Overvoltage Protection Circuit with Automatic Reset
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Solution Overview
Problem
Conventional overvoltage protection systems for communications buses in vehicles, such as those in aircraft, face challenges with single-use fuses and heat-generating positive temperature coefficient (PTC) devices, which are not suitable for all environments, particularly in remote or flammable locations where accessibility and heat sensitivity are concerns.
Innovation Solution
An overvoltage protection arrangement featuring a signal lead with a switch and comparator, where the comparator delays comparison of overvoltage with a reference voltage to distinguish between transient and sustained overvoltages, using a MOSFET switch and transient voltage suppression (TVS) circuit to disconnect the device segment from the bus segment only during sustained overvoltages, thereby reducing heat generation and allowing automatic reset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If PTC devices are used for overvoltage protection, then automatic reset capability is achieved, but heat generation occurs which is not tolerable in heat-sensitive environments
Solution Approach 1:
The patent replaces the thermal-mechanical PTC device with an electronic control system consisting of a comparator, timing circuit, and MOSFET switch. The comparator electronically detects overvoltage conditions and triggers the MOSFET to open the circuit, eliminating the need for thermal heating and cooling cycles while maintaining automatic reset functionality through electronic control rather than thermal physics.
Solution Approach 2:
The invention changes the operating parameters from thermal domain (temperature-based PTC resistance change) to electrical domain (voltage-based comparator detection and electronic switching). By using voltage thresholds and timing circuits instead of temperature-dependent resistance, the system achieves the same protection function without generating harmful heat.
2Reliability
If fuses are used for overvoltage protection, then simple and reliable protection is provided, but single-use limitation requires replacement after tripping
Solution Approach 1:
The patent implements a self-service protection system where the comparator continuously monitors bus voltage and automatically activates the MOSFET switch when overvoltage is detected. The system serves itself by detecting faults and executing protection actions without human intervention, and the MOSFET can be reset electronically without physical replacement, enabling the device to restore functionality automatically or on-demand.
Solution Approach 2:
Instead of discarding the protection device after single use like a fuse, the patent recovers functionality by resetting the MOSFET switch after tripping. The electronic control system can be reset by removing the overvoltage condition, allowing the MOSFET to return to conducting state and restore normal operation without replacing the entire protection device.
3Speed
If comparator immediately compares overvoltage with reference voltage, then rapid response is achieved, but transient overvoltage cannot be distinguished from sustained overvoltage
Solution Approach 1:
The patent applies preliminary action by using a timing circuit (RC circuit) that delays the comparator's voltage comparison operation. When overvoltage is detected, the timing circuit must elapse before the comparator activates the MOSFET. This preliminary time delay allows the system to differentiate between transient overvoltage (which clears before the delay expires) and sustained overvoltage (which persists through the delay period), achieving both rapid response and precise discrimination.
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 provides effective overvoltage protection with automatic reset capabilities, low heat generation, and the ability to differentiate between transient and sustained overvoltages, making it suitable for use in heat-sensitive environments without the need for PTC devices or frequent replacements.
Implementation Method 1
A transient voltage protection (TVS) circuit can be connected to the device segment of the signal lead. The TVS circuit can include a transorb of Zener diode dissipating transient overvoltage.
Implementation Method 2
The comparator is operably connected to the switch to open the switch in response to sustained application of overvoltage to the bus segment of the signal lead.
Implementation Method 3
The MOSFET gate can be connected to the comparator. Application of voltage at the comparator output causes the MOSFET to disconnect the device segment from the bus segment of the signal lead.
Implementation Method 4
A resistor-capacitor (RC) timing circuit can be connected to the comparator input terminal.
Data Source
AI summary
An overvoltage protection arrangement includes a signal lead, a switch, and a comparator. The signal lead has a device segment and a bus segment. The switch is connected in series between the device segment and the bus segment. The comparator is operably connected to the switch to open the switch in response to sustained application of overvoltage to the bus segment of the signal lead. Aircraft electrical systems and methods of controlling voltage applied to electrical devices in electrical systems are also described.