Switching Circuit EMI Suppression via Feedback Modulation
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Solution Overview
Problem
Conventional power supply designs face challenges in reducing electromagnetic interference (EMI) emissions while minimizing the size, weight, and cost of components, as existing methods either increase component size, add weight, or compromise efficiency.
Innovation Solution
An EMI emission suppressing system that modulates the frequency of a switching element when drawing power from the main supply, using low frequency modulation in the feedback loop to transfer higher order harmonic emissions below the standard EMI bandwidth, and discontinues modulation when not drawing power to minimize ripple on the load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the switching frequency is increased to reduce component size, then the size of power supply components is reduced, but electromagnetic interference emissions increase
Solution Approach 1:
The patent applies periodic frequency modulation to the switching element, where the switching frequency is modulated in a periodic manner during the on-state. This periodic action spreads the EMI energy across multiple frequency components rather than concentrating it at a single high frequency, thereby reducing peak EMI emissions while maintaining the high switching frequency needed for compact component size
Solution Approach 2:
The patent dynamically changes the switching frequency parameter during operation by applying frequency modulation. The switching frequency is varied within a range while the element is on, which transforms the fixed high-frequency EMI into a spread spectrum signal, reducing the harmful concentration of EMI at any single frequency while preserving the benefits of high-frequency operation
2Object-generated harmful factors
If conventional jitter is continuously injected into the gate drive to reduce EMI, then EMI is spread over a continuous frequency range, but output ripple increases and feedback loop efficiency is inhibited
Solution Approach 1:
The frequency modulation is applied periodically only during the on-state of the switching element, not continuously throughout the entire switching cycle. This periodic application of modulation during the on-state achieves EMI spreading while avoiding continuous disruption to the feedback loop, thereby maintaining feedback efficiency and reducing output ripple compared to continuous jitter injection
Solution Approach 2:
The patent integrates the frequency modulation within the feedback loop rather than injecting noise externally into the gate drive. The modulated switching signal is generated through the feedback mechanism, ensuring that the modulation does not disrupt the regulation function. The feedback loop continues to operate effectively by sensing and regulating the output based on the modulated switching waveform
3Object-generated harmful factors
If additional filter components are added to reduce EMI harmonics, then unwanted frequency harmonics are reduced, but weight and size of power supplies increase
Solution Approach 1:
The patent converts the harmful concentrated EMI harmonics into a beneficial spread spectrum signal by applying frequency modulation. Instead of adding filters to remove harmonics, the modulation spreads the energy across a frequency range, transforming the harmful narrowband harmonics into less harmful wideband noise, thereby eliminating the need for additional heavy filter components
4Object-generated harmful factors
If snubber circuit is used to reduce large spikes of harmonics, then EMI is reduced, but efficiency of power converter is compromised
Solution Approach 1:
The frequency modulation is applied in a periodic manner during the on-state, creating controlled frequency variations that spread EMI energy. This periodic modulation achieves EMI reduction without the energy-dissipating snubber circuit, as the modulation itself manages the harmonic content rather than requiring additional damping components that waste power
Data Source
AI summary
An EMI emission suppressing system, apparatus and method that enables the EMI produced by high frequency switching of a switching circuit to be suppressed via the transfer of the higher order harmonic emissions to a frequency range below the standard EMI bandwidth of less than 150 KHz by applying low frequency modulation or jitter into the feedback of a switching signal of the switching circuit. The EMI suppression is achieved with minimal added ripple on the output signal of the switching circuit by using discontinuous modulations in the form of only applying the low frequency modulation when the switch or higher order harmonic producing element of the switching circuit is accessing, or drawing power from, the main power supply.