Duty (cycle)

In periodic phenomena, this is the ratio of a 'certain period' to the 'period during which the phenomenon continues within that period'. In the motor control scheme shown in (a) and (b), this refers to the high-voltage period T_H to one cycle T_o as depicted in fig. (c).
Principle of varying mean voltage applied to the motor by PWM. The average voltage can be adjusted by the pulse-width ration T_H/ T_o).