LED Driver Circuit with Parallel Legs and Shunt Resistor for Failure Detection
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Solution Overview
Problem
Existing electrical circuits for powering LEDs are complex and limited in monitoring a large number of LEDs, particularly in railway and traffic signaling applications, where quick failure detection is crucial to avoid impairment of signaling devices.
Innovation Solution
An electrical circuit design with N legs connected in parallel, each comprising LEDs and a leg resistor, where a common shunt resistor amplifies voltage, and comparator units compare leg resistor voltages with the amplified voltage to detect changes in current due to LED failures, allowing for a simple and effective monitoring of a larger number of LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single LED array is monitored by determining voltage across the array, then the monitoring function is achieved, but the number of LEDs that can be monitored is limited and the circuit becomes complex
Solution Approach 1:
The LED array is divided into multiple legs (N≥2) connected in parallel, with each leg containing several LEDs and a leg resistor. This segmentation allows the circuit to monitor multiple LEDs simultaneously while maintaining manageable complexity through modular structure.
Solution Approach 2:
Multiple legs are connected to a common shunt resistor, merging their current paths into a single measurement point. This combining approach enables the circuit to monitor N×M LEDs (N legs × M LEDs per leg) using a unified monitoring mechanism, increasing the number of monitorable LEDs without proportionally increasing circuit complexity.
2Measurement precision
If the amplification factor AF is chosen to be large, then the voltage deviation during normal operation is large, but the ability to detect small current changes due to LED failure is reduced
Solution Approach 1:
The amplification factor AF is carefully selected to optimize the balance between voltage deviation during normal operation and the ability to detect small current changes. By adjusting AF, the circuit maintains sufficient voltage headroom for stable operation while preserving sensitivity to detect LED failures.
Solution Approach 2:
The circuit uses a moderate amplification factor that provides sufficient voltage deviation for reliable operation but not excessive deviation that would mask small changes. This partial action approach ensures that normal operational variations and failure conditions are both detectable within the same measurement range.
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 design enables efficient detection of LED failures, distinguishing between short-circuit and high-resistance conditions, providing a potential-free signal output for reliable failure indication, suitable for small LED currents and scalable for multiple LEDs, enhancing the reliability of railway and traffic signaling systems.
Implementation Method 1
the electrical circuit comprises an amplifier unit amplifying a voltage at the shunt resistor with an amplification factor AF into an amplified voltage
Implementation Method 2
the electrical circuit comprises a comparator unit for each leg, wherein the comparator units each comprise a comparator which compares the voltage at the respective leg resistor with the amplified voltage
Implementation Method 3
the legs are connected to a common shunt resistor
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
An electrical circuit (1) for powering a plurality of LEDs, with a function for indicating an LED failure, is characterized in that the electrical circuit (1) comprises N legs (3, 4) connected in parallel, with N≥2, and with each leg (3, 4) comprising several LEDs and a leg resistor (R1, R2) connected in series with the LEDs, wherein the leg resistors (R1, R2) of the legs (3, 4) have basically the same resistance, and wherein the resistance of each leg (3, 4) is basically the same during normal operation, that the legs (3, 4) are connected to a common shunt resistor (R3), that the electrical circuit (1) comprises an amplifier unit (5) amplifying a voltage at the shunt resistor (R3) with an amplification factor AF into an amplified voltage, that the electrical circuit (1) comprises a comparator unit (6, 7, 17, 18) for each leg (3, 4), wherein the comparator units (6, 7, 17, 18) each comprise a comparator (6a, 7a, 17a, 18a) which compares the voltage at the respective leg resistor (R1, R2) with the amplified voltage, and that the outputs (6b, 7b, 17b, 18b) of the comparator units (6, 7, 17, 18) are connected at a common signal output unit (10). The invention provides an electrical circuit for powering LEDs which is simple in design, and which may power and monitor a larger number of LEDs.