8
votes
Accepted
How to find the nodal voltage when there is a voltage source across two nodes?
I'd just rearrange the diagram and use source-splitting techniques: -
From left to right, it's the same circuit but, breaking it down step by step is easier to analyse. Each step saves maths and is a ...
- 473k
8
votes
Can't find error in nodal analysis
I found out the drop voltage at \$R\$ which is -34. But the solutions say
it is -28V. I can't find what did wrong.
$$\color{red}{\text{Neither answer is correct }}$$
Think about it: How can the ...
- 473k
7
votes
Accepted
LTSpice outputting the incorrect voltage reading?
Make sure the direction of the current for F1 is oriented the way you want it.
LTSpice follows the "passive sign convention" -- namely, the positive current direction through a current or ...
- 5,037
7
votes
6
votes
Accepted
How can you tell what is the net direction of current flow when there are two opposing sources?
Redraw Schematics First
Often, it helps a great deal to redraw a schematic. Not always. But sometimes the manual process of it helps you find an insight or two or, at least, develops a feel for things ...
- 78.7k
6
votes
Accepted
RC Circuit Analysis Direction Changes Formula
The basic constitutive equation for a capacitor is based on these assumed polarities,
The equation being,
$$i(t)=C\frac{dv}{dt}$$
If you want to define your current as leaving the capacitor then you ...
- 3,537
6
votes
Accepted
Strange Nodal Analysis
Your mistake is again the current direction.
For \$V_1\$ node you have wrote:
$$+12A + \frac{V_1 - V_2}{2\Omega}....= 0$$
As we can see from a circuit diagram the \$12A\$ current is entering the node(...
- 15.7k
6
votes
Nodal Analysis - Kirchoffs Current Law
Preface note: I originally used \$3\:\text{A}\$ as the current source. But I mis-read the problem, as stated. They specify, on the schematic, that the out-flowing current source value is \$-3\:\text{A}...
- 78.7k
6
votes
How to find V1 and V2 using Nodal Analysis?
To help you identify the nodes in the circuit:
If the label V1 had been written next to the dependent source 4Ix at the top(i.e., anywhere on the blue area), it would still be equal to VY because ...
- 1,149
6
votes
How can same points have different current?
Aren't B and D the same point and shouldn't it actually be (B and B)?
If you were analysing voltages then yes, B and D are the same node on the circuit. In this case, however, we're looking at ...
- 180k
6
votes
Nodal analysis: negative answers vs book's positive solutions
+1 from me for showing your efforts. It's easily enough to earn a moments response.
You can check your own work. I'll just dash out mine for comparison. I disagree with you on 3.9 and agree with the ...
- 13.2k
6
votes
Why does this op-amp circuit show current flowing like that?
is there any reason why it shows current flowing from the negative side of the bottom battery into the op-amp or why its showing current flowing from the positive end of top battery into the op-amp?
...
- 134k
6
votes
Why do we typically think about circuits with nodes rather than meshes?
A big one for me is voltage sources: nearly all electrical circuits are powered from a voltage source, not a current source. This provides a ground node and a (hopefully) fixed supply node that makes ...
- 23.1k
5
votes
Accepted
What is the op-amp output voltage for a voltage-controlled current source?
You need the MOSFET characteristics. For example, the IRF540 has the following typical characteristics:
So, for example, if your current is 10A the typical Vgs is about 4.75V. You need to add that to ...
5
votes
Where have I gone wrong with this nodal analysis calculation?
Suggestions
The first thing I do before attempting to analyze a circuit is to redraw that circuit. The process of just doing it helps me think and gather up a few details that I may not notice so ...
- 78.7k
5
votes
Determine Thevenin's equivalent circuit
Can anyone tell me what the right answer is/ where I have gone wrong.
Here's where your error is: -
- 473k
5
votes
Can't find error in nodal analysis
Your equations ignore the current through R. You can't do that.
If you don't believe this, think about what happens when R is 0.
For example, your node1 is missing the term
\$ \frac{+v_2 - v_1}{R}\$ ...
- 30.6k
5
votes
Accepted
Circuit analysis: connecting positive terminal of battery to reference node
Direct answer
I'll write more, later. But first....
There's nothing specifically wrong about connecting the positive terminal of a DC voltage supply (battery or mains-powered) to a 'ground'. A ground ...
- 78.7k
5
votes
Conditions for a resistive circuit to have a solution
and you don't put two current sources in series or two voltage sources in parallel
This condition should be rephrased as: "the circuit does not contain a zero-impedance loop with one or more ...
- 81.8k
5
votes
How to solve for \$i\$ using superposition?
First off, redraw the schematic. In fact, you should get into the practice of redrawing every schematic. Even those that already look good. Just do it. And do it every time. The practice is worth its ...
- 13.2k
4
votes
Nodal analysis -> transfer function -> step response
Nodal analysis is based on Kirchoff's Current Laws (KCL), meaning that the sum of all currents will need to sum up to exactly \$0\$.
The issue in your equations is related to the fact that outputs of ...
- 5,257
4
votes
Dependent voltage/current sources
A voltage/current depending source in real life needs to be built from actual electronic components. Usually made from operational amplifiers or transistors. They vary a bit from the ideal voltage/...
- 88.8k
4
votes
Accepted
How to use nodal or mesh analysis with a current source?
My problem here is how current source works.
The beauty of source transformation
If I redrew your original circuit like this: -
Would you find it easier to solve?
Would you know what to do next to ...
- 473k
4
votes
Accepted
Node voltages using a combination of voltage and current sources
The first thing I do before attempting to analyze a circuit is to redraw that circuit. The process of just doing it helps me think and gather up a few details that I may not notice so easily, just ...
- 78.7k
4
votes
What is the op-amp output voltage for a voltage-controlled current source?
Could you please help explain/show how I’d be able to find the voltage at node A?
voltage at A is whatever it takes to make Q1 turn on enough so that the voltage across the shunt (Ishunt *Rshunt) is ...
- 27.9k
4
votes
Determine Thevenin's equivalent circuit
You understood that you considered a series connection of the resistors rather than a parallel connection for \$R_{th}\$. When you have a resistance across measurement terminals - your 2-ohm ...
- 23.5k
4
votes
Why do I read 20 microamperes instead of 5?
Just looking at the schematic, the collector current will be a bit less than 2mA before correcting for drop across Rb. If that transistor is a 2N2222A hFE should be between 50 and 300 so base current ...
4
votes
Accepted
How do I solve the circuit below using nodal analysis?
Feel free to ask questions, if you have them. But what follows is nodal analysis, not mesh.
Assign \$0\:\text{V}\$ to the bottom node. You can do that to exactly one node. That's the one I pick.
Then ...
- 78.7k
4
votes
Why does this op-amp circuit show current flowing like that?
why is it drawn like this
Both the current direction arrow and the actual sign of the current need to be taken into account when establishing the true direction of current. Generally, the picture and ...
- 473k
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