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triac negative gate current

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May 27, 2010
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negative gate current for triac

Hi all,

I need to do mcu based triac for inductive load. Microcontroller will decide when to open and close triac.
As much as i have learnt, there are 4 quadrants to drive triac. and fourth quadrant is not good. So it needs to be done with 2. 3. quadrants.

For that i need to give negative gate current to triac (please correct me, if i am wrong).
Does anyone know, how to create negative gate current for Triac, from Microcontroller?
Thanks a lot
Best regards

On a microcontroller, the usual way to power it is
Vdd= +5, and Vss =0 = common

To create negative current sourcing, it must be powered the other way around.
Vdd= 0 = common, and Vss = -5.

If this confuses you, there are Triacs which are specified to be triggerable in 4 quadrants, like these:

The 4th quadrant trigger current will always be higher than the other three.

Or you can use a Triac optocoupler like the MOC3020 and trigger on quadrants 1 and 3.

thanks for your answer.
i should use 3 quadrant i think, because of my inductive load.

Can i use optocoupler with a microcontroller(microcontroller will give order and optocoupler will create positive and negative impulse),
can it be done like on the photo below?(it will be then 1. and 3. quadrants)

Read the MOC3020 datasheet for the proper driving circuit and snubber.

There are optocoupler variants that require lower LED current (around 5 mA) to trigger properly. I would recommend to use those, to reduce the microcontroller's current output.
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