It doesn’t.
There needs to be a common terminal between the drive circuit and the triac.
Like this:
Also note the snubber circuit, not a diode, across the motor
It doesn’t.
There needs to be a common terminal between the drive circuit and the triac.
Like this:
Also note the snubber circuit, not a diode, across the motor
MT1 is connected to live. The trigger voltage is the voltage between gate and MT1. Therefore a supply of -5V DC referred to LIVE is required to provide the trigger voltage.
The triac operates in quadrants 2 and 3.