Physical electronics devices and ics miscellaneous


Physical electronics devices and ics miscellaneous

Physical Electronics Devices and ICs

  1. A BJT having β = 100 is biased at a dc collector current of 1 mA. The values of gm, re and rπ at the bias point are given respectively by—









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    We know that

    ● gm =IC= 1 mA = 40 mA/V
    VT25 mV

    ● rπ =β=
    100
    = 2·5 kΩ
    gm40 mA/V mV

    ● re ==
    2·5 kΩ
    ≈ 25 Ω
    1 + β(1 + 100)

    Hence alternative (B) is the correct choice.

    Correct Option: B

    We know that

    ● gm =IC= 1 mA = 40 mA/V
    VT25 mV

    ● rπ =β=
    100
    = 2·5 kΩ
    gm40 mA/V mV

    ● re ==
    2·5 kΩ
    ≈ 25 Ω
    1 + β(1 + 100)

    Hence alternative (B) is the correct choice.


  1. A Darlington stage is shown in figure. If the transconductance of Q1 is gm 1 and Q2 is gm 2, then the overall transconductance, gm =
    Ic
    is given by—
    Vbe











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    The given figure (i.e., fig)

    gm =
    Ic
    = gm2
    Vbe

    Hence alternative (C) is the correct choice.


    Correct Option: D

    The given figure (i.e., fig)

    gm =
    Ic
    = gm2
    Vbe

    Hence alternative (C) is the correct choice.




  1. A Si transistor has a thermal ratings, Tmax = 150°C and θ = 0·7°C/W. The power which this transistor could dissipate if the case could be maintained at 50°C is—









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    Given, Tj(max) = 150°C, Q = 0·7°C/W
    Tambient = 50°C, P0 =?

    From relation, P0 =
    Tj (max) – Tambient
    Q

    or P0 =
    150°C – 50°C
    = 142·857 W
    0·7°C/W

    or P0 ≈ 143 W
    Hence alternative (A) is the correct choice.

    Correct Option: A

    Given, Tj(max) = 150°C, Q = 0·7°C/W
    Tambient = 50°C, P0 =?

    From relation, P0 =
    Tj (max) – Tambient
    Q

    or P0 =
    150°C – 50°C
    = 142·857 W
    0·7°C/W

    or P0 ≈ 143 W
    Hence alternative (A) is the correct choice.


  1. An emitter in a bipolar junction transistor is doped much more heavily than the base as it increases the—









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    An emitter in a bipolar junction transistor is doped much more heavily than the base as it increases the forward current gain.

    Correct Option: C

    An emitter in a bipolar junction transistor is doped much more heavily than the base as it increases the forward current gain.



  1. A common collector amplifier uses a transistor whose h-paramters are hic = 900 Ω, hfc = 25 and hrc = 1. If source and load resistances are 10 K and 500 Ω respectively, the voltage gain of the amplifier is—









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    Given, hic = 900 Ω, hfc = 25, hrc = 1, Rs = 10 kΩ = 10,000 Ω, RL = 500 Ω
    We know that voltage gain for common collector configuration is given by expression

    Av =
    V0
    =
    RL
    VsRs / (β + 1) + RL + Ye

    or Av =
    500
    =
    RL
    (neglecting re since re =
    VI
    =
    25 mV
    and β = hfc = 25)
    Vs10‚000 / (25 + 1) + 500IEIE

    or Av ≈ 0·53
    Hence alternative (A) is the correct choice.

    Correct Option: A

    Given, hic = 900 Ω, hfc = 25, hrc = 1, Rs = 10 kΩ = 10,000 Ω, RL = 500 Ω
    We know that voltage gain for common collector configuration is given by expression

    Av =
    V0
    =
    RL
    VsRs / (β + 1) + RL + Ye

    or Av =
    500
    =
    RL
    (neglecting re since re =
    VI
    =
    25 mV
    and β = hfc = 25)
    Vs10‚000 / (25 + 1) + 500IEIE

    or Av ≈ 0·53
    Hence alternative (A) is the correct choice.