Abstract: A protection circuit for protecting the thyristors of a series circuit of several thyristors, each of which has a corresponding firing circuit to which its anode-cathode voltage is applied.

Abstract: The invention concerns a circuit arrangement for firing a controlled semiconductor valve, particularly a thyristor, the control path of which is connected to a d-c voltage source by way of the collector-emitter path of a transistor. In order to obtain a control electrode current at the semiconductor valve, which is independent of the d-c voltage of the d-c voltage source and the control electrode characteristic of the semiconductor valve, provision is made, according to the invention, that a resistor is arranged in series with the collector-emitter path of the transistor, and that a Zener diode is connected between the base of the transistor and that terminal of the resistor which is facing away from the transistor.

Abstract: The invention concerns a circuit arrangement for firing an electric valve, particularly a thyristor, with a pulse capacitor which can be charged from the a-c voltage at the anode-cathode path of the electric valve by means of an external resistor and can be discharged by means of a contactless switching device for firing the electric valve by way of its control path. To increase the firing performance, there is provided in parallel to the anode-cathode path of the electric valve a series circuit comprising an external resistor and the primary winding of a transformer the secondary winding of which is connected to the pulse capacitor by way of a rectifier.

Abstract: The invention relates to a circuit arrangement for the simultaneous ignition of a plurality of thyristors. Control paths of the thyristors are each connected to a secondary winding of a pulse transformer by way of a separate full-wave rectifier, an alternating current of higher frequency being supplied to the primary winding of the pulse transformer by a control current amplifier. In order to obtain a continuous flow of control current when a control signal is given, it is provided, according to the invention, that there is connected to the control path of each thyristor the series arrangement of a storage reactance coil and an uncontrolled diode poled in the direction of the gate current, and that the output of the full-wave rectifier is connected to this uncontrolled diode.