EMI Filtering for Power Supplies
This technical reference document provides detailed information about p-duke product specifications, characteristics, and performance parameters. Use this information to support your design and analysis activities.
Electrical characteristics are specified over the operating temperature range unless otherwise noted. Parameters are guaranteed by design, testing, or statistical analysis. Typical values is the most likely parametric norm at 25°C.
Thermal characteristics require careful attention during system design. The junction-to-ambient thermal resistance depends on the mounting configuration, PCB copper area, and airflow conditions. Use thermal simulation tools to predict operating temperatures under actual conditions.
Reliability data is based on accelerated life testing and field failure analysis. Mean time between failures (MTBF) calculations follow industry-standard methodologies. Contact BeiLuo for detailed reliability reports and qualification data.
💡 FAE Insights
Frequently Asked Questions
1. What is the difference between common-mode and differential-mode noise?
Common-mode noise flows in the same direction on both power lines relative to ground, typically caused by capacitive coupling to ground. Differential-mode noise flows between the power lines, caused by switching currents. Common-mode is filtered using chokes and Y-capacitors to ground. Differential-mode is filtered using X-capacitors across the lines and series inductors. Most power supplies generate both types of noise, requiring filters that address both modes.
2. How do I select the cutoff frequency for my EMI filter?
EMI filter cutoff frequency selection: Typically set at 1/10th to 1/100th of switching frequency; For 300kHz switching, cutoff of 10-30kHz is common; Lower cutoff provides more attenuation but requires larger components; Consider the regulatory frequency range (150kHz-30MHz for conducted); Account for converter's inherent noise spectrum; Verify attenuation at regulatory limit frequencies. The goal is to provide at least 20-40dB attenuation at the switching frequency and its harmonics. P-Duke application notes provide recommended cutoff frequencies for each converter series.