Question Details

Consider ideal diodes D 1 and D 2 with cut-in voltage V γ = 0 V and v i ( t ) = 6 sin ( ω t ) in Volt. The maximum voltage (Volt) of the output v o ( t ) is ____ (rounded off to two decimal places).



Show Answer

Correct Answer :

4.00

Solution :

The correct answer is 4.00.

Analysis of the Circuit Diagram:
Based on the provided circuit diagram, we have:
- An input AC source:
v i ( t ) = 6 sin ( ω t )
which has a peak positive voltage of 6 V and a peak negative voltage of -6 V.
- A series input resistor of value:
R 1 = 10  k Ω
- A first branch connected in parallel to the output containing an ideal diode D1 in series with a resistor:
R 2 = 10  k Ω
and a DC battery of 2 V (with the positive terminal connected to the cathode of D1).
- A second branch in parallel containing an ideal diode D2 in series with a 4 V DC battery (with the positive terminal connected to the cathode of D2).

Step-by-Step State Analysis:

Case 1: When the output voltage is less than 2 V
If the output voltage
v o ( t ) < 2  V
both diodes D1 and D2 are reverse-biased (OFF) because the potential at their anodes (the output node) is less than the potentials at their respective cathodes (2 V and 4 V).
Under this condition, no current flows through the parallel branches. Therefore, the output voltage simply tracks the input voltage:
v o ( t ) = v i ( t )
This state continues as the input voltage rises up to 2 V.

Case 2: When the input voltage exceeds 2 V
When the input voltage
v i ( t ) > 2  V
the output node voltage attempts to go above 2 V, which forward-biases the ideal diode D1, turning it ON (acting as a short circuit). Meanwhile, as long as the output voltage remains below 4 V, diode D2 remains OFF.
With D1 ON and D2 OFF, the circuit acts as a voltage divider between the input voltage source and the 2 V battery. The output voltage can be calculated as:
v o ( t ) = 2 + ( v i ( t ) - 2 ) · R 2 R 1 + R 2
Substituting the resistor values
R 1 = 10  k Ω
and
R 2 = 10  k Ω
gives:
v o ( t ) = 2 + ( v i ( t ) - 2 ) · 10 10 + 10 = 2 + v i ( t ) - 2 2 = 1 + v i ( t ) 2

Determining the Maximum Output Voltage:
The maximum value of the input signal is
v i , max = 6  V
Substituting this peak value into our voltage divider equation:
v o , max = 1 + 6 2 = 1 + 3 = 4  V
Since the maximum output voltage is exactly 4 V, diode D2 (which has its cathode at 4 V) is on the verge of conduction but does not turn on to clamp the voltage any further. Thus, the maximum output voltage is 4.00 V.

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