Synchronous Converter Frequency-Stable Control via Segmented On-Time
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Solution Overview
Problem
Existing synchronous converters for LED operation suffer from frequency-dependent impulse responses and losses, leading to inaccurate regulation due to inductances and capacitances on the load side, which are exacerbated during dimming operations.
Innovation Solution
A synchronous converter design with a control device that sets a constant switch-on time for predefined value ranges of detected LED voltage, using switching means in a push-pull configuration, reducing frequency-dependent losses and enhancing regulation precision by limiting frequency variation from 100 kHz to 10 kHz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the control frequency of switching devices changes with current demand to enable dimming operation, then the adaptability to different LED current requirements is improved, but frequency-dependent losses and control inaccuracy increase due to the frequency-dependent impulse response of inductances, capacitances, and LEDs
Solution Approach 1:
The control approach is segmented into multiple discrete frequency ranges, each with a predefined constant on-time value. Instead of continuously varying frequency with dimming demand, the system divides the operating range into segments and selects the appropriate constant on-time for each segment, thereby limiting frequency variation within each segment and reducing frequency-dependent losses while maintaining adaptability across the full dimming range.
Solution Approach 2:
The system dynamically adjusts the on-time of switching devices based on detected LED voltage to maintain constant frequency within predefined ranges. The control unit modifies the on-time parameter in response to changing LED voltage conditions, enabling the converter to adapt to different current demands while keeping frequency stable and minimizing frequency-dependent losses.
2Adaptability or versatility
If the control frequency changes with current demand, then dimming functionality is enabled, but control precision deteriorates due to frequency-dependent impulse responses
Solution Approach 1:
The control methodology segments the dimming operation into distinct frequency ranges, each associated with a specific constant on-time value. By segmenting the control strategy rather than using continuous frequency variation, the system maintains precise control within each segment while achieving overall dimming functionality across the full range.
Solution Approach 2:
The system changes the on-time parameter of switching devices based on detected LED voltage levels to maintain constant frequency within predefined ranges. This parameter adjustment strategy enables dimming functionality while preserving control precision by compensating for voltage variations through on-time modification rather than frequency variation.
3Reliability
If constant on-time control is used for switching devices, then frequency stability is improved and frequency-dependent losses are reduced, but the ability to continuously adapt to varying LED voltage conditions deteriorates
Solution Approach 1:
The system dynamically selects from multiple discrete on-time values corresponding to different LED voltage ranges. While each individual range uses a constant on-time for frequency stability, the overall system adapts to varying voltage conditions by switching between different constant on-time values, thereby combining frequency stability with adaptability to changing LED conditions.
Solution Approach 2:
The voltage operating range is segmented into multiple predefined ranges, each with its own constant on-time value. This segmentation allows the system to maintain frequency stability within each voltage range while adapting to different voltage conditions by selecting the appropriate segment, thus resolving the contradiction between stability and adaptability.
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a synchronous converter (10) for operating at least one LED (41) comprising: supply and load sides (12, 13) having respective switching elements (14, 15); sensing elements (11C, 16) for sensing an LED voltage (17); and a control device for controlling the switching elements (14, 15) in a push-pull mode that depends on the sensed LED voltage (17). The control device is designed to control the switching element (14) on the supply side (12) with a particular constant switch-on time (Tp) for a particular value range in which the sensed LED voltage (17) falls, from a plurality of specified value ranges for the sensed LED voltage (17).