Wide Range Current Sense Circuit Using Logarithmic Compression
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Solution Overview
Problem
Current sense circuits face challenges in operating over a wide range of currents without experiencing momentary breaks or dips, which can cause loads to reset or fail, especially when using resistor switching circuitry for larger currents.
Innovation Solution
A current sense circuit utilizing a sense bipolar transistor with a connected sense resistor and a front-end circuit that generates an amplified and compensated base-emitter voltage, allowing for continuous current sensing across a wide range without the need for resistor switching, by leveraging the non-linear current characteristics of the base-emitter junction for logarithmic compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resistor switching circuitry is used to handle large currents, then the operational amplifier is prevented from saturating, but momentary breaks or dips in the current occur causing loads to reset or fail
Solution Approach 1:
The patent extracts the problematic resistor switching circuitry from the system and replaces it with a bipolar transistor-based logarithmic compression circuit. This removes the source of momentary current breaks while maintaining the ability to handle wide current ranges, thus improving reliability without the harmful switching interruptions.
Solution Approach 2:
The patent replaces the mechanical/electrical switching mechanism with a continuous analog logarithmic compression mechanism using bipolar transistors. This substitution eliminates the discrete switching action that causes current dips, providing continuous current sensing across the full range from 1 μA to 100 mA without momentary interruptions.
2Device complexity
If a single sense resistor is used, then the circuit is simple, but the operational amplifier saturates when larger currents are present
Solution Approach 1:
The patent changes the electrical parameters handled by the circuit by using bipolar transistors to perform logarithmic compression on the current signal. This transformation allows the operational amplifier to work within its linear range while the circuit as a whole handles a wide current range from 1 μA to 100 mA, effectively expanding the operational range without requiring multiple resistors or switching complexity.
3Adaptability or versatility
If resistor switching circuitry is implemented to extend current range, then wide current measurement is achieved, but momentary current breaks cause loads to reset or fail
Solution Approach 1:
The patent ensures continuous current sensing action across the entire current range by using logarithmic compression through bipolar transistors. This continuous analog transformation eliminates the discrete switching transitions that cause current breaks, maintaining uninterrupted current flow and stable load operation throughout the measurement range.
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
Enables continuous sensing of currents from less than 1 μA to 100 mA without momentary breaks, effectively managing a wide current range through logarithmic measurement and compensation, ensuring stable operation across the load.
Implementation Method 1
utilizing the non-linear current characteristics of the base-emitter junction of a bipolar transistor to compress and sense the current logarithmically
Data Source
AI summary
The magnitude of an output current that flows into a load is determined by placing a sense bipolar transistor and a sense resistor in series with the load, utilizing the non-linear current characteristics of the base-emitter junction of the sense bipolar transistor to compress and sense an emitter current logarithmically, and then performing an inverse log function to determine the emitter current, which is substantially identical to the output current that flows into the load.