Thyristor Protection Circuit for LED String Failure Bypass
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Solution Overview
Problem
Light-emitting device strings, such as LEDs, fail due to electrostatic discharge or single device failure, leading to open circuit conditions and costly interruptions, especially in safety-critical applications like street lighting and emergency lighting, where maintenance is undesirable.
Innovation Solution
A protection circuit with a voltage detection stage and a thyristor (SCR) that detects overvoltage conditions and bypasses the failed device, allowing the string to remain operational without external complex circuitry, using a Zener diode or thermistor for voltage/temperature monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single diode protection circuit is used to protect LEDs from ESD, then the LED is protected against electrostatic discharges up to 2 kV, but the entire string of LEDs still fails when one LED fails due to open circuit condition
Solution Approach 1:
A thyristor is introduced as an intermediary component between the voltage detection stage and the LED string. When overvoltage is detected, the thyristor activates as a mediator to short-circuit the failed LED, allowing current to bypass the open circuit and maintain string operation. This intermediary device resolves the contradiction by providing both protection functionality and failure compensation.
Solution Approach 2:
The protection circuit is segmented into distinct functional modules: a voltage detection stage that monitors individual LED conditions, and a thyristor-based switching mechanism that selectively activates only when needed. This segmentation allows the system to maintain normal LED operation while providing on-demand protection and failure compensation without affecting the entire string.
2Duration of action of stationary object
If LEDs are connected in series to reduce maintenance costs and increase lifetime, then energy efficiency and brightness are improved, but a single LED failure causes the entire string to go out of operation requiring time-consuming repair
Solution Approach 1:
The thyristor is pre-configured in a dormant state within the circuit, ready to activate immediately upon LED failure. This beforehand preparation eliminates the need for rapid detection and manual repair, as the protective mechanism is already in place and can instantly compensate for failures, effectively cushioning against operational interruptions.
Solution Approach 2:
The voltage detection stage continuously monitors the operational status of each LED in real-time. This continuous monitoring ensures that failures are detected immediately, and the thyristor can activate without interruption to maintain continuous light output, preserving the useful action of the LED string throughout its extended lifetime.
3Reliability
If a thyristor is added to the protection circuit to bypass failed LEDs, then continuous operation of the LED string is maintained, but the device complexity increases
Solution Approach 1:
The voltage detection stage and thyristor control are merged into a single integrated protection circuit module that works seamlessly with the LED string. By combining these functions into one cohesive unit with shared components and unified control logic, the circuit complexity is minimized while maintaining the reliability benefit of continuous operation.
Solution Approach 2:
The protection circuit is designed to be self-regulating, where the voltage detection stage automatically detects LED failures and triggers the thyristor without external intervention. This self-service capability eliminates the need for complex external control systems or manual monitoring, reducing overall device complexity while ensuring reliable automatic protection and continuous operation.
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
Prevents interruptions and maintenance costs by keeping the light-emitting device string operational even if one device fails, ensuring continuous operation and safety in critical applications, with the ability to monitor and report device status.
Implementation Method 1
a voltage detection stage coupled between the first and second nodes. The voltage detection stage is adapted to detect an overvoltage condition between the first and second nodes
Implementation Method 2
When an overvoltage condition is detected (e.g. in normal operation), the control gate of the thyristor is triggered so that current can flow through the thyristor
Implementation Method 3
Excess current caused by the overvoltage condition is then allowed to flow through the thyristor, thus bypassing the light-emitting device
Data Source
AI summary
An electronic device is provided that includes a protection circuit for a light-emitting device. The protection circuit comprises a first node adapted to be coupled to an anode of the light-emitting device and a second node adapted to be coupled to a cathode of the light-emitting device. A voltage detection stage is coupled between the first and second nodes. The voltage detection stage is adapted to detect an overvoltage condition between the first and second nodes. Furthermore, the protection circuit comprises a thyristor coupled with its anode to the first node, its cathode to the second node to the voltage detection stage. When the overvoltage condition is detected in normal operation the thyristor is controlled to open so that the current can flow through the thyristor.