Bridgeless PFC Circuit Zero-Cross EMI Reduction
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Solution Overview
Problem
Bridgeless PFC converters experience higher electromagnetic interference (EMI) due to zero-cross transitions of the AC input, which can interfere with neighboring electronic components and degrade regulation, and traditional mitigation methods like passive filters are undesirable due to cost and size.
Innovation Solution
Incorporating current sources in parallel with switches of the low-frequency leg to control voltage transitions during AC zero crossings, reducing the rate of change in voltage and minimizing parasitic capacitance-induced EMI without the need for large passive filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If bridgeless PFC converters are used to eliminate AC rectifier bridge and improve converter efficiency, then converter efficiency is improved and cost is reduced, but electromagnetic interference (EMI) increases during AC zero crossing transitions
Solution Approach 1:
The patent applies preliminary action by detecting AC zero-cross transitions before they occur and preemptively adjusting the switching states of low-frequency leg switches and activating current sources. This提前 intervention prevents the rapid voltage transitions that cause EMI, while maintaining the bridgeless PFC converter's efficiency benefits by avoiding the need for traditional AC rectifier bridges
2Object-generated harmful factors
If passive filters are used to mitigate EMI in bridgeless PFC converters, then electromagnetic interference is reduced, but cost and device size increase
Solution Approach 1:
The patent extracts and removes the need for large passive filters by implementing an alternative EMI mitigation approach using controlled switching and current sources in the low-frequency leg. This extraction eliminates the harmful EMI effects without incorporating the bulky and costly passive filter components that would otherwise be required
Solution Approach 2:
The patent substitutes the mechanical/passive filter system with an active control system that uses electronic switching and current sources to achieve EMI mitigation. This replacement transitions from a passive mechanical filtering approach to an active electronic control approach, reducing device complexity and size while maintaining EMI reduction effectiveness
Data Source
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AI summary
A bridgeless power factor correction (PFC) circuit for reducing electromagnetic interference (EMI) is disclosed herein. A current source is placed in parallel with a switch of a low frequency leg. The current source may be turned on during zero crossings of the AC input voltage to limit current and reduce the rate of change in voltage. In turn, EMI may be advantageously reduced without the need for large passive filters or complicated circuitry.