Constant Power LED Driver Circuit for Automotive Luminosity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
LED drivers in automotive applications face challenges in maintaining constant luminosity due to temperature variations and the 'one-out-all-out' safety feature, which can cause unintended hazards by shutting down LED strings when a single LED is shorted.
Innovation Solution
An LED driver circuit that regulates power rather than current, using a voltage detector and controller to generate a feedback signal and adjust the current inversely with temperature changes, ensuring constant power delivery and preventing shutdowns when an LED is shorted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If constant current regulation is used to maintain LED luminosity, then current stability is improved (within 2-3% of target value), but luminosity consistency deteriorates due to temperature-induced forward voltage changes causing power consumption to drop by 10% at high temperatures
Solution Approach 1:
The patent transitions from constant current regulation to constant power regulation by changing the controlled parameter from current to power. The controller adjusts the LED drive current based on detected forward voltage to maintain constant power delivery, compensating for temperature-induced voltage changes and preventing luminosity drops at high temperatures.
Solution Approach 2:
The patent implements a feedback mechanism where the forward voltage of the LED string is continuously detected and fed back to the controller. The controller uses this feedback signal to dynamically adjust the drive current, ensuring constant power delivery and stable luminosity across varying temperature conditions.
2Illumination intensity
If NTC thermistor temperature compensation is added to maintain luminosity, then luminosity stability is improved, but device complexity and cost increase, and compensation reliability is reduced due to thermal equilibrium delays
Solution Approach 1:
The patent employs a self-service approach where the LED string's own forward voltage is used as the sensing parameter for temperature compensation. The forward voltage detection directly reflects the LED junction temperature, eliminating the need for external thermistors and their associated thermal equilibrium delays. The system uses its inherent electrical characteristic for self-regulation.
3Reliability
If 'one-out-all-out' safety feature is implemented to shut down LED string on single LED short, then safety is improved, but reliability deteriorates by causing unnecessary shutdowns that create hazards such as headlight failure
Solution Approach 1:
The patent implements dynamic response to LED faults by transitioning from static constant current regulation to adaptive constant power regulation. When an LED short occurs, the forward voltage drops and the controller automatically increases current to maintain constant power, keeping the LED string operational. This dynamic adaptation allows the system to handle faults gracefully without unnecessary shutdowns.
Data Source
AI summary
An LED driver includes a voltage detector and a controller. The voltage detector is configured to couple to an LED string comprising a plurality of series-coupled LEDs and to detect a voltage across the LED string to generate a feedback signal. The controller is configured to control an amount of current provided to the LED string in response to the feedback signal, with an amount of power provided to the LED string being substantially constant. The voltage detector can be coupled in parallel with the LED string, and may be a resistor divider. The controller is further configured to couple to a DC-DC converter comprising a switch controlled by the controller and configured to generate an output current and an output voltage coupled to the LED string to provide the amount of power to the LED string.