Electronic dimmer circuit MOC3022 Help

Discussion in 'General Electronics Chat' started by IphoneDeveloper, Dec 22, 2012.

  1. IphoneDeveloper

    Thread Starter New Member

    Sep 17, 2012
    4
    1
    Hi, guys

    I am building the following dimmer circuit however i am having alot of issues.
    I built everything up to the optocoupler the 555 and zero crossing detector work great along with the npn transistor. I had the remove the coupling capacitor 0.001uF between zero crossing and 555 to get it to work.

    http://www.onsemi.com/pub_link/Collateral/AND8011-D.PDF

    The issues I am having are when trying to trigger the MOC3022. currently have an LED at the output however even without input output of MOC3022 is constantly shorted. When I attach my npn transistor with a pulsed waveform saturating at my top rail of 12V the voltage at the input of the MOC3022 drops to about 1.8V PWM.

    Thanks in advance
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    It looks like you have connected the led in the MOC the wrong way around.
    12 Volts at the input of the MOC is not possible, as the led inside the MOC is most likely an IR led wich has a voltage drop of about 1.2 Volts.
    By connecting the led the wrong way around, it is probably blown, as leds can not have more than about 5 Volts in reverse.

    Bertus
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
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    I may just be dense, but not following..
    What do you mean by MOC3022 constantly shorted? 1.8v indicates it's not "shorted"
    You could test the npn/moc3022/triac portion by removing the 1k base resitor from 555 pin 3 and connect it first to gnd (load is on) then to +12v (load is off).
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    896
    What? "I had the remove..."? does not make sense in English. Maybe you did remove the important capacitor but it is needed for the 555 to work properly.

    What? Are you trying to say that when there is no input then the MOC3022 is always turned on?
    That is normal. The 555 must be triggered for its output to turn on the transistor which turns off the MOC3022.

    What? The input of the MOC3022 is an IR LED with a typical forward voltage of about 1.15V. The 620 ohm resistor turns it on and the transistor turns it off.
     
  5. IphoneDeveloper

    Thread Starter New Member

    Sep 17, 2012
    4
    1
    I attached a file that shows the input into the MOC3022 (Red line is input to MOC3022, Blue line is input to NPN). When this input is coupled to pin 1 of the MOC3022 it drops to about 2V. I have many MOC3022 and all perform the same. The output is constantly open, even when no input is attached.
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    What? "I had the remove..."? does not make sense in English. Maybe you did remove the important capacitor but it is needed for the 555 to work properly.

    What? Are you trying to say that when there is no input then the MOC3022 is always turned on?
    That is normal. The 555 must be triggered for its output to turn on the transistor which turns off the MOC3022.

    What? The input of the MOC3022 is an IR LED with a typical forward voltage of about 1.15V. The 620 ohm resistor turns it on and the transistor turns it off.
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    How did you connect pin 2 of the MOC?
    It should be connected to the ground pin of the NE555 (pin 1) and the emittor of the transistor.

    [​IMG]

    For more easy taking about the schematic, I have extracted it from the PDF:

    [​IMG]

    Looking at the powersupply part of the schematic, the mentioned 12 VDC will be more like 15 Volts, as it is unregulated and smoothened with the 1000 uF capacitor.

    Bertus
     
  8. tubeguy

    Well-Known Member

    Nov 3, 2012
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    What do you mean by coupling.
    The MOC3022 does not have an "output". It has to be connected to a circuit like the one you posted.
    To test it, build the circuit as posted and then test.
    If you connect 12v thru a 620 ohm resistor to the opto per the schematic it will have about 2v from pin 1 to 2 because the internal LED has about a 2v drop.
     
  9. IphoneDeveloper

    Thread Starter New Member

    Sep 17, 2012
    4
    1
    Yup I attached as specified in the digital dimmer schematic. Reffering to an earlier question. I shorted the output of the zero crossing to the 555 timer. It would not work with the coupling capacitor dont know why. But its not important because everything up to that point works fine.

    Still unsure at this point how to trigger the MOC3022 to simulate an output using an LED.

    I have attached an image of the output of the 555 timer. Varying the pot changes the PWM and that portion of the circuit works correctly.
     
    SPQR likes this.
  10. tubeguy

    Well-Known Member

    Nov 3, 2012
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    The MOC3022 is meant to trigger a triac, not an LED.
    Build the dimmer circuit to test.
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Did you connect ALL the ground connections together?

    [​IMG]

    Bertus
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    No.
    A red or yellow LED is 2V. The IR LED in the photo-coupler is typically only 1.15V.
     
    tubeguy likes this.
  13. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Build the dimmer fully using a triac, but make sure you connect the Moc to MT2 and G
     
  14. vrainom

    Member

    Sep 8, 2011
    109
    19
    @IphoneDeveloper: I think the problem is you're using d.c. to test the ouput with the led, you should use pulsating d.c. to test the circuit (i.e. the one you're tying to the positive input of the lm339).

    You see, a thyristor, as is the output of the moc3022, when used to switch d.c., once triggered stays on until the supply is cut off, that's why you see the output as "shorted".
     
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