The Hall effect is named after Edwin Hall, who in 1879 discovered that a voltage potential develops across a current-carrying conductive plate when a magnetic field passes through the plate in a direction perpendicular to the plane of the plate, as illustrated in the upper panel of Figure 1. The blue arrows, B, represent a magnetic field passing perpendicularly through a conductive plate. This configuration is referred to as a planar Hall-effect sensor.
The fundamental physical principle behind the Hall effect is the Lorentz force, which is modeled using the equation shown in Figure 1. When an electron moves along a direction, v, perpendicular to the applied magnetic field, B, it experiences a force, F, normal to both the applied field and the current flow. In response to this force, the electrons move in a curved path along the conductor (Hall element). Because of this, a net charge, and therefore, a voltage, develops across the plate. By this property, the Hall effect is employed as a magnetic sensor.
Allegro Hall-effect sensor integrated circuits (ICs) incorporate a Hall element with other circuitry, such as op-amps and comparators, to make digital position sensors and speed sensors, as well as linear and angle sensors with analog outputs. Figure 2 shows the block diagram of a simple Hall-effect switch.
In many cases, Allegro magnetic sensor ICs also incorporate proprietary packaging that includes a “back-bias” magnet to enable the sensor to sense the location of a ferrous (magnetic) target rather than an external magnetic field. The target, e.g., a steel gear, modifies the magnetic field from the integrated magnet. Differential sensing and advanced algorithms are used to optimize performance and compensate for dynamic or sudden air gap changes, vibration, and mechanical tolerances.
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Hall-effect sensors also lend themselves to non-contact current sensing, as the current in a conductor creates a magnetic field that is proportional to the magnitude of the current. Unique packaging creates galvanically isolated, small footprint current sensing ICs with very low insertion losses.
Allegro Hall-Effect Sensor ICs gives an expanded overview of the general topic of Hall-effect sensor ICs. This article and many others on related topics can be found at Hall-Effect Sensor IC Publications.
Since their inception, Allegro has pioneered several major advances in the field of Hall-effect sensor ICs including chopper stabilization, vertical Hall-effect technology, circular vertical Hall (CVH) arrays, and non-intrusive high-speed hardware diagnostics.