Hall Sensor. Design note 8

Hall sensor is a device that generates output current based on the magnetic field in its proximity. When a current carrying conductor is placed in a magnetic field, a voltage is generated perpendicular to the current and the field. This phenomenon is called as Hall Effect. The Hall sensor has a thin semiconducting material called Hall element. A current is passed through the Hall element in a direction perpendicular to the output connections. In the absence of a magnetic field, current distribution is equal without any potential difference across the output. When a perpendicular magnetic field is applied, a force called Lorentz force disturbs the current distribution and a potential difference develops across the output. The output voltage is called as Hall voltage (VH ). Lorentz force is the force acting on the moving charge carriers in a magnetic field.

A 1302 Hall Effect sensor is ideal to use in various application including microprocessor based circuits. A1302 is a continuous-time, linear Hall Effect sensor IC. It is similar to a transistor with three pins, Vcc, Gnd and Out. There is a small window in the IC to receive the magnetic field. Its output is proportional to the applied magnetic field. The Hall sensor has a Hall circuit and an amplifier in a single chip. Its output is CMOS Class A type. It works between 3-6 volts.

Fig.1 shows the pin assignment of A1302 Hall sensor


Fig.2 shows the basic design of the Hall sensor based circuit. IC CA3140 is used as a comparator and the output of the Hall sensor is fed to the Inverting input of IC2. The Non Inverting input of IC2 receives a variable voltage through R2 and VR. Preset VR can be used to adjust the output of comparator through changing the sensitivity. LED indicates the output status. When a South-polarity (+B) magnetic field is applied perpendicular to the face of Hall sensor, it increases the output voltage. When a North- polarity (-B) magnetic field is applied, the sensor decreases its output. Thus depending on the polarity of magnetic field, the output of Hall sensor changes which trips the comparator’s output between high and low states.