Superposition allows you to break down a difficult circuit into multiple (but
simpler) circuits. Here are the steps to analyze a circuit via superposition:
- Write down the basic superposition equation. The unknown you are looking
for is equal to the sum of the effects from each source. For an unknown current
or voltage X in a circuit with n sources,
For example, if you are looking for the value Vx, and there are 4 sources
in your circuit (1 V, 50 mA, 3 V, and 150 mA), then write:
- Draw a circuit for each subproblem (you should have as many circuits as
there are independent sources (current and voltage) in the original problem.
In each circuit, keep one of the sources from the original circuit and deactivate
the rest. If there are 4 sources, you should have 4 circuits, with one source
in each. To deactivate a source, replace voltage sources with shorts (a wire)
and current sources with opens.
- Solve for the unknown in each circuit. The solution should be fairly easy
since there is only one source. Watch for series and parallel combinations.
Be careful! Sometimes the deactivated sources leave you with some strange
circuits. For example, a resistor that is shorted out (connected at both ends
with the same wire) has no voltage across it. A resistor that is not connected
to anything else at one end (just hanging there) has no current through it.
- Add the answers from each subcircuit together (as shown in the equation
of step 1) to get the overall answer to the original circuit.
Back to Superposition Examples
© Calvin College, 2003
This page was written and is maintained by Steve VanderLeest.
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