The classification and characteristics of power amplifier
1. Class A power amplifier (also known as Class A power amplifier) ??The two (or two groups) transistors in the output stage of Class A power amplifier are always in the conductive state, that is to say they maintain the conduction current regardless of whether there is signal input or not The current is equal to the peak value of the alternating current, and the alternating current flows into the load under the maximum signal condition. When there is no signal, the two transistors flow 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 tends to be positive, the output transistor above the line allows more current to flow, and the output transistor below lowers the current relatively. Because the current begins to be unbalanced, it flows into the speaker and pushes the speaker to sound. The working mode of Class A amplifier has the best linearity. Each output transistor amplifies the full wave of the signal, and there is no switching distortion at all. Even if negative feedback is not applied, its open-loop distortion is still very low, so It is said to be the most ideal amplifier circuit design for sound. However, this design has advantages and disadvantages. The biggest disadvantage of Class A amplifiers is low efficiency, because there is still full current flowing when there is no signal, and all the energy is converted to high heat. When 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 tone, transparent and high pitch, these advantages are enough to compensate its shortcomings. Class A power amplifiers generate amazing amounts 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 provide sufficient current. A 25W Class A amplifier power supply has a capacity of at least 100 watts Class AB amplifier. Therefore, the size and weight of the class A machine are larger than the class AB, which makes the manufacturing cost increase and the price is more expensive. Generally speaking, the selling price of Class A amplifier is about twice or more of the same power class AB amplifier. 2. Class B amplifier (Class B 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 in turn to complete a full-wave amplification, and crossover distortion occurs when the two output transistors work alternately, thus forming nonlinearity. Pure Class B amplifiers have less, because the distortion is very serious when the signal is very low, so the crossover distortion makes the sound rough. The efficiency of Class B amplifiers is about 75% on average, and the heat generated is lower than that of Class A machines, allowing the use of smaller radiators. 3. Compared with the first two types of power amplifiers, the AB power amplifier 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 A-type working mode when the signal is small to obtain the best linearity. When the signal increases to a certain level, it automatically switches to the B-type working mode to obtain higher efficiency. The 10 watt class AB amplifier of the ordinary machine works with class A within about 5 watts. Since the power required to listen to music is only a few watts, the class AB amplifier uses the class A amplifier working mode most of the time. It only changes to category B when there is a strong transient sound. This design can obtain excellent sound quality and improve efficiency to reduce heat, which is a quite logical design. Some Class AB amplifiers adjust the bias current so high that they work in 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 power amplifier (Class C power amplifier) ??This type of power amplifier is rarely heard, because it is a very high distortion power amplifier, which is only suitable for communication. The output efficiency of Class C 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. The transistor of the class D amplifier is connected to the load directly when it is turned on. 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, so no power is consumed, so the theoretical efficiency is 100%. The advantage of Class D amplifier is that it has the highest efficiency, the power supply can be reduced, and almost no heat is generated. Therefore, a large radiator is not needed, and the body volume and weight are significantly reduced.