Triac as a switch

Discussion in 'General Electronics Chat' started by boatsman, May 17, 2010.

  1. boatsman

    boatsman Thread Starter Active Member

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    I want to switch on fluorescent lamps working on 22vac 50 hz. The lamps are controlled by a time clock which switches them on every evening for about 5 hours. I need a way of switching each lamp individually but I do not want the lamp to come on automatically every day. I thought of using a latching relay with the on /off switch controlling the coil. Then I came across a circuit using a triac. I have a triac 6075 600v and 4 amps. Anode 1 is connected to one side of the lamp ( the other side to the neutral) and to the gate via a 220 Ohm resistor and a normally open press button switch. Gate 2 is connected directly to the live side of the mains. According to the book I took the circuit from it should work but for some reason it doesn't. I tried swapping between anode 1 & 2 without any result. Can anyone advise me. I don't know how to draw a circuit on this forum so I hope it's clear what I'm trying to say
  2. mik3

    mik3 Senior Member

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    It would be better if you can provide a circuit diagram.
  3. Ron H

    Ron H E-book Developer

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    Are you expecting the triac to stay on after a momentary press of the switch?
    What do you mean by "gate 2"? A triac has only one gate.
    Ah- I'll bet you meant "anode 2".
  4. boatsman

    boatsman Thread Starter Active Member

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    Sorry about mistake. I meant anode 2. The idea is that when I close the N/O switch the gate will fire and current will flow from anode 2 to anode 1 and when I release the switch the current will continue to flow between the two anodes until the time clock switches off the power and when the time clock switches the power back on there will be no current flow between the two anodes until the N/O switch is pressed again. I don't know how to draw a circuit diagram on this forum.
  5. mik3

    mik3 Senior Member

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    Draw the schematic with a design software and take a snapshot of the screen or draw it on paper and scan it. Then save it as png format picture and put it as an attachment.
  6. retched

    retched AAC Fanatic!

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    You have to usa a program to draw the schematic then attach the image to a post in the forum.

    LTSpice is a free schematic capture program and simulator.

    click 'Go Advanced' while posting and under your text box you will see 'Manage Attachments' box. You can upload images and attachments there.

    using the button that looks like a mountain view with a sun in the background: [​IMG]
    Will add the images to the post after they have been uploaded via the 'Manage Attachments' options.

    Link to LTSpice page:
    http://www.linear.com/designtools/software/#Spice
  7. Ron H

    Ron H E-book Developer

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    The triac will turn off whenever the current goes to zero, which is once every half cycle.
    http://en.wikipedia.org/wiki/TRIAC
  8. boatsman

    boatsman Thread Starter Active Member

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    The circuit I have been using is the one shown in vol 3 semiconductors chapter 7 using the triac and is the circuit without the capacitor. I used a 200 ohm resistor instead of the potentiometer and I tried both ways anode 1 and anode 2. The triac I am using is 6075 rated at 4 amps and 600 volt. No results either way. Any advice would be appreciated.
  9. mik3

    mik3 Senior Member

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    Is your supply voltage 22V AC or 220V AC?

    If it is 220V AC then it is probably fried.
  10. mik3

    mik3 Senior Member

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    Is your supply voltage 22V AC or 220V AC?

    If it is 220V AC then it is probably fried with a 200 ohm gate resistor.
  11. boatsman

    boatsman Thread Starter Active Member

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    The supply voltage is 220vac and the internal resistance readings are identical to new unused triacs of the same rating so I don't think that it has burned out.
  12. Ron H

    Ron H E-book Developer

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    As I said, a momentary switch won't work, because the triac turns off at each zero crossing of the AC current.
  13. Ron H

    Ron H E-book Developer

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    The triac shorts out the resistor when it fires, so the power dissipation is low.
  14. boatsman

    boatsman Thread Starter Active Member

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    So how do I get the triac to work? Do I need a diac in series with the gate? Or what?
  15. Ron H

    Ron H E-book Developer

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    Your first post said the supply voltage is 22VAC. Did you mean 220?
  16. boatsman

    boatsman Thread Starter Active Member

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    Sorry about mistake. The mains voltage is 220 VAC. The circuit I have been using is illustrated in (at the top of this page) vol 3 semiconductors, chapter 7 the triac, using the circuit without the capacitor.
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