Good power supply circuit design requires a well-executed PCB layout and routing to effectively carry the signal. The quality of the PCB design is directly tied to the overall performance of the circuit. In product development, many revisions occur due to PCB design issues, especially when excessive changes are needed after the initial design. For example, improper layout of filter circuits or power circuits, such as inadequate spacing and poor angle choices, can lead to severe near-field coupling noise. As a result, repeated adjustments to the EMI filter may fail to significantly reduce noise transmission, forcing a redesign to optimize the layout. During product development, adhering to best practices and avoiding common pitfalls can significantly improve product performance. Below are some key PCB layout and routing recommendations.
**Overall Layout of Power Supply**
When planning the layout of the power PCB, prioritize the following sequence: power input – surge protection circuit – EMI filter – power supply module. Avoid using U-shaped layouts, as they may cause leakage of power within high-frequency magnetic fields (such as from high-frequency transformers, power inductors, etc.) and allow the filtering circuit to couple with the power input. This can lead to excessive low-frequency noise transmission. If a U-shaped layout is necessary due to structural constraints, such as the power supply configuration, use partition shielding to isolate the power and filter circuits. Additionally, position the filter capacitors close to the power connector to reduce interference.
**EMI Filter Circuit Layout**
For the EMI filter circuit, ensure that the differential mode capacitance before and after the common-mode inductor is connected using the Kelvin connection method. The copper area beneath the common-mode inductor should be perforated, with no other signal traces running through it. The Y capacitor, positioned on the right of the common-mode inductor, must be placed as close as possible to the power module to ensure low-impedance grounding. If the Y capacitor is located far from the grounding screw, connect it directly to the screw using a copper trace of at least 250 mils.
**Layout of Key Circuits and Voltage Movement Points**
In the switching and rectifier circuits of the power converter, it is essential to minimize the loop area. A larger loop area increases differential mode near-field radiation, which can interfere with surrounding low-voltage control and feedback signals. Voltage movement points, which experience significant DV/DT, should have their connecting traces (between the switching devices and magnetic components) kept as short as possible. Trace width should be minimized while still supporting the required current. If the loop area is too large, it can increase the parasitic capacitance and radiation efficiency of the enclosure, leading to greater electromagnetic interference.
**Layout of Magnetic Components**
For high-frequency transformers and inductors, ensure that the copper area beneath them is perforated, and avoid running signal traces beneath them. Transformers and inductors are sources of high-frequency magnetic fields, which can easily couple noise to the underlying traces.
**Control Circuit Layout**
Power circuits should be physically separated from control circuits. Power circuits typically operate at high voltage, high current, and high frequency, generating significant near-field interference. In contrast, control circuits generally handle low-voltage signals, which are more susceptible to interference. Therefore, a separate layout for these circuits is essential. Furthermore, power and control grounds should be routed separately, with a single-point ground to prevent common ground impedance coupling between the two.
**Drive Circuit Layout**
Keep the drive circuit close to the switching transistors. Since the drive signal is a significant source of DI/DT interference, control the loop area of the drive signal traces and their associated ground paths to minimize radiated noise.
**Primary-Side Capacitor Layout**
The filter capacitor between the primary-side static point and the secondary-side static point should be placed as close as possible to the transformer and switching transistors. This minimizes the common-mode loop area between the primary-side moving point, transformer primary stage capacitors, secondary-side static point, and the primary-side static point. This layout provides a low-impedance return path for common-mode noise, helping reduce the noise current flowing to the LISN.
**Epilogue**
The above are some fundamental guidelines for PCB layout and routing in power supply design. Organizing the layout by circuit module makes it easier to understand and remember these principles. By studying this article, we hope you have gained a deeper understanding of power EMI management.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
**Overall Layout of Power Supply**
When planning the layout of the power PCB, prioritize the following sequence: power input – surge protection circuit – EMI filter – power supply module. Avoid using U-shaped layouts, as they may cause leakage of power within high-frequency magnetic fields (such as from high-frequency transformers, power inductors, etc.) and allow the filtering circuit to couple with the power input. This can lead to excessive low-frequency noise transmission. If a U-shaped layout is necessary due to structural constraints, such as the power supply configuration, use partition shielding to isolate the power and filter circuits. Additionally, position the filter capacitors close to the power connector to reduce interference.
**EMI Filter Circuit Layout**
For the EMI filter circuit, ensure that the differential mode capacitance before and after the common-mode inductor is connected using the Kelvin connection method. The copper area beneath the common-mode inductor should be perforated, with no other signal traces running through it. The Y capacitor, positioned on the right of the common-mode inductor, must be placed as close as possible to the power module to ensure low-impedance grounding. If the Y capacitor is located far from the grounding screw, connect it directly to the screw using a copper trace of at least 250 mils.
**Layout of Key Circuits and Voltage Movement Points**
In the switching and rectifier circuits of the power converter, it is essential to minimize the loop area. A larger loop area increases differential mode near-field radiation, which can interfere with surrounding low-voltage control and feedback signals. Voltage movement points, which experience significant DV/DT, should have their connecting traces (between the switching devices and magnetic components) kept as short as possible. Trace width should be minimized while still supporting the required current. If the loop area is too large, it can increase the parasitic capacitance and radiation efficiency of the enclosure, leading to greater electromagnetic interference.
**Layout of Magnetic Components**
For high-frequency transformers and inductors, ensure that the copper area beneath them is perforated, and avoid running signal traces beneath them. Transformers and inductors are sources of high-frequency magnetic fields, which can easily couple noise to the underlying traces.
**Control Circuit Layout**
Power circuits should be physically separated from control circuits. Power circuits typically operate at high voltage, high current, and high frequency, generating significant near-field interference. In contrast, control circuits generally handle low-voltage signals, which are more susceptible to interference. Therefore, a separate layout for these circuits is essential. Furthermore, power and control grounds should be routed separately, with a single-point ground to prevent common ground impedance coupling between the two.
**Drive Circuit Layout**
Keep the drive circuit close to the switching transistors. Since the drive signal is a significant source of DI/DT interference, control the loop area of the drive signal traces and their associated ground paths to minimize radiated noise.
**Primary-Side Capacitor Layout**
The filter capacitor between the primary-side static point and the secondary-side static point should be placed as close as possible to the transformer and switching transistors. This minimizes the common-mode loop area between the primary-side moving point, transformer primary stage capacitors, secondary-side static point, and the primary-side static point. This layout provides a low-impedance return path for common-mode noise, helping reduce the noise current flowing to the LISN.
**Epilogue**
The above are some fundamental guidelines for PCB layout and routing in power supply design. Organizing the layout by circuit module makes it easier to understand and remember these principles. By studying this article, we hope you have gained a deeper understanding of power EMI management.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
