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Odd scope waveform.....aliasing?

Discussion in 'General Electronics Discussion' started by eem2am, Jan 26, 2013.

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  1. eem2am

    eem2am

    419
    0
    Aug 3, 2009
    Hello,

    Please can you say if the strange oscilloscope waveform of my SEPIC converter’s current sense resistor voltage is real or not….or is it due to aliasing?

    Here is the sense resistor voltage……its when the timebase is 100us/div that the waveform looks strange…(going up and down)………..

    Current sense resistor voltage waveform (20us timebase on scope)
    http://i47.tinypic.com/2q8bymt.jpg

    Current sense resistor voltage waveform (100us timebase on scope)
    http://i45.tinypic.com/mccdoz.jpg

    the above waveforms are from the simulator, as the scope cant give images to USB. I 'fiddled' the simulator to give the waveform that ive seen
    Velleman HPS10 oscilloscoper (2MHz bandwidth, 10MS/s)
    http://www.farnell.com/datasheets/14532.pdf

    SEPIC converter is 5W, vin=6V, vout=5V, Frequency = ~70KHz
     
    Last edited: Jan 26, 2013
  2. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    with a few google searches that seems perfectly reasonable, the SEPIC works based on Duty Cycle... From Wikipedia:
    Based on the 70kHz frequency you should see a period of 14us (looks about right on the pictures) and then depending on the capacitor and inductor sizes that would determine the slope of the peaks.

    Now at 10MS/s you have 10 samples per microsecond so that should be more than enough to have an accurate show of what is happening
     
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