PCB Fabrication

Power PCB design skills and case analysis

by:A-TECH      2021-03-20
Nowadays, the volume of the switching power supply is getting smaller and smaller, and its operating frequency and internal device density are getting higher and higher. This is undoubtedly more and more stringent for the anti-interference requirements of the power supply PCB layout. Next, Banermei will share with you some skills and cases in the layout and routing of power supply PCB design for everyone to learn and refer to. Power supply PCB design skills 1. Component layout The best way to establish a switching power supply layout is similar to its electrical design. The best design process is as follows: 1. Place the transformer 2. Design the power switch current loop 3. Design the output rectifier current loop 4. Connect to Control circuit of AC power circuit 5. Design input current source circuit and input filter 6. Design output load circuit and output filter According to the functional unit of the circuit, when laying out all the components of the circuit, the following principles should be met: (1 ) First, consider the PCB size. When the PCB size is too large, the printed lines will be long, the impedance will increase, the anti-noise ability will decrease, and the cost will increase; if the PCB size is too small, the heat dissipation will not be good, and adjacent lines will be easily disturbed. The best shape of the circuit board is rectangular, and the aspect ratio is 3:2 or 4:3. The components located on the edge of the circuit board are generally not less than 2mm away from the edge of the circuit board. (2) When placing the device, consider the subsequent soldering, not too dense. (3) Take the core component of each functional circuit as the center and lay out around it. The components should be evenly, neatly and compactly arranged on the PCB, minimize and shorten the leads and connections between the components, and the decoupling capacitor should be as close as possible to the VCC of the device. (4) For circuits operating at high frequencies, the distributed parameters between components should be considered. Generally, the circuit should be arranged in parallel as much as possible. In this way, it is not only beautiful, but also easy to install and weld, and easy to mass produce. (5) Arrange the position of each functional circuit unit according to the circuit flow, so that the layout is convenient for signal circulation, and the signal is kept in the same direction as possible. (6) The first principle of the layout is to ensure the wiring rate, pay attention to the connection of the flying wires when moving the device, and put the devices with the connection relationship together. (7) Reduce the loop area as much as possible to suppress the radiation interference of the switching power supply. 2. Wiring The switching power supply contains high-frequency signals. Any printed line on the PCB can function as an antenna. The length and width of the printed line will affect its impedance and inductance, thereby affecting the frequency response. Even printed lines that pass DC signals can couple to radio frequency signals from adjacent printed lines and cause circuit problems (and even radiate interfering signals again). Therefore, all printed lines that pass AC current should be designed to be as short and wide as possible, which means that all components connected to the printed lines and other power lines must be placed very close. The length of the printed line is proportional to its inductance and impedance, and the width is inversely proportional to the inductance and impedance of the printed line. The length reflects the wavelength of the printed line's response. The longer the length, the lower the frequency at which the printed line can send and receive electromagnetic waves, and it can radiate more radio frequency energy. According to the size of the printed circuit board current, try to increase the width of the power line to reduce the loop resistance. At the same time, make the direction of the power line and the ground line consistent with the direction of the current, which helps to enhance the anti-noise ability. (1) Wiring direction: From the perspective of the soldering surface, the arrangement of the components should be as consistent as possible with the schematic diagram. The wiring direction is best to be consistent with the wiring direction of the circuit diagram, because various parameters are usually required on the soldering surface during the production process. Inspection, so this is convenient for inspection, debugging and overhaul in production (Note: refers to the premise of meeting the circuit performance and the requirements of the whole machine installation and panel layout). (2) When designing the wiring diagram, the wiring should not bend as much as possible, the line width on the printed arc should not be changed suddenly, the corner of the wire should be ≥90 degrees, and the line should be simple and clear. (3) Cross circuits are not allowed in printed circuits. For lines that may cross, you can use 'drilling' and 'winding' two methods to solve them. That is, let a lead 'drill' through the gap under other resistors, capacitors, and triode pins, or 'wind' from one end of a lead that may cross. In special cases, if the circuit is very complicated, to simplify the design, it is also allowed to use wire jumpers to solve the cross circuit problem. (4) Input ground and output ground This switching power supply is a low-voltage DC-DC. To feed the output voltage back to the primary of the transformer, the circuits on both sides should have a common reference ground, so after laying copper on the ground wires on both sides respectively , But also to be connected together to form a common ground. Case study Case 1: Overall layout Case 1 is a six-layer board. The first layout is the control part of the component surface and the power part of the solder surface. During debugging, it is found that the interference is very large because of the PWM IC and optocoupler. The location is unreasonable. As shown in the figure above, the PWM IC and the optocoupler are placed under the MOS tube, and there is only a layer of 2.0mm PCB between them. The MOS tube directly interferes with the PWM IC. The improvement is: remove the PWM IC from the optocoupler and above it No pulsating components flow through the device. Case 2: Wiring problem The power wiring is as short as possible to reduce the area surrounded by the loop and avoid interference. The small signal line has a small enclosing area, such as a current loop: the larger the area covered by the A line and the B line, the more interference it receives. Because it is a feedback circuit, the larger the area covered by the A line and the B line, the more interference it receives. Because it is a feedback coupling, the feedback line should be short, and there can be no pulsating signal crossing or parallel to it. The PWM IC chip current sampling line and driving line, as well as the synchronization signal line, should be routed as far away as possible, and they should not be routed in parallel, otherwise they will interfere with each other. Figure: The current waveform is: PWM IC drive waveform and synchronous signal voltage waveform are: here you can enter the PCB pricing page https://www./
Custom message
Chat Online 编辑模式下无法使用
Chat Online inputting...
Please hold on and we will get back to you soon