Diodes AN1195 Hall Element Application Guide

Introduction

The Hall effect, discovered by Dr. Edwin Hall in 1879, describes the generation of a voltage across a conductor when a magnetic field is applied perpendicular to the current flow. This voltage is proportional to the current and the magnetic flux density.

How does the Hall effect work?

When a current-carrying conductor is placed in a magnetic field, a voltage is generated perpendicular to both the current and the field. This is due to the Lorentz force acting on moving charges (electrons). Figure 1 illustrates the Lorentz force (F = qv x B), where F is the force, q is the charge, v is the velocity, and B is the magnetic field.

Figure 2 shows a Hall element with no magnetic field, where the current distribution is uniform and no output voltage (VH) is observed. Figure 3 demonstrates that when a perpendicular magnetic field (B) is applied, the current distribution is altered, resulting in a Hall voltage (VH) across the output terminals. The Hall voltage is proportional to the product of current (I) and magnetic field (B).

Hall Element

A Hall element is a magnetic sensor that outputs an analog signal proportional to magnetic flux density. The primary semiconductor materials used are InSb (Indium Antimonide), InAs (Indium Arsenide), GaAs (Gallium Arsenide), and Silicon (Si), each with unique characteristics suitable for different applications.

Materials

• InSb: Supersensitive with higher temperature drift, suitable for switch/latch/motor applications.
• InAs: Highly sensitive with low-temperature drift, suitable for precise motion and position control.
• GaAs: Ultra-low temperature drift, suitable for linear-sensing applications like optical image stabilizers.
• Silicon (Si): Very low sensitivity, can be integrated into standard CMOS processes.

Diodes Incorporated offers InSb Hall elements and Si-base integrated Hall ICs. For more details, visit https://www.diodes.com/products/analog/sensors/.

Offset Voltage

An offset voltage (Vos) can be present even without a magnetic field due to mismatches in the Hall element's internal resistors (Figure 3a and 3b). This results in a shift of the output voltage characteristic, as shown in Figure 3c. Offset voltage is dependent on temperature and applied voltage/current.

Drive Mode

Hall elements can be driven in two modes: constant voltage (VC) or constant current (IC), as shown in Figure 4.

• Voltage Mode (VC): The Hall voltage (VH) is expressed as VH = μH • (W / L) • VC • B + Vos, where μH is electron mobility, W is element width, L is element length, and Vos is offset voltage. Temperature characteristics are influenced by μH.
• Current Mode (IC): The Hall voltage (VH) is expressed as VH = RH (1 / d) • IC • B + Vos, where RH is the Hall coefficient, d is semiconductor film thickness, and Vos is offset voltage. The Hall coefficient is defined as RH = 1 / (en), where e is electron charge and n is carrier concentration. Temperature characteristics are influenced by RH.

Figures 5, 6, and 7 illustrate the Hall voltage (VH) characteristics with respect to magnetic flux density (B), electrical stimuli (I/Vc), and ambient temperature (Ta).

Hall Voltage VH vs. Magnet pole

Table 1 lists Diodes' InSb Hall element products (AHE101, AHE108, AHE102, AHE300) with their specifications and magnet pole orientation for generating positive or negative Hall voltages.

Figures 8-14 demonstrate how different Hall element models (AH101/AH108, AH102, AH300/AH322) respond to different magnet pole orientations (N or S) applied to the brand side, resulting in positive or negative Hall voltages (VH).

Note: For SOT23-4 packages, the symmetry between pins can lead to a 180° rotation issue during PCB mounting. However, as shown in Figure 14, rotating the element by 180° does not affect the Hall output voltage (VH) if the setup remains the same.

Applications

Hall elements are primarily used in BLDC (brushless) motor control and linear position detection due to their contactless operation, long lifetime, miniaturization, and fast response times.

Hall elements in BLDC (brushless) motor applications

Unlike brushed DC motors (Figure 15) which suffer from brush wear, brushless DC motors with Hall elements (Figure 16) offer contactless operation, longer life, and reduced maintenance. The Hall element detects the magnetic field, enabling an intelligent driver IC (Figure 18) to control the current to the coils (Figure 17), thereby rotating the motor via magnetic forces. Proper symmetry in duty ratio is crucial for BLDC efficiency; any asymmetry, potentially caused by Vos, can be mitigated by using highly sensitive Hall elements.

Diodes provides smart BLDC drivers and pre-drivers. More information is available at https://www.diodes.com/products/power-management/motor-control/.

Hall elements in linear position detection

The linearity of Hall elements with magnetic flux density makes them suitable for position detection. Figure 19 shows a linear signal amplifier circuit where the Hall element voltage (VH) is amplified by an RF/R ratio to produce an output voltage (VO) proportional to magnetic flux density. Figure 20 illustrates the output transfer function of distance versus magnetic flux density.

Hall elements in current sensors

Hall elements are used in both open-loop and closed-loop current sensors. An open-loop sensor (Figure 21) uses a Hall element in a magnetic core's air gap to measure primary current (IP), providing electrical isolation. The amplified Hall signal represents the sensor output.

A closed-loop sensor (Figure 22) uses a Hall element to monitor the magnetic field generated by the primary current and applies a feedback current to cancel it out. This feedback current, converted to a voltage via a load resistor (RL), is proportional to the primary current.

Table 2 compares open-loop and closed-loop current sensors based on power consumption, accuracy, response time, isolation, dynamic range, and cost.

Important Notice

Diodes Incorporated provides information for illustrative purposes only and assumes no liability for its application or use. Customers are responsible for ensuring their applications comply with all applicable laws, regulations, and safety standards. Diodes' products are subject to their Terms and Conditions of Sale. This document may be translated, but the English version is the definitive one. Unauthorized use or copying is prohibited.