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Патент USA US2413033

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Dec. 24, 1946.
Filed July 29, 1942
2 Sheets-Sheet 1
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Patented Dec. 24, 1946
James A. Potter, Rutherford, N. J., assignor to
Bell Telephone Laboratories, Incorporated,
New York, N. Y., a corporation of New York
Application July 29, 1942, Serial No. 452,728
10 Claims. (Cl. 175-363)
This invention relates to voltage regulators for
' alternating current rectifying systems.
An object of the invention is to provide an in
expensive device for regulating the voltage of rec
ti?ed current.
An additional object of the invention is to cause
the voltage supplied by a rectifying system to
a load to be held substantially constant irrespec
current input lead to the main recti?er or in a di
rect current output lead of that recti?er. The
heat supplied to the thermistor by the auxiliary
heating circuit may be controlled by a relay re
sponsive to the recti?ed voltage impressed upon
the unidirectional current load circuit in such a
manner as to close the auxiliary circuit when
that voltage is low and to open it when it is high.
The relay may thus supply intermittent heating
Another object of the invention is to enable 10 effects to the thermistor which are smoothed out
a thermistor employed in a voltage regulating
by the thermal inertia of the thermistor.
systems to be placed at a sensitive point in its \
Other features and aspects of the invention
tive of variations in the load current.
resistance thermal characteristic under the con
dition of no load.
will be apparent from a consideration of the fol
which the rectifying system supplies unidirec
regulating the voltage supplied to the load in ac
lowing detailed speci?cation taken in connection
In accordance with the invention there is in 15 with the accompanying drawings in which:
terposed between an alternating current source
Fig. 1 is a circuit diagram of an alternating
of a rectifying system and the load circuit to
current rectifying system with provisions for
tional current a series impedance element the
cordance with certain principles of this inven
resistance of which is a function of the tempera 20 tion;
ture of the element. When the element is cold
Fig. 2 is a circuit diagram of a modi?cation of
its resistance is very high. When its temperature
rises the resistance decreases and at a certain
point in its characteristic the rate of fall of the
resistance is extremely high.‘ Such elements, 25
known as thermistors, are described by Pearson
the system of Fig. 1 in which the series thermistor
element is connected in the alternating current
input circuit of the recti?er;
Fig. 3 is another modi?cation in which the aux
iliary heating circuit of the thermistor ‘is provided
with an auxiliary recti?er;
Fig. 4 illustrates a modi?cation of the circuit
of Fig. 3 in which the thermistor is connected
tures associated with low load current is relative 30 between the current supply ?lter and the load;
ly high.‘ As the load current rises the heating
Fig. 5 is a circuit diagram of a voltage regu
' lated rectifying current supply system in which
effect of the current upon the thermistor also
rises reducing the thermistor resistance to com
the series thermistor is provided with an addi
pensate for the increased resistance of the rec
tional indirect heating circuit;
Fig. 6 is a graph employed to explain the op
ti?er and current supply circuit. Additional eration of the circuit of Fig. 5; and
heating of the thermistor to accentuate the
change in its resistance may be obtained by asso
Fig. 7 is a circuit diagram of a system for
ciating it inphysically close relation to the rec
regulating the voltage of recti?ed current in
ti?er or the current supply transformer to facili
which the indirect heating circuit of the regulat
tate heat transfer to the thermistor. The ther 40 ing thermistor is intermittently energized in re
mistor may be initially brought to the proper
sponse to the operation of a Wheatstone bridge
point on its resistance temperature characteristic
connected directly across the load circuit.
at no load by a separate heating circuit connected
Referring to Fig. 1 a source i of alternating
to an auxiliary winding of the current supply
current to be recti?ed is shown connected by a
transformer. In order to prevent the introduc 45 current supply transformer 2 to a full wave rec
tion of ripples by the auxiliary heating circuit in
tifier 3 of well-known type the output leads 4 and
the load current the heating circuit may include
5 of which conduct recti?ed current to the uni
an auxiliary recti?er and ?lter or the thermistor
directional current load 6 through a smoothing
may be connected between the load current rec
?lter ‘I. The transformer 2 is provided with an
ti?er and the load current ?lter.
50 auxiliary secondary winding 9 having a variable
Since the function of the thermistor is to re
tap l0 and variable resistor I l in series therewith
duce the voltage derived from the alternating
for supplying an alternating heating current di
current source by an amount which varies in in
rectly to thermistor 8. At the no load condition
verse manner with the load current, the ther
the only current in the thermistor 8 is alternat
in the Bell Laboratories Record for December
1940. In the operation of the recti?er system the
resistance of the thermistor at the low tempera
mistorimay be placed either in an'alternating
ing Current derived from the secondary winding
9 and the magnitude of which is determined by
the position of variable tap l0 and the setting of
IT through the shunt path two additional regu
lating effects are brought about. The ?rst is
variable resistor I l in order to ?x the temperature
of thermistor 8 at a point for which the resistance
of the thermistor lies within the required operat
occasioned by the fact that the shunt current IT
traverses the series thermistor 22 and therefore
ing range.
This is highly desirable for the reason
changes the resistance of thermistor 22 and the
consequent potential drop vacross the thermistor
as does a change in the load current itself. In
that the resistance temperature characteristic of
the thermistor begins with a rapidly rising por
the second place the current T1‘ of the shunt path
tion reaching a point beyond which the resistance
is caused to traverse an indirect heater 2i of the
rapidly falls and it is desired to operate on the 10 thermistor 22 to produce an additional effect
falling portion of the characteristic. At higher
upon the resistance of that thermistor. It will
therefore be apparent that very slight changes
loads there is a potential drop in the current sup
in the voltage applied by the system across l9
ply transformer, the recti?er and the circuit con
ductors which tends to reduce the recti?ed volt
and 20 to the load will set into action correcting
age available at the load input terminals. Since, 15 factors which will tend to hold that potential
very closely constant irrespective of changes in
however, the temperature of the thermistor 8
rises rapidly with increased load current, the re
the magnitude of the load current.
It remains to consider the action of the shunt
sistance of the thermistor consequently under
path in drawing the shunt current IT which
goes a large decrease, thus reducing the potential
drop across the thermistor so that the unidirec 20 changes greatly for small changes in the voltage
tional voltage applied to the load remains sub
applied to the load terminals. Assume that the
system is in operation with the relay 24 energized
stantially constant. The initial setting of the
as shown in Fig. 5 so that its armature 3| is with
transformer tap and of the variable resistance
may be changed from time to time to take care of
drawn from the ?xed contact 30. The shunt path
aging in the recti?er and to allow for operation 25 connecting points l9 and 20 comprises a ther
in several ambient temperature ranges.
mistor 27, a special resistor 26, winding of relay
The ?lter ‘i not only smooths out the recti?ed
2d, variable resistor 23 and the heater 2! of ther
‘mistor 22. The characteristics of the elements
current but also keeps the alternating current
impressed directly upon the thermistor from
of this shunt path are illustrated in Fig. 6, it
being understood that the apparatus is designed
reaching the load. The elements of the full wave
for operation for shunt currents IT extending
recti?er may be of the well-known copper oxide
'over a range of In to Im. The voltage current
characteristic Er of thermistor 21 is such that
In order to still further accentuate the resist
the potential difference across the thermistor
ance change of thermistor 8 with varying load
the thermistor maybe mounted in close prox 35 falls rapidly and non-linearly from its magnitude
at current Io to the magnitude which it assumes
imity to the recti?er 3 to be subjected to the heat
developed by the recti?er. If desired the recti?er
at the larger current Im. In fact, the thermistor
21 considered alone is unstable since the greater
3 and thermistor 8 may be enclosed in a common
thermally insulated enclosure or housing [2 to
its current and internal heating becomes, the
stabilize the thermal environment and reduce 40 less its resistance and the greater the current it
will tend to accept. This large change in current
extraneous effects.
is conducive to e?ective regulation in its e?ect
Fig.2 discloses a modi?cation of the system of
upon the resistance of the series thermistor 22.
Fig. 1 in which the thermistor i3 is connected in
series in one of the alternating current input
However, the fall in potential across the ther
’ leads to the recti?er 3. In this circuit the ther 45 mistor 21 of the shunt path would by itself be
very detrimental to maintenance of a constant
mistor l3 and the transformer 2 may be mounted
in close proximity to each other to facilitate heat
potential across the load terminals I9, 20. To
reduce this potential variation across the shunt
transfer from the transformer to the thermistor.
If desired they may be enclosed within a ther
mally insulated container or housing ill.
path as a whole while retaining the feature of
50 large change in current characteristicof the
The system of Fig. 3 is similar to that of Fig. 1
thermistor 27 there are introduced resistance ele
but adds an auxiliary full wave recti?er l5 in
the circuit connecting transformer winding 9 and
ment 23 and the resistance of winding 26 of relay
25. These may be made substantially linear so
that their aggregate potential drop as represented
the thermistor l6. Accordingly the heating cur
rent for the thermistor introduces into the output 55 by ER will be a straight line. It will be apparent ‘
circuit of the main recti?er 3 only a unidirec
that adding the potentials ER. and ET will yield
tional voltage accompanied by ripples which may
a more nearly horizontal potential throughout
be readily suppressed by the smoothing ?lter ‘i.
the range of In to Im. However, since ET is far
In the system of Fig. 4 the thermistor Ill is
from linear the resultant obtained by adding ER
supplied with unidirectional heating current over 60 and ET will have a corresponding non-linearity
a path including the secondary winding 9 of the
or curvature. This may be much reduced and
current supply transformer, auxiliary full wave
the total shunt path potential made more nearly
recti?er l5, and an auxiliary smoothing ?lter Hi.
horizontal with change in current by the intro
It is accordingly possible to connect, the ther
duction of a resistor 26 which preferably consists
mistor l'i immediately adjacent the input ter 65 of some such material as silicon carbide which
minals of the load 6 since the thermistor is not
has a negative coe?icient of resistance with in
subjected to heating current variations or ripples.
creased current. The terminal potential E26
The system of Fig. 5 adds to the circuit of Fig. 1
which such a negative coe?icient resistance ele
a shunt path connected directly across the input
ment will support rises with current but less rap
terminals [9 and 2D to the load. This shunt path, 70 idly than does the current. The addition of the
as will be later explained in detail, is of such
potential E28 to those of ER and ET yields a nearly
character as to draw a current IT which changes
horizontal electromotive force E1. throughout the
enormously for small variations in the electro-_
range of shunt currents from In to Im. Thus, it
motive force applied to the load input terminals.
is possible to take advantage of the wide varia
Because of this very great change in the current 75 tion in current characteristic of thermistor 21
without permitting the potential difference across
the shunt path connected between points l9 and
tential will exist between points 62 and 18. If
the recti?ed voltage impressed between points
50 and 51 should rise the bridge will be unbal
anced to send unidirectional current over the
circuit 59, 66 in one direction. If the impressed
20 to vary more than a slight amount.
In operation, the shunt current I'r stabilizes
at some magnitude at which the three potentials
ER, E26 and Er will add up to equal the load volt
age Er. which is available after subtracting the
series potential drops across the ?lter 1 and
thermistor 22 from the voltage delivered at the
output terminals of the recti?er. If the system
be designed and the variable resistors adjusted
to cause the apparatus to tend to operate at a
point such that the shunt current I'r lies between
I0 and Im, as the voltage supplied across terminals
l8 and 20 to the load slightly decreases the cur
voltage across points .50 and 51 should fall the
bridge will be unbalanced to send current over
the circuit 59, 63, in the opposite direction.
The two-arm varistor valve includes an asym
metrically conducting arm adjacent the termi
nal 65 which is so poled as to permit current of
rent I'r will greatly increase. Conversely, if the
load voltage Er. increases the current Ir will de
one polarity only to pass to the winding of relay
64. This, in effect, makes the relay 64 a polarized
relay. Similarly current of opposite polarity only
is permitted by the other asymmetric arm ad
jacent terminal 68 to pass through the winding
of relay 61, thus effectively making that relay
polarized but in an opposite manner from relay
The purpose of the third transformer winding
With the apparatus in proper adjustment, as
28, the relay 25 and the variable resistor 29 is to 20
suming that the switches 33 and 44 have just
been closed, the thermistors 52 and 54 of the
shunt control bridge will be cold and the shunt
provide, at the time the circuit is energized, a
high enough voltage to thermistor 21 to bring
it within its operating range. When this operat
ing range of temperatures has been reached the
control bridge will be unbalanced in such direc
7 current through the thermistor 21 becomes great -
tion as to send current from the storage battery
enough to operate marginal relay 25 thus actu
ating its armature 3| to withdraw it from engage
ment with the contact point 36.
Fig. _'7 discloses a system for rectifying alter
nating currents which is similar to that of Fig.
45 through the winding of the starting relay
64. The relay 64 thereupon energizes attracting
its armature 1| and closing at its contact 12 a
5 in that it involves an L network comprising a
shunt control arm to control indirect heating of
a series thermistor arm. As shown the apparatus
is in unenergized condition with its starting
switches open and the various relays and control
circuits in released or idle condition. In this
circuit a source 32 may be connected through
switch 33 with current supply transformer 34
from the secondary winding of which leads 35
and 36 extend to the full wave recti?er 31.
Connected in series in the alternating current
input lead 36 are ballast lamp 38 and a thermistor
39. The unidirectional output current leads 40
and 4| extend from the recti?er by way of the
smoothing choke 42 and the charge fuses 43 and,
the switch 44 to the terminals of a storage bat
tery 45, and from these terminals through the
discharge fuses 46 to the terminals of‘the uni
directional current load 41.
circuit extending through the heater windings
14 and 15 of thermistors 52 and 54, respectively.
In a few seconds thermistors 52 and 54 have
warmed to such a degree as to greatly reduce
their resistance. Under these circumstances cur
rent will traverse these thermistor elements 52
and 54 in su?lcient magnitude to maintain their
temperature within the downward operating
range of their resistance temperature character
istic. In consequence of the reduction of resist
ance of the thermistors 52 and 54 the shunt con
trol bridge becomes unbalanced in the opposite
direction causing the starting relay 64 to re
lease and sending a current through the winding
of relay 61. The release of relay 64 interrupts
the heating current passing through heaters 14
and 15 of thermistors 52 and 54 but the current
which now passes directly through these thermis
tors is su?icient to maintain their operating tem
At the time that switch 44 is closed in starting
The ballast lamp 38 by abruptly changing its 50 the apparatus current is applied through the
fuses 5| over leads 85 and 86, ?xed contact 16
resistance to a higher magnitude when the safe
and armature 11v of relay 61 to operating winding
recti?er current is exceeded prevents overload
18 and resistance winding 19 of relay 80. Relay
ing of the recti?er. The resistance of the therm
istor 39 varies in accordance with the series load
80 thereupon energizes and attracts its outer ar
current therethrough. It is also indirectly af 65 mature 8| to close the circuit through heater 49
fected by an associated heater element 49 which , of series thermistor 39. At the same time it
is intermittently operated in response to the op
attracts inner armature 82, establishing a holding
eration of a shunt control circuit. The shunt
circuit for itself by an alternative path around
control circuit leads from point 50 by way of the
armature 11 so that a: momentary actuation of
regulator fuses 5| to the four-arm Wheatstone 60 relay 61 to open the energizing circuit of relay
bridge comprising thermistor 52, ?xed resistor
88 at contact 16, 11 will not cause relay 88 to
53, thermistor 54, variable tap resistor 55 and
deene'rgize. It will be apparent, therefore, that
resistor 56 to point 6| and by way of conductor
as soon after the switch 44 is closed connecting
85 to point 51. From the conjugate point 58 a
storage battery 45 to the terminals of the con
variable tap 10 and lead 59 provide a path to 65 trol bridge and to the leads 85, 86 of the circuit
junction point 60 of a two-arm varistor valve.
of relay 80 as will afford su?icient time for relay
From the other conjugate point 62 of the shunt
80 to energize heating of the thermistor 39 will
control bridge a lead 63 connects the winding oi.‘ .
relay 64 to' one terminal 65 of the valve while a
path 66 connects the winding of relay 6'! to the 70
remaining terminal 68 of the varistor valve. If
It will continue until such a time as
relay 61 is energized breaking the contact be
tween its armature 11 and the ?xed contact 16
and moving armature 11 into engagement with
the variable tap 16 be properly positioned at a
contact 84, thus short-circuiting winding 18 and
given temperature and a given applied load volt
permitting the release of armature 8|.
age between points 58 and 51 the shunt control
‘In one embodiment of the circuit of Fig. 7
bridge will be balanced and no difference of po 75 with a alternating current supply at the primary
winding of transformer 34? of 115 volts, 50 to 60
cycles, the apparatus was designed for battery
charging service to supply a current varying
the recti?er and a second secondary winding
associated with the primary winding and con
nected to the thermistor to supply heating energy
3. A regulating system for controlling the Volt
from zero to one ampere at 17 volts.
In this
particular embodiment the resistance of element
' 53 was 700 ohms, element 55 was 400 ohms, and
element 56 was 300 ohms.
The heater windings
‘l4 and 15 of thermistors 52 and 54 were of 140
age of the energy supplied to a load comprising an
alternating current transformer having input
terminals and output terminals, a source of unin
ohms resistance. Upon operation of relay 613
terrupted alternating current, a conductive cir
these windings were subjected to an alternating 10 cuit continuously connecting terminals of the al
ternating current source to the input terminals of
voltage of 24 volts. With the control bridge‘
the transformer irrespective of load conditions, a
balanced the potential di?erence between the
conjugate points 58 and 62 is of course zero.
load, a load circuit connecting the output ter
minals of the transformer to the terminals of the
When, however, the circuit is ?rst put into oper
ation by closing switches 33 and M, since ther 15 load and including a series variable resistance
thermistor through which the load energy passes,
mistors 52 and 54! are cold and their resistance‘
is high, the bridge is very much unbalanced so
said thermistor and said transformer windings
being in intimate heat conducting relationship
as to make the point ‘ill highly positive with
whereby the heat generated in the transformer
respect to the point 62. When in a few seconds
the resistance of thermistors 52 and 553 has been 29 may control the resistance of the thermistor to
reduced by the heating effect of heaters ‘Hi and ' vary the voltage supplied to the load terminals.
4. A regulating system for controlling the volt
15 the bridge becomes unbalanced in the opposite
age of the-energy supplied from a source of voltage
direction to make terminal 52 positive with ref
erence to terminal 58. Thereafter in operation
to a load comprising‘a translating device having
the terminal 62 always remains positive with 25 input terminals, a conductive circuit for con
tinuously connecting the terminals to a source of
reference to terminal 58 so that current passes
at all times through the winding of relay Bl.
alternating current irrespective of conditions of
Relay 6‘! is marginal in its operation and is
the load, said translating device also having an
sensitive enough to operate on an unbalanced
output circuit including terminals for connection
_ voltage such as is impressed upon it when the 30 to the load, said circuit being continuously closed,
and said translating device operating to modify
unidirectional voltage across points 50 and 51
the form of the energy transferred from the
rises to 17.3 volts and releases when that im
pressed electromotive force falls to 17.0 volts.
source to facilitate its utilization by the load, said
translating device presenting resistance whereby
Accordingly, so long as the circuit remains in
operation the thermistor 39 will begin to receive 35 heat is generated by the translating device, a
thermistor connected in series relationship in a
heat from its heater Q9 shortly after the load
continuously energized circuit to one of the ter
voltage falls to 17.0 volts and will continue to
minals of the translating device so that energy
receive heat until the load voltage rises to 1743
volts. The output voltage does not rapidly
passed to the load traverses the thermistor where
by the thermistor may impose a varying loss of
change between the limiting values of 17.0 and
potential to regulate the load voltage as the
173 volts since the thermistor 39 and its heating
energy supplied to the load varies, the translating
element have a» considerable thermal inertia.
Accordingly, at the beginning of the heating op
device and the thermistor being mounted in such
intimate heat transfer relationship that heat gen
eration heat is applied slowly and at the end
of the heating operation heat is applied morev 45 erated by the translating device a?ects the tem
slowly than in the middle of the heating period.
perature of the thermistor and hence its resist
Moreover, after the heating current has been
interrupted heat continues to be applied to the
5. In combination, a transformer having a pri
mary winding, 9, main ‘secondary winding induc
thermistor in decreasing degree. This tends to
greatly smooth the regulating operation.
50 tively associated with the primary winding, an
What is claimed is:
auxiliary secondary winding also inductively as
sociated with the primary winding, a full wave
1. In combination a recti?er having input ter
recti?er having input terminals connected to the
minals to which a source of alternating voltage
main secondary winding and output terminals, a
may be connected and output terminals, means
for regulating the voltage of the recti?ed current 55 thermistor and a ?lter connected in tandem to
the ‘output terminals of the recti?er to regulate
delivered from the output terminals of the recti
the voltage supplied to the load and to reduce rip
?er to a pair of load terminals including a ther
mistor connected in series between one of the
ples, and a heating circuit for the thermistor in
output terminals and one of the load terminals
cluding the thermistor and the auxiliary sec
to set up a potential di?erence between the ter 60 ondary winding.
minals which varies inversely with the load cur
6. A source of current, a load, a circuit con
rent traversing the thermistor, and means en
necting the source to the load, a shunt path across
ergized by an external source to heat the ther
the connecting circuit including a thermistor
mistor to a sensitive point on its resistance
temperature characteristic.
whereby the shunt path diverts currentfrom the
65 load to regulate the terminal voltage applied to
2. A transformer having a primary winding on
the load, means for initially heating the ther
which an alternating voltage to be recti?ed may
mistor to a temperature at which its resistance
be impressed, a secondary winding inductively
is suitable for regulating purposes and means re
associated with the primary winding, a full wave
sponsive to current passing through the shunt
recti?er having input terminals connected to the 70 path for disconnecting the initial heating means
secondary winding and having output terminals
when the current in the shunt path attains a pre
adapted to be connected to a load circuit through
determined magnitude.
a regulating system, said regulating system com
'7. A source of voltage, a load, means comprising
prising a thermistor and a ?lter connected in
a series thermistor having a falling resistance
tandem relationship to the output terminals of 75 temperature characteristic throughout a desired
range of temperatures connecting the source to
the load to regulate the voltage supplied to the
load in accordance with the current supplied to
in which the thermistor exhibits the falling re
sistance-temperature characteristic.
9. In combination, a source of alternating cur
rent, a full wave recti?er, a regulating thermistor
the load, an external heater for the thermistor
to supplement the heat supplied by the series load
current passing therethrough, a path connected
in shunt to the load and having two points which
and a load, all in series circuit relation whereby
said source supplies unidirectional current energy
to the load, a shunt circuit including a thermistor
are at the same potential when the total output
electromotive force across the shunt path is at a
connected across said load and means controlled
by the, thermistor of the shunt path to cause
abrupt variations in the temperature of the
normal desired value, a relay having a winding
connected between said two points and having an
thermistor in the series circuit.
armature and a, contact therefor, and a circuit
connected to said source to derive an electro
10. In combination, a source of electrical en
ergy, a series impedor and a load, all connected
motive force therefrom and including in series
said external heater and said armature and con
in series circuit, a Wheatstone bridge path con
nected in shunt to the load and having two points
conjugate to the connection points so that for a
predetermined terminal voltage no di?erence in
8. In combination, a‘recti?er having input ter
minals to which a source of alternating voltage
may be connected and output terminals, means
for regulating the voltage of the recti?ed current
delivered from the output terminals of the rec
ti?er to a pair of load terminals including a ther
potential exists between the conjugate points,
two asymmetrically conducting paths connected
between the conjugate points and each including
an individual relay, means whereby operation of
one relay in response to unbalance potentials
mistor having a falling resistance temperature
serves to initiate a reversal of the direction of
characteristic connected in series between one of
unbalance of the bridge and means whereby op
the output terminals and one of the load ter
eration of the other relay in response to oppositely
minals to set up a potential di?erence between the 25 directed unbalance potentials serves to regulate
terminals which varies inversely with the load
current traversing the thermistor, and means en
ergized by an external source to heat the ther
mistor to a sensitive point in the temperature zone
the impedance of the series impedor to control the
voltage impressed upon the load.
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