Device in a power delivery circuit - Patent Review 5495155

We claim:

1. A power delivery circuit for supplying load current to a load, comprising:

a power FET device comprising a majority current device for supplying a majority current output to a load, a minority current device for supplying a minority current output, and a terminal whose voltage is representative of the voltage at the output of the majority current device;

a current detection circuit for obtaining a signal proportional to said majority current output, the current detection circuit comprising:

a first branch connected between said terminal and a reference potential, and a second branch connected between said minority current output and said reference potential;

said first branch having a first semiconductor device and said second branch having a second semiconductor device, wherein said first and said second semiconductor devices are configured to control the voltage at said minority current output;

said first branch having a third semiconductor device and said second branch having a fourth semiconductor device, said third and fourth semiconductor devices being configured to provide a predetermined current ratio in said first and second branches; and,

at least one output node for providing said signal proportional to said majority current output.

2. The power delivery circuit of claim 1, wherein the signal proportional to the majority current output is a voltage signal.

3. The power delivery circuit of claim 1, wherein the signal proportional to the majority current output is a differential voltage signal comprising the voltage between said at least one output node and a second output node.

4. The power delivery circuit of claim 1, further comprising a fifth transistor to provide a current path for the base currents of said third and fourth semiconductor devices.

5. The power delivery circuit of claim 1, further comprising a fifth transistor to provide a current path for the base currents of said first and second semiconductor devices.

6. The power delivery circuit of claim 1, further comprising fifth and sixth semiconductor devices, said fifth semiconductor device interposed in series connection between said first and third semiconductor devices, and said sixth semiconductor device interposed in series connection between said second and fourth semiconductor devices.

7. A power delivery circuit for supplying load current to a load, comprising:

a power FET device comprising a majority current device for supplying a majority current output to a load, a minority current device for supplying a minority current output, and a terminal whose voltage is representative of the voltage at the output of said majority current device;

a current detection circuit for obtaining a signal proportional to said majority current output, the current detection circuit comprising:

a voltage matching buffer circuit comprising first and second semiconductor devices, said first semiconductor device coupled to said minority current output and said second semiconductor device coupled to said terminal; and

a current controlling circuit comprising third and fourth semiconductor devices driving said voltage matching buffer circuit so as to draw first and second currents through said first and second semiconductor devices, wherein said first and second currents are in a predetermined ratio;

at least one output node for providing said signal proportional to said majority current output.

8. The power delivery circuit of claim 7, wherein said signal proportional to said majority current output is a voltage signal.

9. The power delivery circuit of claim 7, wherein said signal proportional to said majority current output is a differential voltage signal comprising the voltage between said at least one output node and a second output node.

10. The power delivery circuit of claim 7, further comprising a fifth transistor to provide a current path for the base currents of said third and fourth semiconductor devices.

11. The power delivery circuit of claim 7, further comprising a fifth transistor to provide a current path for the base currents of said first and second semiconductor devices.

12. The power delivery circuit of claim 7, further comprising fifth and sixth semiconductor devices, said fifth semiconductor device interposed in series connection between said first and third semiconductor devices, and said sixth semiconductor device interposed in series connection between said second and fourth semiconductor devices.

13. An improved current sensing circuit for use in combination with a current controlling device in a power delivery circuit for supplying load current to a load, the current controlling device being multi-cellular, and having parallel-connected major current-carrying cells for outputting a main device current and at least one minor current-carrying cell to output a current proportional to the main device current, the improvement in the current sensing circuit comprising:

a buffer circuit comprising first and second semiconductor devices, said first semiconductor device coupled to the output of said minor current-carrying cell and said second semiconductor device coupled to output of said parallel-connected major current-carrying cells, for controlling voltage at the output of said at least one minor current-carrying cell; and

a current controlling circuit comprising third and fourth semiconductor devices driving said buffer circuit so as to draw first and second currents through said first and second semiconductor devices, wherein said first and second currents are in a predetermined ratio;

at least one output node for providing a signal proportional to said main device current.

14. The current sensing circuit of claim 13, wherein said first, second, third, and fourth semiconductor devices include first, second, third, and fourth bipolar transistors respectively, said first and second bipolar transistors being of PNP-type conductivity and said third and fourth bipolar transistors being of NPN-type conductivity.

15. The current sensing circuit of claim 14, wherein the bases of said first and second bipolar transistors of said buffer circuit are intercoupled, and the bases of said third and fourth bipolar transistors of said current controlling circuit are intercoupled.

16. The current sensing circuit of claim 15, wherein said intercoupled bases of said first and second bipolar transistors are coupled to the collector of one of said first and second bipolar transistors.

17. The current sensing circuit of claim 15, wherein said intercoupled bases of said third and fourth bipolar transistors are coupled to the collector of one of said third and fourth bipolar transistors.

18. The current sensing circuit of claim 15, further comprising a fifth transistor to provide base currents to said third and fourth bipolar transistors.

19. The current sensing circuit of claim 15, further comprising a fifth transistor to provide a current path for the base currents of said first and second bipolar transistors, said current path extending between said intercoupled bases of said first and second bipolar transistors and a reference potential.

20. The current sensing circuit of claim 14, further comprising fifth and sixth semiconductor devices, wherein said fifth semiconductor is connected in series between said second and said fourth semiconductor devices and said sixth semiconductor is connected in series between said first and said third semiconductor devices.

21. The current sensing circuit of claim 14, further comprising fifth and sixth semiconductor devices, said fifth semiconductor device interposed in series connection between said first and third semiconductor devices, and said sixth semiconductor device interposed in series connection between said second and fourth semiconductor devices.

22. The current sensing circuit of claim 14, wherein the betas (.beta.) of said first and said second transistors are substantially identical, and the betas (.beta.) of said third and said fourth transistors are substantially identical.

23. The current sensing circuit of claim 13, wherein said third and fourth semiconductor devices of said current controlling circuit are intercoupled to form a current mirror.

24. The current sensing circuit of claim 23, wherein said third and said fourth semiconductor devices of said current controlling circuit comprise FET transistors.

25. The current sensing circuit of claim 24, wherein said current controlling circuit further comprises a fifth semiconductor device intercoupled with said third and fourth semiconductor devices no form a current mirror.

26. The current sensing circuit of claim 13, wherein said buffer circuit further comprises a fifth semiconductor device intercoupled with said first and second semiconductor devices.

27. The current sensing circuit of claim 26, wherein said fifth semiconductor device provides a current path for base currents of said intercoupled semiconductor devices and a reference potential.

28. The current sensing circuit of claim 13, further comprising fifth and sixth semiconductor devices, wherein said fifth semiconductor is connected in series between said second and said fourth semiconductor devices and said sixth semiconductor is connected in series between said first and said third semiconductor devices.

29. The current sensing circuit of claim 13, further comprising fifth and sixth semiconductor devices interposed in series connection between said buffer circuit and said current controlling circuit.

30. An improved current sensing circuit for use in combination with a current controlling device in a power delivery circuit for supplying load current to a load, the current controlling device being multi-cellular, and having parallel-connected major current-carrying cells for outputting a main device current and at least one minor current-carrying cell to output a current proportional to the main device current, the improvement in the current sensing circuit comprising:

a buffer circuit comprising first and second semiconductor devices, said first semiconductor device coupled to the output of said minor current-carrying cell and said second semiconductor device coupled to output of said parallel-connected major current-carrying cells, for controlling voltage at the output of said at least one minor current-carrying cell; and

a current controlling circuit comprising third and fourth semiconductor devices driving said buffer circuit so as to draw first and second currents through said first and second semiconductor devices, wherein said first and second currents are in a predetermined ratio;

fifth and sixth semiconductor devices interposed in series connection between said buffer circuit and said current controlling circuit; and,

at least one output node for providing a signal proportional to said main device current.

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TECHNICAL FIELD

The invention relates generally to current sensing circuitry and more particularly to current sensing circuitry in combination with, or for use in combination with, a current controlling device in a power delivery circuit. More particularly, the invention relates to a current sensing circuit for detecting current conditions in a power delivery circuit, especially of the high-side switch type. The invention even more particularly relates to a current sensing circuit useful for detecting over-current conditions in "H"-bridge-type power delivery circuits for bidirectional motors and in which the current controlling devices are provided by current sensing semiconductors.

BACKGROUND ART

The advent of solid state power drivers has created the need to monitor or to sense load current for device protection and other functions. The power delivery circuits for supplying load current to a load and which further include current sensing capabilities are generally known and are of diverse types. In U.S. Pat. No. 4,654,568 to Mansmann, there is disclosed an H-bridge switch circuit for a load such as a motor. More specifically, the various switches of the H-bridge are MOSFET semiconductors, with two of those MOSFETs comprising current sensing MOSFETs. In that described embodiment, the current sensing MOSFETs are connected in the "low" side of the power delivery circuit to the motor. The current sensing MOSFETs are multi-cellular devices in which a major current-carrying cellular portion consists of a large number of cells connected in parallel for carrying the main load current and in which a minor current-carrying cellular portion consists of a relatively small number of cells substantially in parallel therewith and having a separate terminal for carrying a current proportional to that load current. That separate terminal is termed the "current sensing" terminal and may be useful for developing a signal indicative of the major current carried by the current sensing MOSFET.

In U.S. Pat. No. 4,654,568, the current conducted via the current sensing terminal is developed as a voltage level which is applied to an input of an operational amplifier for amplification and subsequent evaluation. The current sensing circuit which converts the current carried at the current sensing terminal to a corresponding voltage level appears in the patent as at least one sensing resistor operatively connected between the current sensing terminal and ground. The operational amplifier is connected to the current sense terminal and amplifies the voltage developed across that resistor (sense voltage). Sensing current in this manner inherently induces errors in the ratioing of the majority current and the sensing current in the current sense MOSFET. More significantly, as the temperature of the current sense MOSFET increases, as under increasing load conditions, the aforementioned induced error percentage and likewise associated sense voltage error percentage increases.

Furthermore, for safety reasons required in automotive applications, power switch protection and current sensing need to be implemented in a "high side" configuration. This configuration places the current switch or power switch in between the positive supply and the load. If the current sensing method demonstrated in U.S. Pat. No. 4,654,568 were to be used in a high side configuration, it would have all of the previously described problems. Further, the operational amplifier supply voltage would have to be higher than the sum of the current sense terminal voltage and the amplified voltage drop across the sensing resistor. Since the voltage drops across the current sense MOSFETs (power MOSFETs) are very low, this would required an operational amplifier voltage supply to be higher than the voltage supply connected to the current sense MOSFET, which is typically the battery, V.sub.BATT, in automotive applications. This method is further complicated by requiring the threshold reference voltage, which needs to be generated and used for comparing the amplified resistor voltage drop to some threshold for protection, to be operatively referenced above the current sense terminal potential, which is changing with varying load conditions and battery voltage.

Alternatively, an operational amplifier could be connected in a current amplifier configuration, sometimes called a virtual ground reference, instead of a voltage amplifier configuration. This would require the operational amplifier to have a high common mode input voltage nearly equal to the supply voltage, a threshold reference voltage to be operatively referenced below the current sense terminal potential which is changing with varying load conditions and battery voltage, and would require an operational amplifier to work at the high voltage transients that are present in automotive applications (typically filtered to 45 volts).

DISCLOSURE OF THE INVENTION

Accordingly, it is a principal object of the present invention to provide an improved current sensing circuit for use in conjunction with a current controlling device such as a current sensing MOSFET, connected to respective ones of two auxiliary terminals associated with the current sensing MOSFET. Included within the object is the provision of such current sensing circuit having a constant load current (I.sub.L)-to-voltage sense (V.sub.S) conversion ratio which is independent of variations in the supply potential and in the load current.

It is a further object of the invention to provide a current sensing circuit of the type described which is particularly suited for use with a current sensing device or switch in a "high side" configuration and which exhibits improved accuracy.

It is a still further object of the invention to provide a current sensing circuit of the type described in which such improvements in accuracy and stability are obtained with a concomitant minimization of cost and complexity associated with the number of resistors required.

In accordance with the present invention, an improved current sensing circuit is provided for use in combination with a current controlling device in a power delivery circuit for supplying load current to a load. The invention finds particular utility in power delivery circuits in which the current controlling device is in the "high side", and especially in the high side of an H-bridge switch arrangement. The current controlling device or switch, which may be a current sensing MOSFET, comprises a multi-cellular device with a major current carrying cellular portion and a minor current carrying portion, a first main current terminal, a gate terminal for receiving a control signal, a second main current terminal connecting the major current-carrying cellular portion, a first auxiliary terminal, or current sense terminal, connected at one end to the minor current-carrying cellular portion so as to provide a current generally proportional to the main device current, and a second auxiliary terminal, the Kelvin terminal, connected at one end to the major current-carrying cellular portion.

The improved current sensing circuit includes first and second branches each connected at one end to a respective one of the first and second auxiliary terminals and includes means for connection in common at the other end to a reference potential in the power delivery circuit. More specifically, the current sensing circuit comprises the first branch including first and third series-connected semiconductor devices, such as transistors; the second branch including second and fourth series-connected semiconductor devices, such as transistors; the first and fourth semiconductor devices each being controlled by bias signals and acting in a transimpedance mode of operation; the second and third semiconductor devices being cross-connected with the first and fourth semiconductor devices respectively to provide the respective bias signals thereto; and the first branch further including impedance means, such as a resistor, connected in series circuit therewith for providing a voltage at a node at one end of the impedance means approximately proportional to the main device current, that node being connectable to a detection circuit.

In accordance with an embodiment of the invention, the first, second, third and fourth semiconductor devices comprise respective bipolar transistors, and the first and second transistors are of one conductivity type and the third and fourth transistors are of the opposite conductivity type. Further, the first main current terminal of the current controlling device is adapted to be connected to one polarity of a source of power having relatively opposite polarities, the second main current terminal of the current controlling device is adapted to be connected to one side of a load, and the other side of the load is adapted to be connected to the other polarity of the source of power. The current controlling device with the current sensing capability is preferably connected in the "high side" of the power delivery circuit such that it is relatively more positive than the load. Both the first and the second transistors are PNP transistors and the third and fourth transistors are NPN transistors. The reference potential in the power delivery circuit, to which the first and second branches of the sensing circuit are adapted to be connected in common, is the other polarity of the source of power, and is typically ground.

The betas (.beta.) of the first and second transistors are substantially identical and the betas of the third and fourth transistors are substantially identical.

Further in accordance with the invention, the second and third transistors are each connected in respective shorted base-to-collector configurations and the base of the second transistor is connected to the base of the first transistor and the base of the third transistor is connected to the base of the fourth transistor. The impedance means in the first branch is a first resistor. In one embodiment, the second branch circuit includes a respective second resistor in series circuit therewith. In an alternate embodiment, a single resistor is connected in common in the first and the second branches and is connected to the reference potential.

In a further embodiment, still further improvement in performance of the current sensing circuit may be realized through the addition of fifth and sixth transistors thereto as an alternative to or modification of the shorted base-to-collector connections. The circuit becomes less sensitive to beta variations, and thus temperature, in the other four transistors.

In a still further embodiment, fifth and sixth transistors are added to the current sensing circuit, a respective one being serially connected in each of the branches intermediate the other transistors. The respective fifth and sixth transistors provide the major voltage drops thereacross to minimize the voltage across the other transistors and thereby minimize variations in the betas of those other four transistors despite variations in the supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration partially in block diagram form providing a generalized view of the current sensing circuit of the invention, connected in operative association with current controlling devices, such as current sensing switches, in an H-bridge switch arrangement;

FIG. 2 is a schematic circuit diagram depicting, in detail, one embodiment of the current sensing circuit of the invention;

FIG. 3 is a schematic circuit diagram depicting, in detail, a second embodiment of the current sensing circuit of the invention;

FIG. 4 is a schematic circuit diagram depicting, in detail, a third embodiment of the current sensing circuit of the invention;

FIG. 5 is a schematic circuit diagram depicting, in detail, a fourth embodiment of the current sensing circuit of the invention; and

FIG. 6 is a schematic circuit diagram depiction in detail, a fifth embodiment of the current sensing circuit of the invention.

BEST MODES FOR CARRYING OUT THE INVENTION

As an alternative to the aforementioned current sensing circuit of U.S. Pat. No. 4,654,568, there has recently been developed a refinement employing a type of current mirror, or more particularl