Isolated current monitoring circuit for measuring direct and high duty factor currents

• US 5,196,784 A
• Filed: 03/18/1991
• Issued: 03/23/1993
• Est. Priority Date: 03/18/1991
• Status: Expired due to Term

• Current Assignee: Hughes Aircraft Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Estes, Earl M. Jr.
• Primary Examiner(s): Karlsen, Ernest F.
• Assistant Examiner(s): BURNS, WILLIAM
• Application Number:
  US07/670,664
• Time in Patent Office: 736 Days
• Field of Search: 324/117 R, 324/127, 307/400, 307/413, 330/8
• US Class Current: 324/117.00R
• CPC Class Codes: G01R 15/183 using transformers with a magnetic core

Abstract

A method and circuit for measuring direct and high duty factor current in a conductor (1) with minimal interference with the operation of a monitored circuit. Current flow in the conductor is magnetically sensed with a transformer T1 having a primary winding connected electrically in series with the conductor (1). The transformer T1 is driven into saturation during a first time interval and brought out of saturation during a second time interval. After the transformer T1 is brought out of saturation, an output signal is provided which is proportional to the flow of current in the conductor (1).

Claims

1. An isolated current monitoring circuit for measuring direct and high duty factor current in a conductor comprising:

A. transformer means for magnetically sensing current flow in said conductor, said transformer means including a transformer having a primary winding connected electrically in series with said conductor and a secondary winding;

B. means for driving said transformer into saturation during a first time interval including;

a. an operational amplifier with an inverting input connected to the first end of said secondary winding of said transformer, a noninverting input connected to means for providing a reference potential and an output terminal connected via a first resistor to the first end of the secondary winding of said transformer; and

b. means connected to said inverting input of said operational amplifier for providing a saturation control signal;

C. means for bringing said transformer out of saturation and operation said transformer as a current transformer during a second time interval, comprising;

c. said noninverting input connected to means for providing a reference potential and an output terminal of said operational amplifier connected via a first resistor to the first terminal of the secondary winding of said transformer; and

d. a second resistor connected to said inverting input of said operational amplifier at one end and the first end of said secondary winding of said transformer at a second end thereof;

D. said means for providing a reference potential comprises;

e. a third resistor connected to said noninverting input of said operational amplifier at one end and a potential well at a second end thereof; and

f. a fourth resistor connected to said inverting input of said operational amplifier at one end and a source of potential at a second end thereof; and

E. means for providing an output signal, after the initiation of the second time interval, which is proportional to the flow of current in said conductor.

2. The invention of claim 1 wherein said means for bringing said transformer out of saturation during a second time interval further includes a diode having a cathode terminal connected to the first end of said secondary winding of said transformer and an anode terminal connected to said potential well.

3. The invention of claim 2 wherein said diode is connected between said second ends of said second and third resistors.

4. The invention of claim 3 wherein said second end of said secondary winding is connected to said potential well.