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Gradual On for Lamp

Discussion in 'General Electronics' started by Nehmo Sergheyev, Sep 19, 2003.

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  1. Gradual On for Lamp

    I dislike the rude assault you get when you flip on a light switch.

    Instead of an abrupt on-off switch on a 120 V circuit, I want something
    that gradually turns on. In other words, you throw a control switch and
    the resistance in the load's circuit goes from infinity to zero in the
    span of, let's say, three seconds. The load would be a 500 W
    incandescent lamp.

    Is there a commercially available product that could accomplish this?
    Or is there a simple way to make this circuit?
  2. Ken Taylor

    Ken Taylor Guest

    Google is your friend. (Someone else coined that phrase, but I like it!)
    Plenty of others like it but that was the first hit. Search for a circuit
    diagram the same way.

  3. x-10 might do this, but I don't really know.
    A PIC chip, a TRIAC, and a few other parts could do this job perfectly.
    There are quite a few examples on the net, just Google 'em up by
    searching for "PIC" and "dimmer". ;-) You would just need a slight
    variation on the code to make it do what you wish.
  4. Beachcomber

    Beachcomber Guest

    The official lingo for this is "Soft Start" ... may help during the

  5. use candles
  6. In days of old they used a power NTC thermistor as a surge arrestor in valve
    TV's to do this.
    On switchon it has high resisance to limit the initial surge current
    for all those discharged capacitors and cold valve heater elements.
    When it heats up it due to the load current it consumes minimum power as the
    resistance drops right down.
    It would have to be carefully matched to the load.
    Whether you can find one the right power for this job, I don't know,
    but I often wondered why someone didn't coin this potential market.
    I guess the lamp manufacturers would soon buy them out.
  7. JeffM

    JeffM Guest

  8. r_p_bayly

    r_p_bayly Guest

  9. Reg Edwards

    Reg Edwards Guest

    Connect a thermistor in series with the lamp. As the thermistor warms up
    its resistance goes down and the lamp gets brighter.
  10. JeffM

    JeffM Guest

    True--in theory--but even the slowest thermistor
    is too fast to achieve what he wants.
  11. Nam Paik

    Nam Paik Guest

    I think there are special turn-on (sliding) switches which does what
    you want to do - it is probably expensive $20 maybe per switch. But
    churches & some expensive homes use this kind of sliding scale
    brightness switch. You can slide the switch as fast as you want or as
    slowly as you want.

    Side benefit will be that brightness can be controlled precisely (I
    guess it is really a more elegant dimmer switch - since the SCR or
    TRIAC controls the pulse width, you will still have 99% efficiency. If
    you try to do it with resistors, it can become pretty dangerous
    (failure of circuitry will make the whole circuit glow & you'll be
    lucky not to burn down your house).

    Worst thing that a TRIAC or SCR can do is become OPEN (bulb does not
    turn on at all) or become SHORT (bulb is always on at max. brightness
    & you lose soft-start & brightness control). Either way, nothing will
    get hot & definitely no fires are started.

    I would still buy a professional dimmer switch in metal box just in
    case the SCR or TRIAC decides to become a flame thrower for a few
    seconds (some cheap dimmer switches did cause housefires in the past &
    I am sure there will always be cheap & dangerous products available
    since 95% of people buy on price only !!!)
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