Shunt Resistor Current Detection Circuit With Reference Voltage Extraction
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Solution Overview
Problem
Current current detection circuits using shunt resistors suffer from accuracy issues due to manufacturing variations in resistors, leading to errors in voltage division and impedance conversion, which affect the accuracy of load current detection.
Innovation Solution
A current detection apparatus that includes a shunt resistor, a differential amplifier circuit with a negative power supply terminal connected to a reference voltage source, and a conversion circuit to output a voltage proportional to the load current by removing the reference voltage from the differential amplification output, thereby improving accuracy and reducing the impact of resistor errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage dividing circuits with multiple resistors are used to reduce shunt resistor voltage, then the withstand voltage of operational amplifiers is not exceeded, but manufacturing variations in resistors cause accuracy degradation in current detection
Solution Approach 1:
The patent extracts the reference voltage component from the differential amplification output through a dedicated conversion circuit. By separating the reference voltage (Vref) from the amplified differential signal, the circuit eliminates the propagation of resistor manufacturing variations into the final measurement, thereby improving current detection accuracy while maintaining compliance with operational amplifier withstand voltage requirements.
Solution Approach 2:
The patent changes the output parameter of the differential amplifier by applying reference voltage to the negative power supply terminal instead of ground. This parameter change allows the circuit to operate with high common-mode voltages without exceeding operational amplifier withstand limits, while the subsequent removal of reference voltage from the output restores measurement accuracy.
2Reliability
If reference voltage is applied to negative power supply terminal of operational amplifier, then high voltage can be handled without exceeding withstand voltage, but output voltage includes reference voltage component that must be removed
Solution Approach 1:
The patent introduces a conversion circuit as an intermediary between the differential amplifier and the final output. This intermediary circuit performs the function of removing the reference voltage component from the amplified signal, thereby simplifying the overall system design while maintaining both operational amplifier protection and measurement accuracy.
3Reliability
If traditional voltage dividing circuit is used, then voltage level is reduced for operational amplifier input, but error rate reaches 86.95% due to resistor manufacturing variations
Solution Approach 1:
The patent extracts only the differential voltage component related to load current from the amplified output by removing the reference voltage. This extraction eliminates the impact of resistor manufacturing variations in the voltage dividing circuits, reducing the error rate from 86.95% to 17.40% while maintaining voltage level compatibility with operational amplifiers.
Data Source
AI summary
A shunt resistor is connected in series to a load. A differential amplifier circuit are inputted a first voltage that is generated at one end of the shunt resistor and a second voltage that is generated at the other end of the shunt resistor. The differential amplifier circuit outputs a third voltage equivalent to a sum of a reference voltage and a voltage obtained by performing differential amplification on the first voltage and the second voltage. A conversion circuit outputs the voltage obtained by performing differential amplification on the first voltage and the second voltage by removing the reference voltage from the third voltage. The voltage is proportional to a load current.