The basic circuit of "digital power amplifier" is the already existing class D amplifier (domestic called a classifier amplifier). Previously, due to price and technical reasons, this amplifier circuit was only used in laboratory or high-priced test instruments. The technological developments of the past few years have integrated the components of digital power amplifiers into one or two chips, and the price has been declining. The theory proves that Class D amplifiers can achieve 100% efficiency. However, the ideal switching element has not been found so far, and it is inevitable that a part of the power loss will occur, and if the device used is defective, the loss will be larger. But in any case, its amplification efficiency is still more than 90%.
Due to power consumption and volume advantages, digital power amplifiers are first used in energy-limited car audio and demanding subwoofer active speakers. With the rapid development of consumer products such as DVD home theaters, mini-audio systems, set-top boxes, personal computers, LCD TVs, flat panel displays and mobile phones, especially the emergence of new high-sampling specifications such as SACD and DVDAudio, and audio The evolution of the system from stereo to multi-channel surround systems has accelerated the development of digital amplifiers. In recent years, the price of digital power amplifiers has been declining, and patents in this area are also emerging.
Class D output power and power consumption and class AB power amplifier consumption ratio A low frequency audio signal is used to modulate a pulse width of a fixed high frequency frequency. It is called a class D amplifier and is also known as a digital audio amplifier. It is extremely efficient (in theory, it can reach 100%, actually more than 85%), and it can produce a very powerful audio amplifier with very small electronic devices.
For a low-power, 1W-3W power amplifier, the power efficiencies of class AB power amplifiers and class D power amplifiers are approximately AB = 15% and D = 75% under the same conditions of playback. In the case of playing 1W music, Class AB power amplifiers consume 6.7W of power, but Class D power amplifiers consume only 1.33W under the same playback conditions. Therefore, the use of Class D power amplifiers can extend battery life by up to 5 times (6.7W/1.33W). In addition to mobile phones, DVD, MP3 and PMP have some popular products such as iPods, mobile phones, and digital photo frames. In the case of medium power, that is, the power amplifier of 10W-30W, the power efficiency of the class AB power amplifier and the class D power amplifier is AB=25% and D=80, respectively, under the condition that the same playing content is mainly voice. %. In the case of playing 10W voice, Class AB power amplifiers need to lose 40W of power, but Class D power amplifiers only consume 12.5Watts under the same conditions. Therefore, the use of Class D power amplifiers can reduce the cost of power supplies by nearly three times (40W / 12.5W), and the 2.5W of heat generated by Class D power amplifiers can be handled by general power packages and PCB designs without the need for additional heat sinks. In the case of high-power output, the 100W-200W class D digital power amplifier will also have a place in the car audio. Under this high power, the class D power amplifier still inevitably uses the heat sink, but the heat dissipation area and heat dissipation ratio AB The class power amplifier needs to be small. Due to high efficiency, the class D power amplifier can have a long service life without starting the car engine without consuming too much battery power. The class D power amplifier becomes the current car. The main application of audio.
Mr. Laojiao of the electronic production network believes that due to the maturity of the Class D digital audio amplifier technology, it is planned to design some representative D-class digital audio amplifier circuits and amplifier-specific audio power for learning and production for a period of time.
Power Supply Cost and Heat Dissipation Cost Advantages of Class D Digital Audio Power Amplifiers When calculating power, manufacturers do not use sound content as a standard, but extend the traditional sine wave signal as input. For sinusoidal signals, the power efficiencies of Class AB power amplifiers and Class D power amplifiers are approximately 45% and 80%, respectively. If the total supply power of the Class D power amplifier is about 30W/80%=37.5W with 15W×2, the total power supply of the Class AB power amplifier is about 30W/45%=66.7W, so the Class D power amplifier can be used. Save nearly 30W of power. Since the power supply of the power amplifier is provided by the power supply device, the power supply device cost of the class D power amplifier is greatly reduced. At the same time, the cost of the heat sink and power amplifier heat sink of the power device and the cost of the circuit space are greatly reduced. Home theater network shopping guide network welcomes you!
Because digital amplifiers work completely differently from traditional analog amplifiers, they overcome some of the inherent shortcomings of analog amplifiers and have some unique features.
1. Overload capability and power reserve
The overload capability of digital power amplifier circuits is much higher than that of analog power amplifiers. The analog power amplifier circuit is divided into Class A, Class B or Class AB power amplifier circuits. When working normally, the power amplifier tube works in the linear region; when overloaded, the power amplifier tube works in the saturation region, harmonic distortion occurs, and the degree of distortion increases exponentially. The sound quality is rapidly deteriorating. The digital power is always in the saturation zone and the cut-off zone when the power is amplified. As long as the power amplifier tube is not damaged, the distortion will not increase rapidly, as shown in Figure 1.
Figure 1 Comparison of overload distortion between full digital power amplifier and ordinary power amplifier
Since the digital power amplifier adopts a switching amplifier circuit, the efficiency is extremely high, up to 75%~90% (the analog power amplifier efficiency is only 30%~50%), and basically does not generate heat during work. Therefore, it does not simulate the quiescent current consumption of the power amplifier. All the energy is almost reserved for the audio output. After adding the analog amplification without negative feedback, it has better "power" characteristics, and the transient response is good. Feeling is extremely strong.
2. Crossover distortion and mismatch distortion
Analog Class B power amplifiers are placed in zero-crossing distortion, which is due to the nonlinearity of the transistor at low currents. The distortion at the positive and negative intersections of the output waveform (the transistor will operate in the cut-off region for small signals, no current will pass, resulting in output Severe distortion). The digital amplifier only works in the switching state and does not generate crossover distortion.
The analog power amplifier has a mismatched distortion of the output waveform due to the inconsistent push-pull characteristics of the tube. Therefore, when designing the push-pull amplifier circuit, the requirements for the power amplifier tube are very strict. The digital power amplifier has no special requirements for the pairing of the switch tube, and basically does not need to be strictly selected to be used.
3. Matching of the amplifier and the speaker
Since the internal resistance of the power amplifier tube in the analog power amplifier is large, when the speakers with different resistance values ​​are matched, the working state of the analog power amplifier circuit is affected by the size of the load (speaker). The internal resistance of the digital power amplifier does not exceed 0.2 Ω (the internal resistance of the switch tube plus the internal resistance of the filter), and the resistance value (4~8 Ω) relative to the load (speaker) is completely negligible, so there is no matching problem with the speaker.
4. Transient intermodulation distortion
The analog power amplifier uses almost all negative feedback circuits to ensure its electroacoustic index. In the negative feedback circuit, in order to suppress parasitic oscillation, a phase compensation circuit is used, which will generate transient intermodulation distortion. The digital power amplifier does not use any analog amplification feedback circuit for power conversion, thus avoiding transient intermodulation distortion.
5. Sound image localization
For analog power amplifiers, there is generally a phase difference between the output signal and the input signal, and the phase distortion is different when the output power is different. The digital power amplifier uses digital signal amplification to make the output signal and the input signal phase exactly the same, and the phase shift is zero, so the sound image is positioned accurately.
6. Upgrade
The digital amplifier can achieve high power by simply replacing the switch amplification module. The high-power switch amplification module has a low cost and has broad prospects in the professional field.
7. Production debugging
Analog power amplifiers have debugging problems at all levels of work, which is not conducive to mass production. The digital power amplification part is a digital circuit, and generally works normally without debugging, and is particularly suitable for mass production.
Third, the difference between digital power amplifier and "digital" power amplifier, "digital" power amplifier
The so-called "digital" power amplifier only uses digital signal processing in the pre-stage. After the analog audio signal or digital audio signal is input, the existing digital audio processing integrated circuit is used to realize some sound field processing, digital delay, Reverb and other functions, and finally through the analog power amplifier module for audio amplification. Its typical circuit block diagram is shown in Figure 2. As can be seen from Figure 2, the interfaces of each module are in analog mode. The schematic block diagram of the digital sound field processing module is shown in Figure 3.
Although various integrated circuit manufacturers have introduced digital sound field processing, digital karaoke and digital Dolby decoding integrated circuits. However, since the current power amplification can only receive analog audio signals, the interfaces of the integrated circuits are mostly analog, which requires repeated analog-to-digital and digital-to-analog conversion, thereby introducing quantization noise and deteriorating the sound quality.
In addition to the interface for the speaker (this is because the speaker can only accept analog audio signals), the audio signal is processed by digital signals (including power amplification) inside the amplifier; for analog audio signals, it must be It can only be processed after being converted into a digital signal.
The introduction of digital power amplifiers in an era of digital audio will have a major impact on the development of sound technology.
Take a deep breath, close your eyes, the world has the freshest oxygen ... Yu Quan's "Deep Breath" is well known to us, but as the environmental problems become more and more serious, the haze sky also increases, PM2.5 PM10 and so on Vocabulary has also been mentioned more and more, and air purifiers have quickly become popular on the market with this "air quality" trend. Along with this, the air-clean brand has sprung up, and various technologies are dazzling. Which ones are indeed effective and which are just tasteless propaganda? How does the Air Purifier bother us to get rid of pollution? And look at the editors for you.
Analysis of air purifier
The critical value of PM2.5 content is 75 μg / m3
The pollutants in the air mainly include soot, total suspended particulates, inhalable particulates (PM2.5) and fine particulates (PM10). The smaller the diameter of the particulates, the deeper the part that can enter the respiratory tract. 10 micron diameter particles It is deposited in the upper respiratory tract, and particles below 2 microns can penetrate 100% into the bronchiole and alveoli.
1k-5k air purifier prices vary greatly
The air purifier products on the market not only have various functions, but also have prices ranging from thousand yuan to tens of thousands. The pricing of imported products is generally higher than that of domestic brands. Except for the core technology of many brands, the promotion of purification effects is similar, and consumers need to choose according to demand.
The air quality standard of 74 key cities is only 4.1%
According to the data of the press conference held by the State Council Information Office on June 4, according to the new "Ambient Air Quality Standards", the six pollutants SO2, NO2, PM10, PM2.5, CO and O3 were evaluated, 74 new standards In the first phase of monitoring and implementation, the proportion of cities that met the ambient air quality standards was only 4.1%, and the other 256 cities implemented the old air quality standards, and the proportion of cities that met the standards was 69.5%.
Air purifier sales increased by 90.5% compared with last year
According to a report recently released by the China Electronics and Information Industry Development Institute, due to the haze weather, air purifiers have become the most concerned home appliance products, with sales of nearly 2.4 million units nationwide last year, a year-on-year increase of 90.5%; retail The amount reached 5.6 billion yuan, a year-on-year increase of 105.9%.
HEPA filter needs to be replaced in March
The filter of the air purifier Air Cleaner is the same as the filter of the water purifier, and it is not effective for a long time. After long-term use, the accumulation of dust on the surface of the filter will also cause the filter to gradually fail. Therefore, when the haze is more serious, the non-washable HEPA filter needs to be replaced every three months.
Merchants claim that the purification rate is more than 99% for the concept of stealing
99% or even 99.99% seems to have become a slogan for many air purifiers on the market. Many brands of products promote their high removal rate of PM2.5 and formaldehyde. In fact, this kind of publicity is more of a kind. The slogan of stealing the concept, the removal rate of 99% is the effect of the material itself on PM2.5 and formaldehyde, not the effect of actually running in space.
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