The ideal EMC filter in just 6 steps

Every developer of electrical devices must ensure compliance with international EMC guidelines and/or European EMC requirements – a growing challenge as mechanical systems are increasingly replaced by electrical ones.

The main issue
EMC issues, often unpredictable, typically arise in the power section of devices, where compact PCB designs can lead to thermal and interference problems. A discrete-component filter, like a current-compensated choke paired with capacitors, is often the most effective solution.

Measurement is key
EMC measurements are essential, and the Evaluation Boards offer an ideal solution for 1-phase and 3-phase systems, handling up to 50 A.

Filter design
An EMC filter ensures emissions and immissions to stay within application-specific limits, typically covering 150 kHz to 30 MHz for conducted and 30 to 1000 MHz for radiated measurements. A common 1-phase filter design uses a current-compensated choke with opposing windings to neutralize magnetic fields, along with two X capacitors (between L and N) and two Y capacitors (to ground). This configuration efficiently attenuates noise across a wide frequency range while minimizing power loss.

The universal LC filter design enables flexible setups, accommodating two X capacitors (positioned before and after the choke) and up to four Y capacitors, with integrated leakage resistors for electric shock protection. Connections can be made via 6.3 x 0.8 mm tabs, a 4 mm mounting hole, or direct soldering to large-surface pads.

For optimal performance, Y capacitors require a flat earth connection using copper tape or wide copper strands, as their effectiveness depends on the connection quality. Before installing filter components, conduct measurements to determine whether the interference is asymmetrical (L/N to PE) or symmetrical (L to N) and identify the maximum interference level to ensure EMC compliance.

Before implementing a chosen circuit from the evaluation board onto the device board, consider these critical factors:

• Y Capacitor Grounding: Ensure a reliable ground connection.

• Leakage Current: Evaluate the Y capacitors' leakage currents, as they are crucial for compliance with application and standard requirements.

• Choke Heating: Measure the choke's temperature at critical load currents to avoid overheating.

• Component Space: Verify the space required for all components to fit the device board layout.

• Temperature Rating: Confirm components can handle the operating temperature range.

• Voltage Rating: Ensure capacitors are rated for the application's voltage requirements.

• Safety Standards: Use safety-rated capacitors (at least X2 and Y2 class) for 250 VAC, per IEC standards.

• High-Voltage Tolerance: Confirm the capacitors meet high-voltage requirements.

Leakage currents are particularly significant and should be measured in the entire system with the filter circuit installed to ensure compliance and functionality.

The normal leakage currents of the capacitors used can be easily calculated:
IL = 2π · fn · Un · Cy