Thermally Sensitive Over-Current Protector Control Circuit
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Solution Overview
Problem
Existing thermally sensitive over-current protectors, such as conductive polymer positive temperature coefficient (PTC) elements, face inaccuracies in transitioning to high resistance states due to manufacturing variations, leading to inconsistent over-current protection in battery packs.
Innovation Solution
A circuit comprising a current sense and control circuit that monitors current and provides a control signal to a current source circuit, which raises current through an electrical heating element to trip the over-current protector accurately, ensuring precise control of the tripping mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PTC element is used for over-current protection, then the device can automatically restrict battery current through thermal sensitivity, but the transition accuracy between resistance states is insufficient due to manufacturing variations
Solution Approach 1:
A heating element is introduced as an intermediary component between the control circuit and the PTC element. The heating element receives controlled current from the current source circuit and converts it to heat, which is transferred to the PTC element to precisely control its temperature and trigger the resistance transition at the desired tripping point, thereby improving tripping accuracy without modifying the PTC element itself
Solution Approach 2:
The invention changes the temperature parameter of the PTC element by controlling the current through the heating element. By adjusting the current magnitude and duration, the heating element raises the PTC element's temperature to the specific transition point, enabling precise control over when the resistance change occurs, thus resolving the accuracy issue caused by manufacturing variations
2Reliability
If a PTC element transitions to high resistance state, then over-current protection is activated, but the transition timing is inconsistent and may occur too late or too early
Solution Approach 1:
The control circuit monitors the current in real-time and detects when it exceeds the threshold. Upon detection, the control circuit immediately activates the current source circuit to drive the heating element, which rapidly heats the PTC element to trigger the transition. This preliminary detection and immediate response mechanism ensures the tripping occurs at the correct time without unnecessary delay
Solution Approach 2:
The control circuit continuously monitors the current flowing through the battery and provides feedback to the current source circuit. When the monitored current exceeds the predetermined threshold, the feedback signal triggers the heating element to activate, creating a closed-loop control system that ensures timely and accurate tripping based on actual current conditions
3Manufacturing precision
If manufacturing variations are reduced to improve PTC element consistency, then tripping accuracy improves, but manufacturing complexity and cost increase
Solution Approach 1:
Rather than attempting to manufacture PTC elements with higher precision, the invention introduces a heating element as an intermediary that decouples the tripping accuracy from the PTC element manufacturing quality. The heating element provides the additional degree of freedom needed to control the transition point, allowing standard PTC elements to achieve precise tripping without requiring complex manufacturing processes
Solution Approach 2:
The invention replaces reliance on mechanical/manufacturing precision of the PTC element with an electrical control system. Instead of depending on tight manufacturing tolerances to ensure consistent tripping, the system uses electrical current control through the heating element to thermally induce the transition at the desired moment, substituting manufacturing precision requirements with electrical control capabilities
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 enables precise and consistent tripping of over-current protectors, improving accuracy and reliability in protecting battery packs from over-current conditions by accurately controlling the transition to high resistance states.
Implementation Method 1
The current source circuit is to raise current through the electrical heating element in accordance with the control signal to a high enough level that causes the over-current protector to trip
Implementation Method 2
a resettable, thermally sensitive, over-current protector element that conducts current in a low resistance state until the current reaches a sufficiently high level, at which time it will drastically change to a high resistance state
Data Source
AI summary
A method for controlling a thermally sensitive over-current protector is described. A battery current is monitored. It is then determined whether or not the monitored current has exceeded a predetermined threshold during the entirety of a predetermined time interval. If yes, then a current source is signaled to raise its current, so as to increase the heat being generated by a heating element that is being driven by the current source thereby tripping the thermally sensitive over-current protector. Other embodiments are also described and claimed.