Overcurrent Protection Device with Time-Dependent Current Threshold
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Solution Overview
Problem
Defining the maximum allowed current for electric devices is challenging due to inrush currents that can be several times higher than nominal currents, especially when devices like incandescent lamps are turned on, as the resistance of conductors increases with temperature, making it difficult for protective mechanisms to differentiate between normal and excessive currents.
Innovation Solution
An overcurrent protection device that includes a pulse width modulation (PWM) unit to adjust the duty cycle of the power supply based on the supply voltage, a switch unit to disconnect the load when excessive current is detected, and a maximum-allowed-current unit that adapts the allowed current based on time and supply voltage, ensuring the power switch remains within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective mechanism uses a fixed maximum allowed current threshold, then it can reliably prevent excessive current damage, but it cannot allow normal inrush currents during device startup
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed current threshold to a time-dependent maximum allowed current that dynamically adjusts during device operation. The control unit increases the maximum allowed current during startup phases to accommodate inrush currents, then gradually decreases it to the normal operating threshold, enabling the system to adapt to different operational states while maintaining protection reliability
Solution Approach 2:
The patent changes the parameter of maximum allowed current from a constant value to a time-varying parameter. The control unit modifies the current threshold based on elapsed time since startup, temperature measurements, and operational phase, allowing the system to differentiate between normal transient inrush currents and dangerous excessive currents that require protection
2Adaptability or versatility
If the maximum allowed current is set to accommodate inrush currents, then normal startup currents are permitted, but excessive currents during steady state operation cannot be distinguished and prevented
Solution Approach 1:
The patent implements periodic action through phased current threshold adjustment. The control unit operates in distinct phases: an initial startup phase with elevated current allowance for inrush currents, followed by a transition phase with gradually decreasing thresholds, and finally a steady-state phase with strict normal operating thresholds. This periodic restructuring of current limits enables the system to maintain flexibility during startup while ensuring strict protection during normal operation
Solution Approach 2:
The patent employs feedback mechanisms where the control unit continuously monitors elapsed time, temperature measurements, and current draw to adjust the maximum allowed current in real-time. This closed-loop control ensures that the system maintains appropriate current thresholds based on actual operational conditions, preventing excessive currents while allowing normal inrush currents
3Device complexity
If a simple fixed threshold protective mechanism is used, then the device complexity is low, but it cannot differentiate between inrush current and excessive current conditions
Solution Approach 1:
The patent applies preliminary action by pre-programming time-dependent current thresholds and operational phases into the control unit before device operation begins. The control unit is预先 configured with knowledge of expected inrush current durations and patterns, allowing it to automatically differentiate between normal startup conditions and excessive current situations without requiring complex real-time analysis or additional sensing hardware
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 allows inrush currents during device startup while preventing excessive current flow, ensuring the power switch operates within safe limits, enhancing the reliability of overcurrent protection by compensating for voltage variations and temperature-dependent resistance changes.
Implementation Method 1
the electric resistance of a conductor usually increases as the temperature of the conductor increases
Implementation Method 2
a pulse width modulation (PWM) unit to adjust the duty cycle of the power supply based on the supply voltage
Data Source
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AI summary
An overcurrent protection device (18) comprises a maximum-allowed-current unit (34) and a power switch (20) having a conductive state and a nonconductive state. The maximum-allowed-current unit (34) determines a time-dependent maximum allowed current (I1; I2) according to a supply voltage. The power switch (20) assumes the nonconductive state in response to an indication that a current through the power switch (20) is exceeding the maximum allowed current (I1, I2). A method of operating a power switch (20) is also described.