Transformer Bias Winding EMI Shielding Design
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Solution Overview
Problem
The existing energy transfer elements in converters, such as transformers, face challenges with parasitic capacitances generating displacement currents and resulting electromagnetic interference (EMI), which are typically mitigated by using multiple shields, but this reduces the window size and efficiency.
Innovation Solution
The proposed energy transfer element incorporates a third winding with a greater width than the primary and secondary windings, coupled to a bias voltage supply circuit, which functions as both a bias voltage supplier and a shield to reduce displacement current and EMI, thereby minimizing the number of shields required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple shields are inserted between primary and secondary windings to reduce EMI, then electromagnetic interference is reduced, but the window size of the transformer core is reduced
Solution Approach 1:
The patent combines the bias voltage supply winding with the shield winding into a single integrated component. The bias winding is wound between the primary and secondary windings and serves dual functions: supplying bias voltage to the control circuit and acting as an electrostatic shield to reduce EMI. This merging eliminates the need for separate shield windings, maintaining EMI reduction while preserving transformer window size.
Solution Approach 2:
The bias winding is designed to perform multiple functions simultaneously: it provides bias voltage to the control circuit, acts as an electrostatic shield between primary and secondary windings, and contributes to the overall magnetic coupling. This multi-functionality allows a single component to address both power supply and EMI reduction requirements without consuming additional window space.
2Object-affected harmful factors
If multiple shields are inserted to control displacement current, then EMI is reduced, but the number of components and device complexity increase
Solution Approach 1:
The patent merges the bias voltage supply function with the EMI shielding function into a single winding structure. The bias winding is positioned between the primary and secondary windings and connected to ground at one end, creating an electrostatic shield that controls displacement current while simultaneously providing bias voltage to the control circuit, thereby reducing component count and simplifying the overall device structure.
Solution Approach 2:
The bias winding serves as a multi-functional component that simultaneously provides bias voltage to the control circuit and acts as an electrostatic shield to control displacement current and reduce EMI. This universal functionality eliminates the need for separate shield components, reducing device complexity while maintaining effective EMI control.
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
This configuration effectively reduces EMI while maintaining efficiency by using a single component to supply bias voltage and block displacement current, thus optimizing energy transfer without the need for multiple shields.
Implementation Method 1
Parasitic capacitances may exist between a primary coil and a secondary coil of the transformer, which may generate a displacement current when the converter is operated. The displacement current generates electromagnetic interference (EMI).
Data Source
AI summary
An energy transfer element includes a first winding coupled to an input circuit and a second winding coupled to an output circuit. The first winding has a first unit and a second unit, and the second winding is wound between the first unit of the first winding and the second unit of the first winding. The energy transfer element further includes a third winding provided between the first unit of the first winding and the second winding. The third winding is used to supply a bias voltage of the input circuit, and a winding width of the third winding is greater than a winding width of the first unit of the first winding and a width of the second winding.