Circuit Theory #29 | Thevenin with Dependent Sources Only - Test Source Method

Instructor: Dr. Süleyman Burak ÇELİK

Twenty-ninth lesson in the Circuit Theory series. This lesson handles two Thevenin examples where the circuit contains dependent sources only. Because there is no independent source, we do not start by finding a separate open-circuit voltage. Instead, we measure the equivalent resistance at terminals `a-b` using a `1 A` test current source. Worked steps: - Explain why a dependent-source-only network is treated as a resistance measurement - Keep the dependent source active - Apply a `1 A` test source from `b` to `a` - Example 1: use `V1 = Vx - Vy` and `Vx = V1 + Vy` - Write KCL at the middle node and at terminal `a` - Get `V1 = -6 V`, `Vy = 3 V`, so `Rth = 3 ohm` - Example 2: use `Vx = Vab` - Write `Vx/2 + 2Vab - 1 = 0` - Get `Vx = 0.4 V`, so `Rth = 0.4 ohm` Main ideas: - Dependent sources are not turned off by themselves - A test source measures the resistance seen at the output terminals - With `Itest = 1 A`, the measured port voltage directly equals the resistance in ohms