Shunt Protection Circuit for LED Arrays Using Back-to-Back Diodes
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Solution Overview
Problem
In LED systems where multiple LEDs are connected in series, if one LED fails in an open circuit, the entire system loses light output due to the lack of a current path, and traditional protection methods like zener diodes require higher power dissipation and cost, limiting the number of LEDs that can fail without affecting the others.
Innovation Solution
A shunt protection circuit using a pair of back-to-back diodes, a resistor, and an MOS gated SCR, which provides an alternate current path with a voltage drop no greater than the LED's forward voltage, minimizing power dissipation and cost, and allowing multiple LEDs to remain operational even if some fail.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a zener diode is connected in parallel with each LED to provide an alternate current path, then the system maintains operation when an LED fails, but the zener diode requires higher power dissipation capability and increases system cost
Solution Approach 1:
The patent changes the voltage parameter of the protection circuit by using a voltage regulator to maintain a constant voltage equal to the LED's forward voltage, rather than using a zener diode with higher reverse voltage. This parameter change reduces the voltage drop across the protection circuit from 6-8V to 3-4V, thereby reducing power dissipation while maintaining reliability
Solution Approach 2:
The patent introduces a voltage regulator as an intermediary component between the power source and the LED array. This intermediary actively maintains the voltage at the LED's forward voltage level, providing an alternate current path when LEDs fail without requiring the high power dissipation capability of zener diodes
2Loss of energy
If a zener diode with reverse voltage of 6 to 8 V is used to minimize leakage current, then leakage current is reduced, but the power dissipation requirement increases to approximately twice the LED's maximum rated power dissipation
Solution Approach 1:
The patent changes the voltage parameter from the zener diode's 6-8V reverse voltage to the LED's forward voltage of 3-4V through the use of a voltage regulator. This parameter change achieves the dual benefit of minimizing leakage current (by maintaining appropriate voltage levels) while reducing power dissipation to match the LED's rated power dissipation rather than doubling it
3Loss of energy
If the reverse voltage of the zener diode is increased to minimize leakage current, then leakage current is reduced, but the number of LEDs that can fail while keeping remaining LEDs operational is limited
Solution Approach 1:
The patent changes the voltage parameter to match the LED's forward voltage (3-4V) rather than using a higher zener voltage (6-8V). This parameter change increases adaptability by allowing multiple LEDs to fail while maintaining operation of remaining LEDs, as the protection circuit operates at the same voltage level as the LEDs without the voltage drop penalty of higher-voltage zener diodes
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
The solution enables low-power dissipation and reduced costs while ensuring that multiple LEDs can continue to function if some fail, with the protection circuit latching into a low resistance state to maintain system operation and allowing for easy replacement of defective LEDs.
Implementation Method 1
the protection circuit latching into a low resistance state to maintain system operation
Implementation Method 2
A shunt protection circuit using a pair of back-to-back diodes, a resistor, and an MOS gated SCR, which provides an alternate current path with a voltage drop no greater than the LED's forward voltage
Data Source
AI summary
In one embodiment, a protection device is used to protect a circuit. The protection device has a maximum rated power dissipation that is less than a maximum rated power dissipation of the circuit that is being protected.