How do you calculate the Thevenin voltage?

To calculate the Thevenin voltage, follow these steps:

Step 1: Identify the terminals of interest

Determine the two terminals across which you want to calculate the Thevenin voltage. These terminals are usually the ones where the load is connected or where you need to find the equivalent voltage.

Step 2: Disconnect all sources

Remove all independent voltage and current sources in the circuit. Independent sources are sources that are not dependent on other circuit variables, such as batteries and constant voltage/current sources. Dependent sources, like voltage-controlled voltage sources (VCVS) or current-controlled current sources (CCCS), can be kept in the circuit.

Step 3: Calculate the open-circuit voltage

After disconnecting all independent sources, treat the terminals of interest as open circuits. This means you leave them unconnected (infinite resistance). Then, use circuit analysis techniques (such as nodal analysis or mesh analysis) to find the voltage across the open terminals. This voltage is the Thevenin voltage (V_th).

Step 4: Reconnect the sources

After calculating the open-circuit voltage, you can reconnect the independent sources you removed in Step 2.

The Thevenin equivalent circuit consists of the Thevenin voltage (V_th) in series with the Thevenin resistance (R_th). The Thevenin resistance (R_th) can be found using the following method:

Step 5: Find the Thevenin resistance (R_th)

To calculate R_th, set all the independent sources back to their original values and then remove any load or resistors connected across the terminals of interest. Then, apply a voltage source (let's say V_test) across the two terminals and calculate the resulting current (I_test) flowing through the terminals. Finally, divide the voltage source value (V_test) by the calculated current (I_test) to get the Thevenin resistance:

R_th = V_test / I_test

Step 6: Create the Thevenin equivalent circuit

Now that you have found the Thevenin voltage (V_th) and the Thevenin resistance (R_th), you can represent the original circuit as a Thevenin equivalent circuit, which consists of a voltage source V_th in series with a resistor R_th.

Keep in mind that Thevenin's theorem is only applicable to linear circuits, which means circuits with linear elements such as resistors, capacitors, and inductors. Non-linear elements like diodes and transistors require different methods for simplification.