Battery Charging Current Measurement Circuit with DC-DC Converter Isolation
Solution Overview
Problem
Existing battery-powered electric appliances face challenges in accurately measuring charging current due to distortion caused by DC-DC converter and other load currents, especially when the battery voltage is insufficient for the control circuit.
Innovation Solution
A circuit design where the DC-DC converter is not at reference potential, with a low pass filter connected to the current sensing resistor, allowing the control circuit to measure charging current only when additional loads are switched off or providing correction values for their current consumption, ensuring accurate measurement by isolating motor and converter currents from the sensing resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a DC-DC converter is used to power the control circuit when battery voltage is insufficient, then the control circuit can operate with single-cell batteries, but the measured charging current value is distorted by the current consumption of the DC-DC converter and other loads
Solution Approach 1:
The patent segments the current measurement function by providing separate current sensing paths: one for measuring battery charging current (through sensing resistor R1) and another for measuring DC-DC converter current (through sensing resistor R2). This allows independent measurement and compensation of each current component, resolving the distortion problem while maintaining adaptability to single-cell batteries
Solution Approach 2:
The patent introduces intermediate correction values representing the DC-DC converter's current consumption. These correction values act as mediators that bridge the gap between the distorted measured value and the actual charging current, enabling accurate measurement by adding the correction value to the measured value
2Productivity
If the control circuit measures charging current continuously, then real-time monitoring is achieved, but the measurement is constantly distorted by varying load currents
Solution Approach 1:
The control circuit periodically switches between measurement modes: during normal operation it measures total current, and during dedicated measurement intervals it switches off additional loads to measure only charging current. This periodic switching enables accurate measurement while maintaining real-time monitoring capability
Solution Approach 2:
The control circuit performs preliminary measurement of the DC-DC converter's current consumption under known conditions and stores this as a correction value. This preliminary action enables subsequent accurate measurements without requiring repeated switch-off of loads, maintaining both accuracy and continuous monitoring
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 approach enables precise measurement of charging current with high accuracy, even in appliances with single-cell batteries, by minimizing distortion from other load currents and allowing for smaller, more efficient current sensing resistors, thus improving measurement reliability and reducing measurement errors.
Implementation Method 1
a low pass filter connected to the current sensing resistor
Implementation Method 2
a DC-DC converter for powering the control circuit
Data Source
AI summary
The invention relates to a circuit for a battery-operated small electric appliance having a rechargeable battery (B), a control circuit (uC) for measuring the charging current of the rechargeable battery (B), and a DC-DC converter (DC/DC) which supplies the control circuit (uC) and possibly further loads from the battery. The circuit has further a current sensing resistor (R1), whose one end lies at a reference potential and whose other end is connected to the battery (B). The control circuit (uC) has a terminal which is at reference potential and a measurement input which is related to the reference potential. A method for measuring the charging current of the rechargeable battery includes that said control circuit (uC) measures the charging current only when the at least one further load is switched off or the control circuit (uC) provides at least one correction value to the measured charging current when the at least one further load is not is switched off during the current measurement.