Abstract: The pulse voltage for the electrode (12) of a dust separator (10) is generated by a thyristor circuit (19) to be transferred to a dust separator through a transformer (16). It being possible that voltage arcings take place at the dust separator (10), there is the risk, in case of a blocked thyristor (20) that from the secondary of the transformer (16) a high voltage is produced at thyristor (20) to destroy the thyristor. To avoid such an occurrence, a detector (27) is provided which is only responsive to sudden voltage drops whereupon the thyristor (20) is enabled to become conductive so that the energy of the secondary circuit may be discharged to the storage capacitor (24) in the primary circuit.