| 摘要 |
<p>A pulse control circuit for a d.c. series motor 10 having an armature 12 and two opposite-wound field windings, 14<Sub>F</Sub> and 14<Sub>R</Sub>, comprises two semiconductor static switching devices, such as thyristors 22<Sub>F</Sub> and 22<Sub>R</Sub>, each connected in series with the armature 12 and a respective one of the field windings 14<Sub>F</Sub>, 14<Sub>R</Sub>, control means 32 for varying the mark-to-space ratio of conduction of each switching device thereby to vary the mean voltage applied to the motor, one or other of the switching devices being brought into operation to energise the associated field winding in dependence on the desired direction of drive of the armature. The control means 32 is adapted, when the mark-to-space ratio of one of the static switching devices 22<Sub>F</Sub> or 22<Sub>R</Sub> has been brought to a predetermined maximum valve, to cause simultaneous operation of the other static switching device 22<Sub>R</Sub> or 22<Sub>F</Sub> at a lower mark-to-space ratio thereby to energise the associated field winding 14R or 14<Sub>F </Sub>so as to reduce the net flux in the motor 10 and further increase the motor speed.</p> |
