Class AB amplifiers are actually a combination of Class A (Class A) and Class B (Class B). The on-time of each device is between 50 and 100%, depending on the magnitude of the bias current and the output level. The bias of this type of amplifier is designed in Class B (Class B) and then the bias current is increased to allow the amplifier to enter Class AB (Class A). Class AB operation is usually carried out by two transistors. When there is no signal, both transistors are turned on, but the current is small. When there is signal input, the current in the transistor will become larger. When one of the transistors is turned off due to the action of the signal, the other transistor must be turned on. The two tubes are always turned off and on, and the current flowing through them is almost all sent to the speaker. The Class A and Class B power amplifiers generate less heat and are much more efficient, at more than 70%. When the output of Class AB (Class A) amplifier is below a certain level, both output devices are turned on, and the state works in Class A (Class A); when the level is increased, the two devices will be completely cut off, and the other device will be completely cut off. One device will supply more current. Thus, at the beginning of the AB (Class A) state, the distortion will suddenly rise, and its linearity is inferior to Class A (Class A) or Class B (Class B). Its proper use is that it complements Class A (Class A) and continues to work well when faced with low load impedance. Class AB power amplifiers (Class AB) have also become Class A and Class B power amplifiers. It is a design that is compatible with Class A and Class B amplifiers. When there is no signal or the signal is very small, the positive and negative channels of the transistor are always open, and the power is lost, but there is no serious class A power amplifier. When the signal is positive, the negative phase channel is normally open before the signal becomes strong, but the signal is strong and the negative channel is closed. When the signal is a negative phase, the positive and negative channels work just the opposite. Class AB power amplifier circuit diagram Class D amplifiers refer to Class D audio power amplifiers (sometimes referred to as digital power amplifiers). By controlling the ON/OFF of the switching unit, the amplifier that drives the speaker is called a Class D amplifier. Class D amplifiers were first proposed in 1958 and have become popular in recent years. It has been published for many years, compared with the general linear class AB power amplifier circuit, Class D power amplifier has high efficiency and small size. Class D power amplifiers are an amplification mode in which the amplifying element is in the operating state of the switch. When there is no signal input, the amplifier is in the off state and does not consume power. In operation, the transistor is brought into saturation by the input signal, and the transistor is equivalent to an on-switch, which directly connects the power supply to the load. An ideal transistor consumes no power because it has no saturation voltage drop. In fact, the transistor always has a small saturation voltage drop and consumes some of the power. This power consumption is only related to the characteristics of the tube, and is independent of the size of the signal output, so it is particularly advantageous for ultra-high power applications. In an ideal situation, the efficiency of the Class D amplifier is 100%, the efficiency of the Class B amplifier is 78.5%, and the efficiency of the Class A amplifier is 50% or 25% (depending on the load mode). Class D amplifiers actually have a switching function, and were only used in switching control circuits for actuators such as relays and motors. However, the switching function (that is, the function of generating digital signals) has been increasingly developed with the development of digital audio technology, and the road of amplification with Hi-Fi audio has become increasingly smooth. In the 1960s, designers began to study Class A amplifiers for audio amplification. In the 1970s, Bose began producing Class D car amplifiers. On the one hand, automotive battery power supply requires higher efficiency. On the other hand, space is small and cannot be placed in a power amplifier with a large heat sink structure. Both of them hope to have such an efficient amplifier as Class D to amplify the audio signal. One of the key steps is the modulation of the audio signal. 1. As a power amplifier, the efficiency of the power directly affects the heat sink volume of the power supply and the power amplifier stage. Class D power amplifiers are very efficient, can reach more than 90%, and the heat is very small when working, and the efficiency of class AB power amplifiers is only 60%. In the case of outputting the same power, the heat of class D power amplifiers is only class AB power amplifiers. The calorific value is about 25%, and the power consumption is only about 60% of the AB category. Therefore, the power supply device cost of the D-type power amplifier will be greatly reduced, and at the same time, the cost of the heat sink and the power amplifier heat sink of the power supply device and the space cost of the circuit board will be greatly reduced. 2. Because Class D power amplifier has high working efficiency, its sound quality can be compared with Class A power amplifier (tone warm), but AB power is easy to appear crossover distortion when it is small signal, and it is easy to heat when power is large, so the sound quality is relatively high. difference. Compared with Class AB amplifiers, Class D amplifiers are not only powerful but also highly efficient. More importantly, the distortion rate is low and the sound quality is outstanding. Wuxi Doton Power , https://www.dotonpower.com
Ab class amplifier