Rear Sign Lamp LED Bypass Circuit for Idling-Stop Voltage Drops
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Solution Overview
Problem
Vehicles with idling stop functions experience battery voltage drops during idling stop, causing rear sign lamps to turn off, which can lead to safety issues as subsequent vehicles may mistakenly think the preceding vehicle has started.
Innovation Solution
A light source module with an LED string of four LEDs connected in series, an LED driver circuit, and a bypass circuit that sinks current from two adjacent LEDs when battery voltage drops, preventing the LED string from turning off, along with a break detection circuit to manage bypass states and maintain consistent light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bypass circuit with one bypassed LED is used to maintain lighting during low voltage, then lighting can be maintained down to 6.2V, but during idling stop with high battery load the voltage drops below 6.2V and the LED string turns off
Solution Approach 1:
The bypass circuit is divided into two independent bypass switches (first bypass switch and second bypass switch) that can independently bypass different LEDs in the string. This segmentation allows the system to adaptively bypass one or two LEDs based on the severity of voltage drop, enabling the lighting to remain operational during extreme voltage conditions such as idling stop with high battery load.
2Reliability
If the bypass switch is turned on to bypass one LED, then minimum lighting voltage decreases to maintain lighting, but the bypassed LED turns off creating non-uniform light output
Solution Approach 1:
The bypass circuit dynamically adjusts the number of bypassed LEDs based on real-time voltage conditions. The control circuit monitors the battery voltage and selectively activates either one or two bypass switches depending on whether the voltage drop is mild or severe. This dynamic adaptation allows the system to maintain both lighting continuity and light output uniformity by matching the bypass configuration to the specific operating conditions.
3Reliability
If two LEDs are bypassed to maintain lighting during severe voltage drop, then lighting can be maintained during idling stop, but the bypass circuit complexity increases
Solution Approach 1:
The bypass circuit is designed with multi-functionality to handle various voltage drop scenarios using a unified structure. The same bypass circuit can bypass one LED for mild voltage drops or two LEDs for severe voltage drops, eliminating the need for separate circuit designs for different conditions. This universal design maintains lighting reliability during extreme voltage drops while avoiding unnecessary complexity.
4Device complexity
If a conventional LED driver circuit is used without bypass circuit, then the circuit is simple, but the LED string turns off when battery voltage drops below minimum lighting voltage
Solution Approach 1:
The bypass circuit is pre-configured and ready to activate before the LED string turns off during voltage drop. The control circuit continuously monitors battery voltage and proactively activates the appropriate bypass switch(es) when voltage drops approach critical levels, preventing the LED string from turning off in the first place. This preliminary action maintains lighting reliability during voltage fluctuations while keeping the circuit structure relatively simple.
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
Enhances safety by maintaining rear sign lamp illumination during idling stops, preventing erroneous signals to following vehicles and ensuring consistent light output despite battery voltage fluctuations.
Implementation Method 1
an LED driver circuit that receives a battery voltage and supplies a drive current stabilized at a target current to the LED string
Implementation Method 2
a bypass circuit that is provided in parallel with a bypassed portion including two adjacent LEDs of the LED string and sinks a bypass current according to the battery voltage
Implementation Method 3
an LED string including four LEDs (light-emitting diodes) connected in series
Data Source
AI summary
There is provided a rear sign lamp capable of enhancing safety. An LED string (502) includes four LEDs (504_1 to 504_4) connected in series. An LED driver circuit (610) receives a battery voltage (VIN) and supplies a drive current (ILED) stabilized at a target current (IREF) to the LED string (502). A bypass circuit (620) is provided in parallel with a bypassed portion (503) including two adjacent LEDs (504_3 and 504_4) of the LED string (502), and sinks a bypass current (IBYPASS) according to a battery voltage (VIN).