Introduction and Application of Hall Elements

Introduction and Application of Hall Elements

The working principle of the Hall element is the Hall effect. The so-called Hall effect is shown in Figure 1. It refers to the phenomenon that when a current I is passed through a material and a magnetic field B is applied in a direction that is at a right angle to the current, a potential difference V is generated in the direction at right angles to the current and the magnetic field. This voltage is generated under the following circumstances: when there is a magnetic field B, due to Fleming's left-hand rule, the Lorentz force (the force that can bend the electrons or positive holes flowing through the material in the direction indicated by the arrow symbol) acts and squeezes the electrons or positive holes to one side of the fixed output terminal. The size of the potential difference V is usually determined by the Lorentz force and the force that pushes
the electrons (that is, the former force is equal to the latter force), and is proportional to the product of the current I and the magnetic field B. The proportionality constant is the value obtained by dividing the Hall constant of the material by the thickness of the material in the direction of the magnetic field.

                     Figure 1 Principle of Hall element

In a flat semiconductor medium, the direction of electron movement (electric field) will be changed by the effect of magnetic force (magnetic field). If the electric field and magnetic field are perpendicular to each other, the carriers (electrons or holes) they conduct will be concentrated on the upper and lower sides of the plate, thus forming a potential difference. This potential difference is the Hall voltage (Hall voltage). In actual Hall components, N-type semiconductor materials in which the current carriers are electrons are generally used. When the output voltage when a certain input is applied to the Hall component is analyzed using the above relationship, the following conclusions can be obtained:
(1) The material properties are proportional to the square root of the product of the Hall coefficient and the electron mobility.
(2) The shape of the material is proportional to the inverse of the square root of the thickness.
Due to the above relationship, in actual Hall components, materials with large Hall coefficients and electron mobility can be processed into a thin cross shape.

Figure 2 shows the use of 3-5 terminal Hall components. The output of a three-terminal Hall element can generate a voltage that is approximately half of the input terminal voltage plus the output signal voltage. In the four-terminal and five-terminal Hall components, although the influence of the input terminal voltage can be avoided in principle, in reality, even in the absence of a magnetic field, there is an unbalanced voltage caused by factors such as the imbalance of the component shape.

(a) 3-pin assembly (b) 4-pin assembly (c) 5-pin assembly

                    Figure 2 How to use the Hall element

Type and connection method
 

structure:

Coreless type
Core type
test probe Hall integrated circuit
 

Connection method:

Three-terminal assembly
Four-terminal assembly
Five-terminal assembly

Uses
Hall components have the following three uses:
(A) A method of passing a certain current through the Hall component in advance to detect the magnetic field or other physical quantities converted into the magnetic field.
(B) A method of using the multiplication of the component's current, magnetic field, and the two quantities as its variables.
(C) A method of using non-oppositeness (i.e., in a certain magnetic field, when a current in the same direction as the output obtained when the input terminal is passed through the output terminal flows through the output terminal, a Hall voltage in the opposite direction to the initial voltage is generated at the input terminal). Specific examples of the above various methods of use refer to the items described in the above-mentioned uses of magnetoelectric conversion components. In many of these specific examples, the Hall component forms a coil of one turn, which is difficult to meet practical requirements due to the sensitivity and temperature characteristics of the component. However, the use of Hall probes to measure magnetic fields has been finalized because it is a relatively simple method. In addition, brushless motor (Hall motor) switches are gradually entering the practical stage, and some people have tried to manufacture magnetic heads.

Hall element power supply

                        Figure 3 Constant voltage drive 1

                                                      Figure 4 Constant voltage drive 2

                                          Figure 5 Constant current drive 1

                                          Figure 6 Constant current drive 2

                 Figure 7 Hall sensor imbalance adjustment method

A solid-state component with a magnetic field-electric conversion function formed in a crystal sheet, which has a Hall component and a circuit that amplifies and controls its output voltage, is called a Hall integrated circuit. The
appearance structure
is shown in Figure 2-19. It has the same structure as resin-enclosed transistors, integrated circuits, etc., that is, it is mostly a structure with four wires attached to a square or rectangular plate component with a size of 5mm square and a thickness of less than 3mm. The wires are formed by metal sheets, and each metal sheet is attached with a semiconductor crystal sheet (usually a silicon chip), and the Hall component and signal processing circuit are formed in the crystal body using integrated circuit technology. In order to prevent the performance of the entire component from deteriorating, it is usually sealed with resin. In addition, in order to facilitate the application of the magnetic field, its thickness is also minimized.

Figure 8 Structure of Hall IC

Working principle
The magnetic field strength can be converted into an electrical signal by using a Hall element formed on a part of the crystal sheet (refer to the working principle of the Hall element mentioned above). The crystal usually uses semiconductor silicon, and the magnetic field sensitivity of the Hall element is 10-20mV/K.Oe. This signal is amplified by the signal processing circuit formed in the same crystal and taken out as a signal voltage suitable for the specified purpose. Usually two of the four wires are connected to a grounded power supply, and a positive signal voltage is taken out from one of the remaining two, and a negative signal voltage is taken out from the other. The input resistance of the Hall element usually needs to match the power supply of the signal processing circuit so that the Hall element can be used with a constant voltage. At this time, the output voltage of the component is not much different whether it is N-type or P-type. Because the output voltage is proportional to the mobility of electrons or positive holes, the temperature characteristics should also be kept constant as much as possible, which is different from the single Hall element.
Type:
When classified according to the nature of the output signal, it is shown in Table 1. As shown in Figure 9, the linear type Hall integrated circuit can obtain an output voltage proportional to the magnetic field strength. Although the magnetic field sensitivity can be adjusted by the circuit's amplification, the proportional range will become narrower at high sensitivity (although the power supply of 5V makes the sensitivity reach 10mV/Oe, the proportional range is below 500Oe).

Table 1 Types classified by output voltage

                 (a) Linear type (b) Switching type

                  Figure 9 Output characteristics of Hall IC

The switch type Hall integrated circuit can obtain the ON-OFF voltage in a certain range of magnetic field. The hysteresis phenomenon of the switch type to the magnetic field is deliberately designed to make the switch action more linear.
When classified according to the manufacturing method, it is shown in Table 2. However, any manufacturing method can obtain the same characteristics. At this stage, bipolar Hall integrated circuits have begun to enter the commercialization stage.

Table 2 Classification by manufacturing method

Applications
Hall ICs are usually used in the applications in the range of (A-1) and (A-2) described in the above-mentioned magnetoelectric conversion components. Among these applications, it is particularly easy to use when using magnetism as a medium to convert physical quantities such as position changes, speed, and rotation into electrical quantities, such as switches. The switch relationship using Hall ICs is shown in Figure 2-21. This switch has the following characteristics: (1) no vibration (Chattering), (2) no noise, (3) long service life, high reliability, (4) fast response speed, etc., and has actually been used as a switch for advanced keyboards.

                   Figure 10 Switch using Hall IC

Figure 11 is an A44E integrated Hall switch. The A44E integrated Hall switch consists of five basic parts: a voltage regulator A, a Hall potential generator (i.e., a silicon Hall chip) (mT), a differential amplifier C, a Schmitt trigger D, and an OC gate output E, as shown in Figure 12 (a). (1), (2), and (3) represent the three lead-out terminals of the integrated Hall switch. The input voltage VCC is applied to the two ends of the Hall potential generator after being stabilized by the voltage regulator. According to the principle of the Hall effect, when the Hall chip is in a magnetic field, a current is passed in a direction perpendicular to the magnetic field, and a Hall potential difference HV output will be generated in a direction perpendicular to the two. The HV signal is amplified by the amplifier and sent to the Schmitt trigger for shaping, so that it becomes a square wave and is sent to the OC gate output. When the applied magnetic field reaches the operating point (i.e., BOP), the trigger outputs a high voltage (relative to the ground potential), turning on the transistor. At this time, the OC gate output outputs a low voltage, which is usually called an open state. When the applied magnetic field reaches the release point (BrP), the trigger outputs a low voltage, the transistor is cut off, and the OC gate outputs a high voltage. This state is off. The two voltage changes make the Hall switch complete a switching action. The difference between BOP and BrP is constant. This difference BH = BOP - BrP is called hysteresis. Within this difference, V0 remains unchanged, so that the switch output is stable and reliable. This is one of the excellent characteristics of the Hall switch sensor.

          Figure 11 Schematic diagram of A44E integrated switch type Hall sensor

    Figure 12 A44E integrated switch type Hall sensor pin diagram

                             Hall element appearance picture

                                              Hall speed sensor application circuit