How to design the switch using Hall Effect IC: Introduction of technologies: Asahi Kasei Microdevices Magnetic Sensors

Switch design examples

The usual structure of a switch using a Hall IC is shown in Figure 4. In type A, the magnet moves vertically to the Hall IC package surface. In type B, the magnet moves in parallel with the Hall IC package surface.

Figure 4. Structure of switch using Hall IC

The configuration examples below show the relation between the magnet and the Hall IC (in case of EW-750B) for types A and B. The calculations are performed using the following two types of general-purpose magnets (Neodymium magnet: 5 mm x 5 mm x t1 mm Br = 1300 mT, ferrite magnet: 25 mm x 15 mm x t10 mm; Br = 300 mT). The NS polarization of the magnet is in the direction of its thickness (vertical to the Hall IC package). (* The size variation of the general-purpose magnet is large.)

The magnetic characteristics of EW-750B is shown in Table 3.

Table 3. Magnetic influence of EW-750B (Ta = 25°C, Vcc = 12 V)

Item	Symbol	Min	Typ	Max	Unit
Operating Point	Bop	3	6	9	mT
Release Point	Brp	2.5	5	9.5	mT
Hysteresis	Bh	0.5	1.1	2.5	mT

The calculations below are based on initial alignment of the magnet center with the Hall IC sensor center.

Type A

Figure 5 shows the relationship between distance d from the magnet surface and the magnetic flux B of two types of squarer magnets.

Figure 5. Relationship between distance d from the magnet surface and the magnetic flux B of two types of square magnets

According to these results,the configuration of the two types of magnets and the Hall IC (EW-750B) is shown below in Table 4.

Table 4. Configuration example of magnet and Hall IC by using EW-750B

Magnet type and size	Distance from Hall IC package surface to magnet surface when Hall IC is L	Distance from Hall IC package surface to magnet surface when Hall IC is H
Neodymium magnet 5 mm x 5 mm x t1 mm	6.7 mm or less (at 25°C)	11.9 mm or more (at 25°C)
Ferrite magnet 25 mm x 15 mm x t10 mm	18.6 mm or less (at 25°C)	35.3 mm or more (at 25°C)

Type B

Figure 6 shows the relationship between the movement distance d and magnetic flux density B calculated when the two types of rectangular magnets move in parallel with the Hall IC package surface, assuming that the distance from the Hall IC package surface to the magnet surface is 5 mm.

Figure 6. Relationship of distance of magnet movement and magnetic flux density (when distance from Hall IC package surface to magnet surface is 5 mm)

According to these results, the configuration of the two types of magnets and the Hall IC (EW-750B) is shown below in Table 5.

Table 5. Configuration example of magnet and Hall IC by using EW-750B
(when the distance from the Hall IC package surface to magnet surface is 5 mm)

Magnet type and size	Distance of magnet movement when Hall IC is H
Neodymium magnet: 5 mm x 5 mm x t1 mm	6.1 mm or more (at 25°C)
Ferrite magnet: 25 mm x 15 mm x t10 mm	13.2 mm or more (at 25°C, movement direction:short-side) 18.1 mm or more (at 25°C, movement direction:long-side)

Note: All the results shown are based on an ambient temperature of 25°C. Allow for temperature characteristics when using with a wide temperature range.