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Патент USA US2404919

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July 30, 1946.
w. P. QVE‘RBECK
2,404,919
ELECTRONIC SWITCHING DEVICE AND CIRCUIT THEREFOR
Filed May 1, 1940
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2,404,919
Patented July 30, 1946
UNITED STATES PATENT OFFICE
2.404.919
SWITCHING DEVICE AND
IBCUH.‘ THEREFOR
ELECTRONCIC
Wilcox P. Overbeck, Waltharn, Mara, assignor to
Research Corporation, New York, N. Y., a cor
poration of New York
Application May 1, 1940, Serial No. 332,854
3 claims (01. 250-27)
~
1
also applied to'the screen grid through a resistor.
Before'describing the circuit of Fig. 3, the two
principal conditions of operation of the tube will
be described. These are illustrated by the elec
tron paths of Figs. 1 and 2. In Fig. 1 the sup
pressor grid is at zeropotential and the anode
circuit is conducting. The flow illustrated in Fig.
1 is due principally to the inertia of the electrons
and the velocity to which they are accelerated by
the screen grid, as~well as to the attraction of
The present invention relates to. electronic
switching devices and circuits therefor, and more
- particularly, to devices and circuits offa type used
for switching, triggering and control applications.
. One object ofthe invention is to provide an
electronic switching device and a switching cir
' cult which will operate at extremely high speed.
Another ‘object of the invention is to provide
an electronicswitching device and circuit which
are simpler and more reliable in operation than
switching devices heretofore obtainable.
with ‘these and other objects in view. as will
hereinafter appear, the invention comprises the
electronic device and circuit hereinafter described
- the positive anode potential.
A few of the elec
trons ?ow directly to the screen grid or return
7
. to it after passing between its
wires.
For the
' ‘In the accompanying'drawing Fig. 1 is a/dia
purpose of reliable switching action, I have found
15 that one requirement is that the number of elec
trons which continue to the anode should be as
grammatic view of the preferred form of elec
large as possible and that the number which strike
and .de?ned in the'claims.
’
' tronic switching device illustrated in one of its
the screen grid shall be as small as possible.
This
is accomplished by the alignment of the screen
stable-conditions; Fig. 2 is a diagram similar to
Fig. 1 but illustrating the other stable condi 20 grid wires with those of the control grid, so that
the electron flow is in the nature of a directed
Qtion-fjFig. 8 is a diagram of the preferred form
beam, which, in the condition of Fig. 1, passes
of switching circuit embodying the present in
through the screen grid with only relatively slight
ventiom'andFig. 4 is a diagrammatic view of
diversion of electrons‘from the beam to the screen
a modi?ed, form of tube.
The tube illustrated in Fig. 1 comprises a cath 25 grid. This directing effect may be enhanced by
the application of a negative potential to the 1
ode lwhichis either directly or indirectly heated,
control grid,'which will tend to restrict the elec
three grids 6, 8 and Ill, and an anode l2. As in
trons to narrower beams and thus to diminish the
attractive effect of the positive screen grid po
are disposed‘helically around the cathode and
the plate is cylindrical. Also, in accordance with 30 tential. The use of a negative control grid po
conventional tube construction the three grids I
conventional nomenclature, the three grids 6, 8
.
tential, however, reduces the total number of elec
trons passing through the tube. An optimum
value of negative control grid potential may be
determined in any given instance by experiment,
from the grids commonly designated by such 35 but for purposes of this description the applica
tion of zero potential to the control grid will be
terms.
assumed.
The control and screen grids are aligned, that
Under conditions shown in Fig. l, the sup
is, wound with the same pitch and spacing to
pressor grid is at or near cathode potential and
define electron beams, as distinguished from the
exerts little or no in?uence on the electron beams’.
usual construction in which these grids are wound
The condition shown in Fig. 2 is one under
with opposite pitch and different spacings to ob
which the anode is at positive potential, the screen
tain greater uniformity of distribution. The sup
grid is also at a positive but lower potential than
pressor grid Ill is also pitched in the same direc
in Fig. 1, but the suppressor grid is at a negative
tion as the other grids and differs from the con
ventional suppressor grid in that the spacing of 45 potential with respect to- the cathode. Under
this condition electrons which get through the
the convolutions is smaller. As shown in the
screen grid are repelled by the negative sup
drawings the suppressor grid spacing is about
pressor grid potential and cannot pass to the
half that of the other grids so that a suppressor
anode so that they are obliged to return to the
grid wire is present within the limits of the elec
50 screen grid which now carries a substantial cur
tron' beam de?ned by the ?rst two grids.
rent. In this condition the anode circuit of the
The tube is enclosed in the conventional vessel
tube is non-conducting.
which is exhausted to an extremely high vacuum.
The two conditions illustrated by Figs. 1 and 2
In the use of the tube in a switching circuit,
are both stable. Furthermore, a shift may be
as illustrated in Fig. 3, a positive potential is
applied to the anode and a positive potential is 55 made from one stable condition to the other
and I0 may be designated the control grid, the
screen grid, and the suppressor grid, respectively,
although they differ in arrangement and function
3
acoaeie
merely by changing the suppressor grid potential.
This change of potential need only be momentary,
as by the application of a rapid pulse. A shift
from the condition of Fig. 1 to that of Fig. 2 may
be effected by the application of a pulse of nega
4
condenser 30 may be connected to the control
grid for a purpose to be later described, in which
1case a resistor 32 is included in the control grid
and.
The operation of the circuit shown in Fig. 3 is
tive potential to the suppressor, and the reverse
described as follows: Assuming the tube to be
shift may be effected by the application of a posi
in the conducting condition of Fig. 1, that is, the
> tive pulse to the suppressor. The in?uence of
condition in which current is flowing to the anode,
variations in suppressor grid potential on the elec
the current to the screen grid and the drop
tron paths depends on the disposition of the sup 10 through the resistor M are relatively small so
pressor with respect to the other electrodes and
that the screen grid is at its highest positive po-'
on the spacing of the convolutions of the sup
tential. The values of the resistors l4, I8 and
pressor. In the construction shown in Figs. 1
20 are such that the suppressor grid is main
and 2, the suppressor is disposed close to the
tained at a slightly positive potential, preferably
screen grid and therefore in a region of high 15 a fraction of a volt, with respect to the cathode.
electron velocity, so that the close spacing of the
This positive potential is so small as not to affect
suppressor convolutions is desirable to exert the
the description heretofore given, wherein zero
necessary control on the electron paths.
potential of the suppressor was assumed, the
A modi?ed tube construction is shown in Fig. 4,
principal purpose of the positive potential being
in which the suppressor grid is disposed farther 20 to maintain stability and to prevent the sup
outward, approximately as far from the screen
pressor from going negative under any slight ?uc
grid as the latter is from the cathode. In this
tuations which might occur accidentally in the
modified form, the suppressor exerts a large in
system. The positive potential at the suppressor,
?uence on the electron paths because it is in a
and consequently the suppressor grid current, are
region of low electron velocity. In order that it 25 necessarily small since any tendency to increase
may not interfere with the flow of electrons in the
the positive potential would produce a compensat
anode-conducting condition, it is preferably
ing voltage drop through the resistor 20. The
wound with its convolutions in alignment with
circuit will, therefore, remain stable in this con
those of the other grids. This modi?ed tube op
dition with the suppressor grid only slightly posi
erates on the same principles as that of Fig. l, 30 tive, with the screen grid at its maximum posi
but the construction of Fig. 1 is ordinarily to be
tive potential (for example, 56 volts) and with
preferred because it makes for a device of smaller
current ?owing to the anode.
size.
For a tube designed for operation at the elec
A switch or trigger circuit involving the use of
trode potentials indicated in Fig. 3 it has been
the tube described above is shown in Fig. 3. The 35 found that the satisfactory values of the re
control grid is at zero potential, the screen grid
sistors are as follows: Resistor M, 100,000 ohms;
8 is excited through a resistor M from a positive
resistor 20, 500,000 ohms; resistor l8, 2 megohms;
voltage source and the anode is connected to a
and resistor 32, 100,000 ohms.
source of positive potential through an output
If a pulse of negative potential is applied to
device l6 which may be a relay for actuating any 40 the input circuit 24 of suf?cient value to swing
desired equipment. The suppressor grid is con
the suppressor grid negative, the non-conducting
nected through a high resistance l8 to a source
condition of Fig, 2 is immediately assumed. This
of negative potential. Typical values of the sev
is brought about by the fact that the ?rst effect
eral'potentials are indicated in Fig. 3.
of the negative potential on the suppressor grid
Since the screen grid is excited through the 45 is to repel the electrons ?owing toward the anode
resistor M the current flowing therethrough pro
and to cause them to ?ow to the screen grid.
duces a voltage drop. In the condition of Fig. 1,
when the anode circuit is conducting, the screen
grid current is small and the positive potential
The screen grid current immediately increases
and through the drop in resistor l4 causes an im
mediate reduction of the screen grid potential.
applied to the screen grid is relatively high. 50 This variation of potential is transmitted through
condenser 22 to the suppressor grid, which then
When the anode current is cut oil‘, as illustrated
in Fig. 2, the accompanying increase in screen
grid current increases the voltage drop through
the resistor I4 and reduces the positive potential
assumes a stable negative value even after the
pulse has terminated. The negative potential as
sumed by the suppressor grid is determined by
of the screen grid.
55 the constants of the tube and its associated cir
These potential variations of the screen grid are
cuits and is independent of the magnitude of the
fed back to the suppressor grid through a cou
pulse by which the transfer was initiated. In the
pling circuit including a resistor 20 and con
typical example illustrated by Fig. 2, the suppres
denser 22 in parallel thereto. The purpose of the
sor grid is at a negative potential of 8 volts and
condenser is to cause the voltage variations of the 60 the screen grid is at a positive potential of 28
screen grid to reach the suppressor grid more
volts. The anode circuit is now non~conducting,
rapidly. Without this condenser the transmis
and the system will remain in that condition until
sion of voltage variations would be slower because
its stability is upset by the application of a posi
of the capacitance between the suppressor grid
tive potential to the suppressor.
and other elements of the tube, which would re 65
A return to the initial conducting condition .a
quire the accumulation of the charge through the
may be initiated by a positive pulse applied to
resistor l8 and would introduce a small time lag.
the input circuit 24. Some of the electrons whose
The condenser 22 thus improves the speed of op
paths terminated on the screen grid will then
eration of the circuit.
be attracted past the screen grid, the screen grid
An input circuit 24, including a condenser 26, 70 current will decrease with a, consequent rise in
is connected to the suppressor grid. Pulses of
screen grid potential, and this variation in poten
short duration, either positive or negative with
tial is transmitted through condenser 22 to the
respect to the cathode, may be applied to the in
suppressor. Thus the stable condition of Fig. 1,
put circuit to effect the switching operation of
with the anode circuit conducting, is assumed.
the tube. A second input circuit 28 including a 75
A feature of the invention resides in the ar
8,404,918
I
pressor grid potentials will be. changed in the
positive direction and, therefore, the tube will
t whereby the two stable 0011411510118
heretofore described are suillciently different so
that there'is no possibility of swinging from one
condition to the other under any circumstances
swing to its Fig. 1 or conducting condition ex
actly as if a positive potential had been supplied '
to the suppressor grid. In any case. the stable
condition persists even after the termination of
other than the application of pulses of su?lcient
magnitude/t6 the input circuit. To shift from
the pulse which causes it.
' one stable condition to the other, it is necessary
_.
As illustrated in Fig. 3, the input circuits 24 and
to apply a pulse greater than some minimum volt
age. which minimum may be considered as ap
28 are bothlncluded. Either one may be omitted,
proximately equal to one-half the swing of sup
pressor grid potential between its stable values.
ifitisdesiredtooperatethetubeby'pulsesfrom ‘I
one source only. But with two input circuits it
is possible to control the tube from either. This
. In actual operation. the value of the minimum
ability for selective operation by pulses to both
pulse which will effect the shift is not of great
input circuits is of considerable importance in
importance, since to insure reliability it is pre
ferred to apply a pulse of a magnitude at least 15 certain practical applications, particularly in a '
as great as the swing of suppressor potential, that . type of electronic counting circuit described in
my co-pending application, Ber. No. 332,853, ill
is, somewhat greater than 8 volts in the example
given. Immediately after the pulse is applied.
of even date herewith.
guishing from trigger circuits using so-called soft
tubes in which delays as well as possible uncer
tainties of operation may occur because of re
liance on ionization effects to obtain the trigger
.
'
~
The advantages of the tube‘ constructed ac
the coupling circuit 20, 22 comes into action to
sustain the e?ect initiated by the pulse. The
action is extremely rapid. The shift occupies a
time measured in micro-seconds, thus distin
cording to the present invention may be explained
by comparison with existing devices used for
switching andgtriggering‘appllcations. In the
past most electronic switching systems have been
con?ned to the use of gaseous discharge tubes
25 of the thyratron type. The speed of operation of
. these tubes has been limited by the fact that the
initiating pulses, particularly those required to
ing action.
‘shut off the ?ow of current, must be of sumciently
Alternative methods of control consist in ap- '
plying initiating pulses either to the screen grid '
long duration to allow de-ionization of the gas.
\
Although attempts have-been made .to obtain
higher speed operation with so-called hard tubes,
to the screen grid di?ers very little from the
such attempts have been largely directed to-cir.
application of pulsesto the suppressor grid, ex
cults employing two or more tubes, thereby in
cept that such pulses, if con?ned to the screen
creasing the cost and complexity of the circuits.
grid alone, would ordinarily need to be of greater
magnitude than if applied to the suppressor grid. 35 The present invention requires only a single tube
of simple construction, and provides for- the
In fact, it will be noted that the system of Fig.
switching action with minimum time lag.
3 in which the condenser 22 is provided serves
It will be observed that the tube of the present
to apply initiating pulses both to the suppressor
invention may be designated as a “pentode,” al
grid and screen grid. Although the foregoing ex
planation has been based on the effect of the 40 though it differs from the conventional pentode
in the respects heretofore noted, particularly in
pulse on the suppressor grid only, the transmis
the provision for directing the ‘electron beams,
sion of the pulse through the condenser 22 to
and in the greater in?uence of the suppressor
the screen grid enhances the effect and con
grid. It has been found that a pentode of con
tributes to reliability of operation with minimum
45 ventional design may be used in the circuit of
time delay.
Fig. 3 and it is intended that the present inven
The second alternative above mentioned, name
tion comprehend the use or such a tube except
ly, the application of initiating pulses to the con
where the appended claims are limited to the
trol grid, makes use of the second input circuit
preferred tube construction. But the tube of the
28. The operation is similar to that previously
described, except that a positive pulse applied to 50 present invention is in all cases to be preferred,
since it offers important advantages over the con
the control grid will cut off a previously ?owing
or the control grid. The application of pulses 30
ventional type for the following reasons:
anode current and a negative pulse will cause
Since the grid wires in the conventional pen
the anode circuit to become conducting.
todes are not in alignment the ratio of screen
To explain the operation of the system under
the action of pulses applied to the control grid 55 grid current to total electron current in the
anode-conducting condition would be relatively
assume first that the tube is initially in the con
high. This means that in the transfer from the
ducting condition of Fig. 1. A momentary posi
' tive ‘pulse applied through condenser 30 to the
a conducting condition to the non-conducting con
dition, the relative increase in screen grid current
control grid will momentarily increase the num
ber of electrons ?owing both to the anode and to 60 would be fairly small. Therefore, the difference
in screen grid voltage for the two conditions of
the screen grid. This momentary increase of
operation would be much smaller than if the pre
screen grid current increases the voltage drop
ferred form of tube were used. Consequently,
through the resistor i4 and reduces the screen
the two conditions of the circuit with the con
grid potential. This reduction of screen grid
ventional tube would be more nearly alike and
potential is transmitted through the resistor 20
the values of the various circuit constants would
and condenser 22 to the suppressor grid to cause
have to be chosen with great care to discriminate
the latter to become negative. The result is
properly between them; furthermore the system
therefore the same as if a negative pulse had
might be unreliable, because of the possibility of
been applied to the suppressor grid and the cir
cuit immediately shifts to the Fig. 2 condition in 70 upsetting one of the conditions of operation by
which no current flows to the anode. If now a
accidental causes.
negative pulse is applied to the input circuit 28,
The tube of the present invention owes its ad
vantages in a large part to the fact that the
electron beam is directed past a positive elec
the total number of electrons ?owing in the tube
will be reduced, the screen grid current will be
decreased, [both the screen grid and the sup
1
75 trode (the screen grid) and the electron paths
7
2,404,919
are largely prevented from terminating thereon,
8
2. An electronic switching circuit comprising
except when they are required to do so under the
in?uence of a negative potential applied to the
suppressor. In the anode-conducting condition
(Fig. 1) the screen" grid current constitutes a
small proportion of the total electron current,
' a tube having a cathode, a control grid, a screen
while in the non~conducting condition (Fig. 2)
potential and a resistor,,a coupling circuit be
tween the screen grid and the suppressor grid
to sustain at each either of two stable conditions
the screen grid current is the total electron cur
rent. There is, therefore, ample discrimination
grid, a‘suppressor grid, and an anode, the control
grid and screen grid having wires in alignment
to determine electronic beams, an anode circuit,
a screen grid circuit including a source of positive
between the two conditions of stability to insure 10 caused by changes of potential at the suppressor
that an unintended shift from one condition to
the other cannot occur. It should be understood
that the invention is not limited to the precise
construction herein described, but that other ar
rangements within the scope oi’ the appended
claims are to be considered within the purview of
the invention.
Having thus described .the‘invention, I claim:
1. An electronic switching circuit comprising
a grid, and an input circuit for applying a pulse
to the control grid and thereby to shift the screen
and suppressor grid potentials from one stable
condition to the other.
3. An electronic switching circuit comprising
a tube having a cathode, a control grid, a screen
grid, a suppressor grid, and an anode, the control
grid and screen grid having wires in alignment
to determine electronic beams, an anode circuit,
a tube having a cathode, a control grid, 8. screen 20 a screen grid circuit including a source oi.’ positive
grid, a suppressor grid, and an anode, the control
potential and a resistor, a coupling circuit be
grid and screen grid having wires in alignment
tween the screen grid and the suppressor grid
to determine electronic beams, an anode circuit,
to sustain at each either of two stable conditions
a screen grid circuit including a source of positive
caused by changes of potential at the suppressor
potential and a, resistor, a coupling circuit be
grid, and input circuits‘ for applying pulses to
tween the screen grid and the__ suppressor grid, 25 the suppressor grid and control grid.
and an input circuit for applying pulses to the
control grid to effect changes in the screen and
WILCOX P. OVERBECK.
suppressor grid potentials.
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