We commonly see the audio power amplifier category has A class, AB class, D class, H class, and what G class and T class, also heard that there are S class. These are names for a particular kind of technology. In the field of professional stage power amplifier, the purpose of using any technology is to achieve high efficiency, so that we can get relatively better stability and low cost, but also the corresponding more complex circuit to complete.
Power amplifier is the abbreviation of power amplification. With voltage or current amplification, power amplifier requirements to obtain a certain, true power, generally in the state of large signal work, therefore, the power amplifier circuit generally contains voltage amplifier or current amplifier circuit does not have special problems, specific performance in :
① output power as large as possible;
② usually work in the state of large signal;
③ outstanding nonlinear distortion;
(4) to improve efficiency is an important concern;
⑤ Safety problems of power devices. But for the audio power amplifier circuit, also need to pay attention to the above problems.
According to the different conduction mode of amplifying circuit, audio power amplifier circuit is classified according to analog and digital two types. Analog audio power amplifier usually has class A, class B, class AB, class G, class H TD power amplifier, while digital power amplifier is divided into class D and class T. The following text makes a detailed introduction and analysis of the above power amplifier circuit.
1. Class A power amplifier (also known as class A power amplifier)
Class A amplifier, shown in the figure above, is an amplifier that does not have A current cutoff (that is, stop output) during the entire cycle of the signal. But class A amplifiers produce high heat and are very inefficient. Although class A power amplifier has the above disadvantages, but the inherent advantage is that there is no crossover distortion, and there are some innate advantages in the internal principle, is the ideal choice of replay music, it can provide very smooth sound quality, sound mellow and warm, high frequency transparent open, mid frequency full and transparent advantages. Single-ended amplifiers are class A operating mode, push-pull amplifiers can be class A, class B or class A B.
2, class B power amplifier (also known as class B power amplifier)
Class B power amplifier is a kind of amplifier that the positive and negative two half cycles of sinusoidal signal are respectively amplified by the two transistors of the push-pull output stage in turn. The conduction time of each transistor is half a cycle of the signal, which usually produces what we call cross over distortion. The distortion can be reduced or even disappeared by adjusting the analog circuit. The efficiency of class B amplifiers is significantly higher than class A amplifiers.
3. Class AB power amplifier (also known as class A and class B)
Class AB power amplifier is between class A and class B, and the conduction time of each transistor in push-pull amplification is longer than half of the signal cycle but less than one cycle. Therefore, class AB power amplifier effectively solves the problem of class B amplifier's crossover distortion, and the efficiency is higher than class A amplifier, so it has been widely used.
4, class D power amplifier (also known as class D power amplifier)
Class D amplifiers, also known as digital amplifiers, use extremely high frequency transfer switch circuit to amplify audio signals. The specific working principle is as follows: Class D power amplifier with the method of asynchronous modulation, the audio signal cycle changes, high frequency carrier signal stays the same, therefore, is low, the audio frequency PWM carrier number remains high, and thus to restrain the high frequency carrier was beneficial to reduce the distortion, and carrier frequency conversion principle of audio signal frequency, Therefore, there is no problem of mutual interference with the fundamental wave. Many class-D amplifiers, with up to 1,000 watts of power, are only about the size of VHS tapes. This type of amplifier is not suitable for use as a broadband amplifier, but it is widely used in active subwoofer speakers.
5. Class G power amplifier
Class G power amplifier is an improved form of class AB power amplifier with multiple power sources. Class G power amplifier takes full advantage of the extremely high peak factor of audio (10-20dB). Most of the time, the audio signal is at a lower amplitude, and very rarely shows a higher peak. The following figure is a typical functional block diagram of class G power amplifier integrated IC.
Class G amplifiers use an adaptive power track and utilize a built-in buck converter to generate a positive power supply voltage for the headphone amplifier. The charging pump inverts the positive power supply voltage of the amplifier and generates the negative power supply voltage of the amplifier. This allows the headphone amplifier output to focus on 0V. When the audio signal amplitude is low, the step-down converter generates a low amplifier negative supply voltage. This minimizes the power consumption of the Class G amplifier while playing back low-noise, high-fidelity audio, which is more efficient than traditional Class AB headphone amplifiers.
The amplification principle of this kind of power amplifier is the same as that of class AB power amplifier. An important feature is that the power supply part adopts two or more groups of voltage. Low power operation uses low voltage, and high power automatically switches to high voltage.
6, H class power amplifier
The amplifying circuit of this kind of power amplifier has the same principle as class AB power amplifier, but the power supply part adopts the switching power supply which can adjust the multi-stage output voltage, and automatically detects the output power to select the power supply voltage.
7. Class K power amplifier
K class internal since the lifting pressure circuit and power amplifier is integrated with all kinds of power amplifier circuit, we all know that class D power amplifier is a power amplifier circuit in one of the high efficiency of digital power amplifier, and K class amplifier just according to the lifting pressure required to integrate the internal circuit and the demand of power amplifier circuit, if demand work plus class D power amplifier efficiency, to sound quality and class AB amplifier.
8, T class power amplifier
The principle of this kind of power amplifier is the same as that of class D power amplifier, but the signal part adopts DDP technology (the core is the adaptive algorithm and prediction algorithm of small signal). The working principle is as follows: the current of the audio signal into the loudspeaker is all controlled by the DDP after operation and processing to turn on or off the high-power high-frequency transistor, so as to achieve the high-fidelity linear amplification of the audio signal. This kind of power amplifier has high efficiency, small distortion, sound quality can be comparable with class AB power amplifier.
9, TD class power amplifier
This kind of audio power amplifier amplifier and AB power amplifier principle is the same, but the power supply part adopts completely independent high precision adjustable stepless output adjustable digital power supply, voltage progressive value is 0.1V, automatic detection of power to adjust the rise or decrease of voltage. Because this kind of power amplifier needs high precision adjustable digital power supply, needs to have the special design to the power supply, but can not be concentrated on a chip, therefore, this kind of power amplifier is mainly used in the advanced sound, and the circuit is more complex.
For the later types 6, 7, and 9 amplifiers, special power supplies are required, so functions cannot be concentrated on a single IC. And for the classic class A, class B, class AB and class D power amplifier has A special IC. In the practical design, various types of power amplifier circuits are needed, which are applied in different fields. They only need to be based on this, plus the corresponding power supply or processing module.
Super-large power products are commonly used according to the characteristics of audio signals, sampling and comparison, and a hierarchical control of the power supply voltage technology, there are also independent power to complete, compared with the AB class can improve the efficiency of the whole machine by up to 25%, but because the power supply is divided and switched, this will bring inevitable shortcomings.
For example, higher requirements are put forward for the consistency of the filter capacitor. If the capacitor is used in series, its capacity will be reduced, the filtering effect is not ideal, and the decline of its durability and stability is also accompanied by. There is also because of the use of multi-stage switching power supply, but also bring its unique distortion - switch distortion. Reflected in the performance of sound quality is the high frequency band to show loose, noise, such as the bad feeling of blasting ears. The low frequency also appears stiffer and thinner. Because of the characteristics of the power supply structure, there is no good protection measure to limit the power consumption of the power tube, and the phenomenon such as tube burning will occur from time to time.