This amplifier is a combination of two amplifiers class A and class B. class B amplifier has a problem of distortion and class A amplifier has low efficiency problem. The class AB amplifier eliminates both of these problems and utilize the advantages of these two amplifiers.
Class AB amplifier operates as a class A amplifier when the power of output is low and operates as a class B amplifier when the current of output is high. The two transistors are pre biased in the amplifier output stage.
The circuit diagram of class AB amplifier is as follows:
Pic. 1. The circuit diagram of class AB amplifier
The purpose of diode D1 and D2 is to set the operating point above cutoff frequency. The cross over distortions which class B amplifiers creates is solved by using class AB amplifier
As the class A amplifier conducts for the full 360 waveform of the input signal, class B amplifier conducts from 180 to 360 of the input signal so by combining the effect of both of the amplifiers, depending on the pre biasing and the output current, each transistor conducts between 180 and 360.
This amplifier is a good compromise between the class A and class B amplifier in term of linearity and efficiency having efficiency between 50-60%. The relationship of input and output of class AB amplifier is as follows:
Pic. 3. The relationship of input and output of class AB amplifier
Like with most electronic circuits, there are a wide range of approaches to structure a amplifiers output amplifiers output stage the same number of varieties and alterations can be made to a fundamental enhancer yield circuit. The activity of a force speaker is to convey an obvious degree of yield power (both current just as voltage) to the associated load with a sensible level of effectiveness. This can be accomplished by working the transistor(s) in one of two fundamental working modes, Class An or Class B.
A little steady current move through the arrangement circuit of R1-D1-D2-R2, creating voltage drops which are balanced either side of the info. With no information signal voltage applied, the point between the two diodes is zero volts. As current moves through the chain, there is a forward inclination voltage drop of around 0.7V over the diodes which is applied to the base-producer intersections of the exchanging transistors.
Advantage of class AB amplifier:
- The circuit of this amplifier is very simple.
- It has very high sound quality.
- The behavior is linear.
- It has less that 0.1% distortion.
- Disadvantage of class AB amplifier:
- This amplifier needs heat sink as the power dissipation generates a lot of heat.
- This amplifier has low average efficiency.
This type of amplifiers are mostly used in hi-fi systems.
Part of class AB power amplifier:
The LM1875 is a power amplifier that offers very high-quality performance and very low distortion for the audio applications. On the 25V power supplies with 4Ω and 8Ω load it delivers 20W. at even high power levels, it offers extreme low power distortion by taking the advantage of circuit processing and techniques.
Other advantages of this amplifier are large voltage swings at output, the wide range of supply voltage, fast slew rate, high gain, high current capability and high power bandwidth. It is stable and compensator for larger gains.
The circuit diagram of this IC is as follows:
Pic.4. The circuit diagram of this IC
- Low frequency amplifiers of this class are most suited for audio amplification
- Operating Voltage of amplifier are 16V to 60V
- Output with 4Ω/8 Ω speaker is 20Watts
- Current at output is 4A
- Open Loop Gain is 90dB
- Bandwidth of amplifier is 70KHz
- Thermal protection and Short circuit is available
- Good at Breadboard
- Available in 5-pin TO220 package
Pic. 5. LM1875T
The price ofUTSource LM1875 (UTSource LM1875) is US $0.36
It is stereo amplifier which can deliver power of 20W with a load of 4 or 8Ω. The external logic is used to control the power conserving mode of this amplifier. It has dynamically save operating area, which protect the circuit against the over load, over voltage and thermal runaways.
The circuit diagram of this part is as follows:
Pic.6. The circuit diagram of this part
- It has SPiKe protection
- It requires Minimal amount of external components
- fade-in/out mute mode is quiet.
- Isolated 15-lead TO-220 package
- Non-Isolated 15-lead TO-220 package
- Supply voltage range is wide that is 20V - 64V
- High-end stereo TVs
- Compact stereo
- Component stereo
Pic. 7. LM1876T
The price of UTSource LM1876 (UTSource LM1876) is US $2.03
This is monolithic power amplifier of type AB, which is used in Hi-Fi applications. It is able to supply high power due to wide range of voltage and high current capability even in the presence of poor regulation of supply. It avoids switching on-off noises due to built in muting function. It operates at a supply voltage of 80V and delivers current at output to about 10A.
It is used in applications which requires high efficiency and high power.
- It has High Operating Voltage Range of about ±40V
- It has DMOS Power Stage
- Output Power is very high.
- It has Muting or Stand-By Functions
- Switch On/Off Noise is nill.
- No Boucherot Cells available
- It has Very Low Distortion.
- It has Very Low Noise.
- IC is Short Circuit Protected
- Thermal Shutdown
Pic. 8. TDA7294
The price of UTSource TDA7294 (UTSource TDA7294) is US $1.57.
The TDA7293 is a solid incorporated circuit in Multiwatt15 bundle, planned for use as sound class AB enhancer in Hi-Fi field applications, such as home sound system, self-fueled amplifiers and Top-class TV. Because of the wide voltage run furthermore, to the high yield current capacity it is capable to flexibly the most noteworthy force into both 4-Ω and 8-Ω loads. The inherent quieting capacity with turn-on delay improves the remote activity maintaining a strategic distance from on-off exchanging clamors.
Equal mode is conceivable by associating a few gadgets and utilizing pin11. High yield force can be conveyed to extremely low impedance loads, so upgrading the warm dispersal of the framework.
Pic. 9. TDA7293/7294
The TDA7293 is a solid incorporated circuit in Multiwatt15 bundle, planned for use as sound class AB enhancer in Hi-Fi field applications, such
as home sound system, self fueled amplifiers and Top class TV. Because of the wide voltage run furthermore, to the high yield current capacity it is capable to flexibly the most noteworthy force into both 4-Ω and 8-Ω loads.
The inherent quieting capacity with turn-on delay improves the remote activity maintaining a strategic distance from on-off exchanging clamors. Equal mode is conceivable by associating a few gadgets and utilizing pin11. High yield force can be conveyed to extremely low impedance loads, so upgrading the warm dispersal of the framework
Pic. 10. TDA7293
The price of UTSource TDA7293 (UTSource TDA7293) is US $1.91.
To be continued...