A real capacitor can be modeled using a series RLC equivalent circuit.

However, there are still discrepancies between the two.

I've generated a waveform from the lab and I've modelled the equivalent series RLC. Why are there discrepancies between the two circuits and how can I generate a model that more closely resembles the lab generated waveform?

The first image is the lab-generated waveform for the voltage across a 2.2uF capacitor, second image is the simulated waveform resulting from the series RLC equivalent. Both have 200k Hz, 10Vp-p square wave input

## Best Answer

If we had an FFT amplitude and phase, one could get a perfect passive model of all the elements, knowing that the source is 50Ω and thus the transfer function.The signal has the following characteristics from which a model can be generated.

Since C=Ic dt/dV = 200mA * 4.5us/V = **0.9 uFand not 2.2 uF**However with a simulator you can model the waveform and adjust the parameters. From this I get RLC1= 0.6uF+ 20nH + 50mΩ and RLC2 = 0.8uF + 0nH + 300mΩ (in //)

It is either Rs=100 Ohm source and 1.8uF or 50 Ohm source and 0.9uF with an ESR=50mΩ approx with about 20nH of ESL and many other RLC smaller networks shunting the RL network.

^{simulate this circuit – Schematic created using CircuitLab}This is also why C(f), ESR and ESL changes value with sine frequency due to reactance model. But SRF and PRF will give a better model and a scatttering s22 plot is the best from the OEM.