LED Converter Frequency Separation to Prevent Low-Dim Flicker
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing LED converters face issues with flicker caused by aliasing due to undersampling, particularly at low dim levels where the LED current is low, leading to measurement errors and light flicker problems.
Innovation Solution
The LED converter adjusts the switching frequency of the DC/DC converter and the sampling frequency to maintain a difference of between 10% and 40% of the switching frequency, ensuring that the sampling frequency is either higher or lower than the switching frequency, thereby avoiding flicker issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the sampling frequency is set close to the switching frequency to improve measurement efficiency, then the sampling rate can be reduced, but aliasing occurs causing measurement errors and flicker
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable rather than fixed. The controller dynamically modifies the switching frequency to maintain a predetermined difference from the sampling frequency, preventing aliasing while allowing the sampling frequency to operate at lower values for improved efficiency. This dynamic adjustment resolves the contradiction between using lower sampling rates and avoiding measurement errors.
2Measurement precision
If the sampling frequency is set much higher than the switching frequency to avoid aliasing, then measurement accuracy improves, but the system complexity and power consumption increase
Solution Approach 1:
The patent applies parameter changes by modifying the switching frequency parameter rather than increasing the sampling frequency. Instead of setting the sampling frequency much higher than the switching frequency (which would increase system complexity), the switching frequency is adjusted to maintain a predetermined difference from the sampling frequency. This resolves the contradiction by achieving accurate measurements through parameter optimization rather than through higher sampling rates.
3Ease of operation
If the switching frequency is varied to control the LED current, then the desired target output current is achieved, but the risk of aliasing increases when the switching frequency approaches the sampling frequency
Solution Approach 1:
The patent applies feedback by implementing a control mechanism that monitors the relationship between switching frequency and sampling frequency. The controller adjusts the switching frequency based on feedback about the sampling rate to maintain a predetermined difference, preventing aliasing while still allowing frequency variation for current control. This resolves the contradiction by adding a feedback layer that ensures reliable operation while maintaining control flexibility.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates LED converter, comprising an actively switched power factor correction, PFC, circuit outputting a DC voltage which is basis for a DC supply voltage of a switched DC/DC converter configured to supply an LED load with a feedback controlled output current, wherein the LED converter comprises means for sampling configured to sample a value representing the output current with a sampling frequency and to supply it to a feedback control unit which is configured to issue a control signal for at least one switch of the switched DC/DC converter, wherein the PFC circuit and the switched converter are designed such that a difference between a switching frequency of the DC/DC switched converter and the sampling frequency of the digital feedback control unit is higher than a first preset value.