# Question About A Particular Circuit in LTSpice

• Engineering
I am simply attempting to design a circuit in LTSpice. We just started on dependent sources.

I am having trouble designing this guy here:

Here's what I've got:

What does this error mean?
What do I need to change to make this circuit work?

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berkeman
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Is H1 a voltage controlled or current controlled voltage source? What current or voltage do you want to be controlling H1's output? It looks like you have a constant 2e3 multiplier, but no quantity to multiply it by. When you double-click on H1, what-all can you fill in? Can you show us that screenshot?

berkeman
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gneill
Mentor
In LTSpice, $H$ is a current-controlled voltage source. You need to specify a (separate) voltage source and transresistance value. The simulator will take the current flowing through that separate voltage source and multiply it by the transresistance value yielding the voltage of the $H$ source. Looks like you'll want to choose VM as your separate source.

Is H1 a voltage controlled or current controlled voltage source? What current or voltage do you want to be controlling H1's output? It looks like you have a constant 2e3 multiplier, but no quantity to multiply it by. When you double-click on H1, what-all can you fill in? Can you show us that screenshot?
Well, I know "H" is supposed to represent a current controlled voltage source, but the first picture of a circuit I posted was what the professor gave us in our HW. So I am unsure as to what he was expecting by giving a voltage source for a current dependent source.

I'm unsure how to answer the rest. Double-clicking H1 doesn't bring up any pop-ups. I figured that the professor's circuit made sense and I just didn't know how to read it. Now I see that it is just confusing for everyone.

berkeman
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Double-clicking H1 doesn't bring up any pop-ups.
There has to be some way to edit its properties (I'm more familiar with MicroCAP than LTSpice). If you right-click H1, can you get to its properties?

There has to be some way to edit its properties (I'm more familiar with MicroCAP than LTSpice). If you right-click H1, can you get to its properties?

The photo below is from right-clicking:

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berkeman
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Right-click in the middle of the circle symbol, not on the text "H1"

Wow, sorry. I right clicked the symbol before and nothing happened. I closed LTSpice and re-opened it and now right-clicking the symbol works.
Here you are:

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berkeman
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Great, much better!

Now you just need to know what to put into those fields to give you the current-controlled voltage source characteristics that are needed. If you look in the Help menu for LTSpice, or search online at the LTSpice website, what do they say about how to fill out those fields?

So I wasn't able to find anything online, but I did figure it out:

When you right click on the symbol you have the ability to add a second value. Then, there is a checkbox next to that 2nd value that enable's it's visibility and utility. If I am understanding correctly, I essentially assigned the dependent source the "VM" source by naming one of it's values "VM" also.

Anyways, thanks for the help. I appreciate the time you've given me.

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berkeman
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Glad you got things basically working. I'm still puzzled by a few things in your circuit, though. It looks like you are using a voltage source VM with 0V output to sense the current that you use in the CCVS H1? Is that a normal practice? Having "VM" be the current that gets multiplied by 2000 to make Vh is a bit confusing for me.

gneill
Mentor
Glad you got things basically working. I'm still puzzled by a few things in your circuit, though. It looks like you are using a voltage source VM with 0V output to sense the current that you use in the CCVS H1? Is that a normal practice? Having "VM" be the current that gets multiplied by 2000 to make Vh is a bit confusing for me.
It's true. The $H$ device requires that you specify the name of a voltage source and it takes the value of the current passing through it. It's a bit frustrating at times since it tends to clutter up the circuit with these "null" voltage sources.

It would be nice if you could specify any two-terminal device as the target for $H$. However, there's also the $bi$ and $bi2$ arbitrary behavioral current source devices for which you can specify an arbitrary function using any voltages or currents in the circuit.

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berkeman
Mentor
It would be nice if you could specify any two-terminal device as the target for HH.
Yeah, like I(R3)...