PM,
thanks for this info, and good observation / thinking about the "real" current.
I remember some statements that scopes are not suitable to be used as a voltmeter, so this confirms it once again.
I normally used a Fluke DMM to confirm the Rload voltage and it was practically always the same as presented
by the scope, but that was in 10 - 30 volts range, not millivolts.
Perhaps the weather, humidity etc. could have effected the scopes ability to more or less accurate measure the
voltages which then produces these different outcomes we have seen.
Concerning your GOOD section, i removed C1 and tuned for resonance (1.76Mhz) across Rload, see screenshot.
Rload rms voltage is 28.55V, this squared and divided by 8140 gives 100mW.
Input as calculated by the scope as normal gives 128.9mW.
We still see that same current difference (calculated 3.5mA versus probe 2.9mA) as you explained above.
Itsu
Itsu, Thanks for doing the "Good" test!  Hopefully something can be salvaged from all this work for your sake and others who have ordered parts for replication as we are not 'dead in the water' yet. This new circuit is actually a Parametric Series Resonance with diode limiting and a series connected load. Later I hope to show a PSR with a parallel load and no diode limiting. Anyway, in order to be able to determine if your current measurement is accurate (has any offset), we need to have the load voltage also measured in 'mean' volts along with the rms. This way we can determine the correct mean current by dividing the mean output voltage by the load resistance. Correction can then be made with a small current injection of the proper polarity in the CSR as shown in the attached schematic. I would recommend using a 10 ohm CSR and then correct your current channel readings. The MDO scope allows this to be done internally with the input gain amplifiers so the offset is reduced by the gain reduction. The attached scope shot the results of my test with the values shown in the schematic. The mean CSR current should be 15.14/7451 = 2.032ma and is measured to be 2.027ma for an error of -0.25%. We will correct pin by this amount so pin(cor) = 43.13mw * 1.0025 = 43.24mw. Pout = 22.05^2/7451 = 65.3 for an apparent COP = 65.3/43.24 = 1.51. This is good but not as easy to work with for looping. I haven't tried removing the schottky diode across the mosfets as of this post, but the performance may actually be improved due to the fact that whatever diode is used limits the resonance so, a higher conduction level may improve the performance. Regards, Pm Edit: Also notice that we are no longer dealing with a large Pin (reactive)/Pout (real) ratio. This means that we can use a lower bandwidth on the current channel without losing accuracy due to slight phase changes. Edit2: Replaced schematic with corrected version-left out RL!
« Last Edit: 2018-10-11, 21:49:14 by partzman »
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Topic: Parametric Charging (Read 74766 times)
