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Патент USA US3034033

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May 8, 1962
Filed June 15, 1959
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C0//ect0r~ Current
C’o/lecl'lor Current
Jerry L. Stratton,
by H/s Attorney.
, rt
Jerry L. Stratton, Schenectady, N.Y., assignor to General
Electric Company, a corporation of New York
Filed June 15, 1959, Ser. No. 820,407
3 tllaims. (Cl. 317-146)
My invention relates to transistor circuits, and particu
larly to such circuits adapted for use in effecting desired
Patented May 8, 1§62
drawing is shown as comprising a full wave recti?er 11,
comprising a transformer 12, the primary of which may
be connected to any suitable alternating current source,
and the secondary of which has its opposite terminals
connected through unilaterally conducting devices 13 and
14 to the negative conductor 15, whereas the midpoint of
the transformer is connected to a positive conductor 16.
A suitable smoothing and ?ltering capacitor 17 is con
nected between these conductors. The negative conduc
control operations such as the operation of relays, etc.
It has for one of its objects to provide an improved 10 tor 15 is connected through the winding 18 of a suitable
relay 19 to the collector 2 of the transistor.
circuit having extremely sensitive response to minute volt
The emitter 3 and base 4 of the transistor are connected
age variations to produce a current variation sut?cient for
to diagonally opposite points 24 and 25 of a Wheatstone
reliable actuation of the desired control apparatus.
A further object of my invention is to provide such 15 bridge, one branch of which comprises resistances 26 and
27 and the other of which comprises resistances 28, 29,
a circuit which is simple and economic to construct and
and 30.
operate, which utilizes a minimum of energy under standby
Resistance 30 may be variable in response to the pri
conditions, but which, in response to a slight voltage varia
mary variable which it is desired to control, which may
tion, which may be produced as the result of variation
be pressure, humidity, temperature, or other quantity. In
of a primary variable such as temperature, light, etc., re~
the event that it is desired to employ the equipment to
liably produces variations to operate control equipment
control the temperature of a room, for example, as in
that compensates for or restores the primary variable to
household heating systems, the resistance ‘30 may be a
its orginal condition, or to eiiect other desired control
thermistor. These devices have a negative temperature
co-e?icient such that the resistance of the thermistor de
A further object of my invention is to e?ect such results
creases as the temperature increases. Resistance 28 in
by the use of a single amplifying device such as a tran~
the branch 28, 29, and 30 may be manually variable by
sister, and to avoid the use of vacuum tubes, saturable
movement of contact 32 thereon, thereby e?ectively short
reactors, or other costly components.
circuiting a part of the resistance. In this way, the tem
I employ a transistor in a regenerative circuit having a
relaxation characteristic and, by varying the gain of the 30 perature to be maintained by the equipment may be man
ually adjusted at any desired temperature in a range of
transistor in response to the minute controlling voltage
variation, the circuit may be varied from an oscillating
The diilerence in potential between points 24 and 25
condition having small effective collector current to a
is applied through resistance 33 across the transistor emit
non-oscillating condition having a large collector current.
Thus, a large collector current variation ample for most 35 ter and ‘base electrodes 3 and 4, thereby to control the
operation of the transistor. The bridge is so adjusted that
control operations may be obtained in’response to very
point 25 is normally negative with respect to point 24,
minute voltage variations applied to the base.
and base 4 is negative with respect to emitter 3, by an
My invention, however, is not limited to construction
amount dependent on the value of resistance 30 which
with a transistor and, as will appear hereinafter, other
types of amplifying devices may be utilized. in its pre 40 varies with the temperature to be controlled.
The collector 2 of the transistor is connected through
ferred form, however, a single transistor amplifying de
relay Winding it?» to the negative terminal of the source.
vice is employed in the circuit.
- '
This winding i8 is inductively coupled to a second wind
The novel features which I believe to be characteristic
ing 34, which may be on the relay, and which is shunted
of my invention are set forth with particularity in the ap
pended claims. My invention itself, however, both as to 45 by the series combination of resistances 35 and 36, the
lower terminal of resistance '36, as shown on the drawings,
its organization andmethod of operation, together with
being connected through a capacitor 37 to the base elec
further objects and advantages thereof, may best be un
trode 4, and through resistance 33 to point 25 of the
derstood by reference to the following description taken
in connection with the accompanying drawing, in which:
bridge. Resistance 35 is normally small, as for example
FIGURE 1 represents an embodiment of my invention; 50 500 ohms, relative to the value of resistance 36, which
may be 4,000 ohms, and it has a variable contact 38
FIGURE 2 represents the (gain vs. collector current
which is connected to the emitter 3 and to point 24 on the
characteristic thereof;
I FIGURE 3 illustrates the collector current during os
bridge, which is at a relatively ?xed potential. Variation
cillation; and
of contact 38 on resistance 35 varies to some extent the
FIGURE 4- represents a modi?cation of the circuit 55 value of the loop gain including the transistor, windings
13 and 34 and coupling therebetween together with the
shown in FEGURE 1 employing the condition sensitive
connections described from winding 34 back to the tran
control element as a part or“ the feedback circuit.
sistor. This results in a variation of the value of collec
Referring now to FIGURE 1 of the drawing, [1 have
tor current at which oscillations start.
indicated at 1 by the conventional symbol for transistors,
Variation in current in winding 18 induces a voltage in
a transistor comprising a collector 2, an emitter 3, and 60
Winding 34;, which, since contact 38 is at ?xed potential,
a base 4. In the circuit here illustrated, this transistor is
is supplied back through condenser 37 to base 4 to sup
preferablypone which, during operation, carries approxi
port oscillations as will presently be described.
mately equal current in both the emitter and collector
Condenser 37 normally is charged to a certain ex
and only the difference in currents in these electrodes
?ows in the base 4;. Such a transistor may be one of 65 tent with its upper electrode, as shown on the drawing,
positive with respect to the lower electrode. The upper
the 2N43 type which employs a slab of semiconductor
having on its opposite sides and partially embedded therein
electrode is connected through resistances 36 and 35 and
the two electrodes designated collector and emitter, each
contact 38 to point 24 which normally is positive with
of them having areas and substantial current carrying
respect to point 25 to which the lower electrode is con
70 nected. This charge on condenser 37 is increased by any
Unidirectional operating potential is supplied to the
potential appearing on resistance 33 due to current ?ow
transistor from any suitable source, but which in the
ing therein.
The gain of the oscillatory loop comprising the transis
tor, windings 18 and S4, and the coupling therebetween,
and the coupling from winding 13/3 back to the base 4,
varies, due to variation in gain of the transistor, with
the current ?owing in the collector in accordance with the
relationship illustrated in FIGURE 2, in which the full
line curve bearing the legend “Loop Gain” represents
the relationship between gain plotted as ordinate against
comprising the base 4 and emitter 3 of the transistor
which is now biased in the forward direction. 7
Finally, the increase in current is limited by the re
sistance in winding lid, and the increase steps. This
causes the voltage on winding 34 to reduce and ?nally
to disappear whereupon the current again starts to de
crease in collector 2 reversing the polarity of the po
tential on winding 34, and the cycle repeats itself.
FIGURE 3 shows the collector current plotted as or
collector current plotted as abscissa. It will be seen that
this curve, over the larger portion of its range, is rela 10 dinate against time plotted as abscissa with the origin
of the coordinates, in the upper left hand corner and
tively flat but varies gradually downward with increas
ing collector current.
The horizontal dash line bearing the legend “Loop
Gain=l” represents the value of loop gain equal to unity.
In the event that the gain be greater than unity, as in
area A of FIGURE 2 left of the vertical dash line, the
circuit described oscillates.
In area B, to the right of
the vertical dash line, the gain is less than unity and the
with dash lines A’ and B’ representing respectively mini
mum and maximum collector currents in alignment with
corresponding dash lines A and B in FIGURE 2.
Again, reiterating the operation with reference to FIG
URE 3, when the temperature is below the desired value,
large current ?ows in the collector in excess of the value,
represented by line B’, or the line B of FIGURE 2, and
the loop gain is less than unity. The relay is, energized
device is non-oscillatory. Assume the circuit is non
and the furnace is operated, applying heat tending to
oscillating and the value of collector current is slightly
raise the temperature of the room.
to the right of the vertical dotted line shown in FIGURE
As the temperature increases, the potential on base
2. Now assume that the base current decreases slightly
4 becomes less negative with respect to that of the emit
to a point slightly to the left of this line. This change
ter 3, and the collector current starts to reduce. When
increases the loop gain and» oscillation starts, the nature
the collector current becomes less than the value repre
of which is shown in FIGURE 3. Oscillations will stop
sented by, the dotted lines 3 in FIGURE 2, or B’ in
any time that the average value of the base current in
creases enough to cause the peak of the collector cur
rent to go above the upper dotted line shown in FIG
URE 3.
FIGURE 3, the loop gain exceeds unity, regeneration
maintain so that the system calls for heat, the resistance
of resistor 30, because of the low temperature, is high,
base 4 in the positive direction
more positive than the emitter.
due to the charge of condenser
condenser 37 leaks off, base 4
. starts and the current drops rapidly to the value repre
sented by line A in FIGURE 2 or A’ in FIGURE 3.
Assuming that the temperature to which resistance 30 30 This drop in current in winding 18 induces voltage in
winding 34 which added to that on condenser 37 drives
responds is at a value below that which it is desired to
and the point 25 is considerably negative with respect to
point 24, thereby biasing base 4 negative and in the for
ward direction with respect to emitter ‘3 causing large
current‘ to flow through the winding 18 and to energize
the relay. Because of the large current in the’ collector
and emitter, the gain of the loop is less than unity and
the device does not oscillate.
Now, let us assume that because of the energized con
dition of the coil 18, the relay is operated to such a po
sition that heat is applied, as by starting the furnace,
thus raising the temperature of the room. As the tem
perature of the room approaches the temperature to be
maintained, resistance 30 decreases and the potential at
point 25' becomes less negative; i.e., approaches the po
tential of point 24, thereby reducing the bias applied to
the base 4 with respect to the emitter and reducing the
until the base becomes
At this point it remains
37. As the charge on
becomes more negative
and the current begins to increase in winding 1%, thereby
inducing a voltage in winding 34 opposed to that and
condenser 37 thereby further to increase the collector
current. When the collector current again approaches
the value X, its further increase is limited by the re
sistance in winding 18 and the loop gain becomes less
than unity and regeneration ceases. The voltage induced
in winding 34 disappears and the potential of base 4
again approaches the emitter potential thereby further re
ducing the collector current.
The effective value of the collector current during oscil
lation, as represented by 'thelcurve of FIGURE 3 is, of
course, much lower than that when the operation started,
with the result that relay winding 18 is sufficiently de
current in winding 18- until the gain of the loop exceeds
energized to cause its armature to drop to its lower posi
unity whereupon the system goes into oscillation; i.e., '
the decrease in current in winding 18 induces voltage in
oscillation may be of any desired value and may be
winding 34' of polarity such that its lower terminal, which
is connected to condenser 3'7, is negative relative to its
upper terminal. Then, since contact 3% is at ?xed po 55
tential, that portion of the potential of winding 34 which
exists between contact 3% and condenser 37 is added to
the charge on condenser 37' and drives base 4 in the
positive direction to such a point that the potential of
base 4 may attain or become more positive than emitter 3.
Thus, the collector current in winding 18 rapidly re
duces until it becomes of very small value. Then the
potential on winding 34- disappears, but the charge on
condenser '37 maintains the potential of base 4 relative
to emitter 3 at such a value as to delay any increase in
collector current. This charge gradually leaks during an
interval determined principally by resistance 33 and cur
rent begins to increase in winding 18. This reverses the
polarity of potential induced in winding 34 thereby rap
tion, thereby stopping the furnace. The frequency of
su?iciently high, as for example 2,000 cycles per second,
to avoid any chattering of the relay.
It will now be seen that it is desirable that the increase
in current during the lower curved portions of the curve
of FIGURE 3 be as slow as possible, thereby to prolong
the intervals between decrease in current and the next
subsequent increase therein relative to the interval be
tween the increase and subsequent decrease in current,
thereby to produce a greater reduction in effective value
of the current during oscillation relative to that occurring
during thenon-operating current.
While the increase in collector current during the initial
periods is delayed by the time required for condenser
37 to discharge, no similar delay occurs during the in
terval when the collector current starts to decrease. The
result is that the periods of maximum collector current
are substantially shorter than the alternate intervals
idly varying the potential of base 4 in a direction to in 70 thereby substantially reducing the e?ective collector cur
crease current in winding 18; i.e., driving base 4 nega
The rapid response and accuracy of the circuit is thus
tive relative to emitter 3. During this time condenser
due‘ to the instantaneous change of oscillator state upon
37 again charges since the potential from winding as
a sensed temperature deviation as well as the rapid action
on resistance 36 is added to that between points 24% and
2s across the condenser through the low impedance path 75 of the switching mechanism upon a change of oscillator
state. It should 'be noted here that the transistor in the
oscillator circuit may have temperature coe?icient char
acteristics, which will vary internal transistor impedance
upon deviation of the sensed temperature. The temper
ature eifects of the transistor in the embodiment were
found to be negligible but by the proper placement of
thermistor 30 in the bridge circuit, any such effects may
be utilized to increase the sensitivity of the device.
In an operable device constructed according to the
preferred embodiment the circuit elements may have the 10
following values: resistor 33=10,000 ohms, capacitor
37:.005 mfd., transistor 4=2N43 pnp junction type,
mately to 1 when the above condition is satis?ed. There
after, it the gain of the circuit varies above or below the
value -1, as shown in FIGURE 2 of the drawings, the cir
cuit will break into oscillation if its gain becomes greater
than 1, or it will fail to oscillate and draw a relatively
large current through relay winding 58 when the gain
is less than 1. Hence, upon a variation in the tempera
ture from the preset condition, the feedback bridge net
work will produce an imbalance potential that is fed back
to the base electrode 52 through the capacitor ‘64 to in
crease or decrease the gain of the circuit depending
upon the direction of the temperature change. In the
event that temperature increases, then the feedback po
tential is adjusted to raise the gain of the circuit in a
direction to cause the circuit to oscillate thereby allow
ing the relay associated with the winding 58 to drop out.
In the event that the temperature decreases below the
- voltage divider 35:500 ohms and resistor 36:4,000
ohms. The switch mechanism including winding 18 and
member 41 may comprise a suitable milli-ampere relay
of medium sensitivity, and secondary Winding 31% may
have a turns ratio of about ?ve percent in respect to the
primary winding 13. The bridge circuit components may
be selected so that the ratio between bridge leg 26 and
the bridge leg 27, as well as the ratio between the op
posite bridge legs, is in the ratio of 25:6, and the ther
mistor 31} maybe of the bar or disk type having a tem—
perature v'coetlicient of about 3 or 4 percent per degree
potential of the juncture of the variable resistor 62 and
thermistor 63 at the predetermined temperature level.
The bias supplied to the base electrode 52 of transistor
51 through resistor 55 is then adjusted so that the gain
of the circuit including transistor 51 is equal approxi
preset value, the polarity of the imbalance potential fed
back through capacitor 64 drives the circuit in a direc
A second embodiment of a condition sensitive control 25 tion to decrease the gain below 1 so that the circuit does
circuit constructed in accordance with the present in
not break into oscillation, and current is drawn through
vention, is illustrated in FIGURE 4 of the drawings.
the relay winding 58 of su?icient magnitude to cause the
This second embodiment of the invention utilizes a
relay to close the contacts thereby actuating the control
transistor 51 having a base electrode 52, a collector elec
mechanism controlled by the circuit. It can therefore be
trode 53, and an emitter electrode 54. The base elec 30 appreciated that the present invention provides a new
trode 52 is connected through a biasing resistor $5 to a
and improved control circuit requiring only a single
voltage dividing network formed by a pair of resistors
amplifying device, such as a transistor, and yet provides
56 and 57 connected in series across a pair of output
a snap action control which is extremely sensitive to
terminals of a direct current voltage supply source (not
changes in the condition being sensed. The control cir~
shown). The emitter electrode 54 of transistor 51 is 35 cuit is reliable in operation, and because it requires only
connected directly to the positive terminal of the direct
a single amplifying device, is relatively economic to pro
current voltage supply and the collector electrode of
transistor 51 is connected through a winding 58 of a
transformer 59 to the negative terminal of the source
Having described several embodiments of a control
circuit constructed in accordance with the present inven
of direct current supply voltage.‘ The primary winding 40 tion it is believed obvious that other modi?cations and
58 of transformer 59 is inductively coupled to a sec
variations of the invention are possible in the light of the
ondary winding 61 which is included in a feedback
above teachings. It is therefore to be understood that
bridge network. The feedback bridge network is com
changes may be made in the particular embodiments of
prised by the two halfs of the secondary winding 61a
the invention described which are within the full intended
and 61b connected in a closed loop with a variable resis 45 scope of the invention as de?ned by the appended claims.
tor 62 and a thermistor 63 or other condition sensitive
What I claim as new and desire to secure by Letters
element whose electrical resistance varies in accordance
with the variations in the condition to be sensed. The
Patent of the United States is:
1. In an electrical condition sensing device whose out
midtap point of the winding 61 is connected through a
put is indicative as to whether a sensed condition is above
capacitor 64 to the base electrode 52 of transistor 51, 50 or below a preselected condition, the combination of
and the juncture of the variable resistor 62 and thermis
a transistorized relaxation oscillating means comprising
tor 63 is connected through a suitable conductor 65 to
a single transistor biased to operate at a point on its gain
versus collector current characteristic where the gain
goes from a value greater than unity to a value less than
the emitter electrode 54 of transistor 51 and to the posi
tive terminal of the source of direct current voltage sup
ply. The bridge comprised by the two halfs of secondary
winding .61, variable resistor 62 and thermistor 63 com
prise a feedback network connected to the transistor 51
in a manner such that when the gain of the overall cir
cuit is greater than 1, the circuit will oscillate in a fashion
similar to that described with relation to the embodiment 60
of the invention shown in FIGURE 1. Conversely,
when the gain of the circuit is less than 1, the circuit will
not oscillate, and current will be drawn by the transistor
51 through the primary winding 58 of transformer 59.
unity with increasing collector current whereby depend
ing upon which side of the gain equal unity value the
gain of the oscillating means is set, the oscillating means
has either an oscillating state or a non-oscillating state,
said oscillating means further comprising a switching
mechanism including an actuating winding connected in
feedback relationship with respect to said oscillating means
whereby said actuating winding draws a relatively large
actuating current when said oscillating means is in a
non-oscillating state and relatively small current inca
Transformer 59 may comprise one part of a relay whose
pable of actuating said switching mechanism when said
armature (not shown) is connected to a switch or other 65 means is in an oscillating state, a voltage divider network
control device, so that this current may be used to actuate
connected across a source of constant potential, said
the switch or other control device in response to a change
network including a condition responsive impedance, cir
in the condition being sensed by the thermistor 63 or
cuit means including a bias resistor for connecting the
other condition sensitive element.
output voltage of said network to said transistor where
Assuming the condition sensitive device 63 to be a 70 by variation in said output voltage resulting from changes
thermistor, and that the control circuit is used to main
in said impedance is effective to determine the state of
tain a predetermined temperature level, the variable
said oscillating means.
resistor 62 may be set at a value such that the potential
2. In an electrical temperature sensing device whose
at the rnidtap point of the winding 61 is equal to the 75 output is indicative as to whether a sensed temperature
single transistor amplifying device biased to operate at
unity to a value less than unity with increasing collector
current whereby depending upon which side of the gain
equal unity value the gain of the oscillating means is
a point on its gain versus collector current characteristic
set, the oscillating means has either an oscillating state
where the gain goes from a value greater than unity
to a value less than unity with increasing collector cur
rent whereby depending upon which side of the gain
equal unity value the gain of the oscillating means is set,
or a non-oscillating state, said oscillator means further
is above or below a preselected temperature, the com
bination of a relaxation oscillating means comprising a
the oscillating means has either an oscillating state or
a non-oscillating state, said osciliating means further
comprising a switching mechanism including an actuating
winding, with the actuating Winding being connected in
the output current circuit of the transistor and being ener
gized when said means is in a non-oscillating state and
substantially de-energized when said means is in van oscil
comprising a switching mechanism including an actua
lating state, a bridge network having four legs, means
ting winding connected in feedback relationship with re.
for applying potential across two opposite leg junctions,
spect to the oscillating means and drawing a relatively
circuit means for applying a network output signal from
large current sui?cient to operate said switching rnecha- .
the other two leg junctions to said transistor so as to con
nism when said oscillating means is in a non-oscillating 15 trol the state of operation of said oscillating means, one
of said bridge legs including a temperature selection vari
state and drawing a relatively smallcurrent insui?cient
able resistance having a resistance propontional to said
to operate said switching mechanism when said means is
preselected temperature, and another of said legs includ
in an oscillating state, a feedback bridge network having
ing a thermistor, the resistance change of said thermistor
two of the four legs thereof formed by the two halves
of a winding inductively coupled to said actuating wind 20 upon 1a deviation of sensed temperature vfrom the prese
lected temperature unbalancing said bridge network, said
ing whereby a feedback potential is developed across two
opposite leg junctions, circuit means for applying a feed
output signal varying in accordance with said unbalanc
back network output signal from the other two leg junc
ing so as to control the state of said oscillating means in
tions from said feedback bridge network back to said
accordance to the direction of temperature deviation.
transistor ‘for controlling the state of operation of said
oscillating means, one of said bridge legs including a
References Cited in the ?le of this patent’
temperature responsive impedance, said impedance vary
ing said output signal in response to sensed temperature
Donle et a1. ___________ .. Feb. 6, 1940
for controlling the state of operation of said oscillating
3. In an electrical- temperature sensingv device whose
output is indicative ‘as to the direction of deviation of a
sensed temperature from a preselected temperature, the
combination of a transistorized blocking oscillator means
including a single transistor amplifying device biased to
operate at ‘a point on its gain versus collector current char
acteristic where the gain goes from a value greater than
Michel _______________ -_ Feb; 5,
Sulzer ______________ .._ Sept. 25,
Aron ________________ __ Dec. 4,
Coles _______________ __ Dec. 18,
Schaeve ______________ __ Oct. 4,
Great Britain ________ __ May 22, 1931
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