The Growth of Hall Effect Sensors Based on Low-Power Features

It seldom takes nearly 90 years to find a viable application for a technology breakthrough, but engineers took 86 years to develop an application for the Hall Effect Sensor. The Hall Effect Sensor was discovered by Edwin H. Hall, a doctoral candidate who stumbled upon a strange electrical event while attempting to verify Kelvin’s theory of electron flow. In Hall’s experiment, he placed a thin layer of gold in a strong magnetic field and connected a battery to the opposite side of the film. He discovered a small voltage appearing across the film when he measured the current flowing through it. He also found that the voltage was proportional to the magnetic field’s strength multiplied by the current. As Hall applied current to this metal square between two magnets, a secondary voltage appeared in the metal at a right angle to the voltage applied. His discovery evolved into a switching mechanism that could create an on-off square-wave voltage signal.

Hall’s discovery dates back to 1879, and in 1965, development engineers Everett Vorthmann and Joe Maupin of MICRO SWITCH Sensing and Control integrated the technology into a single silicon chip as a low-cost solid state sensor. Based on Vorthmann and Maupin’s integration, more than a billion Hall Effect devices and sensor products have been delivered using Honeywell’s Hall Effect technology. These devices and sensor products are primarily used in keyboard applications.

Hall Effect Sensors are often called switches based on the on-off digital voltage signal produced. The sensors’ differentiating characteristic is that the constant voltage signal can change suddenly from maximum voltage to nearly zero and back again, no matter the engine speed. This capability is easily adapted for timing purposes, making the sensors extremely useful in a variety of applications. The highly-reliable, solid state sensors are most widely used in industrial brushless motor applications.

Hall Effect Sensors are essentially transducers that vary output voltage depending on the changes in the magnetic field. They typically feature three wires or terminals for ground, supply and output signals. When used in an automotive application, the output signal requires that the sensor be supplied with a reference voltage from an onboard computer (between 5 and 12 V). This supply voltage creates the switching effect in the sensor. The sensors also may require analog circuitry to interface to microprocessors. These interfaces may have input diagnostics, short/open circuit detection, input diagnostics, and the ability to monitor and provide current directly to the sensor.

Applications

Hall Effect Sensor applications include proximity switching, speed detection, current sensing, and positioning. The sensors are also used in industrial automotive applications including pneumatic cylinders and brushless DC electric motors to detect the permanent magnet position. Other industrial automotive applications include internal combustion engine ignition timing, tachometers, anti-lock braking systems, ignition system distributors, and to determine the position of crankshafts and camshafts.

Consumer applications include printers and keyboards. More recently, Hall Effect Sensors are increasingly used in battery-operated mobile equipment such as the door or lid closure detection in computer notebooks, scanners, hand-held industrial computers and instrumentation. Other consumer applications include mobile printer head position sensing, hand-held medical and dental equipment, as a trigger switch in hand tools, a reed switch replacement in battery-operated security systems, a magnetic encoder for building access, power switch and open/close detection in small vacuum cleaners and fans, and in remote, battery-operated utility meters to measure gas or water consumption.

One example of a Hall Effect Sensor is the Honeywell Sensing and Control's SL353 Series (see table below). The sensor ICs are small, versatile, and digital Hall-effect devices operated by the magnetic field from a permanent magnet or electromagnet. They are designed to suit a wide range of applications with low power requirements. The series responds to either a North or South Pole and do not require magnet polarity to be identified, simplifying installation and potentially lowering system cost. The SS50AT series are low-cost bipolar Hall-effect sensors in a surface-mount package that have a thermally balanced IC over the full temperature range. The bipolar magnetics respond to alternating North and South poles. A built-in regulator provides stable operation over a 4.5 to 24 Vdc supply voltage range, and internal circuitry prevents sensor damage if the supply voltage polarity is accidentally reversed.

DigiKey P/N	Honeywell P/N	Description	Current - Supply
480-3327-1-ND	SL353HT	SENSOR OMNIPOLAR HALLEFFECT DGTL	640μA
480-3328-1-ND	SL353LT	SENSOR OMNIPOLAR HALLEFFECT DGTL	3μA
480-3612-1-ND	SS50AT	SENSOR BIPOLAR HALLEFFECT SENSOR	10mA

Energy efficiency is paramount. For example, these low-power sensing devices use Bipolar Complementary Metal Oxide Semiconductor (BiCMOS) technology and a timing circuit that turns the power on for a short time. Power is turned off for the rest of the period, or duty cycle, to significantly reduce the average current consumption. The SL353HT and SL353LT can operate from a supply voltage as low as 2.2 V, promoting energy efficiency.

Features include:

• Digital or analog output
• Unipolar, bipolar, bipolar latching, or omnipolar magnetic actuation types
• A variety of package styles and sizes, including SOT-23, SOT-89, and SOT-92-style
• Very low supply voltage ranges
• Tape and reel packaging
• Cost-effective

Specific targeted applications include:

• Speed and RPM sensing
• Motor, fan, and robotics control
• Motion control/detection
• Brushless DC motor commutation
• Magnetic encoding
• Lid closure detection
• Presence-absence detection
• Flow rate sensing

Growth Predicted

In a research report titled “Automotive Active Speed and Position Sensors Grow, but Passive Sensors May Make a Comeback” analyst Simon Schofield explains that active non-contacting sensing strategies based on the Hall Effect, magneto resistive, and variable reluctance transformer technologies are beginning to penetrate markets and take market share from more established passive sensors. The report covers active versus passive automotive speed and position sensors that are expected to grow to 880 million units by 2012. The need for improvements in automotive system reliability and reduced warranty costs are the main drivers.