Every electronic engineer must know that PCB design occupies a very important position when designing. Taking the power supply as an example, the PCB design will directly affect the EMC performance, output noise, anti-interference ability, and even basic functions of the power supply. The PCB layout of the power supply part is slightly different from other hardware, how should it be designed? This article reveals the secret for you.

Spacing For high voltage products, line spacing must be considered. The spacing that can meet the corresponding safety requirements is of course the best, but in many cases, for products that do not require certification, or cannot meet the certification, the spacing is determined by experience.

What is the proper spacing? It must be considered whether the production can guarantee the cleanliness of the board surface, environmental humidity, other pollution, etc.

For the mains input, even if the board surface is clean and sealed, the distance between the drain and source of the MOS tube is close to 600V, and it is actually dangerous if it is less than 1mm!

Components on the edge of the board, chip capacitors or other vulnerable devices on the edge of the PCB, must consider the direction of the PCB sub-board when placing them.

Figure 1 The stress comparison of the device when the board is split

From this, it can be seen that the components should be kept away from and parallel to the edge of the sub-board, otherwise the components may be damaged due to the PCB sub-board.

The loop area, whether it is input or output, power loop or signal loop, should be as small as possible. The electromagnetic field emitted by the power loop will result in poor EMI characteristics or larger output noise; at the same time, if it is received by the control loop, it is likely to cause anomalies.

On the other hand, if the power loop area is large, its equivalent parasitic inductance will also increase, which may increase the drain noise spike.

The inductance at the dynamic node must be reduced due to the effect of di/dt on the key traces, otherwise a strong electromagnetic field will be generated. To reduce the inductance, the main thing is to reduce the length of the wiring, and increasing the width has less effect.

Signal lines For the entire control section, consider routing them away from the power section. If the two are close to each other due to other restrictions, the control line and the power line should not be connected in parallel, otherwise the power supply may work abnormally and oscillate.

In addition, if the control line is very long, the back and forth pair of lines should be close to each other, or they should be placed on two sides of the PCB and face each other, so as to reduce the loop area and avoid being interfered by the electromagnetic field of the power part. Figure 2 illustrates the correct and incorrect wiring methods of signal lines between points A and B.

Figure 2 Correct and incorrect wiring methods for signal lines.

Of course, there should be as few vias as possible on the signal lines for connections!
Copper plating Sometimes copper plating is completely unnecessary and should even be avoided. If the copper area is large enough and its voltage is constantly changing, on the one hand, it may act as an antenna, radiating electromagnetic waves to the surrounding; on the other hand, it is easy to pick up noise.

Usually, only copper is allowed to be placed at the static node. For example, copper is placed on the "ground" node of the output end, which can equivalently increase the output capacitance and filter out some noise signals.

Mapping For a loop, copper can be laid on one side of the PCB, and it will be automatically mapped according to the wiring on the other side of the PCB to minimize the impedance of this loop. It is as if a group of impedances with different impedance values are connected in parallel, and the current will automatically choose the path with the least impedance to flow through.
In fact, one side of the control part of the circuit can be wired, and the other side of the "ground" node is copper, and the two sides are connected by vias.

Output Rectifier Diodes If the output rectifier diodes are relatively close to the output, they should not be placed in parallel with the output. Otherwise, the electromagnetic field generated at the diode will penetrate into the loop formed by the output of the power supply and the external load, increasing the measured output noise.

Figure 3 Correct and Incorrect Diode Placement Orientation Ground Wire The ground wire must be routed with great care, otherwise it may cause EMS, EMI performance and other performance degradation. For the "ground" of the switching power supply PCB, do at least the following two points:

Power ground and signal ground should be connected at a single point;

There should be no ground loops.

The input and output of the Y capacitor are often connected to the Y capacitor. Sometimes, for some reasons, it may not be possible to hang it on the input capacitor ground. At this time, remember that it must be connected to a static node, such as a high-voltage terminal.

When designing other actual power supply PCBs, other issues may also be considered, such as "varistor should be close to the protected circuit", "common-mode inductance should increase discharge teeth", "chip capacitor should be added to the VCC power supply", etc. Wait. In addition, whether special treatment is required, such as copper foil, shielding, etc., also needs to be considered in the PCB design stage.

Sometimes there are situations where multiple principles conflict with each other, and satisfying one of them cannot satisfy the others. This requires engineers to apply their existing experience and determine the most suitable wiring according to the actual project requirements!
Summary In order to create a highly stable product, there are many design details required in the hardware design. This article only introduces the most common power supply design in hardware. In order to make the overall product or system have a stable and reliable power supply, most engineers will choose the power supply module as the basis of the system power supply.

The isolated power modules independently developed and produced by ZLG have been accumulated in the industry for nearly 20 years. At present, the products have a wide input voltage range, isolation of 1000VDC, 1500VDC, 3000VDC and 6000VDC series, various packaging forms, and are compatible with international standard SIP, DIP and other packaging.

At the same time, in order to ensure the performance of power supply products, ZLG has built a first-class testing laboratory in the industry, equipped with the most advanced and complete testing equipment. The whole series of isolated DC-DC power supplies have passed the complete EMC test. It can be applied to most complex and harsh industrial sites, providing users with stable and reliable power isolation solutions.