Using triac driver moc3021

Discussion in 'Homework Help' started by pujulde, Jul 24, 2013.

  1. pujulde

    Thread Starter Member

    Jul 24, 2013
    95
    1
    i use this scheme and when i give impulse to the base of transistor the bulb is turned on, but when there is no signal on the base it remains turned on and i cant turn bulb off until removing supply voltage , can anybody help me. i measure voltages and when there is no signal on base of transistor it not conduct current.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    Is your power to the bulb AC or DC?
     
  3. pujulde

    Thread Starter Member

    Jul 24, 2013
    95
    1
    As my circuit did not work, i check only the transistor and moc3021 excluding BT136. i supply 5 volt to the pin 6 of moc3021 and connect the positive pin of LED to the 4th of moc3021 and to the ground the another pin of LED. I used to check this circuit as described: "1" to the base of transistor and its turn on LED and "0" on base of transistor did not turn LED off. may be the moc3021 does not work or there are a small leakage current in transistor and its support the optosimistor closed?
     
  4. pujulde

    Thread Starter Member

    Jul 24, 2013
    95
    1
    Is there anybody who can explain me why this circuit does not work? I check components separately and they work, suggest anything
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    The datasheet of the MOC states that the current through the led should be higher as 15 mA, but less than 60 mA.
    In your case the current is about (Vcc - Vled - Vtransistor) / R2 = (5 - 1.5 - 0.3) / 220 = 14.5 mA.
    Try to lower R2 to 150 Ohms and see what happens.

    Bertus
     
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  6. #12

    Expert

    Nov 30, 2010
    16,310
    6,817
    Try adding a 33k resistor from the base of the 2N2222 to the emitter of the 2N2222 to insure turn off.
     
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