US3753078A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Foldback current control circuit
Assignee: General Electric Co
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Filing: 1972-05-03
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Granted: 1973-08-14
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Expires: 1992-05-03
Abstract
Abstract In a foldback current control circuit, a sensing resistor is connected in series between a source and an output transistor. The sensing resistor biases the emitter of a first transistor of a matched pair included in a comparison circuit. The emitter of the second transistor of the pair is biased by a reference resistor which provides a reference voltage in response to load voltage. When a fault in the load circuit of the output transistor occurs, the reference voltage exceeds a threshold, and the potential at the collector of the second transistor exceeds that of the first in order to turn on a third transistor. The third transistor shunts base drive from the output transistor to prevent damage to the output transistor and load. Selfcompensation of the circuit for temperature is achieved through use of the matched transistors in the comparison circuit and by maintaining nearly equal collector currents in the matched pair during an overload condition.
Inventors
- 👤 K Hedel
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 14:47
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: 6
Claim 1
Independent Claim
201 words
A foldback current control circuit comprising, in combination: a. an output transistor having a collector output for connection between a source and a load; b. a sensing resistor connected in series with the emitter of said output transistor; c. a bias transistor coupled for biasing said output transistor; d. a control transistor for controlling bias of said biasing transistor; e. a reference resistor coupled to provide a voltage drop responsive to the voltage across the load; and f. a current balancing comparison circuit including first and second semiconductors connected for current balancing said second semiconductor being coupled to bias said control transistor, and said first and second semiconductors being respectively coupled to compare the voltage across said sensing resistor and said reference resistor, and said first semiconductor being coupled to provide a current responsive to the voltage across said sensing resistor, the values of the components of said comparison circuit being chosen such that the voltage across said sensing resistor increases above a threshold voltage determined by the value of said reference resistor in response to an overcurrent condition at the load, whereby biasing of said control transistor by said second semiconductor is responsive to an overcurrent condition at the load.
Claim 2
Dependent Claim
201 words
A foldback current control circuit comprising, in combination: a. an output transistor having a collector output for connection between a source and a load; b. a sensing resistor connected in series with the emitter of said output transistor; c. a bias transistor coupled for biasing said output transistor; d. a control transistor for controlling bias of said biasing transistor; e. a reference resistor coupled to provide a voltage drop responsive to the voltage across the load; and f. a current balancing comparison circuit including first and second semiconductors connected for current balancing said second semiconductor being coupled to bias said control transistor, and said first and second semiconductors being respectively coupled to compare the voltage across said sensing resistor and said reference resistor, and said first semiconductor being coupled to provide a current responsive to the voltage across said sensing resistor, the values of the components of said comparison circuit being chosen such that the voltage across said sensing resistor increases above a threshold voltage determined by the value of said reference resistor in response to an overcurrent condition at the load, whereby biasing of said control transistor by said second semiconductor is responsive to an overcurrent condition at the load.
Claim 3
Dependent Claim
78 words
A current control circuit according to claim 1 in which said comparison circuit comprises first and second tranistors having their bases connected together and their emitters respectively connected to said sensing resistor and said reference resistor, the collector of said first transistor being connected to the base of said first transistor, said comparison circuit further including first and second resistors respectively connected between the collectors of said first and second transistors and the base of said biasing transistor.
Claim 4
Dependent Claim
53 words
A control circuit according to claim 2 in which said first and second transistors comprise a matched pair, such that said first and second transistors have the same temperature coefficient, whereby the comparison of the collector voltage of said second transistor to the voltage across said first resistor is self compensating for temperature.
Claim 5
Dependent Claim
41 words
A foldback current control circuit according to claim 2 in which said bias transistor is connected having its emitter-collector circuit connected coupled from the base of said output transistor across the source and having its base connected to said control transistor.
Claim 6
Dependent Claim
56 words
A foldback current control circuit according to claim 4 including means for making said reference resistor responsive to low voltage comprising a transistor having its emitter-base circuit being connected across the load and its collector connected to a first end of said reference resistor, the other end of said reference resistor being connected to the source.
References Cited (Backward Citations)
US2445751A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-08-13 | 1977-02-12 | 1977-08-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-08-13 | 1981-02-12 | 1981-08-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-08-13 | 1985-02-12 | 1985-08-14 | $7700.00 | Window Closed / Lapsed |