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MSP430G2231+TRIAC

bala krishnan
Prodigy 95 points

Hi there,

Actualy i am firing a triac using a optocoupler thru a transistor from the msp 430 output pin.I am getting the desired outputs when i connect the output pins to LED but when i connect a 1K resistance to drive the transistor it is not getting the drive.Kindly help.

Regards ,

Bala

  • 0
    Guru 58965 points

    You did not supply enough information about the optocopler, the transistor, and how they are connected to the 1k resistor.

  • 0 in reply to old_cow_yellow
    Guru 35605 points

    old_cow_yellow said:

    You did not supply enough information about the optocopler, the transistor, and how they are connected to the 1k resistor.

    Indeed!

    You really need to post a schematic - trying to describe a circuit in words (especially in a foreign language) is a prettty futile exercise.

    It would also help to give links to the datasheets of the components concerned; or, at the very least, full manufacturer's name & part number.

    If possible, use original datasheets direct from the manufacturer's own website - use 3rd-party sites only as a last resort.

     

  • 0 in reply to Andy Neil
    Prodigy 95 points

    Details of the circuit are as follows.

    From the Microcontroller output there is an 1K quarter watt resistor which is connected again to the transistor BC-107 Base.The emitter of the same is grounded and there is a 330 ohm resistance connected to pin numbr 2 of optocoupler MOC-3021 and then the triac is BT136 which is connected to MOC via a 360 ohm and a 470 ohm resistance in series with pin number6 of MOC .Pin number4 of MOC is connected to pin number 1 of BT136.The load is connected through pin number 2 and a snubber circuit to the load. 

  • 0 in reply to bala krishnan
    Guru 227245 points

    And what is your supply voltage that goe sinto the MOC?

    The internal LED of a typical optocoupler usually has a voltage drop of ~2V on 10mA. Now there is the transistor C-E voltage and the 330Ohm resistor in series.
    To have 10mA flowing through teh diode, you'd need ~6V supply voltage. 2V for the diode, 330Ohm*10mA=3.3V for the resistor and >0.5V or even more for the C-E.

    IF you try this with the MSPs VCC of 3.6V max, you'll likely have only a very small LED current. And an even less output current from the MOC, asthese devices usually have a transmission ration of <50%.

    It is definitely better, easier and cheaper to just use the MSP output, maybe with a small series resistor (100R or less) if you don't want the full port driving capability to go into the LED.

  • 0 in reply to Jens-Michael Gross
    Prodigy 95 points

    """"""And what is your supply voltage that goe sinto the MOC?""""""

    Suply voltage is 5v.

  • 0 in reply to bala krishnan
    Guru 227245 points

    bala krishnan said:
    Suply voltage is 5v.

    Well,

    worst case, the MOC requires a trigger current of 15mA. And has a diode voltage of 1.5V. So 5V minus 1.5V minus 0.5V for the transistor leaves 3V on the resistor. 3V/330Ohm is 9mA and not enough to trigger the MOC worst case.

    Anyway, teh MOC already has an internal TRIAC. Triggering a triac by a triac is not trivial. Maybe your circuit is unable to fire the second triac at all.

    Besides this, you're torturing your transistor with VCC/1k = ~3.3mA base current. Way too much unless your transistor has a beta <5 :) You can use a 10k.

    Also, if I understood right, the AC/HV side has a BT136 with 830Ohm in series to the MOC triac and the gate. The BT136 requires a gate trigger voltage of 0.7 to 1.5V and a  gate current of (worst case) 25mA. This means the minimum operating voltage (worst case) would be 22V, since only then 25mA will flow through your resistors and the MOV to the BT136 gate. But even best case, 12V are needed.

  • 0 in reply to Jens-Michael Gross
    Prodigy 95 points

    I am sorry fr the late post.was out of town....any ways now my circuit is absolutely working and achieved the desired output......thanks a lot fr ur help all of u..looking ahead for more help.....

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