| 摘要 |
1,103,716. Converting circuits, protective arrangements, control of D.C. motors. W. J. BROWN. 11 Feb., 1966 [19 Feb., 1965], No. 6141/66. Headings H2F, H2J and H2K. [Also in Division G3] In a control circuit for a dynamo-electric machine the current supply to the machine is controlled by the current flowing through a free-wheel diode connected across it. In one embodiment, Fig. 12, current through free-wheel diode 311 and the voltage from a manual speed control 602 are fed to a magnetic amplifiers 1106 which generates the firing pulses for the SCR 307. Any increase in the load on a series wound motor 501 varies the current through diode 311 and increases the firing angle of the SCR to compensate for this increased load requirement. To provide overload protection, the current through the diode 311 is fed to the heater 902 of a thermal switch so that an excess current existing for a predetermined time opens contacts 903 to disconnect the supply to the motor, a resistor 1001 and indicator 1003 providing a current path to maintain the contacts open. The current through the diode 311 is higher at low motor speeds, so that the circuit will trip at a lower motor current at low speed, than at high speed. In a modification. Fig. 14 (not shown), the trip circuit shorts out the trigger pulse circuit to the SCR to prevent it firing. Modifications of the control circuit are also described in which the control of the free-wheel diode only becomes effective above a threshold level determined by a Zener diode, Fig. 7 (not shown), or a bias circuit, Fig. 8 (not shown). The overload cut-out circuits may also be employed without the control circuts, Figs. 9, 10, 11 (not shown).
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