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AC to DC wall adapter

  1. Oct 9, 2005 #1
    On the adapter, Vout is 12Vdc but when I measured it with a voltmeter it shows 19.5V. Is there a typo or does the voltage somehow drops down to 12V when in use with a load?
  2. jcsd
  3. Oct 9, 2005 #2


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    Staff Emeritus

    Are you sure you not measuring RMS value?

    Vrms = Vo/sqrt(2)
  4. Oct 9, 2005 #3
    RMS?? The output is DC.
  5. Oct 9, 2005 #4


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    Gold Member

    The output probably has a lot of ripple. Your measuring meter is probably is seeing it.
    If your meter can measure AC try it an see how much.
  6. Oct 9, 2005 #5
    I've seen this a lot of times. I think there must be a lot of "droop" in the converter's output. At rated load it's probably at stated voltage, but open circuit, it's high. I think if you should use these converters at their rated load. Load too high -- burn them out; load too low -- maybe damage your load.
  7. Oct 9, 2005 #6


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    Homework Helper

    I agree. Most voltage values given are rated values at full load (i.e. rated current).
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