LED Driver Buffer Switching for Fast Start-Up and Low Flicker
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Solution Overview
Problem
LED driving circuits face challenges in meeting the new Single Lighting Regulation (SLR) standards for low flicker and fast start-up, particularly when using a reduced stage topology with large output capacitors, which prolong start-up times and fail to meet EU requirements.
Innovation Solution
A buffer circuit with adjustable capacitance is implemented, dynamically changing from a low to a high capacity during start-up and normal operation to quickly charge the LEDs and reduce flicker, using capacitors and switches to control the effective capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the capacitance of the output capacitor is increased to smooth the ripple current, then the flicker in normal operation is reduced, but the start-up time is prolonged
Solution Approach 1:
The patent applies the dynamics principle by making the capacitance value time-dependent. A switch dynamically changes the configuration of capacitors: during start-up, only a small capacitor is connected to enable fast charging; during normal operation, a large capacitor is connected to smooth ripple. This dynamic adjustment resolves the contradiction between fast start-up and low flicker.
Solution Approach 2:
The patent segments the buffering function into two distinct capacitive elements: a small capacitor for fast start-up and a large capacitor for ripple smoothing. By dividing the single capacitor function into separate segments that operate at different times, the system achieves both fast start-up and low flicker without requiring a single large capacitor that would prolong start-up time.
2Reliability
If a large output capacitor is used to smooth ripple current, then the SVM requirement is met, but the time to charge the capacitor to sufficient voltage is extended
Solution Approach 1:
The patent uses dynamic switching to change the effective capacitance based on operational phase. During start-up, the switch connects only the small capacitor, enabling fast charging and quick LED activation. During normal operation, the switch connects the large capacitor to ensure SVM compliance by smoothing ripple current. This dynamic approach satisfies both productivity and reliability requirements.
Solution Approach 2:
The patent applies preliminary action by using the small capacitor to quickly establish the necessary voltage during start-up before the large capacitor is engaged. This preliminary charging action enables fast start-up, after which the large capacitor takes over for ripple smoothing, ensuring SVM compliance without compromising start-up speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves both fast start-up and low flicker by ensuring rapid voltage buildup during start-up and effective ripple absorption in normal operation, meeting regulatory requirements.
Implementation Method 1
a buffer circuit adapted to buffer said LED driving current
Implementation Method 2
a buffer adjustment circuit adapted to adjust the buffer capability of the buffer circuit
Data Source
AI summary
In order to provide a balance between a fast start-up in start-up phase and a low light output ripple in normal operation phase, it is provided a LED driving circuit comprising: an input to receive a LED driving current, a buffer circuit adapted to buffer said LED driving current, and an output to be connected to LED and adapted to output the LED driving current, after buffered, to the LED, characterized in that, further comprises a buffer adjustment circuit adapted to adjust the buffer capability of the buffer circuit at a first level, in a start-up phase of the LED driving circuit when the LED driving circuit starts to receive said LED driving current, and adjust the buffer capability of the buffer circuit at a second level larger than the first level in a normal operation phase later than the start-up phase.