PTC Thermistor Over-Temperature Protection in LED Illuminant Devices
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Solution Overview
Problem
LEDs face heat dissipation issues due to infrared radiation limitations and multiple packages, leading to over-temperature problems that cause light attenuation, color shift, and reduced lifespan, with existing solutions like fuses being disposable and inconvenient and thermistors being sensitive to high temperatures and blocking light uniformity.
Innovation Solution
An illuminant device with a housing containing an AC LED, a resistor, and a positive temperature coefficient (PTC) thermistor connected in series, where the thermistor's resistance increases above a trigger temperature to block power, automatically resetting when temperature decreases, preventing over-temperature damage and maintaining light uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fuse is used for over-temperature protection, then the manufacturing cost is reduced, but the convenience of use is reduced because the fuse cannot automatically reset
Solution Approach 1:
The patent employs a PTC thermistor that automatically detects temperature changes and adjusts its resistance accordingly. When the temperature exceeds the threshold, the PTC thermistor's resistance increases sharply, automatically cutting off power without requiring external intervention. When the temperature drops, it automatically resets, eliminating the need for manual fuse replacement and achieving self-service protection.
2Measurement precision
If a thermistor is placed close to the LED for temperature sensing, then the temperature detection sensitivity is improved, but the thermistor is exposed to high temperature environment causing it to be damaged and the light uniformity is reduced
Solution Approach 1:
The patent divides the housing into two separate accommodating spaces: the first accommodating space houses the LED, while the second accommodating space houses the PTC thermistor and resistor. This spatial segmentation allows the thermistor to be positioned away from the high-temperature LED while still effectively monitoring temperature through thermal coupling, thereby protecting the thermistor from damage and maintaining light uniformity.
3Measurement precision
If the thermistor is placed close to the LED, then the temperature sensing accuracy is improved, but the light emitted from the LED is blocked causing decreased emitting uniformity
Solution Approach 1:
By separating the LED and thermistor into different accommodating spaces, the patent eliminates the obstruction of light paths. The PTC thermistor can still accurately sense temperature through thermal conduction via the heat dissipation plate, while the light emitted by the LED remains unobstructed, maintaining uniform light distribution.
4Illumination intensity
If the PTC thermistor is placed in a separate accommodating space, then the light emitting uniformity is improved, but the device complexity increases
Solution Approach 1:
The heat dissipation plate serves multiple functions: it acts as a thermal conduction path for the PTC thermistor to sense temperature, serves as a structural support component, and functions as part of the light guiding structure. This multi-functionality reduces the need for additional separate components, thereby minimizing device complexity despite the segmented arrangement.
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
Effectively prevents LED aging and light attenuation by automatically cutting off power at high temperatures and resetting when safe, thereby extending the device's lifetime and ensuring consistent light output.
Implementation Method 1
the resistance of the thermistor 26 is sharply increased when an operating temperature of the illuminant device 20 is higher than a predetermined value
Implementation Method 2
Light emitting diodes (LEDs) have the advantages of small volume, long lifetime, difficulty damage, without mercury and lower power consumption
Implementation Method 3
The resistor 12 and the fuse 16 are respectively electrically connected to the illuminant element 12 in series
Data Source
AI summary
An illuminant device includes a housing, a illuminant element, a resistor, and an over-temperature protective element. The housing includes an upper portion, a lower portion opposite to the upper portion, and two accommodating spaces, respectively formed in a first tubular configuration arranged between the upper end and the lower end and a second tubular configuration spatially isolated from the first accommodating space. The illuminant element is placed on the upper portion. The resistor is located within one of the accommodating space and electrically connected to the illuminant element. The over-temperature protective element is located within the other accommodating space and electrically connected to the illuminant element.