One-Quadrant Drive
The simplest form of drive, in which the motor is run in only one direction and only in the driving (motoring) mode. A single power switch and one freewheeling diode are enough; braking and reverse direction are not supported, and stopping happens by free deceleration.
The speed–torque plane is divided into four regions; a one-quadrant drive uses only one of them, the region of positive speed and positive torque. The motor consumes energy and never produces it. Applications that are unidirectional and do not hold a load against gravity, such as fans, pumps and conveyors, fall into this class.
It is the cheapest structure in hardware: a single low-side MOSFET, a freewheeling diode across the motor and a controller generating the PWM are enough. Compared with an H-bridge, both its cost and its failure surface are smaller.
Its limit is clear. If direction changes are wanted you need a bridge structure, and if controlled braking is wanted you need at least two-quadrant operation. Because typical AXI applications such as automatic doors, barriers and linear actuators require both forward and reverse motion, they are naturally solved with H-bridge based modules; the ST42 is the plainest answer to this need, providing forward–reverse and on–off control.
Where this term is used: DC Motor Driver Selection Guide