According to the coordinates of the working quadrant of the thyristor, we know that it is possible for the triac to work in the fourth quadrant, but not all of the triacs support working in the Q4 quadrant.
For a 4-quadrant thyristor, although it can work in all quadrants, it is necessary to avoid working in the Q4 quadrant in practical applications.
On the one hand, it is considered to be compatible with the 3-quadrant thyristor design, which can ensure that the circuit can still work normally when other thyristors are replaced;
Secondly, the thyristor working in quadrant 4 has low sensitivity, is easy to be triggered by mistake, and has weak dIT/dt capability and is easy to damage.
Finally, operating at the Q4 quadrant, gate drive requires a higher drive current.
Therefore, the Q4 quadrant should be avoided as much as possible in the design, which is also the consideration of why we should design the power supply as a negative voltage output under non-isolated drive.