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Value Added Services Switching Without Mechanical Contacts With Magnetic Field Sensors

From Margit Kuther 2 min Reading Time

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Taiwan Machine Tool & Accessory Builders' Association (TMBA)

When switching a current via a mechanical switch, problems can arise due to the switching time, low switching currents and a limited number of switching cycles. These should already be taken into account during the development of electronic assemblies. Distributor Endrich reveals how.

Switching without mechanical contacts(Image: Endrich)
Switching without mechanical contacts
(Image: Endrich)

Reed contacts use mechanical switching contacts and are switched on and off by a magnetic field. This eliminates many of the disadvantages of mechanical switches, such as increased noise, limited switching cycles and a mechanical force for switching. The reed contacts are sensitive to mechanical stress and vibrations. Mechanical switches and reed contacts generally have the advantage that they are completely passive, i.e. they do not require any additional electrical energy to operate.

The Hall effect describes the occurrence of an electrical voltage in a current-carrying conductor that is located in a magnetic field. Sensors based on this principle that are integrated into circuits are known as Hall switches. By comparing the Hall voltage with defined threshold values, the output signal is switched to the states H (high) and L (low). Various behaviors such as switch, latch and omnipolar can be generated, taking into account the direction of the magnetic field. The output stage can be designed as an open drain/open collector or push-pull.

TMR technology stands for Tunnel Magneto Resistance and is mainly used in modern magnetic sensors and MRAM memories (Magnetoresistive Random Access Memory). TMR is based on the quantum mechanical tunnel effect. Electrons "tunnel" through a very thin insulator layer between two ferromagnetic layers. The electrical resistance depends on whether the magnetization directions of the two layers are parallel or antiparallel. Parallel stands for low resistance and antiparallel for high resistance. The relative change is often very large, which makes TMR sensors very sensitive and precise. The advantages of this TMR technology are low power consumption and high sensitivity to magnetic fields.

Both Hall effect switches and TMR effect switches have better properties than reed switches or mechanical switches. Magnetic switches of these two technologies are characterized by a very fast switching behavior, are vibration-resistant, available in different switching modes and have a practically unlimited number of switching cycles. The power consumption of some types is lower than the self-discharge current of a rechargeable battery or battery as a power supply. (mk)

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