MR Bridge Current Sensor Saturation Prevention via Hall Feedback
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Solution Overview
Problem
Closed loop current sensing systems using magnetoresistive (MR) bridge circuits face inaccuracies in measuring current due to saturation effects at high magnetic fields, leading to unreliable control of secondary coils and inaccurate current sensing, especially during large and rapid fluctuations.
Innovation Solution
A modification circuit is introduced, incorporating a second magnetic field sensor, such as a hall sensor, and adjustable loads to prevent output voltage saturation in MR bridge circuits, ensuring a reliable and predictable output voltage even at high magnetic fields, thereby maintaining accurate control of the magnetic field and current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If MR bridge circuits are used to measure magnetic fields in closed loop current sensing systems, then measurement precision is improved for normal operating conditions, but reliability deteriorates at high magnetic fields due to saturation effects
Solution Approach 1:
A second magnetic field sensor (Hall sensor) is introduced as an intermediary device to monitor the magnetic field strength. This mediator provides information about the field conditions to a control circuit, which then adjusts the excitation current to prevent the MR bridge from saturating, thereby maintaining reliable operation at high fields while preserving measurement precision.
Solution Approach 2:
The patent implements a feedback mechanism where the output of the second magnetic field sensor is fed back to the control circuit. This feedback loop continuously monitors the magnetic field strength and adjusts the excitation current accordingly, preventing saturation of the MR bridge circuit and ensuring predictable output voltage behavior across all operating conditions.
2Measurement precision
If the magnetic field sensor sensitivity is increased to detect smaller currents, then measurement precision improves, but the sensor becomes more susceptible to saturation at high currents
Solution Approach 1:
The patent makes the system dynamic by allowing the excitation current to vary based on real-time magnetic field conditions. The control circuit adjusts the excitation current dynamically according to feedback from the second Hall sensor, enabling the system to maintain optimal sensitivity while avoiding saturation through adaptive operation rather than fixed parameters.
Solution Approach 2:
The patent changes the operating parameters of the MR bridge circuit dynamically. By adjusting the excitation current magnitude based on the magnetic field strength detected by the second sensor, the system maintains high sensitivity for small currents while preventing saturation at high currents through parameter adaptation.
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 modification circuit enables accurate and reliable measurement of current through the current carrying wire even during large and rapid fluctuations, by maintaining a predictable output voltage and preventing saturation effects, thus improving the precision of closed loop current sensing systems.
Implementation Method 1
magnetoresistive (MR) bridge circuits to measure the strength and direction of magnetic fields
Implementation Method 2
incorporating a second magnetic field sensor, such as a hall sensor
Implementation Method 3
a ferromagnetic core that defines a gap region in which the magnetic field generated around the wire is concentrated
Implementation Method 4
a secondary coil that may be wrapped around the core... generate a magnetic field in the gap region
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A
AI summary
A system includes a magnetoresistive (MR) bridge circuit, a magnetic field sensor, and an adjustable load. The MR bridge circuit receives a supply voltage and generates an output voltage that indicates a strength/direction of a magnetic field. The MR bridge circuit includes first and second MR elements connected in series between a supply node and a ground node, and third and fourth MR elements connected in series between the supply node and the ground node. The output voltage is generated between a first node that is common to the first and second MR elements and a second node that is common to the third and fourth MR elements. The sensor generates signals based on the strength/direction of the magnetic field. The adjustable load is connected in parallel with one of the MR elements, and has a resistance that is controlled based on the signals generated by the sensor.