GB1507716A - Method and circuit arrangement for the transmission of turn-on pulses for controlled semi-conductor devices - Google Patents

Abstract

1507716 Firing circuits for thyristors BBC BROWN BOVERI & CO Ltd 25 July 1975 [27 July 1974] 31188/75 Heading H2F Thyristors 17, 18, which may form part of a three phase converter bridge, are fired by transmitting turn-on pulses from a electronic control circuit (not shown) connected to earth, turn-on energy and turn-on information being transmitted from the control circuit through a common isolating transformer 2 as at least two rectangular constant amplitude pulses of alternately opposite polarity, a preliminary pulse being used to cause storage of the turn-on energy preparatory to turning on the thyristors and a following turn-on pulse being used to turn-on an electronic switch which transmits the stored energy to the control electrodes of the thyristors to turn them on. In Fig. 1 the control circuit produces a long turn on pulse, which is converted to a high frequency rectangular A.C. voltage of the same duration (Fig. 2a) applied to the winding 2 to produce the following operations: (1) with the voltage beginning so that winding end 3 is positive, capacitor 7 is charged through diode 5 by the first voltage half cycle to produce, with diode 6, the voltage of Fig. 2a (2) the second voltage half cycle produces a rapid voltage rise at winding end 4 and hence rapid firing of thyristor 9 through members 10, 11; (3) capacitor 7 discharges through members 9, 13, 16 to produce the turn-on current 15 Fig. 2d for thyristors 17, 18, the current being maintained by the voltage of Fig. 2a (as rectified by diodes 5, 6) until the pulse producing it is terminated. Capacitor 7 has a large capacity to smooth the turn-on current and ensure that interference pulses transmitted through transformer 2 cannot charge the capacitor sufficiently to exceed the breakdown voltage of Zener diode 13. In a modification a relatively short turn-on pulse is transmitted through transformer 2 as a negative pulse (t 1 t 2 ) to charge capacitor 7 followed by a positive pulse (t 2 t 3 ) to turn on the thyristors, Fig. 3 (not shown).