US3671879A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Transistor protection circuit
Assignee: Emerson Electric Co
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Filing: 1970-11-09
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Granted: 1972-06-20
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Expires: 1990-11-09
Abstract
Abstract A protection circuit for use with a transistor amplifier comprises a normally non-conductive transistor adapted to be connected across the input and output terminals of the output transistors of a power amplifier. An impedance network is coupled to the power amplifier so that it can derive voltages dependent upon the current flow in the emitter-collector circuit of the power amplifier and the emitter-collector voltage drop. These voltages are applied to the base of the protection transistor to drive it into conduction in the event either one of the signals, or the combination of both exceeds a predetermined limit. Thus, in the event of an overload (due, for example, to excessive load currents or overdriving the transistor), the drive signal is shunted from the power amplifier output stages. This action is analogous to a limiting action and prevents overload conditions from injuring or destroying the power amplifier.
Inventors
- 👤 John J Klanatsky
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 00:30
CPC Classifications
H; H03; H03F; H03F1/00; H03F1/52
Claims Analysis
Total Claims: 2
Claim 1
Independent Claim
295 words
A transistor protection circuit for use with a power amplifier having input terminals to which a drive signal can be coupled and a common output terminal to which a load can be connected, said power amplifier comprising a push-pull amplifier having two power amplifier stages comprising a. a normally non-conductive protection transistor associated with each said power amplifier stage, each protection transistor having its emitter-collector circuit connected between an input terminal for its associated power amplifier stage and said output terminal, b. a pair of diodes connected respectively to the collectors of each of said protection transistors for preventing forward biasing of the collector-base junctions thereof c. a pair of resistive networks associated with said power amplifier stages, respectively, each said resistive network including i. a first resistor series-connected in the emitter-collector circuit of its associated power amplifier stage for producing a voltage dependent upon the magnitude of current flowing in said emitter-collector circuit, and ii. three additional resistors, said additional resistors of each network having a common junction coupled to the base of the associated protection transistor, the other ends of two of said additional resistors being connected, respectively, to said collector and emitter of the associated power amplifier stage, and the other end of the third additional resistor being connected to said common output terminal, said three additional resistors of each network producing a voltage at said common junction primarily dependent upon the emittercollector voltage across the associated power amplifier stage, the values of said resistors being selected so that the associated protection transistor is driven into conduction when the sum of the voltages at said common junction exceeds a predetermined level to thereby provide a shunt current path through the emitter-collector circuit of said protection transistor around its associated power amplifier stage.
Claim 2
Dependent Claim
295 words
A transistor protection circuit for use with a power amplifier having input terminals to which a drive signal can be coupled and a common output terminal to which a load can be connected, said power amplifier comprising a push-pull amplifier having two power amplifier stages comprising a. a normally non-conductive protection transistor associated with each said power amplifier stage, each protection transistor having its emitter-collector circuit connected between an input terminal for its associated power amplifier stage and said output terminal, b. a pair of diodes connected respectively to the collectors of each of said protection transistors for preventing forward biasing of the collector-base junctions thereof c. a pair of resistive networks associated with said power amplifier stages, respectively, each said resistive network including i. a first resistor series-connected in the emitter-collector circuit of its associated power amplifier stage for producing a voltage dependent upon the magnitude of current flowing in said emitter-collector circuit, and ii. three additional resistors, said additional resistors of each network having a common junction coupled to the base of the associated protection transistor, the other ends of two of said additional resistors being connected, respectively, to said collector and emitter of the associated power amplifier stage, and the other end of the third additional resistor being connected to said common output terminal, said three additional resistors of each network producing a voltage at said common junction primarily dependent upon the emittercollector voltage across the associated power amplifier stage, the values of said resistors being selected so that the associated protection transistor is driven into conduction when the sum of the voltages at said common junction exceeds a predetermined level to thereby provide a shunt current path through the emitter-collector circuit of said protection transistor around its associated power amplifier stage.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-06-20 | 1975-12-20 | 1976-06-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-06-20 | 1979-12-20 | 1980-06-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-06-20 | 1983-12-20 | 1984-06-20 | $7700.00 | Window Closed / Lapsed |