Quasi-Resonant Converter Frequency Modulation for EMI Reduction
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Solution Overview
Problem
Quasi-resonant switching converters face challenges in effectively reducing electromagnetic interference (EMI) due to their natural frequency modulation, which is dependent on input voltage and output load, and is not very effective with quasi-peak detection methods, necessitating additional EMI reduction techniques.
Innovation Solution
A control device for quasi-resonant switching converters that modulates the switching frequency by incorporating a modulator to introduce a higher-frequency forced modulation signal, independent of an oscillator, to scatter EMI emissions and reduce peak harmonic amplitudes, thereby enhancing EMI reduction across various detection methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If natural frequency modulation at twice line frequency is used in QR converters, then some EMI reduction benefit is achieved with average detection method, but the effect is strongly dependent on input voltage and output power, and not very effective with quasi-peak detection method
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable and controllable through a dedicated control circuit. The control circuit dynamically adjusts the switching frequency based on feedback signals, enabling the system to adapt to different operating conditions and detection methods. This transforms the static natural frequency modulation into a dynamic, controllable frequency modulation system that can be optimized for both average and quasi-peak detection methods.
Solution Approach 2:
The patent changes the frequency parameter from a naturally determined value to a controlled variable. By introducing a control circuit that can independently adjust the switching frequency, the system can modify the frequency parameter to achieve effective EMI reduction across different detection methods. The control circuit varies the switching frequency to scatter EMI emissions, making the solution effective for both average and quasi-peak detection methods regardless of input voltage and output power conditions.
2Object-affected harmful factors
If input filters and snubbing components are added to control EMI, then EMI emissions are reduced, but the size and weight of the power supply increase
Solution Approach 1:
The patent replaces mechanical/physical EMI filtering components (input filters and snubbing components) with an electronic control system. Instead of using passive components to physically filter EMI emissions, the system uses an active control circuit to modulate the switching frequency, thereby scattering EMI emissions in the frequency domain. This substitution eliminates the need for additional heavy filtering components while achieving EMI reduction through electronic frequency control.
3Object-affected harmful factors
If input filters and snubbing components are added to control EMI, then EMI emissions are reduced, but the production cost increases
Solution Approach 1:
The patent replaces expensive passive EMI filtering components with a cost-effective electronic control circuit. The control circuit uses standard electronic components to generate frequency modulation signals, which is more economical than purchasing and installing additional input filters and snubbing components. This approach reduces production costs by eliminating the need for trial-and-error component selection and reducing the bill of materials for EMI filtering.
4Object-affected harmful factors
If natural frequency modulation is used, then EMI reduction benefit is achieved, but additional EMI reduction techniques are needed to ensure compliance with regulations
Solution Approach 1:
The patent merges the EMI reduction function with the existing control system by integrating a frequency modulation capability into the control circuit. The control circuit generates a modulation signal that varies the switching frequency, combining EMI reduction with the existing control functionality. This integration avoids adding separate EMI reduction circuits and reduces overall system complexity while ensuring compliance with EMI regulations.
Data Source
AI summary
A control device for a QR switching power converter is described; said power converter is adapted to convert an input signal to a DC output signal and comprises a power switch connected to said input signal and adapted to regulate said DC output signal and magnetic storage means. The control device is able to determine the switching frequency of the power switch and it is supplied by a feedback signal deriving from a feedback circuit coupled to the output signal of the power converter; said control device performs a control loop regulating the DC output signal by controlling a control variable. The control device comprises modulating means adapted to modulate said control variable as a function of at least one modulating signal having a frequency higher than the control loop bandwidth.