In recent years, portable multimedia players have become the main force driving the growth of consumer electronics. Although the growth rate of the global MP3 market has slowed down, MP3s that provide high-quality audio quality are still in consumers' hearts. This shows that consumers have changed from simply pursuing playback capabilities to pursuing high-quality experiences. This also poses new challenges for design engineers who develop portable multimedia players. In response to this trend, here, we will extract some wonderful views to benefit more engineers. 1. How to deal with input clipping? A design problem encountered by the engineer "Xiao Lai" is: At present, because of the need to adapt to different MP3s, the general design is to make the sensitivity higher, but in large songs output devices (such as IPOD), but in some songs The output current of the battery (the battery of Nokia 7210) will be too large due to the excessive signal. How to limit the input signal for this problem? In response to this problem, guest Kong Yixing suggested to solve it through two methods: 1. Add a resistor divider to limit the maximum input level, but he pointed out that this method is not good for the design of multiple input sources. 2. Add an AGC circuit to automatically adjust the input level. However, the engineer "Stone 3" questioned the method of increasing the AGC circuit. He pointed out: "When using ALC / AGC, care must be taken to set the control range and startup and recovery time. For music signals, I am not in favor of using ALC / AGC, because It will reduce the dynamic range of the music and change the original mood of the music. If possible, it is recommended to automatically set the attenuation of the digital potentiometer by detecting the maximum music amplitude, so that after a few "steps", the music can be original Replayed. But the change range must be as small as possible, so the first thing to do is to measure the sound source level extensively. "And emphasized:" Must not use the method of adjusting the battery protection current! This will cause broken sound. " The engineer "Zhu Yibo" said: "If you want to be compatible with most audio players, the best way is to do DC-DC to increase the Power Supply voltage of the amplifier, and then set the amplifier's gain to be large, so that no matter small or large signals, It can be restored very well without distortion. " Finally, "Xiao Lai" uses the method of AGC circuit, but the distortion is a bit large at the maximum volume, so the user has to adjust the volume down to complete the adjustment. Obviously, this solution is not perfect enough. Here, we also hope to have experience Engineers contribute better solutions. 2. Removal of noise in standby The problem encountered by the engineer's "three ears" is related to the TPA1517 audio power amplifier. He said that he always hears some noise every time when he exits from the standby mode. Should I remove such noise? In this regard, the guest pointed out: "There are many reasons for noise products, and it is recommended to solve this problem from three points: 1. Check the hardware design, which may be related to the PCB design and the ground. Bad design will cause capacitive coupling and feedback Send to the speaker. 2. The TPA1517 mixer should be turned off before power off. 3. Add a switch to isolate the speaker from the circuit. 3. How to start audio design? In fact, for many newcomers, they may only know to amplify a signal, but they face a series of problems in the specific design, such as how to get started with audio design and how to design? What key points should be paid attention to, etc. In response to this problem, many senior engineers have made valuable suggestions. The engineer "Zhao Yuzhong" proposed a five-step method for audio design: 1. First determine the voltage amplification factor, and then determine the current amplification Multiple, the output power requirements can be reached at the end; 2. Determine whether to design with discrete components or integrated circuits; 3. Consider input impedance matching and static operating points at all levels; 4. Plan for maximum distortion, flatness, and bandwidth; 5. Design the feedback circuit, output protection circuit and temperature protection circuit. The strategy of engineer Zhang Xufeng is simple and clear: 1. From the audio source to the audio output, the number of signal amplification stages is minimized. 2. The signal flow is from small to large, do not cross or flow backward, pay attention to grounding. 3. Use expensive devices. The engineer "Mr. Zhu" pointed out: "The design of the audio amplifier circuit is actually very simple. Basic knowledge of electronic technology is almost the same, but knowledge of electromagnetic compatibility is required to do well. If you want to achieve the ultimate, you need devices, Knowledge of materials, production processes, etc. "Therefore, a small design often incorporates a variety of engineers' knowledge and personal wisdom. To make a design perfect, you must master multi-disciplinary knowledge. Fourth, about the connection of speakers and microphones The problem encountered by engineer "joos" is about the connection of speakers and microphones, which requires differential input and output. Because the speaker and microphone are also two wires, how to connect the speaker and microphone? In this regard, the engineer "James Bai" pointed out: "The differential connection method here is that the N terminal / P terminal of the speaker and the microphone are respectively connected to the differential +/- of the two inputs or the +/- of the two outputs. The corresponding single-ended connection is that the P terminal is connected to one input or output, and N and the other input or output are grounded. As for the speaker and microphone, the matching of output power and impedance should be considered. " In the forum, engineers also discussed the isolation of left and right channels, the design of class E audio amplifier, etc. Interested friends can log on the media player website to obtain relevant information.
This kind of power supply is also called industrial
switching mode power supplies (SMPS) – It is a type of AC to DC, it
obtains energy from the power grid, a DC high voltage is obtained through high
voltage rectifier filtering, DC/DC converter obtains one or more stable DC
voltage at the output end, and the power can be produced from several watts to
several kilowatts for different occasions. The specifications of Switching Power Supply are various, the standard are
5V 12V 24V LED Power Supply, including single
output, dual output and triple output power supply. They are widely used for LED
strip, led module, led lamp and CCTV camera.
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