Two-Port Test Apparatus for Common-Mode Parasitic Capacitance
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Solution Overview
Problem
Current methods for measuring common-mode parasitic capacitance in switching mode power supplies are inaccurate due to their reliance on one-port network measurements that do not account for voltage variations along transformer windings, leading to incomplete characterization of equivalent common-mode capacitance, which hinders effective EMI filter design and quality control in mass production.
Innovation Solution
A test apparatus utilizing a two-port network with a signal generating device connected to one element and a signal receiving device connected between isolated elements, allowing for accurate measurement of common-mode parasitic capacitance by simulating the real operating state of the transformer and calculating capacitance based on signal responses using internal impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional one-port network measurement methods are used, then the measurement process is simple, but the measurement precision of common-mode parasitic capacitance is inaccurate
Solution Approach 1:
The patent divides the measurement system into two separate ports: a first port connected to the first element and a second port connected to the second element. This segmentation allows independent signal generation and measurement at each port, enabling accurate capture of voltage variations across isolated elements while maintaining a manageable device structure through modular functionality.
Solution Approach 2:
The patent introduces internal impedances as intermediary elements between the signal sources and the isolated elements under test. These internal impedances serve as mediators that enable the measurement of displacement currents flowing through the parasitic capacitance, providing a controlled interface that accurately represents real operating conditions without directly exposing the measurement equipment to high-voltage transient environments.
2Reliability
If static electric field calculation methods are used, then the calculation process is simple, but the reliability of parasitic capacitance values deviates from actual operating conditions
Solution Approach 1:
The patent employs dynamic measurement by applying actual switching waveforms and transient voltage signals that replicate real operating conditions. Instead of using static DC voltage calculations, the system measures parasitic capacitance under dynamic voltage variations and displacement currents, ensuring the reliability of capacitance values reflects actual switching mode power supply operation where voltages rapidly change along transformer windings.
3Manufacturing precision
If conventional measurement methods are used, then the design cycle is shorter, but the manufacturing precision of EMI filter design is compromised
Solution Approach 1:
The patent enables preliminary and accurate measurement of common-mode parasitic capacitance values during the transformer manufacturing or prototyping stage, before EMI filter design begins. By obtaining reliable capacitance values early in the development process through this specialized two-port measurement method, designers can immediately proceed to accurate EMI filter design without iterative adjustments, ultimately reducing total development time despite the more sophisticated measurement approach.
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
Enables precise measurement of common-mode parasitic capacitance, improving EMI filter design and reducing production costs by providing accurate parameters early in the design cycle and ensuring transformer quality during mass production.
Implementation Method 1
measuring a signal response between the first element and the second element by the signal receiving device, and calculating the common-mode parasitic capacitance
Implementation Method 2
The common-mode current 3 goes to earth ground via a primary side capacitance CP, a transformer parasitic capacitance CPS and a secondary side capacitance CS—G
Implementation Method 3
calculating the common-mode parasitic capacitance existed between the first element and the second element based on the signal response
Data Source
AI summary
Disclosed is a test apparatus for measuring the common-mode parasitic capacitance between a first element and a second element being isolated from the first element. The test apparatus includes a signal generating device connected to the first element and having an internal signal source connected in series with a first internal impedance for sending a signal to the first element, and a signal receiving device connected between the second element and the first element and having a second internal impedance for measuring a signal response between the first element and the second element, thereby calculating the common-mode capacitance between the first element and the second element based on the signal response.