Newton C. Braga
For many, the relay is considered a component overcome, but this is not true. The basic function of controlling a circuit from a signal via a switch controlled by voltage or current, it still requires a multitude of applications. It is clear that the relay in its traditional form can, in many cases be replaced by solid state versions, but this is not a rule. The important thing to remember is that, despite everything, he is still an indispensable component.
It is for this reason that concerned about it, the manufacturers of these components have been improving, creating ever more efficient components, whether electromechanical, whether solid state.
Types
Today we rely primarily on two types of relays. The first is the traditional electromechanical relay, consisting of a coil where it is applied the control signal and a set of contacts that controls the external circuit, as shown in Figure 1.
This type of relay has the advantage of completely isolating the control circuit of the controlled system and also address current in both directions, or perform complex switching functions.
The disadvantage is in the operating speed (slow), noise and fire arcs produced when the contacts and reliability (low) because it is an electromechanical system.
Of course, many electromechanical relays are still used very elaborate designs that improve their performance in relation to ancient types. The use of magnets in conjunction with the coil in order to polarize the magnetic circuit, thereby increasing the sensitivity and speed of response, is an example of resources that we find in modern electromechanical relays.
The second type of relay is the Photo MOS, mainly composed of an infrared LED emitter and a photosensor system that controls one or more field effect transistors power (Power MOS), as shown in Figure 2.
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