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Triac light bulb flasher

Discussion in 'Electronic Projects' started by ElectroMaster, Jul 24, 2002.

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  1. ElectroMaster

    ElectroMaster Administrator

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    This 800 W light bulb flasher operates directly off the line and needs no transformer. Power for the timer circuit is derived by limiting the current using a 330 nF capacitor (acts like a 9.6 k resistor at 50 Hz), rectifying with a full-wave rectifier composed of four diodes (you may also use a pre-made bridge rectifier instead of the diodes, of course, but make sure the voltage rating is 400 V, or 250 V RMS). Then the voltage is limited with a 9 V zener diode (almost any of this voltage will work), a 1 W type. The 100 µF capacitor filters the power, a 16 V rating may be a bit safer. Remember: if the zener diode fails, the capacitor will blow because it gets peaks of up to 330 V, although current-limited). In this configuration, the timer gives long pulses at 1.3 Hz.

    Now there's one problem: we can't drive the triac directly, because the controlling voltage is not isolated from the line since there is no transformer. The easiest way to drive it is thus by using a triac optocoupler. The K3021 or MOC3021 is well suited for this purpose, as it works like a small triac and thus allows it to directly drive the gate of the larger triac. The coupler is connected to turn on when the timer outputs a low, so we get short pulses.

    Please note that this only works with resistive loads like incandescent light bulbs or heaters. It does not work with fluorescent lamps (need a snubber network to do that).

    [​IMG]
     
  2. lobitoferoz

    lobitoferoz New Member

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    thanks for the circuit ,excellente'''
     
  3. Hero999

    Hero999 Banned

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    You don't need an opto-isolator or a bridge rectifier though.
     
  4. dave

    Dave New Member

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  5. kumyanski

    kumyanski New Member

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    I need the full detail for knowlegde gaining
     
  6. kumyanski

    kumyanski New Member

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    I need the full detail for knowlegde gaining
     
  7. Hero999

    Hero999 Banned

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    WTF does that mean?
     
  8. shokjok

    shokjok Member

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    You may want to add a resistor off the diode bridge, to save the zener diode and yourself from injury. I've tried a similar circuit as an extension phone ringer, to flash an LED or buzzer.
     
  9. Leftyretro

    Leftyretro New Member

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    Knowlege gaining is best obtained by individual study, research and experiance. Asking to be spoon fed such information will just further prevent you from being able to work out future knowlege on your own. There is nothing used in this circuit that would not be learned by the normal study and experiance in electronics circuits and components.

    It's kind of the give a man a fish and feed him for a day, teach him to fish and he is fed for life....or something like that :p

    A better question you might ask is how best to learn knowlege of electronics such that the above circuit would be understandable to me.

    Lefty
     
  10. pohchinpoh

    pohchinpoh New Member

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    optoisolator for Halogen lamp control

    I agree that we'll only gain knowledge through trying and reading up. It'll be good with guidance.

    Here I am trying to use an optoisolator to drive a triac. I tried to pump in a square-wave kind of pulse into the optoisolator MOC 3010 and tried MOC 3020 too. The connection is as attached. This circuit is adapted from the application circuit from the datasheet. Triac I'm using is BT139-600 which I'll like to eventually drive halogen lamp up to 2kW. (My main objective is to be able to use software to vary the brightness of halogen lamps up to 2kW)

    Can someone please advise me if my approach is wrong? I'm not really getting the output right, it actually flicker! My mains is 230V, 50Hz, & I tried pumping in 100hz, up to 500Hz then no more flicker. But....I can't control the brightness! I've read and searched for examples, some are using zero-crossing detector then drive the optoisolator. I tried to build that circuit, but it is also not working.

    I feel quite dishearted that nothing works, and was thinking is it that triac is not suitable to vary halogen lamps?
     

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  11. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    Driving the Triac with a pulse generator in order to switch 'ac' will give a flickering/flashing light or it be on constantly.

    It will not control the brightness/intensity of the light.

    EDIT:
    To control the brightness, you need to change the trigger point within the mains cycle, at which the Triac is triggered.

    Look here:
    Light Dimmer Circuit Using A Triac
     
    Last edited: Jul 3, 2008
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The micro-controller needs to be sync'd to the mains frequency to enable it to trigger the triac early for each mains pulse for bright lights, or trigger the triac late for each mains pulse for dim lights. That is how a light dimmer works.
     
  13. pohchinpoh

    pohchinpoh New Member

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    Thanks for the replies, think I will try to detect the zero crossing and add delay from there to have a phase control.
    I was actually trying to build a PWM ac-ac converter. However as I look through there don't seem to have anyone who really do that. commonly will be converted to DC, then invert back to AC for control of the rms voltage. Anyone have any comments on a PWM ac-ac converter to dim up to 2kW kind halogen lamp? or should I stick to triac?
     
  14. Ubergeek63

    Ubergeek63 Well-Known Member

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    You should not be dimming a halogen, it breaks the halogen cycle and causes the bulb to burn out.
     
  15. Ubergeek63

    Ubergeek63 Well-Known Member

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    Sure you can...If you get a three quadrant triac.
     
    Last edited: Jul 7, 2008
  16. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi Uber,

    Interesting effect, if its correct.:)

    Regards
     
  17. Ubergeek63

    Ubergeek63 Well-Known Member

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    It sounds plausible, since that is what the halogen cycle does (redeposits vaporized carbon onto the filament) but I am not sure if there would be degraded lamp life from it or not.

    Doing that repetitively might leave weak spots in the filament that would not be there otherwise. I suppose you would have to ask a mfg apps guy that one.
     
    Last edited: Jul 7, 2008
  18. pradeep.durai

    pradeep.durai New Member

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    hi am goin to do mini project in this......does dis really work?
    what's the use of this?is it cost effective?
    why do we want to flash light? any application oriented?
     
  19. pohchinpoh

    pohchinpoh New Member

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    Hi!

    After reading through, dimming of halogen is possible and the effects of degrading will only comes in if it's too dim. In fact lowering of the voltage slightly below mains voltage will prolong the life span of the lamp and saves energy (If light intensity need not be too high).

    I actually used a variable transformer to vary the light output of 4 x 500W halogen lamps and they are atill working well. I have yet to have time to work on the electronic circuit to do the control. I will be starting on that soon.

    my project is mainly to acquire data using LabVIEW, and I am intending to figure a way to use it to synchronize witht the grid and do a phase delay control. If any progress or doubts will update again!
     
  20. sabahat

    sabahat New Member

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    Can anyone help me ?,
    brothers i am using traic BTA41 for element dimmer of 1KW.I am using its driver MOC3021 it works well but after some time it becomes heats up, i have added a big heat sink and i am using it in closed envoirnament, its temperature goes up than 100 deg c. what should i do?
    thanku
    sabahat
    sabahat63@yahoo.com
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    If the voltage is 230VAC and the mains frequency is 50Hz then this triac should be warm driving only 1kW. it has a current rating of 40A but you are using only 4.3A.

    Its datasheet shows that with a current of 30A and more then it gets hot without a huge heatsink.
    A heatsink does not work properly when it is enclosed.
     
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