Hershey's Kiss Frequency Sweep for EMI Noise Reduction
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Solution Overview
Problem
Current switching power supply devices face challenges in reducing conducted EMI noise within the expanded frequency range of 9 kHz to 150 kHz, as existing noise reduction measures, such as EMI filters and spread spectrum clocking, become costly and complex due to increased component sizes and complexities in implementing Hershey's Kiss waveforms using dedicated ICs.
Innovation Solution
A control circuit for switching power supply devices that generates a modulating signal approximating a Hershey's Kiss waveform for frequency modulation, allowing for efficient conducted EMI noise reduction without the need for large-scale Hershey's Kiss waveform generating circuits, thereby minimizing the scale of EMI filter enhancements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If EMI filter components are increased to suppress lower frequency conducted EMI noise (9 kHz to 150 kHz), then noise reduction performance is improved, but component size and cost increase
Solution Approach 1:
The patent changes the frequency parameter of the switching power supply by introducing frequency modulation through a Hershey's Kiss waveform. This spreads the energy spectrum across a wider frequency range, reducing peak emissions at any single frequency, thereby satisfying EMI requirements without increasing filter component sizes
Solution Approach 2:
The patent employs periodic frequency modulation using a Hershey's Kiss waveform to continuously vary the switching frequency. This periodic variation in frequency causes the EMI energy to be distributed over time and frequency, reducing the need for large filter components that would otherwise be required to suppress concentrated low-frequency noise
2Object-affected harmful factors
If Hershey's Kiss waveform generating circuit is implemented using dedicated IC, then conducted EMI noise reduction is improved, but device complexity and cost increase
Solution Approach 1:
The patent creates a simplified copy of the Hershey's Kiss waveform generating function using basic circuit components (resistors, capacitors, and operational amplifiers) rather than implementing the complete, complex dedicated IC waveform generator. This copy achieves sufficient EMI reduction performance with much lower complexity
Solution Approach 2:
The patent extracts only the essential frequency modulation function needed for EMI reduction from the complete Hershey's Kiss waveform generator. By taking out just the core functionality and implementing it with simple components, the patent avoids the complexity and cost of dedicated IC solutions while maintaining effective noise suppression
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 approach maximizes conducted EMI noise reduction while maintaining a simple configuration, reducing the need for enhanced EMI filter performance and minimizing costs, achieving similar noise reduction effects to using a Hershey's Kiss waveform without the complexity of dedicated ICs.
Implementation Method 1
A switching power supply device rectifies and smoothes a commercial AC voltage and switches the smoothed voltage using a switching element in order to generate a prescribed DC voltage
Implementation Method 2
a modulating signal generating circuit that generates and supplies a modulating signal for frequency modulation to the oscillation circuit
Data Source
AI summary
A conducted EMI noise reduction effect close to that achieved by using an optimal modulating waveform as a modulating wave is achieved when employing a frequency spreading technique as a measure against noise when a conducted EMI standard is extended to a low-frequency range. A triangular wave/Hershey's Kiss approximation signal generating unit and a triangular wave generation control unit generate a fundamental triangular wave by a transistor charging a capacitor with a current and a transistor discharging the current from the capacitor. A slope switching signal generating unit generates signals expressing the start and end of a charge period and the start and end of a discharge period. An additional charge or additional discharge is carried out in response to the signals turning a transistor on, and the slope of the triangular wave temporarily increases in that period only.