A, B, C, D four types of power amplifiers are different
Amplifiers can be divided into Class A power amplifiers (also known as Class A), Class B power amplifiers (also known as Class B), Class A power amplifiers (also known as Class AB), Class D power amplifiers (also known as Class D), and so on. What are the characteristics? The four types of power amplifiers A, B, C, and D each have different working principles. 1. Class A power amplifier (also known as class A power amplifier) Two (or two) transistors in the output stage of a class A power amplifier are always in a conductive state, that is to say, they keep conducting current regardless of whether there is a signal input or not, and make these two currents equal to the peak value of the alternating current. In case of load. When there is no signal, the two transistors each pass the same amount of current, so there is no unbalanced current or voltage at the output center point, so no current is input to the speaker. When the signal goes to the positive side, the output transistor above the line allows more current to flow, while the output transistor below decreases the current relatively. Because the current starts to unbalance, it flows into the speaker and pushes the speaker to make a sound. The working method of Class A power amplifier has the best linearity. Each output transistor amplifies the full wave of the signal. There is no switching distortion at all. Even without negative feedback, its open-loop distortion is still very low. Known as the most ideal amplifier circuit design for sound. However, this design has advantages and disadvantages. The biggest disadvantage of Class A power amplifiers is their low efficiency, because when there is no signal, full current flows in, and all electrical energy is converted to high heat. As the signal level increases, some power can enter the load, but many still turn into heat. Class A amplifier is ideal for replaying music. It can provide very smooth sound quality, round and warm sound, transparent and open treble, these advantages are enough to compensate for its shortcomings. Class A power amplifiers have an amazing amount of heat. In order to effectively deal with heat dissipation, class A power amplifiers must use large radiators. Because of its low efficiency, the power supply must be able to provide sufficient current. A 25W Class A power amplifier is capable of at least 100 Watt Class AB power amplifiers. Therefore, the size and weight of the A-type machine are larger than the AB, which increases the manufacturing cost and the price is more expensive. Generally speaking, the price of a class A power amplifier is about twice or more than that of a class AB power amplifier of the same power. 2. Class B power amplifier (Class B power amplifier) The working mode of Class B amplifier is that when there is no signal input, the output transistor is not conductive, so it does not consume power. When there is a signal, each pair of output tubes amplifies half of the waveform, turns on and off each other to complete a full-wave amplification, and crossover distortion occurs when the two output transistors rotate, thus forming a non-linearity. Pure class B amplifiers are less, because the distortion is very serious when the signal is very low, so the crossover distortion makes the sound rough. Class B amplifiers have an average efficiency of about 75% and generate less heat than Class A machines, allowing smaller radiators to be used. 3.Class AB amplifier Compared with the first two types of power amplifiers, AB power amplifiers can be said to be a compromise in performance. Class AB amplifiers usually have two bias voltages, and a small amount of current flows through the output transistor when there is no signal. It uses the type A working mode when the signal is small, and obtains the best linearity. When the signal increases to a certain level, it automatically switches to the type B working mode to obtain higher efficiency. The class AB amplifier of 10 watts in a normal machine works within about 5 watts and works with class A. Since the power required to listen to music is only a few watts, the class AB amplifier uses the class A amplifier mode most of the time. Only when the transient strong sound changes to class B. This design is a very logical design to obtain excellent sound quality and improve efficiency and reduce heat. Some class AB amplifiers adjust the bias current so high that it can work as a class A in a wider power range, making the sound close to a pure class A machine, but the heat generated is also relatively increased. 4. Class C amplifier (Class C amplifier) This type of power amplifier is rarely heard because it is a very high distortion power amplifier that is only suitable for communication purposes. The output efficiency of the Class C machine is extremely high, but it is not suitable for HI-FI amplification. 5. Class D amplifier (Class D amplifier) This design is also called digital amplifier. Once the transistor of the Class D amplifier is turned on, the load is directly connected to the power supply. The current flows but the transistor has no voltage, so there is no power consumption. When the output transistor is turned off, all the power supply voltage appears on the transistor, but there is no current and therefore no power is consumed, so the theoretical efficiency is 100%. The advantages of class D amplifier amplification are the highest efficiency, the power supply can be reduced, and almost no heat is generated. Therefore, a large radiator is not required, the body size and weight are significantly reduced, and theoretically, the distortion is low and the linearity is good. However, this kind of power amplifier is complicated to work, and the added circuit itself is inevitable to have deviations, so there are very few successful products and the price is not cheap. There are some Class D amplifier integrated blocks with good sound quality, but they are currently only used in car audio, and some interested DIY masters have adapted them to home audio.