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flyback transformer question

Discussion in 'General Electronics Discussion' started by mahone, Mar 14, 2014.

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  1. mahone


    Dec 21, 2013
    hi all. I'm looking to make a small Jacobs ladder. I have a flyback from an old tv and wondered if I could power it with 12vac? and if so, would I need to connect to the primary as I assume, or does the feedback need to be connected in some different configuration?
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    A flyback transformer is not used like a typical transformer.

    Normally it is driven using a sawtooth waveform so that the current rises in the primary and is suddenly shut off. This sudden shutoff causes a massive voltage to appear on the output (and incidentally a pretty high one on the input side too).

    You may be better off looking for a design based on a car ignition coil as they have a lower voltage primary winding more suited to what you have. They likewise are driven in a similar way (current is allowed to build up and is then suddenly interrupted)
  3. mahone


    Dec 21, 2013
    thanks Steve, good advice as always.

    I thought that ac would be a better option than building a dc driver, unfortunately I don't have an ignition coil, so I will probably go with building the driver for the flyback.

    many thanks :)
  4. Laplace


    Apr 4, 2010
    It is true that a flyback transformer is not used like a normal transformer, since it is normally driven by the horizontal oscillator on an old-style television (Do they even make those anymore?) Nevertheless, it does generate high voltage in the same manner as an ignition coil. But there are differences. The flyback transformer has a ferrite core, whereas the ignition coil has an iron core, reflecting the difference in the operating frequency.

    For a gasoline engine the cylinder spark fires once for two revolutions of the crankshaft, so with eight cylinders the ignition coil fires four times for every revolution. At 6,000 RPM the ignition coil fires (4x6000/60) 400 sparks/second. For NTSC video 525 lines at 30 frames/sec, the horizontal oscillator has a frequency of ~16 KHz or 40 times the frequency of an ignition coil. Also, the flyback transformer has a damper circuit but this can probably be dispensed with for powering a Jacobs Ladder.

    With a flyback transformer there will be a high-frequency, high-current, & high-voltage environment. That is a place I dont' care to go. But good luck to you!
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