PCB Tech - Do you know what are the requirements for power supply pcb board design?

Do you know what are the requirements for power supply PCB board design?

In circuit board production,PCB design occupies a very important position. It can be said that a good printed circuit board starts with PCB design. Take the power supply as an example, the PCB design has a direct impact on the EMC performance, output noise, and anti-interference ability of the power supply. So, do you know what are the requirements for power supply PCB board design? The following PCB factory editor will explain to you.

What are the requirements for power supply PCB board design

spacing

The power PCB is a high-voltage product, and the line spacing must be considered. If the spacing required by the corresponding safety regulations can be met, it is the best, but those products that do not require certification and cannot meet the certification must rely on rich experience to determine Spacing out. How wide is the appropriate spacing? This requires consideration of whether the production can guarantee the cleanliness of the board surface, environmental humidity, and other pollution.

If it is a mains input, even if the board surface is clean and sealed, the drain-source gap of the MOS tube is close to 600V, which is actually more dangerous if it is less than 1mm.

When placing the chip capacitors or other easily damaged devices on the edge of the PCB, the direction of the PCB sub-board must be considered. The following figure shows the comparison of the stress levels when the devices are placed differently.

It can be seen that the device should be far away and parallel to the edge of the sub-board, otherwise the components may be damaged due to the PCB sub-board.

Regardless of input, output, power loop, signal loop, the loop area should be as small as possible. The electromagnetic field emitted by the power loop will cause poor EMI characteristics or greater output noise. At the same time, if it is received by the control loop, it may cause abnormalities. 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.

Due to the effect of di/dt, the inductance at the dynamic node must be reduced, otherwise a strong electromagnetic field will be generated. The inductance can be reduced by reducing the wiring length, and increasing the width can also be reduced, but the effect is small.

When wiring the entire control part, consider staying away from the power part. If the two are closer together due to other restrictions, you should not parallel the control line and the power line, otherwise it may cause abnormal and oscillating power supply operations.

In addition, if the control line is very long, the next pair of lines should be close, or the two should be placed on the 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 section. As shown in the figure, it illustrates the correct and incorrect signal wiring method between points A and B.

Right or wrong signal line layout method

Reminder: Minimize the vias used for connection on the signal line.
Copper

Sometimes copper laying 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 can easily pick up noise. Usually, it is only allowed to pour copper on static nodes. For example, pour copper on the “ground” node of the output terminal, 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 automatically map 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. Wires can be made on one side of the control part of the circuit, while copper is laid on the "ground" node on the other side, and the two sides are connected through vias.

Output rectifier diode

If the output rectifier diode is close to the output terminal, it should not be placed in parallel with the output. Otherwise, the electromagnetic field generated at the diode will penetrate the loop formed by the power supply output and the external load, which will increase the measured output noise.

Diode placement

Ground wire

It is necessary to be 100% careful about the wiring of the ground wire. A slight error may cause deterioration of EMS, EMI performance and other performance. Regarding the "ground" of the switching power supply PCB, the following two points need to be noted:

1. The power ground and signal ground should be connected at a single point;

2. There should be no ground loop.

Y capacitor

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

In addition to the above-mentioned requirements for the power supply PCB design, some other issues need to be considered, including: "The varistor should be close to the protected circuit", "Common mode induction increases the discharge teeth", "The chip VCC power supply should be increased Ceramic capacitors" and so on. There is also the need for special treatment such as copper foil, shielding, etc. These are issues that need to be considered during PCB design.

The above is the "what are the requirements for power supply PCB board design" shared by the editor today. Of course, what the editor shared today is only the most common power supply PCB design. Most engineers will choose the power module as the basis of system power supply. The overall product or system has a stable and reliable power supply.