Infrared LED Driver Circuit Temperature Compensation
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Solution Overview
Problem
Infrared transmitter LEDs and receivers are highly temperature-dependent, leading to incorrect results due to temperature fluctuations, and maintaining a constant current through these LEDs is challenging, affecting light efficiency.
Innovation Solution
A circuit using a voltage/current converter with a programmable current source and analog-to-digital converter to measure and digitally compensate for temperature-dependent LED voltage, adjusting the drive current to maintain constant light output, incorporating a Digital Signal Processor for auto-zero offset cancellation and resistor load compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If temperature compensation is implemented for infrared LED, then temperature stability is improved, but device complexity increases due to additional measurement and control circuits
Solution Approach 1:
The system uses the infrared LED itself as the temperature sensor by measuring its forward voltage, eliminating the need for separate temperature sensors. The LED's electrical characteristics are exploited to derive temperature information, which then feeds back to adjust the drive current and compensate for temperature effects.
Solution Approach 2:
The infrared LED serves dual functions: as the light-emitting component and as the temperature sensing element. By measuring the forward voltage across the LED, the system simultaneously monitors both the drive current and the junction temperature, reducing the need for dedicated temperature sensing hardware.
2Use of energy by moving object
If constant current is maintained through infrared LED, then light efficiency is improved, but temperature fluctuations cause measurement errors in forward voltage
Solution Approach 1:
The system continuously measures the forward voltage of the infrared LED and uses this information to adjust the drive current through a feedback control mechanism. The measured forward voltage serves as feedback to maintain the LED at optimal operating conditions, compensating for temperature drift and ensuring constant light output.
Solution Approach 2:
The drive current is dynamically adjusted based on real-time measurements of the LED's forward voltage. Rather than using a fixed current source, the system adapts the current level to compensate for temperature changes, maintaining optimal light efficiency across varying operating conditions.
3Temperature
If forward voltage measurement is used for temperature sensing, then temperature detection capability is improved, but offset errors and load effects reduce measurement accuracy
Solution Approach 1:
The system performs offset cancellation and load compensation measurements before the actual temperature measurement. By pre-characterizing and subtracting systematic errors such as amplifier offsets and resistive load effects, the system ensures that subsequent temperature readings are accurate and free from these systematic errors.
Solution Approach 2:
The system introduces intermediate measurement steps that separate the temperature sensing function from the drive current function. By using separate measurement cycles and intermediary calculations to remove offset errors and load effects, the system accurately extracts temperature information from the forward voltage measurements without contamination from other factors.
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
Achieves accurate temperature compensation for infrared transmitter LEDs, ensuring constant light efficiency and accurate current ratios, applicable in rain sensing systems and other applications requiring stable LED performance.
Implementation Method 1
a transmitter (such as an infrared light emitting diode (LED)), which transmits light in the infrared range
Implementation Method 2
an optical receiver (phototransistor or photodiode or photoresistor), which converts the optical infrared signal into a proportional electrical signal
Data Source
Figure 1
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Figure 3~5
AI summary
Systems and methods to achieve a circuit for driving one or more infrared transmitter LEDs with temperature compensation have been disclosed. In a preferred embodiment of the invention the circuit has been applied for a rain sensing system. The junction temperature of the LED is measured and compensated by adjusting the driver current of a voltage-to-current converter driving the LED. The LED junction temperature is measured by comparing the difference in the forward diode voltage at different current densities. This voltage difference is extracted when switching the drive currents between different constant values. The measurement results are converted to digital values, which are used by a buffered dual ladder resistive DAC structure to adjust the drive current to temperature variations.