Relay and TRIAC

          Relay is an Electromechanical switch. I used it to control heavy current devices with Microcontroller. Signal from the microcontroller goes to transistor which controls the relay.

         Now I want to replace it with TRIAC. TRIAC is an electronic component which can conduct in both directions, so it is suitable for AC. I am using BT136 TRIAC to control home appliances with microcontroller. It has current rating of 4 A and gate current 25 mA and holding current 20 mA. Gate voltage is  0.7 -1.5 V.

Advantages of TRIAC over Relay

1. No Wear and Tear
2. No Electromagnetic Interference with other circuits
3. Very low gate voltage(0.7-1.5V) and current compared to relay
4. No need of Transistor
5. No contacts which can Weld

Circuit for interfacing of TRIAC with Microcontroller:

       Also it is very easy to control the output voltage with the TRIAC by controlling the firing angle of TRIAC which is not possible with Relay. So these are the Reasons due to which I am using TRIAC instead of Ralay.

Circuit to control the output voltage by changing the firing angle: