US3641407A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Inductor surge protection for transistors
Assignee: AT&T Teletype Corp
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Filing: 1970-10-26
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Granted: 1972-02-08
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Expires: 1990-10-26
Abstract
Abstract A circuit for clamping a voltage induced across an inductor utilizes a Zener diode to control the energy dissipation of the inductor through a transistor. A driver circuit for an inductor includes a Zener diode and an opposing diode connected across the series combination of the base-emitter junction of an emitterfollower output transistor and the inductor driven thereby. When the transistor is conducting, the inductor is energized and no current flows through the Zener diode. When the transistor is caused to cease conduction, the field of the coil of the electromagnet collapses, generating a voltage that is applied to the emitter of the output transistor. If the voltage thus generated is greater than the Zener breakdown voltage, the Zener diode breaks down and provides a bias current to the base of the output transistor to permit further conduction of the transistor and clamps the voltage at the emitter of the transistor to substantially the value of the Zener breakdown voltage. The voltage generated by the inductor is thus prevented from applying too high a voltage across the collector-emitter circuit of the output transistor, which might damage the transistor. The transistor continues to conduct during the dissipation of the energy stored in the inductor until the inductor is almost fully deenergized and can no longer generate a voltage equal to the Zener diode breakdown voltage. The output transistor is then rendered nonconductive, completing the deenergization of the inductor.
Inventors
- 👤 Richard D Scott
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 06:01
CPC Classifications
H; H02; H02H; H02H9/00; H02H9/005; H03; H03K; H03K17/00; H03K17/08; H03K17/081; H03K17/0814; H03K17/08146
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
97 words
A method of controlling the induced potential associated with the energy dissipation of an inductor connected to a transistor having at least a base and an emitter to avoid damage to said transistor when said transistor is rendered nonconductive, comprising the steps of: connecting the inductor to the emitter of the transistor; clamping the base of the transistor to a predetermined limiting value of induced potential to forward bias the transistor and provide a current path for the induced current through said inductor; and removing said forward bias when the induced potential falls below a predetermined value.
Claim 2
Independent Claim
97 words
A method of controlling the induced potential associated with the energy dissipation of an inductor connected to a transistor having at least a base and an emitter to avoid damage to said transistor when said transistor is rendered nonconductive, comprising the steps of: connecting the inductor to the emitter of the transistor; clamping the base of the transistor to a predetermined limiting value of induced potential to forward bias the transistor and provide a current path for the induced current through said inductor; and removing said forward bias when the induced potential falls below a predetermined value.
Claim 3
Dependent Claim
24 words
A method according to claim 1 wherein the clamping is accomplished by: limiting the potential that can exist at the base of the transistor.
Claim 4
Dependent Claim
20 words
A method according to claim 1 further including isolating the transistor from similar transistors after removal of said forward bias.
Claim 5
Dependent Claim
99 words
A circuit for contrOlling the energy dissipation of an inductor connected to a conducting transistor having at least a base and an emitter when said transistor is rendered nonconductive, comprising: means for connecting the inductor between a voltage reference and the emitter of the transistor; means connected to the base of the transistor and responsive to the induced voltage across said inductor for forward biasing the base-emitter junction of said transistor to provide a current path for the induced current through said inductor; and means for removing said forward bias when the induced potential falls below a predetermined value.
Claim 6
Dependent Claim
99 words
A circuit for contrOlling the energy dissipation of an inductor connected to a conducting transistor having at least a base and an emitter when said transistor is rendered nonconductive, comprising: means for connecting the inductor between a voltage reference and the emitter of the transistor; means connected to the base of the transistor and responsive to the induced voltage across said inductor for forward biasing the base-emitter junction of said transistor to provide a current path for the induced current through said inductor; and means for removing said forward bias when the induced potential falls below a predetermined value.
Claim 7
Dependent Claim
35 words
A circuit as set forth in claim 4 wherein said means connected to the base of the transistor includes a Zener diode connected in parallel with the base-emitter junction of said transistor and said inductor.
Claim 8
Dependent Claim
95 words
In a circuit for driving an inductor, an output transistor having a base, a collector, and an emitter connected as an emitter follower, inductor being connected as a load in the emitter circuit of said transistor; means for rendering said transistor conductive to energize said inductor; means for rendering said transistor nonconductive to deenergize said inductor whereby said inductor applies a voltage to said emitter; and means responsive to the voltage applied by said inductor to said emitter for clamping the voltage applied to the emitter to a predetermined value insufficient to damage the transistor.
Claim 9
Dependent Claim
95 words
In a circuit for driving an inductor, an output transistor having a base, a collector, and an emitter connected as an emitter follower, inductor being connected as a load in the emitter circuit of said transistor; means for rendering said transistor conductive to energize said inductor; means for rendering said transistor nonconductive to deenergize said inductor whereby said inductor applies a voltage to said emitter; and means responsive to the voltage applied by said inductor to said emitter for clamping the voltage applied to the emitter to a predetermined value insufficient to damage the transistor.
Claim 10
Dependent Claim
27 words
In a circuit for driving an inductor as recited in claim 6, wherein said clamping means includes a Zener diode connected to the base of said transistor.
Claim 11
Dependent Claim
139 words
An improved circuit for protecting a transistor with at least a base, a collector, and an emitter and having an inductive load from the effect of an increasing potential difference between its collector and emitter when the transistor undergoes a change from a conducting to a nonconducting state and the field of said inductor collapses, wherein the improvement comprises: means for connecting the inductive load to the emitter of the transistor; and means connected in parallel with the inductor and the base-emitter junction of the transistor and response to an initial increase in potential between said collector and emitter by the induced potential of the inductor for forward biasing the base-emitter junction of said transistor to dissipate the energy of said inductor through said transistor while limiting the potential of the emitter thereof to a predetermined increase in value.
Claim 12
Dependent Claim
139 words
An improved circuit for protecting a transistor with at least a base, a collector, and an emitter and having an inductive load from the effect of an increasing potential difference between its collector and emitter when the transistor undergoes a change from a conducting to a nonconducting state and the field of said inductor collapses, wherein the improvement comprises: means for connecting the inductive load to the emitter of the transistor; and means connected in parallel with the inductor and the base-emitter junction of the transistor and response to an initial increase in potential between said collector and emitter by the induced potential of the inductor for forward biasing the base-emitter junction of said transistor to dissipate the energy of said inductor through said transistor while limiting the potential of the emitter thereof to a predetermined increase in value.
Claim 13
Dependent Claim
21 words
A circuit according to claim 8 wherein the inductor is connected between the emitter of the transistor and a reference potential.
Claim 14
Dependent Claim
26 words
A circuit according to claim 9 wherein the forward biasing means comprises a Zener diode connected between the reference potential and the base of the transistor.
Claim 15
Dependent Claim
18 words
A circuit according to claim 10 further including an isolation diode connected in series with the Zener diode.
Claim 16
Dependent Claim
25 words
A circuit according to claim 11 wherein the isolation diode is arranged to conduct current in series with the forward-biased base-emitter junction of the transistor.
Claim 17
Dependent Claim
22 words
A circuit according to claim 12 wherein the isolation diode is connected between the Zener diode and the base of the transistor
Claim 18
Dependent Claim
27 words
A circuit according to claim 13 further including at least one additional diode connected to the Zener diode at its point of connection with the isolation diode.
Claim 19
Dependent Claim
21 words
A circuit according to claim 14 further including at least one additional transistor having a base connected to the additional diode.
Claim 20
Dependent Claim
52 words
A circuit for protecting a transistor having at least a base and an emitter from the voltage applied by an inductor comprising: the inductor connected between the emitter of said transistor and a terminal at a reference potential; and a Zener diode connected between the base of the transistor and the terminal.
Claim 21
Dependent Claim
52 words
A circuit for protecting a transistor having at least a base and an emitter from the voltage applied by an inductor comprising: the inductor connected between the emitter of said transistor and a terminal at a reference potential; and a Zener diode connected between the base of the transistor and the terminal.
Claim 22
Dependent Claim
21 words
A circuit according to claim 16 further comprising a diode connected between said Zener diode and the basE of the transistor.
References Cited (Backward Citations)
US3340407A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-02-07 | 1975-08-09 | 1976-02-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-02-07 | 1979-08-09 | 1980-02-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-02-07 | 1983-08-09 | 1984-02-08 | $7700.00 | Window Closed / Lapsed |