Question 1 |

The Zener diode in circuit has a breakdown voltage of 5 \mathrm{~V}. The current gain \beta of the transistor in the active region in 99. Ignore baseemitter voltage drop \mathrm{V}_{\mathrm{BE}}. The current through the 20 \Omega resistance in milliamperes is ____ (Round off to 2 decimal places).

287.36 | |

145.36 | |

250 | |

547.36 |

Question 1 Explanation:

Redraw the circuit :

We know,

\begin{aligned} \mathrm{I}_{\mathrm{E}} & =(1+\beta) \mathrm{I}_{\mathrm{B}} \\ & =100 \mathrm{I}_{\mathrm{B}} \\ \Rightarrow \quad \mathrm{I}_{\mathrm{B}} & =\frac{\mathrm{I}_{\mathrm{E}}}{100} \end{aligned}

Apply KVL in loop,

\begin{aligned} & 25-\frac{\mathrm{I}_{E}}{100} \times 7000-I_{E} \times 10-I_{E} \times 20=0 \\ & \Rightarrow \quad \mathrm{I}_{\mathrm{E}}=0.25 \mathrm{~A} \text { or } 250 \mathrm{~mA} \end{aligned}

We know,

\begin{aligned} \mathrm{I}_{\mathrm{E}} & =(1+\beta) \mathrm{I}_{\mathrm{B}} \\ & =100 \mathrm{I}_{\mathrm{B}} \\ \Rightarrow \quad \mathrm{I}_{\mathrm{B}} & =\frac{\mathrm{I}_{\mathrm{E}}}{100} \end{aligned}

Apply KVL in loop,

\begin{aligned} & 25-\frac{\mathrm{I}_{E}}{100} \times 7000-I_{E} \times 10-I_{E} \times 20=0 \\ & \Rightarrow \quad \mathrm{I}_{\mathrm{E}}=0.25 \mathrm{~A} \text { or } 250 \mathrm{~mA} \end{aligned}

Question 2 |

All the elements in the circuit shown in the following figure are ideal. Which of the following statements is/are true?

When switch S is O N, both D_{1} and D_{2} conducts and D_{3} is reverse biased | |

When switch \mathrm{S} is ON, \mathrm{D}_{1} conducts and both D_{2} and D_{3} are reverse biased | |

When switch S is OF F, D_{1} is reverse biased and both D_{2} and D_{3} conduct | |

When switch S is OFF, D_{1} conducts, D_{2} is reverse biased and D_{3} conducts |

Question 2 Explanation:

Case (i): Switch \mathrm{S} is ON

Assume \mathrm{D}_{3} \rightarrow OFF, D_{2} \rightarrow OFF and \mathrm{D}_{1} \rightarrow \mathrm{ON}

Redraw the circuit :

\therefore Our assumption is correct.

Case (ii) : Switch \mathrm{S} is OFF.

Then, \mathrm{D}_{3} \rightarrow \mathrm{ON}, \mathrm{D}_{2} \rightarrow \mathrm{ON} and \mathrm{D}_{1} \rightarrow \mathrm{OFF}

Redraw the circuit :

\therefore Circuit satisfy this condition also.

Hence, option (B) and (C) will be correct.

Assume \mathrm{D}_{3} \rightarrow OFF, D_{2} \rightarrow OFF and \mathrm{D}_{1} \rightarrow \mathrm{ON}

Redraw the circuit :

\therefore Our assumption is correct.

Case (ii) : Switch \mathrm{S} is OFF.

Then, \mathrm{D}_{3} \rightarrow \mathrm{ON}, \mathrm{D}_{2} \rightarrow \mathrm{ON} and \mathrm{D}_{1} \rightarrow \mathrm{OFF}

Redraw the circuit :

\therefore Circuit satisfy this condition also.

Hence, option (B) and (C) will be correct.

Question 3 |

Consider the OP AMP based circuit shown in the figure. Ignore the conduction drops of diodes D_{1} and D_{2}. All the components are ideal and the breakdown voltage of the Zener is 5 \mathrm{~V}. Which of the following statements is true?

The maximum and minimum values of the output voltage \mathrm{V}_{0} are +15 \mathrm{~V} and -10 \mathrm{~V}, respectively. | |

The maximum and minimum values of the output voltage \mathrm{V}_{0} are +5 \mathrm{~V} and -15 \mathrm{~V}, respectively. | |

The maximum and minimum values of the output voltage \mathrm{V}_{0} are +10 \mathrm{~V} and -5 \mathrm{~V}, respectively. | |

The maximum and minimum values of the output voltage \mathrm{V}_{0} are +5 \mathrm{~V} and -10V, respectively |

Question 3 Explanation:

During positive hall cycle:

\therefore \mathrm{D}_{1} \rightarrow \mathrm{ON} and \mathrm{D}_{2} \rightarrow \mathrm{OFF}

Redraw the circuit :

\therefore V_0=-V_i

\quad (V_0)_{min}=-10V

During negative half cycle :

\mathrm{V}^{+} \gt \mathrm{V}^{-}

Zener diode \rightarrow ON, \mathrm{D}_{1} \rightarrow OFF and \mathrm{D}_{2} \rightarrow \mathrm{ON}

Redraw the circuit:

\therefore \quad (V_0)_{max}=5V

\therefore \mathrm{D}_{1} \rightarrow \mathrm{ON} and \mathrm{D}_{2} \rightarrow \mathrm{OFF}

Redraw the circuit :

\therefore V_0=-V_i

\quad (V_0)_{min}=-10V

During negative half cycle :

\mathrm{V}^{+} \gt \mathrm{V}^{-}

Zener diode \rightarrow ON, \mathrm{D}_{1} \rightarrow OFF and \mathrm{D}_{2} \rightarrow \mathrm{ON}

Redraw the circuit:

\therefore \quad (V_0)_{max}=5V

Question 4 |

The current gain (I_{out}/I_{in}) in the circuit with an ideal current amplifier given below
is

\frac{C_f}{C_c} | |

\frac{-C_f}{C_c} | |

\frac{C_c}{C_f} | |

\frac{-C_c}{C_f} |

Question 4 Explanation:

Redraw the circuit:

From circuit,

\begin{aligned} V_o&=V_c \\ &=\frac{1}{C_f}\int I_{in}dt \\ I_{out}&=C_c\frac{dV_o}{dt} \\ &= C_c\frac{d}{dt}\left ( \frac{1}{C_f} \int I_{in}dt\right )\\ &=\frac{C_c}{C_f}I_{in}\\ \Rightarrow \frac{I_{out}}{I_{in}}&=\frac{C_c}{C_f} \end{aligned}

From circuit,

\begin{aligned} V_o&=V_c \\ &=\frac{1}{C_f}\int I_{in}dt \\ I_{out}&=C_c\frac{dV_o}{dt} \\ &= C_c\frac{d}{dt}\left ( \frac{1}{C_f} \int I_{in}dt\right )\\ &=\frac{C_c}{C_f}I_{in}\\ \Rightarrow \frac{I_{out}}{I_{in}}&=\frac{C_c}{C_f} \end{aligned}

Question 5 |

The output impedance of a non-ideal operational amplifier is denoted by Z_{out} . The
variation in the magnitude of Z_{out} with increasing frequency, f , in the circuit shown
below, is best represented by

A | |

B | |

C | |

D |

Question 5 Explanation:

Bode plot of negative feedback amplifier:

Given amplifier is a voltage series feedback amplifier.

Therefore, Output impedance is given by

Z_{out}=\frac{Z_o}{1+A\beta } =\frac{Z_o}{1+A } \;\;\;(\beta=1 \text{ for buffer})

From Bode plot ; at low frequency, the open loop gain (A) is constant.

when \omega \uparrow, A \downarrow,Z_{out}\uparrow

At A=0, Z_{out}=Z_o\rightarrow constant

Therefore, z_{out} with frequency represented by

Given amplifier is a voltage series feedback amplifier.

Therefore, Output impedance is given by

Z_{out}=\frac{Z_o}{1+A\beta } =\frac{Z_o}{1+A } \;\;\;(\beta=1 \text{ for buffer})

From Bode plot ; at low frequency, the open loop gain (A) is constant.

when \omega \uparrow, A \downarrow,Z_{out}\uparrow

At A=0, Z_{out}=Z_o\rightarrow constant

Therefore, z_{out} with frequency represented by

There are 5 questions to complete.