Thevenin and Norton Equivalent Calculator: Equivalent Source, Load Current and Maximum Power Transfer
Replace a circuit with a simple equivalent source.
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Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.
How this calculator works
Enter the source voltage and the two resistors.
Enter the load resistance.
The calculator gives the equivalent circuit and the load values.
Formulas used
- V_{th} = V_s\frac{R_2}{R_1 + R_2}
- R_{th} = \frac{R_1R_2}{R_1 + R_2}
- I_N = \frac{V_{th}}{R_{th}}
- P_{max} = \frac{V_{th}^2}{4R_{th}}
Worked example
With the default numbers in the calculator above:
- Thevenin voltage (open-circuit voltage at the load terminals): 8 V
- Thevenin resistance (R1 and R2 in parallel, with the source shorted): 66.6667 ohms
- Norton current (short-circuit current): 0.12 A
- Load current: 0.0369231 A
- Load voltage: 5.53846 V
- Power in the load: 0.204497 W
- Maximum power the circuit can give to a load (when the load equals Rth): 0.24 W
- Efficiency of the source at your load: 26.37 %
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
What is Thevenin's theorem?
Any linear circuit seen from two terminals can be replaced by one voltage source in series with one resistor.
What is Norton's theorem?
The same circuit can be replaced by a current source in parallel with a resistor. The two equivalents are linked by the source transformation.
When does a load get the most power?
When its resistance equals the Thevenin resistance of the circuit feeding it.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Any circuits text (Thevenin and Norton equivalents, maximum power transfer).
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