LED Control Device Using Characteristic Curve for Short Circuit Detection
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Solution Overview
Problem
Existing LED control devices for motor vehicle lighting, such as daytime running lights and position lights, face challenges with low pulse duty factors making short circuit detection difficult and require complete startup for each light function, leading to inefficient operation and prolonged startup times.
Innovation Solution
A characteristic curve is stored in the control unit to map duty cycles of the control signal, allowing for a duty cycle of 0 below a threshold value, enabling a 'light off' state without shutting down the control device, and using a higher frequency for pulse width modulation to improve detection and reduce flickering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a very low pulse duty factor is used for position light operation, then the brightness requirement is met, but short circuit detection capability deteriorates
Solution Approach 1:
The control device remains in a ready state with the control unit active before light output is required. This preliminary preparation allows the system to quickly respond to status changes and maintain detection capabilities without needing to fully startup each time light functions are activated.
Solution Approach 2:
The patent introduces a characteristic curve that maps the duty cycle of the supplied control signal to a duty cycle of the pulse width modulated activation of the converter. This non-linear mapping allows the system to operate at very low brightness levels while maintaining adequate pulse widths for reliable detection, effectively decoupling the control signal duty cycle from the actual LED drive duty cycle.
2Loss of energy
If the control device is completely switched off when not in use, then energy consumption is reduced, but startup time increases when light functions are needed
Solution Approach 1:
The control unit is kept in a ready state with clock signal generation active, maintaining essential functions while consuming minimal power. This allows the system to quickly transition to full operation when needed, avoiding complete shutdown and restart cycles.
Solution Approach 2:
The system dynamically adjusts its operational state, transitioning between different levels of activity rather than being statically on or off. The control unit can operate in a low-power monitoring mode and quickly scale up to full functionality when light output is required.
3Device complexity
If a single lighting device is used for multiple functions, then device complexity is reduced, but the control unit must constantly startup which increases time loss
Solution Approach 1:
A single lighting device integrates multiple light functions (daytime running light, position light, direction indicator) using a unified control architecture. The control unit is designed to handle various light functions through software control rather than requiring separate hardware for each function.
Solution Approach 2:
The control unit remains active and ready to handle different light functions without requiring constant shutdown and restart. This preliminary preparation allows the system to switch between functions (position light to direction indicator) instantly without startup delays.
4Ease of operation
If a 0 duty cycle control signal is used to switch off the lighting device, then the light can be turned off, but the control unit cannot distinguish between off state and error state
Solution Approach 1:
The patent introduces a threshold value for the duty cycle of the control signal. Duty cycles below this threshold are interpreted as 'light off' commands, while duty cycles above the threshold indicate active light operation. This creates an unambiguous mapping between control signals and system state.
Solution Approach 2:
The characteristic curve acts as an intermediary layer between the control signal and the converter operation. It maps the control signal duty cycle to the converter duty cycle in a non-linear fashion, allowing the system to interpret control signals unambiguously and translate them appropriately for LED drive.
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 allows for a faster response to status changes, improved short circuit detection, and reduced startup times by maintaining the control device active, while enabling precise brightness control and eliminating errors associated with zero duty cycles.
Implementation Method 1
a control unit for controlling the converter as a function of a control signal supplied to the control unit, the control unit for setting the brightness of the lighting device by pulse-width-modulated control of the converter
Data Source
Figure 1~2
Figure 3
AI summary
Disclosed is a control device (5) for an illumination device (3) of a motor vehicle (1), said illumination device (3) comprising at least one LED (4) and being especially a daytime running light and/or a parking light. The control device (5) comprises a converter (7) and a control unit (8) for controlling the converter (7) in accordance with a control signal, the brightness of the illumination device (3) being adjusted by having the control unit (8) control the converter (7) in a pulse width-modulated manner in accordance with a sampling degree of the control signal. According to the invention, a characteristic curve (13) which transforms a sampling degree of the control signal into a sampling degree of the converter (7) is stored in the control unit (8), at least a range (14) of the sampling degree of the control signal lying below a threshold value (15) being transformed into a zero sampling degree for the converter (7).