Patent US4270159A successfully refreshed from Google Patents.
US4270159A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Transistor protection circuits
Assignee: ZF International UK Ltd
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Filing: 1979-05-01
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Granted: 1981-05-26
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Expires: 1999-05-01
Abstract
Abstract A circuit employing parallel power transistors intended to share the load current, includes a separate current sensing resistor for each transistor and independently operating protection circuits controlled by the voltage drop across the associated sensing resistor to limit the current in each power transistor to a safe level. The protection circuits each include zener diodes and resistors connected to vary the current limit in accordance with the voltage across the power transistors.
Inventors
- 👤 Allan S. Buckle
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 06:51
CPC Classifications
H; H03; H03F; H03F1/00; H03F1/52
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
159 words
A transistor circuit comprising a power supply rail, a return rail, a load terminal for connection by a load to the supply rail, first and second power transistors having their collector-emitter paths in parallel between the load terminal and the return rail so as to share between them a load current, first and second means sensitive to the current carried by the first and second power transistors, respectively, and operating to limit the current in each power transistor, means sensitive to the voltage across the collector-emitter paths of the power transistors and connected to vary the current limit in accordance with said voltage, said voltage circuits each including a zener diode and a resistor, a diode having one pole connected to the load terminal, and a capacitor connecting the other pole of said capacitor to the return rail, the first and second series circuits being connected between said other pole of the diode and the respective current sensitive means.
Claim 2
Dependent Claim
159 words
A transistor circuit comprising a power supply rail, a return rail, a load terminal for connection by a load to the supply rail, first and second power transistors having their collector-emitter paths in parallel between the load terminal and the return rail so as to share between them a load current, first and second means sensitive to the current carried by the first and second power transistors, respectively, and operating to limit the current in each power transistor, means sensitive to the voltage across the collector-emitter paths of the power transistors and connected to vary the current limit in accordance with said voltage, said voltage circuits each including a zener diode and a resistor, a diode having one pole connected to the load terminal, and a capacitor connecting the other pole of said capacitor to the return rail, the first and second series circuits being connected between said other pole of the diode and the respective current sensitive means.
Claim 3
Dependent Claim
65 words
A transistor circuit as claimed in claim 1 in which each current sensitive means comprises a resistor in series with the associated power transistor and a protection transistor controlled by the voltage across said resistor and connected to the base of the associated power transistor so as to shunt base current from that power transistor when the voltage across the resistor exceeds a predetermined limit.
Claim 4
Dependent Claim
57 words
A transistor circuit as claimed in claim 2 in which said resistor connects the emitter of the power transistor to a supply conductor and the protection transistor has its collector-emitter path connected between the base of the power transistor and said supply conductor, the protection transistor conducting when the voltage across said resistor exceeds said predetermined limit.
Claim 5
Dependent Claim
42 words
A transistor circuit as claimed in claim 3 in which the protection transistor is of the same conductivity type as the power transistor and has its emitter and collector connected to said supply rail and the base of the power transistor respectively.
Claim 6
Dependent Claim
31 words
A transistor circuit as claimed in claim 4 in which the base of the protection transistor is connected to a point on a resistive voltage divider chain connected across said resistor.
Claim 7
Dependent Claim
29 words
A transistor circuit as claimed in claim 5 including a further resistor and a further zener diode in parallel with said zener diode and resistor which are in series.
Claim 8
Dependent Claim
32 words
A transistor circuit as claimed in claim 4 or claim 5 including reactance means connected to the collector of each protection transistor and acting to slow down switching of the protection transistor.
Claim 9
Dependent Claim
25 words
A transistor circuit as claimed in claim 7 in which said reactance comprises a capacitor connected between the base and collector of said protection transistor.
Claim 10
Dependent Claim
31 words
A transistor circuit as claimed in claim 7 in which said reactance means comprises a inductor connected between the collector of the protection transistor and the base of the power transistor.
Claim 11
Dependent Claim
27 words
A transistor circuit as claimed in claim 4 or claim 5 further comprising a capacitor connected between the base of each protection transistor and said supply rail.
Claim 12
Dependent Claim
31 words
A transistor circuit as claimed in claim 6 further comprising a plurality of capacitors respectively connecting the junction of each zener diode and its associated series resistor to said supply rail.
References Cited (Backward Citations)
US3668545A
Cited
US4105944A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-05-25 | 1984-11-24 | 1985-05-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-05-25 | 1988-11-24 | 1989-05-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-05-25 | 1992-11-24 | 1993-05-26 | $7700.00 | Window Closed / Lapsed |