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Triac quadrant operation.

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Suraj143

Active Member
I’m trying to detect a zero cross & fire the triac after a delay angle to dim an AC bulb.

The microcontroller will detect ZX nicely & it’s controlling the triac gate input.

My only problem is on every quadrants do I have to apply positive supply to the gate?

Or do I have to apply negative supply to the triac gate?

Because my uC has only a 5V supply.
 

crutschow

Well-Known Member
Most Helpful Member
A triac will normally trigger in all four quadrants with either polarity gate voltage. The triac data sheet should show that.

Is you AC supply isolated from the mains? If not you either need to provide such isolation, or use an opto isolator to drive the triac gate.
 

mneary

New Member
My only problem is on every quadrants do I have to apply positive supply to the gate?

Or do I have to apply negative supply to the triac gate?
Please clarify: Have you built it and it doesn't work? Or are you asking for design hints?

Any triac probably will work to some extent in all 4 quadrants, but most that I've seen are significantly more sensitive in some quadrants than others. In either case, the triac part number would help you receive an answer that doesn't have to include the words 'probably' and 'most'....:rolleyes:

There's a little known issue with triacs that has probably burned out many a microprocessor. When they are conducting, a significant amount of current is available on the gate pin, in phase with the load current. When the load current is negative, this current is negative, and if you connect directly to the processor I/O it might not like it. :eek:
 

Suraj143

Active Member
Hi for both of you thanks for the response.I'm using TIC206 Triac.

I'm driving the gate pin via a 470R resistor from the uC pin.

The uC detects ZX.On every 10mS time (50Hz) it will detect ZX.

When it detects rising edge on ext interrupt pin I turn on a timer for the desired angle.After timer value expires I'll apply positive trigger signal to the triac.

Same applies to the negative side.When it detects falling edge on ext interrupt pin I turn on a timer for the desired angle After expires the timer I'll apply positive trigger signal to the triac.

Now you see in both side wave forms I'm applying positive signal.

Is this the correct way?I still cannot understand what gate trigger voltage positive or negative to provide in all four quadrants?
 
Last edited:

Suraj143

Active Member
I have the datasheet of my triac can somebody view it & tell how to drive the gate considering what polarity on gate voltage.
 

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