# LTSpice Thevin circuit with voltage dependent voltage source

#### SteveLs

Joined Jun 26, 2020
5
Hello, I am trying to implement this circuit below on LTSpice, but I have trouble setting dependent sources
I need to check Thevnin Impedance and Voltage, but something is wrong with what I've implemented.

#### ericgibbs

Joined Jan 29, 2010
12,964
hi Steve,
Welcome to AAC
What is the value of the Cap marked 0.05F.?

E

#### SteveLs

Joined Jun 26, 2020
5
Hi ericgibbs!,
And I've attached asc file. Thanks!

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#### ericgibbs

Joined Jan 29, 2010
12,964
hi S,
As this is an Homework assignment, please post your calculations and explain what you think is wrong.?

E

#### SteveLs

Joined Jun 26, 2020
5
Yeah, through manually calculating the Voltage and impedance of the circuit, I've found that the Voltage is a sine wave. But what I've simulated with LTSpice does not show a sine wave.

Vout is around 71cos(10t-67degree) Volts

#### WBahn

Joined Mar 31, 2012
26,398
Check your Iout carefully. Most SPICE programs define the current in a two-terminal device to be the current flowing INTO pin #1.

#### SteveLs

Joined Jun 26, 2020
5

However, I cannot solve the problem by re-defining Iout. I've tried to set another component(R1) as the variable for current source, since I set Iout to flow toward that resistor. But it didn't work.

Could you recommend any other method or tips for it?

#### WBahn

Joined Mar 31, 2012
26,398

However, I cannot solve the problem by re-defining Iout. I've tried to set another component(R1) as the variable for current source, since I set Iout to flow toward that resistor. But it didn't work.

Could you recommend any other method or tips for it?
You don't have to redefine Iout. If your schematic has Iout flowing out of the pin #1 and the controlled current is +3*Iout, then if your simulation variable is actually flowing into pin #1 you simply have your controlled current be -3*Iout. Do yourself and anyone looking at your simulation schematic a favor and include a note explaining the reason for the apparent sign discrepancy.

#### SteveLs

Joined Jun 26, 2020
5
Thank you so much. you just gave me an insight to understanding the circuit.

I need to review and study the basics of circuit.

but by the way what does your last sentence mean? you said you also want me to do others a favor when they encounter problems as I did?

#### ericgibbs

Joined Jan 29, 2010
12,964
hi Steve,
Try I=I(V1) *-3
Also Right Click on the B1 Current source, then Click Open Symbol, what do you see.??
Which current source have you selected from the F2 selection.?
E

#### WBahn

Joined Mar 31, 2012
26,398
Thank you so much. you just gave me an insight to understanding the circuit.

I need to review and study the basics of circuit.

but by the way what does your last sentence mean? you said you also want me to do others a favor when they encounter problems as I did?
That's not what I meant.

If someone looks at your paper schematic or the problem statement and sees that the controlled source outputs 3*Iout and then they see your simulation schematic and sees that you have it outputting -3*Iout, they are likely to assume that you've made a mistake since, at first glance, there is a discrepancy between the two. So do everyone a favor and put a note in your simulation schematic explaining why the sign difference is there.

#### MrAl

Joined Jun 17, 2014
8,257
Hello again,

This circuit is a little interesting if we make the input a unit step we can get the output to look like an impulse in the frequency domain, which would be a sinusoid in the time domain but lightly damped depending on the value of the resistor.
Maybe not hugely interesting, but a little i think. The value of R acts inversely to what it would do if it was just a passive RLC circuit.