PCB-Integrated Electric Filter for Motor EMI and Grounding Control
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Solution Overview
Problem
Household appliances with electric motors face challenges in reducing motor noise and electromagnetic interference (EMI) emissions, which are stringent according to standards like BS EN 55014-2:1997.
Innovation Solution
A printed circuit board with an electrically conductive material on one side, grounded to the motor chassis, combined with an electric filter comprising a freewheeling diode, X2Y capacitor, ferrite bead, and RC filter, effectively reduces noise emissions by providing a common ground and filtering signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an electric filter is used to reduce noise emissions, then electromagnetic interference is reduced, but grounding problems persist
Solution Approach 1:
The patent combines the electric filter and the grounding system into a single integrated printed circuit board structure. The conductive material on the back side of the PCB merges the grounding function with the filter circuitry, creating a unified solution that simultaneously addresses both EMI filtering and grounding reliability.
Solution Approach 2:
The patent utilizes the third dimension by placing conductive material on the back side of the PCB, opposite to the circuitry side. This dimensional approach allows the grounding system to be established without interfering with the front-side circuitry layout, effectively solving grounding problems while maintaining filter functionality.
2Reliability
If a printed circuit board is mounted directly to the motor chassis for grounding, then grounding is improved, but heat dissipation becomes problematic
Solution Approach 1:
The patent incorporates vent holes through the printed circuit board, creating a porous structure that allows heat to pass through. This enables the PCB to function as both a grounding connection to the motor chassis and a heat dissipation pathway, simultaneously addressing both grounding reliability and thermal management.
3Object-affected harmful factors
If the printed circuit board completely covers the motor end for shielding, then noise emissions are reduced, but the structure becomes more complex
Solution Approach 1:
The printed circuit board is designed to perform multiple functions simultaneously: it serves as the structural mounting platform for the electric filter, provides the grounding connection through its conductive back side, acts as an EMI shield by completely covering the motor end, and facilitates heat dissipation through vent holes. This multi-functionality reduces the need for additional separate components, thereby simplifying the overall structure despite the enhanced shielding capability.
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
The solution significantly mitigates noise emissions, ensuring compliance with strict noise and EMI requirements for household appliances by using the motor chassis as a shield and employing specific filtering components to dissipate energy and reduce voltage overshoot.
Implementation Method 1
the other side of the printed circuit board being arranged with an electrically conductive material via which a ground point common to the electric circuitry and a device contacting the conductive material is accomplished
Implementation Method 2
the chassis will act as a shield for noise emissions of the motor
Implementation Method 3
current induced in the bead is advantageously dissipated as heat instead of inducing an opposing current back in the electric filter
Implementation Method 4
When the motor is turned off, the diode becomes forward-biased with respect to the inductive motor and will conduct current until the energy stored in the inductive motor is dissipated
Implementation Method 5
any common-mode noise appearing on the motor terminals advantageously is filtered to the common ground formed by the motor chassis by the two capacitors comprised in the X2Y capacitor
Implementation Method 6
a resistor-capacitor (RC) filter coupled in parallel to the motor
Data Source
AI summary
A printed circuit board and an electric filter. The printed circuit board is arranged to accommodate an electric circuitry on one side, and an electrically conductive material on the other side which forms a common ground point with the electric circuitry and a device contacting the conductive material. The electric filter for filtering electric signals of a DC motor includes a freewheeling diode coupled in parallel to the motor, a capacitor coupled in parallel to the motor, where a ground terminal of the capacitor is coupled to a chassis of the motor, a low pass filter including a ferrite bead and another capacitor is connected to each motor terminal (M+, M−), and a resistor-capacitor filter is coupled in parallel to the motor.