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LTSpice Series Impedence Accuracy

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ACharnley

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I have three identical inductive circuits which are fed a current derived from a frequency sweep. The second has a capacitor in parallel and the third a capacitor in series.

LTSpice is considering the reactance for the parallel capacitor correctly but the series capacitor only affects the phase not the expected amplitude. Any ideas?
 

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alec_t

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The series cap does affect amplitude. This is particularly noticeable at low frequencies. At the higher frequencies the cap impedance drops, so the effect becomes less noticeable.
 

ACharnley

Member
Is it working differently for you? In the screenshot the red/blue graph are almost the same. There should be a significant difference like the green hump but a bit further along and/or a little less amplitude.
 

alec_t

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In the screenshot the red/blue graph are almost the same.
They're quite different at the left side (low frequency) of the screenshot.
like the green hump but a bit further along
No. To get that effect you'd need to reduce the cap value and have the cap in parallel (as in the first circuit).
 

rjenkinsgb

Well-Known Member
Most Helpful Member
300uF and 0.12F in a series resonant circuit have a low impedance at 26.5Hz, if I'm working it out correctly.

You sweep frequency does not appear to be low enough to properly register it, if it is that.
 
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