1. PCB Protection Design Principles
• Shielding Measures: Use metal enclosures, conductive coatings, or shielding covers to shield the equipment, reducing electromagnetic radiation and interference.
• Grounding Design: Reasonably layout a low-impedance grounding network to avoid ground loop interference, ensuring the device grounding terminal is well connected to the earth.
• Layout Optimization: Separate analog, digital, power, and protection circuits to avoid overlap on the surface; keep high-current, high-voltage, and high-radiation components away from sensitive components.
• Interface Protection: Interface lines must first pass through protective or filtering devices before connecting to the signal receiving chip.
• Static Electricity Protection: Implement anti-static measures, such as wearing anti-static wristbands and conducting regular electrostatic discharge tests.
2. Filtering Circuit Design Principles
• Power Filtering: Add a low-pass filter (such as an LC filter) at the power input to suppress high-frequency noise. For example, a combination of ferrite beads and capacitors or inductors and capacitors can effectively filter out differential mode noise.
• Signal Filtering: Add filters such as common mode inductors and filter capacitors on signal lines to reduce electromagnetic interference on the signal lines.
• Filter Layout: Filter devices should be placed close to the interface to avoid re-coupling of the filtered lines.
• Decoupling Capacitor Selection: Choose appropriate decoupling capacitors based on noise frequency, ensuring their self-resonant frequency is higher than the noise frequency.
• Wiring Optimization: Key signal lines should avoid crossing splits, long routes, or “U” shaped routing to reduce crosstalk and radiation.
EMC Case Analysis
1. In the automotive electronics field, a certain automotive electronic control unit (ECU) exceeded radiation emission limits during vehicle electromagnetic compatibility testing, interfering with other devices in the vehicle. Rectification measures included:
• Redesigning the PCB layout to keep high-frequency clock circuits away from I/O interfaces.
• Adding a π-type filter circuit at the power pins to filter out high-frequency noise.
• Optimizing the electromagnetic shielding of the enclosure to ensure good sealing at the gaps.
After rectification, radiation emission intensity was significantly reduced, meeting industry EMC standards.
2. In the consumer electronics field, a certain smartphone frequently crashed and exhibited screen flickering during electrostatic discharge (ESD) testing. Rectification measures included:
• Adding transient voltage suppressors (TVS) in the circuit to absorb high-energy pulses.
• Optimizing the enclosure and internal structure, increasing insulation materials and grounding designs.
After rectification, the ESD immunity of the smartphone was significantly improved.
3. In the industrial motor field, a certain air pump motor needed to meet EMC level requirements from automotive manufacturers. Solutions included:
• Using low-pass filter circuits (capacitor + inductor) to filter out interference in the 150kHz to 2.5GHz frequency range.
• Adding energy storage and high-frequency filter capacitors on the PCB to reduce the area of large current loops.
After rectification, the EMC performance of the motor was significantly improved, meeting industry standards.
Conclusion
PCB protection and filtering design is a key aspect of ensuring the electromagnetic compatibility (EMC) of electronic devices. Through reasonable shielding, grounding, layout optimization, and filter design, electromagnetic interference can be effectively reduced, enhancing the device’s anti-interference capability and stability. In practical applications, targeted design and rectification should be carried out based on specific devices and environments.