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    help with MCU controlled Dimmer circuit

    hello Guys
    i need a circuit to control a single phase Motor but i dont know where to start
    i have tried to control BT136 Triac with Moc3021 but its not ok as i guess

    any hardware circuit to control the triac from 0-5v?
    your help will be appriciated

    John

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  2. #2
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    Re: help with MCU controlled Dimmer circuit

    Hi,

    start with specifications, not with random devices like "BT136" or "MOC3021".
    * Motor specifications
    * which microcontroller
    * what and how you want to control. feedbacked or not?

    AC motor control is no new application, thus you find a lot of information in the internet.
    --> go to the microcontroller manufacturer homepage, often they have application notes on AC motor control

    * there are many examples in the internet. Read through them. Often they provide schematic and code.

    ****
    You are welcome to ask detailed questions ... then refer to the documents you have read.

    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: help with MCU controlled Dimmer circuit

    Quote Originally Posted by KlausST View Post
    Hi,

    start with specifications, not with random devices like "BT136" or "MOC3021".
    * Motor specifications
    * which microcontroller
    * what and how you want to control. feedbacked or not?

    AC motor control is no new application, thus you find a lot of information in the internet.
    --> go to the microcontroller manufacturer homepage, often they have application notes on AC motor control

    * there are many examples in the internet. Read through them. Often they provide schematic and code.

    ****
    You are welcome to ask detailed questions ... then refer to the documents you have read.

    Klaus
    Hi Klaus
    I've started with random selection of parts just to start making it simply
    & yes alot of circuits on the internet but it seems no one is working good &
    i started a simple one with present parts so i can test its work
    if you have any link on how to control the triac smoothly from 0-5v so i can test it on any external power supply & start to control just a lamp as a start 7 understand the idea of Main AC phase Cut.
    i have downloaded the Moc3021 datasheet but no clear information about its output regarding to its input
    i was thinking it must be something like input 0-2v output = 1 M Ohm-0 Ohm
    im searching on microchip application notes now as you suggest

    thx



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    Re: help with MCU controlled Dimmer circuit

    Hi,

    I've started with random selection of parts just to start making it simply
    Do you think itīs a good idea to start with 3 eggs and 50g of wheat to bake a cake?
    Or do you think itīs better to first decide which cake you want to bake, then look for an suitable receipt?

    Note: a "simple" circuit" may work as phase control for a (resistive) heating. But to control an (inductive) AC motor isnīt that simple
    (itīs not that difficult either). You just have to take care about the

    & yes alot of circuits on the internet but it seems no one is working good &
    How do you know they are not working good?
    True, random internet search gives a lot of unreliable designs. Thus I recommeded to look at the semiconductor manufacturers. They earn their money to sell their devices. But no one will buy the devices if the datasheet is faulty or the application notes are faulty...--> they are interested in giving reliably working designs.

    i have downloaded the Moc3021 datasheet but no clear information about its output regarding to its input
    From function the datasheets says you need typically 8mA LED current to trigger the output = trigger the triac.

    Itīs a digital input and itīs a trigger output, thatīs all.
    Itīs not the job of the MOC to control the phase angle. This is the job of the microcontroller (code)..
    But theses are basics you already should know before you think about using "BT136"...

    BTW:A forum cant replace school and canīt replace reading tutorials, books, application notes, datasheets,
    And there are a lot of video tutorials about AC motor phase control.



    Klaus
    Please donīt contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


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    Re: help with MCU controlled Dimmer circuit

    Opto devices with an internal LED are always current driven and the output is not a controlled resistance. MOC302x devices are opto-triacs with special output characteristics, they need a voltage across the output side to do anything and they abruptly switch from non-conducting to fully conducting states and stay there until the current through them drops to almost zero. You can't turn them off, even if the LED current is removed except by stopping current flowing through the output side. You might consider them as a latching switch that stays on until the power is removed.

    To control the output power into a lamp you have to convert the 0-2V you propose into a variable delay. The delay has to start from a fixed point in the AC voltage cycle and run until a point somewhere before the cycle ends. To do this you need a circuit called a "zero crossing detector" (ZCD) that produces a pulse coinciding with the point where the polarity of the AC reverses, in other words where it has fallen to zero but yet risen in the opposite polarity. Zero crossing point starts the timer to produce the delay and the period of the delay is set by your control voltage. The timer resets at the next zero crossing point.

    Remember that a triac, whether the one at the output of the MOC3021 or the BT136 turns off when there is no voltage across it so it 'resets' twice per AC cycle. Your timer has to turn it on again to allow power to the lamp. The sooner you turn it on, the more power reaches the lamp, if you delay the turn on to the end of the cycle it gets less of the cycle and therefore appears dimmer. You therefore need a voltage controlled timer, it can be analog or digital (using an ADC) that pulses the LED in the opto-triac at the end of the delay period.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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    Re: help with MCU controlled Dimmer circuit

    Well, using TIP120 with micro-controller output will be somewhat basic and old and not much reliable but I should suggest the 8 Bit FET driver which will send pulsed output using micro-controller using I2C connection which will be much helpful to work with DC PWM controlled application.



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