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  1. #1
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    Power supply duel_5v/15v from 230:15v 1amp transformer

    Along with subject and ckt attached,
    why getting 19.5v(more than tranformer sec rating) insted of 15v.

    The measurement of volt as follows with digital meter:
    The tr sec o/p-> 15.96v,
    o/p-1 ->>5.2v
    o/p-2 ->>19.5v


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    Can u explain the fact behind it and do i get ~15v.

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  2. #2
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    Re: Power supply duel_5v/15v from 230:15v 1amp transformer

    if the 230V is a little high, you'll get a little more on the 15 V side

    15V RMS is 21.2 V peak
    one diode drop through the bridge, a second diode drop through D1,
    and a third diode drop on the return through the bridge yields 21.2 V - 3(0.7 V) = 19.1V

    you need to put a load across C5 to see anything besides the peak voltage
    diode D1 and capacitor C5 act as a peak detector, so you are seing the peak voltage

    how much current should the 15 V supply provide?
    connect R = 15V / (expected current in amps) across C5

    you might want a three terminal regulator after C5 to provide regulated 15V
    as you did for the 5V supply



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  3. #3
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    Re: Power supply duel_5v/15v from 230:15v 1amp transformer

    Hi,

    Most transformer and power supply ratings are at full power load .... not without load.

    Klaus
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