HELP24

Question

Answer 1

3.4)

Disadvantages of half-wave rectifier :

Half-wave rectifier is seldom used in practice because

1) The rectification efficiency is low.

2) The D.C output is small.

3) Secondary transformer carries the rectified current, thus producing direct magnetisation of the transformer core.

4) Because of short heavy pulses of current, the heating of transformer winding is large compared to the current delivered.

Answer 2

4.2)

• A push pull amplifier is an amplifier which has an output stage that can drive a current in either direction through the load.
• Whether delivering power to a loudspeaker or a servo amplifier, the push-pull output stage (Class B) can be a good choice for the job.
• One advantage is that there is no power dissipated in the output transistors when there is no signal present.
• Class AB amplifiers are conventionally used as loudspeaker drivers in audio systems because they are efficient enough to be able to drive the required maximum output power, often on the order of 100 W, without dissipating excessive heat, but can be biased to have acceptable distortion.
• Audio signals tend to be near zero most of the time, so good performance near zero output current is critical, and that is where class A amplifiers waste power and class B amplifiers suffer zero-crossing distortion.
• A class AB push-pull amplifier is also conventionally used as the output stage of a commercial operational amplifier.

Answer 3

4.5)

There is two types of feedback, one is positive feedback and other is negative feedback.

Positive feedback :

Positive feedback is when a part of the output is given back to the input so that the output increases more. this is done to produce oscillations.

Positive feedback is also known as regenerative feedback.

Positive feedback is feedback that is used in ossilators to maintain ossilation, a portion of the output is feedback to the input.

Positive feedback is usually in oscilator circuit.

Generally positive feedback leads to increasing input to the system as time progresses.

Negative feedback :

Negative feedback is when a part of the output is given back to the inputs so that the output decreases more. this is done to stabilize the gain of an amplifier.

Negative feedback is also known as degenerative feedback.

Negative feedback is used to improve the performance of an amplifiers the output is feedback but inverted to produce a reduction in gain and therefore reduce distortion.

In negative feedback, use some part of output signal which have opposite phase with input signal, as input signal.

Negative feedback is usually in amplifier circuit.

Negative feedback helps the transitor circuit independently with temperature.

Answer 4

5.2)

Purpose of the feedback resistor in an amplifier :

Feedback resistor effectively lowers the gain of the op-amp to a usable level, by providing negative feedback.

Without a feedback resistor, the gain of your typical op-amp is ridiculously high(around 200,000).

With a gain that high, even the slightest difference in input signals at the inverting and non-inverting pins causes the amp to go into saturation.

The feedback and input resistors set the closed loop gain.

The ratio of the feedback resistor and the input resistor sets the op-amp's gain.

Answer 5

4.3)

 

Step 1 :

 

Input and output specifications :

Output current, .

Output impedence, .

Input voltage, .

Input impedence, .

Input current, .

Step 2 :

Find the power gain of the circuit in decibel, by using the formula : , where is the power applied to the input and is the power from the output.

.

Substitute corresponding values in above formula.

Solution :

The power gain of the circuit in decibel is .

Answer 6

3.3.1)

Supply voltage of full wave bridge rectifier is V.

Full wave bridge rectifier turns ratio is .

Voltage transfomation ratio is .

Here , and .

Substitutue corresponding values in .

.

Peak secondary voltage is 40 V.

Solution:

Peak secondary voltage is 40 V.

Answer 7

3.3.2)

Peak secondary voltage is 40 V.

Average volatage is defined as .

Here, V.

Average secondary voltage is 25.46 V.

Solution:

Average secondary voltage is 25.46 V.

Answer 8

3.3.3)

Peak inverse voltage of diodes:

Peak inverse voltage of diode is 80 V.

Solution:

Peak inverse voltage of diode is 80 V.

Answer 9

(4.1)

Crossover Distortion is a type of distortion that occurs in push-pull class AB or class B amplifiers.

It happens during the time that one side of the output stage shuts off, and the other turns on.

Crossover distortion occurs when the signal changes or “crosses-over” from one transistor to the other at the zero voltage point it produces an amount of “distortion” to the output wave shape.

Graph :

Observe the graph :

Crossover distortion occurs when the signal changes its sign.

Crossover Distortion produces a zero voltage “flat spot” or “deadband” on the output wave shape.

To eliminate crossover distortion, both transistors in the push-pull arrangement must be biased slightly above cut-off when there is no signal.

Answer 10

(4.4)

CMOS :

CMOS is known as Complementary Metal Oxide Semiconductor.

CMOS circuit consists of combination of PMOS and NMOS.

Figure :

Figure shows basic connection of CMOS using PMOS and NMOS

Application wise, CMOS based realization of logic gates is used everywhere.

This is because of the flexibility in the usage of both types of NMOS and PMOS in CMOS.