Is strange SMPS current waveform due to aliasing?

[treez]

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)
https://i47.tinypic.com/2q8bymt.jpg

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


Velleman HPS10 oscilloscope (2MHz bandwidth, 10MS/s)
https://www.farnell.com/datasheets/14532.pdf

SEPIC converter is 5W, vin=6V, vout=5V, Frequency = ~70KHz

 

[FvM]

How can we determine possible scope aliasing in a LTspice wafeform?

 

[treez]

The HPS10 scope cannot transfer waveform to computer, so i just mocked up the waveforms with the simulator.

 

[FvM]

It may be aliasing respectively an oscilloscope software artefact. It should be easy to find out by varying the oscilloscope settings. It the there's a real oscillation, it would show at other nodes as well, e.g. output voltage.

 

[treez]

it doesnt show much at output voltage......but it is faintly there when on 50mV/div.

Scope sample rate is 10MS/s so surely aything above 5MHz should be faithfully reconstructed.?

I am used to seeing this kind of "starnge waveform" with better scopes, but at timebases of say 10ms, not 100us.