FET current sensor for active balancing or regulating circuits

• US 5,592,394 A
• Filed: 08/31/1995
• Issued: 01/07/1997
• Est. Priority Date: 01/31/1995
• Status: Expired due to Term

• Current Assignee: Dell USA LP (Dell Technologies Inc.)
• Original Assignee: Dell USA LP (Dell Technologies Inc.)
• Inventors: Wiscombe, Nathan
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Vo, Hien
• Application Number:
  US08/522,038
• Time in Patent Office: 495 Days
• Field of Search: 364/492, 364/483, 364/482, 363/21, 363/89, 363/71-72, 323/285, 307/64-66, 307/43-44, 307/85-87, 307/80, 307/82, 307/31-32, 307/71-72
• US Class Current: 700/298
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers

Abstract

A method and apparatus for balancing shared power supplies or regulating a power supply device includes disposing a transistor (310) in series with a power supply current that is supplied to a load resistor (316) The gate of the transistor (310) is controlled by a control circuit (320) to set the gate-to-source voltage thereon to define a desired current therethrough. The voltage across the transistor (310) is measured with a voltage detector (322) and then a current conversion device (324) is operable to use a look up table to determine from the gate voltage on the transistor (310) what the impedance across the drain-to-source is and then calculate the current. This current is then utilized by the control circuit (320) to control the current through transistor 310. This therefore allows transistor (310) to both provide the control operation and provide the sensing operation, thus eliminating the requirement for a separate sense resistor.

Claims

1. An apparatus for regulating a flow of current in a power supply device, comprising:

a transistor disposed in a current path of said power supply device on an output thereof and having its source/drain path connected between the output of the power supply device and an external load, a series impedance of said transistor controlled by a received control signal and said transistor having a known impedance relationship to a voltage level of said control signal;

a voltage detector for detecting a voltage across said transistor;

a control processor for receiving said control signal and determining an impedance value of said transistor from said voltage level of said received control signal in conjunction with said known impedance relationship and calculating a current through said transistor from said detected voltage across said transistor and said determined impedance value of said transistor; and

a control system for controlling said power supply device utilizing said calculated current through said transistor through generation of said control signal.

2. The apparatus of claim 1, wherein said control processor comprises:

a look up table for storing said known impedance relationship of said transistor; and

a processor for receiving said control signal and retrieving from said look up table the impedance value associated with said voltage level of said received control signal, said processor then operable to receive said detected voltage across said transistor and calculate said current utilizing said impedance value retrieved from said look up table.

3. The apparatus of claim 2, wherein said processor is further operable as a part of said control system calculate a new value for said control system in accordance with information stored in said look up table in order to provide regulation of the flow of current from the power supply device to an external load in accordance with a predetermined power supply control scheme.

4. The apparatus of claim 1, wherein said voltage detection device comprises an analog-to-digital converter.

5. The apparatus of claim 1, wherein said transistor comprises a MOS transistor.

10. The apparatus of claim 1, wherein said transistor is turned off by said control signal, said control processor further providing a power on/off signal to said power supply, wherein said control processor turns off said power supply by said on/off signal upon determining by said control signal that said transistor is turned off and said voltage detector detects a voltage across said transistor above a predetermined level.

6. The method for regulating a flow of current in a power supply device, comprising the steps of:

connecting the source/drain path of an transistor in series with a current path of the power supply device, such that current flows therethrough, and connecting a control signal to the gate thereof, an impedance of the transistor controlled by the received control signal and the transistor having a known impedance relationship to a voltage level of the control signal;

detecting a voltage across the transistor;

determining an impedance value of the transistor that is associated with the voltage level of the control signal as defined by the known impedance relationship and utilizing the determined impedance of the transistor in conjunction with the detected voltage across the transistor to calculate a current through the transistor; and

controlling the power supply utilizing the calculated current through the transistor and generating the control signal.

7. The method of claim 6, wherein the step of determining the impedance value of the transistor comprises:

storing the known impedance relationship of the transistor in a look up table;

retrieving the impedance associated with the voltage level of the control signal from the look up table; and

calculating the current through the transistor utilizing the detected voltage across the transistor in conjunction with the impedance value retrieved from the look up table.

8. The method of claim 7, and further comprising the step of calculating a new value for the control signal in accordance with information stored in the look up table in order to provide regulation of the flow of current from the power supply device to an external load in accordance with a predetermined power supply control scheme.

9. The method of claim 6, wherein the step of detecting the voltage across the transistor comprises inputting the voltage level across the transistor to an analog-to-digital converter and outputting a digital value therefor.

11. The method of claim 6, wherein said transistor is a MOS transistor.