Apparatus for adjusting the filament current of an X-ray tube

Claim 2

Apparatus for adjusting the filament current supply for an x-ray tube as a function of a control voltage V RA comprising, means responsive to the control voltage for converting said control voltage into a first signal component of the form a 1 V RA + b 1 which is linearly dependent upon V RA and wherein a 1 and b 1 are constants, means for converting the x-ray tube operating voltage V B into a second signal component of the form a 2 log V B + b 2 which is linearly dependent upon the logarithm of the operating voltage and wherein a 2 and b 2 are constants, means responsive to the control voltage and to a voltage proportional to the logarithm of the tube operating voltage for combining said voltages to produce a third signal component proportional to the product of the deviation of the control voltage from a given value of the control voltage and of the deviation of the logarithm of the tube operating voltage from a given value of the operating voltage, and means responsive to said first, second and third signal components for summing said signal components to produce an output signal indicative of the desired value of the filament current supply for the x-ray tube.

Claim 3

Apparatus as claimed in claim 1 further comprising means responsive to the x-ray tube operating current for converting said operating current into a second control voltage which is linearly dependent upon the logarithm of said operating current, and means for comparing the second control voltage with the first control voltage to produce a further signal correction component of said output signal.

Claim 4

Apparatus as claimed in claim 2 further comprising comparison means having first and second inputs connected to receive said output signal and a voltage proportional to the actual filament current, and a pulse width modulator coupled to the output of the comparison means for deriving width modulated current pulses for the filament of the x-ray tube and controlled by the output of the comparison means.

Claim 5

Apparatus as claimed in claim 1 further comprising a comparator having first and second inputs which receive said output signal and a voltage proportional to the actual filament current of the x-ray tube, and means including the output of the comparator for controlling a pulse duration modulator which supplies width modulated current pulses to the filament of the x-ray tube.

Claim 6

A filament current supply for an x-ray tube comprising, a function generator responsive to first and second control voltages related to the logarithm of the tube operating current and the logarithm of the tube operating voltage, respectively, and including means for combining said first and second control voltages to derive a first output signal indicative of the desired value of the tube filament current, means responsive to the actual filament current to derive a second output signal determined thereby, and comparison means responsive to said first and second output signals for deriving a third output signal for controlling the amplitude of the tube filament current.

Claim 7

A filament current supply for an x-ray tube comprising, a function generator responsive to first and second control voltages related to the logarithm of the tube operating current and the logarithm of the tube operating voltage, respectively, and including means for combining said first and second control voltages to derive a first output signal indicative of the desired value of the tube filament current, means responsive to the actual filament current to derive a second output signal determined thereby, and comparison means responsive to said first and second output signals for deriving a third output signal for controlling the amplitude of the tube filament current.

Claim 8

A filament current supply as claimed in claim 5 wherein said function generator combining means comprises, means responsive to the first control voltage for deriving a first signal component that is linearly dependent on said first control voltage, means responsive to the second control voltage for deriving a second signal component that is linearly dependent on the logarithm of the tube operating voltage, means for multiplying said first and second control voltages to derive a third signal component, and means for summing said first, second and third signal components to derive said first output signal.

Claim 9

A filament current supply as claimed in claim 6 further comprising means for supplying to an input terminal of the function generator said first control voltage which is of the form c 1 log i a -c 2 wherein i a is the tube operating current and c 1 and c 2 are constants.

Claim 10

A filament current supply as claimed in claim 6 further comprising means responsive to the tube operating current for deriving a third control voltage linearly dependent upon the logarithm of the operating current, and means for comparing said first and third control voltages to derive a further signal component which is degeneratively fed back to the summing means of the function generator.

Claim 11

A filament current supply circuit as claimed in claim 6 wherein said comparison means further comprises means responsive to the first and second output signals for deriving a first control signal determined by the difference thereof and a pulse width modulator including a differential amplifier having first and second inputs, means for supplying the first control signal to said first input and a periodic signal to the second input thereby to produce pulse width modulated signal pulses at the output of said modulator.

Claim 12

A filament current supply circuit as claimed in claim 5 further comprising means responsive to the tube operating current for deriving a third control voltage linearly dependent upon the logarithm of the operating current, and means for comparing said first and third control voltages to derive a further signal component which is applied to an input of the function generator to correct said first output signal.

Claim 13

A filament current supply circuit as claimed in claim 5 wherein said function generator combining means comprises, means responsive to the first control voltage for deriving a first signal component of the form a 1 V RA + b 1 wherein a 1 and b 1 are constants and V RA is the first control voltage, means responsive to the second control voltage for deriving a second signal component of the form a 2 log V B + b 2 wherein a 2 and b 2 are constants and V B is the tube operating voltage, means for multiplying said first and second control voltages to derive a third signal component, and means for summing said first, second and third signal components to derive said first output signal.

Claim 14

In an x-ray tube filament current supply of the type having a filament current transformer and means for controlling the flow of current in the transformer, the improvement comprising means for adjusting the tube filament current to a desired value prior to the application of the normal operating voltage V B across the x-ray tube, said adjusting means comprising, a first input terminal for a first control voltage, a second input terminal for a second control voltage determined by the tube operating voltage V B , function generator means coupled to said first and second input terminals and responsive to the first and second control voltages to derive at its output a first output signal indicative of the desired value of the tube filament current, said function generator means comprising, means responsive to the first control voltage for deriving a first signal component dependent thereon, means responsive to the second control voltage for deriving a second signal component dependent on the logarithm of the tube voltage V B , means for combining said first and second control voltages to derive a third signal component, and means for summing said first, second and third signal components to derive said first input signal at the output of the function generator means, said current controlling means being responsive to said first output signal to adjust the flow of current in the filament transformer to obtain the desired value of tube filament current prior to the application of the operating voltage V B to the x-ray tube.

Claim 15

In an x-ray tube filament current supply of the type having a filament current transformer and means for controlling the flow of current in the transformer, the improvement comprising means for adjusting the tube filament current to a desired value prior to the application of the normal operating voltage V B across the x-ray tube, said adjusting means comprising, a first input terminal for a first control voltage, a second input terminal for a second control voltage determined by the tube operating voltage V B , function generator means coupled to said first and second input terminals and responsive to the first and second control voltages to derive at its output a first output signal indicative of the desired value of the tube filament current, said function generator means comprising, means responsive to the first control voltage for deriving a first signal component dependent thereon, means responsive to the second control voltage for deriving a second signal component dependent on the logarithm of the tube voltage V B , means for combining said first and second control voltages to derive a third signal component, and means for summing said first, second and third signal components to derive said first input signal at the output of the function generator means, said current controlling means being responsive to said first output signal to adjust the flow of current in the filament transformer to obtain the desired value of tube filament current prior to the application of the operating voltage V B to the x-ray tube.

Claim 16

A filament current supply as claimed in claim 12 wherein said current controlling means comprises, means responsive to the flow of filament current in said transformer prior to the application of the tube operating voltage V B to derive a second output signal determined thereby, and comparison means responsive to said first and second output signals for deriving a third output signal for controlling the flow of current in the filament transformer in a manner tending to reduce the difference signal at the input of the comparison means to zero.

Claim 17

A filament current supply as claimed in claim 13 further comprising means responsive to the flow of tube operating current subsequent to the application of the tube operating voltage V B for deriving a third control voltage dependent upon the logarithm of the operating current, and means for comparing said first and third control voltages to derive a further signal component which is degeneratively fed back to the summing means of the function generator means to correct said first output signal.