Detailed introduction and analysis of the most complete power amplifier circuit

The audio power amplifier categories we commonly see are A, AB, D, H, what are the G and T types, and I have heard that there are S types. These are all named for a certain unique technology. In the field of professional stage power amplifiers, the purpose of what technology is used is to achieve high efficiency, so that relatively better stability and low cost can be obtained, but it also requires more complicated circuits to complete.

Power amplifier is the abbreviation of power amplifier. In terms of voltage or current amplification, the power amplifier requires a certain amount of undistorted power, and generally works in a large signal state. Therefore, the power amplifier circuit generally contains special problems that the voltage amplification or current amplification circuit does not have, and the specific performance is: ①Output The power is as large as possible; ②Usually work in a large signal state; ③Outstanding nonlinear distortion; ④Improving efficiency is an important concern; ⑤Safety issues of power devices. As for the audio power amplifier circuit, the above problems should also be paid attention to.

According to the different conduction modes of the amplifying circuit, audio power amplifier circuits are classified into two types: analog and digital. Analog audio power amplifiers usually have A, B, AB, G, H TD power amplifiers, and digital circuit power amplifiers are classified into D types. , T category. The following is a detailed introduction and analysis of the above power amplifier circuit.

1. Class A power amplifier (also known as Class A power amplifier)
The Class A power amplifier is shown in the figure above. There will be no current cut-off (that is, stop output) in the entire cycle of the signal. However, the Class A amplifier generates high heat when it is working, and the efficiency is very low. Although Class A power amplifier has the above drawbacks, its inherent advantage is that there is no crossover distortion, and there are some inherent advantages in the internal principle. It is an ideal choice for replaying music. It can provide very smooth sound quality, mellow and warm sound, and high frequency. The advantages of transparency and openness, full and transparent intermediate frequency. Single-ended amplifiers all work in Class A, and push-pull amplifiers can be Class A, Class B or Class A and B.

2. Class B power amplifier (also known as Class B power amplifier)
Class B power amplifier refers to a type of amplifier in which the positive and negative half cycles of the sine signal are amplified and output by two transistors in 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 The crossover distortion. The distortion can be reduced or eliminated as much as possible through the adjustment of the analog circuit. The efficiency of the Class B amplifier is significantly higher than that of the Class A power amplifier.

3. Class AB power amplifier (also known as Class A and B)
Class AB power amplifiers are between Class A and Class B. The on-time of each transistor of push-pull amplification is longer than half a cycle of the signal and less than one cycle. Therefore, the class AB power amplifier effectively solves the crossover distortion problem of the class B amplifier, and the efficiency is higher than that of the class A amplifier, so it has been extremely widely used.

4. Class D power amplifier (also known as Class D power amplifier)
Class D power amplifier is also called digital amplifier. It uses extremely high-frequency switch circuit to amplify audio signals. The specific working principle is as follows: Class D power amplifier adopts asynchronous modulation. When the period of the audio signal changes, the high-frequency carrier signal remains No change, therefore, when the audio frequency is relatively low, the number of PWM carriers is still high, so it is very beneficial to suppress high-frequency carriers and reduce distortion, and the frequency conversion band principle of the carrier audio signal frequency, so there is no basis The problem of mutual interference between waves. Many Class D amplifiers with power up to 1000W are only as big as VHS video tapes. This type of amplifier is not suitable for use as a wide-band amplifier, but it has more applications in active subwoofer speakers.

5. Class G power amplifier
Class G power amplifier is an improved form of multi-power class AB power amplifier. Class G power amplifiers take full advantage of the advantageous condition that audio has a very high crest factor (10-20dB). Most of the time, the audio signal is at a lower amplitude, and very few times will show a higher peak. The following figure is a typical functional block diagram of the integrated ic of the G class power amplifier.

Class G amplifiers use adaptive power rails and use a built-in buck converter to generate the positive power supply voltage of the headphone amplifier. The charge pump reverses 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 be concentrated at 0V. When the audio signal amplitude is low, the buck converter generates a low amplifier negative supply voltage. This minimizes the power consumption of the Class G amplifier while playing low-noise, high-fidelity audio. Compared with the traditional Class AB headphone amplifier, the Class G amplifier has higher efficiency.

The amplification principle of this type of power amplifier is the same as that of the AB power amplifier. An important feature is that the power supply part uses two or more sets of voltages, low power operation uses low voltage, and high power automatically switches to high voltage.

6. Class H power amplifier
The amplifying circuit part of this type of power amplifier has the same principle as the AB power amplifier, but the power supply part adopts a switching power supply that can adjust multi-level output voltage, and automatically detects the output power to select the power supply voltage.

7. Class K power amplifier
Class K power amplifier integrates an internal bootstrap boost circuit and various power amplifier circuits. Everyone knows that Class D power amplifier is just one of the more efficient digital power amplifiers among many power amplifier circuits, and Class K power amplifiers are only integrated internally according to needs. For the bootstrap booster circuit and the required power amplifier circuit, if high efficiency is required, add a class D amplifier, and if the sound quality is good, add a class AB amplifier.

8. Class T power amplifier
The principle of this type of power amplifier is the same as that of the Class D power amplifier, but the signal part uses DDP technology (the core is the small signal adaptation algorithm and prediction algorithm). The working principle is as follows: the current that the audio signal enters the speaker is all processed by the DDP, and then the high-power high-frequency transistor is controlled to be turned on or off, so as to achieve the high-fidelity linear amplification of the audio signal. This type of power amplifier has high efficiency, low distortion, and sound quality comparable to class AB power amplifiers.

9. TD class power amplifier
The amplification part of this type of audio power amplifier has the same principle as the AB power amplifier, but the power supply part adopts a completely independent high-precision adjustable stepless output adjustable digital power supply, the voltage progression value is 0.1V, and the power is automatically detected to adjust the voltage rise. High or low. Because this type of power amplifier requires a high-precision and adjustable digital power supply, it needs a special design for the power supply and cannot be concentrated on one chip. Therefore, this type of power amplifier is mainly used for high-end audio, and the circuit is more complicated.

A special power supply is required for the following categories 6, 7, and 9 power amplifiers, so the functions cannot be concentrated on one IC. There are special ICs for the classic Class A, Class B, Class AB and Class D power amplifiers. In the actual design, various types of power amplifier circuits used in different fields are needed, and only need to be based on this, plus the corresponding power supply or processing module.

Ultra-high-power products generally use a technique of sampling and comparing according to the characteristics of the audio signal, and controlling the power supply voltage in stages, and it is also done by using an independent power supply. Compared with the AB class, it can increase the efficiency of the whole machine by up to 25%, but because of the power supply It is divided and switched, which brings unavoidable shortcomings.

For example, higher requirements are put forward for the consistency of filter capacitors. When capacitors are used in series, their capacity will also be reduced, the filtering effect is not ideal, and their durability and stability will also be reduced. And because of the use of multi-level switching power supply, it also brings its unique distortion-switching distortion. Reflected in the performance of the sound quality, the high frequency band presents a bad feeling of looseness, noise, and ears. The low frequencies also appear harder and thinner. Because of the characteristics of its power supply structure, this limits the power consumption of the power tube without good protection measures, and it will also cause tube burning and other phenomena to occur from time to time.