LED Driver SSFM Circuit for EMI Reduction
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Solution Overview
Problem
Conventional LED driver circuits for backlight modules in LCDs generate significant electromagnetic interference (EMI), which is not effectively mitigated by existing solutions, posing challenges for electromagnetic compatibility (EMC) in electronic devices.
Innovation Solution
The integration of a spread spectrum frequency modulation (SSFM) circuit within the saw-tooth generator of the LED driver circuit, which generates a time-variant current and saw-tooth voltage, varying the frequency of the driving pulse to reduce EMI by dispersing energy across side bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional LED driver circuit uses fixed frequency pulse width modulation, then power conversion efficiency is maintained, but electromagnetic interference is significant and EMC compliance is difficult to achieve
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The saw-tooth generator produces a frequency-modulated signal where the frequency varies over time, transforming the static fixed-frequency PWM system into a dynamic frequency-modulated system that reduces EMI by spreading energy across a broader frequency spectrum
Solution Approach 2:
The patent changes the frequency parameter of the driving pulse from a constant value to a time-variant value. By modifying the frequency parameter dynamically through the saw-tooth generator, the system achieves spread spectrum frequency modulation, which disperses electromagnetic energy across multiple frequency components rather than concentrating it at a single frequency
2Reliability
If spread spectrum frequency modulation is introduced to reduce EMI, then electromagnetic compatibility is improved, but device complexity increases
Solution Approach 1:
The patent merges the frequency modulation function with the existing saw-tooth generator circuit. Instead of adding a separate SSFM module, the frequency variation is integrated into the saw-tooth generation process itself, combining multiple functions (timing generation, frequency modulation, and PWM control) into a single unified circuit structure
Solution Approach 2:
The saw-tooth generator is designed to serve multiple functions: it generates the timing signal for PWM operation, implements frequency modulation for EMI reduction, and provides the frequency variation necessary for spread spectrum techniques. This multi-functional design eliminates the need for separate dedicated circuits for each function
Data Source
AI summary
The present invention relates to an LED driver, power control circuit and display panel using the same. The LED driver has the function of spread spectrum frequency modulation (SSFM). The circuit topology of the driver includes a power converter, an error amplifier, a feedback circuit, a saw-tooth generator and a driving circuit. The present invention adds the SSFM circuit in the saw-tooth generator to generate a time variant current according to time variant function, so that the saw-tooth wave could be changed by the time variant current as mentioned above. Therefore, the frequency of the driving pulse generated by the LED driver will be varied as time. As the result, the reduction of the electro-magnetic interference (EMI) can be achieved.