5
\$\begingroup\$

I am trying out the following parallel RLC circuit configuration: enter image description here

On trying out other similar parallel circuits (like with an RL coil in parallel with C or with RC and RL branches in parallel) I got the frequency curves I had expected and seen in textbooks. However with this one, I get the following response:

enter image description here

which appears to be pretty erratic. There is a "dip" at the resonant frequency (of around 1000 rad/s or 160 Hz) but I dont understand why the curve leading upto it and after it is so jagged?

enter image description here

When I step the resistances, this gets even more erratic. Is this normal behavior for this circuit. There was nothing in my text book to suggest this kind of response. I expected something like this:

enter image description here

\$\endgroup\$
2
  • \$\begingroup\$ It happens; I missed it too at first glance. Andy's on the ball though. \$\endgroup\$
    – rdtsc
    Jan 24 at 18:53
  • 2
    \$\begingroup\$ "-300dB" on the vertical scale is a pretty strong hint you are looking at rounding noise from a calculation that really should produce 0. ANd rounding noise tells you nothing useful about analog circuit behaviour. \$\endgroup\$ Jan 24 at 22:42

1 Answer 1

6
\$\begingroup\$

This is a likely candidate for show-stopper of the month: -

enter image description here

Then, when you fix that you'll realize that a voltage source (V1) is ideal and won't care a damn about C1 and L1 being present i.e. you'll just plot the spectrum of I(R1) as a straight horizontal line.

\$\endgroup\$
2
  • \$\begingroup\$ That was easy. Thanks, I'll certainly be more careful in the future about that. Actually, I was more interested in the current through the source (IR + IC + IL) and the plot for that seems to be inline with what I expected. Lastly should I take this question down or keep it up ? \$\endgroup\$
    – First User
    Jan 24 at 18:28
  • 1
    \$\begingroup\$ @FirstUser given that I've taken the time (albeit only 5 minutes) to answer and, that this site runs on upvotes and answer-acceptance (and a lot of goodwill), I'd be livid if you took it down!! Oh, I see you've done the right thing now. \$\endgroup\$
    – Andy aka
    Jan 24 at 18:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.