Question and answer of speaker class D amplifier
What are the advantages of speaker Class D amplifiers?
The use of Class D switching amplifier circuit can significantly improve the efficiency of the power amplifier. The class D amplifier converts the audio signal into a high-frequency pulse whose width changes with the amplitude of the signal, controls the power tube to saturate on or off at the corresponding frequency, and the signal output by the power tube drives the speaker to sound through a low-pass filter. Because the power tube is in the saturated conduction and cut-off state most of the time, the power loss is very small, and its efficiency can reach more than 90%. A typical Class D amplifier can provide 200W output with an efficiency of 94% and harmonic distortion of 1% to 2.8%.
Since its introduction, Class D audio amplifiers have been widely concerned by designers for their high efficiency and small size. In recent years, with the price reduction and the audio quality comparable to Class AB audio amplifiers, in some popular consumer electronics fields, including households In the fields of cinema, DVD player, desktop audio, and portable multimedia, there is a tendency to gradually replace Class AB audio amplifiers, and has gained a lot of room for growth.
The fidelity of Class D amplifiers is not as good as linear amplifiers, but it can meet the requirements in many occasions. For example, car audio systems only require less than 2% distortion at low power output, less than 5% at full power output, and improved performance of Class D amplifier It will be improved. In addition, Class D amplifiers have no crossover distortion.
The concept of Class D switching amplifier originated 50 years ago, but because its operating frequency should be at least 4 to 5 times the upper limit frequency of the audio signal (20kHz), the circuits that used tubes and transistors in the early days could not be fully reflected in power and efficiency. Its superiority. In the 1980s, MOSFETs with satisfactory switching speed and conduction loss appeared. In recent years, integrated pre-driver circuits, such as Harris ’HIP4080, have emerged, which has promoted the practical development of Class D amplifiers. The MOSFETs used in Class D amplifiers are N-channel type, because the conduction loss of N-channel MOSFETs is only 1/3 of the corresponding specifications of P-channel MOSFETs.
Class D switching amplifier is composed of integrator, duty cycle modulator, switch driving circuit and output filter. Class D amplifier with half-bridge drive is adopted. It adopts fixed frequency duty cycle modulator and square wave output by power tube. The signal is mixed with the audio signal and sent to the integrator as a negative feedback signal. The integrator also has a filtering function, and the output correction signal is sent to the duty cycle modulator. The duty cycle modulator is composed of a comparator and a triangle wave generator. The correction signal is used to modulate the triangle wave to generate a modulated output, which promotes the power tube. Negative feedback should be taken before the low-pass filter, otherwise the filtered signal and the input signal have a phase difference (the second-order filter may cause a 180 ° phase difference), which may cause the circuit to self-excite, and complex phase compensation is required Circuit.
The modulation signal of the driving power tube is a square wave whose duty ratio changes with the audio input signal. The half-bridge driving circuit drives the two power tubes in opposite phases, one is turned on when the other is turned on. The use of square wave drive is to make the MOSFET change its working state as much as possible, reduce its time in the linear amplification region, thereby reducing heat loss and improving efficiency. The efficiency of this circuit mainly depends on the switching loss and conduction loss of the power tube. The output filter converts the square wave into an amplified audio signal, which pushes the speaker to sound.
What is the state of soft distortion?
Soft distortion means that the output of the power amplifier begins to suppress before it reaches saturation. In this way, the harmonic content at saturation can be reduced, and the class D amplifier has a similar phenomenon. The oscillation you see near saturation is essentially a combined frequency phenomenon. The actual frequency is far beyond 20KHz, and no oscillation noise will be emitted. The efficiency of Class D power amplifier is very high, and the effect of power supply voltage on efficiency is very limited. It is recommended to increase the working voltage to avoid the saturated output of the power amplifier to improve the sound quality when conditions permit.
How to choose the speaker class D amplifier and class G amplifier?
Class G power amplifier is a product between the class and Class D and Class AB. There is no way to get rid of Class AB working mode, but the power consumption is optimized from the power supply side. The power supply part is complicated, and the efficiency and damping coefficient are also much worse. From the perspective of indicators and actual performance; Class D amplifiers are much better, and Class G does not have any advantages.
What is the difference between Class D amplifier and Class AB amplifier?
Class D and class AB amplifiers, like switching regulators and linear regulators, have completely different operating modes. The efficiency of Class D amplifier is up to 94%.
What is the efficiency of Class D amplifier? How is power consumption calculated?
The loss of Class D power amplifier mainly comes from two aspects. On the one hand, its auxiliary circuit, internal audio signal processing and auxiliary circuit, etc., and a part of the power loss comes from the switch part, regardless of the size of the power amplifier, the difference between the auxiliary circuit It is not very large, mainly because the switching loss is quite different. In general, the power consumption of the analog circuit in the front stage is about one watt, the switching efficiency of the hardware in the rear stage is about 96%, and the power consumption calculation of the MOSFET is mainly It comes from the two parts of switching loss and on-state loss.
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