250+ TOP MCQs on Characteristic Equation of Diode-1 and Answers

Analog Circuits Multiple Choice Questions on “Characteristic Equation of Diode 1”.

1. Calculate the forward bias current of a Si diode when forward bias voltage of 0.4V is applied, the reverse saturation current is 1.17×10^-9A and the thermal voltage is 25.2mV.
A. 9.156mA
B. 8.23mA
C. 1.256mA
D. 5.689mA

Answer: A
Clarification: Equation for diode current
I=I₀×(e^(V/ηV_T)-1) where I₀ = reverse saturation current
η = ideality factor
V_T = thermal voltage
V = applied voltage
Since in this question ideality factor is not mentioned it can be taken as one.
I₀ = 1.17 x 10^-9A, V_T = 0.0252V, η = 1, V = 0.4V
Therefore, I = 1.17×10^-9xe^0.4/0.025 -1 = 9.156mA.

2. Calculate the thermal voltage when the temperature is 25°C.
A. 0V
B. 0V
C. 0.026V
D. 0.25V

Answer: B
Clarification: Thermal voltage V_T is given by k T/q
Where k is the boltzman constant and q is the charge of electron. This can be reduced to
V_T = T_K/11600
Therefore, V_T = 298.15/11600 = 0.0257V.

3. Calculate the reverse saturation current of a diode if the current at 0.2V forward bias is 0.1mA at a temperature of 25°C and the ideality factor is 1.5.
A. 5.5x 10^-9 A
B. 5.5x 10^-8 A
C. 5.5x 10^-7 A
D. 5.6x 10^-10 A

4. Find the applied voltage on a forward biased diode if the current is 1mA and reverse saturation current is 10^-10. Temperature is 25°C and takes ideality factor as 1.5.
A. 0.658V
B. 0.726V
C. 0.526V
D. 0.618V

5. Find the temperature at which a diode current is 2mA for a diode which has reverse saturation current of 10^-9 A. The ideality factor is 1.4 and the applied voltage is 0.6V forward bias.
A. 69.65°C
B. 52.26°C
C. 25.23°C
D. 70.23°C

6. Consider a silicon diode with η=1.2. Find the change in voltage if the current changes from 0.1mA to 10mA.
A. 0.154V
B. 0.143V
C. 0.123V
D. 0.165V

7. If the temperature increases 10°C, the ratio of final reverse saturation current to initial reverse saturation current is _______
A. 1
B. 2
C. 1.5
D. 3

Answer: B
Clarification: The equation relating final reverse saturation current (I_o2 ) to initial reverse saturation current (I_o1 ) is given by
I_o2 = 2^(∆T/10)I_o1 Where ∆T is temperature change
Ratio will be 2^(∆T/10) = 2¹ = 2.

8. The reverse saturation current of a diode at 25°C is 1.5 x 10^-9A. What will be the reverse current at temperature 30°C?
A. 3 x 10^-9A
B. 2 x 10^-9A
C. 2.12 x 10^-9A
D. 1.5 x 10^-9A

Answer: C
Clarification: The equation relating final reverse saturation current (Io2) to initial reverse saturation current (I_o1) is given by
I_o2 = 2^(∆T/10)I_o1 Where ∆T is temperature change
Here ∆T = 5, Therefore, I_o2 = 25/10 Io1 = 1.414 x 1.5 x 10^-9A = 2.121 x 10^-9A.

9. How much times reverse saturation current will increase if temperature increases 15^oC?
A. 2.52
B. 4.62
C. 4.12
D. 2.82

Answer: D
Clarification: The equation relating final reverse saturation current (I_o2) to initial reverse saturation current (I_o1) is given by
I_o2 = 2^(∆T/10)I_o1
Where ∆T is temperature change
Ratio is 2^15/10 = 2.82.

10. If V1 is 5V and resistance R₁ is 5KΩ and the cut-in voltage of the diode is 0.7V, what will be the voltage V_out across the diode? Take reverse saturation current as 10^-8A and operating temperature as 25°C.
A. 0V
B. -4.5V
C. -5V
D. -3.2V

Answer: c
Clarification: Since diode is in reverse bias mode voltage across diode will be almost the same as the applied voltage. Since the current in the circuit is in micro amperes voltage drop at R₁ is negligible.