Introduction to Switch-Mode Power Supplies and EMI
Switch-Mode Power Supplies (SMPS) offer significant advantages like higher efficiency and smaller size compared to linear counterparts. However, they inherently generate noise due to high dv/dt and di/dt transitions, leading to Electromagnetic Interference (EMI). This document explores techniques to mitigate this noise.
Spread-Spectrum Frequency Dithering (SSFD)
When standard noise mitigation techniques are insufficient, Spread-Spectrum Frequency Dithering (SSFD) can be employed. SSFD involves modulating the switching frequency within a limited range to spread the spectral energy, thereby reducing peak harmonic content. This technique is crucial for achieving Electromagnetic Compatibility (EMC).
The paper details:
- Quantifying SMPS noise problems and EMI coupling mechanisms.
- Fundamental noise mitigation strategies.
- Methods for measuring EMI using spectrum analyzers.
- The principles of spread-spectrum modulation using Frequency Modulation (FM) theory.
- Comparison of different modulation waveforms (sinusoidal, triangular, exponential, pseudo-random).
- Simulation and analysis of SSFD implementation.
Practical Applications and Results
The document presents real-world examples and simulations, focusing on:
- Power-Factor Correction (PFC): Examining conducted emissions and the impact of SSFD on PFC circuits, referencing the UCC28070 controller.
- Automotive DC/DC Conversion: Investigating radiated emissions using the TPIC74100 buck/boost regulator and the effects of modulation and slew-rate control.
The findings demonstrate that SSFD effectively reduces spectral peaks in both conducted and radiated emissions, contributing to improved EMC performance.
About Texas Instruments
This technical paper originates from a Texas Instruments Power Supply Design Seminar. Texas Instruments is a global semiconductor company dedicated to enabling a better, safer, and more sustainable world through its innovative solutions.
For more information on power supply design and EMI mitigation, visit the Texas Instruments Power Seminar page.
