Chopper Drive
It is the type of driver that adjusts the average armature voltage by rapidly chopping a fixed supply voltage and applying it to the motor in pulses. Because the switch is either fully on or fully off its losses are low, and because the voltage can be raised starting from zero its start-up is naturally soft.
The name chopper comes from the fact that it changes the average of a continuous voltage by chopping it along the time axis. As the width of the applied pulses increases, the average voltage the motor sees rises and the speed increases. The motor winding filters these pulses into a relatively smooth current.
The efficiency advantage comes from the way the switch operates. When off there is no current through it, when on there is almost no voltage across it; the loss occurs only in the channel resistance and during the transitions. If you tried to achieve the same speed reduction with a series resistor or linear drive, the voltage dropped would turn directly into heat.
The second natural benefit of the chopper structure is the start-up behaviour. Because the voltage can be raised starting from zero, the current surge stays limited; for this reason a separate soft starter is generally not needed for DC drivers. On modules that allow the ramp time to be adjusted, this behaviour is opened to user control: on the PT500 the RMP trimmer sets the ramp and the HIZ trimmer sets the target speed.
The context in which this term is used: DC Motor Driver Selection Guide