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Патент USA US3035132

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May 15, 1962
J. K. LIVINGSTONE
3,035,122
CONSTANT CURRENT LINE CIRCUIT FOR LOOP TELEPHONE .LINES
Filed Sept. 30, 1958
2 Sheets-Sheet 1
TELEPHONE
TELEPHONE
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INVENTOR.
JAMES K. LIVINGSTONE
ATTORNEY
May 15, 1962
3,035,122
J. K. LIVINGSTONE
CONSTANT CURRENT LINE CIRCUIT FOR LOOP TELEPHONE'LINES
Filed Sept. 30, 1958
2 Sheets-Sheet 2'
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INVENTOR.
JAMES K. LIVINGSTONE
32%;”; 2544
ATTORNEY
United States Patent G ” ice
3,035,122
Patented May 15, 1962
1
2
3,035,122
to be representative of the line resistance which, of course,
may vary with the length of the line from the telephone
CONSTANT CURRENT LINE CIRCUIT FOR
LOOP TELEPHONE LINES
exchange to the subscriber subset. The constant cur
rent line circuit of the invention is located in the tele
James K. Livingstone, Webster, N.Y., assignor to General
Dynamics Corporation, Rochester, N.Y., a corporation
11 Claims. (Cl. 179—16)
phone exchange and is connected to the respective tip
and ring conductors of the loop telephone line at the tele
phone exchange so that the majority of the telephone
line resistance is present between the telephone exchange
more particularly, to line circuit arrangements for feed
ing line current from the telephone exchange over a
positive terminal grounded, as is customary in telephone
of Delaware
Filed Sept. 30, 1958, Ser. No. 764,387 7
and the telephone subset at the end of the telephone
This invention relates to telephone line circuits and, 10 line. The telephone exchange battery is indicated at 13
and is a conventional direct current source having its
practice.
loop telephone line to the subscriber subset.
Power transistors 14 and 15 are provided with their
The so-called telephone line circuit for introducing the
operating line current into a loop telephone line from 15 emitter collector electrode circuits connected in series
between respective terminals of the station battery 13
a telephone exchange to a subscriber subset is well
known. The principal functions of the line circuit are
to introduce so-called talking battery or line current into
the line and to respond to on-hook and off-hook condi
tions of the line, such as when the loop is opened or 20
closed, respectively, to provide signaling supervision be
tween the subscriber and the central o?‘ice. One of the
problems with conventional line circuit arrangements is
and a respective one of the conductors 16 and 17 of the
loop telephone line.
More particularly, transistor 14
is a N'PW type of power transistor whose emitter elec
trode is connected in series with a balancing resistor 20
to the negative terminal of the battery 13. Similarly,
the transistor 15 is a PNP type of power transistor whose
emitter electrode is connected in series with a balancing
resistor 21 to the positive terminal of the station battery.
the variation of line current due to differences in the
loop resistance of the line for varying lengths of lines 25 The line conductors 16 and 17 may be connected into
the telephone switching system of the exchange through
between the exchange and the subscriber. Very long loop
suitable isolating capacitors 22 and 23. The base elec
telephone lines have comparatively high resistance and
trode of transistor 14 is connected by circuit means in
the voltage drop of such line is appreciable such that
the line current tends to decrease below a minimum de
cluding a resistance 25 to the telephone line conductor
sirable amount for ef?cient operation of the subset appa
30 17 which is the line conductor other than the conductor
to which the emitter collector circuit of transistor 14 is
connected. Similarly, the base electrode of transistor 15
is connected in a circuit including resistance 26 to the
telephone line conductor 16 which is the conductor other
source of power such as a station battery to a loop
telephone line in a manner to maintain a substantially 35 than the line conductor to which the emitter collector
circuit of transistor 15 is connected. Such connection of
constant line current over varying lengths of loop tele
the base electrode of either transistor 14 or 15 through
phone lines.
either resistor 25 or 26, respectively, to the respective
Another object of the present invention is to provide a
telephone line conductor causes the potential on the base
constant current line circuit for a loop telephone line
that will be relatively insensitive to the frequencies of 40 electrode of the respective transistor to vary in accordance
with variations in resistance of the telephone line between
alternating speech currents normally applied to the
ratus.
It is the principal object of the present invention to
provide an improved arrangement for connecting a
line by the subset apparatus.
Yet another object of the invention is to provide an
improved constant current line circuit for loop telephone
lines employing simple and reliable solid-state compo
nents.
Further objects, features, and the attending advantages
of the invention will be apparent with reference to the
the telephone exchange including the resistance of the
line as indicated at 11, 12, and the subset apparatus 10.
The described arrangement of connection to the respec
tive base electrodes of transistors 14 and 15 is such that
generally good automatic current regulation is obtained
over a fairly wide range of variation of telephone line
loop resistance.
To further improve and stabilize the automatic line
FIG. 1 is a schematic diagram of a preferred embodi 50 current regulation, a reference potential circuit including
resistor 27 may be connected between the base electrode .
ment of the invention as arranged for balanced line oper
following speci?cation and drawings in which:
ation;
FIG. 2 is a schematic diagram of a modi?ed form of
the invention shown in FIG. 1 for use with balanced
lines;
FIGURE 3 is another modi?ed form of the invention
for use with unbalanced telephone lines; and
of transistor 14 and the telephone line conductor 16 to
which the collector electrode of transistor 14 is connected.
Similarly, a reference potential circuit including resistance
55 28 may be connected from the base electrode of transis
tor 15 to the telephone line conductor 17 to which the
collector electrode of transistor 15 is connected. It
should also be mentioned that the previously described
balancing resistances 2i) and 21 are provided for the pur
form of the invention as devised for unbalanced line
operation.
80 pose of obtaining balanced line operation, as should be
understood by those skilled in the art.
The various modi?ed forms of the constant current
A modi?ed form of the line circuit arrangement de
line circuit of the invention will be described in simpli
scribed above in connection with FIG. 1 of the drawings,
?ed arrangements wherein the line circuit supervision
is shown in FIG. 2 of the drawings. The same reference
details are omitted. ‘It should be understood that any
suitable supervision circuits may be provided to respond 65 numerals will be applied to similar circuit elements for
both FIGS. 1 and 2 of the drawings and will not be fur
to the ?ow of line current over the loop telephone line
ther described at this time. The principal difference be
when the subscriber subset is oft-hook to thereby close
tween the circuit of FIG. 2 and that of FIG. 1 is that the
the loop over the telephone line and cause line current to
reference potential circuit including resistors 27 and 28
?ow.
Referring now to FIG. 1 of the drawings, a loop tele 70 is connected directly to the respective terminals of the
station battery instead of to the line conductors 16 and
phone line and subscriber subset is indicated by the box
17. This modi?ed arrangement may be desirable when
designated 10 and the resistances 11 and 12 are shown
. FIG. 4 is a schematic diagram of yet another modi?ed
3,035,122
3
4
certain characteristic types of transistors are employed.
Referring to FIG. 1 of the drawings, a typical arrange
ment of the invention found to be operative and employ
ing power transistors of the type designated may use the
following table of values:
Referring now to FIG. 3 of the drawings, a modi?ed
form of the invention as may be used with unbalanced
loop lines is disclosed. The telephone subset apparatus
or other utilization device 30 and the loop line having
Battery ____________________________ __
loop resistance indicated at 31 and 32, which may vary
Transistor:
with length of loop line, may be connected at the tele
14 ____________________________ __
phone exchange through capacitors 33 and 34 to the tele
15 ____________________________ __
phone switching system. The telephone station battery is
not shown but its negative terminal is connected through 10 Resistor:
27 _________________ __'_________ _.
a resistance 35 to a ?rst conductor 36 of the telephone’
24 volts.
Type 2N365.
Type 2N368.
3,300 ohms.
28 ____________________________ _. 3,300 ohms.
line. The other conductor 37 of the loop line is con
25 ____________________________ _. 27,000 ohms.
nected to the positive grounded terminal of the station
26 ____________________________ _. 27,000 ohms.
battery in series with the emitter collector circuit of a
20 ____________________________ _. 67 ohms.
current regulating power transistor 38 of the PNP type. 15
21 ____________________________ _. 67 ohms.
A resistance 39 may be included in series with the emitter
electrode of the transistor 38 and the grounded terminal
The values for the circuit shown in FIG. 2 when using
of the station battery. The base electrode of transistor
a station battery of 48 volt potential may be as follows:
38 is connected in a circuit including the resistor 40 to
the line conductor 36 which is the conductor other than 20 Transistor:
14 __________________ __'____ Sylvania type 1305.
the conductor with which the emitter collector electrode
15 _____________________ _'__ Sylvania type 1304.
circuit of the transistor 38 is connected. With this ar
Resistor:
rangement, the voltage drop proportional to line loop
25 ______________________ __ 56,000 ohms.
length and resistance is applied across the collector base
circuit of the transistor 38 to provide an automatic cur
rent regulation action. A reference potential circuit in
cluding resistor 40 may also be connected between the
base electrode of transistor 38 and the positive terminal
25
of the station battery, much in a similar manner as the
reference circuit resistors 27 and 28 in the form of the 30
invention shown in FIG. 2 were connected.
Referring now to FIG. 4 of the drawings, yet another
form of unbalanced line constant current line source is
disclosed. The battery source is not shown but its posi
26 ____________________ __-__
27 ______________________ __
28 ______________________ __
20 ______________________ __
56,000 ohms.v
9,100 ohms.
9,100 ohms;
100 ohms,
21 ______________________ .._
100 ohms’.
Considering the table of values given above’ for the
circuit of FIG. 2, it has been found that the loop current
variation for ‘a telephone _ line loop resistance varying
from 100 ohms to 1332 ohms is substantially constant in
the range of 32 or 33 milliamperes.
tive terminal connected to ground and negative terminal 35 A table of values for a typical circuit arrangement
‘are indicated by the conventional positive and negative
shown in connection with FIG. 3 of the drawings using a
symbols. The loop line resistances 31 and 32 and the
station battery of 48 volts may be as follows:
subset apparatus 30 may be the same as described in con
nection with FIG. 3 of the drawings and are given the
Transistor 38 _________________ __ Sylvania type 1304.
same reference numerals. The positive terminal of the 40 Resistor:
station battery is connected in series with the emitter
40 ______________________ __ 56,000 ohms.
collector electrode circuit of a PNP power transistor 38
41 ______________________ __ 9,100 ohms.
to the ?rst conductor 36 of the unbalanced loop line.
39 ______________________ __ ‘100 ohms.
The other conductor 37 of the unbalanced loop line is
connected in series with a resistance 35 to the negative
terminal of the station battery.
The base electrode of 45
35 ______________________ __ 200 ohms.
With the values given above for the circuit of FIG. 3,
the current regulating transistor 38 is connected in a
the line current over the loop line having a loop re
circuit including resistor 40‘ to the second conductor 37
sistance varying from 100 ohms to about 1250 ohms will
be maintained within the range of ‘approximately 38 mil
of the unbalanced loop line which is the conductor other
liamperes.
than the conductor 36 to which the collector electrode
of the transistor 38 is connected. The reference potential 50
vIt should perhaps be pointed out that the use of a con
circuit including the resistor 41 in this form of the inven
ventional shunt inductor feed telephone line circuit with
tion may be connected between the base electrode of
a station battery of 24 volts would provide a variation of
transistor 38 and the ?rst conductor 36 of the telephone
between 48 milliamperes and 15 milliamperes of line cur
line instead of to the positive terminal of the station bat
rent for a loop variation of 100 to 1350 ohms, respec
tery as was shown in connection with FIG. 3 of the draw 55 tively. This may be compared with the improved re
ings. As thus far described, the arrangement of FIG. 4
sults obtained with the constant current line circuit ar
is essentially the same as that of FIG. 3 of the drawings
rangement of FIG. 1, for example, in which for a varia
and provides a degree of line current regulation with the
tion of loop resistance in the range of 100 to 1350 ohms
principal difference being the aforementioned method of
the loop current extreme variations are onlybetween 8
connecting the reference resistance 41 to the line con 60 and 12 milliamperes with ‘a station battery of 24 volts.
ductor 36 instead of to‘ the source ground terminal. To
It will be seen, therefore, that the arrangement of the
provide additional current regulation, a power transistor
subject invention reduces the range of line current varia
50 may be connected with its emitter collector circuit in
tion from a variation of about 33 milliarnperes to a total
shunt with the resistance of the telephone line 31, 32, and
variation of only about 4 milliamperes. With this im
the telephone subset 30. The base electrode of the PNP 65 provement in line current regulation it is possible to ob
power transistor 50 is connected for control purposes
tain improved operation and simpli?ed arrangements for
through ‘a circuit including the resistance ‘51 to the ?rst
the supervisory signaling at the central o?ice responding
conductor 36 of the telephone line and through a refer
to variations in loop telephone line loop current and it
ence resistance 52 to the second conductor 37 of the tele
is also possible to provide improved e?iciency of opera
phone line. It should be apparent that this arrange 70 tion of the telephone subset apparatus since it is required
ment is such that the shunt resistance of the transistor
to function over a much smaller range of variation of
line current.
50 automatically decreases for decreased resistance of
the loop line in a manner to further regulate the current
Various modi?cations will occur to those skilled in
flow through the line by the division of current through
the art within the spirit of the invention and the scope of
the shunt connected transistor 50.
75 the appended claims.
3,035,122
5
What is claimed is:
1. In a telephone system, a central o?ice, a plurality
of subscriber telephones, a two conductor loop telephone
1line individually connecting each telephone to said cen
tral office, each of said lines having a particular resis
tance which is determined by the size and length thereof,
6
a source of direct cunrent, circuit means for connecting
the negative terminal of said source in series with a ?rst
resistance and to one conductor of said line in series with
the emitter collector circuit of said NPN transistor, cir
cuit means for connecting the positive terminal of sai
source in series with a second resistance and to the other
conductor of said line in series with the emitter collector
circuit of said NPN transistor, and circuit means for con
necting the base electrode of each of said transistors to
and collector electrodes, ?rst circuit means in said central
o?ice for connecting one terminal of said power source 10 the conductor of said line other than the conductor to
which the respective emitter collector circuit of each tran
through the emitter-collector circuit of said transistor to
sistor is connected.
one conductor of one of said telephone lines at the cen
6. A “constant current line circuit for a two conductor
tral of?ce end thereof, second circuit means for connect
loop telephone line whose impedance may vary with
ing the other terminal of said power source through an
length comprising, a ?rst transistor, -a second transistor,
impedance device to the other end of said one of said
a direct current power source of constant potential in
said central o?ice, a ?rst transistor having base, emitter,
telephone lines at the central office end thereof, whereby
the potential appearing at said central o?ice end of said
a source of direct current, circuit means for connecting
one terminal of said source in series with a ‘?rst resistance
other conductor is a function of the series circuit formed
and to one conductor of said line in series with the emitter
collector circuit of said ?rst transistor, circuit means for
by the emitter-collector resistance of said transistor, the
particular resistance of said one of said telephone lines, 20 connecting the other terminal of said source in series
with a second resistance and to the other conductor of
and the resistance of said impedance device, third circuit
said line in series with the emitter collector circuit of
means for connecting the base electrode of said tran
said second transistor, circuit means for connecting the
sistor to said central o?ice end of said other conductor of
base electrode of each of said transistors to the conductor
said one of said telephone lines to vary the emitter-col
lector resistance of said transistor in accordance with the 25 of said line other than the conductor to which the re
spective emitter collector circuit of each transistor is con
potential of said other conductor to make the current
nected, and circuit means for connecting the base elec
through said series circuit substantially independent of
trode of each of said transistors to the terminal of said
the magnitude of said particular resistance of said one
source with which the respective transistor is connected
of said telephone lines.
2. A constant current line circuit for a two conductor 30 in series to a conductor of the line.
7. A constant current line circuit for a two conductor
loop telephone line whose impedance may vary with
comprising, a ?rst transistor, a second transistor, a source
loop telephone line whose impedance may vary with length
of direct current, ?rst circuit means for connecting one
terminal of said source to one conductor of said line in
length comprising, a NPN transistor, a PNP transistor,
a source of direct current, circuit means for connecting
the negative terminal of said source in series with a ?rst
series with the emitter collector circuit of said ?rst tran
resistance and to one conductor of said line in series with
sistor, second circuit means for connecting the other
the emitter collector circuit of said NPN transistor, cir
terminal of said source to the other conductor of said
cuit means for connecting the positive terminal of said
line in series with the emitter collector circuit of said
source in series with a second resistance and to the other
second transistor, and third circuit means for connect
ing the base electrode of each of said transistors to the 40 conductor of said line in series with the emitter collector
circuit of said PNP transistor, circuit means for connect
conductor of said line other than the conductor to which
ing the base electrode of each of said transistors to the
the respective emitter collector circuit of each transistor
conductor of said line other than the conductor to which
is connected.
the respective emitter collector circuit of each transistor
3. A constant current line circuit for a two conductor
is connected, and circuit means for connecting the base
loop telephone line whose impedance may vary with
electrode of each of said transistors to the terminal of
length comprising, a NPN transistor, a PNP transistor,
a source of direct current, ?rst circuit means for con
necting the negative terminal of said source to one con
ductor of said line in series with the emitter collector cir
cuit of said NPN transistor, second circuit means for con
necting the positive terminal of said source to the other
conductor of said line in series with the emitter collector
circuit of said PNP transistor, and third circuit means
for connecting the base electrode of each of said tran
sistors to the conductor of said line other than the con
ductor to which the respective emitter collector circuit of
each transistor is connected.
4. A constant current line circuit for a two conductor
loop telephone line whose impedance may vary with
length comprising, a ?rst transistor, a second transistor,
:11 source of direct current, ?rst circuit means for con
nectlng one terminal of said source in series with a ?rst
resistance and to one conductor of said line in series with
the emitter collector circuit of said ?rst transistor, sec
said source with which the respective transistor is con
nected in series to a conductor of the line.
8. A constant current line circuit for a two conduc
tor loop telephone line whose impedance may vary with
length comprising, a ?rst transistor, a second transistor,
a source of direct current, circuit means for connecting
one terminal of said source in series with a ?rst resistance
and to one conductor of said line in series with the emitter
collector circuit of said ?rst transistor, circuit means for
connecting the other terminal of said source in series
with a second resistance and to the other conductor of said
line in series with the emitter collector circuit of said
second transistor, circuit means for connecting the base
electrode of each of said transistors to said one conductor
of said line, and circuit means for connecting the base
electrode of each of said transistors to the said other
conductor of said line.
9. A constant current line circuit ‘for a two conductor
ond circuit means for connecting the other terminal of
loop telephone line whose impedance may vary with
said source in series with a second resistance and to the
length comprising, a NPN transistor, a PNP transistor,
a source of direct current, circuit means ‘for connecting
other conductor of said line in series with the emitter
the negative terminal of said source in series with a ?rst
collector circuit of said second transistor, and third cir
resistance and to one conductor of said line in series with
cuit means for connecting the base electrode of each of
said transistors to the conductor of said line other than 70 the emitter collector circuit of said NPN transistor, cir
cuit means for connecting the positive terminal of said
the conductor to which the respective emitter collector
source in series with a second resistance and to the other
circuit of each transistor is connected.
conductor of said line in series with the emitter collector
5. A constant current line circuit for a two conductor
circuit of said NPN transistor, circuit means for con
loop telephone line whose impedance may vary with
necting the base electrode of each of said transistors to
length comprising, a NPN ‘transistor, a PNP transistor,
3,035,122
7
8
said one conductor of said line, and circuit means for
connecting {the base electrode ‘of each of said transistors
to said other conductor of said line.
sistor, circuit means for connecting one terminal of said
source to one conductor of said line in series with the
10. A constant current line circuit for a two conductor
loop telephone line whose impedance may vary with
length comprising, a source of direct current, a ?rst PNP
‘transistor, circuit means for connecting the positive termi
nal of said source to one conductor of said line in series
with the emitter collector circuit of said ?rst transistor,
circuit means for connecting the negative terminal of said 10
References Cited in the ?le of this patent
source in series with a resistance to the other conductor
of said line, a second NPN transistor, circuit means con
necting the emitter collector circuit of said second tran
sistor between said other conductor of said line and the
positive ‘terminal of said source, and circuit ‘means for 15
cross connecting the base electrode of each of said tran
sistors to the conductors of said line.
11. A constant current line circuit for a two conduc
tor loop telephone line whose impedance may vary with
length comprising, a source of direct current, a tran
emitter collector circuit of ‘said transistor, a resistance
device interconnecting the other terminal of said source
‘and the other conductor of said line, circuit means for
connecting the base electrode of said transistor ‘to said
other conductor of said line, and circuit means for con
necting the base electrode of said transistor to said one
terminal of said source.
20
UNITED STATES PATENTS
2,693,568
Chase _____________ __V__ Nov. 2, 1954
2,751,549
Chase _______________ __ June 19, 1956
2,832,035
2,841,757
2,897,430
2,897,431
2,897,432
Bruck et a1 ___________ __ Apr. 22,
Shields ______________ __ July 1,
Te Winkel ____________ __ July 28,
Wolfendale __________ __ July 28,
'Jackson _____________ __ July 28,
1958
1958
1959
1959
1959
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent No. 3,035, 122
May 15, 1962
James K. Livingstone
It is hereby ce
rtified that error appears in the ab
ant requiring correcti
corrected below.
ove numbered pet
on and that the said Letters Patent 8
hould read as
line 19,’ for "NPW“ read -— NPN --; column 6,
Column 2, for "NPN", each occurrence, read —— PNP —-.
lines 8 and 74,
Signed and sealed this 16th day of October 1962.
SEAL)
kttest:
ERNEST w. SWIDER
Attesting Officer
DAVID L. LADD
Commissioner of Patents
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