Electronic Amplifier Model Analysis (EAMA)

Substance:

1. class A amplifier
2. class B amplifier
3. class AB amplifier
4. class C amplifier
5. class D amplifier

Efficiency of Signal Amplifier Class Model

1. Class A Amplifier

Class A Amplifier 

Circuit Analysis:

• IE = IB+IC (THEORY)
• IE = IC (ACTUAL)
• VCC = ICE+IC.RC+IC.RE
• VCC = NCE+IC (RC+RE)
• IC isomorphic (has similarities with) IE

The way to determine that the transistor working point is in the middle of the linear characteristic line is as follows:

For example, it is known: 

• VCC= 12volts,
• hfe= 100, 
• RC= 4k7ohm, 
• RE= 120ohm.

Solution:

The load line equation is VCC = VCE + IC (RC + RE), when VCE = 0, then IC is maximum, IC MAX = (vcc / Rc) + RE = 12 / 4700 + 120 = 2.5 mA. When IC = 0, then VCE = VCC 12 volts, so that in the middle then;

IC Q = IC MAX/2 = 2.5/2 = 1.25 mA
VCE Q = VCE MAX/2 = 12/2 = 6 volts

Class A Amplifier Operating Point

So a class A amplifier is an amplifier whose working point is located in the middle of the load line, the conduction angle of a class A amplifier is 360 degrees, meaning that all input signals will be included intact as long as they are still within the limits of its active area.

Characteristics of Class A Amplifier:

• Can strengthen IC signal 360 degrees with good amplification quality
• Minimum current does not reach the cut off point
• IC usage is very wasteful
• If there is no input signal, the collector current continues to flow at IC, which is called the bias current.
• The working point is in the middle of the load line (VCE = 1/2 vcc).
• Less efficient in power usage.
• Large input power
• Input power (PC) = VC.IC in
• Efficiency 25% - 50%
• Class A functions as an initial amplifier (pre Amp).

2. Class B Amplifier

In this amplifier, the transistor's working point shifts to the left, so that it is right at the cut-off point. In a class B amplifier, when there is no input signal, the IC does not flow, because the working point is right at the cut-off point. If there is an AC signal, only the phase signal (+) is amplified, while the phase signal (-) is not amplified, so that the output signal is only 1/2 full wave or its conduction is 180 degrees.

Class B Amplifier Operating Point

Characteristics of class B amplifier:

• Only amplifies 180 degree AC signal, poor quality.
• Work right on the cut off point
• When there is no input signal, no current flows in the collector, so the current consumption is very minimal.
• Good efficiency -+ 75%
• The input signal is 1 wave, while the output is 1/2 wave.

Advantages and disadvantages of class B amplifier:

• High output power (2x class A)
• Good efficiency between 70%-80%
• It is very easy for crossover to occur, to prevent this a forward bias voltage is applied to the base of the final amplifier.
• Functions as a final amplifier, because it has good efficiency.

3. Class AB Amplifier

It is an amplifier whose working point is between the working points of class A and B, namely the Q AB point, the conduction angle of the class AB amplifier is 360 degrees and greater than 180 degrees, this circuit is widely used in push pull amplifiers.

Class AB Amplifier Working Point

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Properties of class AB amplifier:

• Amplifies AC signal greater than 180 degrees.
• The reinforcement quality is above class B
• The working point is between class A and B
• Better power efficiency above class A
• Input signal 1 wave, output > 1/2 wave
• There is already a transistor current flowing, efficiency 50%-75%
• This circuit is usually used for final class amplifiers.

4. Class C Amplifier

In this amplifier, the transistor's working point shifts beyond the cut-off point, as a result, a new output signal will appear if the input signal has a very large amplitude, the (+) signal will appear only at peak amplitude.

Class C Amplifier Working Point

Properties of class C amplifiers:

• Strengthens AC signal less than 180 degrees
• Highest power efficiency (better than class B even approaching 100%)
• The working point is below the cut off point
• Input signal 1 wave output is less than 1/2 wave
• Class C amplifiers are widely used in transmitter circuits, because transmitter circuits prioritize frequency efficiency, as a result only the peak signal is amplified, so that harmonization can reduce or even eliminate noise/interference.

Tracking 1-Level Amplifier Circuit Failure

Subject

1. BASIC PRINCIPLES
2. HOW THE CIRCUIT WORKS
3. CALCULATION RESULTS
4. DAMAGE ANALYSIS
5. OTHER POTENTIAL DAMAGES

1. BASIC PRINCIPLES

The subject of this section is devoted to the effects of each damaged component in a single-stage common emitter amplifier circuit.

This circuit usually has eight components, keeping in mind that:

• Resistors can be damaged by becoming open circuits or short circuits.
• Capacitors are damaged due to open circuits or short circuits.
• And the transistor is damaged because one of the connections is an open circuit or short circuit.

2. How the Circuit Works

In a class A amplifier current flows through the transistor and the input signal causes the current to increase or decrease. This change in collector current in turn induces a voltage signal across the collector load resistor R3.

The collector voltage operating point is the dc voltage between the collector and ground (0V), which is a value that allows the output signal to swing equally in the positive and negative directions.

From the circuit, calculate the voltage at measuring points 1, 2 and 3? And do the analysis with circuit maker software!

3. Calculation Results

VB = R2/R1+R2 x 12V = 2.4V
VE = VB -- VBE = 2.4V -- 0.7V = 1.7V
Vc = Vcc -- IcR3
Ic = IE= VE/R4
Vc = 12 -- (3.05mA x 2.2 k) = 12 -- 6.7 = 5.3 V

4. Damage Analysis

Damage Analysis

Resistor Damage

Case 1: R1 is open - If R1 is open the current flowing in R2 and base is zero. This event is followed by the transistor being blocked, so the base and emitter voltages are both zero. Therefore no collector current flows, the voltage across the collector load R3 drops to zero and the collector voltage itself is equal to the supply voltage vcc

5. Other Potential Damage

At the same measuring point, it is also used to analyze other damage, such as the following:

• R2 open
• R3 open
• R4 open
• C1 or C2 is open
• C3 open 
• C4 short circuit
• Open collector/base junction
• Short-circuited collector/base junction
• Open emitter/base junction
• Short collector/base connection
• Short circuit collector/emitter junction

Quick & Practical Ways to Repair Electronic Devices

Uncertain or intermittent problems (sometimes error / sometimes normal again), this kind of thing comes and goes suddenly, almost always due to bad connections, corrosive solder, cold solder (not cooked), internal or external connectors that need to be cleaned and reseated. It's amazing, trivial problems like this are often found and the percentage is very large, so our paradigm includes it in the category of common problems and one thing of suspicion that should not be missed in the world of troubleshooting.

Problems that change gradually - usually they decrease or then disappear - as components get warm or hot easily, such as drying out of ELCO (electrolytic capacitors).

Problems that result in the unit completely shutting down or affecting some functions usually involve the power supply and are fairly easy to fix.

Catastrophic failures often result in units burning, scorching, cracking, exploding, or melting. Use your senses of sight and smell to look for evidence of this.

Hearing a buzzing or corona or some kind of hissing sound. A component is on the verge of failure due to overheating, this could be a clue.

Most VCR problems are mechanical, naturally worn or corrosive, such as rubber or valves deteriorating, hardening, stiffening or becoming porous. Lubricating rubber is a big mistake, and it is best to replace it.

The most common CD player problems are mechanics blocked by dust, dirty lenses, and some others short circuit flexible cables or spindle motors. No matter what the symptoms, always make it a habit to clean the lens first to start troubleshooting. Many strange failures in mode are simply caused by dirty lenses.

TV and Monitor problems are most often found to be damaged in the power supply or related deflection. Tend to have obvious causes, such as blown posistor, rectifier diode, filter capacitor, HOT, or Chopper. Flyback with shorted or double-voltage windings (if used). The screen / focus divider network is also common. Where HOT or Chopper is also involved, then after repairing the surrounding components, you still need to observe changes that are not far from HOT or Chopper for a certain period of time, because most often new failures are found in other parts, after that. Generally HOT (Horizontal Output Transistor) is not hot, but if the driver and B + exhaust are weak, then HOT can get hot.

Microwave oven problems are almost always related to power. Component failure occurs in the generator (magnetron, HV diode, HV capacitor, HV transformer), relatively easy to identify. Sometimes primary side components can cause confusing symptoms such as parallel interlocks, blown fuses or weakened triacs causing the main fuse to blow or due to power surges. Control problems are also possible, such as on the touchpad.

Even the most reliable ink-jet printers also have their share of failures. The problem is often found in the ink layer (service station area), misaligned print-head contacts, or cartridges that are empty of ink while the printing process is still running, resulting in problems that develop.

Problems that develop in Laser Printers tend to be in the fuser, scanner, or power control module. Symptoms that can arise include burnt out lamps, deteriorating motors, or bad connections.

Problems with tape decks like VCRs are more likely to be mechanical. It is suspected that damage to the wires for the tape head, before damage leads to the chip.

Telephones connected to modems are susceptible to power surges. Devices that appear to respond to user commands but actually do not, this is thought to be due to sparks around the connector after a surge occurs, then what you need to do is clean it.

"Sam Magic Spit" is a trick by Sam, which is done to approach damage tracking, by slightly wetting the cloth, then with the tip of the finger touching the pcb track to respond the unit (ONLY APPLIES TO UNITS WITH LOW VOLTAGE). Or using a fingernail or probe to trigger a specific pin.

Logic circuits - marginal timing or signal levels will produce dramatic changes in the behavior of the unit. This has happened, and was done to find the signal characteristics of the PGA chip pin 305.

Analog circuits - In the case of audio amplifiers, changing the behavior of the unit can be done with the use of fingers, as effectively as the injector signal. The principle of equipment and what you do is always useful. With a little spell of hum, buzz, clicks and pops, then your unit is made or died, hehehe just kidding (but I'm sure there must be a point where you are stuck and want to use a technician's magic trick).

Unknown circuits - The circuit schematic is not available / not found, so what a technician can do is investigate the most sensitive parts, then touch several components to find out the effects caused.

For example, I can quickly identify the transistor trigger on a wireless doorbell using my finger to find the point where the chimes are heard, thus firmly stating that the problem is in the RF front end or decoder and not the audio circuitry.

Do not bring the unit to a humid place, or you will be shown unexpected consequences by the unit.

WARNING!! - Make sure that you do all these tips on a LOW VOLTAGE unit or circuit. Using these tips, you can easily troubleshoot your TV, Computer Monitor, photoflash, or microwave oven!!

Signal Processing Process

There are several waveforms that are frequently used:

Waveforms (a) Sinusoidal; (b) pulse; (c) triangular; (d) sawtooth; (d) right angle

1. Waveform generation

1. Sinusoidal wave. Usually produced by an LC or RC circuit connected to an amplifier (oscillator).
2. Square wave. Produced by a multivibrator oscillator that uses the relaxation principle of charging and discharging an RC circuit.
3. Other waves. Usually produced from right or sinusoidal waves.

2. Differentiation and Integration Network

• Differentiation: A measure of the rate of change of a given waveform.
• Integration: A measure of the area under a given wave.

Series (a) differentiation; (b) integration

3. Amplifier

Amplifiers are divided into several classes:

• Class A: Current flows in the load during the entire period of the input signal cycle.
• Class AB: Current flows in the load for more than half a cycle, but less than a full cycle of the input signal.
• Class B: Current flows in the load during half the cycle of the input signal.
• Class C: Current flows in the load for less than half a cycle of the input signal.

Regulated and irregular voltage amplifiers and low-power af (audio frequency) amplifiers typically operate in class A, while high-power af amplifiers operate in class B. RF (radio frequency) amplifiers and oscillators typically operate in class C.

4. Signal adjustment / impedance matching

It may happen that the existing amplifier system cannot work according to its function, this happens because of the impedance of the source and the amplifier itself.

These problems can be overcome by signal conditioning:

• Matching high impedance and low voltage sources to the pre-amplifier;
• Matching a low impedance load, such as a loudspeaker or relay, to an amplifier to produce maximum power in the load.

5. Basic amplifier configuration

The basic amplifier configuration is divided into three, namely:

• Common Basis
• Common Emitter
• Common Collector.

Normal base

Normal Base Configuration

• Achievable current, hFB ? 0.99
• Achievable voltage = 50
• Input impedance, Zin = 50 ohms
• Output impedance, Zout = 250 Kohm
• Power that can be achieved ? 50

Normal emitter

Common Emitter Circuit

• Achievable current, hFE ? 200
• Achievable voltage = 50
• Input impedance, Zin = 1 Kohm
• Output impedance, Zout = 50 Kohm
• Achievable power? 2500

Ordinary collector

Typical Collector Circuit

• Achievable current, hFE ? 200
• Achievable voltage = 1
• Input impedance, Zin = 100 Kohm
• Output impedance, Zout = 1 Kohm
• Power that can be achieved ? 50

Darlington Couple

Darlington Couple

This amplifier produces a high input impedance (typically 1 Mohm) and produces a very high current reach (typically several thousand). The current reached is approximately equal to hFE1xhFE2.

Feedback in Amplifiers

There are two types of feedback:

• Positive Feedback: In line with the original signal, used to produce an oscillator.
• Negative Feedback: Opposite to the original signal, which usually reduces the achieved results, but improves the stability of the achieved results.

Open loop gain capability:

Closed-loop amplification capability (with feedback):

6. Feedback characteristics

Negative feedback

If Ab >> 1
then Ac @ 1/ Ab

Main effects:

• The reinforcement is reduced and stabilized.
• Frequency response is improved with larger bandwidth.
• Wheezing and blemishes (which are generated internally) are reduced.
• The method of applying feedback can modify the input and output impedance.

Negative Feedback Circuit Example

Positive feedback

If Ab ? 1
then Ac ? µ

Main effects:

• Strengthening is increased with a reduction in stability.
• If Ab ? 1 there may be oscillations occurring at a particular frequency.

7. Power Amplifier

Power amplifier output with M Load (motor)

Maximum power is transferred from a source to a load when Zout = Zload

The degree of impedance matching can be done by using a transformer. The transformation ratio n is obtained from:

If more power is needed, a class B push-pull amplifier can be used.

Power amplifier with transformer matching

Class B push-pull power amplifier

Class D Amplifier Design

Substance:

1. Driver Gate
2. MOSFET
3. Packaging
4. 200W Amplifier Circuit Example

Class D Amplifier

Advantages of Class D Amplifier

1. Smaller amplifier
2. High Efficiency
3. Smaller Size
4. Half Bridge
5. Better Sound
6. THD Improvement
7. Digital Modulation Process

Class D Audio Amplifier Model

Traditional/Ancient Amplifier

• Class AB amplifiers use linear regulation to modulate the output.
• Efficiency =30% at elevated temperature test conditions.

How Does a Class D Amplifier Work?

Class D Amplifier Concept

Class D amplifiers use MOSFETs instead of ON/OFF switches. PWM techniques are used to express analog audio signals with two ON and OFF states at the voltage output.

Basic Operation of PWM (Pulse Width Modulation)

Pulse Width Modulation

Analogy With Buck Converter

Amplifier Analogy D

Half Bridge vs Full Bridge

Main Causes of Defects

Dead Time & THD (Total Harmonic Distorion)

Voltage Pump

Driver Gate

Bootstrap Voltage Source

When the pull down voltage to ground through the bottom FET, the bootstrap capacitor charges through the diode. From the Vcc voltage, then as a supply of Vbs voltage.

Driver Layout

Stray inductance LD1 + LS1 provides undershoot / drift down the VS voltage through ground.

Driver Blog Diagram

Benefits:

• Full operation up to 200V
• Low power dissipation at high frequencies
• Logic input voltage 3.3-5V 
• Propagation delay is suitable for both channels
• Small in size

How Does MOSFET Work?

• MOSFET is a voltage controlled power switch. Voltage must be applied to the gate and source to allow current to flow from the Drain.
• MOSFETs are available in the form of IC packages for PCB design, the real form of the component is required.

Switching Time Calculation

FET Switching

Gate resistance increases and gate current decreases loading Qg increases causing switching time to increase.

Class D Amplifier Design Reference

Class D Amplifier Schematic