PTC-Transistor Circuit Protection for Surge-Endurable Overcurrent Trips
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Solution Overview
Problem
Existing PPTC over-current protection devices face challenges in balancing operating current and high-voltage surge endurability, with enhancements in one aspect often compromising the other, and transistors are prone to damage from over-voltage or over-current surges.
Innovation Solution
A composite circuit protection device combining a PTC component and a transistor, with a PTC matrix made of non-grafted olefin-based polymer and conductive filler, and optionally including a resistive element, where the PTC component's rated voltage exceeds the transistor's maximum gate-source voltage, and features like holes for thermal expansion accommodation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the thickness or area of the PTC polymer matrix is decreased to enhance operating current, then the operating current is improved, but the high-voltage surge endurability deteriorates
Solution Approach 1:
The patent combines a PTC component and a transistor into a composite circuit protection device. The PTC component provides over-current protection while the transistor provides over-voltage protection, creating a synergistic system that resolves the contradiction between operating current enhancement and high-voltage surge endurability maintenance
Solution Approach 2:
The PTC polymer matrix is formulated as a composite material containing conductive filler particles dispersed in the polymer matrix. This composite structure enables the PTC component to achieve both high operating current capacity and adequate surge endurability through the synergistic properties of the polymer and conductive filler
2Reliability
If the thickness or area of the PTC polymer matrix is increased to enhance high-voltage endurability, then the high-voltage surge endurability is improved, but the size of the device increases and operating current is reduced
Solution Approach 1:
The composite device merges the functions of PTC component and transistor, allowing the PTC component to be optimized for operating current (smaller thickness/area) while the transistor compensates for surge protection, thus maintaining high-voltage endurability without increasing device size or reducing operating current
3Reliability
If the PTC component trips late to maintain transistor operation, then the transistor remains functional, but the transistor may be damaged by over-voltage or over-current surges
Solution Approach 1:
The circuit creates a feedback protection mechanism where the transistor's gate-source voltage controls the circuit state. When over-voltage occurs, the gate-source voltage exceeds the breakdown voltage, causing the transistor to switch off and disconnect the circuit, thereby protecting against over-voltage damage while maintaining transistor reliability
Solution Approach 2:
The circuit design incorporates prior cushioning by setting the transistor's breakdown voltage higher than the normal operating voltage but lower than the damaging over-voltage level. This creates a safety buffer zone that prevents transistor damage before it occurs
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 composite device effectively protects the transistor by tripping the PTC component before the transistor is damaged, ensuring high-voltage surge endurance and preventing burnout, while maintaining compact size.
Implementation Method 1
a positive temperature coefficient (PTC) component... a PTC matrix disposed between the first electrode and the second electrode
Data Source
AI summary
A composite circuit protection device includes a transistor, a positive temperature coefficient (PTC) component, a first lead pin, a second lead pin and a third lead pin. The transistor includes a drain electrode, a gate electrode and a source electrode. The PTC component includes a first electrode, a second electrode, and a PTC matrix disposed between the first electrode and the second electrode. The second electrode is in contact with the gate electrode of the transistor. The first lead pin is bonded to the drain electrode of the transistor. The second lead pin is bonded to one of the first electrode and the second electrode of the PTC component. The third lead pin is bonded to the source electrode of the transistor.