Wirewound Resistor with Embedded Thermal Fuse for Overheating Protection
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Solution Overview
Problem
Existing current-limiting resistors and thermal fuses in high-frequency circuits and appliances are inefficient in providing over-current and over-temperature protection, often requiring external components that increase size and energy loss, and fail to quickly respond to abnormal conditions, posing safety risks.
Innovation Solution
A wirewound resistor with a built-in thermal fuse, where the thermal fuse is integrated within the resistor's ceramic base and connected in series, providing a compact, quick-response over-heating protection solution by melting at a rated temperature to prevent damage, and can be used in various applications including power tools and aromatherapy diffusers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an external contact type thermal fuse is connected in series and placed inside a ceramic box, then over-heating protection function is achieved, but additional area in the PCB is occupied and 4 bonding pads are needed
Solution Approach 1:
The patent combines the thermal fuse and resistor into a single integrated component. The thermal fuse is embedded within the resistor's ceramic base, merging two previously separate components (resistor and thermal fuse) into one unified structure. This eliminates the need for separate PCB mounting areas and bonding pads for the thermal fuse, while maintaining the over-heating protection function.
2Reliability
If a wirewound resistor with high melting point alloy is used, then resistor function is achieved, but the alloy wire will melt to realize fuse function only if subjected to current over 20 times of rated current
Solution Approach 1:
The patent applies local quality by using different materials in different parts of the resistor. The resistor wire uses high melting point alloy for normal operation, while the thermal fuse element embedded in the ceramic base uses low melting point material specifically for protection. This localized differentiation allows the protection function to activate at much lower currents (not requiring 20x rated current) while the main resistor continues to function normally.
Solution Approach 2:
The thermal fuse acts as an intermediary protection mechanism between the high melting point alloy resistor wire and the circuit. Instead of relying on the resistor wire itself to melt (which requires extreme currents), the thermal fuse provides an intermediate protection layer that melts at lower temperatures, preventing the resistor from reaching dangerous temperature levels in the first place.
3Reliability
If thermal fuse and resistor are assembled inside a ceramic box filled with solidifiable insulation material, then over-heating protection is achieved, but the size of the product becomes large
Solution Approach 1:
The patent implements nesting by placing the thermal fuse inside the ceramic base of the resistor, similar to nested dolls. The thermal fuse element is embedded within the resistor's existing structure, utilizing the same ceramic base that already houses the resistor winding. This nested arrangement eliminates the need for a separate ceramic box and insulation material, significantly reducing the overall product volume while maintaining protection functionality.
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 integrated solution effectively protects against over-current and over-temperature conditions, reducing the risk of damage and energy wastage, while being compact and efficient, and can save significant power consumption when used in aromatherapy diffusers and mosquito repellent vaporizers.
Implementation Method 1
the thermal fuse melts and provides an over-heating protection function
Implementation Method 2
the current makes the thermal fuse cut off by self-heating
Data Source
AI summary
The present invention discloses a device comprising a thermal fuse and a resistor, the solid ceramic base of the wirewound resistor is changed to be hollow, forming a ceramic tube; the thermal fuse is placed in the solid ceramic base, the ceramic tube provides housing for the thermal fuse; a lead wire of the thermal fuse passes through an end cap of an end of the wirewound resistor, the other end of the thermal fuse extends out of the end cap of the other end of the wirewound resistor, the end cap of the wirewound resistor extends outwardly with a lead wire, then an epoxy resin is used to encapsulate the device. The present invention can be used as a basic unit and directly installed in an existing high-frequency charger; it is capable of replacing the existing simple wirewound resistor or the wirewound resistor with an external contact type thermal fuse, and realizing triple functions of general impedance, over-current fuse protection, and over-temperature protection in case of overload.