Blocking circuit for thyristors

#This invention relates to DC circuit systems and particularly to thyristor circuits.

#It is known in the prior art that thyristors, which are used as electronic switches in DC circuit systems, are easily triggered but difficult to block. Reverse blocking must be done with a high power current pulse which has the duration of the thyristor settling time and which absorbs the full power of the thyristor current rendering the thyristor currentless. Generally, the power pulse originates from a suitable capacitor which might be switched into the main thyristor circuit for blocking purposes.

#The present invention eliminates the need for a plurality of capacitors and power sources where a number of thyristor circuits are involved. The power pulse for all thyristors is drawn from a common circuit arrangement with a DC power output and a switching transistor. Auxiliary thyristors may be provided for double-pole locking.

#Other objects and advantages of the invention may be more clearly seen from the following description when viewed in conjunction with the accompanying drawings wherein:

#FIG. 1 is a circuit diagram of the invention, and,

#FIG. 2 is a partial circuit diagram of a second embodiment of the invention .

#Referring now to FIG. 1 of the drawings, the invention comprises a blocking circuit 10 for thyristors which is coupled to a plurality of thyristor circuits 20, 30 and 40. Since the thyristor circuits 20, 30 and 40 are essentially similar, the circuit details are illustrated only in the first circuit 20.

#The blocking circuit 10 includes a transformer 11 which is connected to a power supply 12 and to the rectifier 13 in order to supply current to the capacitor 14. The high-power current pulse for reverse blocking of the thyristor 15 in circuit 20 or a corresponding thyristor (not shown) in circuits 30 and 40 originates from the capacitor 14. Thus, the power pulse for blocking all the thyristors 15, etc. is drawn not from a plurality of capacitors, but from a single capacitor 14 and a source 12. A conventionally biased switching transistor 16 is also employed within the blocking circuit 10 to direct the blocking power pulse in a predetermined manner.

#The power pulse from the blocking circuit 10 is switched into the thyristor circuit 20 through an auxiliary thyristor 17. The capacitor 14 is coupled to the circuit 20 in such a way that the auxiliary thyristor 17 becomes blocked by itself after discharge of the capacitor 14. The size of the capacitor 14 is related to the thyristor switch power since reverse blocking must be accomplished with a high power current pulse having the duration of the thyristor settling time.