| 摘要 |
<p>1,137,959. Gating circuits. ENGLISH ELECTRIC CO. Ltd. 13 Dec., 1967 [13 Dec., 1966], No. 55805/66. Heading H3T. [Also in Division H2] A rectified timed output signal is obtained from a plurality of A.C.-fed thyristors which are fired sequentially by a train of pulses gated by a pulse of predetermined duration produced from the leading edge of an initiating pulse. In Fig. 1, such a circuit is used to energize the operating coil 11 of an electromagnetic circuit breaker at a precise instant. Unit 17 produces a pulse for each cycle of each phase of the A.C. supply and applies these pulses continuously to transistor 15. Unit 21 produces long negative pulses of much lower repetition rate which are differentiated by an RC circuit 18-20 and applied to transistor 16 to allow a certain number of pulses from 17 to reach transformer 14 and fire the thyristors T1-T3. These conduct sequentially in successive halfcycles of the A.C. supply and their conduction periods overlap to send a fluctuating D.C. pulse through the coil 11 (Fig. 2f, not shown). The commencement of this pulse is set by the instant of the first pulse from 17 which follows the leading edge of a pulse from 21. The duration of the pulse through the coil 11 can be varied by resistor 20 which determines how many pulses from 17 can pass through the transistors before transistor 16 is cut-off by the end of the differentiated pulse. The unit 17 can be an independent pulse generator of high frequency, in which case the leading edge of the pulse from 21 determines the start of current through the coil 11. The half-wave arrangement of T1-T3 can be replaced by a three-phase bridge using three thyristors and three diodes. Separate trains of phased pulses can be generated for each thyristor.</p> |
