Mastering Magnetism: Hall Effect Sensors and Applications for PCBs
Thales of Miletus obviously had a magnetic personality. People noticed when Aristotle celebrated his achievements when writing his best-selling Περὶ Ψυχῆς (On The Soul). Aristotle praised Thales for reasoning that magnets have souls: “Thales, too, to judge from what is recorded about him, seems to have held soul to be a motive force, since he said that the magnet has a soul in it because it moves the iron.”
The reputation of Thales spread. Philosophers call him the “father of philosophy.” Some describe him as the first physicist. Mathematicians see Thales as the “father of mathematical proof.” Others describe Thales as “one of the seven wise men of early Greece.” Talk about a rock star. Unfortunately, Thales of Miletus missed the mark. Magnets do not have souls.
However, magnetism allows us to do some really cool things—especially when electrons move through a magnetic field and an electric field. Some of those cool things translate into Hall effect sensors used in the automotive, manufacturing, consumer, and other industries. Understanding the operation of the sensors gives greater insight into other potential uses.
The Hall Effect Feels the Force
Electrons moving in a direction perpendicular to an applied magnetic field experience the Lorentz force. When the magnetic field passes through a thin conductive plate, the right-hand rule and the Hall effect come into play. Accumulating the charge along one side of the conductor creates an electric field that counteracts the force of the magnetic field.
The transverse Lorentz force pushes the electrons to follow a curved path along and to one side of the conductive material. Then, the right-hand rule tells us that the direction of the Lorentz force has a relationship with the direction of the electrons. If the electrons move in one direction, the Lorentz force pushes upward. Electrons moving in the opposite direction cause the Lorentz force to push downward.
Placing the output connections on the conductive plate perpendicular to the direction of current flow forms a Hall element. A difference in potential exists between the positive upper side and the negative side of the conductor. With that difference in potential, a measurable voltage—called the Hall voltage—occurs.
While the direction of the applied magnetic field determines the polarity of the Hall voltage, the voltage remains proportional to the applied field strength. Take away the magnetic field and the current distribution becomes uniform and the potential difference across the output drops to zero. At this point, the different influences on the voltage become interesting. The Hall voltage depends on the:
- Amplitude of current flowing through the conductor
- Strength of the magnetic field
- Elementary electron charge
- Charge carrier number density
- Thickness of the conductive plate.
Semiconductors Under the Influence
Each of those factors impact semiconductors influenced by the Hall effect. Placing a current-carrying silicon chip at a right angle to a magnetic field produces the low-level Hall voltage. The Hall voltage is a function of the input current.
When applied to semiconductors, the Hall effect creates a digital switch that produces an efficient on-off square wave signal. Disrupting the window between the magnetic field and the silicon chip produces a zero output. Connecting additional circuitry to the semiconductor produces the opposite effect and allows the interruption to the magnetic field to produce an increase in output voltage.
Hall Effect Sensors Need Strength
Hall effect sensors require a low noise, high input, moderate gain amplifier to amplify the 30µV Hall voltage and the addition of a voltage regulator to hold current constant. The amplified output voltage of the sensor occurs only as a function of the magnetic field. With all this, a Hall effect switch works as an ideal sensor.
A digital Hall effect sensor senses the magnetic field and switches state when it reaches the operating point. Decreasing the magnetic field until the sensor reaches its release point causes the sensor to return to its original state. The fundamental points for designing a Hall effect sensor circuit include:
- Determining the physical quantity to be sensed
- Defining the best approach for sensing the physical quantity
- Establishing the best input interface for the sensor
- Deciding on the best magnetic system
- Selecting the Hall effect sensor
- Finding the best output interface
Different types of Hall effect sensors integrate into PCB design and include vane operated position sensors, gear tooth sensors, digital current sensors, linear current sensors, latches, closed loop current sensors, unipolar switches, and mechanically-operated switches.
While a Hall effect sensor can be a powerful tool within your PCB design, the first step when approaching any PCB design will always be in knowing what kind of PCB design software to use and which software has the right tools for your needs. Finding software with features such as an intuitive interface, features like multi-board layout and auto-interactive routing, and a power distribution are all vital to your design health, and thankfully easily accessible from Altium’s CircuitStudio®.
If you’d like to talk more about how choosing the right PCB design software can make even your most complicated designs much more efficient and intuitive, consider talking to the experts at Altium today.