P-N Junction Diode: Assignment | Solid State Physics, Devices & Electronics PDF Download

Q.1. An abrupt p-n junction diode is formed with two sides of resistivities 2 Ωcm in the p -side and 1 Ωcm on the n-side at temperature 300 K . Find the height of the potential energy barrier for Ge. (μ_n = 3800 cm²/Vs, μ_P = 1800 cm²/Vs, and n_i = 2.5x10¹³ cm^-3) 

Q.2. Draw output waveforms for the circuit given below.

Let i_d = 0 and v_d = -0.7V.
For transition voltage, apply KVL in input section
-v_i + 1 - 0.7 + 0 = 0 ⇒ v_i = 0.3V = V_T
Thus if v_i < 0.3 V, diode is ON and if v_i > 0.3V, diode is OFF.
If v_i = 0
0 + 1 - 0.7 + v₀ = 0 ⇒ v₀ = -0.3V
If v_i = -5V
+ 5 + 1 - 0.7 + v₀ = 0 ⇒ v₀ = -5.3V

Q.3. A diode at room temperature (kT = 0.025eV )with a current of 1μA has a forward bias voltage V_F = 0.4V. Find the diode current when V_F = 0.5.

Q.4. A sine wave of 5V amplitude is applied at the input of the circuit shown in the figure. Draw output waveforms for the circuit given below. (Assume diode is ideal)

If V_in > -3V, diode is OFF and V₀ = V_in.
If V_in < -3V, diode is ON and V₀ = -3V

Q.5. (a) Consider a Si diode with η = 1.5 . Find the change in voltage if the current changes from 0.1 mA to 10 mA at 300 K.
(b) Consider a Si diode with η = 1 has v = 0.7V at i = 1 mA . Find the voltage drop at i = 0.1 mA and i = 10 mA at 300 K.

Q.6. Draw output waveforms for the circuit given below.

Let i_d = 0 and v_d = 0.7V.
For transition voltage, apply KVL in input section -v_i + 0 + 0.7 - 2 = 0 ⇒ v_i = -1.3V = V_T 
Thus if v_i > -1.3V, diode is ON then v₀ = -1.3V and if v_i < -1.3V, diode is OFF.
v₀ = v_i

Q.7. The circuit shown in figure has two oppositely connected ideal diodes in parallel. Assume diodes are ideal.

(a) Find current through diode D₁.
(b) Find current through diode D₂.

Diode D₁ is OFF and diode D₂ is ON.
Thus current through diode D₁ is 0 A and
Thus current through diode D₂ is

Q.8. Draw output waveforms for the circuit given below take |V_m| >|V|.
(Assume diodes to be ideal)

Let i_d = 0 and v_d = 0V.
For transition voltage, apply KVL in input section -v_i + 0 + 0 - V = 0 ⇒ v_i = -V = V_T 
Thus if v_i > -V, diode is OFF then v₀ =v_i
and if v_i < -V, diode is ON then v₀ = -V.

Q.9. For the circuit shown in figure below  
(a) Find current through diode.
(b) Find output voltage V_o.

(a) Under given biasing condition diode is ON. Let current through 5 kΩ resistance 

is I.
Apply KVL in the input section,
-15 + I x 5k + 0.7 + I x 2k - 5 = 0 ⇒ I = (19.3/7) mA = 2.76mA
(b) V₀ = 2.76 x 2 - 5 = 0.51V

Q.10. Draw output waveforms for the circuit given below (RC >> T/2).

Q.11. In the following circuit, the voltage drop across the diode in forward bias condition ism 0.7 V. Find the current I and I_D.

Apply KVL in two loops
-25 + I x 10 + (I-I_D) x 5 = 0 ⇒ 15I - 5I_D = 25 ...(i)
0.7 + I_D x 3 -(I-I_D) x 5 = 0 ⇒ 5I - 8I_D = 0.7 ...(ii) 

From (i) and (ii), I = 2.06 mA and I_D = 1.21mA.

Q.12. Draw output waveforms for the circuit given below (RC >> T/2). Take |V_m| > |V₁|.

Q.13. The I - V characteristics of the diode in the circuit below is given by

where V is measured in volts and I is measured in amperes. 

Find the current I in the circuit.

Applying K.V.L.
-5 + 1000 x I + V = 0 ⇒ -5 + 1000 x (V - 0.7)/500 +V = 0
⇒ -5 + 2 (V - 0.7) + V = 0 ⇒ 3V = 6.4 ⇒ V = 2.13 Volts
Thus I = (V - 0.7)/500 = (2.13 - 0.7)/500 = 1.43/500 = 2.86 mA

Q.14. Draw output waveforms for the circuit given below (RC >> T/2). Take |V_m| > |V₁|.

Q.15. An a.c. supply of 220 V, 50 Hz is applied to a half wave rectifier circuit through a transformer of turn ratio 5 :1 . The forward resistance of the diode is 100 Ω and the load 

resistance is 5 kΩ.
(a) Find output d.c. voltage.
(b) Find r.ms. value of the output voltage.
(c) What should be PIV rating of the diode?

Q.16. Consider the circuit shown in figure below.
(a) Find the maximum Zener current I_Z,max, when R_L = 2kΩ.
(b) Find the minimum Zener current I_Z,min, when R_L = 4kΩ.
(c) Find I_L and I_Z with V_in = 22V and R_L = 2kΩ.
(d) Find the power dissipated across the Zener when R_L = 5kΩ and V_in = 20V.

 ⇒ P_Z = V_ZI_Z = 10 x 8 = 80mW

Q.17 For the rectifier circuit shown in the figure, the sinusoidal voltage ( V₁ or V₂) at the output of the transformer has a maximum value of 10 V. The load resistance R_L is 2 kΩ.
(a) Find the average current I_av through the resistor R_L.
(b) Find the rms current I_rms through the resistor R_L.
(c) What should be PIV rating of the diode?

(a)
(b)
(c) PIV Rating ≥ 2V_m = 20V

Q.18. A variable power supply (5V - 20V) is connected to a Zener diode specified by a breakdown voltage of 10 V (see figure).

(a) The ratio of the maximum power to the minimum power dissipated across the load 

resistor.

(b) Find the minimum power dissipated across the zener diode.
(c) Find the maximum power dissipated across the zener diode.

(a) When V = 5V ⇒ open circuit voltage V_i =  

When V = 20V ⇒ open circuit voltage V_i =

(b) When V = 5V ⇒ open circuit voltage  

⇒ P_z,min = V_ZI_Z = 0.
(c) When V = 20V ⇒ open circuit voltage

⇒ P_z,max = V_ZI_Z = 10 x 10 = 100mW

Q.19. An a.c. voltage of 220 V , 50 Hz is applied to the primary of a 20 :1 step down transformer. The secondary of the transformer is bridge type and connected to a full wave rectifier with a load resistance 500Ω. Forward resistance of the diode is 10Ω.
(a) Find output d.c. voltage.
(b) Find r.ms. value of the output voltage.
(c) What should be PIV rating of the diode?

Q.20. The figure below shows the current voltage characteristics of a diode over a range of voltage and current where it is safe to operate the diode. 

(a) Find the approximate diode current, in mA .
(b) Find the approximate current, in mA , through the 600 Ω resistance.
(c) Find the approximate current, in mA , through the 200 Ω resistance.

Characteristics shows that the diode used is a zener diode.
(a) Open circuit voltage
 
(b) Open circuit voltage

(c) Open circuit voltage
⇒ I_R = 5/0.2 = 25mA