Do you know the difference between Class A, Class B, Class AB, Class D, and Class D power amplifiers? First, according to the different amplification types of the power amplifier, it can be divided into: Class A (Class A is also called Class A), Class B (Class B is also called Class B), Class AB (Class AB is also called Class A and B), Class D (Class D is also called Class A) Called digital class). () The above are all common power amplifiers in cars. 1. Pure Class A power amplifier Pure Class A power amplifier is also called Class A power amplifier (Class A), which is a completely linear amplifier. When a pure Class A power amplifier is working, the positive and negative channels of the transistor are always open regardless of whether there is a signal or not, which means that more power is consumed as heat, but the distortion rate is extremely low. Pure Class A power amplifiers are relatively rare in the application of car audio, such as Italy's Sinfoni advanced series only have such power amplifiers. This is because the efficiency of pure Class A power amplifiers is very low, usually only 20-30%, but audio enthusiasts talk about its sound performance. 2. Class B power amplifier Class B power amplifier, also called Class B power amplifier (Class B), it is also called linear amplifier, but its working principle is completely different from pure Class A power amplifier. When the Class B power amplifier is working, the positive and negative channels of the transistor are usually closed unless there is a signal input, that is, when the positive phase signal comes, only the positive phase channel works, and the negative phase channel is closed, and the two channels are absolutely closed. It will not work at the same time, so there is no power loss in the part where there is no signal. However, when the positive and negative channels are turned on and off, crossover distortion is often generated, especially at low levels, so the Class B power amplifier is not a true high-fidelity power amplifier. In actual applications, many early car audio amplifiers were actually Class B amplifiers because of their higher efficiency. 3. Class A and B power amplifier Class A and B power amplifiers are also called Class AB power amplifiers (Class AB), which is a design compatible with the advantages of Class A and Class B power amplifiers. When there is no signal or the signal is very small, the positive and negative channels of the transistor are always open. At this time, the power is lost, but it is not as serious as the Class A amplifier. When the signal is in positive phase, the negative phase channel is normally open before the signal becomes stronger, but the negative channel is closed when the signal becomes stronger. When the signal is negative, the positive and negative channels work just the opposite. The disadvantage of class AB power amplifier is that it will produce a little crossover distortion, but relative to its efficiency ratio and fidelity, it is better than class A and class B power amplifiers. Class AB power amplifier is currently the most used in car audio Extensive design. The difference and application of ab class power amplifier class AB class D class power amplifier 4. Class D power amplifier The Class D amplifier is different from the above-mentioned Class A, B or AB amplifiers. Its working principle is based on a switching transistor, which can be completely turned on or completely turned off in a very short time. The two transistors will not turn on at the same time, so little heat is generated. This type of amplifier has extremely high efficiency (about 90%), which can reach 100% under ideal conditions, compared to 78.5% for class AB amplifiers. On the other hand, the switching mode also increases the distortion of the output signal. The circuit of the class D amplifier is divided into three stages: input switch stage, power amplifier stage and output filter stage. Class D amplifiers can use pulse width modulation (PWM) mode when operating in the on-off state. Use PWM to convert the audio input signal into a high-frequency switching signal, and compare the audio signal with a high-frequency triangle wave through a comparator. When the voltage at the inverting terminal is higher than the voltage at the non-inverting terminal, the output is low; when the inverting terminal When the voltage is lower than the voltage of the non-inverting terminal, the output is high. In a class D amplifier, the output of the comparator is connected to the power amplifier circuit, and the power amplifier circuit uses metal oxide field effect transistors (MOSFET) instead of bipolar transistors (BJT). This is because the former has a faster response time, so it is suitable In high-frequency working mode. Class D amplifiers require two MOSFETs, which can be completely turned on or off in a very short time. When a MOSFET is fully turned on, its tube voltage drop is very low; and when the MOSFET is fully turned off, the current through the tube is zero. The switching speed of the two MOSFETs alternately working in the on and off states is very fast, so the efficiency is extremely high, and the heat generated is very low, so the class D amplifier does not require a large heat sink. There are many other names for class D power amplifiers, such as class T, etc., which are all variants of class D power amplifiers. In practical applications, it was not until 1980 that this switching power amplifier was able to develop rapidly due to the emergence of MOSFETs. In the actual development process, although there is high efficiency, there are also high distortion, high noise and poor damping factors. With the development of technology, such defects will become less and less, and it is estimated that class D power will be more widely used in the field of car audio in the future. Here, we will introduce the operation mode and characteristics of these power amplifiers one by one according to the common so-called class A, class AB, and class D power amplifier classification methods. Type A: Sound is a waveform signal, so the amplifier amplifies the sound signal, which is equivalent to increasing the amplitude of the waveform. In Class A power amplifier, as long as the power is turned on, each amplifying component will maintain sufficient power supply at any time to amplify each complete sound waveform. Therefore, the sound of Class A power amplifier is sweet, natural and photogenic, which is not groundless! However, even when there is no signal input, A Class amplifier components still maintain high power consumption. A lot of power will be converted into heat and wasted. Therefore, the power consumption, low output power, and high operating temperature are all its shortcomings. , It’s a bit unwise to use it to listen to the sound quality very suitable, and to drive the subwoofer that requires high power. Class AB: Class AB power amplifier divides the amplifying component into two parts, one amplifies the sine wave of the sound signal waveform, and the other class ab power amplifier. Amplify the negative sine wave, and when the amplifying component that amplifies the sine wave is working hard, the other half of the amplifying component responsible for amplifying the negative sine wave can only use a small amount of standby current to rest, and vice versa. Therefore, the AB Class power consumption, The performance of output power is much better than that of A Class. However, Class AB power amplifiers will face the problem of combining sine waves and negative sine waves of sound signals. Products that are not handled well may have "crossover distortion" and reduced sound quality. Fortunately, today's car audio power amplifier manufacturing technology is very advanced, and the technology to avoid crossover distortion has become a basic condition, so that class AB power amplifiers have satisfactory performance in sound quality and power output! Class D: Class D power amplifier uses a "switching amplification" method of operation, that is, it controls the power output on and off at a speed that is at least twice higher than the frequency of the sound signal. Therefore, the D Class power amplifier consumes electricity. The amount is very small, almost 90% of the electric energy can be used to drive the power of the speaker, which is suitable for driving the subwoofer system that requires high power. However, due to the amplification principle of the on and off of the Class D power amplifier, it is inevitable that the sound will be rough at high frequencies. It is not conducive to the sound quality performance when used to push the middle and tweeters. In addition to class A, class AB, and class D power amplifiers, there are actually class B, class T, and class G power amplifiers with operating principles, but they are quite rare in car audio, so I won't introduce more here! Regular GFCI Receptacle Outlet Lishui Trimone Electrical Technology Co., Ltd , https://www.3gracegfci.com
The difference and application of AB class D power amplifier