Transformer Capacitor Balancing for Common-Mode Noise Reduction
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Solution Overview
Problem
Conventional switching power supply apparatuses with LLC-resonant insulated DC-DC converters face issues with common mode noise due to asymmetry in line-to-ground capacitances, which existing symmetric circuit configurations fail to adequately address.
Innovation Solution
The apparatus incorporates a switching circuit with a transformer and capacitors connected to the primary winding terminals, where the capacitances of the capacitors are set to specific ratios relative to the line-to-ground capacitances to minimize common mode noise, including configurations where C21>C22, C21=C22, and C21<C22, to counteract asymmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If symmetric circuit elements are configured to cancel common mode voltages, then common mode noise is reduced, but asymmetry occurs due to parasitic line-to-ground capacitances causing common mode noise
Solution Approach 1:
The patent applies asymmetry by configuring different capacitance values for the first and second capacitors connected to the primary winding terminals. Specifically, when C31 > C32, the first capacitor is set with larger capacitance than the second capacitor, and vice versa. This asymmetric configuration compensates for the asymmetric line-to-ground capacitances, restoring balance to the common mode voltage and reducing common mode noise.
Solution Approach 2:
The patent changes the capacitance parameters of the capacitors connected to the primary winding terminals based on the measured or estimated line-to-ground capacitances. By adjusting the capacitance values to satisfy specific relationships (C21 > C22 when C31 > C32, C21 = C22 when C31 = C32, C21 < C22 when C31 < C32), the system optimizes common mode noise reduction while accounting for parasitic effects.
2Object-affected harmful factors
If line-to-ground capacitances are asymmetric, then circuit asymmetry occurs generating common mode noise, but adding compensation capacitors increases device complexity
Solution Approach 1:
The patent introduces compensating capacitors as intermediary elements between the primary winding terminals and ground. These capacitors act as mediators that balance the asymmetric line-to-ground capacitances, enabling common mode noise reduction without requiring fundamental changes to the existing circuit topology or adding complex active compensation circuits.
3Object-affected harmful factors
If capacitor capacitances are adjusted to compensate for line-to-ground capacitance asymmetry, then common mode noise is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent defines specific parameter relationships for the compensating capacitors based on the line-to-ground capacitance ratios. By establishing clear design criteria (C21 > C22 when C31 > C32, C21 = C22 when C31 = C32, C21 < C22 when C31 < C32), the patent provides manufacturing guidance that balances noise reduction performance with practical component selection and assembly tolerances.
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 significantly reduces common mode noise propagation by equalizing current flow through line-to-ground capacitances, thereby minimizing noise interference and optimizing the design for reduced size and cost.
Implementation Method 1
The switching power supply apparatus has a first line-to-ground capacitance between the first winding terminal of the transformer and the conductor portion, and a second line-to-ground capacitance between the second winding terminal of the transformer and the conductor portion. The switching power supply apparatus is further provided with first and second capacitors, the first capacitor being connected between the first output terminal of the switching circuit and the first winding terminal of the transformer, and the second capacitor being connected between the second output terminal of the switching circuit and the second winding terminal of the transformer.
Implementation Method 2
Patent Document 1 discloses that the plurality of series resonant circuits are connected to both ends of the primary winding of the transformer, respectively, so as to make voltage waveforms in the primary winding of the transformer symmetric, thus cancelling common mode voltages inputted to the primary winding of the transformer.
Data Source
AI summary
A switching power supply apparatus has a line-to-ground capacitance C31 between a first winding terminal of a transformer and a conductor portion, and a line-to-ground capacitance C32 between a second winding terminal of the transformer and the conductor portion. The switching power supply apparatus is provided with a capacitor being connected between a first output terminal of a switching circuit and the first winding terminal of the transformer, and a capacitor being connected between a second output terminal of the switching circuit and the second winding terminal of the transformer. Capacitances of the capacitors C21, C22 are set to satisfy: C21>C22, for C31>C32; C21=C22, for C31=C32; and C21<C22, for C31<C32.