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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I decided to do some more rigorous measurements of the multilayer coil I wound, hoping to characterize it well enough so that I could see how it would behave in a transformer with simulated high power throughput without actually having to power it up.
The first thing I did was use CST EM Studio to get an idea of the inductance matrix of the transformer, comprising the secondary coil under test, the ferroxcube double "U" core, and a 16 turn test primary coil that I happened to have lying around. An added post-processing step gave me an estimated coupling coefficient of about 0.978.
Then, for a low power test, I put the transformer together and loaded it with 50 kohms (the load required for a power throughput of 1 kw at 10 kvp).
While keeping the input voltage constant at 1 Vpp, I measured the output voltage at four different frequencies within the range of about 7 to 30 kHz.
Then, I simulated the transformer and load circuit using the spice simulator "CircuitMaker 2000", using for the transformer the numbers from EM Studio. By a process of trial and error, I varied the capacitive loading on the secondary until the frequency response matched closely to the numbers I actually measured.
After doing that, I came up with a capacitive load of about 340 pF.
Then I generated a frequency response curve which came out as follows:
The ultimate conclusion I came to was that I need to get a life...
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Patrick,
The frequency response I get from the transformer depends on how I load it.
When I first wound the coil, I did a quick test of it on the core using whatever resistor happened to be handy. I'm not sure exactly what value it was but I know it was much lower than 50k. It might have been 7.5k or 10k or something like that.
Loaded like that, the coil showed a different frequency response. It appeared reasonably flat up to about 15 or 16 kHz and then the output started falling off.
Apparently that's because the lower value of resistance spoils the "Q" of the resonance. But with a lighter load (greater resistance), where the reactive current is much greater that the load current, then you get the "resonant rise" in the output voltage.
BTW, as far as EM Studio goes, it is part of "Studio Suite".
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
i see. yeah your coil is wacked. it can go in the shit-can. build a pi one and youll avoid these propblems with freq roll off and excessive capactence. id like steve wards oppinion too. he saved me from this very result.
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Winding multilayer coils is a big PITA...
