LED Bridge Circuit for Ambient Light Sensing
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Solution Overview
Problem
Existing LED arrangements for ambient-light-dependent brightness control in applications like cockpit illumination require separate light sensors and microprocessors, which increase complexity and cost, and can be affected by dirt and suboptimal light measurement directions.
Innovation Solution
An LED arrangement using a bridge circuit with at least one LED and two transistors, where the first transistor applies an illumination voltage as a square-wave signal, and the second transistor applies a voltage with inverted polarity during LED off times to measure photocurrent, allowing the LED to function as a light sensor and adjust its brightness based on ambient luminosity without a separate sensor or microprocessor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate light sensor is used to measure ambient luminosity, then the brightness control function is achieved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The LED is made to perform dual functions: emitting light during illumination phases and sensing ambient light during non-illumination phases. By switching the LED between these two modes using the transistor bridge circuit, the system eliminates the need for a separate light sensor, thereby reducing device complexity and manufacturing cost while maintaining the brightness control function
Solution Approach 2:
The invention merges the illumination function and light sensing function into a single component (the LED). The bridge circuit with two transistors enables the LED to be rapidly switched between providing illumination and measuring ambient light, combining what were previously separate functions into one integrated system
2Reliability
If a microprocessor is used to control LED brightness based on ambient light, then the brightness control is achieved, but the device complexity and cost increase
Solution Approach 1:
The system uses the LED itself to perform the light measurement function that would otherwise require a separate sensor and microprocessor. The LED measures ambient luminosity during its non-illumination periods and automatically adjusts its own brightness based on the measured photocurrent, eliminating the need for external control electronics
Solution Approach 2:
The invention replaces the electronic control system (microprocessor and separate sensor) with a simpler transistor-based bridge circuit that directly controls the LED switching between illumination and measurement modes. This substitution of a complex electronic control mechanism with a simpler circuit achieves the same brightness control function
3Measurement precision
If a separate light sensor is used, then the ambient light measurement is achieved, but the sensor can be influenced by LED light and shaded by dirt
Solution Approach 1:
Instead of using a separate sensor that is vulnerable to LED light interference and dirt accumulation, the invention uses the LED itself as the sensor. By switching the LED to measurement mode during non-illumination periods, the system ensures that the measurement is performed by the same component that emits the light, eliminating interference from separate sensor placement and reducing susceptibility to dirt accumulation on separate sensor surfaces
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 enables ambient-light-dependent brightness control with minimal expenditure, using few active components and avoiding the need for a microprocessor, while maintaining accurate light measurement and reducing sensitivity to dirt and light direction issues.
Implementation Method 1
the brightness of the LED is dependent on the ambient luminosity, which is measured by means of the LED, which is connected in a non-illuminated state as a light sensor
Data Source
AI summary
An LED arrangement comprising at least one LED, which receives an LED illumination voltage in accordance with a square-wave signal, wherein the brightness of the LED is dependent on the ambient luminosity, which is measured by means of the LED, which is switched in a non-illuminated state as a light sensor. The at least one LED is arranged together with a first and a second transistor in a bridge circuit such that the first transistor applies the LED illumination voltage to the LED in accordance with the square-wave signal, and the second transistor applies a voltage having inverted polarity as the LED illumination voltage to the LED in intervals of the turned-off times of the LED, wherein the duty cycle of the square-wave signal is dependent on the strength of a photocurrent, which flows through the LED when the voltage having inverted polarity is applied thereto.