US3796943A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Current limiting circuit
Assignee: National Semiconductor Corp
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Filing: 1973-01-02
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Granted: 1974-03-12
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Expires: 1993-01-02
Abstract
Abstract A current sense voltage is derived which is proportional to the current to be limited. The current sense voltage is applied in phase opposition to a difference voltage obtained by opposing the base-to-emitter diode voltage drops of a temperature compensating transistor and a current control transistor for substantially reducing the value of the current limit sense voltage necessary to cause current limiting. Temperature compensation is obtained by superimposing a selected temperature compensating portion of the base-to-emitter diode drop of a temperature compensating transistor on the base-to-emitter turnon voltage of the current control transistor, whereby any desired temperature coefficient including zero is obtained for the current limiting circuit over the operating temperature range of - 55* C to + 125* C.
Inventors
- 👤 C Nelson
- 👤 R Dobkin
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 07:33
CPC Classifications
G; G05; G05F; G05F1/00; G05F1/10; G05F1/46; G05F1/56; G05F1/565; G05F1/569; G05F1/573; G05F1/5735
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
209 words
In a current limiting circuit, means for sensing the current to be limited and for deriving a current sense voltage proportional to the current to be limited, current limiting means for limiting the current flowing through said current sensing means, said current limiting means including a current control transistor responsive to said current sense voltage for generating a current limiting signal to cause said current limiting means to limit the current to said current sensing means when the current sense voltage exceeds a current limiting value, a current limiting input circuit interconnecting said current control transistor and said current sense means, said current limiting input circuit means including means for developing and applying in circuit with and in phase opposition to the base-toemitter turn on diode junction voltage drop of said current control transistor at least a substantial portion of a second diode junction voltage drop of different magnitude than said base-to-emitter turn on diode junction voltage drop of said current limiting transistor for creating a difference voltage in said current limiting input circuit in series with said current sense voltage, whereby the magnitude of said current sense voltage is reduced to a value substantially less than said turn on base-to-emitter voltage drop of said current control transistor means.
Claim 2
Dependent Claim
209 words
In a current limiting circuit, means for sensing the current to be limited and for deriving a current sense voltage proportional to the current to be limited, current limiting means for limiting the current flowing through said current sensing means, said current limiting means including a current control transistor responsive to said current sense voltage for generating a current limiting signal to cause said current limiting means to limit the current to said current sensing means when the current sense voltage exceeds a current limiting value, a current limiting input circuit interconnecting said current control transistor and said current sense means, said current limiting input circuit means including means for developing and applying in circuit with and in phase opposition to the base-toemitter turn on diode junction voltage drop of said current control transistor at least a substantial portion of a second diode junction voltage drop of different magnitude than said base-to-emitter turn on diode junction voltage drop of said current limiting transistor for creating a difference voltage in said current limiting input circuit in series with said current sense voltage, whereby the magnitude of said current sense voltage is reduced to a value substantially less than said turn on base-to-emitter voltage drop of said current control transistor means.
Claim 3
Dependent Claim
49 words
The apparatus of claim 1 wherein said turn on base-to-emitter voltage drop of said current control transistor exceeds the second diode junction voltage drop, and wherein said current sense voltage is applied in phase opposition in said input circuit to said base-to-emitter voltage drop of said current control transistor.
Claim 4
Dependent Claim
51 words
The apparatus of claim 1 wherein said turn on base-to-emitter voltage drop of said current control transistor is less than said second diode junction voltage drop, and wherein said current sense voltage is applied in phase addition in said input circuit to said base-to-emitter voltage drop of said current control transistor.
Claim 5
Dependent Claim
92 words
The apparatus of claim 1 wherein said means for developing and applying said second diode junction voltage drop in circuit with said base-to-emitter junction of said current control transistor includes, a second transistor connected as a diode with its base connected to its collector and connected with its collector and emitter terminals in series circuit relation with the base terminal of said current contrOl transistor, and said collector-to-emitter connection of said second transistor being polarized for conduction of current in a direction away from said base terminal of said current control transistor.
Claim 6
Dependent Claim
79 words
The apparatus of claim 2 wherein said means for developing and applying at least a substantial portion of said second diode junction voltage drop in circuit with and in phase opposition to said base-to-emitter junction voltage of said current control transistor includes, means for developing said second diode junction voltage drop and for applying only a portion of said developed second diode junction voltage drop in phase opposition with said base-to-emitter junction voltage drop of said current control transistor.
Claim 7
Dependent Claim
91 words
The apparatus of claim 3 wherein said means for developing and applying at least a substantial portion of said second diode junction voltage drop in circuit with and in phase opposition to said base-to-emitter junction voltage drop of said current control transistor includes, means for developing said second diode junction voltage drop plus a substantial fraction of said second diode junction voltage drop and for applying both of said developed voltage drops in said input circuit means in phase opposition with said base-to-emitter junction voltage drop of said current control transistor.
Claim 8
Dependent Claim
55 words
The apparatus of claim 1 wherein said means for developing and applying said second diode junction voltage drop includes, a second diode junction, and a current source for supplying current to said second diode junction, and said current source providing current to said second diode junction in proportion to the temperature of said current source.
Claim 9
Dependent Claim
83 words
The apparatus of claim 1 wherein said current limiting means includes, series pass transistor means having base, emitter and collector terminals connected for passing current through said current sensing means, current source means connected for supplying base drive current to said base terminal of said current pass transistor means, shunt transistor means connected for selectively removing the base drive current from the base terminal of said pass transistor means in response to said current limiting output signal of said current control transistor means.
Claim 10
Dependent Claim
88 words
The apparatus of claim 8 wherein said current source means also sources base current for said shunt transistor means and for the collector-to-emitter current of said current control transistor means, and including a parallel connection of a current controlling resistor and the emitter-to-base diode junction voltage drop of said shunt transistor means, and wherein the collector terminal of said current control transistor is connected to said current source means via said parallel connection of said current control resistor and said emitter-to-base diode junction of said shunt transistor means.
Claim 11
Dependent Claim
79 words
The apparatus of claim 9 wherein said current source means is connected for sourcing current to said second diode junction, a second current control resistor series connected between said current source means and said second diode junction, said series pass transistor means including a pair of series connected base-to-emitter junctions parallel connected with said series connection of said second current control resistor and said second diode junction for developing one base-to-emitter voltage drop across said second current control resistor.
Claim 12
Dependent Claim
66 words
The apparatus of claim 10 wherein the reistances of said first and second current control resistors are proportioned relative to each other and the emitter junction areas of said current control transistor and of said second diode junction are proportioned relative to each other for causing the voltage drop of said second diode junction to be substantially less than that of said current limiting control transistor.
Claim 13
Dependent Claim
116 words
The apparatus of claim 5 wherein said means for developing said second diode junction voltage drop includes a temperature compensating transistor connected as a diode and connected with its collector and emitter terminals in circuit with the base terminal of said current control transistor, and said temperature compensating transistor being connected with its collector-to-emitter terminals connection polarized for conduction in direction away from said base terminal of said current control transistor, and including a resistor connected between the collector and base terminals of said temperature compensating transistor for reducing that portion of the base-to-emitter diode junction voltage of said temperature compensating transistor that is applied in circuit with said base terminal of said current control transistor.
Claim 14
Dependent Claim
114 words
The apparatus of claim 8 wherein said series pass transistor means includes a connection of first, second and third pass transistors each having base, emitter and collector terminals with the base-to-emitter junctions of said three pass transistors connected in series, and said current source means connected for supplying base current to said first pass transistor, a parallel connection of a current control resistor and an emitter-to-base diode junction of a shunt transistor means, the collector terminal of said current control transistor means being connected to the emitter of said first pass transistor via the intermediary of said parallel connection of said current control resistor and said emitter-to-base diode junction of said shunt transistor means.
Claim 15
Dependent Claim
70 words
The apparatus of claim 13 including, a second current control resistor, said second diode junction being connected to said emitter terminal of said first pass transistor via the intermediary of said second current control resistor, and wherein said second current control resistor and said second diode junction are parallel connected with said series connection of said second and third base-to-emitter diode junctions of said second and third pass transistor means.
Claim 16
Dependent Claim
112 words
The apparatus of claim 1 wherein said means for developing said second diode junction voltage drop includes, a temperature compensating transistor connected as a diode and connected with its collector and emitter terminals in circuit with the base terminal of said current control transistor, said temperature compensating transistor being connected with its collector-to-emitter terminal connection polarized for conduction of current in a direction away from said base terminal of said current control transistor, a transconductance compensating resistor connected between the collector and base terminals of said temperature compensating transistor, and wherein said compensating resistor is of a value of resistance approximately equal to the diode resistance of said temperature compensating diode junction.
Claim 17
Dependent Claim
65 words
The apparatus of claim 5 wherein said means for applying only a portion of said developed second diode voltage drop in phase opposition with said base-to-emitter junction voltage of said current control transistor means includes, voltage divider means parallel connected with said second diode junction, and means for connecting the base terminal of said current control transistor to a node of said voltage divider means.
Claim 18
Dependent Claim
76 words
The apparatus of claim 8 including means for sensing the power dissipation of said pass transistor means for deriving a power dissipation sense voltage in accordance therewith and means for applying said power dissipation sense voltage into said input circuit means to said base-to-emitter diode junction voltage drop of said current control transistor means in phase addition with said current sense voltage, for limiting the power in said pass transistor means of said current limiting circuit.
Claim 19
Dependent Claim
52 words
The apparatus of claim 17 wherein said power sensing means includes, potential divider means parallel connected with the collector-to-emitter terminals of said pass transistor means, and means for applying a portion of the potential drop across said potential divider means in circuit with said base-to-emitter junction of said current control transistor means.
Claim 20
Dependent Claim
66 words
The apparatus of claim 8 incluDing, output voltage sensing means for deriving a voltage signal proportional to the output voltage of said current limited circuit, and means for applying said derived voltage signal into said input circuit to said current control transistor in phase opposition with said current sense voltage for reducing the limiting value of current with decreasing output voltage of said current limited circuit.
Claim 21
Dependent Claim
67 words
The apparatus of claim 19 wherein said voltage sensing means includes, potential divider means connected for dropping substantially the output voltage of said current limiting circuit thereacross and a portion of said potential divider means connected in said input circuit to said current control transistor such that the potential drop across said portion of said potential divider is connected in phase opposition with said current sense voltage.
Claim 22
Dependent Claim
28 words
The apparatus of claim 1 wherein said current control transistor means and said means for developing said second diode junction voltage drop utilize a matched pair of transistors.
Claim 23
Dependent Claim
13 words
The apparatus of claim 8 wherein all of said transistors are npn transistors.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-03-11 | 1977-09-10 | 1978-03-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-03-11 | 1981-09-10 | 1982-03-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-03-11 | 1985-09-10 | 1986-03-12 | $7700.00 | Window Closed / Lapsed |