BeginnerTopic 28 of 106Electrical Engineering
Superposition theorem
In linear circuits the response is the sum of responses from each source acting alone.
In depth
In a linear circuit with several independent sources, the response equals the sum of responses to each source acting alone (others turned off: voltage sources shorted, current sources opened). Not valid for power, which is nonlinear.
Key points
- Only linear circuits
- Dependent sources stay active
- Handy with mixed AC and DC
ExampleA DC bias plus AC signal in an amplifier is analysed separately.
What is Superposition theorem?
In linear circuits the response is the sum of responses from each source acting alone.
Why is it important to understand superposition theorem?
Superposition breaks a complex linear circuit into simpler cases, which is useful for checking a result and for analysing multiple sources.
When can I not use superposition?
When the circuit is nonlinear, such as one containing diodes or power dissipation, because the responses do not add.
How do I turn off a source for superposition?
Set a voltage source to zero, which means a short circuit, and a current source to zero, which means an open circuit.
How is Superposition theorem used in practice?
Typical applications include finding the output of an amplifier with both a signal and a bias supply, checking the effect of a second supply on a sensor reading and analysing a circuit with a DC and an AC source together.
What should I learn before Superposition theorem?
Study "Mesh-current analysis" first (topic 27 of 106 in Electrical Engineering). It covers the groundwork this topic builds on.
What are the key points of Superposition theorem?
Only linear circuits. Dependent sources stay active. Handy with mixed AC and DC.
Can you give an example of Superposition theorem?
A DC bias plus AC signal in an amplifier is analysed separately.
What comes after Superposition theorem?
The next topic is "Thevenin equivalent", which builds directly on this one.
How difficult is Superposition theorem?
It is classed as Beginner in Electrical Engineering (topic 28 of 106). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.