Tag: the bipolar junction transistor

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Questions Related to the bipolar junction transistor

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

The input resistance of a silicon transistor is $1 k\Omega $.If base current is changed by $100 \mu A$ it causes the change in collector current by $2 mA$. This transistor is used as a CE amplifier with a load resistance of $5 k\Omega$ What is the ac voltage gain of amplifier?

  1. $10$
  2. 44100$
  3. $500$
  4. $200$
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

In a silicon transistor the base current is changed by $25\mu A$. This results in a change of $0.04\ V$ in the base to emitter voltage and a change of $4\ mA$ in the collector current. The trans-conductance of the transistor (in $\Omega^{-1}$) is

  1. $0.1$
  2. $1$
  3. $1000$
  4. $0.01$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Trans-conductance (g_m) is defined as the ratio of change in collector current (Delta I_C) to the change in base-emitter voltage (Delta V_BE). Thus, g_m = 4 mA / 0.04 V = 4 * 10^-3 A / 0.04 V = 0.1 Omega^-1.

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

For a common emitter configuration, If $\alpha $and $\beta $ have thier usual meanings. The incorrect relationship between $\alpha $and $\beta $ is:

  1. $\alpha =\dfrac { \beta }{ 1-\beta } $
  2. $\alpha =\dfrac { \beta }{ 1+\beta } $
  3. $\alpha =\dfrac { { \beta }^{ 2 } }{ 1+{ \beta }^{ 2 } } $
  4. $\dfrac { 1 }{ \alpha } =\dfrac { 1 }{ \beta } +1$
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

For a common emitter connection the values of constant collector current and base current are $5\ mA$ and $50$$\mu A$ respectively. The current gain will be

  1. $10$
  2. $20$
  3. $40$
  4. $100$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Given that:
$I _c = 5\ mA$
$I _b = 50\ \mu A = 5 \times 10^{-2}\ mA$
The current gain is
$\beta = \dfrac{I _c}{I _b}$
$\beta = \dfrac{5}{5 \times 10^{-2}} = 100$

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

In a silicon transistor, the base  current is changed by 20 change of 0.02V in base to emitter voltage and a change of 2mA in the collector current.
(a) Find the input  resistance ${ \beta  } _{ ac }$ 
(b) If this transistor is used as an-amplifier. Find the voltage gain of the-amplifier with the load resistance 5k amplifier.

  1. a)100b)-500

  2. a)1000b)-500

  3. a)2000b)-5000

  4. a)10b)-5
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

(a) $n=\frac { { \triangle v } _{ BE } }{ { \triangle | } _{ B } } =\frac { 0.02 }{ 20\times { 10 }^{ -6 } } =1k\Omega $
${ \beta  } _{ ac }=\frac { { \triangle | } _{ c } }{ { \triangle | } _{ B } } =\frac { 2\times { 10 }^{ -3 } }{ 20\times { 10 }^{ -6 } } =100$
(b) Voltage gain,${ A } _{ v }=-{ g } _{ m }{ R } _{ L }=-\left( 0.1 \right) \left( 5\times { 10 }^{ 3 } \right) =-500$. $\left( since\quad { g } _{ m }={ \beta  } _{ ac }/n \right) $

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

The ac current gain of a transistor is $120$. What is the change in the collector current in the transistor whose base current changes by $100\ \mu A$?

  1. $6\ mA$
  2. $12\ mA$
  3. $3\ mA$
  4. $24\ mA$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given that,

Current gain$\beta =120\,A$

Base current $\Delta {{I} _{b}}=100\,\mu A$


We know that,

  $ {{\beta } _{ac}}=\dfrac{\Delta {{I} _{C}}}{\Delta {{I} _{B}}} $

 $ \Delta {{I} _{C}}=120\times 100\times {{10}^{-6}} $

 $ \Delta {{I} _{C}}=12\times {{10}^{-3}}\,A $

 $ \Delta {{I} _{C}}=12\,mA $

Hence, the collector current in the transistor is $12\ mA$

 

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

For a CE transistor amplifier, the audio signal voltage across the collector resistance of $2k\Omega $ is 2 V.Suppose the current amplification factor of the transistor is 100. The value of ${R _B}$ in series with ${V _{BB}}$ the supply of 2V, if the DC base current has to be 10 times the signal current is 

  1. $4k\Omega $
  2. $14k\Omega $
  3. $28k\Omega $
  4. $54k\Omega $
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

When a collector to emitter voltage is constant in a transistor, the collector current changes by $8.2mA$ when the emitter current changes by $8.3mA$. The value of forward current ratio $B$ is

  1. $82$
  2. $83$
  3. $8.2$
  4. $8.3$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The current gain beta is defined as delta_Ic / delta_Ib. Since delta_Ie = delta_Ic + delta_Ib, delta_Ib = delta_Ie - delta_Ic = 8.3mA - 8.2mA = 0.1mA. Thus, beta = 8.2mA / 0.1mA = 82.

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

In the CB mode of a transistor when the collector voltage is changed by $0.5V$. The collector current changes by $0.05mA$. The output resistance will be

  1. $10k\Omega$
  2. $20k\Omega$
  3. $5k\Omega$
  4. $2.5k\Omega$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Output resistance r_o = delta_Vcb / delta_Ic = 0.5V / 0.05mA = 0.5 / 0.00005 = 10,000 Ohms = 10k Ohm.