LED Driver Circuit for Thermally Induced Colour Drift Compensation
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Solution Overview
Problem
Modern multi-colour LED systems face challenges in achieving high brightness resolution and colour stability due to temperature-dependent colour drift, requiring complex brightness control and fast switching currents that compromise electromagnetic compatibility.
Innovation Solution
A circuit arrangement for driving multi-colour LEDs includes a temperature sensing circuit, current sources, modulators, and a calibration circuit to generate control signals that adjust load currents based on temperature and desired colour, using sigma-delta modulation to achieve stable and efficient colour mixing with improved EMC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse width modulation with high switching frequency is used to achieve high brightness resolution, then brightness control precision is improved, but electromagnetic compatibility deteriorates
Solution Approach 1:
The patent uses pulse width modulation (PWM) with a PWM frequency of at least 200 Hz to control the brightness of LEDs. By periodically switching the current through the LEDs at this frequency, the invention achieves high brightness resolution (at least 10 bits) while the periodic nature of the switching allows for smoother current transitions compared to abrupt switching, thereby reducing electromagnetic interference.
Solution Approach 2:
The invention pre-calculates and stores compensation values in a lookup table that account for thermal drift effects on LED wavelength. This preliminary preparation of compensation data allows the system to quickly adjust current values in response to temperature changes without requiring complex real-time calculations, thus maintaining high brightness control precision while minimizing processing delays and associated electromagnetic disturbances.
2Stability of the object's composition
If current is varied to compensate for temperature drift, then colour stability is improved, but device complexity increases
Solution Approach 1:
The patent pre-calculates and stores compensation values in a lookup table that account for thermal drift effects on LED wavelength. This preliminary preparation of compensation data allows the system to quickly adjust current values in response to temperature changes without requiring complex real-time calculations, thus maintaining high brightness control precision while minimizing processing delays and associated electromagnetic disturbances.
Solution Approach 2:
The invention implements a feedback mechanism where the actual wavelength or colour output of the LEDs is monitored and compared to the desired wavelength. Based on this feedback and the stored compensation values, the system automatically adjusts the current through the LEDs to compensate for thermal drift, thereby maintaining colour stability without requiring complex manual intervention or system redesign.
3Productivity
If fast switching currents are used to achieve high brightness resolution, then productivity is improved, but electromagnetic compatibility deteriorates
Solution Approach 1:
The patent uses pulse width modulation (PWM) with a PWM frequency of at least 200 Hz to control the brightness of LEDs. By periodically switching the current through the LEDs at this frequency, the invention achieves high brightness resolution (at least 10 bits) while the periodic nature of the switching allows for smoother current transitions compared to abrupt switching, thereby reducing electromagnetic interference.
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
The solution provides high-resolution brightness control and colour stability across a wide temperature range, reducing electromagnetic interference and enhancing electromagnetic compatibility while maintaining effective colour mixing.
Implementation Method 1
a temperature sensing circuit (100) configured to provide a digital temperature signal representing the temperature(s) of the light emitting diodes
Implementation Method 2
A first and a second modulator unit (10, 20) are configured to generate the control signals which are modulated such that the time average value of each control signal corresponds to the value of a corresponding input signal of the respective sigma-delta modulator
Implementation Method 3
a first light emitting diode (1R) and a second light emitting diode (1G) which emit light of different colours
Implementation Method 4
light emitting diodes (LEDs), especially for use in multi-colour LED applications
Data Source
Figure 1~2
Figure 3~5
Figure 6~7a
AI summary
Disclosed is a circuit arrangement and a method for driving a multi-colour LED arrangement. The circuit arrangement comprises: at least a first light emitting diode (LDR) and a second light emitting diode (LDG) emitting light of different colours arranged adjacent to each other for additive colour mixing to provide a desired colour; a temperature sensing circuit (2R, 2G; 3; 4) configured to provide a temperature signal (TR', TG') representing the temperature(s) of the light emitting diodes (LDR, LDG) ; a current source (QR, QG) for each light emitting diode (LDR, LDG) configured to provide the light emitting diodes (LDR, LDG) with respective load currents (iR, iG) in accordance with corresponding control signals received by the current sources (QR, QG); a first and a second modulator unit (1; 1b, 1c) configured to generate the control signals which are modulated such that the time average value of each control signal corresponds to the value of a corresponding input signal (IR, IG) of the respective sigma-delta modulator (1); and a calibration circuit (10', 12; 10, MUX, 12) configured to provide the input signals (IR, IG) dependent on a colour signal (CS) defining the desired colour and dependent on the temperature signal (TR', TG').