Patent Publication Number: US-5894502-A

Title: High-frequency voltage generator for an X-ray tube

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a high-frequency voltage generator for supplying an X-ray tube, the X-ray tube being of the type having a metallic, centrally disposed part. 
     2. Description of the Prior Art 
     A high-frequency voltage generator for an X-ray tube is known that supplies an X-ray tube of the type having metallic, or centrally disposed part. The cathode current is thereby unequal to the anode current since a part of the current flows off via the grounded metal middle part. Since the positive side of the high-voltage supply then is less loaded than the negative side, an asymmetrical voltage division with a higher anode voltage occurs. Due to the asymmetrical voltage division, thus, a shift of the center point of the high-voltage occurs. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a high-frequency generator for supplying an X-ray tube having a metallic middle part wherein a shift of the center point of the high-voltage is avoided. 
     The above object is achieved in accordance with the principles of the present invention in a high-frequency voltage generator for supplying an X-ray tube having a metallic middle part, the generator having a first high voltage rectifier with a (preceding inverter inverse rectifier) connected across the x-ray tube for supplying the overall voltage to the X-ray tube, and a second high voltage rectifier with another preceding inverter connected across the metallic middle part and the cathode, the first and second high voltage rectifiers and respectively following inverters being separately controlled by a control circuit. 
     In the inventive high-frequency high-voltage generator, an rectifier is provided for the overall voltage across the X-ray tube and another inverse inverter is provided for the cathode voltage. These voltages are regulated independently of one another by controlling the frequency of each inverse rectifier. The ripples of these voltages therefore have different frequencies, but this is not disturbing since the influence of the cathode voltage ripple on the cathode or on the anode current is slight. The metallic middle part acts like the grating of an amplifier with little steepness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The single FIGURE is a circuit diagram of a high voltage generator for supplying an X-ray tube, constructed and operating in accordance with the principles of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawing shows an X-ray tube 1 with metallic middle part 2. The overall voltage across the X-ray tube 1 is supplied by a high-voltage rectifier 3. The high-voltage rectifier 3 is connected to a inverter 6 via a high-voltage transformer 4. The inverter 6 is supplied from the mains via a rectifier in a known way. 
     The cathode voltage of the X-ray tube 1, i.e. the voltage between the metallic middle part 2 and the cathode 7, is supplied by a high-voltage rectifier 8 that is connected to a inverter 11 via a high-voltage transformer 9. The inverter 11 is also supplied from the mains via a rectifier in a known way. 
     The overall voltage at the X-ray tube 1 is controlled as a manipulated variable dependent on the frequency of the inverter 6. The actual value is taken at a potentiometer 12. The cathode voltage is regulated as a manipulated variable dependent on the frequency of the inverter 11. The actual value is taken at a potentiometer 13. 
     The illustrated generator is particularly suited for X-ray tubes having a highly pronounced asymmetry. Both inverters 6 and 11 are loaded about the same in the asymmetry range I A  =0.35*I K  which is generally the range of interest. I A  is thereby the anode current, I K  the cathode current. As a result, the two inverters 6 and 11 can be identically structured and equipped with the same power semiconductors, thereby making of the high voltage generator easier to facilitate realization. 
     A further advantage is that a certain voltage asymmetry can be intentionally set, thereby reducing the anode dissipated power, and thus also reducing heating of the anode. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.