Dynamic Threshold Overcharge Detection Circuit for Battery Packs
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Solution Overview
Problem
Existing battery packs lack accurate temperature protection, which hinders appropriate charging control, especially when the voltage from the charging device changes or the resistance of the voltage divider resistor has significant errors, leading to difficulties in detecting the battery pack's temperature effectively.
Innovation Solution
Incorporating an overcharge detecting circuit with a thermistor and resistor series circuit, thermally coupled with the secondary battery, and a comparator system that adjusts the threshold voltage based on temperature, allowing for accurate temperature protection and charging control by changing the division ratio of the voltage divider in response to temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage divider resistor is used to detect battery pack temperature, then the temperature detection circuit can be implemented, but the detection accuracy deteriorates when the voltage from the charging device changes or the resistance has significant errors
Solution Approach 1:
The patent changes the detection parameter from voltage-based temperature detection to current-based temperature detection. By measuring the current through the thermistor rather than the voltage across it, the system eliminates errors caused by charging device voltage variations and resistor tolerance, significantly improving temperature detection accuracy and charging control reliability
Solution Approach 2:
The patent replaces the voltage-based detection mechanism with a current-based detection mechanism. This substitution fundamentally changes how temperature is measured, making the detection independent of voltage fluctuations and resistor value variations, thereby resolving the contradiction between detection accuracy and control reliability
2Device complexity
If the threshold voltage is fixed, then the overcharge detection circuit is simple, but it cannot provide accurate protection at different temperatures
Solution Approach 1:
The patent makes the threshold voltage dynamic by changing it according to temperature. The threshold voltage is adjusted based on the temperature-dependent current measurement, allowing the overcharge detection circuit to maintain high accuracy across different temperature conditions while remaining relatively simple in structure
Solution Approach 2:
The patent changes the threshold voltage parameter dynamically based on temperature conditions. By adjusting the threshold voltage according to the measured temperature, the system achieves accurate overcharge protection at all temperatures without significantly increasing circuit complexity
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 temperature protection and appropriate charging control, preventing overcharging of lithium ion batteries at high temperatures, thereby ensuring the battery's safety and extending its lifespan.
Implementation Method 1
a thermistor R13 and a resistor R14 which are connected in series, the series circuit being arranged in a vicinity of the lithium ion battery 12, so as to be thermally coupled with the lithium ion battery 12
Implementation Method 2
a first comparator 162 arranged to compare a voltage at a junction point of the thermistor R13 and the resistor R14 in the series circuit with a first reference voltage corresponding to a first predetermined temperature
Data Source
AI summary
In a battery pack, an overcharge detecting circuit compares a voltage between a positive electrode and a negative electrode of a secondary battery with a threshold voltage to detect an overcharge of the secondary battery, and turns off a switching element. A series circuit including a thermistor and a resistor is arranged near the secondary battery and connected in parallel to the secondary battery. A comparator compares a voltage at a junction point of the thermistor and the resistor with a reference voltage corresponding to a predetermined temperature. In response to an output signal of the comparator, a changing unit changes the threshold voltage to a first value when a temperature of the secondary battery is below the predetermined temperature, and changes the threshold voltage to a second smaller value when the temperature of the secondary battery is above the predetermined temperature.