GB1142513A - Firing circuits for controllable rectifier devices - Google Patents

Abstract

1,142,513. Thyrister control circuits. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. 23 Oct., 1967 [26 Oct., 1966], No. 47969/66. Heading H3T. [Also in Division H2F] In a thyristor control circuit, energy stored in a device 5 is applied to trigger a thyristor 1 or la, when a control element 6 or 6a is triggered. In a rectifier circuit, Fig. 5, a capacitor 5 is charged during one half cycle via capacitor 3 and diode 4 and during the other half cycle via capaciter 3a and diode 4a, to a potential determined by Zener diode 9. When sufficiently charged, thyristor 6 or 6a is fired to switch thyristor 1 or la in the bridge rectifier. In order to prevent the thyristor 6 being fired until sufficient voltage has developed, the control circuit of thyristor 6 may include a Zener diode coupled to the capacitor, 5 via a transistor, Fig. 3 (not shown). The Zener diode 9 may be connected to the other side of the diode D. In place of the thyristor 6 a trigger diode (16), Fig. 6 (not shown), a transistor, or a light sensitive device, may be employed. In a further modification, Fig. 4 (not shown), the diode 4 and capacitor 5 are shunted by a diode (13) in series with a resistor (12) to suppress voltage transients. In a still further embodiment, Fig. 8, the control input signal circuit is modified so that the input signal, e.g. a pulse train, applied to terminals 10, 11 is applied to thyristor 1 as well as to thyristor 6. In order to allow capacitor 5 to recharge if the first control pulse fails to fire the thyristor 1, the thyristor 6 is blocked by transistor 31. The trigger drive to thyristors is applied via capacitor 35 to delay the switching of transistor 31. This modified form of drive prevents indeterminate triggering which may damage the device 1 when using an inductive load. The capacitor 5 may be replaced by a secondary cell.