EMI troubleshooting on a battery charger — solving EMI in a power electronics product

Client Context

A U.S.-based technology company had developed a compact battery charger designed for home energy storage applications. The charger featured an integrated power factor correction (PFC) circuit, allowing wide input voltage operation from 100 V to 240 V AC and delivering a regulated 12 V DC output.

During initial testing, the charger failed both conducted and radiated emissions (CE & RE), which posed a significant risk to the project’s timeline. With a critical product launch scheduled, the client urgently needed engineering support to resolve the EMI issues and ensure compliance with both FCC and CE marking requirements.

Scope of Work

• Identify and resolve conducted and radiated emission failures.

• Implement design-level fixes to achieve full EMC compliance for global markets.

• Document the root causes, solutions, and lessons learned to inform the next-generation product design.

Technical Approach

Our in-house lab was leveraged to perform accurate conducted emissions testing, following CISPR principles. This allowed us to establish a clear emissions benchmark and validate fixes in real time. 

Although a full anechoic chamber was not available for radiated emissions, we employed our own hybrid RE prediction methodology, which included:

• RF current probe analysis to estimate far-field emissions

• TEM cell measurements for consistent near-field emissions 

• Antenna checks in a controlled environment to assess field emissions patterns

Initial CE and RE measurements were captured and documented as reference baselines.

Troubleshooting & Mitigation

We used a combination of near-field probes and RF current probes to localize EMI sources across the PCB. Focus areas included:

• Input filtering topology

• PCB layout

• Grounding strategy

• PFC circuit behaviour under load

Key actions taken:

• Designed and implemented a two-stage input filter to effectively suppress differential- and common-mode noise.

• Revised grounding scheme to reduce parasitic loop coupling.

• Introduced targeted improvements to the PFC stage, minimising switching noise contributions.

• All modifications were implemented directly on the prototype, enabling iterative testing and rapid validation.

Results & Validation

After applying the design fixes, the charger was retested using the same lab setup. The results demonstrated:

• Conducted emissions were brought well within Class B limits.

• Radiated emissions were reduced significantly, with confidence established for passing at an accredited lab.

• A comprehensive report, including measurement data, design changes, and troubleshooting rationale, was delivered to the client. This documentation will serve as a design reference for future product iterations.

Conclusion

This case highlights the value of in-house EMC capability and targeted design expertise in resolving complex EMI problems. We enabled the client to avoid costly delays, reduce certification risk, and bring their product to market on time—fully compliant and technically robust.