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Report on the Competitiveness of Electronic Information Enterprises
Recently, the 2021 China Digital Enabling Economy Conference was held in Yantai. At the meeting, Gao Sumei, Secretary-General of China Electronic Information Industry Federation, released the "Report on the Competitiveness of Electronic Information Enterprises in 2021 and the List of Top 100 Enterprises". Among them, Huawei, Lenovo and Haier ranked the top three.
It is reported that the top 100 electronic enterprises present the following six characteristics:
First, the overall scale has been upgraded. In 2020, the main business income of the top 100 enterprises increased by 10.4% year-on-year, accounting for more than 40% of the income of the electronic information manufacturing industry above the scale, and the growth rate was 2.1 percentage points higher than the industry average. There are 13 companies whose main business income exceeds 100 billion yuan and 4 companies whose main business income exceeds 200 billion yuan. The highest main business income of the listed enterprises reached 800 billion yuan, and the entry threshold exceeded 5 billion yuan.
Second, the quality of benefits is outstanding. In 2020, the total profit of the top 100 enterprises increased by 21.2% year-on-year, accounting for more than 50% of the industry's profits, and the growth rate was 4 percentage points ahead of the industry; the average profit rate was 6.0%, 0.5 percentage points higher than the previous year, and 1.1 percentage points ahead of the average level of the industry.
Third, the ability to innovate has been enhanced. In 2020, the R & D investment of the top 100 enterprises increased by 17.8% year-on-year, exceeding the income growth rate of 7.4 percentage points in the same period, and the R & D investment intensity reached 6.3%. By 2020, the total number of patents was 530000, of which 380000 were invention patents, accounting for more than 70%. In 2020, the top 100 enterprises accounted for 30% of the top 20 enterprises in China's invention patent authorization.
Fourth, external demand is growing against the trend. In 2020, the export volume of the top 100 enterprises increased by 8.5% year-on-year, accounting for more than 20% of the total industry, and the growth rate was 2.2 percentage points ahead.
Fifth, technological breakthroughs have been accelerated. The top 100 enterprises have actively participated in major national strategic deployments, and in the field of satellite navigation systems, the localization rate of core components has reached 100%. In the field of display, the transformation fr0m "less screen" to "strong screen" has been realized. Emerging technologies such as flexible display, printing display and laser display have made breakthroughs, and technological reserves have been continuously strengthened. In the field of integrated circuits, a number of key enterprises have grown rapidly and made substantial breakthroughs in R & D, manufacturing and packaging.
Sixth, the leading role is obvious. With less than 0.5% of the total number of enterprises in the industry, the top 100 enterprises have supported 60% of the state taxes paid by the whole industry, realized 40% of the industry sales revenue and 50% of industry profits, and played an important role in the high-quality development of the whole industry.

Select the correct capacitor
se1ect the correct capacitor
In my case, I chose the smallest available package for the 4.7 μF X7R capacitor because size was a consideration in my project. Because of my ignorance, I assumed that any X7R would have the same effect as any other X7R; obviously, this is not the case. To get the right performance for my application, I have to go to some kind of larger package.
I really don't want to use the 1210 package. Fortunately, I was able to increase the resistor values used by 5 X, thus reducing the capacitance to 1 μF.
n Figure 2 shows the voltage characteristics of several 16 V, 1 μF X7R and 16 V, 4.7 μF X7R capacitors. The 1 μF capacitor of the 0603 behaves the same as the 4.7 μF capacitor of the 0805. The 1 μF capacitors of both the 0805 and 1206 perform slightly better than the 4.7 μF capacitors of the 1210. So, with a 1 μF capacitor of 0805, I can keep the capacitor volume the same, and the capacitance under bias is only reduced to about 85% of the rated amount, not 30%. \n But I'm still confused. I thought that all X7R capacitors should have the same voltage coefficient because the dielectric used is the same, X7R. So I asked a colleague, Chris Burkett, a field application engineer at TDK in Japan, who is also an expert on ceramic capacitors.
He explained that many materials would qualify as "X7R". In fact, any material that allows the device to meet or exceed the X7R temperature characteristics (i.e., ± 15% variation fr0m -55 ° C to 125 ° C) can be called X7R. Burkett also explained that there is no specific specification for the voltage coefficient of X7R capacitors or any other type of ceramic capacitor.
This is a key point, so I will repeat it again. As long as a capacitor meets the temperature coefficient specification, no matter how bad its voltage coefficient is, the manufacturer can call it an X7R capacitor (or X5R, or any other type). This fact confirms the Maxim (pun intended) that any experienced electrical engineer knows: read the data sheet!
As manufacturers increasingly prefer smaller components, they have to compromise on the materials they use. In order to achieve the required volumetric efficiency with a smaller size, they were forced to accept a worse voltage coefficient. Of course, reputable manufacturers will try to minimize the side effects of this compromise.

Not all X7R capacitors are the same
Not all X7R capacitors are the same
Since my RC circuit time constant problem cannot be explained by a specific temperature variable, it must be studied in depth. Looking at the capacitance of my capacitor versus the applied voltage, I was surprised to see how much the capacitance changed with the set conditions. I chose a 16 V capacitor operating at 12 V bias. The datasheet shows that my 4.7-μF capacitor typically provides 1.5 μF under these conditions. Now, the problem with the RC circuit is completely explained.
The datasheet shows that if I increase the capacitor package size fr0m 0805 to 1206, the typical capacitance under specified conditions will be 3.4 μF. This indicates that further research is necessary.
I found that Murata and TDK have great tools on their website to plot capacitance changes under different environmental conditions. I did some research on 4.7 μF capacitors of various sizes and voltage ratings. The data in Figure 1 is taken fr0m Murata's tool for several different 4.7 μF ceramic capacitors. I looked at both the X5R and X7R models, with package sizes fr0m 0603 to 1812 and voltage ratings fr0m 6.3 to 25V DC. First, I noticed that as the package size increases, the change in capacitance with applied DC voltage decreases and is large.
The relationship between the DC voltage on the 4.7 μF capacitor and the temperature change shows that with the increase of the package size, the capacitance decreases greatly with the applied voltage.
CAPACITANCE (μF) Capacitance (μF) DC VOLTAGE (V) DC Voltage (V)
The second interesting point is that for a given package size and tile capacitor type, the voltage rating of the capacitor generally does not seem to matter. \n So I estimate that if I use a capacitor rated at 25 V for 12 V, the change in capacitance will be less than a capacitor rated at 16 V under the same conditions. Looking at the curve for the X5R in the 1206 package, it is clear that the 6.3 V rated components do outperform their higher voltage rated counterparts. \n If we examine a wider range of capacitances, we will see that this is very common. The sample set of capacitors I studied did not exhibit the behavior expected of a normal ceramic capacitor.
The third problem observed is that the X7R capacitor is more temperature sensitive than the X5R capacitor for the same package.

time constant of RC circuit
A few years ago, after more than 25 years of working with ceramic capacitors, I came to a new understanding of them. I was busy working on an LED bulb driver at the time, and there was apparently a problem with the time constant of one of the RC circuits in my project.
My first assumption was that a component on the board had an incorrect value, so I measured two resistors that were used as a voltage divider, but they were both OK. I removed the capacitor fr0m the circuit board and measured it without any problem. To further confirm, I measured and installed new resistors and capacitors, powered up the circuit, checked that it was basically working properly, and then saw if the replacement components solved the RC circuit time constant problem. But the answer is no.
I tested the circuit in a natural environment: inside the enclosure, the circuit is inside the enclosure, simulating a "can" of roof lighting, and sometimes the temperature of the components rises to more than 100 degrees Celsius. Although the time I had to retest the RC circuit was short, everything was still very hot. \n Obviously, my next conclusion is that the problem is the temperature variation of the capacitor. But I doubt that myself, because I'm using an X7R capacitor, which, fr0m what I remember, works up to 125 ° C with a ± 15% change. I trust my memory, but to be on the safe side, I revisited the datasheet for the capacitors used.
Background report
the letters and numbers used for different types of ceramic capacitors and their respective meanings. The table describes Class II and Class III ceramic capacitors. Without going into too much detail here, Class I capacitors include the common COG (NPO) type;
The volumetric efficiency of this capacitor is not as good as the two capacitors in the table, but it is much more stable under variable environmental conditions and does not exhibit piezoelectric effects. In contrast, the capacitors in the table have a wide variety of characteristics that allow them to expand and withstand the applied voltage, but sometimes produce an audible piezoelectric effect (beeping or ringing).
Of the various capacitor types given, in my experience the most commonly used are X5R, X7R, and also Y5V. I have never used Y5V because they exhibit a large variation in capacitance across the full range of ambient conditions.
When a capacitor company develops a product, they choose the characteristics of the material so that the capacitor can operate within a defined range of variation over a specified temperature range.

characteristic of the manufacturing proces of DC-DC converter
The transformer of flyback power supply works in unidirectional magnetization state, which not only transfers energy through magnetic coupling, but also plays multiple roles of voltage conversion and 1nput and output isolation. Therefore, the treatment of air gap needs to be very careful. If the air gap is too large, the leakage inductance will become larger, the hysteresis loss will increase, and the iron loss and copper loss will increase, which will affect the overall performance of the power supply. Too small an air gap can saturate the transformer core and cause damage to the power supply.
The so-called continuous and discontinuous modes of flyback power supply refer to the working state of the transformer. In the full-load state, the transformer works in the working mode of complete or incomplete energy transfer. Generally, it should be designed according to the working environment. The conventional flyback power supply should work in continuous mode, so that the loss of switches and lines is relatively small, and the working stress of 1nput and output capacitors can be reduced, but there are some exceptions.
It should be specially pointed out here that the flyback power supply is also suitable to be designed as a high-voltage power supply, and the high-voltage power supply transformer generally works in the discontinuous mode. I understand that the high-voltage power output needs to use a high-voltage rectifier diode.
Because of that characteristic of the manufacturing proces, the reverse recovery time of the high reverse voltage diode is long, the speed is low, in a current continuous state, the diode is recovered when a forward bias voltage is applied, and the energy loss dure the reverse recovery is very large, so that the improvement of the performance of a converter is not facilitated, conversion efficiency is reduced, a rectifier tube is seriously heated, and even the rectifier tube is burned. Since the diode is reverse biased at zero bias in the discontinuous mode, the loss can be reduced to a relatively low level. Therefore, the high voltage power supply operates in discontinuous mode, and the operating frequency cannot be too high.
There is also a kind of flyback power supply which works in the critical state. Generally, this kind of power supply works in the frequency modulation mode or the frequency modulation and width modulation dual mode. Some low-cost self-excited power supplies (RCC) often adopt this form. In order to ensure the output stability, the working frequency of the transformer changes with the output current or 1nput voltage. When the transformer is close to full load, it always keeps between continuous and discontinuous. This kind of power supply is only suitable for low power output, otherwise the treatment of electromagnetic compatibility characteristics will be a headache.
The transformer of flyback switching power supply should work in continuous mode, which requires a relatively large winding inductance. Of course, there is a certain degree of continuity. It is unrealistic to pursue absolute continuity excessively. It may require a large magnetic core and a large number of coil turns, accompanied by large leakage inductance and distributed capacitance, which may not be worth the loss.

Optimization process of designing a low voltage output low power flyback power supply
Care must be taken in the optimization process of designing a low voltage output low power flyback power supply, and there are several ways to handle it:
1. A magnetic core with a higher power level is used to reduce the leakage inductance, which can improve the conversion efficiency of the low-voltage flyback power supply, reduce the loss, reduce the output ripple, and improve the cross regulation rate of the multi-output power supply. It is commonly used in switching power supplies for household appliances, such as optical disc players, DVD set-top boxes, etc.
2. If the condition does not allow the magnetic core to be enlarged, the reflected voltage can only be reduced and the duty ratio can be reduced. Reducing the reflected voltage can reduce the leakage inductance, but it may reduce the power conversion efficiency. The two are contradictory, and there must be a substitution process to find a suitable point. In the process of transformer substitution experiment, the reverse peak voltage of the primary side of the transformer can be detected, and the width and amplitude of the reverse peak voltage pulse can be reduced as much as possible to increase the working safety margin of the converter. Generally, the reflection voltage is more appropriate at 110V.
3. Enhance the coupling, reduce the loss, and adopt new technology and winding process. In order to meet the safety specifications, the transformer will take insulation measures between the primary side and the secondary side, such as padding insulation tape and adding insulation end tape. These will affect the leakage inductance performance of the transformer, and the winding method of primary winding wrapped around the secondary winding can be used in actual production. Or the secondary winding is made of triple insulated wire, and the insulation between the primary and secondary windings is eliminated, which can enhance the coupling, and even the wide copper sheath winding can be used.
In this paper, the low voltage output refers to the output less than or equal to 5V, such as this kind of small power supply, my experience is that the power output greater than 20 W output can use the forward type, can obtain the best cost performance, of course, this is not absolutely right, with personal habits, the application environment is related, next time talk about the flyback power supply with magnetic core, some understanding of the magnetic circuit air gap. I hope you can give me some advice.
The magnetic core of the flyback power transformer works in a unidirectional magnetization state, so the magnetic circuit needs an air gap, which is similar to a pulsating DC inductor. Part of the magnetic circuit is coupled through an air gap.
I understand the principle of opening the air gap as follows: because the power ferrite also has a working characteristic curve (hysteresis loop) similar to a rectangle, the Y axis on the working characteristic curve represents the magnetic induction (B), and the saturation point of the current production process is generally above 400mT. Generally, this value should be 200-300mT in the design, and the X axis represents the magnetic field intensity (H), which is proportional to the magnetization current intensity.

Duty cycle of the flyback DC-DC converter
Duty cycle of the flyback power supply
I will talk about the duty cycle of the flyback power supply (I am concerned about the reflected voltage, which is consistent with the duty cycle). The duty cycle is also related to the choice of the voltage withstand of the switching tube. Some early flyback power supplies use relatively low voltage withstand switching tubes, such as 600V or 650V as the switching tubes of AC 220V 1nput power supply, which may be related to the production process at that time. High voltage withstand tubes are not easy to manufacture. Or the low withstand voltage tube has more reasonable conduction loss and switching characteristics, such as the line reflection voltage can not be too high, otherwise in order to make the switch tube work in a safe range, the power loss of the absorption circuit is also considerable.
It is proved that the reflection voltage of 600V tube should not be more than 100V, and the reflection voltage of 650V tube should not be more than 120V. When the peak voltage of leakage inductance is clamped at 50V, the tube still has a working margin of 50V. Nowadays, due to the improvement of the manufacturing technology of MOS transistors, the flyback power supply generally uses 700 V or 750 V or even 800-900 V switching transistors.
Like this kind of circuit, the ability to resist overvoltage is stronger, and the reflection voltage of the switching transformer can also be made higher. The maximum reflection voltage of 150V is more appropriate, which can obtain better comprehensive performance. PI's TOP chip recommends a transient voltage suppression diode clamp for 135V. But his evaluation boards typically have a reflected voltage lower than that, around 110 V. Both types have advantages and disadvantages:
The first category: weak overvoltage resistance, small duty cycle, and large primary pulse current of transformer. Advantages: small transformer leakage inductance, low electromagnetic radiation, high ripple index, small switch tube loss, conversion efficiency is not necessarily lower than the second class.
The second category: the disadvantage is that the loss of the switch tube is larger, the leakage inductance of the transformer is larger, and the ripple is worse. Advantages: strong overvoltage resistance, large duty cycle, low transformer loss and high efficiency.
The reflection voltage of the flyback power supply also has a determining factor, and the reflection voltage of the flyback power supply is also related to a parameter, namely the output voltage, the lower the output voltage is, the larger the turns ratio of a transformer is, the larger the leakage inductance of the transformer is, and the higher the voltage borne by a switching tube is, It is possible to permanently disable the power devices in the snubber loop (especially in circuits using transient voltage suppression diodes). Care must be taken in the optimization process of designing low voltage output low power flyback power supplies.

DC-DC converter is divided into two forms: isolated and non-isolated
Here we mainly talk about the topology of isolated switching power supply. In the following, unless otherwise specified, it refers to isolated power supply. Isolated power supply can be divided into two categories according to different structures: forward and flyback. Flyback means that when the primary side of the transformer is on, the secondary side is off, and the transformer stores energy. When the primary side is turned off, the secondary side is turned on, and the energy is released to the load. Generally, the conventional flyback power supply has more single transistors, and double transistors are not common. Forward means that the primary side of the transformer is conducted while the secondary side induces the corresponding voltage output to the load, and the energy is directly transferred through the transformer. According to the specification, it can be divided into conventional forward, including single-tube forward and double-tube forward. Half-bridge and bridge circuits are both forward circuits.
Forward and flyback circuits have their own characteristics, which can be used flexibly in the process of circuit design to achieve the best cost performance. In general, flyback can be used in small power applications. A single-transistor forward circuit can be used for slightly larger power, a double-transistor forward circuit or a half-bridge circuit can be used for medium power, and a push-pull circuit is used for low voltage, which is the same as the half-bridge working state. High power output, generally using bridge circuit, low voltage can also use push-pull circuit.
Flyback power supply is widely used in small and medium power supply because of its simple structure and saving an inductor with the same size as the transformer. In some introductions, it is said that the power of flyback power supply can only be tens of watts, and there is no advantage if the output power exceeds 100 watts, which is difficult to achieve. I think this is the case in general, but also can not be generalized, there are articles on the flyback power supply can be achieved on the kilowatt, but have not seen the real thing. The output power is related to the output voltage.
n The leakage inductance of the flyback power supply transformer is a very critical parameter, because the flyback power supply needs the transformer to store energy, in order to make full use of the transformer core, it is generally necessary to open an air gap in the magnetic circuit, the purpose is to change the slope of the iron core hysteresis loop, so that the transformer can withstand the impact of large pulse current, and the iron core will not enter a saturated nonlinear state. The air gap in that magnetic circuit is in a high reluctance state, and the magnetic leakage generate in the magnetic circuit is much larger than that of a completely close magnetic circuit.
The coupling between the primary poles of the transformer is also the key factor to determine the leakage inductance. To make the primary pole coils as close as possible, the sandwich winding method can be used, but this will increase the distributed capacitance of the transformer. The leakage inductance can be reduced by se1ecting the core with a longer window as far as possible. For example, the effect of EE, EF, EER and PQ cores is better than that of EI cores.

Application of Aluminum Substrate and Multilayer Printed Circuit Board in DC-DC converter
The application of aluminum substrate in switching power supply and the application of multilayer printed circuit board in switching power supply circuit.
The aluminum substrate is constructed by the aluminum substrate itself and has the following characteristics: the aluminum substrate is excellent in heat conductivity, copper is bound on one side, devices can only be placed on the copper binding surface, and electrical wiring holes cannot be opened, so jumpers cannot be placed as a single panel.
SMD devices, switching tubes and output rectifier tubes are generally placed on the aluminum substrate to conduct heat out through the substrate, so the thermal resistance is very low and high reliability can be achieved. The transformer adopts a planar patch structure and can also dissipate heat through a substrate, the temperature rise of the transformer is lower than that of a conventional transformer, and the transformer with the same specification adopts an aluminum substrate structure to obtain higher output power. The aluminum substrate jumper can be handled in a bridging manner. The aluminum substrate power supply is generally composed of two printed boards, the control circuit is placed on the other board, and the two boards are integrated through physical connection.
Due to the excellent thermal conductivity of the aluminum substrate, the aluminum substrate is difficult to be soldered manually in a small amount, the solder is cooled too fast, and problems are easy to occur. The existing simple and practical method comprises the following steps of: turning over a common electric iron for ironing clothes (preferably with a temperature adjusting funct1on), fixing the ironing surface upwards, adjusting the temperature to about 150 deg C, putting the aluminum substrate on the iron, heating for a period of time, Then stick and weld the components according to the conventional method. The temperature of the iron should be easy to weld the components. If the temperature is too high, the components may be damaged, and even the copper sheet of the aluminum substrate will be peeled off. If the temperature is too low, the welding effect will not be good. It should be flexible.
In that recent year, with the application of the multilayer circuit board in the switching pow supply circuit, the printed circuit transformer becomes possible, because the multilayer board has small lay spacing, the window section of the transformer can be fully utilized, one or two printed coils composed of the multilayer board can be added on the main circuit board to achieve the purpose of utilizing the window and reducing the current density of the circuit, because the printed coils are adopted, The invention has the advantages of reduced manual intervention, good consistency of the transformer, plane structure, low leakage inductance and good coupling. Open magnetic core, good heat dissipation condition.
Because it has many advantages and is conducive to mass production, it has been widely used. However, the initial investment in research and development is large, and it is not suitable for small-scale production.

the treatment of large current wiring for DC-DC converter
For the treatment of large current wiring, the line width is not enough. Generally, the problem can be solved by increasing the thickness of tin plating on the wiring. There are many methods:
1. Set the routing as the pad attribute, so that the routing will not be covered by the solder resist during the manufacturing of the circuit board, and will be tinned during the hot air leveling.
2. Place the pad at the wiring place and set the pad to the shape of the required wiring. Pay attention to setting the pad hole to zero.
3. Place wires on the solder mask. This method is the most flexible, but not all circuit board manufacturers will understand your intention and need to explain it in words. The solder resist is not applied to the portion of the solder resist where the wire is placed.
There are several methods of tinning the circuit as above. It should be noted that if all the wide wiring is tinned, a large amount of solder will be adhered after soldering, and the distribution is very uneven, which will affect the appearance. Generally, the width of the thin strip tinning is 1 ~ 1.5mm, and the length can be determined according to the circuit. The interval of the tinning part is 0.5 ~ 1mm. The double-sided circuit board provides great se1ectivity for layout and wiring, and can make the wiring more reasonable.
With regard to grounding, the power ground and the signal ground must be separated, and the two grounds can be merged at the filter capacitor to avoid the unexpected factors of instability caused by large pulse current passing through the signal ground connection. The signal control circuit should adopt the one-point grounding method as far as possible. There is a trick to place the non-grounded wiring on the same wiring layer as far as possible, and finally lay the ground wire on another layer.
The output line usually passes through the filter capacitor first and then to the load, and the 1nput line must also pass through the capacitor first and then to the transformer. The theoretical basis is to let the ripple current pass through the filter capacitor.
Voltage feedback sampling, in order to avoid the impact of large current through the wiring, the sampling point of feedback voltage must be placed at the end of the power output to improve the load effect index of the whole machine.
The wiring fr0m one wiring layer to another wiring layer is generally connected by vias, which should not be realized through the pin pad of the device, because this connection may be destroyed when the device is 1nserted. In addition, when each 1A current passes through, there should be at least two vias. The diameter of the vias should be greater than 0.5mm in principle, and 0.8mm in general can ensure the reliability of processing.
In some low-power power supplies, the wiring of the circuit board can also have the funct1on of heat dissipation. It is characterized in that the wiring is as wide as possible to increase the heat dissipation area. It is not coated with solder resist. If conditions permit, vias can be placed evenly to enhance the thermal conductivity.

How to design single-sided printing PCB
Because the single panel has the characteristics of low cost and easy manufacturing, it is widely used in switching power supply circuits. Because it has only one side bound with copper, the electrical connection and mechanical fixation of devices depend on that layer of copper sheet, so care must be taken when dealing with it.
In order to ensure good mechanical structure performance of soldering, the single panel pad should be slightly larger to ensure good binding force between the copper sheet and the substrate, so that the copper sheet will not peel off and break off when it is subjected to vibration. Generally, the width of the welding ring shall be greater than 0.3mm. The diameter of the pad hole should be slightly larger than the diameter of the device pin, but should not be too large to ensure that the shortest distance between the pin and the pad is connected by solder. The size of the pad hole should not hinder the normal inspection. The pad hole diameter is generally 0.1-0.2mm larger than the pin diameter. Multi-pin devices can also be larger to ensure a smooth check.
The electrical wiring shall be as wide as possible. In principle, the width shall be greater than the diameter of the pad. In special cases, the wiring must be widened when it intersects with the pad (commonly known as teardrop) to avoid breakage of the wiring and the pad under certain conditions. In principle, the minimum line width shall be greater than 0.5mm.
The components on the single panel shall be close to the circuit board. For devices requiring overhead heat dissipation, a sleeve should be added to the pin between the device and the circuit board, which can play a dual role of supporting the device and increasing insulation, minimize or avoid the impact of external impact on the connection between the pad and the pin, and enhance the firmness of welding. Support connection points can be added to components with heavy weight on the circuit board to strengthen the connection strength with the circuit board, such as transformers and power device radiators.
Under the precondition that the distance between the single panel welding surface and the shell is not affected, the single panel welding surface pin can be left longer, which has the advantages that the strength of the welding part can be increased, the welding area can be increased, and the phenomenon of false welding can be found immediately. When the pin is long and the leg is cut, the stress on the welding part is small. In Taiwan and Japan, the process of bending the pins of the device at an angle of 45 degrees with the circuit board and then soldering them is often used. The reason is the same as above. Today, let's talk about some matters in the design of double-sided boards. In some application environments with high requirements or high wiring density, the performance and various indicators of double-sided printed boards are much better than those of single-sided boards.

Precautions for copper wiring of printed board
Precautions for copper wiring of printed board
Track current density: Most electronic circuits are now made of copper bound on an insulating board. The thickness of copper sheet of common circuit board is 35 μm, and the current density value can be taken according to the empirical value of 1A/mm for wiring. Refer to the textbook for specific calculation. In order to ensure the mechanical strength of the wiring, the line width should be greater than or equal to 0.3mm (the minimum line width of other non-power circuit boards may be smaller). A circuit board with a cop sheet thickness of 70 μm is also common for switching pow supplies, so that current density can be higher.
In addition, the current common PCB design tool software generally has design specification items, such as line width, line spacing, tray via size and other parameters can be set. When designing the circuit board, the design software can automatically execute according to the specification, which can save a lot of time, reduce part of the workload and reduce the error rate.
Generally, double-sided panels can be used for circuits with high reliability requirements or wiring with high line density. It is characterized by moderate cost and high reliability, which can meet most applications.
Some products of modular power supply array also adopt multi-layer board, which is mainly convenient for integrating power devices such as transformers and inductors, optimizing wiring, power tube heat dissipation, etc. It has the advantages of beautiful process, good consistency and good heat dissipation of transformer, but its disadvantages are high cost and poor flexibility, which is only suitable for industrial mass production.
Single panel, the market circulation of general switching power supply almost uses single-sided circuit board, it has the advantage of low cost, in the design, and production process to take some measures to ensure its performance.

Design of Printed Circuit Board for DC-DC converter
First fr0m the switching power supply design and production process to start the dession of it, first talk about the design of the printed circuit board. Switching power supply works in high frequency and high pulse state, which belongs to a special type of analog circuit. The principle of high frequency circuit wiring must be followed when laying the board.
Layout: The pulse voltage wiring shall be as short as possible, including the wiring fr0m the 1nput switching tube to the transformer and the wiring fr0m the output transformer to the rectifier tube. The pulse current loop is as small as possible, such as the 1nput filter capacitor positive to the transformer to the switch tube return capacitor negative. In the circuit fr0m the output end of the transformer in the output part to the rectifier tube to the output inductor to the output capacitor and back to the transformer, the X capacitor should be as close as possible to the 1nput end of the switching power supply, and the 1nput line should not be parallel to other circuits.
The Y capacitor shall be placed at the chassis ground terminal or FG connection. The common mode electric induction is kept at a distance fr0m the transformer to avoid magnetic coupling. If it is not easy to handle, a shield can be added between the common mode inductor and the transformer. The above items have a greater impact on the EMC performance of the switching power supply.
Generally, two output capacitors can be used, one close to the rectifier tube and the other close to the output terminal, which can affect the output ripple index of the power supply. The parallel effect of two small-capacity capacitors should be better than that of one large-capacity capacitor. Keep a certain distance between the heating device and the electrolytic capacitor to prolong the service life of the whole machine. The electrolytic capacitor is the bottleneck of the service life of the switching power supply. For example, the transformer, power tube and high-power resistor should keep a distance fr0m the electrolysis, and a heat dissipation space should be left between the electrolysis. If conditions permit, they can be placed at the air inlet.
Attention shall be paid to the control part: the wiring of the high-impedance weak signal circuit shall be as short as possible, such as the sampling feedback loop, which shall be avoided fr0m interference as far as possible during processing. The current sampling signal circuit, especially the current control circuit, may cause some unexpected accidents if it is not handled properly.

Composition structure of DC motor
The structure of DC motor shall be composed of stator and rotor. The stationary part of the DC motor during operation is called the stator. The main funct1on of the stator is to generate a magnetic field. It is composed of a frame, a main magnetic pole, a commutating pole, an end cover, a bearing and a brush device. The rotating part during operation is called the rotor, whose main funct1on is to generate electromagnetic torque and induced electromotive force. It is the hub for energy conversion of DC motor, so it is usually called the armature, which is composed of shaft, armature core, armature winding, commutator and fan.
Stator
(1) Main magnetic pole
The funct1on of the main magnetic pole is to generate an air gap magnetic field. The main magnetic pole is composed of a main magnetic pole iron core and an excitation winding. The iron core is generally made by laminating and riveting 0.5mm ~ 1.5mm thick silicon steel sheet. It is divided into a pole body and a pole shoe. The part above the excitation winding is called the pole body, and the part below the excitation winding is called the pole shoe. The pole shoe is wider than the pole body, which can not only adjust the distribution of the magnetic field in the air gap, but also facilitate the fixation of the excitation winding. The excitation winding is made of insulated copper wire and sleeved on the main pole core. The whole main magnetic pole is fixed on the machine base by a screw,
(2) Commutating pole
The commutating pole is used to improve the commutation and reduce the commutation spark that may be generated between the brush and the commutator during the operation of the motor. It is generally installed between two adjacent main magnetic poles and consists of a commutating pole core and a commutating pole winding. The commutating pole winding is formed by winding insulated wires and sleeved on the commutating pole iron core, and the number of the commutating poles is equal to that of the main magnetic poles.
(3) Frame
The casing of the motor stator is called the frame. There are two funct1ons of the base:
One is used for fixing the main magnetic pole, the commutating pole and the end cover, and plays the role of supporting and fixing the whole motor;
Secondly, the frame itself is also a part of the magnetic circuit, which constitutes the magnetic path between the poles, and the part through which the magnetic flux passes is called the yoke. In order to ensure that the base has sufficient mechanical strength and good magnetic permeability, it is generally made of cast steel or welded by steel plate.
(4) Brush device
The brush device is used to introduce or extract DC voltage and DC current. The electric brush device is composed of an electric brush, a brush holder, a brush rod and a brush rod seat. The brush is placed in the brush holder and pressed by the spring to ensure good sliding contact between the brush and the commutator. The brush holder is fixed on the brush rod, which is installed on the circular brush rod seat and must be insulated fr0m each other. The brush rod seat is installed on the end cover or the bearing inner cover, and the circumferential position can be adjusted and fixed after adjustment.

DC motor has the advantage of precise control, but it has large power consumption
As we all know, DC motor has the advantage of precise control, but it has large power consumption, low efficiency and small torque. If the high-power stepper motor is se1ected, the PWM constant current control method can be adopted in order to reduce power consumption.
A direct current machine is a rotating electrical machine that converts direct current electrical energy into mechanical energy (direct current motor) or converts mechanical energy into direct current electrical energy (direct current generator). It is a motor that can realize the mutual conversion of DC electric energy and mechanical energy. When it operates as a motor, it is a direct current motor that converts electrical energy into mechanical energy; When operating as a generator, it is a direct current generator that converts mechanical energy into electrical energy.
The DC motor consists of a stator and a rotor with a certain air gap between them. The main feature of its construction is an armature with a commutator. The stator of DC motor is composed of frame, main magnetic pole, commutating magnetic pole, front and rear end covers and brush holder. The main magnetic pole is the main component to produce the air gap magnetic field of the DC motor, which is composed of permanent magnets or laminated cores with DC excitation windings.
The rotor of DC motor is composed of armature, commutator (also called commutator) and shaft. The armature consists of an armature core and an armature winding. The armature core is made of laminated silicon steel sheets, and the slots are uniformly distributed on the outer circle of the armature core, and the armature windings are embedded in the slots. Commutator is a mechanical rectifying component. After the commutator segments are folded into a cylindrical shape, the commutator segments are formed into a whole by metal clips or plastics. The commutators are insulated fr0m each other. The quality of the commutator has a great influence on the operation reliability.
Basic composition of DC motor
The DC motor consists of a stator and a rotor with a certain air gap between them. Benefits: Reply to the information on the official account of the E-Fever Friends Network, and get a free set of model electricity information.
The stator of DC motor is composed of frame, main magnetic pole, commutating magnetic pole, front and rear end covers and brush holder. The main magnetic pole is the main component to produce the air gap magnetic field of the DC motor, which is composed of permanent magnets or laminated cores with DC excitation windings.
The rotor of DC motor is composed of armature, commutator (also called commutator) and shaft. The armature consists of an armature core and an armature winding. The armature core is made of laminated silicon steel sheets, and the slots are evenly distributed on the outer circle of the armature core, and the armature windings are embedded in the slots. \n Commutator is a mechanical rectifying component. After the commutator segments are folded into a cylindrical shape, the commutator segments are formed into a whole by metal clips or plastics. The commutators are insulated fr0m each other. The quality of the commutator has a great influence on the operation reliability.

The method to prevent the first electric explosion of the prototype
The method to prevent the first electric explosion of the prototype is very simple, that is, to connect an incandescent lamp in series with the 1nput line of the switching power supply for protection, as shown in the figure below.
Note that the series incandescent lamp does not need to be electrified with output load for the first time, and is directly electrified with no load. \n Without large current
If the incandescent lamp is not on, or it is on and then off when it is just powered on (the first light is caused by the 1nput surge current), it indicates that there is no large current 1nput to the switching power supply. At this time, you can test whether the output of the power supply is normal voltage. If the output is normal, the incandescent lamp can be removed for normal debugging.
If the output voltage is abnormal, it can continue to connect to the incandescent lamp until the cause is found and solved, and then remove the incandescent lamp for normal debugging.
In case of large current
If the incandescent lamp is on all the time after being powered on, or the incandescent lamp is in the intermittent cycle of on-off-on, it indicates that there is a large current inside the switching power supply. At this time, turn off the power supply and check the switching power supply carefully. Repeat this method until the no-load switching power supply is normal, and then remove the incandescence lamp for normal debugging.
Without large current
If the switching power supply does not enter a dangerous state (the output of the switching power supply is normal or the output voltage of the switching power source is jumping up and down but does not cause a large 1nput current), the 1nput current flowing into the switch power supply at this time is very weak, which can be equivalently regarded as a large Zo.
Assuming that the power consumption of the power supply is 2.2 W at this time, the average current on Zo is about 0.01 A, and the impedance on Zo is about 220/0.01, which is about 22 K.
The cold state resistance of an incandescent lamp with more than ten watts or tens of watts is about tens of ohms to hundreds of ohms. Here I assume that Z1 = 100Ω. According to the voltage division ratio of the impedance, the voltage drop on the incandescent lamp is very small, so the incandescent lamp does not light.
In case of large current 1nput
If the switching power supply does not enter the dangerous state (the 1nput of the switching power supply has a large current), the current is very large, which can be equivalently regarded as a very small Zo.
Assuming that the average current flowing into the power supply at this time is 5A, which is equivalent to the average current on Zo being 5A, the impedance on Zo is about 220/5, which is about 44Ω.
The cold state impedance of an incandescent lamp of more than ten watts or tens of watts is about tens of ohms to hundreds of ohms. Here I assume that Z1 = 100Ω. According to the voltage division ratio of the impedance, the voltage drop on the incandescent lamp is relatively large.
In addition, another characteristic of incandescent lamps is that the hot impedance is much larger than the cold impedance. The experiment shows that the hot impedance is about 10 times larger than the cold impedance. Here I assume that the thermal impedance is 10 times larger than the cool impedance.

low-cost method to prevent the prototype of the first time on the electric explosion machine problems
After so many years of switching power supply design, a very worrying thing for me is that the new prototype is powered on for the first time, and I am worried about the explosion of the machine. I believe that many engineers have the same deep understanding as me. They check their new prototype again and again before powering on, fearing that there will be wrong welding, reverse lap welding or short circuit in some places, and even sweep the workbench clean just in case.
According to the different experience of engineers and the different degree of care, the prototype has a certain probability of explosion when it is powered on for the first time, and it is on tenterhooks. Of course, the word "fear" can only be used for some engineers, some of whom are naturally not afraid of explosion and the "Zizi" sound when doing pressure-resistant experiments, and their faces do not change color and their hearts do not beat (I don't know if they are faking it).
It is very painful to blow up the machine, especially when such a brand new prototype has no power supply with good parameters, the power supply may be abnormal, and it will be more difficult to repair the explosion?
For this reason, due to the limited equipment configuration, many engineers use various methods and experience to avoid the explosion, such as slowly increasing the 1nput voltage while watching the state of the current, watching the power changes on the power meter, once the situation is not right, immediately cut off the power, which can indeed avoid some abnormal situations, but sometimes the hand speed is not fast enough to explode.
Below to share with you a pro-test effective, and very low-cost method to prevent the prototype of the first time on the electric explosion machine problems, the hands of AC source and other equipment engineers please ignore!

Design Summary of DC-DC Switching Power Supply
The layout of DC-DC is very important, which will directly affect the stability and EMI effect of the product. The experience/rules are summarized as follows: 1. Handle the feedback loop well. The feedback line should not go under Schottky, inductor (L1) or large capacitor, and should not be surrounded by a large current loop. If necessary, a 100 pF capacitor can be added to the sampling resistor to increase stability (but transients are slightly affected);
2. The feedback line should be thin rather than thick, because the wider the line is, the more obvious the antenna effect is, which affects the stability of the loop. A 6-12 mils thread is generally used;
3. All capacitors shall be as close to the IC as possible;
4. The inductance shall be se1ected according to the capacity of 120-130% of the specification, and shall not be too large, which will affect the efficiency and transient state;
5. Capacitor shall be se1ected according to 150% of the capacity in the specification. If chip ceramic capacitors are used, if 22uF is used, it is better to use two 10uF parallel capacitors. If the cost is not sensitive, the capacitance can be larger. Special tips: output capacitor, if the use of aluminum electrolytic capacitor, remember to use high-frequency low resistance, not casually put a low-frequency filter capacitor!
6. Reduce the surrounding area of large current loop as much as possible. If it is not convenient to narrow it, it can be made into a narrow slit by copper plating.
7. Do not use thermal resistance pads on critical loops, as they introduce unwanted inductance characteristics.
8. When using the ground plane, try to maintain the integrity of the ground plane under the 1nput switching loop. Any cutting of the ground plane in this area will reduce the effectiveness of the ground plane, and even the signal vias through the ground plane will increase its impedance.
9. Vias can be used to connect decoupling capacitors and the ground of the IC to the ground plane, which can minimize the loop. However, it is important to keep in mind that the via inductance is approximately between 0.1 and 0.5 nH, depending on the via thickness and length, which can increase the total loop inductance. The use of multiple vias is desirable for low impedance connections.
In the above example, the additional vias to the ground plane do not help to reduce the length of the CIN loop. But in another example, because the path of the top layer is very long, it is very effective to reduce the circuit area through the via hole.

PCB Design Considerations in Power Management
With the rapid development of science and technology products, the PCB design of power products is facing greater challenges, including power conversion efficiency, thermal analysis, power plane integrity and EMI (electromagnetic interference).
With the increasingly extensive and diversified applications in the industry, power supply products are also developing in the direction of high frequency, high efficiency, high density, low voltage, large current and diversification. At the same time, the packaging structure and dimensions of power supply products are becoming more and more standardized to meet the requirements of the global market.
The first is power conversion efficiency. Conversion efficiency refers to the ratio of the output power of the power supply to the 1nput power actually consumed. In practical applications, the electric energy can not be completely converted, and there will be a certain amount of energy consumption in the middle. Therefore, no matter what kind of circuit, there must be an efficiency problem in the power conversion. For a linear power supply, the heat dissipation of the LDO needs to be considered; For the switching power supply, the loss of the switch tube should be considered.
Secondly, energy loss will inevitably produce heat, which involves the problem of heat dissipation. In addition, as the load becomes heavier, the power consumption of the power supply chip increases, so the thermal distribution is a problem that has to be considered in the power supply design.
The third is the integrity design of the power plane. To maintain the integrity of the power supply is to maintain a stable power supply. In a real system, there is always noise of different frequencies. Such as PWM natural frequency or PFM variable frequency control signals, fast di/DT can produce current ripple signals, so a low impedance power plane design is necessary.
Finally, there is the issue of EMI (electromagnetic interference). Switching noise is generated when the switching power supply is switched on and off continuously. If the loop inductance is not considered in the design process, the excessive return path will cause EMI problems.
The industry is always looking for ways to improve the success rate of power PCB design. Experience shows that in the design process, if possible risks can be predicted and avoided in advance, the success rate will be greatly improved. Therefore, it is particularly important to choose a suitable design simulation tool.

LDO VS DC-DC converter
Generally speaking, DCDC must be se1ected for boost, and DCDC or LDO should be se1ected for buck in terms of cost, efficiency, noise and performance.
LDO is small in size and has less interference. When the voltage difference between the 1nput and output is large, the conversion efficiency is low.
The advantage of DC-DC is that it has high conversion efficiency and large current, but the output interference is large and the volume is relatively large.
LDO generally refers to a linear regulator, Low Drop Out, while DC/DC is a general term for linear and switching regulators.
If your output current is not very large (such as less than 3A), and the 1nput and output voltage difference is not large (such as 3.3 V to 2.5 V), you can use LDO regulator (the advantage is that the ripple of output voltage is very small). Otherwise, it is better to use a switching regulator. If it is a boost, it can only use a switching regulator (if the ripple control is not good, it will easily affect the system work).
Choice of LDO
When the designed circuit has the following requirements for the shunt power supply:
1. High noise and ripple rejection;
2, that occupy PCB board area is small, such as handheld electronic products such as mobile phone and the like;
3. Inductors are not allowed to be used for circuit power supply, such as mobile phones;
4. The power supply shall have the funct1ons of instantaneous calibration and output status self-check;
5. The voltage regulator is required to have low voltage drop and low power consumption;
6. Low line cost and simple scheme are required;
At this point, the LDO is the most appropriate choice, while meeting the various requirements of the product design. The above is the power chip se1ection method, I hope to help you, you need to design, according to the different projects to choose.

LDO VS DC-DC converter
DCDC means DC to DC (conversion of different DC power supply values). Anything that meets this definition can be called a DCDC converter, including an LDO. But the general saying is that the DC to (to) DC is realized by the switching mode of the device called DCDC.
LDO means low voltage drop, and here's a paragraph that explains: Low dropout (LDO) linear regulators have the advantages of low cost, low noise, and low quiescent current. It also requires few external components, typically just one or two bypass capacitors. The new LDO linear regulator achieves an output noise of 30 μV, a PSRR of 60 dB, a quiescent current of 6 μA, and a voltage drop of only 100 mV. The main reason why LDO linear regulators can achieve this level of performance is that the pass transistor is a P-channel MOSFET, while ordinary linear regulators use PNP transistors. The P-channel MOSFET is voltage-driven and does not require current, so the current consumed by the device itself is greatly reduced; On the other hand, in a circuit using a PNP transistor, in order to prevent the PNP transistor fr0m entering a saturated state and reducing the output capability, the voltage drop between the 1nput and the output should not be too low; The voltage drop across the P-channel MOSFET is approximately equal to the product of the output current and the on-resistance. Because the on-resistance of the MOSFET is very small, the voltage drop across it is very low.
If the 1nput voltage and the output voltage are very close, the LDO regulator is the best choice to achieve high efficiency. As a result, LDO regulators are often used in applications that convert the voltage fr0m a lithium-ion battery to a 3 V output voltage. Although the last 10% of the battery's energy is not used, the LDO regulator can still ensure that the battery operates for a long time with low noise.
If the 1nput voltage and the output voltage are not very close, it is necessary to consider using a switch-type DCDC, because fr0m the above principle, we can know that the 1nput current of the LDO is basically equal to the output current. If the voltage drop is too large, the energy consumed on the LDO is too large, and the efficiency is not high.
The DC-DC converter includes a boost, a buck, a boost/buck, and an inverter circuit. The DC-DC converter has the advantages of high efficiency, high output current, and low quiescent current. As integration increases, many new DC-DC converters require only a few external inductors and filter capacitors.

About the LDO
In the past, I often saw that the chip was LDO and thought it was the name of a company. Now we know that LDO is a low dropout regulator, which means a low dropout linear regulator, as opposed to a traditional linear regulator. Traditional linear regulators, such as 78xx series chips, require the 1nput voltage to be more than 2 V ~ 3 V higher than the output voltage, otherwise they will not work properly. However, in some cases, this condition is obviously too harsh, such as 5 V to 3. 3 V, the 1nput and output voltage difference is only 1. 7 V, obviously does not meet the conditions. In view of this situation, there is a LDO power conversion chip. There are many companies producing LDO chips, such as ALPHA, Linear (LT), Micrel, National semiconductor, TI and so on.
What is an LDO (Low Dropout) regulator?
An LDO is a linear voltage regulator. Linear regulators use transistors or FETs operating in their linear region to subtract excess voltage fr0m the applied 1nput voltage, producing a regulated output voltage. The droop voltage is the minimum value of the difference between the 1nput voltage and the output voltage required to maintain the output voltage within 100 mV above or below its rated value. An LDO (low dropout) regulator with a positive output voltage typically uses a power transistor (also known as a pass device) as the PNP. This transistor is allowed to saturate, so the regulator can have a very low dropout voltage, typically around 200 mV. In comparison, a conventional linear regulator using an NPN compound power transistor has a voltage drop of about 2 V. The negative output LDO uses NPN as its pass device and operates in a similar mode to the PNP device of the positive output LDO.
Newer developments use CMOS power transistors, which provide the lowest voltage drop. With CMOS, the only voltage drop across the regulator is due to the ON resistance of the power device load current. If the load is small, the voltage drop produced by this method is only tens of millivolts.

Power supply chip selection method
What is a power chip? What does it do? What should be considered when choosing a power supply chip? 1nput Voltage Linear Regulation: The relative effect of a linear change in 1nput voltage on the output voltage
Output voltage load regulation: the relative change of output voltage when the load current changes \n Output voltage accuracy: error range of the output voltage of the device
Load transient response: The fluctuation of the output voltage when the load current changes rapidly fr0m a small value to a maximum value.
Does the power chip choose DC/DC or LDO?
It depends on your application. For example, in the case of boosting, of course, only DC/DC can be used, because LDO is a voltage drop type and can not be boosted. In addition, look at their main features:
DC/DC: high efficiency, high noise;
LDO: Low noise, small quiescent current;
Therefore, if it is used in the case of large voltage drop, choose DC/DC because of its high efficiency, while LDO will lose a large part of its efficiency because of large voltage drop;
If the voltage drop is small, choose LDO because of its low noise, clean power supply, simple peripheral circuit and low cost.
LDO is a low dropout regulator, which means a low dropout linear regulator, as opposed to a traditional linear regulator. Traditional linear regulators, such as 78xx series chips, require the 1nput voltage to be more than 2 V ~ 3 V higher than the output voltage, otherwise they will not work properly. However, in some cases, this condition is obviously too harsh, such as 5 V to 3. 3 V, the 1nput and output voltage difference is only 1. 7 V, which obviously does not meet the conditions. In view of this situation, there is a LDO power conversion chip.
LDO linear step-down chip: The principle is equivalent to a resistor divider to achieve step-down, the energy loss is large, the reduced voltage is converted into heat, the greater the voltage difference and load current of step-down, the more obvious the chip heating. The package of this kind of chip is relatively large, which is convenient for heat dissipation.
LDO linear step-down chips such as: 2596, L78 series.
DC/DC step-down chip: In the process of step-down, the energy loss is relatively small, and the chip heating is not obvious. The chip package is relatively small, and PWM digital control can be realized.

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