Anonymous
Anonymous asked in Science & MathematicsEngineering · 7 years ago

# what is an electronic relay?

for homework i was stuck with this question and it is what is a electronic relay.

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• Anonymous
7 years ago

An electronic relay is a solid state device. A common electromechanical relay uses an electromagnet to close the circuit. A solid state relay does not use an electromagnet.

A semiconductor is used to close the circuit. Transistors(BJT, FET) and thyristors(SCR, TRIAC) can be used as electronic relays.

• 7 years ago

an electromechanical relay uses electromagnets to move contacts.

an electronic relay is a device which *mimics* significantly how an electromechanical relay controls a large current/voltage using a small control signal BUT it's built using semiconductors.

the "How" an electronic relay works is different, but from just "looking at the box", the inputs/outputs/ general behaviour looks quite similar, so if you didn't know what was in the box, you'd might be tempted to assume they were build/work in similar way, see http://en.wikipedia.org/wiki/Black_box

eg an optocoupled TRIAC has a 4 terminals. pair 1 are like a relays contacts, and pair 2 are for the control signal. When a signal is passed through the control pair (one side could be to ground), an internal LED lights up. in effect light from that LED falls on a photodiode which generates a small voltage/current when is fed to the Gate of a normal TRIAC and turns it. Provides very good electrical isolation, and decent current handling capacity just like a electromechanical relay. Difference is TRIACS don't turn off until the current drops to very low levels. That's not usually a problem for AC use, as the current stops for a short time every "1/mains frequency" seconds. Can even be useful in DC as a latching relay.

So for AC where the device is just to be turned on off at up to mains frequency times a second use of an electromechanical relay can often substituted with an optocoupled TRIAC electronic relay. An optocoupled TRIAC might even be a better solution- so long as it's rating aren't exceeded, there's no "limited number of operations", like there is with electromechanical relays.

• Anonymous
7 years ago

I come at the is a different way:

a relay uses a small current to operate an electro magnet which pulls an armature to operate springs to switch current in a somewhat more powerful circuit. That's an electromechanical device such as the relay to flash car headlights, for example.

Doing that electronically is doing it with no moving parts in a semiconductor device. Now if I remember my electronics from years ago, a power transistor in common base will pass current from the collector to the emitter when the potential or bias on that base is correct.

The base has a high impedance and so only draws a small current from the switch to operate the device and so the lamp. The ratio of what the transistor can switch to the current used to bias it is known as the transistor's gain.

So connecting the collector to the power rail, the lights to the emitter and earth, makes the main circuit equivalent to the relay contacts which are waiting to be energised. When the small current is applied to the base, the transistor switches and passes the current to the light. It's a solid state version of the relay.

• 7 years ago

Rellay is an electric operated switch. Relay are used where it is necessary to control a circuit by a lower power signal. A relay can handle high power reqquired to directly control an electric motor.

• 7 years ago

Electronic is an Electrical Switch

when power is given to relay then there is a electromagnetic system which change the pole then ur switch is turn on, it remain on until and unless power is on

when power is off then electromagnet discharge then it change to pole then switch is turn off....

• 4 years ago

There are IC analog switches that are SPDT such with the aid of fact the MAXIM MM74HC4066 that can paintings for you. The proscribing factor would be present day draw throughout the chip. you are able to continually use the chip to force man or woman JFET or ability Transistors.

• 7 years ago

A relay is a switch, it uses a relative low current cicuit to operate a switch on a much higher current circuit by using a electromagnetic coil.

• 7 years ago

basically an electrical current creates a magnetic field which activates a switch to turn something off or on.

Source(s): facts