Hall sensor is a magnetic field sensor based on the Hall effect. The Hall effect is a kind of magnetoelectric effect, which was discovered by Hall (A.H.Hall, 1855-1938) in 1879 when he studied the conductive mechanism of metals. Later, it was found that semiconductors, conductive fluids, etc. also have this effect, and the Hall effect of semiconductors is much stronger than that of metals. Various Hall elements made of this phenomenon are widely used in industrial automation technology, detection technology, information processing, etc. The Hall effect is a fundamental method to study the properties of semiconductor materials. The Hall coefficient measured by the Hall effect experiment can determine important parameters such as the conductivity type, carrier concentration, and carrier mobility of the semiconductor material.
Hall Effect Principle
The Hall effect is essentially the deflection of moving charged particles in a magnetic field by the Lorentz force. When charged particles (electrons or holes) are confined in a solid material, this deflection leads to the accumulation of positive and negative charges in the direction perpendicular to the current and magnetic field, resulting in an additional transverse electric field, the Hall field EH.
The current IS passes through the N-type or P-type Hall element. The direction of the magnetic field B is perpendicular to the direction of the current IS, and the direction of the magnetic field is from the inside to the outside. For the N-type semiconductor and the P-type semiconductor, the generated directions are as shown in the figure below. (from which, the properties of the Hall element can be judged – N-type or P-type).
The Hall potential difference EH prevents the carriers from continuing to shift to the side. When the lateral electric field force FE on the carriers is equal to the Lorentz force FB, the accumulation of charges on both sides of the Hall element reaches a dynamic balance.
Let the width of the sample be b, the thickness be d, and the carrier concentration be n, then:
From (1) and (2), we can get:
Hall potential difference UH=EHb=(1/ne)(ISB/d)=RH(ISB/d)
RH=1/ne is the Hall coefficient of the material, which is an important parameter reflecting the strength of the Hall effect of the material.
For a fixed Hall element, the thickness d is fixed, and KH is the Hall coefficient of the Hall element, we can get:
That is: the Hall potential difference UH is proportional to the current IS and the magnetic induction intensity B.
3144 Hall Sensor
3144 Hall sensor circuit diagram
The output valid signal is low level, which can also be designed by modifying the non-inverting and inverting inputs of the comparators in the 3144 and 3296 circuits.
It can be seen from the signal principle that the sensitivity can be adjusted by adjusting the standard voltage output by the 3296. Because of the precise adjustment of the reference voltage of the multi-turn precision adjustable resistor, the adjustment of the sensitivity here is also very precise.
The magnetic field sensing surface of the 3144 Hall sensor is the top plane. As long as there is enough magnetic field strength to trigger the comparison in the sub-plane, the output level of the 2 terminals of JP1 in the circuit will remain unchanged. That is to say, adjusting the reference voltage output by the 3296 is equivalent to adjusting the trigger value of the magnetic field strength of this module. The closer the magnet is to the top face of 3144, the stronger the magnetic field and the higher the voltage output by 3144.
When programming, pay attention to:
(1) If the level state of the pin is continuously detected while(1), this circuit module is equivalent to an independent button, requiring a delay of 20ms to debounce.
(2) If the external interrupt of the single-chip microcomputer is connected, the level trigger or edge trigger should be selected according to the specific situation. The trigger edge of the LM393 is still very neat, and the edge trigger effect is good.
Hall Sensor Pin Definition and Hall Sensor Wiring
Under normal circumstances, the Hall switch has three leads: brown, blue, and black. The brown and blue wires are connected to the positive and negative poles of the power supply respectively, and the black wire is connected to the signal output wire. There are two types of NPN and PNP, which need to be judged according to the actual circuit conditions.
Reference circuit diagram:
The output of the Hall sensor, in most cases, is three pins, which are based on the printed word, in order: pin 1 for working power (VDD), pin 2 for grounding (GND), and pin 3 for output (OUT), as shown in the figure below:
The Hall sensor wiring with four pins is also relatively common. The pins (1, 3 or 2, 4) on any two diagonal lines can be used as the positive and negative poles of the power supply. For example, the positive pole is pin 1, and the ground is pin 3. The other 2/4 pin is the differential voltage output. It doesn’t matter if you don’t know 1234, as long as you choose any two feet on the diagonal.
Hall Sensor Types
Hall sensors are divided into two types: line Hall sensors and switch Hall sensors.
(1) The switch Hall sensor consists of a voltage regulator, a Hall element, a differential amplifier, a Schmitt trigger, and an output stage, which outputs digital quantities. There is also a special form of switch-type Hall sensors, called key-lock Hall sensors.
(2) Linear Hall sensor consists of Hall element, linear amplifier, and emitter follower, which outputs analog quantity.
Linear Hall sensors can be divided into open-loop and closed-loop. Closed-loop Hall sensors are also called zero-flux Hall sensors. Linear Hall sensors are mainly used for AC and DC current and voltage measurement.
Switch Hall sensor
As shown in the figure below, where BNP is the magnetic induction intensity of the operating point “on”, and BRP is the magnetic induction intensity of the release point “off”. When the applied magnetic induction intensity exceeds the action point Bnp, the sensor outputs a low level. When the magnetic induction intensity drops below the action point Bnp, the sensor output level does not change. When the magnetic induction intensity drops to the release point BRP, the sensor changes from a low level to a high level. The hysteresis between Bnp and BRP makes the switching action more reliable.
Linear Hall sensor
Linear Hall sensors are mainly used for AC and DC current and voltage measurement. The output voltage has a linear relationship with the strength of the applied magnetic field, as shown in the figure below, it can be seen that there is good linearity within the range of the magnetic induction intensity of B1~B2, and when the magnetic induction intensity exceeds this range, it is in a saturated state.
Hall Sensor Applications
Application of Hall sensor in mobile phones
It is mainly used for opening or closing the screen. Close the protective case, the phone will automatically go to sleep. Flip open the case to wake the phone instantly, without having to tap any buttons.
After all, it is still inseparable from the word “switch”. In the telephone, there is a key that we don’t use much but is essential, yes, the on-hook key. The on-hook key is located in the groove where the handset is placed. When the call is over, as long as the handset is put back into the groove, the on-hook key is compressed under the gravity of the handset, thereby cutting off the call state. Conversely, when the handset is picked up, the telephone is in a connectable state.
Here, the function of “on/off” the phone state played by the telescopic on-hook key can be realized by the Hall sensor. If the Hall sensor is installed at the position corresponding to the handset of the phone, due to the magnet in the handset, the sensor can detect a change in the magnetic field no matter when the handset is left or returned to its original position, so that the phone is in on or off state.
Application of Hall sensor in BLDC motor
In order to make up for the shortcomings of contact sensors, Hall sensors have been vigorously developed. Because of their solid structure, no contact, long life, low power consumption, vibration resistance, pollution prevention, and corrosion resistance, they are widely used in various electronic control systems. Among them, brushless DC motor, or BLDC for short, is a kind of motor equipment with rapid development and wide application. Next, the application of Hall sensor in the detection of brushless DC motor rotor is briefly introduced.
Unlike brushed DC motors, currently the most widely used 3-phase BLDC, brushless DC motors use electronic commutation. To make the BLDC spin up, the stators must be energized in a certain order. At this time, we need to know the position of the rotor in order to energize the corresponding stator coils according to the energization sequence. The position of the stator is sensed by Hall sensors embedded in the stator.
Hall Sensors in BLDC motors
Typically, 3 Hall sensors are installed around the rotational path of the BLDC motor rotor. Whenever the magnetic pole of the rotor passes over the Hall element, the Hall element will output the corresponding high or low level according to the polarity of the current magnetic pole of the rotor, so the current position of the rotor can be judged, and the stator windings can be energized accordingly based on the timing of the levels generated by the three Hall elements.
Hall sensor measurement principle
The figure above shows the cross-section of the rotor with the NS magnetic poles arranged alternately. The Hall element is placed in a fixed position of the motor. It is more complicated to place the Hall element on the stator of the motor, because if the position is not tangent to the magnetic field of the rotor. Then, the measured value of the Hall element may not accurately reflect the current position of the rotor. In view of the above reasons, in order to simplify the installation of the Hall element, a redundant magnet is usually installed on the rotor of the motor. This magnet is specially used for the Induction Hall element so that it can have the same effect as the rotor magnet induction. The Hall element is generally placed on the printed circuit board according to the circumference and is equipped with an adjustment cover so that the user can easily adjust the Hall according to the direction of the magnetic field. position the components so that they work optimally.