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　　The role of capacitor in 3.3v voltage stabilizing circuit Typical circuit diagram and analysis of 3.3v voltage stabilizing circuit

　　Generally speaking, the input capacitor of the 3.3V voltage stabilizing chip is for filtering, and the capacitor at the output is to prevent oscillation and degradation of voltage stabilizing performance. But this is really not so absolute. Nowadays, chip design is getting better and better, and the craftsmanship is getting more and more sophisticated. Some chips can work even without adding capacitors, and you will not find problems immediately. This is something I have done an experiment on. However, from practical application considerations, it is better to add a capacitor, insurance! There are already chips that can work stably with a 1uF capacitor and do not take up much circuit board area.

　　Typical circuit diagram and analysis of 3.3v voltage stabilizing circuit

　　The picture below is a typical schematic diagram of ASM1117-3.3V. Since I chose a four-pin schematic diagram, here is the typical circuit of the four-pin schematic diagram:

　　When I was drawing the circuit diagram of the SD card module today, I found that the working voltage of the SD card is 3.3V, so a voltage stabilizing chip is needed to convert the 5V power supply into a voltage of 3.3V, so I looked for a little information about the voltage stabilizing chip.

　　The voltage regulator chip we chose is ASM1117-3.3, packaged in SOT-223

　　However, we encountered some problems when drawing the schematic diagram. We found two schematic diagrams of the ASM1117-3.3V chip in the schematic library, which are:

　　The first one is four-pin, and the second one is three-pin. But after checking the package, the packages of both schematic diagrams are SOT-223, but the package of SOT-223 is four-pin. The question that bothers me is why. The three-pin schematic diagram can correspond to the four-pin package. This doubt was solved after reading the chip manual. It turns out that pins 2 and 4 of the chip are connected, so it doesn’t matter even if the three-pin schematic diagram corresponds to the four-pin package.

　　We also encountered a problem when drawing this circuit. The components at the inductor position between the network labels VDD3.3 and VCC3.3 were not determined at the beginning because we searched a lot of ASM1117-3.3 circuits and found that Some use inductors, and some use resistors. Later, after carefully reading the chip manual and asking teachers with relevant knowledge, I learned that the components at this position can be connected or not, and it will not have much impact on the circuit.

　　The following is an analysis of the circuit:

　　1. The function of D1 is to prevent reverse connection of the power supply.

　　2. C01 and C02 are power input filtering.

　　3. VDD3.3 is a 3.3V power supply for digital circuits.

　　4. L1 and L2 are isolation filter inductors.

　　5. VCC3.3 is a 3.3V power supply for analog circuits.

　　The advantage of separating the voltage regulator chip into a module is that when level conversion is required, all peripherals can be directly connected through the network label without having to draw the circuit again. This can not only save drawing time, but also save money. Cost of components.

　　In addition to the 3.3V voltage stabilizing chip, a 2.5V voltage stabilizing chip is also used in this project. The circuit connections are very similar, so I won’t go into details.

　　Technical Zone ams1117-3.3 Wiring Principle and How to Wire 3.3v Voltage Stabilizer Circuit Capacitor Function of 3.3v Voltage Stabilizer Circuit Typical Circuit Diagram and Analysis of 7805 Stabilized Power Supply How to 12V to 5V Circuit Diagram and Wiring Method Vicor DC-DC converter module adds 25 new products It can still work as low as -55°C. The advantages and disadvantages of the three contactless voltage regulators and the reliability of the "Pandeng" contactless voltage regulator.

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