LED Arrangement Voltage Limiter Startup Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
LED arrangements with smoothing capacitors exhibit slow response times during startup and shutdown procedures due to the need for charge storage and discharge, leading to inefficiencies in brightness level changes, especially when switching from an OFF or low brightness state to an ON state.
Innovation Solution
Incorporating a controllable voltage limiter that limits the voltage across the LED string to a level below its forward voltage during startup and shutdown, allowing rapid charging or discharging of the capacitor without activating the LED string, and using a controllable current source with pulse width modulation to achieve desired brightness levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a smoothing capacitor is connected in parallel with the LED string to improve power factor and efficiency, then power factor and efficiency are improved, but the response time during startup and shutdown procedures becomes slow
Solution Approach 1:
The controller performs preliminary charging of the capacitor at full current before dimming, so that when dimming is requested, the capacitor is already charged and ready to provide immediate current to the LED string, eliminating startup delay
Solution Approach 2:
The system dynamically adjusts the charging current based on operational state: using full charging current during startup/shutdown to quickly charge the capacitor, and reducing to dimming current during steady-state operation, optimizing both response time and energy efficiency
2Loss of time
If the capacitor is charged rapidly to reduce turn-ON time, then turn-ON time is reduced, but the LED string may activate prematurely causing light flash
Solution Approach 1:
The circuit includes an alternative current path with a resistor connected in parallel with the LED string. During capacitor charging, current flows through this resistive path instead of the LED string, preventing light flash while still allowing rapid capacitor charging
Solution Approach 2:
The controller enables the alternative current path before charging the capacitor, so that when charging begins, the LED string is already protected from activation. The alternative path is disabled only after charging completes and the LED string is safely activated
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 significantly reduces turn-ON and turn-OFF times, prevents light flash during startup, and minimizes 'fade' during shutdown, making the LED arrangement more responsive to brightness level changes.
Implementation Method 1
a capacitor connected in parallel with the LED string
Implementation Method 2
an LED string comprising one or more LEDs and adapted to receive power from the voltage source
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An LED arrangement having a LED string and a smoothing capacitor connected in parallel. A controllable voltage limiter is able to limit a voltage across the LED string to selectively prevent the LED string from outputting light. As the LED arrangement is turned ON, the controllable voltage limiter may activate so that the smoothing capacitor can be charged with a high current without activating the LED string.