threshold and drives transistor Q1 and in turn the LED of opto-triac U5. This triac switches the lamp-driving triac U6.
    R12/C7 are for transient suppression. R13/C8 are a snubber.
    Pot U3 controls the rate at which the lamp fades up and down.

    Edit: A respective 47k resistor should be added in series with C4 and likewise C5, to limit current into the gate U1a inputs.
     
    Last edited: Apr 23, 2012
  9. roabish

    roabish New Member

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    Hi alec_t, thanks for the effort, I will purchase all the components this weekend and build it and report back once complete.
     
  10. alec_t

    alec_t Well-Known Member Most Helpful Member

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    I've just noticed a couple of omissions from the circuit; see the edited text of post #7.
     
  11. roabish

    roabish New Member

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    Brilliant, thanks a million. This should put the finishing toutch on my son's project and I learnt something as well.
     
  12. panic mode

    panic mode Well-Known Member

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    also note that CD4030 need to be powered (pins 14 and 7 are usually not shown but still need to be connected). there are also two more XOR gates in the chip (unused) and in CMOS all unused inputs should be connected to zero volt, and unused outputs should be left unconnected.
     
  13. shijumax69

    shijumax69 New Member

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    hi ,
    i need help in the same , to the project that i am doing, i need a old filament lamp of 230 volt to be faded in and faded out in equal intreval of time using triac . please help me with the circuit
     
  14. alec_t

    alec_t Well-Known Member Most Helpful Member

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    The attachment seems to have vanished from my original post, so here it is again :
    LampFader.PNG
    Diodes D1-4 can be any in the 1N400x series, or a 1A bridge rectifier.
    Take due care with mains voltage.
     
    • Thanks Thanks x 1
  15. shijumax69

    shijumax69 New Member

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  16. shijumax69

    shijumax69 New Member

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    hi,
    Thanks for the circuit, IT all looks logically great , is their any circuit where in i can eliminate the opto isolator moc3021 , and trigger gradually via gate terminal of triac? also can i replace the LED section of moc3021 with a 555 timer and build just the 555 timer and convert it into triangle wave by giving the output pin no 3 to npn transistor base and drive a led through emitter while connecting a capacitor from base to emitter of the same npn transistor? (if at all driving triac is possible only through opto isolator)
     
  17. alec_t

    alec_t Well-Known Member Most Helpful Member

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    The opto-isolator is there as a safety feature to isolate the mains-voltage part from the timing/control section.
    I don't follow the modifications you are suggesting, but if you have a particular circuit in mind then please post it. A 555 is not mains voltage rated.
     

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