High voltage sensing circuit for an X-ray tube power supply

• US 5,420,781 A
• Filed: 09/02/1993
• Issued: 05/30/1995
• Est. Priority Date: 09/02/1993
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Schmidt, Jonathan R.
• Primary Examiner(s): Dougherty, Thomas M.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/116,148
• Time in Patent Office: 635 Days
• Field of Search: 363/95, 363/96, 363/98, 363/131, 363/132, 363/136, 363/16, 363/17, 363/71, 378/112, 378/114
• US Class Current: 363/98
• CPC Class Codes: H02M 3/3376 with automatic control of output voltage or current
• CPC Class Codes: H05G 1/265 Measurements of current, voltage or power
• CPC Class Codes: H05G 1/32 Supply voltage of the X-ray apparatus or tube

Abstract

A system senses a voltage that exists across two nodes using first and second resistors connected in series between the two nodes. A differential amplifier acts as a detector and produces a first signal having a magnitude that corresponds to the voltage across the second resistor. A variable gain circuit changes the magnitude of the first signal by a gain factor to produce a second signal which indicates the voltage that exists across two nodes. A mechanism coupled to said variable gain circuit and adjusts the gain factor to compensate for changes in resistivity of said first and second resistors. The mechanism determines the resistor gain provided by the first and second resistors and uses the resistor gain to derive a new value for the gain factor.

Claims

1. A system for sensing a voltage that exists across a pair of nodes in a high voltage supply for an X-ray tube, the system comprises:

first and second resistors connected in series between the two nodes;

a detector that produces a first signal which has a magnitude corresponding to a voltage across said second resistor;

a variable gain circuit that changes the magnitude of the first signal by a gain factor to produce a second signal that indicates the voltage that exists across the two nodes; and

a mechanism coupled to said variable gain circuit and which adjusts the gain factor to compensate for changes in resistance of said first and second resistors.

2. The system as recited in claim 1 further comprising:

a circuit that applies a reference voltage to the detector during a calibration mode of the system;

means for sensing a voltage level indicated by the second signal during the calibration mode; and

a comparator that compares the voltage level indicated by the second signal to a value of the reference voltage, thereby determining whether said detector and said variable gain circuit are operating accurately.

3. The system as recited in claim 2 wherein said mechanism further adjusts the gain factor in response to said comparator to compensate for inaccuracy in said detector and said variable gain circuit.

4. The system as recited in claim 1 wherein said mechanism comprises a means for determining the resistor gain of said second resistor;

and a means for deriving a new value for the gain factor in response to the resistor gain provided by said means for determining.

5. A system for sensing a voltage that exists across a pair of nodes in a high voltage supply for an X-ray tube, the system comprises:

first and second resistors connected in series between the two nodes;

a differential amplifier with a pair of inputs coupled to said second resistor and producing a first signal having a magnitude which corresponds to a voltage across said second resistor;

a multiplying digital to analog converter connected to an output of said differential amplifier and which changes the magnitude of the first signal by a gain factor to produce a second signal that indicates the voltage that exists across the two nodes; and

a gain adjust circuit including means for determining a resistor gain of said second resistor, a means for deriving a new value for the gain factor in response to the resistor gain; and

a mechanism connected to said multiplying digital to analog converter for setting the gain factor to the new value.

6. The system as recited in claim 5 further comprising:

a circuit that applies a reference voltage to said differential amplifier during a calibration mode of the system;

means for sensing a voltage level indicated by the second signal during the calibration mode; and

a comparator that compares the voltage level indicated by the second signal to a value of the reference voltage, thereby determining whether said differential amplifier and said multiplying digital to analog converter are operating accurately;

wherein said gain adjust circuit responds to said comparator by setting the gain factor of said multiplying digital to analog converter to a new value which compensates for inaccuracy in said differential amplifier and said multiplying digital to analog converter.

7. A system for sensing a voltage that exists across a pair of output terminals of a high voltage supply for an X-ray tube wherein the high voltage supply has an anode voltage source and a cathode voltage source;

the system comprises;

first and second resistors connected in series between output terminals of said anode voltage source;

third and fourth resistors connected in series between output terminals of said cathode voltage source;

a first differential amplifier with a pair of inputs coupled to said second resistor, and producing a first signal having a magnitude which corresponds to a voltage across said second resistor;

a first multiplying digital to analog converter connected to an output of said first differential amplifier, and changing the magnitude of the first signal by a first gain factor to produce a second signal that indicates a voltage level produced by the anode voltage source, wherein the second signal is coupled to the anode voltage source;

a second differential amplifier with a pair of inputs coupled to said fourth resistor, and producing a third signal having a magnitude which corresponds to a voltage across said fourth resistor;

a second multiplying digital to analog converter connected to an output of said second differential amplifier, and changing the magnitude of the third signal by a second gain factor to produce a fourth signal that indicates a voltage level produced by the cathode voltage source, wherein the fourth signal is coupled to the cathode voltage source; and

a gain adjust circuit including a first mechanism that determines a first resistor gain of said second resistor and a second resistor gain for said fourth resistor, a second mechanism for deriving a first new value for the first gain factor in response to the first resistor gain and a second new value for the second gain factor in response to the second resistor gain and an adjustment mechanism connected to said first multiplying digital to analog converter for setting the first gain factor to the first new value and connected to said second multiplying digital to analog converter for setting the second gain factor to the second new value.

8. The system as recited in claim 7 further comprising:

a first circuit that applies a first reference voltage to said first differential amplifier during a calibration mode of the system;

a second circuit that applies a second reference voltage to said second differential amplifier during the calibration mode;

a switch connected to said first and second multiplying digital to analog converters, and having a first state in which the second signal is coupled to an output terminal of said switch and a second state in which the fourth signal is coupled to the output terminal;

a comparator connected to the output terminal of said switch to compare a value of the first reference voltage to a voltage level indicated by the second signal thereby determining whether said first differential amplifier and said first multiplying digital to analog converter are operating accurately, and to compare a value of the second reference voltage to a voltage level indicated by the fourth signal thereby determining whether said second differential amplifier and said second multiplying digital to analog converter are operating accurately;

wherein said gain adjust circuit responds to said comparator by setting the gain factors of said first and second multiplying digital to analog converters to new values which compensate for inaccuracies determined by said comparator.