Building triac switching circuit

Other Hardware General Electronics
1

Hello guys

Was thinking to building my first triac switching circuit for home automation. but was just confused about some points in using triac .

  1. Will triac work as active default closed switch bcoz during power failure i want it to automatically in on state

  2. Does it require external power supply? Just like in relay ?

Any tutorial for building triac switching circuit is much appreciated

2
  1. Will triac work as active default closed switch bcoz during power failure i want it to automatically in on state

You'd have to build that into your circuit. You could make it default to "on" by making whatever is driving the TRIAC on by default. If you are using an Arduino, you just initialize the particular output pin as "on" (unless your logic is inverted) and you'll turn it on every time the Arduino is re-started.

You need voltage on the gate in order to turn it on. Once it's on, you can remove the gate voltage and it stays on until power is removed (or until the voltage goes to zero on the next AC zero-crossing).

  1. Does it require external power supply? Just like in relay ?

Well... You'll probably have some kind of control circuit (an Arduino?) which needs a separate DC power supply and the TRIAC is probably switching AC power. You CAN run a TRIAC with just the AC power line voltage and no other power supply. (Look at a schematic for a regular manual light dimmer.)

I assume you are using an optoisolator? You need to isolate your Arduino from the dangerous line voltage. If you don't already have that worked-out yet, look at Figures 10, 11, and 12 on the [u]MOC3023 datasheet[/u]

3

DVDdoug:
You'd have to build that into your circuit. You could make it default to "on" by making whatever is driving the TRIAC on by default. If you are using an Arduino, you just initialize the particular output pin as "on" (unless your logic is inverted) and you'll turn it on every time the Arduino is re-started.

You need voltage on the gate in order to turn it on. Once it's on, you can remove the gate voltage and it stays on until power is removed (or until the voltage goes to zero on the next AC zero-crossing).
Well... You'll probably have some kind of control circuit (an Arduino?) which needs a separate DC power supply and the TRIAC is probably switching AC power. You CAN run a TRIAC with just the AC power line voltage and no other power supply. (Look at a schematic for a regular manual light dimmer.)

I assume you are using an optoisolator? You need to isolate your Arduino from the dangerous line voltage. If you don't already have that worked-out yet, look at Figures 10, 11, and 12 on the [u]MOC3023 datasheet[/u]

Thanks for replying

Yup optoisolator is necessary as I don't need to fried my arduino

What if I want this circuit to use as dimmer? Is it simple by connecting it to pwm pin?

4

saifkazi:
What if I want this circuit to use as dimmer? Is it simple by connecting it to pwm pin?

No.

5

Triacs and thyristors switch off when the main terminal current falls to zero (or near zero),
the voltage will be < 2V whenever the device is on anyway.

The gate requires a minimum current to trigger, again the voltage will always be small.

6

MarkT:
Triacs and thyristors switch off when the main terminal current falls to zero (or near zero),
the voltage will be < 2V whenever the device is on anyway.

The gate requires a minimum current to trigger, again the voltage will always be small.

But coming to external power supply. Don't you feel low power if activated a pin because I feel that when using relay