| 摘要 |
1,143,774. Transistor pulse circuits. MULLARD Ltd. 24 Feb., 1966 [29 March, 1965], No. 13150/65. Heading H3T. [Also in Divisions G3 and H2] In a three-phase A.C. supply circuit for an electrically-heated temperature-controlled furnace, of the type in which the current in each phase is controlled by a respective thyristor connected in parallel with an oppositely-poled diode, Fig. 1 (not shown), each trigger circuit 12, 13, 14 is energized from the other two phases of the supply to ensure that the trigger circuits are balanced and the phases operate with a constant time relationship. As shown in Fig. 3, the circuits 12, 13, 14 are energized from the secondary winding 15 of a synchronizing transformer connected to the main A.C. supply, and the trigger circuit for the red phase (shown in Fig. 4) is supplied at terminals 21, 22 from the yellow and blue phases respectively and is connected at 47 to the star point of the transformer 15. Voltage exists across the lines 26, 28 for a period of 300 degrees, Fig. 5 (not shown), thus enabling a capacitor 42 to charge through members 39, 40, 41 until, at a predetermined voltage, transistor 34 conducts to supply a pulse to the red phase thyristor via transformer windings 37, 43 and terminals 44,45. Regeneration takes place as in a blocking oscillator and capacitor 42 discharges when the voltage across the Zener diode 27 falls to zero. The charging rate of capacitor 42 is determined by a signal, representative of furnace temperature, applied across terminals 46, 47, automatic temperature control by varying the firing instants of the thyristors thereby being achieved. Resistor 41 may be made large to improve the temperature stability of the circuit, since the period during which power is supplied at terminals 21, 22 is 300 degrees whereas the actual control period for the thyristor is 210 degrees, Fig. 5 (not shown). |
