Class A amplifiers (class A amplifiers)
Class A amplifier output stage in the two group (or two) transistors in A conducting state forever, that is to say, no matter whether they all keep the conduction current signal input, and make the two peak current is equal to the alternating current (ac), the communication in the case of the maximum signal into the load. When no signal, two transistor each the same amount of current flow, so there is no imbalance in the center of the output current or voltage, therefore, no current input. When the signal to the anode, the line at the top of the output transistor allowed into the more current, at the bottom of the output transistor is relatively reduced current, due to the unbalanced current start, then flows into the speaker and speaker voice.
Pure class a power amplifier in car audio applications are relatively rare. This is because the pure class a power amplifier efficiency is very low, usually only 20-30%, but the audio enthusiasts to its sound performance. The alarming calorific value, in order to effectively deal with the cooling problem, class A amplifier must adopt large radiator. Because of its low efficiency for electric equipment must be able to provide sufficient current. So the volume and weight of the class A machine than class AB, this let the manufacturing costs have gone up, price is more expensive. In general, the price is about the same power of the class-a power amplifier class AB borne power amplifier twice or more.
Sound is A class A power waveform signal, so the power amplifier amplified voice signal, also is to enhance the amplitude of the waveform. Simply does not exist in the Distortion (Switching Distortion), even if they don't use of negative feedback, its open loop Distortion is still very low, so is known as the ideal sound amplification circuit design. In class A amplifiers, as long as the communication power supply, after every amplifier components will keep the adequate power supply, to enlarge each full waveform, therefore, class A amplifier sweet voice, natural, photo, is not unfounded. However, due to class A amplifier even when no signal input, amplification components also remain high power consumption state, many electric power would be converted into heat energy wasted, so fierce, low output power consumption, high operation temperature, are its shortcomings, to enjoy the sound quality is very suitable for, to promote need high-power subwoofer can not wise. But class A power amplifier is the ideal choice of replay music, it can provide A very smooth timbre, tone and warm, high transparent, open these advantages to compensate its drawbacks.
Class B power amplifier (class B power amplifier)
Class B power amplifier, which is also known as linear amplifier, but it works with pure class A power amplifier is completely different. Class B power amplifier at work, plus or minus of the transistor channel is usually is in a state of closed unless there is a signal input, that is to say, in the positive phase signal came only work are interlinked, and negative mutually close, two channels will never work at the same time, so there is no signal, no power loss. But was closed in positive and negative channels open, often can produce cross distortion, the sound become coarse. Especially in the case of low level, so the class B power amplifier is not the true sense of hi-fi power amplifier. Class B power amplifier efficiency is about 75% on average, the heat generated by the relatively low class A machine, permitted use smaller radiators. In practical applications, in fact, many of the early car audio power amplifier is a class B amplifier, because its efficiency is higher.
Class AB amplifier (class AB amplifier)
New car, car stereo audio sound that compared with the former two types of power amplifier, it is compatible with the advantage of class A and class B amplifier of A design. Class AB amplifier has two bias, usually in the absence of signal also has a small amount of current through the output transistor. It in signal hours with A kind of work mode, get the best linear, when the signal to A certain electricity automatically converted to A class B at ordinary times working mode in order to obtain higher efficiency. PuTongJi 10 watts class AB amplifier about within 5 watts work with class A, because listening to music when the required only A few watts, so the class AB amplifier is to use most of the time in class A power amplifier working mode, only in the event of A music into A class B transient forte. This design can obtain excellent sound quality and improve efficiency to reduce quantity of heat, is a rather logical design. Some class AB amplifier dispatch deviation is very high, make it in A wide range of power with A kind of work, make the sound close to pure class A machine, but the heat generated by the relative increase.
Class AB amplifier is faced with the voice signal sine wave, the combination of negative wave problem, poor processing products could happen "in the distortion of the" but for its efficiency ratio and fidelity, are better than the class A and class B power amplifier, class AB amplifier is currently the most widely used in car audio design. Well today's car audio amplifiers are very advanced manufacturing technology, the technology to avoid the distortion has become a basic condition, let the class AB amplifier on the quality, the power output has a satisfactory performance! The current trend is more and more high class ab drift, in order to reduce low level signal distortion.
Class D power amplifier (D class amplifier)
Class D power amplifier is also called the digital power amplifier, the Angle of the design considerations and the class AB amplifier is completely different. The linear power amplifier tube have no too big significance, more important switch response and saturated pressure drop. Because of the power amplifier tube processing the pulse frequency is several dozen times the audio signal, and require good before and after the pulse along, so better switch response of the pipe. In addition, the efficiency of the whole machine depends on pipe saturated pressure drop caused by the loss. So, small saturated pressure drop tube not only high efficiency, power amplifier tube heat dissipation structure could be simplified. Several years ago, the high frequency power tube is expensive, to a certain extent, restrict the development of class D power amplifier. Now small current to control large current of MOSFET has been widely used in industrial field, especially in recent years the UHC MOSFET has been on the Hi - Fi amplifiers used, device barriers have been eliminated.
Class D amplifier with the A, B or class AB amplifier is different, its working principle is based on the switch transistor, it can be completely in A very short time conduction or completely stop. Not at the same time two transistor conduction, so the heat generated by the few. This type of amplifier efficiency is very high (about 90%), ideally can amount to 100%, compared with the class AB amplifier can only reach 78.5%. But on the other hand, the switch working mode also increased the distortion of the output signal. Class D amplifier road will be divided into 3: the input level switch, power amplifier and the output filter. Class D amplifier working in the condition of switch can be used in a pulse width modulation (PWM) mode. Using PWM to convert audio input signal to the high frequency switch signal, through a comparator will audio signal with high frequency triangular wave comparison, when the reverse voltage of the terminal voltage is higher than in phase, the output is low level; When reverse voltage of the terminal voltage is lower than the same phase, the output of high level.
Class D power amplifier and many other France, such as T, etc., they are a distortion of class D power amplifier. In practice, until 1980 years later, as a result of the MOSFET out of the field effect tube, this kind of switch type power amplifier to rapid development. In the actual development process, although there is a high efficiency, but also have high distortion, high noise and low damping factor. With the development of technology, this kind of defect will be less and less, the class D amplifier will get more extensive application in the field of car audio.
Class D power amplifier is to use a method of "switching amplification", which is faster than sound signal frequency at least more than twice the speed, power output on and off control, so the class D power amplifier consume electricity quantity is very less, almost more than 90% of the electricity can be used in the drive of power, used to drive need high-power subwoofer system perfect.
