Switched Power Supply EMI Reduction via Feedback Loop Disturbance
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Solution Overview
Problem
Existing solutions for reducing electromagnetic interference (EMI) in power supplies, such as variable frequency operation and EMI filters, are inadequate for light loads or no-load conditions, leading to inefficient noise reduction and increased costs or size.
Innovation Solution
Injecting a small low-frequency disturbance into the feedback loop of a switched power supply, using a low-frequency square wave oscillator to vary the switching frequency and spread the EMI spectrum, thereby reducing noise concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If variable frequency operation is used to spread EMI noise spectrum, then peak EMI values are reduced, but the solution becomes ineffective for light loads or no-load conditions
Solution Approach 1:
The patent implements dynamic frequency variation by injecting a low-frequency disturbance signal into the feedback loop, causing the switching frequency to dynamically fluctuate within a range rather than operating at a fixed frequency. This dynamic approach ensures effective EMI spectrum spreading under all load conditions, including light loads and no-load conditions where conventional variable frequency operation fails.
Solution Approach 2:
The patent changes the operating parameters by introducing a low-frequency disturbance signal that modulates the switching frequency. This parameter change transforms the fixed frequency operation into a fluctuating frequency operation, effectively spreading the EMI noise spectrum across a wider frequency range and reducing peak values even under light load conditions.
2Object-affected harmful factors
If large EMI filters are used to reduce EMI noise, then EMI protection is improved, but device cost, size, and efficiency are negatively impacted
Solution Approach 1:
The patent converts the harmful EMI noise into a beneficial effect by deliberately injecting a low-frequency disturbance signal that spreads the noise spectrum. Instead of trying to filter out the noise, the invention transforms the concentrated EMI peaks into a distributed noise profile, reducing peak values and eliminating the need for large EMI filters.
Solution Approach 2:
The patent extracts the EMI filtering function from the physical filter components and implements it through control signal processing. By removing the need for large EMI filters and extracting only the essential filtering function through frequency modulation, the device achieves EMI protection with minimal additional components and cost.
3Object-affected harmful factors
If bleeder resistor is used to reduce EMI noise, then EMI protection is improved, but power efficiency is significantly reduced
Solution Approach 1:
The patent converts the energy that would be wasted in the bleeder resistor into a useful control signal. Instead of dissipating energy through resistive heating, the invention uses a low-frequency disturbance signal to modulate the switching frequency, achieving EMI reduction without the continuous energy loss associated with bleeder resistors.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively disperses EMI noise over a wide range, reducing peak values and improving efficiency without the need for large EMI filters, while maintaining acceptable output stability.
Implementation Method 1
Injecting a small low-frequency disturbance into the feedback loop of a switched power supply, using a low-frequency square wave oscillator to vary the switching frequency
Data Source
Figure 1~2
Figure 3~5
AI summary
A switched power supply (10) includes a sensor (R1, R2) for sensing a load (L) fed by the power supply (10) and a feedback path (22, 24, 26) to control the switching frequency of the switched power supply (10) as a function of the load (L) as sensed by the sensor (R1, R2). The arrangement includes an oscillator (30, 38) to inject into the feedback path (22, 24, 26) an oscillating signal, which produces a spread in the spectrum of the electromagnetic noise produced by the switched power supply (10). The oscillating signal is a low frequency (e.g. 300 Hz) signal, that is a signal having a frequency substantially lower than the switching frequency of the switched power supply (10). A switch (34) may be provided to selectively switch off the oscillating signal to prevent fluctuations in the output of the power supply (10) in the presence of a high load.