GB1112606A - Improvements in current control - Google Patents

Abstract

1,112,606. Inverting. GENERAL ELECTRIC CO. 12 Aug., 1965 [14 Aug., 1964], No. 34608/65. Heading H2F. [Also in Division G3] A control system for maintaining constant the tube current of an X-ray tube 10 comprises: an amplifier 11 which compares a reference voltage derived from a Zener diode 15 with a voltage which is proportional to the tube current and which is derived from a potentiometer 12 connected to an accelerating electrode of the tube 10; a pulse generator 16 producing trigger pulses at a repetition frequency controlled by the error signal at the output of amplifier 11; and an oscillator 22 including a thyristor 23 which is triggered by the pulses from generator 16 to produce gating pulses for an inverter 28 supplying the current for the emitting electrode 35 of the tube 10 whereby the frequency of this current is controlled in dependence upon variations in the tube current so that the latter, being determined by the emission characteristics of the electrode 35, tends to remain constant. A D.C. source 44 powers the circuits 11, 16 and 22. A resonant transformer 46 supplies the high-voltage accelerating electrodes of the tube 10, and the D.C. input voltage to the inverter 28 is derived, over rectifiers 47, 48 and a capacitor 49, from a winding 45 on this transformer. The inverter 28 comprises a thyristor 29, a capacitor 30 and a saturable transformer 31 having a square loop characteristic, the cathode 33 of thyristor 29 being connected to an intermediate point C on a winding 34 of transformer 31, and the control electrode 65 of the thyristor being connected to the secondary winding 43 of a signal transformer 27 to the primary winding 26 of which are applied the gating pulses from oscillator 22.