I'm studying AC adapters, and to check about waveforms while changing parameters I did a simulation of this circuit:

simulate this circuit – Schematic created using CircuitLab

Then I wanted to plot also the rectified waveform, so I added a second diode and a big resistance (sorry if this circuit doesn't use the internal CAD, but I was unable to find how to insert two schematics: if I tried to insert a second one, the first was deleted):

so on the 1G resistance there should be the rectified voltage, and the resistance should be big enough to not influence the circuit.

It seems to work, but what I don't understand is that there seem to be a disturbance on the secondary of the transformer, and on the rectified waveform (green on the left graph is the primary of the transformer):

So the secondary voltage has the positive part of the wave distorted, and the negative which is thicker, like there was some very rapid oscillation; and the rectified wave has the same distortion.

I tried experimenting with the simulation, and it seems to be due to the capacitor, since if I delete it the waveforms are a non distorted sines and the rectified waveform with no distortion; I'm not sure if this is something real, or an error of the simulator.

As for the diode, there is a parameter I don't know ("Current At Above Voltage"), but their model as given in the simulator is:

• saturation current: 171 nA
• forward voltage: 806 mV (but the distortion are the same with 0)
• current at above voltage: 1 A
• emission coefficient: 2

Are those distortions something to be expected? If so, why?

As simulator I used Circuit JS.

• This is LC distortion from the transformer and the cap. It's common. Apr 27 at 13:58