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NEET-XII-Physics

14: Semiconductor Electronics: Materials Devices and Simple Circuits

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  • #14
    In a p-n junction diode, the current I can be expressed as



    where I0 is called the reverse saturation current, V is the voltage across the diode and is positive for forward bias and negative for reverse bias, and I is the current through the diode, kBis the Boltzmann constant (8.6×10-5 eV/K) and T is the absolute temperature. If for a given diode I0 = 5 × 10-12 A and T = 300 K, then
    (a) What will be the forward current at a forward voltage of 0.6 V?
    (b) What will be the increase in the current if the voltage across the diode is increased to 0.7 V?
    (c) What is the dynamic resistance?
    (d) What will be the current if reverse bias voltage changes from 1 V to 2 V?
    (a) What will be the forward current at a forward voltage of 0.6 V?
    (b) What will be the increase in the current if the voltage across the diode is increased to 0.7 V?
    (c) What is the dynamic resistance?
    (d) What will be the current if reverse bias voltage changes from 1 V to 2 V?
    Ans : In a p-n junction diode, the expression for current is given as:



    Where,

    I0 = Reverse saturation current = 5 × 10-12 A

    T = Absolute temperature = 300 K

    kB = Boltzmann constant = 8.6 × 10-5 eV/K = 1.376 × 10-23 J K-1

    V = Voltage across the diode
    (a) Forward voltage, V = 0.6 V

    ∴Current, I



    Therefore, the forward current is about 0.0256 A.
    (b) For forward voltage, V’ = 0.7 V, we can write:





    Hence, the increase in current, ΔI = I‘ - I

    = 1.257 - 0.0256 = 1.23 A
    (c) Dynamic resistance


    (d) If the reverse bias voltage changes from 1 V to 2 V, then the current (I) will almost remain equal to I0 in both cases. Therefore, the dynamic resistance in the reverse bias will be infinite.
    (a) Forward voltage, V = 0.6 V

    ∴Current, I



    Therefore, the forward current is about 0.0256 A.
    (b) For forward voltage, V’ = 0.7 V, we can write:





    Hence, the increase in current, ΔI = I‘ - I

    = 1.257 - 0.0256 = 1.23 A
    (c) Dynamic resistance


    (d) If the reverse bias voltage changes from 1 V to 2 V, then the current (I) will almost remain equal to I0 in both cases. Therefore, the dynamic resistance in the reverse bias will be infinite.
  • #14-a
    What will be the forward current at a forward voltage of 0.6 V?
    Ans : Forward voltage, V = 0.6 V

    ∴Current, I



    Therefore, the forward current is about 0.0256 A.
  • #14-b
    What will be the increase in the current if the voltage across the diode is increased to 0.7 V?
    Ans : For forward voltage, V’ = 0.7 V, we can write:





    Hence, the increase in current, ΔI = I‘ - I

    = 1.257 - 0.0256 = 1.23 A
  • #14-c
    What is the dynamic resistance?
    Ans : Dynamic resistance


  • #14-d
    What will be the current if reverse bias voltage changes from 1 V to 2 V?
    Ans : If the reverse bias voltage changes from 1 V to 2 V, then the current (I) will almost remain equal to I0 in both cases. Therefore, the dynamic resistance in the reverse bias will be infinite.