LED Switched Converter Control for Low-EMI Flicker-Free Dimming
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Solution Overview
Problem
Switched-mode power converters (SMPCs) used in LED lighting systems suffer from high levels of electromagnetic interference (EMI) and visible flicker in light output due to improper switching frequency modulation (SFM), particularly when the activation/deactivation of SFM occurs at high modulation signal amplitudes.
Innovation Solution
A feedback-controlled switched converter that enables/disables the periodic modulation signal only at time periods with amplitudes lower than a preset threshold, centered at zero-crossings, or delayed until the next zero-crossing event, to minimize visible flicker and EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If switching frequency modulation is applied to reduce EMI, then electromagnetic interference levels are reduced, but visible flicker in light output occurs
Solution Approach 1:
The patent applies periodic switching frequency modulation to spread EMI across multiple frequencies, reducing peak EMI levels. The modulation is implemented periodically with a specific frequency that is optimized to minimize both EMI and visible flicker, creating a balanced periodic action that addresses both concerns simultaneously.
Solution Approach 2:
The patent dynamically changes the switching frequency parameter based on modulation depth and frequency adjustments. By varying the switching frequency around a nominal value with controlled modulation, the system reduces EMI spectral peaks while maintaining operation outside the visible flicker range for human perception.
2Object-affected harmful factors
If spread-spectrum technique is used to reduce EMI, then electromagnetic interference is reduced, but light output stability deteriorates
Solution Approach 1:
The patent implements preliminary action by pre-defining modulation parameters and thresholds before operation. The system is configured with predetermined modulation depths and frequency ranges that are optimized to prevent visible flicker while achieving EMI reduction, ensuring stable light output from the start of operation.
Solution Approach 2:
The patent employs feedback control to monitor light output stability and adjust modulation parameters accordingly. By using feedback from the LED load and EMI measurements, the system dynamically optimizes the spread-spectrum modulation to maintain stable light output while achieving EMI reduction goals.
Data Source
AI summary
The invention relates to a feedback-controlled switched converter, comprising: at least one switch, terminals for supplying an LED load, a control unit being supplied with a feedback signal indicating a load current of the LED load. The control unit is configured to: generate an output signal on the basis of the feedback signal, combine the output signal with a periodic modulation signal in order to obtain a control signal, the control signal being configured to set an operation parameter of the at least one switch, apply the control signal to the at least one switch. Moreover, the switched converter comprises means for enabling/disabling the periodic modulation signal, wherein the means for enabling/disabling is configured to enable/disable the periodic modulation signal only at time periods of the periodic modulation signal in which an amplitude of the periodic modulation signal is lower than an amplitude threshold, or wherein the means for enabling/disabling the periodic modulation signal is configured to only enable/disable the periodic modulation signal at first time periods of the periodic modulation signal being centered at zero-crossings of the periodic modulation signal, these first time periods being separated from each other by time periods in which no enabling/disabling of the modulation signal is performed.