The Design Of X-ray Tube Filament Driving Control Circuit

The Metal Oxide Semiconductor Field Effect Transistor(MOSFET)is generally regarded as the power switching component of the Digitized Radiography(DR)filament driver,which takes advantages of the full bridge inverter that produces high frequency alternating current,and the TL594 is used as the impulse modulation chip,the controlling of the x-ray tube filament current can be realized by changing the output pulse width.However,certain risks are frequently found in terms of the x-ray tube filament protection of the old-fashioned filament driver circuit.Merely utilizing TL594 dead zone voltage to control the maximum duty cycle,thus restricting the filament maximum current is impractical.The chip pins,especially those of the sampling reactive circuit chips in some hospitals of southern China are likely to be corroded since the high humidity in the equipment room,as well as the intensive salinity content in the air.Damages of the chips are going to incur the loop loosing of the sampling circuit,the out of controlling of the filament current,gradually over burning the filament.The thesis designs and realizes a new x-ray tube filament driver circuit.Using the principle that pulse transformer can only transfer the pulse signals with limited width,as well as the scheme that drive filament uses pulse transformer to drive MOSFET.Therefore,even the pulse signal reaches to its maximum,the maximum output filament circuit will not exceed the filament specified circuit,which not only solves the filament closed-loop problem that caused by human and environmental factors,but also removes the matter of tube filament fusing.Both the principle and the scheme are instructive for the scientific development of the filament control in the high pressure generator system.This thesis mainly discusses the electrical designing of the x-ray tube filament driver circuit.The major aspects that will be illustrated in this thesis are listed as follows: Functional Requirements,Schematic Diagram Designing,PCB Designing,Circuit Debugging,and High Voltage Generator Test etc.The thesis begins with the current research about the high voltage generator technology,combining the filament transmission characteristics with the projects practical requirements,designing the general scheme of the filament driver circuit.Because the pulse transformer is characterized by its transmitting finite-width pulse signal,the scheme of Silicon Controlled Trigger Pulse Transformer Driver MOSFET is selected according to this principle.Filament closed-circuit design is adopted so as to guarantee the controlling accuracy of the filament current,which ensures the mA controlling precision of the high voltage generator.Next,making PCB design according to PCB locating and wiring principle and producing circuit board.Besides,making compare and analysis of the filament transformer iron core materials,and choosing nanocrystalline as the filament transformer iron core.Last,having the functional test for the filament drive circuit so as to guarantee the correctness of the circuit board principle and the perfection of its functions.Also examining the protective effect for the filament circuit,and gaining the results of the filament transformer turn ration as well as the linear rules of the filament circuit.Conducting the stability test for the filament circuit in the high pressure generator system and the consistency test for the redial output.Finally,the following statement can be realized in the end of this thesis: the x-ray tube filament current will be controlled accurately by the upper computer,the maximum output current will be less than the tube filament maximum rated current even when the closed-loop reactive sampling signal is mal-functioning,and the filament will not be burnt out.