How Do You Calculate Thevenin Voltage Using Superposition?

In summary, the conversation discusses a problem with calculating the Thevenin voltage and resistance in a circuit. The conversation highlights the use of the principle of superposition, voltage division, and suppressing sources to accurately calculate the Thevenin voltage and resistance.
  • #1
DiamondV
103
0

Homework Statement


http://puu.sh/lQPvh/d0efa216ff.png

Homework Equations

The Attempt at a Solution


http://puu.sh/lQPAR/2456db4783.jpg
http://puu.sh/lQPCJ/f142c25f63.jpg
http://puu.sh/lQPER/5eb4af107e.jpg

Is this correct? I used principle of superposition to calculate the Thevenin voltage[/B]
 
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  • #2
Check your Thevenin resistance. When you calculated 60 || 30 you seem to have ended up with 15, although you did it correctly elsewhere.

Check your ##V_{th1}## calculation. You have a voltage divider and shouldn't end up with the same voltage as the source driving it on its output.

For ##V_{th3}##, when you suppress the 1.2 A source you remove it, not short it. And suppressing the 18 V supply shorts it. Draw the remaining circuitry. You'll see that the 0.25 A supply does make a contribution to Vth (it's still in parallel with a 20 Ohm resistor).
 
  • #3
gneill said:
Check your Thevenin resistance. When you calculated 60 || 30 you seem to have ended up with 15, although you did it correctly elsewhere.

Check your ##V_{th1}## calculation. You have a voltage divider and shouldn't end up with the same voltage as the source driving it on its output.

For ##V_{th3}##, when you suppress the 1.2 A source you remove it, not short it. And suppressing the 18 V supply shorts it. Draw the remaining circuitry. You'll see that the 0.25 A supply does make a contribution to Vth (it's still in parallel with a 20 Ohm resistor).

Yeah. My thevenin resistance should be 40 and not 35.

Ah yes. I see my mistake there for Vth1. I added the resistances even though thevenin voltage was only across one of the resistors and not the sum of them so I should use voltage division for it since voltage is divided in series. Forgot about that.

So is this correct for Vth3 -
http://puu.sh/lR1gV/9cd3848fff.jpg

That black oval, removing that completely?(and shorting the voltage) So the 0.25A would still be connected in parallel to 20ohms.
 
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  • #4
Right. When you suppress sources, currents are replaced by open circuits, voltages by short circuits.
 
  • #5
gneill said:
Right. When you suppress sources, currents are replaced by open circuits, voltages by short circuits.
Awesome. Thanks so much
 

FAQ: How Do You Calculate Thevenin Voltage Using Superposition?

1. What is a Thevenin Equivalent Circuit?

A Thevenin Equivalent Circuit is a simplified representation of a complex electrical circuit. It consists of a single voltage source and a single resistor, which can be used to model the behavior of a more complex circuit.

2. How is a Thevenin Equivalent Circuit calculated?

To calculate a Thevenin Equivalent Circuit, you need to find the Thevenin voltage and the Thevenin resistance. Thevenin voltage is the open-circuit voltage at the output terminals of the circuit, while Thevenin resistance is the resistance seen at the output terminals when all voltage sources are removed and replaced with short circuits.

3. What is the purpose of a Thevenin Equivalent Circuit?

Thevenin Equivalent Circuits are used to simplify complex circuits and make them easier to analyze. They can also be used to find the maximum power transfer from a circuit to a load.

4. Can a Thevenin Equivalent Circuit accurately model any circuit?

No, a Thevenin Equivalent Circuit can only be used to model linear circuits. It cannot accurately model circuits with non-linear elements such as diodes or transistors.

5. How does changing the load in a Thevenin Equivalent Circuit affect the output voltage?

The output voltage of a Thevenin Equivalent Circuit will remain the same regardless of the load connected to it. However, the current flowing through the load will change, and the power delivered to the load will be maximum when the load resistance is equal to the Thevenin resistance.

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