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enter image description here

I am completely new to LTSpice. I am trying to build this circuit in LTSpice on mac. The first problem I notice is that I can't rotate the components. I googled for a while and only found solutions to rotate components on Windows, so I bent the wires to fix this.

The real problem is that, I'm having trouble to add the dependent voltage source. As shown in the image, I need to have a 3v0 voltage source. So, 1) how to I tell the software which voltage is v0? and 2) how do I set the voltage source as 3v0?

Thank you so much in advance.

This is what I have right now, v0 is the voltage across A & B. enter image description here

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First, I never used LTspice on Mac OS X so I can't 100% confirm, but I watched a video and the rotate command looks to be the same as it is in Windows. To rotate, either while you are first placing the component or while you are in the process of moving it with the move tool, you press CTRL-R to cycle through each of the 90° orientations.

Second, it looks like what you want here is a voltage-controlled-voltage-source (VCVS), or "E-source". The B1 in your circuit right now is a behavioral voltage source or "B-source", which is a type I would try to avoid until you get more familiar in this software. The VCVS is simply listed as "e" in the component library. It has (+) and (-) control nodes, and its value is the "gain". So for your specific circuit, we want (+) going to A, (-) going to B, and the gain set to 3.

Third, you need to put a ground symbol on your circuit before it will let you simulate it. The obvious spot to place it would be on the negative side of V1.

So, if I redraw your circuit with all the above enhancements it should look like this:

circuit with modifications

Now, when you go to run it (by clicking the little running man icon at the top) it should ask you what type of simulation you would like to do. Since this is a basic DC circuit, I would select "DC op pnt". Then, after it runs it will give you a report of all node voltages (respect to ground) and all branch currents, as shown:

op point report

I prefer closing this window and then begin exploring the circuit interactively. You can hover your mouse over a resistor to see its current and power dissipation. I'm not sure on Mac, but on Windows this shows up at the bottom bar of the application window. You can look at node voltages by clicking on nodes to bring up annotated text (blue on Windows) showing their voltages. These text labels can be left on the schematic, then if you change one of the resistor values and re-run the simulation the voltage values will auto-update themselves. Here's an example of a few nodes being monitored. I also took this screenshot while my mouse was hovering over R1 so you can see the current and wattage shown:

interactive dc op point analysis

One last point I'd like to make is that resistors in SPICE have unique pin numbers (1 & 2) which are normally not visible to the user in "DC op pnt" mode. These will switch around as you rotate them. Basically, what this means is that if a current value shows up as positive it is flowing from 1 -> 2, and negative if it's going from 2 -> 1. If a negative current bothers you in a specific instance, you can either rotate the resistor in question twice with CTRL-R or mirror it once with CTRL-E. However, this isn't ambiguous because the voltages will "drop" across resistors in the direction of the current flow, and you should be able to see this and gather the proper context.

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  • \$\begingroup\$ Thank you very much, that helped me more than I expected. \$\endgroup\$
    – Brandon Swift
    Oct 13, 2020 at 7:06
  • \$\begingroup\$ Some information that might be helpful for people who are seeing this thread later: 1) On mac, the "E" label isn't "gain", it's "value". 2) I didn't manage to set (+) to A, and (-) to B, instead I attached two wires from those nodes to A and B manually. 3) On mac you can't just "select DC op pnt" to run the circuit, what I did was go into Draft -> Spice Directive and typed something like ".tran .1 10", meaning a transient simulation with samples every .1 seconds that ends at 10 seconds. After I did all that, I got the same result as Ste. \$\endgroup\$
    – Brandon Swift
    Oct 13, 2020 at 7:10
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    \$\begingroup\$ @BrandonSwift Dang. I didn't realize Mac doesn't have a simulation type selection screen. Then if you want to run the op point you can simply enter in .op as the SPICE directive. Also, I did explicitly say that you change the "value" of the E-source to 3. The value for E-sources are known as their gain, just as when you change values for resistors you are changing their resistance. \$\endgroup\$
    – Ste Kulov
    Oct 13, 2020 at 15:16
  • \$\begingroup\$ Ah, I see what you mean by the value part, I misinterpreted that sentence before. Thank you so much again! \$\endgroup\$
    – Brandon Swift
    Oct 14, 2020 at 6:26
  • \$\begingroup\$ @BrandonSwift No worries, man. I just re-read it too, and it could've been written much more clearly than it was. Godspeed! \$\endgroup\$
    – Ste Kulov
    Oct 14, 2020 at 10:26

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