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I looking figure 5 in beginning - is not so 'stupid' misstake as you measure in AC-input on your oscilloscope? - you have High pass filter-function on input in this case and with low frequency, voltage lower @ RC-function on your display if voltage spend longer time compare to your RC-constant on your input and this way make loop on your display.
Try measue with DC-coupling on oscillosope input and see if changes.
I looking figure 5 in beginning - is not so 'stupid' misstake as you measure in AC-input on your oscilloscope? - you have High pass filter-function on input in this case and with low frequency, voltage lower @ RC-function on your display if voltage spend longer time compare to your RC-constant on your input and this way make loop on your display.
Usually, we select the DC input mode rather than the AC input mode, when using an oscilloscope. Normally, in the AC input mode, the lower pole is about 2 - 10 Hz, thus, little change might appear between in both cases, switching to the DC or AC mode.
I still have no time to try out all the ideas suggested in the thread. Hopefully I can test the circuit again next week and feedback u guys the outcomes.
Dear Friend
i think that there is no mistake in your test procedure
but the problem arise from that at saturation when input current increase there will be a distorted output voltage composite from main frequency ( 50 Hz ) and its harmonics
because your scope draw the relation between input & output voltage you see a distorted hysteresis loop as you draw the relation between a pure 50 Hz input signal & an 50 Hz & Harmonics output signal
There are two choises for a solution to draw a standard husteresis loop
1. Lowering the frequency of input signal to a value near zero
2. add a filter on output circuit to reject the frequencies more than 50 Hz
finaly please note that for ferrite cores the frequency must be higher
yjkwon57 explained before. However, I still don't understand one thing, i.e. why when the core is saturated (as shown by the measured Vo or flux plot where some portion is flat), the input current Ip is still sinuisoidal? I thought if the core is saturated, the permeability of the core will drop and therefore the inductance of the primary winding will drop as well. If the inductance become less, then the reactance jwL will be less. The current should be higher when the reactance become less when the core is saturated. As the result, the current waveform should distorted right?
The current is sill sinusoidal because at 50Hz the reactance of your primary coil have very minor impact on the primary circuit impedance. Try this experiment at 20...100kHz and the current will not be sinusoidal any longer. The circuit with OP amp is useless at such frequencies... Use higher oscilloscope amplification instead.
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