Electrical and Electronics Tutorials: Electronics

Showing posts with label Electronics. Show all posts

Explanation of Cathode Ray Tube

Cathode Ray Tube (CRT)

A cathode ray tube is the heart of the CRO. The below fig shows the various parts of CRT.

1. Glass Envelope: It is conical highly evacuated glass housing maintains vacuum inside and supports the various electrodes. The inner walls of CRT between neck and screen are usually coated with the conducting material called aquadag. This coating is electrically connected to the accelerating anode so that electrons which accidently strike the walls are returned to the anode. This prevents the walls of the tube from charging to a high negative potential.

Pic 1. Cathode Ray Tube

Block diagram of CRO

The below fig gives the block diagram of a CRO. A CRO consists of the following main blocks.

1. Cathode Ray Tube (CRT)

2. Vertical amplifier

3. Delay line

4. Trigger circuit

5. Time-base generator

6. Horizontal amplifier

7. High / low voltage supply.

Pic 1 Block Diagram of CRO

Classification of Oscillators

The oscillators can be classified in the following ways.

1. According to the generated waveform.

(a) Sine wave oscillation

(b) Relaxation or non-sinusoidal oscillators.

2. According to the fundamental mechanism involved

(a) Feedback oscillators

(b) Negative resistance oscillators.

Oscillation from Tank Circuit

If there were no losses in the tank circuit to consume the energy the interchange of energy between inductor (L) and capacitor © would continue indefinitely. But in practical tank circuit there are resistive and radiation losses in the coil and dielectric losses in the capacitor. Due to these losses the oscillating waveform gradually decreases and eventually it becomes zero.

Integrator

The circuit diagram of integrator using operational amplifier is shown in the below fig. This circuit is same as inverting amplifier except that the capacitor C is placed in the place of feedback resistor. The input current to the ideal amplifier is zero. The feedback through the capacitor C forces a virtual ground to exist at the inverting input terminal. Thus the voltage across C is simply the output voltage.

Applications of Operational Amplifiers

The operational amplifier can be used for several applications few of them are:

1. Inverter

2. Sign changer

3. Buffer

4. Summer

5. Integrator

6. Differentiator

Operational Amplifier

The operational amplifier is a basic analog building block common to a number of electronic functions performed in instrumentation, computation and control. Op-amp is basically a differential amplifier whose function is to amplify the difference between two input signals. Op-amp is available in IC form.

Ideal Op Amp Characteristics

The ideal operational amplifier is shown in the below fig, and its equivalent circuit. A signal appearing at the negative terminal V₁ is inverted at the output, a signal at the positive terminal V₂ appears at the output with no change in sign.

Differential Amplifier

A differential amplifier serves to amplify the difference between tow signals. A differential amplifiers forms the basic stage of an integrated op-amp with differential inputs.

The circuit diagram of the emitter coupled differential amplifier is shown in the below fig. it uses two identical npn transistors. The transistors are connected in CE mode. The emitter bias is used here. The two inputs V₁ and V₂ and the output is V_o. The output is derived from the two collector points.

Advantages and Disadvantages of Push Pull Amplifier

Advantages:

1. Even harmonics are absent in the output.

2. The problem of core saturation and non-linear distortions will not appear because of cancellation of D.C. components of collector current.

3. The output is double as that offered by a single ended stage.

Push Pull Amplifier

In single ended amplifiers, appreciable distortion may result due to non-linearity of transfer characteristics. This distortion may be reduced considerably by push pull operation of transistors. A push pull amplifier uses two active devices that excited by the same input signal but with a phase difference of 180^o. The input signal is applied to the input of the two transistors through a centre tapped transformer T₁.

Single Ended Class A Power Amplifier with Transistor Load

The single ended class A power amplifier with transformer collector load is shown in fig. the resistors R₁,R₂ and R_E form the biasing and stabilization network. The emitter bypass capacitor C_E offers low reactance path to the signal.

Single Ended Class A power Amplifier with Resistor load

The below fig shows a simple series-fed class A amplifier with resistive load R_C. The transistor used here is under fixed biasing condition. As the input signal is applied, the transistor operates in active-region and hence the amplified power output appears across the load resistor. The static output characteristics along with input, output waveforms are shown in the below Pic 2.

Difference Between Voltage and Power Amplifiers

A voltage amplifier is designed to have maximum voltage amplification. However, there is no importance of power amplification. On the other hand power amplifier is designed to achieve maximum power output.

Definition of power amplifier

A transistor amplifier which raises the power level of the signals that have audio frequency range is known as transistor power amplifier. In general the last stage of multistage amplifier is the power stage. A power amplifier differs from the voltage amplifier. A transistor that is suitable for power amplification is generally called as power transistor.

Classification of Power Amplifier

The power amplifiers can be classified in the following ways.

1. According to the usage of Frequency Signals:

Comparison of Different Types of Coupled Amplifiers

S.No	Particular	R-C Coupled Amplifier	Transformer Coupled Amplifier	Direct Coupled Amplifier
1.	Frequency Response	Excellent	Poor	best
2.	Cost	Less	More	Least
3.	Space and Weight	Less	More	Least
4.	Impedance matching	Not good	Excellent	Good
5.	Applications	Voltage amplification	Power amplification	Amplifying very low frequencies

Working, Advantages and Disadvantages of Direct Coupled Amplifier

Direct Coupled Amplifier

The direct coupled amplifier suits well for very low frequency applications. Since the circuit especially works at low frequencies, the coupling capacitor and transformers are not used because the electrical size of these components become very large at these frequencies.

Advantages and Disadvantages of Transformer Coupled Amplifiers

Advantages:

1. No signal power is lost in the collector or base resistors.

2. An excellent impedance matching and can be achieved in a transformer coupled amplifier.

3. Due to excellent impedance matching, transformer coupling provides higher gain.

4. D.C isolation between first and second stages.

Transformer – Coupled Amplifier

The main drawback of RC coupled amplifier is low voltage and power gains and poor impedance matching. This is because of the decrease in effective load R_AC of each stage. If the effective load resistance of each stage could be increased, the voltage and power gain could be increased. This van be achieved by transformer coupling. Transformer coupling is generally employed when the load is small. It is mostly used for power amplification.

Transformer Coupled Amplifier

Advantages and disadvantages of RC Coupled Amplifier

Advantages:

1. The frequency response is excellent.

2. This circuit is very compact and extremely light.

3. Cost is low because it employ resistors and capacitors which are cheap.

Frequency response of RC Coupled Amplifier

Frequency response of R.C coupled amplifier is uniform over mid frequency range of 50 Hz to 20 KHz. The voltage gain drops off at low < 50 Hz and high > 20 KHz frequencies. The frequency response curve of RC coupled amplifier is shown in the below fig. the behaviour of the amplifier is given below.

Frequency Response of RC Coupled Amplifier