Circuit Theory #27 | Thevenin with a Test Voltage Source - Dependent Source Example

Instructor: Dr. Süleyman Burak ÇELİK

Twenty-seventh lesson in the Circuit Theory series. This lesson continues Thevenin equivalents for circuits with dependent sources. First, we return to the previous circuit and find `Rth` using a `1 V` test voltage source. Then we solve a second example with a dependent voltage source `2Vx`. Worked examples: - Example 1: keep the dependent source active and apply a `1 V` test source - Use `i_b = (0 - 1)/100 = -0.01 A` - Apply KCL: `10i_b + i_x = 1/10` - Get `i_x = 0.2 A`, so `Rth = 1 / 0.2 = 5 ohm` - Example 2: remove `R3` and solve `(Vx - 2Vx)/15 + Vx/5 - 2 = 0` - Get `Vth = 15 V` - Short `a-b`: `Vx = 0`, so `2Vx = 0 V`, and `Is = 2 A` - Compute `Rth = Vth / Is = 15 / 2 = 7.5 ohm` Main ideas: - Do not turn off dependent sources by themselves - For test-source methods, turn off only independent sources - Keep the controlling variable in the equations - `Rth` can be found from a test source or from `Vth / Is`