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smps for rf power unit , scr freq and measuring rf voltage with a dmm?

Discussion in 'Electronic Basics' started by nanotech1, Feb 24, 2005.

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  1. nanotech1

    nanotech1 Guest

    i have a question to ask about switching mode power supply ,scr switching
    frequency and measuring rf voltage with digital multimeter

    1) i want to use an old smps for making a fix freq rf power unit

    is it possible to used the smps transformer output tap as a rf power source

    leaving only the converter portion of the ps intact

    most of these smps have a optocoupler for circuit isolation

    i am going to use the optocoupler circuit for controling the ouput power

    and a matching inductor at the transformer output tap for protection before
    the load

    i plan to used an old pc power supply for rf source and a rf air coil for
    load

    i want to use it for small induction heating system

    can it be done with a minimum of circuit modification to a stock pc smps


    2) what maximum switching frequency can i expect form a generic type
    standard switching speed SCR

    3) can it be possible to do a rf voltage reading with a standard digital
    multimeter if so what kind of circuit do i need between the dmm and the rf
    voltage source

    any help appreciated
     
  2. mike

    mike Guest

    If you really have an SCR switcher, it's probably switching at 60
    Hz...at least
    where I live. That's all the faster it can go. Now if you don't really
    have a SCR switcher, we can't help 'till we figger out what you do have.

    FWIW, isn't induction heating done at 13 MHz? Probably ain't gonna get
    there with ANY commercial switching supply.
    mike


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  3. nanotech1

    nanotech1 Guest

    i know that high speed scr can be drive to 10khz but for low speed one i
    guees thats above 60hz
    may be somewhere in the 400 hz i am not an expert in electronic


    for my rf power unit i only need rf freq in the 100 to 200khz and rf output
    of 100w to 200w range

    the 13mhz induction heating band is used for labotary equipment most of the
    time
     
  4. mike

    mike Guest

    You need to be VERY MUCH more specific.
    It's likely that you can build an SCR switcher that runs at 200 KHz.
    Not at all clear why you'd do this when a simple oscillator can easily
    do this.
    Your original post related to an "old" whateverthatis "smps" whateverthatis.
    It's likely that an "old" scr smps swtiches at line frequency. The way
    to convert it to 200 KHz. is to take out all the parts, lay them out on
    the table, replace the scrs with MUCH faster units, design a circuit
    using them, throw away any existing parts that don't fit, buy new parts,
    put them all back in the box.

    Or you could wire up one or two transistors as a Colpitts or Hartley
    oscillator at any frequency you want and be done with it.

    First thing I'd do is borrow a ham radio transmitter, couple it to the
    load and make sure the thing works. But probably can't get below 1 MHz.
    that way.

    mike


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  5. nanotech1

    nanotech1 Guest

    it is possible to make a scr oscillate at 200khz !

    so do you know any schematic that do so please give me a lead to where
    i can get it :) a web site would be great

    i want to build a high power SCR oscillator ( it simplyfied the circuit
    without having any amplification stage to bather with)
    but i dont think that scr can oscillate at 200khz unless it is a really
    specific expensive device

    as for the smps especially the ones for pc computer they have high power
    transistor oscillator circuit in them that could be salvage i want to use
    sutch a circuit to drive a small coil with it
     
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