Abstract: The anode and cathode of an X-ray tube are connected to a high-voltage power source respectively, through corresponding tetrode tubes, and the center metal electrode of the X-ray tube is grounded. The tetrode tubes are simultaneously turned on and off upon receipt of a control signal. An abnormal current, which flows through the center metal electrode due to a short-circuiting fault of the tetrode tube connected to the cathode of the X-ray tube, is detected during an OFF period of the tetrode tubes. Upon detection of the abnormal current, the tetrode tube connected to the anode of the X-ray tube is forcedly turned on, thus preventing the fusion of the center metal electrode in the X-ray tube.

Abstract: A capacitor connected between the anode and cathode of an X-ray tube through an X-ray switch is charged by a DC output voltage including ripple component from a rectifier connected to the secondary of a high-tension transformer. The primary of the high-tension transformer is connected to a switching circuit. A switching control circuit produces a turn-on signal for the switching circuit when a pulse signal derived from a phase detector in synchronism with a given phase of the ripple component, an X-ray exposure instruction signal and a charge instruction signal formed in a comparator are logically processed, and a turn-off signal when the charge voltage of the capacitor reaches a given value. The switching circuit is ON-OFF controlled by the switching control circuit.