Produce a resonance curve for this circuit between 6 kHz and 10 kHz

[leejohnson222]

Homework Statement

circuit is as follows

Relevant Equations

series circuit
Voltage 20V 5khz - R10 ohms Inductor 1.5mh Capacitor = 270 nF

this is what i created so far, but not quite sure how to get the resonance curve, i tried to enter it in settings and do an AC sweep

 

[DaveE]

What voltage are you measuring? Where is the ground node?

 

[leejohnson222]

20V 5khz, should i be looking at the current ?

 

[DaveE]

I don't know what you are supposed to do. Your supposed to tell us.

But, that looks good to me. Except somethings wrong with the magnitude scale. At resonance the current should be $I = V1/R1$. This is because at resonance the complex impedances of the reactive components will cancel each other and sum to zero. Does your voltage source have any impedance built in?

The phase looks good though, so it's something about the plot scale, I think.

edit: Oops! No sorry. There is something wrong with the magnitude. With Q=7.5 you should have more peaking at resonance. The asymptotes should intersect about 7.5x lower than the current peak at resonance.

edit#2: Never mind the peaking bit. I misread the plot. I'm more familiar with a log(f) scale which will show the linear asymptotes more clearly.

 

[gneill]

The same circuit as simulated by LTSPICE. The magnitude, in dB, is of the current in the series circuit.

 

[Jody]

I would imagine plotting magnitude of impedance Z would be a valuable learning experience :) what does L and C do at the resonant frequency, and impedance should you see when that happens?

If you had time and wanted to explore, then I would put another pair of these in parallel to it with a different set of LRC something like 500 uH, 100 Ohm, and... 561 nF just to see what happens. I think that would be fun.

 

[leejohnson222]

i think i need to download LT spice and try to run some circuits, been struggling to install it for some reason

 

[DaveE]

LT Spice is quite good and, I would guess, the most popular on-line Spice tool. But Spice has been around for a really long time, and for basic circuits like this they are all going to give you a good answer. Whatever that green one you used in previous posts is probably fine for this. So, go for it, if you like, but don't expect that a different simulator is going to clear anything up.

Honestly, most EEs that I know learned this stuff from a physics or EE text book, not a simulator. Simulators are good at giving answers, but are usually not good for teaching concepts.