nightcatz said:
gayan....where should i keep the back emf proection diode,can utell me how should i choose the relay according to the component ...pls explain
A RELAY is an Electrically Operated Switch. The Relay allows one circuit to switch a second circuit which can be completely separate from the first.
This is happening when the Current flowing through the coil of the relay creates a magnetic field which moving a lever and changes the switch contacts.
When choosing a RELAY these basic things are very important.
* Coil voltage
* Coil resistance
* Switch ratings
You can see the coil voltage it’s printed on the relay.
You can measure the coil resistance in the relay by the multimeter.
Let say you choose a 5V relay & its resistance showed you 400 ohms.
According to the ohm’s law you can calculate the current required to the coil.
5/400 = 0.0125 A
So the relay driving circuit must provide these requirements.
Regarding switch rating its better you choose big values for the safety matters.
The switch rating is also printed on the relay.
Ex: 230V/10A …..It means it can handle 10A load by the 230V AC mains.
Also there are some different kinds of relays
SPDT, DPDT, Reed relays etc…..
To control one application or two you can use a SPDT relay.
The back EMF protection diode is in the correct place in your picture.