Differential Current Sensor Stray Field Rejection
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Solution Overview
Problem
Conventional current sensors face challenges in accurately measuring currents due to immunity to stray magnetic fields, which can be mitigated by employing shields like ferrite cores, but these solutions may not provide sufficient isolation and can be complex in design.
Innovation Solution
A current sensor system utilizing two or more magnetic field sensing elements oriented to sense the magnetic field generated by a current through an external conductor in the same direction, with one element vertically aligned and the other not, generating differential signals that reject stray fields and indicate the current, while a lead frame with a die attach paddle and substrates provides high isolation through strategic lead placement and spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current sensors use shields or ferrite cores to concentrate magnetic field and provide shielding against stray fields, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The current sensor is segmented into multiple discrete magnetic field sensing elements arranged in a specific geometric pattern around the conductor. Each element senses the magnetic field from the conductor and from adjacent conductors, and the individual signals are combined through subtraction to reject stray fields while maintaining measurement accuracy.
Solution Approach 2:
The patent converts the harmful effect of stray magnetic fields from adjacent conductors into a beneficial differential measurement scheme. By positioning sensing elements symmetrically and subtracting their outputs, the stray fields that would normally degrade accuracy are rejected, while the desired current measurement is preserved and enhanced.
2Measurement precision
If conventional current sensors use ferrite cores to concentrate magnetic field, then measurement precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent extracts the magnetic field concentration function from the traditional ferrite core structure and replaces it with a geometric arrangement of sensing elements positioned around the conductor. This eliminates the need for complex ferrite core fabrication while achieving the same field concentration effect through spatial configuration.
Solution Approach 2:
The patent replaces the mechanical/ferrite-based magnetic field concentration system with an electronic sensing array system. Instead of using magnetic materials to guide and concentrate flux, the invention uses multiple electronic magnetic field sensors positioned in specific locations, simplifying manufacturing while maintaining measurement precision.
3Measurement precision
If magnetic field sensing elements are positioned close to the conductor for accurate sensing, then measurement precision is improved, but isolation from the conductor deteriorates
Solution Approach 1:
The patent transitions from a single-plane sensing arrangement to a three-dimensional configuration where sensing elements are positioned at different radial distances and angular positions around the conductor. This spatial distribution allows accurate magnetic field sensing while maintaining electrical isolation, as the elements can be mounted on a package body at optimized positions without direct contact.
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 system effectively rejects stray fields and provides accurate current measurement by generating a difference signal indicative of the current through the conductor, while maintaining high isolation and simplifying the design with strategic lead frame and substrate configurations.
Implementation Method 1
two or more magnetic field sensing elements that are oriented to sense a magnetic field generated by a current through an external conductor
Implementation Method 2
The current sensor generates an output signal having a magnitude proportional to the magnetic field induced by the current through the conductor
Data Source
AI summary
Systems and methods described herein are directed towards differential current sensing a current sensor having two or more magnetic field sensing elements that are oriented to sense a magnetic field generated by a current through an external conductor in the same direction. The current sensor can be positioned such that at least one first magnetic field sensing element is vertically aligned with the external conductor and at least one second magnetic field sensing element is not vertically aligned with the external conductor. The magnetic field sensing elements may be spaced from each to measure a gradient field and can generate a magnetic field signal indicative of a distance between the respective magnetic field sensing element and the current carrying external conductor. A difference between the magnetic field signals can be determined that is indicative of the current through the external conductor.