1
\$\begingroup\$

Please, take a loot at this circuit:

enter image description here

Obviously, this is a circuit that is very easy to solve using lots of different methods. However, I'm trying to solve it using Nodal Analysis (I'm not sure if it's possible).

I tried to use node B as reference. When I do it, I notice that the voltage from C to B is known (10V). The voltage from A to B is already known (20i). So, there's no equation to find.

I would like to know if this circuit is already "solved" (voltages are known) or if I'm missing something here. I just can't find any useful equation taking B as the reference. Even if I try to find a equation using node A, I can't go forward since I can't find find the current that is passing through the dependent source.

Thanks!

\$\endgroup\$
3
  • \$\begingroup\$ I'm not sure you can say you know the voltage itself from A to B. Yes, you have a current source which sets a voltage, but you don't have the voltage itself. I'd recommend setting up for KCL on the nodes to get the whole system with certainty. \$\endgroup\$
    – OFRBG
    May 6, 2015 at 3:55
  • \$\begingroup\$ @Fiire Yes, I agree with you. The point is that I just can't find a way to find the voltage itself using only Nodal Analysis. This is strange, since the point of this method is to find all the voltages related to the reference node. I would expect to get Va as a known number after applying nodal analysis, instead of an equation with an unknown variable i. \$\endgroup\$
    – felipeek
    May 6, 2015 at 4:05
  • \$\begingroup\$ Sorry! I thought the i stood as an indicative for current in ampere. If i is a variable, then yes, the system of equations depends (most probably) on the value of i. \$\endgroup\$
    – OFRBG
    May 6, 2015 at 4:20

2 Answers 2

Reset to default
1
\$\begingroup\$

At Node C: (C+20i)/10 + (C+20i)/30 = i

But C=10, hence you can solve for i.

Then, voltage at A is -20i

\$\endgroup\$
1
  • \$\begingroup\$ Thanks, I didn't realize that a node could be useful even if I already knew its voltage. \$\endgroup\$
    – felipeek
    May 7, 2015 at 3:59
0
\$\begingroup\$

You won't be able to set up a traditional Nodal equation for node A because of the dependent voltage source. This brings you down one equation, but in return you get the equation for the dependent voltage source: Va = -20*i ('i' which would also be referenced in your nodal equaton for node C).

So to answer to "can you solve this using nodal analysis" well... I would say yes, but that's assuming that dependent voltage source stuff is somewhat orthogonal.

\$\endgroup\$
3
  • \$\begingroup\$ So, basically, the only result I get by applying Nodal Analysis in this circuit is the Va = -20i equation? It's kinda strange, since I've solved other circuits using Nodal Analysis and everytime I was able to find exactly the value of each voltage (in this case, Vc and Va). I feel like I didn't successfully applied the method since the results (Vb = 10V and Va = -10i) are still using an unknown variable i. \$\endgroup\$
    – felipeek
    May 6, 2015 at 4:02
  • 1
    \$\begingroup\$ That's not including the nodal equation for node C. Although you already know Vc, you can still set up a nodal equation for the currents coming in and out of that node. \$\endgroup\$
    – Gabe Noblesmith
    May 6, 2015 at 13:08
  • \$\begingroup\$ Thanks, I didn't realize that a node could be useful even if I already knew its voltage. \$\endgroup\$
    – felipeek
    May 7, 2015 at 3:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.