April.04,2025
In the design and manufacturing of electronic devices, Electromagnetic Compatibility (EMC) is a crucial challenge that determines whether a product can pass certifications (such as CE, FCC) and achieve market access.
Ⅰ、EMC Pain Points
1. Emission Issues (EMI)
Radiated Emission Exceedance
High-frequency switching power supplies (e.g., flyback transformers) and clock circuits (MCU crystals) become major interference sources, with the 30MHz-1GHz frequency band being prone to exceedance.
Case: A 60W LED driver power supply exceeded the emission limit by 6dB at 80MHz due to the antenna effect formed by transformer leakage inductance and PCB traces.
Conducted Emission Exceedance
The power input terminals (L/N lines) exceed the CLASS B limits in the 150kHz-30MHz frequency band, commonly seen in low-cost designs without PFC circuits.
Case: Conduction noise in a frequency converter exceeded the limit at 500kHz due to impedance mismatch in the return path of common-mode current caused by IGBT switching.
2. Immunity Issues (EMS)
Electrostatic Discharge (ESD) Failure
Device interfaces (USB, buttons) crash when subjected to ±8kV contact discharge due to poor grounding design preventing charge dissipation.
Surge Damage
The power port fuse blows after a 4kV surge impact due to the lack of TVS tube or MOV protection.
Electrical Fast Transient (EFT) Susceptibility
Industrial control equipment exhibits communication bit errors under ±2kV EFT interference due to unfiltered signal lines.
Ⅱ、Rectification Priority
1. Locating Interference Paths
2. Hierarchical Governance Principle
3. Cost Priority
Ⅲ、Solution
YET has an expert team that can offer free assistance to customers regarding EMC issues. The team can propose targeted solutions from the following aspects:
● Radiated Emission Exceedance Rectification
● Conducted Emission Exceedance Rectification
● Immunity Issue Rectification
Ⅳ、Typical Cases
YET has provided EMC's solutions for many customers.
Case 1: Radiated Emission Exceedance of Smart Home Gateway
Problem: The 2.4GHz WiFi module caused harmonic radiation at 1.2GHz to exceed Class B limits by 10dB.
Rectification Steps: Add a π-type filter (22μH + 100nF + 100nF) at the power pins of the WiFi module. Lay ground copper beneath the antenna and add grounding vias (5mm spacing). Software-disable unused
Bluetooth broadcast channels.
Result: Test values were 4dB below the limit, with a cost increase of ￥1.2.
Case 2: EFT Failure of Industrial Motor Drive
Problem: ±2kV EFT interference caused CAN communication interruptions.
Rectification Steps: Install common-mode inductors (CMH1205-901, 90Ω@100MHz) at both ends of the CAN bus. Connect the metal housing of the driver to the cabinet with a braided strap (impedance ＜10mΩ).
Deploy a 10μF electrolytic capacitor in parallel with a 100nF ceramic capacitor at the PCB power entry.
Result: Passed ±4kV EFT tests with a communication bit error rate ＜0.001%.
