DC-DC Converter Frequency Modulation for Lower EMI Peaks
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Solution Overview
Problem
Existing frequency modulation DC-DC converters face challenges in reducing electromagnetic interference (EMI) noise across various load conditions, leading to inefficiencies and the need for larger EMI filters.
Innovation Solution
An EMI reduction device and method that adjusts the operating frequency of switching elements in a DC-DC converter based on the output voltage, injecting a fluctuation modulation frequency to disperse energy and reduce EMI amplitude by spreading the frequency spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If direct switching frequency modulation is used to reduce EMI noise in PWM controlled switching power supply, then EMI noise level is reduced, but it is not suitable for frequency modulation switching power supply and causes large fluctuation in output voltage under full load condition
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable and adaptive rather than fixed. The frequency modulation input unit dynamically adjusts the switching frequency based on load conditions, allowing the system to optimize between EMI reduction and output voltage stability for different operating scenarios.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically through frequency modulation. By modulating the switching frequency around a central value, the system achieves EMI reduction while maintaining output voltage stability through the frequency variation that prevents energy concentration at discrete frequencies.
2Reliability
If switching frequency is kept constant to maintain stable output voltage, then output voltage stability is maintained, but EMI energy concentrates at specific frequency points causing high EMI amplitude
Solution Approach 1:
The patent transforms the static switching frequency into a dynamic parameter through frequency modulation. The switching frequency varies around a central frequency, which disperses EMI energy across a frequency range rather than concentrating it at a single frequency point, thereby reducing peak EMI amplitude.
Solution Approach 2:
The patent employs periodic frequency modulation where the switching frequency oscillates between minimum and maximum values. This periodic variation in switching frequency creates a spread spectrum effect that distributes EMI energy over time and frequency, reducing concentrated EMI peaks while maintaining overall system stability.
3Object-affected harmful factors
If frequency modulation is applied to reduce EMI noise, then EMI performance is improved, but the system complexity increases due to additional control mechanisms
Solution Approach 1:
The patent achieves multi-functionality by integrating the frequency modulation capability into the existing control architecture. The frequency modulation input unit can work with various switching power supply topologies and control methods (PWM, frequency modulation), making the EMI reduction mechanism universally applicable without requiring completely separate control systems.
Solution Approach 2:
The patent introduces a frequency modulation input unit as an intermediary component that bridges the control signal and the switching elements. This intermediary module generates the frequency-modulated control signals, isolating the complexity of frequency modulation from the main control logic and simplifying the overall system architecture.
Data Source
AI summary
An EMI reduction device for a DC-DC converter. The DC-DC converter includes: input voltage terminal; output voltage terminal; plurality of switching elements with an operating frequency thereof being adjusted to modulate an output voltage of the DC-DC converter; and control terminal which changes the operating frequency of the switching elements based on output terminal voltage at output voltage terminal of the DC-DC converter. The EMI reduction device includes: a frequency modulation input unit connected to control terminal and injects fluctuation modulation frequency into the operating frequency of switching elements, wherein the fluctuation modulation frequency is based on output voltage at the output voltage terminal and is set according to desired EMI performance. The EMI reduction device can disperse energy concentrated on frequency point fc and its high frequency harmonic waves to nearby frequency bands, to reduce EMI amplitude at each frequency point, improving the EMI performance of the DC-DC converter.