Calculating Thevenin Voltage by superposition

[markusz]

Hi experts,

I'm calculating Thevenin Voltage by superposition, and the whole process can be seen in the attached picture.

To sum it up:

• The circuit has one Voltage source and one Current source
• By superposition, I can take the sources one by one
• First, I take Voltage source and open the Current source
• Next, I take the Current source and short the Voltage source
• Finally I add them up

.

The right answer is V_thev = V*R2/(R1+R2) - I0 * R3. I got the first part correct but the second part wrong.
Can you please let me know where did I go wrong? Thanks!

[ledtester]

Working backwards you can see that your step 1 is correct, so your problem is in step 2.

Hint: no current flows through R1 or R2. All of I_0 flows through R3 and back into the current source.

The circular arrow in the middle isn't valid since it doesn't represent a circuit.

[markusz]

Working backwards you can see that your step 1 is correct, so your problem is in step 2.

Hint: no current flows through R1 or R2. All of I_0 flows through R3 and back into the current source.

The circular arrow in the middle isn't valid since it doesn't represent a circuit.

Thanks for the tip, I think I get the idea: If I look at the node south of the current source (call it B), using KCL, so apparently the current coming into the node (from R3) is I0, and the current coming through the source is also I0, which means there is 0 amp going to R1 and R2.

I'm also reading node analysis and it says I can ground any node and it shouldn't affect the outcome. I guess if I ground node B this becomes more obvious.