Triac

[Gantronics]

Hello ...

I have a question about Triac ...

As I understand the Triac is a trigger conditioned "wire" ...

So I connected Terminal1 of the Triac to the cathode of the LED and the anode of the LED to a resistor then to the +Ve of the battery and terminal2 of the Triac to the -Ve of the battery then I triggered the triac by connecting the gate to the +Ve of the battery then the LED gave light (The circuit diagram at the right of the attached picture)...

And that is what suppose to happen ...

Then I connected Terminal2 of the Triac to the cathode of the LED and the anode of the LED to a resistor then to the +Ve of the battery and terminal1 of the Triac to the -Ve of the battery then I triggered the triac by connecting the gate to the +Ve of the battery then the LED DID NOT gave light (The circuit diagram at the left of the attached picture)...

And that is what NOT suppose to happen ...

Can someone tell me what is it?...

Isn`t current suppose to go both ways from T1 to T2 & from T2 to T1 ?...

Is it me that understood the triac wrong or that triac I used was not good or what?...

And thanks ...^_^...

 

[dr pepper]

I might be wrong here, however I think the trigger voltage is sposed to be positive referenced to mt1.
You should also have a resistor in series with the gate.

Some triacs have different trigger currents for forward and reverse conduction too.

Try another battery for the trigger and put say a 100r resistor in series with the trigger.

 

[KeepItSimpleStupid]

The actual p/n matters A LOT. All points above are on the money especially the resistor. Triggering is all about quadrants. Each quadrant may have different characteristics.

Also pay attention to minimum currents from MT1 to MT2.

 

[MrAl]

Hi,

I agree with the comments about MT1 and the gate. To turn a triac on you apply a drive signal to the gate but it must be relative to the MT1 only. So if you use a battery with a resistor in series, the resistor goes to the gate and the battery other terminal goes to MT1 always. So you apply a signal between the gate and MT1 only.

Now depending on what triac you are using, you may be able to trigger it with either a plus or minus signal. Some triacs only work with certain polarities so you have to check the data sheet.

The polarity of the main power battery however can be plus or minus with respect to the MT1.

So that means you have two polarities (like two batteries) to think about. The polarity of MT1 with the load and main battery and MT2, and the polarity of the gate with respect to MT1 only (the smaller battery).

To test then you should use two batteries. One to drive the load and one to drive the gate (through a resistor). To test the LED with the reverse main battery polarity, simply reverse the battery and reverse the LED, then try using the small battery to drive the gate in both polarities by making the gate positive and then reversing the small battery to make the gate negative.
So that means four tests are required:
1. Main battery forward, LED forward, gate positive
2. Main battery forward, LED forward, gate negative
3. Main battery reverse, LED reverse, gate positive
4. Main battery reverse, LED reverse, gate negative

As Keep mentioned you also have to make sure you use enough gate current but dont overpower the gate either. You also want to look at the hold current (data sheet) because if the LED doesnt draw enough current the triac may turn off when the gate signal is removed (and it should really stay on).