Q1: How to evaluate the power requirements of a system
Answer: For an actual electronic system, carefully analyze its power requirements. Not only care about the input voltage, output voltage and current, but also carefully consider the total power consumption, the efficiency of the power supply, the transient response of the power supply to the load change, the tolerance of the critical components to the power supply fluctuations, and the corresponding allowable Power ripple, heat dissipation issues, and more. Power consumption and efficiency are closely related, and the efficiency is high. The total power consumption is small under the same load power consumption. It is very beneficial to the power budget of the whole system. Compared with LDO and switching power supply, the switching power supply is more efficient. some. At the same time, the efficiency of the evaluation is not only to look at the efficiency of the power circuit at full load, but also to consider the efficiency level at light loads.
As for the load transient response capability, there are strict requirements for some high-performance CPU applications, because when the CPU suddenly starts running heavy tasks, the required starting current is very large, if the power circuit response speed is not enough, causing an instant The voltage drops too much and too low, causing the CPU to run incorrectly.
In general, the actual value of the required power supply is mostly +-5% of the nominal value, so the allowed power supply ripple can be calculated accordingly, of course, the margin must be reserved.
The heat dissipation problem is important for high-current power supplies and LDOs, and calculations can also be evaluated for suitability.
Q2: How to choose the right power supply implementation circuit
Answer: According to the specific technical indicators obtained by analyzing the system requirements, you can choose the appropriate power supply implementation circuit. Generally for the weak current part, including LDO (linear power converter), switching power supply capacitor buck converter and switching power supply inductor-capacitor converter. In contrast, the LDO design is the easiest to implement, and the output ripple is small, but the disadvantage is that the efficiency may not be high, the heat is large, and the current that can be supplied is not much larger than that of the switching power supply. The switching power supply circuit is flexible in design and high in efficiency, but the ripple is large, the implementation is complicated, and the debugging is cumbersome.
Q3: How to choose the right components and parameters for the switching power supply circuit
Answer: Many engineers who have not used switching power supply design will have certain fears, such as concerns about switching power supply interference, PCB layout problems, component parameters and type selection issues. In fact, as long as you understand, using a switching power supply design is very convenient.
A switching power supply generally consists of a switching power supply controller and an output. Some controllers integrate the MOSFET into the chip, which makes it easier to use and simplifies PCB design, but the design flexibility is reduced.
The switch controller is basically a closed-loop feedback control system, so there is generally a sampling circuit that feeds back the output voltage and a control loop for the feedback loop. Therefore, this part of the design is to ensure accurate sampling circuit, and to control the feedback depth, because if the feedback loop response is too slow, there will be a lot of impact on the transient response capability.
The output part design includes output capacitors, output inductors, MOSFETs, etc. These choices are basically to balance a performance and cost, such as high switching frequency can use small inductance values ​​(meaning small package and Cheaper cost), but high switching frequency increases interference and switching losses to the MOSFET, resulting in reduced efficiency. The result of using a low switching frequency is the opposite.
The ESR of the output capacitor and the Rds_on parameter selection of the MOSFET are also critical. A small ESR can reduce the output ripple, but the cost of the capacitor will increase, and a good capacitor will be expensive. Switching power supply controller drive capability should also be noted that too many MOSFETs cannot be driven well.
In general, the supplier of the switching power supply controller will provide specific calculation formulas and usage plans for engineers to learn from.
Q4: How to debug the switching power supply circuit
Answer: Some experience can be shared with everyone
1: The output of the power circuit is connected to the board through a low-resistance high-power resistor, so that in the case of no soldering resistor, the power circuit can be debugged first, avoiding the influence of the latter circuit.
2: Generally speaking, the switch controller is a closed-loop system. If the output deteriorates beyond the range that the closed-loop can control, the switching power supply will not work properly. Therefore, the feedback and sampling circuits need to be carefully checked. In particular, if a large ESR output capacitor is used, a lot of power supply ripple will occur, which will also affect the operation of the switching power supply.
Discussion of grounding technology
Q1: Why should I ground?
Answer: The introduction of grounding technology was originally designed to prevent lightning strikes on equipment such as electricity or electronics. The purpose is to introduce lightning strike current generated by lightning into the earth through a lightning rod to protect the building. At the same time, grounding is also an effective means to protect personal safety. When the phase line caused by some reason (such as poor wire insulation, aging of the line, etc.) and the equipment casing touch, the equipment's outer casing will have dangerous voltage. The generated fault current flows through the PE line to the ground for protection. With the development of electronic communication and other digital fields, it is far from satisfactory to consider only lightning protection and safety in the grounding system. For example, in a communication system, the interconnection of signals between a large number of devices requires that each device have a reference 'ground' as a reference ground for the signal. Moreover, with the complication of electronic devices, the signal frequency is getting higher and higher. Therefore, in the grounding design, electromagnetic compatibility problems such as mutual interference between signals must be given special attention. Otherwise, improper grounding will seriously affect the reliability of the system operation. Sex and stability. Recently, the concept of "ground" has also been introduced in the signal reflow technique of high-speed signals.
Q2: Definition of grounding
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