Odd scope waveform due to aliasing?....SEPIC converter sense resistor voltage

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 oscilloscoper (2MHz bandwidth, 10MS/s)
https://www.electro-tech-online.com/custompdfs/2013/01/14532.pdf

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

Are you sure those pictures are from an oscilloscope? It looks awfuly a lot like a result from LTspice simulation. Or what scope does label it´s results V(n016)?

The HPS10 scope cant transfer images to the computer, so i just mocked them up with the simulator.

So how do you mock up scope aliasing in LTSpice?

The waveforms, as you see in top post, are close to what i am seeing on the scope.

...to get the waveforms like that, i just made the control voltage go up and down in ltspice

Flyback said:

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?

Click to expand...

I think it is aliasing. I have a hand held scope that works differently than the big scopes. If the memory is small and the sampling rate is low I see wave forms like this. On the big scopes I can push the number of samples up and this problem goes away.