Current Sense Circuit Offset Calibration Switching
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Solution Overview
Problem
Existing current measurement circuits face challenges in accurately determining the no-load output voltage without disconnecting the load, as the no-load offset can drift over time due to temperature and component aging, and recalculating this offset is impractical in many circuits.
Innovation Solution
A system that uses a microprocessor-controlled switching device to selectively configure the circuit between measurement and calibration modes, allowing the no-load offset to be determined by connecting the inputs of the measuring circuit with a small value resistor, simulating the no-load condition without turning off the load, and applying this to both high-side and low-side circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the load is disconnected to recalculate the no-load offset, then the offset calibration accuracy is improved, but the circuit operation continuity deteriorates
Solution Approach 1:
The patent introduces a switching device as an intermediary component that can selectively connect or disconnect the shunt resistor from the measurement circuit. This switching mechanism enables the system to transition between measurement mode (load connected) and calibration mode (load disconnected) without manual intervention, resolving the contradiction by automating the calibration process while maintaining operational continuity through rapid switching.
2Measurement precision
If the no-load offset is recalibrated frequently to account for drift, then the measurement accuracy is improved, but the system complexity increases
Solution Approach 1:
The patent implements a self-calibrating system where the microcontroller automatically controls the switching device to perform offset recalibration at predetermined intervals or when drift is detected. This self-service approach eliminates the need for manual calibration operations and reduces system complexity by integrating the calibration control logic into the existing microcontroller, rather than requiring separate calibration hardware or manual procedures.
3Ease of operation
If a switching device is added to enable calibration without load disconnection, then the ease of operation is improved, but the device complexity increases
Solution Approach 1:
The patent integrates the switching device control logic into the existing microcontroller unit, making it multi-functional. The microcontroller continues to perform its primary function of monitoring current measurements while also controlling the calibration switching sequence. This universal approach eliminates the need for separate calibration control circuitry, thereby improving ease of operation without proportionally increasing device complexity.
Data Source
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AI summary
A switching device is controlled by a microprocessor to selectively configure the circuit between a current measurement mode and a calibration mode. When the switch is set to the "on" state, the circuit acts as a normal prior art circuit, with the output Vout being read by the microprocessor to determine the current to the load. However, when the switch is set to the "off state, a small value resistor (which may be roughly three orders of magnitude greater than Rshunt) connects the inputs of the measuring circuit so that the circuit can generate an output Vout corresponding to the zero load current. By connecting the V+ and V_ inputs together with a low resistance resistor, the no-load condition Vdiff = V+ - V- ≈ 0 applies. In this state, the no-load offset can be determined by measuring the output voltage of the circuit without turning off the load.