Thevenin Calculator

Thevenin Equivalent Calculator

Circuit Topology: Voltage Source (Vs) in series with R1, connected to R2 in parallel.
Terminals A and B are across Resistor R2.

Understanding Thevenin's Theorem in Circuit Analysis

Thevenin's Theorem is a fundamental principle in electrical engineering that simplifies the analysis of complex linear circuits. It states that any linear electrical network containing only voltage sources, current sources, and resistances can be replaced at terminals A-B by an equivalent combination of a single voltage source (V_th) in series with a single resistor (R_th).

Why Use a Thevenin Calculator?

Analyzing circuits with varying loads can be tedious if you have to recalculate the entire circuit every time the load resistor changes. By converting the complex part of the circuit into its Thevenin equivalent, calculating the current and voltage for any specific load becomes a simple Ohm's Law calculation.

Key Concept: The Thevenin Voltage (V_th) is the open-circuit voltage at the terminals, while the Thevenin Resistance (R_th) is the resistance measured at the terminals with all independent sources turned off (voltage sources shorted, current sources opened).

Formulas Used in This Calculator

This calculator assumes a standard voltage divider configuration where a source V_s is in series with R₁, and the output terminals are across R₂. The formulas are derived as follows:

1. Calculating Thevenin Voltage (V_th)

The Thevenin voltage is found by calculating the voltage drop across R₂ using the voltage divider rule:

V_th = V_s × [ R₂ / (R₁ + R₂) ]

2. Calculating Thevenin Resistance (R_th)

To find the Thevenin resistance, we short-circuit the voltage source V_s. This places R₁ and R₂ in parallel relative to the output terminals:

R_th = (R₁ × R₂) / (R₁ + R₂)

3. Calculating Load Parameters (with R_L)

Once the equivalent circuit is established, if you connect a load resistor (R_L), the current flowing through it (I_L) is calculated as:

I_L = V_th / (R_th + R_L)

Example Calculation

Let's say you have a circuit with the following parameters:

• Source Voltage (V_s): 12 Volts
• Resistor 1 (R₁): 1000 Ohms (1 kΩ)
• Resistor 2 (R₂): 2000 Ohms (2 kΩ)

Step 1: Find V_th
V_th = 12 × (2000 / (1000 + 2000)) = 12 × (2/3) = 8 Volts

Step 2: Find R_th
R_th = (1000 × 2000) / (1000 + 2000) = 2,000,000 / 3000 = 666.67 Ohms

Now, the entire complex circuit acts exactly like an 8V battery with a 666.67Ω internal resistance.