It is a fairly straight forward setup and procedure Brad. Here's what you do:
1) Use the CVR1 setup as in the attached pic. Same common ground for both probes.
2) CH1 is v(t), and CH2 is i(t) (and is v(cvr1)/10).
3) Set up a MATH trace with CH1 x CH2.
4) Set up a measurement for the MEAN (or average) of the MATH trace. Divide the indicated measurement by 10 to correct for the current. This is the total corrected power going into the circuit after the diode.
5) Set up a measurement for the RMS value of CH2, and divide that by 10. This is the corrected RMS input current.
6) Make note of the total corrected average power in step 4).
7) Calculate the power dissipated in CVR1 by using the corrected RMS current in step 5), as: P(cvr1)=I(rms)2 x 10
8] Subtract the CVR1 power calculated in step 7) from the total power noted in step 6).
9) The subtraction in step 8] results in you obtaining the net power going into the primary of the transformer, aka P(in).
Ok,i have done what you suggested(see scope shot below),but i disagree with the highlighted above,where this is not showing total corrected P/in. This is showing total power dissipated by the CVR and Primary of the transformer,which is 69.4mW
By doing it this way,the scopes math is including power being sent back to the source-i would suspect via the diodes junction capacitance for a brief time,and then once the voltage inverts across the coil,current then flows to the SG via the ground rail,through the SGs circuit,and then back into the DUT.
How do we know this?--
Well,lets have a look at the scope shot below.
See the time period i have circled in green.
If this was power being sent to the circuit by the SG,how come the voltage is inverted across the primary?
This area in green is the primary coils magnetic field collapsing(the flyback period).
So,we know from years of testing,that this is the time when the supply is cut off,and we get our inductive kickback,where the voltage inverts. During the 80% off time of the SG,the transformer is now the source--not the SG,but the scope math still sees this as power flowing through the primary of the transformer,and so is adding that to it's calculations.
What we want to know is the power being delivered to the DUT by the SG only,during it's 20% delivery cycle.
Please see next post,where i show clearly when power is being delivered by the SG to the DUT.
Brad
Never let your schooling get in the way of your education.
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Topic: Parametric Charging (Read 61650 times)
