| 摘要 |
1537398 Control of D.C. motors K VOCKEKTHUBER & R HAUSER 30 Sept 1976 [13 Oct 1975] 40587/76 Heading H2J A D.C. motor 1 driving a tape is rotated in one direction by on/off switching of a transistor T1, whose mark/space ratio may be determined by the constant speed control loop (7, 8) of a known motor control system, Fig. 1 (not shown), the motor current being maintained during transistor OFF periods by energy discharge from a choke 12 through a thyristor 17, and is rotated in the reverse direction by application of a signal 16 which turns off thyristor 17 and turns on a transistor T2 connected via Zener diode 14 to a tap 120 on the choke 12, the arrangement being such that when transistor T1 is switched on it completes a circuit from D.C. source 3 via members T2, 14, 12, thus causing the choke 12 to act as an autotransformer and pass reverse current through the motor via members T2, 14. Speed control in the reverse direction is again provided by on/off switching of transistor T1. In a modification, Fig. 3 (not shown), the transistor T1 is replaced by a Darlington pair (T3) and the choke 12 has a winding extension (19) whose end, with that of the main choke winding, is connected to a respective collector of the Darlington pair. |
