LED Driver Current Regulation for Stable Color Rendering
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Solution Overview
Problem
Existing methods for driving light-emitting diodes in illumination devices for film, video, and photographic recordings face challenges in maintaining consistent color rendering and color temperature due to current-dependent emission wavelengths, leading to exposure fluctuations at high recording frequencies and short exposure times.
Innovation Solution
A method and device that utilize pulse-width modulation with freely selectable frequencies up to the megahertz range, employing a current sensor to detect the current-time integral instead of peak values, allowing for exact current regulation and maintaining constant color rendering and color temperature, even with temperature fluctuations, using cost-effective standard components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If pulse-width modulation is used to control LED brightness, then energy efficiency is improved, but color rendering stability deteriorates due to current-dependent emission wavelengths
Solution Approach 1:
The patent implements a feedback mechanism where the actual LED current is continuously measured and compared with the reference current. The error signal is amplified and fed back to the switching element to adjust the pulse width, ensuring that the average current through the LED matches the reference current. This closed-loop control maintains stable color rendering while preserving the energy efficiency of pulse-width modulation.
Solution Approach 2:
The patent replaces direct mechanical/current control with an electronic feedback control system. Instead of directly controlling the LED current through simple switching, the system uses a feedback loop with error amplification to indirectly control the current, substituting the direct mechanical control approach with an electronic regulation mechanism that maintains stability.
2Reliability
If high-frequency pulse-width modulation is used for film recording, then exposure fluctuations are reduced, but detection precision deteriorates when measuring peak current values
Solution Approach 1:
The patent substitutes direct peak current measurement with average current measurement through a feedback loop. The system measures the average current over the pulse period and uses this information to control the pulse width, avoiding the precision problems of peak detection at high frequencies while maintaining exposure consistency.
Solution Approach 2:
The patent changes the measurement parameter from peak current to average current. By measuring and controlling the average current instead of the peak current, the system achieves reliable exposure control at high modulation frequencies without suffering from detection precision limitations of peak value measurement.
3Stability of the object's composition
If additional temperature-dependent compensation is added to regulate color correction, then color rendering stability is improved, but device complexity increases
Solution Approach 1:
The patent uses a feedback mechanism that automatically compensates for temperature effects without requiring additional temperature sensors or complex regulation circuits. The feedback loop detects current deviations caused by temperature-dependent LED characteristics and adjusts the pulse width accordingly, providing automatic compensation through the existing current measurement and error amplification infrastructure.
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
Enables reliable and efficient control of light-emitting diode brightness and fixed color settings, eliminating exposure fluctuations at high recording frequencies and short exposure times, while minimizing heat loss and maximizing luminous intensity.
Implementation Method 1
at least one light-emitting diode, which emits blue light and which is referred to as transmission LED and emits directly used light primarily in the wavelength range of 470 to 490 nm
Implementation Method 2
another light-emitting diode, which operates with conversion and is accordingly referred to as conversion LED and which emits light primarily in the wavelength range of at most 465 nm
Implementation Method 3
an analog/digital converter, which is connected via a connecting line to an electrode terminal of the light-emitting diodes and detects a voltage that is dropped across the light-emitting diodes and is proportional to the ambient brightness
Data Source
AI summary
A method for driving series-connected light-emitting diodes of an illumination device, in particular an illumination device for film, video and photographic recordings with a pulse-width-modulation of the light-emitting diode current, is provided. In the method the pulse-width-modulated light-emitting diode current is detected and a current sensor signal is derived and fed to a microprocessor, which outputs a drive signal for the pulse-width-modulation and for the setting of the light-emitting diode voltage applied to the light-emitting diodes, depending on the detected current sensor signal. The current-time integral of the pulse-width-modulated light-emitting diode current flowing through the light-emitting diodes is determined and a controllable voltage source for setting the light-emitting diode voltage is driven in such a way that a predetermined pulse-width-modulated light-emitting diode current flows through the light-emitting diodes.