The whole process of PCB design for switching power supply

As a PCB engineer, what should I pay attention to in Lay PCB?

1. After the power supply comes in, it goes to the filter capacitor first, and then comes out of the filter capacitor before sending it to the following equipment. Because the wiring on the PCB is not an ideal conductor, there are resistances and distributed inductances. If electricity is taken from the front of the filter capacitor, the ripple will be larger and the filtering effect will be bad.

2, the lines are exquisite: the lines that are conditional to be wide will never be thin, there must be no sharp chamfers, and right angles should not be used when turning. The ground wire should be as wide as possible, and it is best to use a large area of copper plating, which greatly improves the problem of docking location.

3. Capacitors are set for switching devices (gate circuits) or other components that need filtering/decoupling. When arranging these capacitors, they should be as close as possible to these components. If they are too far away, they will have no effect.


When laying out PCB (power board), what matters should be paid attention to in combination with safety requirements?

1. The minimum safe distance between the two wires before the AC power supply enters the wire and the fuse is not less than 6MM, and the minimum safe distance between the two wires and the casing or internal grounding is not less than 8MM.

2. Wiring requirements behind the fuse: The minimum creepage distance of the zero and live wires shall not be less than 3 mm..

3. The minimum creepage distance between high voltage area and low voltage area is not less than 8MM, less than 8MM or equal to 8 mm.. 2MM safety groove must be opened.

4. Screen printing of high-voltage warning signs is required in high-voltage areas, that is, triangular symbols with exclamation marks; The high-pressure area must be framed by silk screen printing, and the silk screen printing of the frame should be not less than 3 mm.

5, the minimum safe distance between the positive and negative of high voltage rectification filtering is not less than 2MM.


What is the design process of switching power supply pcb?

1. Make the schematic diagram according to the design.

2. After the schematic diagram is compiled, the corresponding network table can be generated.

3. Make a physical frame (Keepout Layer)

4. Introduction of components and networks

5. Layout of components: The layout and wiring of components have a great influence on the life, stability and electromagnetic compatibility of products, which should be paid special attention to. Generally speaking, there should be the following principles: (1) Place the components related to the structure in a fixed position first, such as power sockets, indicator lights, switches, connectors, etc. After these components are placed, use the lock function of the software to lock them so that they will not be moved by mistake in the future. Then place special components and large components on the line, such as heating elements, transformers, IC, etc. Finally, place the small device. ⑵ Pay attention to the layout of heat dissipation elements and pay special attention to heat dissipation. For high-power circuits, those heating elements, such as power tubes and transformers, should be laid aside as far as possible to facilitate heat dissipation, not concentrated in one place, and the high capacitance should not be too close to avoid premature aging of the electrolyte.

6. Wiring

7. Adjustment and perfection: After the wiring is completed, all we need to do is to make some adjustments to the characters, individual components and wiring and apply copper (this work should not be done too early, otherwise it will affect the speed and bring trouble to the wiring), also for the convenience of production, debugging and maintenance. Copper plating usually refers to filling the blank area left by wiring with a large area of copper foil, which can be paved with GND copper foil or VCC copper foil (but it is better to ground the device once it is short-circuited, unless it is necessary to increase the conduction area of the power supply to withstand a large current before connecting VCC). Covering the ground usually refers to wrapping a pinch of signal lines with special requirements with two ground wires (TRAC) to prevent it from being interfered or interfered by others. If copper plating is used instead of ground wire, we must pay attention to whether the whole ground is connected, the current size, flow direction and whether there are special requirements to ensure that unnecessary mistakes are reduced.

8. Check and check: sometimes the network relationship of the drawn board is different from the schematic diagram due to misoperation or negligence, so it is necessary to check and check. Therefore, after painting, you must not rush to hand it over to the plate-making manufacturer. You should check it first and then carry out the follow-up work.

How to unify PCB design and mechanism design in design?

Height limit requirements, component layout should not lead to assembly interference; The design of PCB shape, positioning holes and mounting holes should consider that the shape and size of PCB should be consistent with the structural design, the device selection should meet the machining error of the structure and the machining error of the structural parts, and the assembly process of PCB layout should make the production efficiency the highest; Designers should consider whether the shape design can minimize the assembly process, that is, can the design of multi-layer or double-panel be replaced by single panel? Can each side of PCB be completed by one assembly process? Can you avoid manual welding to the maximum extent? Can the used plug-in components be replaced by patch components? The packaging of selected components should be unified with the physical object, and the pad spacing and size should meet the design requirements; The components are evenly distributed, especially the high-power components should be dispersed to avoid the stress caused by local overheating on the PCB when the circuit works, which will affect the reliability of solder joints; Considering the heat dissipation design of high-power devices; Under the condition of design permission, the layout of components should be arranged in the same direction as far as possible, and modules with the same function should be arranged together; Components in the same package are placed at equal distances to facilitate component mounting, welding and testing; Screen printing is clearly identifiable, with clear polarity and direction indication, and is not blocked by assembled devices.

What are the PCB materials? What are the common PCB materials of switching power supply?

1. 94V-0 and 94V-2 belong to a class of flame retardant materials, and 94V-0 belongs to the highest flame retardant material of these two kinds.

In terms of materials, it can be divided into organic materials and inorganic materials.

A. organic phenolic resin, glass fiber/epoxy resin, polyurethane, BT/Epoxy, etc.

B. Inorganic materials such as aluminum, Copper-invar-copper, ceramic, etc.

2, aluminum substrate PCB

Briefly describe the material recognition process.

1. Carry out monomer test on samples, and put forward a "sample test report", which can be used as a reference for some items that need special instruments to be tested. For crystal semiconductors, plastic parts and packaging materials of well-known foreign brands, individual tests are not required, but samples of various materials need to be actually installed and used, and the results will be an important basis for final judgment;

2. Using the test and taking this result as an important basis for the final judgment, the R&D department checks the test result of the sample with the specifications in the acceptance letter, determines the consistency between the acceptance letter and the sample, and checks the integrity of the content of the acceptance letter;

3. For materials that fail to pass the single test or the acceptance letter does not meet the requirements, the procurement is required to provide samples and acceptance letters again;

4. For some key materials, after the monomer test of the R&D department has passed, the R&D department will apply for small batch trial investment, the production department will lead the trial investment work, and the quality control department will be responsible for the verification of the trial investment materials;

5. After the material sample acceptance and trial investment (key materials) are all qualified, attach the cover of "Material Acceptance" and seal the samples (plastic parts and packaging materials can only be sealed as samples), and issue them to relevant departments after being approved by the R&D manager.

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