Battery Pre-Charge Circuit Using PTC-NTC Inrush Protection
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Solution Overview
Problem
Existing electrical systems face challenges in managing inrush currents, particularly in battery systems where high initial currents can damage lithium-ion batteries and other components, and existing solutions like NTC thermistors may not provide adequate protection across a range of temperatures.
Innovation Solution
A system utilizing a combination of positive temperature coefficient (PTC) and negative temperature coefficient (NTC) thermistors in series, which maintains a non-negligible total resistance across a range of temperatures, effectively limiting inrush currents and providing controlled pre-charge power by adjusting impedance based on temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If only an NTC thermistor is used for inrush current protection, then inrush current is reduced at low temperatures, but protection is insufficient at operating temperatures
Solution Approach 1:
The patent combines an NTC thermistor and a PTC thermistor in series to create a composite temperature compensation circuit. The NTC thermistor provides high impedance at low temperatures to limit inrush current, while the PTC thermistor provides high impedance at high temperatures to maintain protection during normal operation. This merging of two opposing temperature coefficient elements solves the contradiction by ensuring reliable inrush current protection across the entire temperature range.
2Reliability
If a conventional resistor is used to minimize inrush current, then inrush current is limited, but power loss increases due to continuous resistance
Solution Approach 1:
The patent uses thermistors with dynamic resistance characteristics that change with temperature. The NTC thermistor starts with high resistance to limit inrush current, then its resistance decreases as it self-heats from the current flow. The PTC thermistor maintains low resistance during normal operation but increases resistance when overheating occurs. This dynamic behavior provides inrush current limitation only when needed, eliminating continuous power loss associated with fixed resistors.
3Productivity
If battery charging current is not limited, then charging speed is fast, but battery damage or degradation occurs
Solution Approach 1:
The patent applies preliminary anti-action by placing the NTC-PTC thermistor combination in series with the battery charging circuit before the inrush current can reach the battery. The circuit proactively limits current based on temperature conditions: the NTC thermistor blocks excessive initial current at low temperatures, and the PTC thermistor prevents overheating-related damage at high temperatures. This preliminary protection mechanism enables fast charging while preventing battery degradation from current spikes.
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 combination of PTC and NTC thermistors effectively reduces inrush currents across a temperature spectrum, protecting both the source and target devices from excessive current drain and ensuring controlled power delivery, thereby extending battery life and preventing damage.
Implementation Method 1
a negative temperature coefficient (NTC) thermistor may be used to reduce inrush currents when a device is below an operating temperature (e.g., when the device is first turned on) by providing a higher impedance to current at colder temperatures while providing a lower impedance at higher temperatures
Implementation Method 2
In one or more aspects, the system may comprise a combination of a positive temperature coefficient (PTC) thermistor and a negative temperature coefficient (NTC) thermistor. In general, for the PTC thermistor, resistance may increase based on an increase in temperature
Implementation Method 3
The two or more thermistors may be arranged in series such that, through a range of temperature changes, a total resistance across the two or more thermistors remains at a non-negligible value
Data Source
AI summary
A system for suppressing inrush currents is described. The system may include a positive temperature coefficient (NTC) thermistor and a positive temperature coefficient (PTC) thermistor arranged in series between a power source and a battery system to be charged. At a low temperature, while the PTC thermistor provides only minimal resistance to minimize an inrush current, the NTC thermistor provides increased resistance. As the temperature increases, the resistance provided by the PTC thermistor increases as the resistance from the NTC thermistor decreases. The system may be used in conjunction with a battery charging system has at least one current pathway from the power source to the battery system.