Multiple voltage x-ray switching system

A system for controlling an x-ray tube to emit high and low energy x-ray pulses, comprising:

• an x-ray tube having an anode, a filament and a control element,
• a high voltage dc source and a high voltage supply circuit for coupling said anode to the positive side of the source, said circuit and source having a predetermined impedance,
• first and second dc bias voltage sources for providing negative bias voltage of predetermined values, the negative side of said first bias voltage source being coupled to said control element and the positive side being coupled to the negative side of said second source and the positive side of the second bias voltage source being coupled to said filament, whereby said bias voltages are additive and can apply sufficient negative bias voltage to said control electrode to cut off current flow through the x-ray tube,
• a first shunting circuit including first switch means connected between the negative and positive sides of the first bias voltage source and a second shunting circuit including second switch means connected between the negative and positive sides of the second bias voltage source,
• means for putting the respective switch means selectively in conductive or nonconductive states independently of each other such that if neither switch means is conductive the sum of the bias voltages is applied to said control electrode for cutting off current flow through said x-ray tube, if one of said switch means is conductive and the other is nonconductive the conductive switch means will shunt one bias source between whose sides it is connected and the nonconductive switch means will enable the bias voltage from the other source to be applied to said control element for causing predetermined low current flow through the tube and a correspondingly low voltage drop due to said predetermined impedance in said circuit and source such that there is a higher voltage drop between the anode and filament of said tube, and if both of said switches are conductive both bias sources will be shunted to substantially remove bias voltage from said control element to thereby cause predetermined higher current flow through the tube and a correspondingly higher voltage drop due to said predetermined impedance in said circuit and source such that there is a low voltage drop between the anode and filament of said tube.

A system for controlling an x-ray tube to emit alternate low and high photon energy x-ray pulses whose photon energy is determined by the voltage drop across the tube during the pulse and whose intensity is dependent on the current passing through the tube during respective pulse intervals, comprising:

• an x-ray tube having an anode, a filament and a control element,
• a high voltage dc source and a circuit for coupling the positive output of the source to the anode and the negative output to the filament,
• an adjustable device in said circuit for inserting a selected amount of impedance in addition to the impedance of said source,
• first and second sources for providing predetermined bias voltages, said sources being connected in series and the negative output of the first source being connected to said x-ray tube control element and the positive output of the second source being connected to said filament,
• circuits including switch means respectively connected between the negative and positive outputs of the first and second bias voltage sources, said switch means being selectively operable between nonconductive states wherein they do not shunt the bias voltage source to which they are connected to enable the bias voltage to be applied to said control element and conductive states wherein they shunt the respective bias voltage sources,
• means for selectively controlling said switch means to change between nonconductive and conductive states to thereby permit selective application of the sum of the bias voltages or one or the other of the bias voltages to said control element for affecting the magnitude of the current through the x-ray tube and the voltage drop across said tube for the x-ray pulse produced while the particular bias voltage is applied,
• controlling said switch means to cause the sum of the bias voltage to be applied to said x-ray tube control element resulting in no current flowing between the anode and filament of said tube controlling said switch means to cause one of the bias voltages to be applied to said control element causing said tube to conduct low current and said impedance to develop a relatively low voltage drop such that there is a correspondingly higher voltage drop between the x-ray tube anode and filament, and controlling such switch means to apply none of the bias voltages to said control element causing said tube to conduct higher current and said impedance to develop a higher voltage drop such that there is a correspondingly lower voltage drop between the x-ray tube anode and filament.