Head-Up Display Backlight Overcurrent Detection for Blinding Prevention
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Solution Overview
Problem
Existing head-up displays in vehicles face the challenge of preventing driver blinding due to excessive light emission, which is typically addressed by costly current measurement methods to cut off or reduce electric current, requiring additional and expensive components.
Innovation Solution
A head-up display unit with a control unit that utilizes a high side switch with an integrated current mirror to derive input current signals indirectly, eliminating the need for direct current measurement and allowing the use of non-ASIL compliant backlight drivers, combined with a local dimming driver for precise overcurrent detection and blinding prevention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct current measurement methods are used to prevent driver blinding, then reliable overcurrent detection is achieved, but additional costly components and increased device complexity are required
Solution Approach 1:
The patent uses an intermediary approach by measuring the input current to the backlight driver instead of directly measuring the output current through the backlight unit. This indirect measurement method employs the high side switch with integrated current mirror to derive input current signals, avoiding the need for complex direct current measurement components while maintaining reliable overcurrent detection capability
Solution Approach 2:
The patent replaces traditional direct electrical current measurement mechanisms with an alternative electrical approach using voltage signal derivation. By utilizing the high side switch's integrated current mirror to generate a mirror voltage signal that represents the input current, the system substitutes complex current sensing hardware with a simpler voltage-based indirect measurement system
2Reliability
If ASIL compliant backlight drivers are used to ensure safety, then driver blinding prevention is reliable, but component cost increases
Solution Approach 1:
The patent applies the principle of using cost-effective components by selecting a non-ASIL compliant backlight driver that is cheaper to manufacture. The system compensates for the lower inherent safety level of this cheaper component by implementing the indirect current measurement and overcurrent detection system through the high side switch and control unit, achieving the required safety performance at lower overall system cost
Solution Approach 2:
The patent changes the approach from relying on the backlight driver's inherent ASIL compliance to using a different safety achievement method. By modifying the system architecture to include indirect current measurement via the high side switch and implementing overcurrent detection through the control unit, the system achieves the same safety outcome without requiring expensive ASIL-compliant driver components
3Measurement precision
If complex current measurement circuits are implemented, then precise overcurrent detection is achieved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the current measurement function from the backlight driver itself and places it in the high side switch circuitry. By separating the measurement function into the high side switch with integrated current mirror, the system achieves precise current measurement capability without burdening the backlight driver with complex measurement circuits, thereby reducing overall device complexity
Solution Approach 2:
The high side switch serves multiple functions: it acts as a power switch for the backlight driver and simultaneously provides current measurement capability through its integrated current mirror. This multi-functionality eliminates the need for separate dedicated current measurement circuits, reducing device complexity while maintaining measurement precision
Data Source
Figure 1
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AI summary
The invention is directed to a head-up display unit (1) comprising: a mirror (21, 22), a picture generating unit (10) for creating an image to be displayed as a virtual image (VB) to a viewer, a backlight unit (13) with backlight driver (BL) for the picture generating unit (10), and a control unit (12) for the backlight unit (13). The control unit (12) is provided to receive an input voltage signal (VIN) and an input current signal (IIN,VMIRROR) of the backlight driver (BL), and an output voltage signal (VOUT) of the backlight driver (BL), and to output an overcurrent signal (IOVER).