LED String Protection Capacitors for Reverse Voltage Mitigation
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Solution Overview
Problem
Existing LED lighting apparatuses face challenges in preventing the increase in size and cost of protection elements when the number of light-emitting diodes connected in series increases, due to the need for higher capacitance bypass capacitors to protect against excessively high reverse voltages during insulation and withstand voltage tests.
Innovation Solution
Incorporating protection capacitors with a lower impedance than parasitic capacitances between the LED string and the power supply path, ensuring that the voltage difference between the anode and cathode of each light-emitting diode is minimized, thereby reducing the stress from high-voltage alternating-current voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the number of light-emitting diodes connected in series is increased, then the lighting output and efficiency are improved, but the reverse voltage during insulation and withstand voltage tests increases excessively, requiring larger and more expensive protection elements
Solution Approach 1:
The patent divides the series-connected LED string into multiple groups, with protection capacitors placed at intermediate connection points between groups. This segmentation allows the protection capacitors to handle only a portion of the total reverse voltage, rather than requiring a single capacitor to handle the entire string's reverse voltage, thereby reducing the capacitance value and size of protection elements needed.
Solution Approach 2:
The patent introduces protection capacitors as intermediary elements at the connection points between LED groups. These capacitors act as mediators that provide a low-impedance path for discharge currents during withstand voltage tests, protecting the LEDs from excessive reverse voltage without requiring the capacitors to be excessively large.
2Reliability
If larger protection capacitors are used to protect against excessive reverse voltage, then the protection effectiveness is improved, but the size and cost of the protection elements increase
Solution Approach 1:
The total protection capacitance requirement is segmented across multiple smaller capacitors distributed at different connection points in the LED string. Each capacitor handles a portion of the voltage stress, allowing the use of smaller, more compact protection elements while maintaining overall protection effectiveness.
Solution Approach 2:
The patent applies protection capacitors at specific local positions (connection points between LED groups) rather than requiring a single large capacitor. This local placement strategy provides targeted protection where reverse voltage stress occurs, using smaller capacitance values at each location while achieving system-wide protection.
3Reliability
If the capacitance of protection capacitors is increased to mitigate reverse voltage, then the protection capability is improved, but the cost of the lighting apparatus increases
Solution Approach 1:
The protection capacitance is segmented into multiple smaller capacitors distributed throughout the LED string. This segmentation reduces the cost by using multiple affordable, small-capacitance components rather than requiring one or two large, expensive high-voltage capacitors, while maintaining the same overall protection capability.
Solution Approach 2:
The patent changes the parameter distribution of capacitance from a concentrated single large capacitor to multiple distributed smaller capacitors. This parameter transformation maintains the total protection effect while using lower individual capacitance values that are more cost-effective and easier to manufacture with standard components.
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 approach prevents the excessive reverse voltage from being applied to the light-emitting diodes, reduces current flow, and maintains the size and cost of the protection element, even as the number of LEDs in series increases, effectively mitigating electrical stress during tests and normal operation.
Implementation Method 1
a protection capacitor C, which provides a discharge path for a current flowing through the parasitic capacitance
Implementation Method 2
Between each of copper connections N (N1-N5) which is located between the adjacent light-emitting diodes and a case ground, a corresponding one of parasitic capacitances CP (CP1-CP5) exists
Data Source
AI summary
In various embodiments, a light-emitting apparatus is disclosed. In one example, the light-emitting apparatus comprises a substrate, an LED string mounted on the substrate, in which LED string a plurality of LEDs are connected in series, a power supply path connected in series to the LED string, and a plurality of protection elements, each protection element having a first node commonly connected to the power supply path and a second node connected between a pair of the LEDs in the series, wherein the protection elements include capacitors or zener diodes, and an AC impedance of each protection element is smaller than an impedance between the pair of LEDs and a case ground.