@Engineer, what you need to know about PCB power and ground design

In PCB design, the handling of power and ground wires deserves engineers’ attention. Because even if the wiring in the entire PCB board is completed well, interference caused by insufficient consideration of power and ground wires will degrade the performance of the product and sometimes even affect the success rate of the product. Therefore, the handling of power supply and ground wires must be taken seriously, and the noise and interference generated by power supply and ground wires should be reduced to a minimum to ensure the quality of the product.

Handling of power and ground wires

1. Try to widen the width of the power and ground wires. It is best to make the ground wire wider than the power wire. Their relationship is: ground wire-power wire-signal wire.

2. For the PCB of the digital circuit, a wide ground wire can be used to form a loop, that is, a ground network can be used (the ground of the analog circuit cannot be used in this way)

3. A large area of copper layer is used as a ground wire, and all unused areas on the printed board are connected to the ground as a ground wire. Or a multi-layer board, with power and ground wires occupying one layer each.

Power supply PCB wiring tips

The switching power supply contains high-frequency signals. Any printed wire on the PCB can function as an antenna. The length and width of the printed wire will affect its impedance and inductive reactance, thus affecting the frequency response. Even traces passing DC signals can couple to RF signals from adjacent traces and cause circuit problems (or even re-radiate interfering signals). Therefore, all traces carrying AC current should be designed to be as short and wide as possible, which means that all components connected to the traces and to other power traces must be placed close to each other.

The length of a printed line is directly proportional to the inductance and impedance it exhibits, while the width is inversely proportional to the inductance and impedance of the printed line. The length reflects the wavelength at which the printed wire responds. The longer the length, the lower the frequency at which the printed wire can send and receive electromagnetic waves, and the more radio frequency energy it can radiate. 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 ground wire consistent with the direction of the current, which will help enhance the anti-noise capability.

(1) Wiring direction: From the welding surface, the arrangement of components should be consistent with the schematic diagram as much as possible. The wiring direction should be consistent with the wiring direction of the circuit diagram, because during the production process, various parameters usually need to be adjusted on the welding surface. detection, so this facilitates inspection, debugging and maintenance during production (Note: This refers to the premise of meeting the requirements of circuit performance, complete machine installation and panel layout).

(2) When designing the wiring diagram, the wiring should have as few turns as possible. The line width on the printed arc should not change suddenly. The wire corners should be ≥90 degrees, and strive to keep the lines simple and clear.

(3) Cross circuits are not allowed in printed circuits. For lines that may cross, “drilling” and “winding” can be used to solve them. That is, let a certain lead “drill” through the gap at the foot of other resistors, capacitors, and transistors, or “go around” one end of a lead that may cross. In special cases, if the circuit is very complex, it is also allowed to use wire jumpers to simplify the design and solve the problem of cross circuits.

(4) Input ground and output ground. This switching power supply is a low-voltage DC-DC. If you want to feed the output voltage back to the primary of the transformer, the circuits on both sides should have a common reference ground. Therefore, after laying copper on the ground wires on both sides,  but also connected together to form a common ground.

Principles of ground wire design

1. Separate digital ground and analog ground

If there are both logic circuits and linear circuits on the circuit board, they should be kept as separate as possible. The ground of the low-frequency circuit should be grounded in parallel at a single point as much as possible. If there are difficulties in actual wiring, it can be partially connected in series and then grounded in parallel. High-frequency circuits should be grounded at multiple points in series. The ground wire should be short and flat. Try to use a large-area grid-shaped ground foil around high-frequency components. PCB power supply

2. The grounding wire should be as thick as possible

If the ground wire is very thin, the ground potential will change with the change of current, which will reduce the noise immunity performance. Therefore, the ground wire should be thickened so that it can pass three times the allowable current of the printed board. If possible, the ground wire should be above 2~3mm.

3. The ground wire forms a closed loop

For printed boards that are only composed of digital circuits, most of the ground circuits arranged in group loops can improve noise immunity.

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