Question

For the circuit below, assuming the diode is a pn junction diode with a turn-on voltage at 0.7V: find the output voltage Vₒ's expression in terms of Vᵢ when D₁ is off and D₂ is on.

a) Vₒ = Vᵢ
b) Vₒ = 0
c) Vₒ = -0.7V
d) Vₒ = Vᵢ - 0.7V

Answer 1

The correct option is Vo = Vi - 0.7V.

When diode D1 is off and diode D2 is on, with a turn-on voltage of 0.7V, the output voltage Vo becomes Vi minus 0.7V. Therefore, the correct expression for Vo is Vo = Vi - 0.7V.

Step-by-step explanation:

When determining the output voltage Vo for a circuit with two diodes, one must consider the state (on or off) of each diode. Given that diode D1 is off and diode D2 is on, and that D2 has a turn-on voltage of 0.7 V, we can establish the following:

If D1 is off, it behaves like an open circuit, meaning no current flows through it. Since D2 is on and it has a turn-on voltage of 0.7 V, it will drop a voltage of 0.7 V across it.

Therefore, the output voltage Vo is the input voltage Vi minus this turn-on voltage of the conducting diode D2. This gives us the expression: Vo = Vi - 0.7V. Hence, the correct answer is (d) Vo = Vi - 0.7V.