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Light dimming circuit

Discussion in 'LEDs and Optoelectronics' started by n0nesense, Sep 14, 2012.

  1. n0nesense

    n0nesense

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    Aug 25, 2011
    Guys, i need help with my light dimming circuit. i need it to auto dim according to the intensity set at variable resistor when the circuit is switched on. but when i simulate it, the light bulb keep on blinking. the waveform obtained also weird. circuit is attached. please help.. :(

    Circuit:
    [​IMG]

    Waveform:
    [​IMG]
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You're running a triac-based light dimmer at 12VAC. Did you take a mains design and just reduce the input voltage? Also, what is the part number of D2? I get no hits for "1N5758" on Digikey and Mouser.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    One of the problems is that this circuit relies on the diac to trigger the triac.

    The diac requires a certain voltage, and that may exceed your 12V input rail.

    Have you built this, or is it just the simulation you're looking at?

    If you're running the simulation at slow speed, then yes, it will show the light flashing, if all is well, the position of the pot should alter the mark-space ration of the flashes.
     
  4. n0nesense

    n0nesense

    8
    0
    Aug 25, 2011
    i reduced the voltage to 12VAC. The actual circuit is 230VAC. supposedly i have to use diac DB3202 but the simulation program dont have. so i just replaced it with something else, i wonder if that's the problem
     
  5. n0nesense

    n0nesense

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    0
    Aug 25, 2011
    As of now im still trying out with the simulation. But i have to get it finish by next week for my presentation. what do you mean? i have to change the position of the pot? im sorry i dont understand
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    OK, so you changed the working voltage from 230VAC to 12VAC without changing any of the components, and your simulation program didn't have the proper DIAC so you chose one at random. Is there anything else you should have mentioned?

    SCRs and triacs are not well suited to low voltage operation. Even if you replace the DIAC with a suitable low-voltage phase control trigger circuit, there's an area a few volts either side of the zero crossing where the device doesn't conduct. You might be better using MOSFETs, but you'll need two, and some clever interconnection, if you want to feed AC to your bulb. You could feed bridge-rectified voltage to the bulb, which would need only one MOSFET.

    What's the purpose of this project? What are the requirements? A quick fix for a one-off job would be a variac (variable transformer), or you could use a variable regulator (linear or switched mode; modules are available online) and run the whole thing at DC. Need a lot more information from you.
     
  7. n0nesense

    n0nesense

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    0
    Aug 25, 2011

    The purpose of my project is when the switch is turned on, the light ( at full capacity/intensity) will slowly dim according to the intensity set at pot (earlier set). and not directly turned on already dim.
    i dont have any specification. what i mean is, i just need a light dimming circuit with nothing in particular. i dont really know how to redesign the circuit to fix it or what components model to be used. i am still learning about circuit :(
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That explanation is far too brief.
    Is this a one-off project? What has been decided, and what do you need to decide? For example, do you need to use that light bulb? What is its current or power rating? What's the budget? When is it needed? Can you borrow stuff for it or will it be permanent? What experience do you have? There are so many questions.

    Seriously, you need to tell us a whole lot more about this project.
     
  9. n0nesense

    n0nesense

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    0
    Aug 25, 2011
    No, this is only a part of a bigger project. the other part are good to go. i just have problem with this light dimmer part. the parts will be joined using PLC.

    Basically my project is a sleep mode initiator. when a person lays on a bed, the pressure will trigger a lots of things to fit in the 'sleep mode' ie light dim, close curtain, adjust the aircond etc.

    i need to buy all the parts and built it when i finished my presentation next week. no borrow. will go buy when i have a definite circuit. Budget wont be a problem. i have prepared it all.
    As for the light bulb, an normal 12V, 60W will do.
    but it doesn't matter really, i will buy components according to the final working(simulated) circuit. (if light bulb simulated as 100W, i will find that one)

    Do you think this circuit is poor? not good to go? should i try the one with MOSFET?
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    So you need a circuit that is mains powered, that drives a 60~100W light bulb. When you power it up, it starts with the bulb running at 100% power, then gradually dims the bulb until it reaches the percentage that has been set on a potentiometer, and leaves the light bulb running at that brightness. Is that right?

    Do you need to use a 12V bulb? Could you use a 230VAC bulb instead?

    Can your PLC generate a voltage output to control the lamp brightness? For example, an output voltage that would start at 5V (to cause maximum brightness) and gradually drop to the percentage that has been programmed?

    Your circuit is not suitable for a 12V bulb. Dimming a 60~100W bulb is probably best done at mains voltage.

    Have a look at these:
    http://www.apogeekits.com/light_dimmer.htm
    http://pcbheaven.com/circuitpages/Voltage_Controlled_AC_Light_Dimmer/
    http://www.jaec.info/Home Automation/efficient-energy-management/light-dimmers.php
     
  11. n0nesense

    n0nesense

    8
    0
    Aug 25, 2011
    Yes. that it how my circuit should work. I have no problem changing the light bulb to 230VAC.

    Thank you so much for the links. i will try to run it.
     
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