LTSpice Series Impedence Accuracy

[ACharnley]

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?

 

[alec_t]

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]

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]

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]

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.