Switching Charger Current Mirror for Accurate Small-Current Sensing
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Solution Overview
Problem
Conventional switching chargers fail to accurately sense small charging currents, leading to inefficiencies and inaccuracies in charging processes.
Innovation Solution
A switching charger design that includes a first current mirror, operational amplifier, and control circuit to selectively adjust the ratio of input and output currents through transistors, reducing the influence of offset voltages and enhancing sensing accuracy for small currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional switching charger circuits are used, then the device complexity is low, but the measurement precision of small charging currents deteriorates
Solution Approach 1:
The charger circuit is divided into multiple functional modules: a first current mirror circuit for current replication, a second current mirror circuit for additional current control, operational amplifiers for signal amplification, and a control circuit for coordination. Each module performs a specific function in the current sensing process, allowing the system to achieve high precision without requiring a single complex circuit
Solution Approach 2:
Current mirror circuits are introduced as intermediary elements between the charging current source and the sensing mechanism. These current mirrors replicate and transfer the charging current through controlled transistor pathways, enabling indirect but precise measurement of small currents while isolating the sensing circuit from direct exposure to high current variations
2Measurement precision
If the charging current is small, then the energy consumption is low, but the measurement precision of the current deteriorates
Solution Approach 1:
The control circuit continuously monitors the output of the operational amplifiers and adjusts the control signals to the current mirror circuits accordingly. This feedback mechanism allows the system to maintain high sensing precision by dynamically compensating for offset voltages and adapting to varying small current levels, ensuring accurate measurement even when charging currents are minimal
Solution Approach 2:
The circuit dynamically adjusts operational parameters including the gain of operational amplifiers and the control signals to transistors based on the detected current level. By changing these parameters in response to small current conditions, the system optimizes sensing precision without requiring increased energy input, adapting the measurement sensitivity to match the low current environment
3Measurement precision
If offset voltages are present in the circuit, then the device complexity is low, but the measurement precision of small currents deteriorates
Solution Approach 1:
The circuit intentionally introduces controlled offset compensation mechanisms that convert the harmful effect of inherent offset voltages into a beneficial calibration process. By measuring and compensating for offset voltages through the operational amplifiers and control circuit, the system transforms what would be measurement errors into opportunities for precision calibration, thereby eliminating the negative impact of offset voltages on small current sensing
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 charger accurately senses small currents, improving charging efficiency by adjusting the voltage difference between system and battery voltages, thereby reducing the impact of offset voltages on sensing accuracy and enabling precise control by external processors.
Implementation Method 1
The first current mirror includes a plurality of first transistors and a second transistor. A first terminal of each of the plurality of first transistors and a first terminal of the second transistor are coupled to a system voltage.
Implementation Method 2
A control terminal of the third transistor is connected to an output terminal of the first operational amplifier. The second current mirror includes a fourth transistor, a plurality of fifth transistors and a plurality of sixth transistors.
Implementation Method 3
A first input terminal of the first operational amplifier is connected to the battery and obtains a voltage of the battery. A first terminal of the third transistor is connected to a second terminal of the second transistor and a second input terminal of the first operational amplifier.
Data Source
AI summary
A switching charger for accurately sensing a small current is provided. First terminals of first transistors and a second transistor are coupled to a system voltage. Second terminals of the first transistors and a first input terminal of an operational amplifier are connected to a battery. A first terminal of a third transistor is connected to a second terminal of the second transistor and a second input terminal of the operational amplifier. A control terminal of the third transistor is connected to an output terminal of the operational amplifier. A first terminal of a fourth transistor is connected to a second terminal of the third transistor. First terminals of fifth transistors are coupled to an input voltage. Control terminals of the first transistors and the fifth transistors are connected to a control circuit. First terminals of sixth transistors are respectively connected to second terminals of the fifth transistors.