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solid state dimmer

Discussion in 'Electronic Basics' started by Micah, Jul 1, 2004.

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  1. Micah

    Micah Guest

    I'm looking for a solid state relay that I can use basically as a dimmer. I
    have a circuit board hooked up to an AMD 186 evaluation board that I am
    using to do temperature control. I'd like to control the vac 120 output by
    varying vcd input (ideally 0-5 vcd as my power supply is 5 vcd -- of course
    I could add another power supply and voltage regulator if need be).

    I'm not quite sure what the industry terminology for such a relay is.
    "Solid state dimmer" doesn't find me exactly what I'm looking for. Is there
    an attribute for relays that I should use in my on-line search?

    Thanks
     
  2. Randy Day

    Randy Day Guest

    Are you referring to a Silicon Controlled
    Rectifier or a Triac, or are you looking
    for something else?

    A quick search on 'triac dimmer opto
    schematic' brought up this, for example:

    http://www.commlinx.com.au/schematics.htm

    HTH
     
  3. Micah

    Micah Guest

    I'm not familiar with these terms. Basically I want a solid state relay
    that I can control the vcd output by varying the vcd input. I'm currently
    using several solid state "hocky puck" style relays to turn things on and
    off but there are some devices that I would like to "dim" instead.
     
  4. Micah

    Micah Guest

    Oops I meant "vac" output...
     
  5. Randy Day

    Randy Day Guest

    If you're talking 120Vac, you don't control
    "vcd output", if I understand what you mean
    by the term.

    If you're looking for something to provide a
    0-120Vac sine wave output, you want either a
    variable autotransformer or something equally
    expensive.
    Your 'hockey puck' relays are probably opto-
    isolated SCR's or Triacs; check your specs.

    You can set an SCR or Triac to switch on for
    only part of each AC cycle; how much of each
    cycle is used determines the 'brightness' of
    the output.

    The website I listed has several 120Vac
    dimmer circuits. They should give you some
    ideas.
     
  6. John Fields

    John Fields Guest

     
  7. CFoley1064

    CFoley1064 Guest

    Subject: Re: solid state dimmer
    Mr. Fields is correct. If you Google the phrase, eventually you'll come up
    with the Velleman K8003 kit, which optoisolates an input DC voltage, and uses
    that to control an AC load up to 750 watts (resistive, heater and lamp loads
    work best here.) It's about $25 USD per I/O poinit, and should do what you
    want (it is a kit, so you'll have to put it together yourself).

    One small issue you might have here is that the kit triac won't turn on at all
    until you've got the Vf of the opto LED covered (about 1.5VDC or so). If
    you've got a -5VDC supply for your EVB, it might help to externally convert the
    voltage into a current to feed the LED. Something like this would be
    relatively easy, and you could make 4 with one LM324 quad op amp (view in fixed
    font or M$ Notepad):

    K8003 Dimmer Kit Mod.
    Jumper out
    series resistor
    +
    .-----------o------o - - - - o----o---.
    | | |
    | K8003 DC Dimmer Kit - V ~
    | ^ - ~
    | - | |
    | .--o---------------------o---'
    220 ohm | +5V |
    ___ | |\| |
    o--|___|-o--|-\ |
    0-5VDC In | >--'
    .---|+/
    | |/|
    | -5V
    ===
    GND


    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
    If this isn't good enough, you may want to run a calibration curve, then have
    a lookup table (use a true RMS AC meter for this).

    http://www.velleman.be/Downloads/0/Manual_K8003.pdf

    Good luck
    Chris
     
  8. Micah

    Micah Guest

    Thanks guys. I'll look into this. Knowing the terminology will help
    greatly.

    So can I assume that there are no variable output relays out there as I
    described? It seems like there would be quite a market for such a thing.
     
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