Switchable-Gain Current Measurement Circuit to Prevent Saturation
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Solution Overview
Problem
Current measurement circuits in load drivers face challenges in achieving high resolution at low currents while preventing saturation at high currents, leading to increased component costs and complexity due to the need for dual current measurement and additional amplifiers.
Innovation Solution
A current measurement circuit with a switchable gain amplifier that selectively varies its gain based on the ratio between the input connector and the selected current path, using a gain control sub-circuit with multiple current paths and a controller to automatically adjust the gain and prevent saturation, allowing for high resolution at low currents and accommodating high currents without signal saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt or current-sense resistor is used to monitor current, then current measurement capability is achieved, but measurement saturation occurs at high currents which reduces measurement resolution at lower currents
Solution Approach 1:
The patent implements a dynamic gain control system that automatically adjusts the gain of the current measurement amplifier based on the detected current level. When current exceeds a threshold, the gain is reduced to prevent saturation; when current is low, the gain is increased to improve measurement resolution. This dynamic adaptation resolves the contradiction between maintaining high measurement precision across a wide current range.
Solution Approach 2:
The patent changes the operational parameter (gain) of the measurement circuit based on the current amplitude. By switching between different gain values (e.g., high gain for low currents, low gain for high currents), the system maintains optimal measurement resolution across the entire current range, preventing both saturation at high currents and noise amplification at low currents.
2Measurement precision
If dual current measurement with separate amplifiers is used to improve measurement resolution, then measurement precision is improved, but component costs and device complexity increase
Solution Approach 1:
The patent makes a single current measurement amplifier multi-functional by equipping it with switchable gain stages. Instead of requiring separate amplifiers for different current ranges, one amplifier can operate in multiple gain modes (e.g., high-gain mode for 0-10A, low-gain mode for 0-100A), achieving the same measurement precision across different ranges while halving the number of amplifiers needed.
Solution Approach 2:
The patent introduces dynamic gain switching that allows a single amplifier to adapt its sensitivity based on the input signal level. This dynamic behavior replaces the need for multiple static amplifiers, reducing component count while maintaining high measurement precision across the full current range through automatic gain selection.
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Current measurement circuit including an operational amplifier (3) comprising two inputs and an output. An input connector (4) for connecting the two inputs across a current-sense resistor (21), wherein the input connector (2) comprises an input resistor (4). A gain control sub-circuit (5) is connected to the output and includes a plurality of output resistors (51,52) and a switch (53) operable to select a current path through one or more of the plurality of output resistors (51,52) for controlling the gain across the operational amplifier. A measurement output (61,62) is provided connected to the gain control sub-circuit (5) for outputting a signal indicating the measured current based on the selected current path.