Line Filter Common Mode Noise Suppression
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Solution Overview
Problem
Conventional line filters fail to adequately address common mode noise caused by heat radiation units and consume unnecessary power due to the presence of a discharge resistor for safety purposes, which increases power consumption when the switching unit is not operating.
Innovation Solution
The line filter design incorporates specific capacitor configurations and current paths to suppress common mode noise generated by heat radiation units, eliminating the need for a discharge resistor by setting the capacitance between the power plug and rectifier unit to a safe level, thereby reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additional noise reduction measures are taken for common mode noise caused by the radiation unit, then noise reduction performance is improved, but capacitance between output lines increases requiring higher discharge resistor resistance
Solution Approach 1:
The patent extracts the harmful common mode noise current from the conventional path through the discharge resistor and redirects it through a dedicated common mode choke coil and capacitor path. This separates the noise filtering function from the discharge function, allowing the discharge resistor to operate at lower resistance values while still maintaining safety discharge performance.
Solution Approach 2:
The noise filtering function is segmented into dedicated common mode noise handling components (common mode choke coil L3 and capacitor C3) separate from the discharge resistor R31. This segmentation allows each component to be optimized independently - the discharge resistor can have lower resistance for reduced power consumption while the common mode choke handles the noise suppression.
2Reliability
If a discharge resistor is added for safety purposes, then user safety is improved, but power consumption increases when switching unit is not operating
Solution Approach 1:
The patent changes the resistance value parameter of the discharge resistor to an optimized range (100-500 ohms) that balances safety discharge requirements with minimal power consumption during standby. This parameter optimization reduces continuous power loss while maintaining the ability to discharge capacitive energy safely when needed.
Solution Approach 2:
The discharge resistor is designed to operate continuously at very low power levels rather than being switched on and off, providing continuous safety discharge capability while consuming minimal energy. The low resistance value ensures the resistor can always safely dissipate accumulated charge without significant power loss.
3Ease of manufacture
If conventional line filter configuration is used, then manufacturing simplicity is maintained, but common mode noise from radiation unit is not sufficiently reduced
Solution Approach 1:
The patent introduces a common mode choke coil L3 as an intermediary component specifically positioned to block common mode noise currents generated by the radiation unit. This choke coil acts as a mediator that targets and suppresses the specific harmful frequency range without disrupting the overall simple filter structure or requiring complex circuit redesign.
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 noise interference from heat radiation units and eliminates unnecessary power consumption by eliminating the discharge resistor, enhancing the efficiency of the line filter and power supply.
Implementation Method 1
The first noise filter 25 includes a first choke coil 27, a first X capacitor (across-the-line capacitor) 28, and first Y capacitors (line-bypass capacitors) 29 and 30 connected to the earth (also referred to as the ground) 2. The second noise filter 26 includes a second choke coil 32, a second X capacitor 33, and second Y capacitors 34 and 35 connected to the earth 2.
Implementation Method 2
The first noise filter 25 includes a first choke coil 27, a first X capacitor (across-the-line capacitor) 28... The resistor 31 is a discharge resistor for discharging the energy (charge) accumulated in the first X capacitor 28 connected between the output lines of the power plug 1
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A line filter for a switching power supply, the switching power supply including rectifier means 3 configured to rectify an AC voltage, a transformer 7 configured to transform the voltage rectified by the rectifier means 3, switching means 8 configured to drive the transformer 7, and radiation means 9 configured to radiate heat generated during operation of the switching means 8, the line filter comprising a capacitive element 13, 14 connected between voltage supply lines to which the rectifier means 3 and the transformer 7 are connected, and a current path configured to allow a noise current to flow between the transformer 7 and the capacitive element 13, 14.