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Inverter transformer question

Discussion in 'General Electronics' started by Robert W. Mudge Miller, Jan 29, 2004.

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  1. I'm looking for a transformer (or some other passive device) that will
    step-up the 2 volt max. RMS speaker output from my PC to about 70-90
    volts RMS. I want to simulate a telephone ringer voltage with about a
    60Hz, ~70V sine wave. I know the spec calls for 20Hz at 90V but I
    understand that most modern phones -- i.e. ones that have no
    mechanical ringer -- will respond to ring signals of 70V or less and
    frequencies of 60Hz or more (and draw very little current in ring

    Now, I've already tried the obvious idea of turning around a small
    power transformer and driving the secondary winding with my speaker
    output. But instead of the appr. 20:1 voltage gain I would expect from
    a 120=>6.3volt transformer, I get only about a 4-5X step-up even with
    no load. I noticed that the voltage step-up improves to about 10X if I
    increase the frequency to 1KHz or more.

    So my questions are this: Why don't I get the same step-up ratio when
    driving the secondary winding as the step-down ratio I get when
    driving the primary with 120VAC 60Hz? Is there any transformer that
    can produce a 40:1 voltage step-up that I need for a 2V, 60Hz input?
    If so, where can I get it? Is it something that can be made, salvaged
    (from old electronics) or can it be purchased?

    Any thoughts highly appreciated. Also, is there a better place (usenet
    or elsewhere) to ask this question?

    Robert Miller
    San Jose, CA
  2. Not going to happen! (Passive device)
    Your transformer is NOT all that efficent running backwards.
    Because the transformer is NOT bidirectional.
    The primary has a MUCH better coupling to the core than the secondary.
    Telephone ringing is NOT 60 Hz, try 20 Hz.
  3. GPG

    GPG Guest

    Not enough power available Transformers have losses.
    Google "ring generators"
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