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isolated feedback for SG3525

Discussion in 'Electronic Design' started by Anthony C Smith, Jun 12, 2006.

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  1. Does anyone have a schematic/ experience on isolated secondary feedback on
    the SG3525, I only need 5% regulation.
    lots of people mention using an opto, but I have never used this on 3525,
    only non isolated feedback, and I cannot fing an apps note on the subject.
    regards & TIA
  2. Terry Given

    Terry Given Guest

    go look at some TI appnotes, they have one in particular about how to
    isolate the feedback network.

    for 5% regulation you could get away with a zener + opto. Zener in
    series with opto led in series with resistor, across output.

    opto transistor pulls up (or down) on 3525 error amp, such that output
    too high turns on opto transistor which reduces duty cycle.

    pick Vz = Vout_desired - Vopto_led - Iopto_led*R

    after picking Iopto_led (say 5-10mA).

  3. Guest

    The opto collector goes to the 3525 supply, emitter goes to pin 1.
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