Hardware power module design and considerations

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Hardware power module design and considerations [Copy link]

Recently, I have been studying embedded systems and found that I have many questions when I first started learning embedded systems. I think most of my friends who have not had much experience and have just entered the field of embedded systems will have the same questions as me. Therefore, I would like to write a series of articles here to share my questions and experiences in learning embedded systems. I hope that experts can point out the errors in the articles. I also welcome beginners like me to raise your questions and let us study and discuss together so that we can make progress together. Here, I will briefly introduce the design ideas of the power module of the embedded system. Generally, we first understand the voltage requirements of each module of the entire system. For example, the I/O module generally requires 3.3V power supply, the USB module generally requires 5V power supply, and some MCU main chips often require 1.2V or 1.8V power supply, etc. Then select the appropriate board inlet power supply voltage (the first part below mainly discusses the board inlet power supply voltage), and then select the relevant voltage regulator chip for voltage conversion and voltage regulation (the second part below describes how to choose the voltage regulator circuit) to obtain the voltage supply of each module of the board. So, how to choose the input power supply voltage of the board in embedded system design? 1. Choice of the input power supply voltage of the board Nowadays, the typical board power supply often first allows 220V AC to pass through a transformer, convert it to DC 12V or 5V and then connect it to the board. Of course, there are boards with other power supply voltages, and there are also designs that directly connect to 220V AC and convert it through the board's internal bridge circuit. Here we mainly discuss the choice of 12V power supply and 5V power supply, that is, is it appropriate to choose 12V or 5V? First, we need to analyze the total power consumption of the board we designed (by analyzing the datasheet of the relevant chips of each module, we can roughly estimate the total power consumption P of the entire system). Then, when the total power consumption P of the system is constant, the larger the power supply voltage U input to the board, the smaller the input current of the board, and the smaller the input current of the board, the more helpful it is for the stability of the board, especially the power module. Therefore, many boards with high power consumption are now designed to be powered by 12V, which is also the purpose. However, if the total power consumption P of the entire system is not large, it can be known from P = U * I that if a larger input voltage is used, the input current of the board will become smaller, so that the current may not meet the minimum input current requirement of the subsequent circuit. Therefore, the selection of the board input voltage needs to be carefully and comprehensively considered in order to achieve a relatively perfect effect. 2. Selection of voltage regulator circuit The voltage regulator circuit generally realizes two functions. One is to convert the voltage to obtain the various voltages required by the subsequent stage. The other function, as the name implies, is to stabilize the output voltage so that the voltage output by the power module to the subsequent stage remains relatively stable, so that the entire system can work stably. We know that there are two solutions for converting DC voltage. One is to use a switch regulator and the other is to use a linear regulator. The switch regulator has a larger output current and higher conversion efficiency, but it is also accompanied by a more complex conversion circuit and higher noise. The linear conversion device is just the opposite, with a simpler circuit and lower noise. Generally, linear converters are suitable for voltage conversions with small voltage differences, such as 5V to 3.3V, 3.3V to 1.8V, etc. This is because, for linear converters, the voltage difference that is reduced is mainly used for heating the resistor. If the voltage difference is relatively large, such as 12V to 5V, the 7V voltage difference is all consumed by the resistor to heat up. Not only is the circuit inefficient, but it will also generate a lot of heat, causing the circuit to be unstable or the related chip to be burned. So, what about the conversion of large voltage differences such as 12V to 5V? Of course, a switching voltage regulator is generally used. It has high conversion efficiency. Although it has relatively high noise, it can generally meet the system requirements after being filtered out by a special circuit. I will not go into details about the principle of the switching voltage regulator here. You can find relevant information on the Internet.