PCB News - Guidance on electrical aspects of PCB board layout and wiring

Guidance on electrical aspects of PCB board layout and wiring

Switching power supply PCB layout and line is very important for the correctness and reliability of the circuit function, relative to the simple simulation circuit and digital circuit, switching power supply has a very high voltage and high current, therefore, its go go line spacing and line width is particularly important, in addition, the pursuit of high efficiency makes the work of modern switching power supply frequency is higher and higher (& gt; 50KHz), and the switching time is getting shorter and shorter (& LT; 1000 nS), and all this (high voltage; Large current; High frequency; Short time) knots and make the wiring requirements of the main parts of the switching power supply very short and thick (ensure positive spacing below).

The rapid switching of the switch tube will cause EMI noise problems, which will interfere with the

normal operation of the switch power supply and other electrical appliances. Or the system may exceed the allowable EMI range. EMI noise cannot be completely eliminated. However, we can use some methods to reduce it to a minimum value or to a permissible range, including the isolation of noise sources and sensitive circuits; Shield the ground wire with high current, and reduce EMI influence by placing ceramic capacitors and ferrite magnetic beads on key parts.

PCB design of switching power supply is not simple, in fact, it is impossible to determine everything at the beginning. Only through the interaction and communication between PCB layout designer and power supply designer, after several times of repeated modification, can the whole PCB design finally obtain a reliable scheme.

Parts placement

Because it is sometimes impossible to meet all the terms, the result is often a compromise. However, it is very important to place the parts properly.

Preliminary layout of parts

The power designer should provide a rough Layout. This may be a manuscript, but it is best to provide a rough Layout CAD. In the design process, the most important part is the placement of the main loop components. And all other important parts placement.

Regional layout of parts

In practical work, parts should be distributed according to the function of the circuit, and parts with the same function should be evenly; Compact together, and there should be an effective separation between parts of different functions. Subject to clause. The power supply designer shall provide a diagram of the placement of the important parts on the PCB and the parts placement of the functional modules of the main circuit.

Circuit layout

The parts should be in the right place. In order to facilitate wiring and reduce cross wiring and reduce some long wiring, as for which wiring must be short. Its contents should be taken seriously. In addition, some important wiring should be sufficient width. In addition,safe spacing and important spacing

Sensitive circuit and noise circuit

Sensitive circuits are those that are particularly sensitive to noise. Noise circuit refers to the source of noise. For most power supplies, there are usually some sensitive circuits and noise circuits. These circuits must be effectively isolated from each other, and the best method is to keep the distance between them at least 1inch. In this way, faults can be effectively reduced. Sensitive and noisy circuits should be clearly marked on the schematic diagram.

Temperature rise and mechanism considerations

Temperature rise and mechanism issues are very important, the power supply designer should provide a very detailed guidelines, and need to evaluate PCB layout and heat sink and design integrity. Usually these issues will be dealt with first. In the case of power supply, correct layout and wiring are critical to the correctness of the circuit. It is the first condition to ensure the correctness of the circuit, followed by thermal and mechanical and manufacturing considerations.

Production considerations

Production considerations are a common issue for PCB layers, and all details should be determined by the power supply designer.

Definition of Layer:

The power supply designer must determine whether the PCB is single-layer or multi-layer, and if so. The designer must define the power layer, the layer, the shield layer, and the wiring layer. In addition, the size of the copper foil for each layer must be defined. This helps to minimize the bending and balance of the PCB. Finally, any specific constraints should be considered, which may include the isolation of the main circuit from the signal circuit, the isolation of the sensitive circuit from the noise circuit, and the segmentation of the ground plane.

Cable Width

The power supply designer must specify a minimum (default) wiring width. In addition, the schematic diagram provided by the designer must specify the minimum line width for all wiring. Any minimum wire diameter and maximum current value must be determined in detail. If the latter, the minimum line width will be determined by the table below. Preferred values are those listed in the column for temperature rise less than 10 degree Celsius.

Short Cabling

Some wiring should be kept as short as possible. In general, others show up in some switching current and high δ I/ δ T wiring. These lines should be shown on a schematic diagram. The power supply designer must determine which wiring should be short enough. And which should take precedence in the event of a conflict with other provisions.

Wiring and copper laying

Wiring of parts shall be manually routed as per 3.3 and other guidelines. It is hoped that the designer can discuss with the PCB layout maker to determine some priority Settings in the wiring and make a perfect scheme. In addition, PCB layout should send updated PCB progress to the power supply designer once a day. The power supply designer should check and evaluate the PCB layout status and report back to the PCB layout designer immediately to minimize the number of repeated PCB layout modifications.

Of course, if there is an unexpected problem, it is necessary to go back to modify and adjust parts.This situation must be determined before the first version is confirmed, or before making a large revision, and not when the PCB comes out of the Gerber File.

Considerations for heat sink

spacing

For AC lines, the spacing must meet leakage current requirements and specified safety requirements.

Electrical interference

Some cases show that there is high-frequency PCB noise and interference between some circuits and heat sink. Interference such as this can affect the integrity and functionality of the circuit. It is up to the power supply designer to determine whether it is necessary to cut the fins or make necessary shielding.