Electrical Relay Definition
Relays are electrically operated switches that open and close the circuits by receiving electrical signals from outside sources. Some people may associate “relay” with a racing competition where members of the team take turns passing batons to complete the race.
The “relays” embedded in electrical products work in a similar way; they receive an electrical signal and send the signal to other equipment by turning the switch on and off.
For example, when you push the button on a TV remote to watch TV, it sends an electrical signal to the “relay” inside the TV, turning the main power ON. There are various types of relays used in many applications to control different amounts of currents and number of circuits.
Electrical Relay Types and Classification
Relay technology can be divided into two main categories: Movable contacts (mechanical relay) and no movable contacts (MOS FET relay, solid state relay).
This type of relay has contacts that are mechanically actuated to open/close by a magnetic force to switch signals, currents and voltages ON or OFF.
Unlike mechanical relays, this type of relay has no moving contacts but instead employs semiconductor and electrical switching elements such as triac and MOS FET. By the operation of these electronic circuits, signals, currents and voltages are switched ON or OFF electronically.
Electrical relay Structure and Operating Principles
Relay consists of a coil, which receives an electric signal and converts it to a mechanical action and contacts that open and close the electric circuit.
Let's take a closer look at how a lamp is turned on using a switch and a relay.
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MOS FET relay is a semiconductor relay that uses power MOS FETs in output elements.
MOS FET relay consists of the following three components:
1.
LED ( light-emitting diode ) chip
2.
PDA ( photodiode array ) chip
*Photodiode Array ( solar cell + control circuit )
3.
MOS FET chip
*Metal Oxide Semiconductor Field Effect Transistor ( metal, oxide, semiconductor, field, effect, transistor )
MOS FET relays operate according to the following principles.
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Electrical relay Characteristics and Mechanism
One of the major characteristics of a mechanical relay is the physical spacing between the coil and the contact component in order to achieve appropriate level of insulation (insulation distance) on both input and output.
The electromagnet attracts the armature.
The combination of fixed and movable contacts opens and closes the control circuit.
One of the major characteristics of a MOS FET relay is that it utilizes semiconductor so the contacts do not mechanically open/close. As a result, benefits include reduction of footprint, quiet operation, longer operating life, and eliminating the need for additional maintenance.
Ultra small and weight In addition to SSOP and USOP, our new ultra-compact VSON package size offers substantial space-saving of the entire system. Low driving current The standard driving current should be 2-15 mA. Ultrasensitive models are also available featuring drive currents as low as 0.2 mA(max), allowing it to conserve energy of the entire system. Longer operating life The structure uses light signal hence no contacts; avoids reduction of life caused by contact wear and extends its operating life. Small leakage current MOS FET relay can withstand external surge current without addition of snubber circuit. Under normal condition, leakage current is about 1 nA or below and very small leakage when closed. (Model: G3VM-□GR□, -□LR□, -□PR□, -□UR□) Excellent shock resistance All the internal parts use casting method and no movable parts are used; increases resistance to shocks and vibrations. Silent operation Unlike an electromechanical relay, MOS FET relay does not use mechanical contacts; hence, no switching noise, contributing to silent system operation. High insulation Allows electric I/O isolation by converting voltage signal into light signal for transmission. The standard models offer withstanding voltage of 2,500 VAC between the input and output. Superior products offering 5000 VAC are also available, achieving high insultation level. High-speed switching Achieves 0.2 ms (SSOP, USOP, VSON) of switching time; much faster speed compared with the mechanical relay (3 to 5 ms), achieveing quick response performance. Accurate control of the micro analog signal Compared to the triac, MOS FET significantly reduces the dead zone, allowing very little occurrence of input waveform distortion of the micro analog signal to correctly convert into output waveform.When voltage is supplied to the coil, small current passes through the coil, resulting in a larger amount of current passing through the contacts to control the electrical load.
AC loads can also be electrically controlled (Switching) from DC power source.
One input signal to the coil can simultaneously control several independent circuits (switched).
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A Control Relay is also known as a Relay, is a switch, an electromagnetic switch. A control relay allows electrical current to flow through a conducting coil that opens or closes a switch. It also protects the circuit current. With a control relay, users do not need to manually turn the switch to isolate or change the state of an electric circuit. Currently, control relays play a crucial role in today’s electronic devices. They are electronic parts that power electronic parts such as motors, power plants, power supply systems, transistors, and many more.
There are different types of Control Relays depending on the operating principle and structural features. Solid State Relays – It uses solid-state components to perform the switching operations without moving any parts. Contactor – A large relay used to switch a large amount of electrical power through its contacts. Electromagnetic Relays – Constructed with electrical, mechanical and magnetic components and have operating coils and mechanical contacts. Hence, when the coil is activated by a supply system, the mechanical contact is either open or close. The supply system has 2 types of AC and DC. Thermal Overload Protection Relay – works on the principle of the thermal effect of electrical energy. When excessive current flows through the circuit, the circuit opens due to the bimetallic strip experiencing an increase in temperature.
Every Control Relay has a Contact type such as SPST-NO but what does it mean?
Poles represent the number of circuits controlled by a switch. Throws represent the number of positions the switch can adopt.
Single Pole Single Throw, SPST, has two terminals that can be connected and disconnected. Including two for the coil, such a relay has four terminals in total. Single Pole Double Throw, SPDT, has a common terminal that connects either one of two others. Including two for the coil, this relay has five terminals in total. Regardless of whether the coil is active or inactive, either ‘A’ or ‘B’ is always resting while the other needs to be the coil to be powered.
Double Pole Single Throw, DPST is equal to two SPST activated by a single coil. Including two for the coil, this relay has 6 terminals in total. Double Pole Double Throw, DPDT is equal to two SPDTs activated by a single coil. Including two for the coil, this relay has 8 terminals in total.