LED Reference Voltage Circuit with Temperature Compensation
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Solution Overview
Problem
Existing circuit arrangements for generating a reference voltage for LED power supplies are costly and fail to effectively address fluctuations in input voltage and temperature, which affect LED luminance consistency in automotive lighting applications.
Innovation Solution
A circuit arrangement using three voltage dividers, with two ohmic resistors in each, connected to a constant power supply and an input voltage, and a temperature-dependent resistor thermally coupled to the LED, along with diodes and an optional amplifier stage to generate a reference voltage that adjusts based on input voltage and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex circuit arrangements are used to generate temperature-dependent and input-voltage-dependent reference voltage, then luminance constancy is improved, but cost and device complexity increase significantly
Solution Approach 1:
The circuit is divided into three independent voltage divider branches, each handling a specific function: one for temperature compensation (with thermistor), one for input voltage dependency (with input voltage input), and one as the main reference voltage source. This segmentation allows each branch to be simple while the combination achieves the desired complex functionality for maintaining luminance constancy.
Solution Approach 2:
The patent combines three simple voltage divider circuits into one integrated reference voltage generation system. By merging these branches at their output nodes and using diodes for selective activation, the circuit achieves temperature-dependent and input-voltage-dependent reference voltage generation without requiring a single complex circuit design.
2Reliability
If multiple voltage dividers and diodes are used to create temperature and voltage dependent reference voltage, then luminance constancy is improved, but manufacturing cost increases
Solution Approach 1:
The patent uses inexpensive, readily available components such as standard ohmic resistors, a single thermistor, and conventional diodes to build the voltage divider network. These are basic electronic components with low manufacturing costs, making the overall circuit cost-effective despite the multiple components required for temperature and voltage dependency.
Solution Approach 2:
The reference voltage is made adjustable and adaptive by changing its parameters based on temperature and input voltage conditions. The circuit automatically modifies the reference voltage magnitude through the voltage divider network in response to temperature changes (via thermistor) and input voltage variations, providing dynamic adaptation without additional cost.
3Temperature
If the reference voltage is made dependent on input voltage and temperature, then LED temperature control is improved, but circuit complexity increases
Solution Approach 1:
The circuit automatically adjusts the reference voltage based on temperature and input voltage conditions without requiring external control signals or complex control logic. The thermistor inherently responds to temperature changes, and the voltage divider network automatically scales the reference voltage, making the system self-regulating and simplifying the overall control architecture.
Solution Approach 2:
The patent utilizes the thermal properties of the thermistor (temperature-dependent resistor) to automatically adjust the reference voltage in response to temperature changes. As temperature varies, the thermistor's resistance changes, which directly modifies the voltage division ratio and thus the reference voltage, providing passive thermal compensation without additional sensors or active control elements.
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 solution provides a cost-effective and efficient method to maintain consistent LED luminance by derating the reference voltage in response to input voltage fluctuations and temperature changes, ensuring high luminance constancy and preventing excessive LED temperatures.
Implementation Method 1
a third voltage divider (R5/R6) which consists of an ohmic resistor (R5) and a temperature-dependent resistor (R6) and which is connected to the constant power supply voltage (UV)
Implementation Method 2
a voltage proportional to the voltage at the centre terminal of the second voltage divider is supplied to the centre terminal of the first voltage divider via a first diode (D1), a voltage proportional to the voltage at the centre terminal of the third voltage divider is further supplied to the centre terminal of the first voltage divider via a second diode (D2)
Data Source
AI summary
A circuit arrangement (1) for generating a reference voltage (Uref) for the power supply (2) of an LED arrangement (LED), wherein the power supply supplies a feed current (IS) to the LED arrangement on the basis of an input voltage (UB), which current is determined by the magnitude of the reference voltage, wherein the circuit arrangement comprises: a first voltage divider (R1/R2), located on a constant power supply voltage (UV), a second voltage divider (R3/R4), located on the input voltage (UB) of the power supply (2), and a third voltage divider (R5/R6) which consists of an ohmic resistor (R5) and a temperature-dependent resistor (R6) thermally coupled to the LED arrangement, a voltage proportional to the voltage on the centre connection of the second voltage divider (R3/R4) is supplied via a first diode (D1) to the centre connection of the first voltage divider (R1/R2), a voltage proportional to the voltage on the centre connection of the third voltage divider (R5/R6) is further supplied via a second diode (D2) to the centre connection of the first voltage divider (R1/R2), and the voltage on the centre connection of the first voltage divider (R1/R2) is supplied to the power supply (2) as a reference voltage (Uref).