Definition of class A power amplifier:
class A power amplifier is an electronic device that increases the power of an input signal. In a Class A amplifier, the output current flows for the entire cycle of the AC input supply.
A power amplifier is a device that increases the intensity of an input signal, which can be in the form of voltage or current, and is used to drive a load like as a loudspeaker or antenna. As compare to other amplifier classes class a is relatively simple devices. As We have already discussed, in previous article “Introduction to the Amplifier-Definition and working”
Classification of power amplifiers:
Classification of power amplifiers is based on its size, processing speed, I/O configurations, load capacity etc.
On this basis, the power amplifiers are classified as given below. In this article, we will discuss Class A Amplifier in detail.
- Class A power amplifier
- Class B power amplifier
- Class C power amplifier
- Class AB power amplifier
Note: The class A amplifier must have conducted 360-degree full cycle waveform for output.
Class A power amplifier:
The arrangement of two devices conducted through a full 360-degree cycle, with one handling more load during the positive cycle and the other handling the negative cycle, reduces distortion compared to single-ended designs. This also helps in the reduction of noise sensitivity. as single-ended designs often require special power supply attention to resolve this issue
The Q point is located exactly in the middle of the amplifier’s load line. The collector voltage is kept at approximately half the supply voltage in class A biasing, but this means that the transistor is permanently passing the collector current even when no signal is being applied. This results in wasting power, and while class A provides very low distortion, it is also relatively inefficient in its use of power.
Certainly! A Class A amplifier is a type of electronic amplifier that operates over the entire range of the input cycle. In a Class A amplifier, the output transistors conduct throughout the entire 360 degrees of the input cycle.
Class A push/pull Amplifier:
- Class A Push-Pull Amplifier Configurations: Class A push-pull amplifiers can be configured as Class A, Class AB, or Class C.
- Typical Circuit Configuration: The amplifier circuit consists of two identical transistors (Q1 and Q2) with their emitter terminals connected, and they are biased using resistors R1 and R2. The collector terminals of these transistors are linked to the primary of the output transformer(T1), and a power supply is connected to the center tap of this transformer’s primary.
- Input and Output: Input signals are applied to the base terminals of the transistors through a coupling transformer (T1). An output load (RL) is connected across the secondary of the output transformer (T2).
- Phase Splitting Signals: The base of each transistor receives phase-splitting signals, with one transistor (Q1) being driven positively using the first half of its input signal the collector current of Q1 increases while the other (Q2) is driven negatively the collector current of Q2 decreases. This arrangement results in amplified output without excessive harmonics due to current cancellation. The current I1 and I2 flows in same direction in T2 primary as result amplified signal of signal is generated in T2 secondary.
| Amplifier Class | Description | Conduction Angle |
|---|---|---|
| Class-A | Full cycle 360o of Conduction | θ = 2π |
characteristics of Class A power amplifier:
- The output current flows during the entire cycle of the ac input signal
- The operation of the amplifier is limited to smaller central region of the load line, so that it can operate in the linear region of the load line (It can amplify small signals)
- As transistors operates over the linear region of the load line, The output waveform is almost like the input waveform
- The ac power output per active device (transistor) is smaller than that of Class B or C
- The maximum possible overall efficiency of a class A series fed resistive load is 25% (Very Poor) and for transformer coupled load it may increases to 50%
Power Efficiency:
The overall power efficiency is
η = (Pout / PDC) × 100%
Where:
- η is the power efficiency, expressed as a percentage.
- Pout is the output power delivered to the load (usually a speaker or antenna).
- PDC is the DC power input to the amplifier.
AC Voltage Gain:
The voltage gain for a Class A amplifier is typically calculated as:
Av= −g m⋅ (RC ∣∣ RL)
Where:
- Av is the voltage gain.
- gm is the transconductance of the transistor.
- RC is the collector resistor.
- RL is the load resistance.
- ∣∣ represents parallel resistance.
Power Dissipation:
Due to its continuous conduction, a Class A amplifier generates significant power and heat. The power dissipation equation is:
PD=IC⋅VCE
Where:
- PD is the power dissipation.
- IC is the collector current.
- VCE is the collector-to-emitter voltage.
DC Biasing Equation:
VCC=IC⋅ (RC + RE) +VCE
Where:
- VCC is the supply voltage.
- IC is the collector current.
- RC is the collector resistor.
- RE is the emitter resistor.
- VCE is the collector-to-emitter voltage.
Transformer-Coupled Class A Amplifier Efficiency
Power input from the DC source:
Pi(dc)=VccIcQ
Power dissipated as heat across the transistor:
PQ=Pi(dc) – Po(ac)
Note: The larger the input and output signal, the lower the heat dissipation.
Maximum efficiency:
Note: The larger VCEmar and smaller VCEmin, the closer the efficiency approaches the theoretical maximum of 50%.
Advantages of Class A amplifier:
This design offers high AC output, minimal even harmonics, and can balance out the effects of ripple voltages in the power supply, making it ideal for audio applications. It can eliminate distortions that have been occurred in the circuit. It can generate high gains.
- High linearity
- Minimal crossover distortion
- Suitable for low-power applications
- Simplicity in circuit design
- Smooth and natural sound
- No switching noises
- Popular in high-end audio products
Disadvantages of Class A Amplifier
- Inefficiency
- Heat generation
- Limited power output
- Bulk and weight
- Short battery life
- Lower efficiency at low output
Applications of Class A Amplifier
- High-fidelity audio systems
- Audiophile-grade amplifiers
- Musical instrument amplification (e.g., guitar amplifiers)
- Studio and professional audio equipment
- Low-power signal amplification
- Laboratory and test equipment
- Small-scale boutique audio products
- Sensitive measurement equipment
- Where high linearity and minimal distortion are crucial.
Frequency Asked Questions [FAQs]:
Q. What is the main use of Class A amplifier?
Ans: The main purpose and uses of class A amplifier is outdoor musical system, because the amplifier and transistor produce full waveform so audio is not cut. therefore, the sound is more clear and has less distortion.
Q. Why is Class A amplifier better?
Ans: As we discussed in above applications and advantages class A amplifier deliver the smoothest and highest sound fidelity that’s why its more better.
Q. What are the 3 types of amplifiers?
Ans: Please check out previous post “Introduction to the Amplifier-Definition and working” so basically there are 3 types are:
Voltage amplifier
Current amplifier
Power amplifier
In summary, a Class A amplifier is characterized by its continuous conduction of output transistors, providing high-quality amplification but with lower efficiency compared to other amplifier classes.
This is all about Class A amplifier its working principle – definition, characteristics so In next tutorial we will look Class B Amplifier-its working principle and is another type of audio amplifier circuit.
Follow to the blog ETechSpark.com for more articles on electrical engineering, electronic and Tech updates.
please leave your question in the comment section, give us your valuable feedback.
Thank You
4 thoughts on “Fundamentals of The Class A power amplifier”