LED Outage Detection Circuit with PWM Dimming Support
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Solution Overview
Problem
Existing LED outage detection systems are complex and costly, and they are not suitable for detecting defective LEDs, especially when dimmed using pulse width modulation (PWM) dimming, and they fail to provide a warning for defective tail or brake lighting in automotive applications.
Innovation Solution
A simple and cost-effective LED outage detection circuit that uses a top voltage detector and differential amplifier to differentiate between the operating voltage and supply voltage of an LED, outputting a signal indicating whether the LED is defective, and is compatible with PWM dimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a test mode is used to detect defective lamps, then detection capability is provided, but the system cannot detect defects occurring during normal operation and requires complex circuitry
Solution Approach 1:
The LED lamp performs self-detection by monitoring its own voltage characteristics. The control circuit continuously compares the actual voltage across the LED with expected voltage values during normal operation, enabling automatic defect detection without requiring external test equipment or complex additional circuitry.
Solution Approach 2:
The detection method monitors changes in voltage parameters across the LED. By detecting abnormal voltage deviations from expected operating ranges, the system identifies defective LEDs through parameter analysis rather than requiring complex structural modifications to the circuit.
2Ease of operation
If PWM dimming is used to control LED brightness, then dimming capability is achieved, but conventional detection systems cannot detect defective LEDs
Solution Approach 1:
The control circuit implements feedback by continuously monitoring the voltage across the LED during PWM dimming operation. The system compares the actual voltage measurements with expected voltage characteristics at different duty cycles, enabling defect detection that adapts to the PWM dimming regime rather than being disrupted by it.
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 circuit effectively detects defective LEDs, providing a clear signal for driver notification and reducing system complexity and cost, while being suitable for use with dimmed LEDs in automotive lighting systems.
Implementation Method 1
a top voltage detector (20) coupled to the LED for detecting a voltage across the LED
Implementation Method 2
the differential amplifier is configured to output an outage detection signal based on a difference between the reference voltage and the top voltage signal
Data Source
Figure 1~2
Figure 3~4
AI summary
In order to detect a defective light source, such as a LED coupled to a DC-DC converter circuit for receiving a power signal, an outage detection circuit comprises a top voltage detector coupled to the LED for detecting a voltage across the LED. The top voltage detector has an top voltage terminal for supplying a top voltage signal. The detection circuit further comprises a differential amplifier coupled to the top voltage terminal for receiving the top voltage signal as a first input signal and coupled to a reference voltage terminal. The reference voltage terminal is configured to supply a reference voltage as a second input signal. The differential amplifier comprises an output terminal for supplying an outage detection signal.