Reed Switch Basics: Operation, Manufacturers, and Applications

As we know, relays operate comparatively slower. Hence, for fast switching, they are not useful. For such fast switching applications, such as in a telephone exchange, reed switches are used.

The reeds are thin strips of easily magnetizable and demagnetizable material. They are usually manufactured such that the reeds are sealed in a glass tube containing inert gas such as nitrogen. This helps reduce corrosion of the contacts.

Let’s explore how a reed switch works, as depicted in the figure with normally open contacts. The switch is operated either by bringing a magnet near or by passing a current through the coil surrounding it. By doing so, the reeds get magnetized and attract each other, completing the electric circuit. They get separated when the magnet is removed or the current flow stops through the coil.

The circuit shown is used to protect transistor-controlled relays and reed switches. As shown, when the current in the coil of a reed switch falls to zero, a large voltage gets induced in the coil due to its inductance. This voltage could damage any transistor used to control the current in the coil, as shown.

If a diode is connected in reverse bias for the supply voltage, it offers an easy path to the induced voltage. This stops it from building to a very high voltage.

Reed Switch Manufacturers

Following are some reputed reed switch manufacturers:

1. MEDER electronic
2. Hamlin electronics
3. Reed Relays and Electronics
4. Standex Electronics
5. Mouser electronics
6. STG Germany
7. HSI Sensing
8. Comus international
9. Jameco Electronics
10. Littelfuse
11. Cherry electrical products

Littelfuse has recently released a high-precision extension to its reed switch product lineup. The part numbers are MACD-14 and MASM-14 (surface mount version) series. They have the following silent features:

• Switching capability of 200V DC at up to 10W power.
• Sensitivity range: 10-30 AT
• Hermetically sealed to withstand harsh environments
• Through-hole and surface mountable