Power adapter PCB reasonable arrangement of components
First, the aesthetics should not only consider the neat and orderly placement of components, but also consider the beautiful and smooth routing. Since the average layman sometimes emphasizes the former, to evaluate the advantages and disadvantages of the circuit design one-sidedly, for the image of the product, the former should be given priority when the performance requirements are not critical. However, in high-performance applications, if you have to use a double-panel, but also packaged inside, usually can not see, you should give priority to the aesthetics of the trace.
2. The stressed circuit board should be able to withstand various external forces and vibrations during installation and operation. For this reason, the circuit board should have a reasonable shape, and the positions of various holes (screw holes, shaped holes) on the board should be reasonably arranged. Generally, the distance between the hole and the edge of the plate is at least greater than the diameter of the hole. At the same time, it should be noted that the weakest section of the plate caused by the shaped hole should also have sufficient bending strength. The connectors that directly "stretch" out the device casing on the board must be reasonably fixed to ensure the reliability of long-term use.
Third, the heat for high-power, severely heated devices, in addition to ensuring heat dissipation conditions, but also pay attention to placed in the appropriate position. Especially in precision analog systems, special attention should be paid to the adverse effects of the temperature field generated by these devices on the fragile preamplifier circuit. Generally, the part with very large power should be made into a single module and take certain thermal isolation measures from the signal processing circuit.
Fourth, the signal; signal interference is the most important factor to consider in the power adapter PCB layout design. The most basic aspects are: the weak signal circuit is separated or even isolated from the strong signal circuit; the AC portion is separated from the DC portion; the high frequency portion is separated from the low frequency portion;
Pay attention to the direction of the signal line; the arrangement of the ground line; appropriate shielding, filtering and other measures. These are a lot of arguments that have been repeatedly emphasized and will not be repeated here.
V. Installation refers to the specific application, in order to smoothly install the circuit board into the chassis, the outer casing, the slot, and not cause space interference, short circuit and other accidents, and make the specified connector in the specified position on the chassis or the casing. A series of basic requirements.
EMC considerations: Bypass or decoupling capacitors enhance stability and reduce interference
In PCB design, both analog and digital devices require this type of capacitor, with a bypass capacitor connected to the pin of their power adapter. This capacitor is typically 0.1uF. The layout requires that the pins be as short as possible and as close as possible to the device to reduce the inductance of the traces.
Bypass capacitors are often used in bypass circuit design for high frequency signals on the power adapter. In general, the frequency of these high frequency signals exceeds the ability of analog devices to reject high frequency signals. If bypass capacitors are not used, noise can be introduced into the signal path, and even more severe conditions can cause vibration and false response.
Digital circuit design Digital devices such as controllers and processors also require decoupling capacitors. One of the capacitor functions is used as a "mini" charge bank. Because the gate state switching or switching is performed in the digital circuit, a large current is usually required, and the transient current generated during the switching does not have enough electric charge when the switching operation is performed, which causes a large change in the power adapter voltage. A voltage change that is too large can cause the digital signal level to go into an unstable state, which is likely to cause a misstatement of the state of the digital device. Therefore, it is good practice to add bypass or decoupling capacitors to the power supply adapter pins or power adapter pins of digital devices.
The most sensitive signals in a microcontroller-based (MCU)-based system are timing, reset, and interrupt signals. The oscillator is especially sensitive when switching. These circuits cannot be parallel to high current traces to avoid signal interference and false positives. An oscillator or ceramic resonant clock is an RF circuit that must be effectively laid out to the nearest distance with the shortest trace to reduce its sensitivity. The following figure uses a DIP-packaged oscillator or ceramic resonator as an example. The oscillating circuit should be placed close to the microcontroller layout, and the position should be symmetrical, so that the trace distance is the shortest. The ground of the oscillating circuit should be connected to the ground pin that the component may use the shortest path. The power adapter and ground pin should be connected directly to the power adapter portion of the PCB.
Similarly, when the logic switch on the board is switched, a transient derivative current is generated on the power adapter line. Since the power adapter line has a slight inductivity, the inductivity of the power adapter line can pass through a multi-layer printed circuit board (power adapter plane). To lower, or use slower logic to reduce the switching speed. But the former increases costs, and the latter reduces system performance. In this case, the communication interference of the power adapter line can be reduced by the decoupling capacitor. The decoupling capacitors (also called sharpening capacitors) on the PCB for the digital chip should be placed as close as possible to the power adapter pins of the chip to minimize the trace distance and minimize the loop area. The left side of the figure below shows the unreasonable decoupling capacitor layout, which should be laid out like the right side of the figure.
2. 3D device inspection avoids conflicts - connectors
In the PCB layout, because the real components can not be seen in real time, including the volume and height of the components. Does the entire circuit board match the outer casing, and does the horizontal direction of the components inside the circuit board conflict with each other, resulting in a situation in which the installation is not possible? The most terrible thing is, is the height of the component appropriate and will it conflict with the outer casing? This requires real-time realistic simulation and presentation in 3D to detect problems early. In order to ensure that the board and the shell shape match, the height is matched, and the mounting holes are matched.
The layout of the PCB board is also critical, and the good connector layout should take into account the convenience of plugging and unplugging in the future. Generally speaking, the connector needs to be close to the edge of the board and the interface is outside the board. It should not be too close to the board, so that the plug at the end of the cable is blocked by the edge of the PCB and cannot be inserted. As shown below, the unreasonable connector layout of the DB9 serial port causes the cable connector to be disconnected.
For the failure case of this connector, if you can visually find the problem through the 3D view before making the PCB board, and modify it in time, it will save a lot of unnecessary time and effort. Instead of doing the PCB board, the device is mounted, and the problem is discovered when the connection is finally made.
3. Grid application: place the components in a circular shape
Not long ago, a colleague in the electronics industry chatted with me. He wanted to place the LED lights in a standard circular shape to maintain the same spacing. It is said that it is very troublesome in the process of placing, and the precise circular position is not guaranteed at all, and the spacing is also difficult to calculate. I don't know which tool can easily implement this idea. To be honest, I haven't tried this placement, but I suddenly remembered Altium Designer's ability to set up a polar grid, along with several other grid forms. Try this polar coordinate fan grid. Don't try, don't know, try it. With this fan-shaped grid, it is very easy to place the LED components on the PCB in a circular shape! As shown below.
In this board, an ARM7 microprocessor is placed in the center of the board at an angle of 45°. Then, with the center of the chip as the origin, a conventional rectangular grid with a 45° angle tilt is set.
A polar coordinate fan-shaped grid is placed on the outer ring to surround the LED. The LEDs arranged on the grid are accurate and beautiful. At the same time, when the component is placed, the mouse cursor will automatically capture the grid points, the positioning is accurate, and the operation is extremely simple.
Whether in schematic design or in PCB design, using a grid to place the target object makes the drawings you design very clean, clean, and organized. In the PCB design, when you place components, you can use multiple grid combination applications. You can place the components to the desired position as you wish. You can think of this design magician, it can help you achieve. This is a wonderful and valuable feeling for engineers who are boring every day! The following figure shows the bare board view of the front and back of the design project PCB in 3D state.
The circular PCB board above is another case of clever use of the grid. The five mounting holes in the center of the green circle are distributed symmetrically around the center point. The outside of the board is precisely symmetrical along the four mounting holes.http://www.original-phoneaccessories.com/product_category/power-adapter-wholesale/
2. The stressed circuit board should be able to withstand various external forces and vibrations during installation and operation. For this reason, the circuit board should have a reasonable shape, and the positions of various holes (screw holes, shaped holes) on the board should be reasonably arranged. Generally, the distance between the hole and the edge of the plate is at least greater than the diameter of the hole. At the same time, it should be noted that the weakest section of the plate caused by the shaped hole should also have sufficient bending strength. The connectors that directly "stretch" out the device casing on the board must be reasonably fixed to ensure the reliability of long-term use.
Third, the heat for high-power, severely heated devices, in addition to ensuring heat dissipation conditions, but also pay attention to placed in the appropriate position. Especially in precision analog systems, special attention should be paid to the adverse effects of the temperature field generated by these devices on the fragile preamplifier circuit. Generally, the part with very large power should be made into a single module and take certain thermal isolation measures from the signal processing circuit.
Fourth, the signal; signal interference is the most important factor to consider in the power adapter PCB layout design. The most basic aspects are: the weak signal circuit is separated or even isolated from the strong signal circuit; the AC portion is separated from the DC portion; the high frequency portion is separated from the low frequency portion;
Pay attention to the direction of the signal line; the arrangement of the ground line; appropriate shielding, filtering and other measures. These are a lot of arguments that have been repeatedly emphasized and will not be repeated here.
V. Installation refers to the specific application, in order to smoothly install the circuit board into the chassis, the outer casing, the slot, and not cause space interference, short circuit and other accidents, and make the specified connector in the specified position on the chassis or the casing. A series of basic requirements.
EMC considerations: Bypass or decoupling capacitors enhance stability and reduce interference
In PCB design, both analog and digital devices require this type of capacitor, with a bypass capacitor connected to the pin of their power adapter. This capacitor is typically 0.1uF. The layout requires that the pins be as short as possible and as close as possible to the device to reduce the inductance of the traces.
Bypass capacitors are often used in bypass circuit design for high frequency signals on the power adapter. In general, the frequency of these high frequency signals exceeds the ability of analog devices to reject high frequency signals. If bypass capacitors are not used, noise can be introduced into the signal path, and even more severe conditions can cause vibration and false response.
Digital circuit design Digital devices such as controllers and processors also require decoupling capacitors. One of the capacitor functions is used as a "mini" charge bank. Because the gate state switching or switching is performed in the digital circuit, a large current is usually required, and the transient current generated during the switching does not have enough electric charge when the switching operation is performed, which causes a large change in the power adapter voltage. A voltage change that is too large can cause the digital signal level to go into an unstable state, which is likely to cause a misstatement of the state of the digital device. Therefore, it is good practice to add bypass or decoupling capacitors to the power supply adapter pins or power adapter pins of digital devices.
The most sensitive signals in a microcontroller-based (MCU)-based system are timing, reset, and interrupt signals. The oscillator is especially sensitive when switching. These circuits cannot be parallel to high current traces to avoid signal interference and false positives. An oscillator or ceramic resonant clock is an RF circuit that must be effectively laid out to the nearest distance with the shortest trace to reduce its sensitivity. The following figure uses a DIP-packaged oscillator or ceramic resonator as an example. The oscillating circuit should be placed close to the microcontroller layout, and the position should be symmetrical, so that the trace distance is the shortest. The ground of the oscillating circuit should be connected to the ground pin that the component may use the shortest path. The power adapter and ground pin should be connected directly to the power adapter portion of the PCB.
Similarly, when the logic switch on the board is switched, a transient derivative current is generated on the power adapter line. Since the power adapter line has a slight inductivity, the inductivity of the power adapter line can pass through a multi-layer printed circuit board (power adapter plane). To lower, or use slower logic to reduce the switching speed. But the former increases costs, and the latter reduces system performance. In this case, the communication interference of the power adapter line can be reduced by the decoupling capacitor. The decoupling capacitors (also called sharpening capacitors) on the PCB for the digital chip should be placed as close as possible to the power adapter pins of the chip to minimize the trace distance and minimize the loop area. The left side of the figure below shows the unreasonable decoupling capacitor layout, which should be laid out like the right side of the figure.
2. 3D device inspection avoids conflicts - connectors
In the PCB layout, because the real components can not be seen in real time, including the volume and height of the components. Does the entire circuit board match the outer casing, and does the horizontal direction of the components inside the circuit board conflict with each other, resulting in a situation in which the installation is not possible? The most terrible thing is, is the height of the component appropriate and will it conflict with the outer casing? This requires real-time realistic simulation and presentation in 3D to detect problems early. In order to ensure that the board and the shell shape match, the height is matched, and the mounting holes are matched.
The layout of the PCB board is also critical, and the good connector layout should take into account the convenience of plugging and unplugging in the future. Generally speaking, the connector needs to be close to the edge of the board and the interface is outside the board. It should not be too close to the board, so that the plug at the end of the cable is blocked by the edge of the PCB and cannot be inserted. As shown below, the unreasonable connector layout of the DB9 serial port causes the cable connector to be disconnected.
For the failure case of this connector, if you can visually find the problem through the 3D view before making the PCB board, and modify it in time, it will save a lot of unnecessary time and effort. Instead of doing the PCB board, the device is mounted, and the problem is discovered when the connection is finally made.
3. Grid application: place the components in a circular shape
Not long ago, a colleague in the electronics industry chatted with me. He wanted to place the LED lights in a standard circular shape to maintain the same spacing. It is said that it is very troublesome in the process of placing, and the precise circular position is not guaranteed at all, and the spacing is also difficult to calculate. I don't know which tool can easily implement this idea. To be honest, I haven't tried this placement, but I suddenly remembered Altium Designer's ability to set up a polar grid, along with several other grid forms. Try this polar coordinate fan grid. Don't try, don't know, try it. With this fan-shaped grid, it is very easy to place the LED components on the PCB in a circular shape! As shown below.
In this board, an ARM7 microprocessor is placed in the center of the board at an angle of 45°. Then, with the center of the chip as the origin, a conventional rectangular grid with a 45° angle tilt is set.
A polar coordinate fan-shaped grid is placed on the outer ring to surround the LED. The LEDs arranged on the grid are accurate and beautiful. At the same time, when the component is placed, the mouse cursor will automatically capture the grid points, the positioning is accurate, and the operation is extremely simple.
Whether in schematic design or in PCB design, using a grid to place the target object makes the drawings you design very clean, clean, and organized. In the PCB design, when you place components, you can use multiple grid combination applications. You can place the components to the desired position as you wish. You can think of this design magician, it can help you achieve. This is a wonderful and valuable feeling for engineers who are boring every day! The following figure shows the bare board view of the front and back of the design project PCB in 3D state.
The circular PCB board above is another case of clever use of the grid. The five mounting holes in the center of the green circle are distributed symmetrically around the center point. The outside of the board is precisely symmetrical along the four mounting holes.http://www.original-phoneaccessories.com/product_category/power-adapter-wholesale/
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