Split Bridge Rectifier LED String with NTC Thermistor Protection
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Solution Overview
Problem
Existing LED light strings face challenges with manufacturing costs, safety, and reliability due to the need for additional wiring and the lack of shunts in direct current applications, which can lead to fire hazards and reduced LED lifespan.
Innovation Solution
A split bridge rectifier with a negative temperature coefficient (NTC) thermistor is used to power LEDs with direct current, allowing alternating current to be passed to the receptacle while minimizing conducting wires and providing fuse-like protection against overheating LEDs, using a combination of diodes and thermistors to manage current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a rectifier is placed in the plug to convert AC to DC for LEDs, then electricity consumption is reduced and operating temperature is lowered, but additional wiring is required to deliver AC to the receptacle
Solution Approach 1:
The bridge rectifier is divided into two separate parts: two diodes are placed in the plug and the other two diodes are placed in the receptacle. This segmentation allows the circuit to function as a full-wave rectifier while using the existing two wires for both AC delivery and rectifier operation, eliminating the need for additional wiring.
2Use of energy by moving object
If LEDs are used instead of incandescent lamps to reduce electricity consumption and operating temperature, then energy efficiency is improved, but LEDs lack shunts and can short out when hot junctions melt, creating safety hazards
Solution Approach 1:
An NTC thermistor is placed in series with the LED string to preemptively detect temperature increases. Before an LED can short out and create a fire hazard, the thermistor detects the rising temperature and opens the circuit, preventing the short circuit condition from developing.
Solution Approach 2:
The NTC thermistor acts as an intermediary protective device between the power source and the LED string. It monitors temperature conditions and intermediates the circuit by opening it when unsafe conditions are detected, preventing direct short circuits through the LEDs.
3Ease of manufacture
If manufacturing costs are reduced by minimizing materials and labor, then production expenses are lowered, but safety features and reliability may be compromised
Solution Approach 1:
The two wires required for AC delivery are made to serve dual purposes: they carry AC power to the receptacle and simultaneously serve as two of the four diodes in the bridge rectifier. This multi-functionality eliminates the need for additional wires, reducing material costs while maintaining full rectifier functionality and safety features.
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 solution reduces manufacturing costs, enhances safety by preventing overheating, and extends LED lifespan by managing current flow effectively, allowing for efficient and cost-effective production of LED light strings that are safer and more reliable.
Implementation Method 1
a fuse that is activated by a rise in circuit temperature, namely, a negative temperature coefficient (NTC) thermistor
Implementation Method 2
The present light string employs a full wave rectifying bridge to produce the direct current required to power the LEDs
Data Source
AI summary
A string of lights has an electrical plug at one end and a receptacle at the other end and plural light-emitting diodes (LEDs) in series with a negative temperature coefficient (NTC) thermistor. The device also includes a bridge rectifier providing direct current to the LEDs and the thermistor but split between the plug and receptacle of the light string so that alternating current from the plug is delivered to the receptacle but direct current flow through the LEDs. Light string fuses protect the string but the NTC fuses protect the LEDs at a lower current rating. The LEDs can be arranged in a simple electrical series, or, in an alternative embodiment, an electrical series of groups of plural LEDs each of which is arranged electrically in parallel with other LEDs of the same group. The use of the lower-current-rating NTC thermistor allows the LEDs in one light string to fail without necessarily jeopardizing the current flow to subsequent light strings unless the current is high enough to blow the light string fuses in the plug.