Reduce EMI in Switching Power Supplies — PatSnap Eureka
Reduce Electromagnetic Noise in Switching Power Supplies Without Shielding or Extra PCB Area
Five patented technology clusters — from shieldless transformer LC bridge networks to active phase cancellation — enable CISPR-compliant EMI suppression in compact SMPS designs. This landscape covers 60+ patent and literature records spanning 1991–2026.
Two Root Causes, Five Solution Clusters
Switching power supplies generate electromagnetic noise through two primary mechanisms: rapid voltage and current transitions (high dv/dt, di/dt) at switching transistors and rectifier diodes that produce conducted and radiated EMI, and parasitic inter-winding capacitances in transformers that couple high-frequency common-mode noise between isolated primary and secondary circuits.
Among retrieved results, the dominant noise types addressed are common mode (CM) noise and differential mode (DM) noise, with common mode being the harder problem and the primary focus of most recent filings. Conventional solutions — metal shielding enclosures, large passive EMI filter banks, and expanded PCB ground planes — are increasingly untenable in compact, high-frequency designs.
The dataset reveals five broad technical clusters addressing this constraint: shieldless transformer noise networks, passive LC/RC snubber and filter integration, coupled-inductor phase cancellation, frequency spread/spectrum dithering, and active neutralization circuits. For deeper context on EMC regulatory frameworks, IEC and CISPR publish the governing standards, while PatSnap Analytics enables competitive patent landscape analysis across all five clusters.
- Shieldless transformer with passive LC bridge networks
- Passive RC/LC snubber integration & harmonic blocking
- Coupled-inductor phase cancellation
- Frequency spread / spectrum dithering
- Active neutralization & shield winding turn adjustment
Five Patented Approaches to SMPS EMI Suppression
Each cluster targets a different point in the noise generation and propagation chain, enabling engineers to select the most appropriate technique for their design constraints.
Shieldless Transformer with Passive LC Bridge Networks
The core mechanism inserts two series capacitors between the transformer primary and secondary circuits, with an inductor connecting the capacitor mid-point to chassis earth. Capacitor values present low impedance to noise signals; the inductor presents high impedance. This reroutes CM switching noise to earth without requiring any inter-winding Faraday shield, saving transformer size and cost. Covered by at least 6 patent records across AU, WO, GB, US, and NZ — dominated by Eaton Power Quality and Invensys.
Eaton / Invensys · US, GB, NZ · Pre-2006Passive RC/LC Snubber Integration & Harmonic Current Blocking
This cluster targets noise at the source — across switching transistors (MOSFET/IGBT) and rectifier diodes — using RC snubber networks, ferrite bead absorption circuits, common-mode choke coils, and ground-path harmonic blocking. Several approaches eliminate or reduce buffer circuits while achieving equivalent noise suppression. Key filers include Hewlett-Packard, TRW Automotive, Shenzhen Diyi Technology, and ZTE Corporation. ZTE’s ferrite bead + capacitor absorption at all diode junctions passes B-class EMI without additional shielding.
HP · TRW · ZTE · Shenzhen DiyiCoupled-Inductor Phase Cancellation via Integrated Magnetics
Developed primarily by Xidian University, this approach uses E-E core integrated magnetic components with a balance winding and programmable analog switch. By dynamically adjusting the balance impedance value, the port characteristics of the coupled inductor are altered, shifting the phase and amplitude of noise signals. When multiple SMPS units share a DC bus, each unit’s noise is phase-shifted so that they mutually cancel on the bus — reducing aggregate conducted emissions without adding PCB area. Active CN grants, limited US/EP coverage — potential white-space for international filing.
Xidian University · CN · 2015–2017Frequency Spread (Spectrum Dithering) & Soft Switching
Rather than filtering noise at a fixed frequency, this approach deliberately spreads the switching spectrum by modulating the switching frequency with a low-frequency signal, dispersing peak EMI energy across a wider band so that no single frequency exceeds regulatory limits. Osram S.p.A. injected a low-frequency (~300 Hz) oscillating signal into the feedback path to spread the switching frequency spectrum. A related sub-approach uses resonant soft-switching topologies to eliminate voltage spikes and current transients at the source — as demonstrated by BAE Systems for high-voltage sensor applications.
Osram · BAE Systems · Shenzhen Youbo · 2006–2019Active Neutralization & Shield Winding Turn Adjustment
This advanced cluster uses active circuits or precisely calculated winding configurations to inject equal-and-opposite displacement currents that cancel the noise currents generated by interwinding capacitance. Power Integrations’ shield winding approach (multiple filings 2010–2020, US/EP/IN) calculates an optimal winding turn count, deliberately over-winds it, then trims a series impedance to achieve precise cancellation. AES Global Holdings’ neutralization signal generator applies an adjustable-amplitude, adjustable-phase signal to a conductive shield layer for broadband CM noise suppression. Murata Manufacturing’s 2025 filing employs half-bridge capacitor balancing circuits that reduce CM noise without requiring feedback loop redesign. IP positions are active and competitive in US jurisdiction; licensing or design-around strategies are advisable before entering this sub-space. See also PatSnap Analytics for freedom-to-operate analysis tools.
Power Integrations · AES Global · Murata · 2010–2026Three Decades of SMPS EMI Innovation
This landscape is derived from a limited set of patent and literature records retrieved across targeted searches. It represents a snapshot of innovation signals within this dataset only and should not be interpreted as a comprehensive view of the full industry.
Assignee Filing Volume & Technique Maturity
Top assignees by filing volume and the maturity distribution of the five technology clusters across the retrieved dataset.
Top Assignees by Filing Volume
Eaton leads with 6 records; Power Integrations follows with 5. Murata and Xidian University each hold 3–4 records in the most recent and emerging clusters respectively.
Technology Cluster Maturity & IP Risk
Shieldless transformer networks are the most mature with highest prior art density. Active neutralization offers the highest performance but carries the highest IP risk in US jurisdiction.
Where These Techniques Are Deployed
The dataset spans five distinct application domains, each with unique EMC constraints and design trade-offs.
Inverter-Fed Motor Drives & EV Compressors
The Electric Power Research Institute and TRW Automotive drove significant innovation for inverter-fed motor drives and automotive switching regulators, where conducted EMI must comply with CISPR limits without adding bulk. Sanden Corporation’s 2022 EP filing addresses the EV-specific constraint of eliminating large EMI filters in compact vehicle-mounted converters by physically separating primary and secondary windings in the transformer itself.
DC Bus Parallelisation & Server Power Delivery
Multiple DC bus parallelisation scenarios (telecom rack power) and data storage systems are addressed. Tandberg Data’s common-mode inductor insertion and GlobalFoundries’ PDN (Power Delivery Network) voltage compression methods target servers and storage arrays. Xidian University’s phase-cancellation approach is particularly relevant here — when multiple SMPS units share a DC bus, each unit’s noise is phase-shifted so that they mutually cancel.
Four Signals from the 2020–2026 Filing Frontier
Based on the most recent filings in this dataset, four directional signals are apparent for R&D teams designing next-generation isolated DC-DC converters.
Top Assignees by Filing Volume & Jurisdiction
| Assignee | Records | Jurisdictions | Primary Cluster | IP Position |
|---|---|---|---|---|
| Eaton Power Quality / Eaton Industries | 6 | US, GB, NZ | Shieldless Transformer LC Networks | Mature — crowded prior art pre-2006 |
| Power Integrations, Inc. | 5 | US, EP, IN | Active Neutralization / Shield Winding | Active & competitive in US |
| Tandberg Data A/S | 4 | EP, US, CA | Common-Mode Inductor Insertion | Foundational — early filings |
SMPS Electromagnetic Noise Reduction — Key Questions Answered
Switching power supplies generate electromagnetic noise through two primary mechanisms: rapid voltage and current transitions (high dv/dt, di/dt) at switching transistors and rectifier diodes that produce conducted and radiated EMI, and parasitic inter-winding capacitances in transformers that couple high-frequency common-mode noise between isolated primary and secondary circuits. The dominant noise types are common mode (CM) noise and differential mode (DM) noise, with common mode being the harder problem and the primary focus of most recent filings.
The core mechanism is inserting two series capacitors between the transformer primary and secondary circuits, with an inductor connecting the capacitor mid-point to chassis earth. Capacitor values are selected to present low impedance to noise signals; the inductor presents high impedance. This reroutes CM switching noise to earth without requiring any inter-winding Faraday shield, saving transformer size and cost.
Rather than filtering noise at a fixed frequency, this approach deliberately spreads the switching spectrum by modulating the switching frequency with a low-frequency signal, dispersing peak EMI energy across a wider band so that no single frequency exceeds regulatory limits. For example, Osram S.p.A. injected a low-frequency (~300 Hz) oscillating signal into the feedback path to spread the switching frequency spectrum.
Developed primarily by Xidian University, this approach uses E-E core integrated magnetic components with a balance winding and programmable analog switch. By dynamically adjusting the balance impedance value, the port characteristics of the coupled inductor are altered, shifting the phase and amplitude of noise signals. When multiple SMPS units share a DC bus, each unit’s noise is phase-shifted so that they mutually cancel on the bus, reducing aggregate conducted emissions without adding PCB area.
Based on the most recent filings in the dataset (2020–2026), four directional signals are apparent: decoupling EMI suppression from feedback loop redesign (Murata 2023–2026), soft-switching as a source-elimination strategy, active noise detection and cancellation circuits (Taicang Tongwei Electronics, CN, 2022), and automotive and EV power electronics integration (Sanden Corporation, 2022).
Among the retrieved records, Eaton Power Quality Company dominates the shieldless transformer passive-network cluster with 6 records across US, GB, and NZ. Power Integrations and AES Global Holdings lead active/shield winding cancellation. Xidian University holds a cluster of CN active filings in phase-cancellation. Murata Manufacturing represents the most recent (2025–2026) activity and is the sole active filer at the frontier of integrating EMI suppression with feedback control decoupling.
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