April 18, 1939-
4
w. H’ T. HOLDEN
2,155,230
PEAK VOLTAGE LIMITER
Filed June 30, 1936
FIG. 1
6
K
h?“
R
<‘
5
-
+
$1;
AMP
2
Y
R/
CURRENT- CONTROL
ELECTRODE TO CA THODE
FIG. 2
12.332
2,000
I. 000
200
I DO
o. o
I
20
MICRQOAMPS
a»
I0
_/ VOLTAGE- BETWEEN CONTROL
_20 ELECTRODE AND CA THODE
RESISTANCE-BETWEEN CONTROL
1,000,000
—00 —.r0 —40 -J0 —20 —/0
7
ELECTRODE AND CATHODE
0
/0
20
30
40
50
6'0
VOLTAGE-BETWEEN CONTROL ELECTRODE AND 04 move
INVENTOR
W H. 7.' HOLDEN
A 7' TORNEV
Patented Apr. 18, 1939
2,155,230
UNITED ‘STATES
PATENT OFFICE
alssaso
m vouracn IJMI'I‘ER
William H. '1‘. Holden, New York, N. Y., ~assignor
one Laboratories, Incorporated,
New York, N. Y., a corporation of New York
Application rm 30, 1936, Serial No. 88,138
7 Claims. (Cl. 171-119)
The invention relates to peak voltage limiting . saturation e?ect described by Langmuinbut rises
circuits and more particularly to ‘voltage limiters in value as the collector electrode becomes a
employing space discharge devices for use in cathode and hence the impedance between col
speech transmission circuits.
.
,
,
lector and cathode dropto a very low value.
Voltage limiters employing hot cathode gas
OI
When the collector electrode is raised in volt- 5
filled discharge tubes in shunt to a tron
circuit in which peak voltages are to be limited
are well known as for example Patent 1,869,484
to W. A. Knoop issued August 2, 1932. Such
10 arrangements, however, are of the so-called
_ breakdown voltage type and therefore when the ‘
critical voltage, at which the limiter is ‘to func
age, from a value near that of the cathode,‘ 'elec-
'
tron current and positive ion current will both
?ow to it, the former increasing and the latter
decreasing slowly as the voltage is raised so that
at some potential the total current vanishes and 10
then reverses and rises rapidly, the electrode now ‘
becoming a collector of electrons or an anode,
tion, is reached‘ there is an abrupt change “in the positive ion sheath disappearing and the cur- '
the shunt circuit, from a very high impedance rent increasing about 400 to 1.
'
15 to a relativelyiow impedance, which has a tend . Thus it will be seen that in the region where 15 ,
ency to cause distortion in’ the signals being the collecting electrodeis su?iciently negative,
transmitted whose amplitudes are
and if activated, it will function as a cathode and
The present invention is an improvement on will exhibit a low impedance. In the interme
limiters heretofore known in that it employs a diate range oi.’ voltages where it is positive with
20 gas-?lled discharge‘ tube of the three-element respect to the cathode yet negative (by approxi- 20 '
cold cathode type which functions in a new and mately the cathode fall of potential) to the‘
novel manner.
plasma it will be surroundedby a positive ion
In the Journal of the Franklin Institute, for sheath and as the current changes only slowly
September 1922, page‘ 275, et seq., Irving Lang- ’ with voltage the alternating current impedance
25 muir,‘ in ‘discussing electric discharges in gases will be high. Finally, when the electrode becomes 25
- , at low pressure states that a discharge between
a collector of electrons and the positive ion sheath
two electrodes, in a gas at low pressure, produces disappearsit will become an anode and again ex
an ionized state, in the gas which is described hibit a low impedance. Now. if a discharge is
‘as a “plasma”, 1. e., a region of intense ioniza
established and maintained between the anode
30 .tion containing positive ions and negative elec
and one cathode of a discharge tube of the type 30
trons in about equal numbers and that a variable described in U. 8. Patent ‘1,977,254 the impedance
potential collector placed in the discharge path looking into the other cathode is subject to wide
and given a negative bias will draw positive ions variations depending upon the voltage applied
to itself and under typical conditions the ion thereto. Then, at zero voltage between the two
35 current will saturate when the collector is given’ cathodes, the one of variable voltagewhich will 35
a five to ten volt negative bias. The present hereinafter be called the control electrode, beinvention is based in part on the foregoing dis
comes, electrically a part of the other cathodev
vvcovery but instead oi‘ the collector electrode and, therefore, will exhibit ‘an impedance of about
drawing a positive ion current when it is at the the same value as the discharge gap between the
40 cathode potential or slightly negative thereto, anode and ?rst cathode which is, of the order 40‘
» it emits electrons, thereby becoming a cathode, of 100 ohms. This impedance, however, rises’
if it together with the cathode is coated with as the control electrode is made more positive-I
electron emitting, material, 1., e., activated, when
it is bombarded. with Positive ions vat voltages
45 of the order of 40 to 50 volts.
The same eil'ect
will, however, be produced if the collector elec
trode and cathode are uncoated, but in this case
‘
the cathode fall will be several times greater
' I than 40 and 50 volts which is the characteristic
50 of the coatedltype electrodes. In this case the
same- operation will take place, but voltages of
the order of 150-170 volts will be required. >
and attains values of ,from 100,000 to 500,000 ~
ohms when the control electrode potential lies.
between plus 25 and plus 50 volts,_these|v'o1t'- 45
ages being measured between it and the .?rst' -
cathode.
If the control electrode ‘potential is
still further increased in a positive direction the _
impedance ceases to rise and starts to rapidly
decrease as the control electrodeub'ecomes the 5-0
anode of a discharge across the gap to the cath
‘Under the ?rst condition, i. _e., coated elec-,-~ ode and continues to drop to 100'ohms or less. 1
trodes and 40-50 volts ion bombardment, 'the These ?gures are basedv on theu‘se of a‘ dis
55 collector ‘electrode, current does not’ exhibit the charge tube containing pure argon at 10-milli
~
2,155,230
2
meters of mercury pressure.
tubes show similar performance.
However, other
An object‘of-the present invention is to limit
peak voltages in signal transmission lines with
out distorting the signals whose amplitudes are
and thence to battery B and through resistance
R to anode A. It will be observed that for volt
ages of the order of 30 vets, positive from con
trol electrode to cathode a very small current, of
the order of a microampere or less, flows in the
control electrode-cathode circuit. Accordingly a
linear scale from plus ten to minus ten micro
A feature of the invention whereby the fore
going object is attained resides in the employ- ‘ amperes has been used, but it is found that when
limited.
ment of a three-element cold cathode gas-?lled
10 space discharge device .comprising an anode and
two other electrodes, which are preferably coated
the control electrode potential approaches that
of the cathode, or that of the anode, that a rapid
increase in current takes place. In order to show
this conveniently, the current scale has been made
with an electron emitting material, so arranged
logarithmic beyond the ten microampere point in
either direction. This phenomenon will be read
that a continuous discharge takes place between
the anode and one of the other electrodes, 8 pre
15 determined lower potential is continuously applied
ily understood when it is noted that the control
electrode becomes e?ectively a part of the oath
ode at voltages near zero, and that at voltages 01!
about 55 or more it becomes an anode. At inter
mediate voltages it collects positive ions or elec
trons from the positive column or plasma of the
glow discharge, but these currents are small and
to the third electrode and that said other elec
trodes are connected to opposite sides of the line
in which the peak voltages are to be limited.
By this arrangement the normal impedance of
the
gap between the two electrodes connected
‘20
across the line is very high but, as before de
scribed, when the line voltage rises the impedance
of the gap decreases thereby limiting the ampli
tude of the signal wave.'
change but slowly with voltage.
Hence, the alternating current resistance of
the control electrode
'
15
The invention will be understood from the fol
lowing description when read in connection with
all
Fig. 1 showing a high impedance connection be
tween two ampli?ers forming a part of the trans
30 mission circuit in which it is desired to limit the
amplitude of the voltage wave transmitted and
having bridged thereacross a voltage limiter com
prising a three-element cold cathode discharge
device arranged in accordance with the fore
eoins;
35
above zero to about 50 volts, but drops to very
low values at zero or negative voltages, or at
positive voltages in excess of 50, as shown by the
~ curve of Fig. 3.
.
Fig. 2 illustrates the current voltage character
As long as no potential di?’erence exists be
tween the two sides of theline the impedance between cathode and control electrode, due to the
fact that the control electrode is 30 volts posi
tive with respect to the cathode, is of the high
istics of the control electrode of the discharge
order 0! 200,000 ohms.~ When voltage is applied
device when a glow‘ discharge exists between
cathode and anode ;~ and
Fig. 3 illustrates the resistance-voltage char
acteristics under the same conditions.
to the line and the potential of the control elec
trode increases in a positive direction, the im
‘pedance between the cathode and control elec- ‘
trodes increases until it reaches a maximum of
the order of 500,000 ohms at a potential of ap
proximately 50 volts positive on the control elec
Referring to Fig. 1 the voltage limiting arrange
ment I, of the invention, is connected in bridge
or the transmission circuit between the output
45
.
is of a large value in the region from slightly
the accompanying drawing: 7
trode, but beyond this critical point the imped
transformer 2 of the ?rst ‘ampli?er I and the in
ance ceases to; increase and as the control elec
put transformer 4 of the‘ second ampli?er 5.
trode still further increases its potential in a posi
This limiting arrangement consists of a three?
element gas-?lled discharge device 0 comprising
tive direction, and becomes the anode of a dis
charge across the gap to the cathode, the im
an anode A, cathode.K and a third orso-Called
pedance rapidly decreases to a very low value of
control electrode CG, a battery B of the order of
180 volts, resistances R and R1, and condenser ‘I.
As previously mentioned the cathode K and
the order oi’ 100 ohms or less.
the control electrode CG are preferably coated
with respect to the cathode, its impedance will
with some well-known electron emitting material. -
remain substantially constant until it attains a
voltage near or equal to that of the_cathode.
65 The cathode K is connected to one side of the‘
' line, the control electrode CG to the other side of
'
It on the other hand, the‘control electrode volt
age is lowered below the initial value of +30 volts
When this occurs, the control electrode will func
the line through the condenser ‘I and the anode tion as a cathode, and the impedance looking into
A is connected to the cathode K in series with this element will again drop to a low value of the
resistance R. and the battery B which is so poled‘ ‘order of 100 ohms.
It will then be apparent vthatin the circuit
60 that the cathode is negative with respect to the
anode. Under this condition there will be a con
arrangement shown, alternating voltages having
tinuous discharge between the anode and cathode.
A_ further connection also exists, including the
peak values of 20 volts or‘less will suffer little or
no e?ect, the only attenuation in passing from
high resistance R1, from the control electrode CG - transformer 2 to 4 being that due to‘th’e presence
to an intermediate point in the battery B so of a shunt path through the tube, of an imped
chosen that the control electrode is positive, by the ance of from 100,000 to 500,000‘ ohms. However,
order of 30 volts, with respect to the cathode and if the alternating voltage amplitudes are in
approximately 150 volts negative to the anode. J
creased, to!‘ example, to approximately 60 volts,
Fig. 2 illustrates the properties 01' the control during those portions or the cycle at which the
70 electrode and cathode circuit, K to CG oi the a voltage is in excess of 25 volts, there will be a
device 6.
The voltages are those between con
trol electrode and cathode, and the currents those
?owing in the lead to the control electrode, when
16
a glow discharge current of from 10 to 15 milli
amperes is ?owing from anode A to cathode K,
low impedance path through condenser ‘I’. and
thence from control electrode CG to cathode B
and the other side of the line, and this will be
the case on both positive and negative half cyclel
2,155,230
of the alternating voltage. Hence, these peaks
3
multivoltage source of direct current and con
will be suppressed or chopped o? by the action’ nectionstherefrom to all three electrodes of the
01 the tube 6, as explained.
device for initiating'and maintaining a continu
It is, of course, understood that the speci?c . ous glow discharge between the anode and one
values mentioned are approximate only and are of said cold electrodes and for maintaining a pre
based on a particular tube construction, battery determined positive biasing potential on the
voltage, etc., and such values are subjected to other cold electrode with respect to the ?rst cold
ccnsiderablefvariation, under varying conditions,‘ electrode less than that necessary to maintain a
- without departingi’rom the fundamental theory glow discharge between them, and means for iso
of operation herein described and claimed.
lating said direct current source from the line, 10
What is claimed is:
the gap between said cold electrodes forming an
1. In a full wave peak voltage limiter a line in impedance bridge across said transmission cir
which alternating current potentials transmitted cuit which varies with the line voltage, the value
thereover are to be limited, a gas-?lled discharge of the direct current potential bridged across
said gap being so chosen with respect to the line
15 device having an anode and two similar cold elec
trodes, each of which is adapted to operate as an voltage peaks to be'limited and the sustaining
. anode with respect to theother and as a cathode
voltage of the gap that when, due to the com
with respect to the anode, said electrodes being bined e?ects oi’ said direct current potential and
connected to opposite sides or. the line, direct line potential, said cold electrodes are either at
current means independent of the line for main
substantially zero potential with respect to each
taining a constant glow discharge between the other or at a potential di?erence suilicient to
anode and oné‘ot the electrodes and other direct maintain a glow‘ discharge therebetween, the
current means independent of the line for apply
impedance of said gap to line potential will be
ing a di?erence of potential between said ‘cold relatively low.
"
‘
electrodes, the value of which is substantially
5. The combination in a voltage limiting system
one-half that required to maintain a discharge ‘ of a transmission line, means for impressing volt
therebetween,
,
~
‘
ages of both polarities and of varying magnitude
2. An arrangement for limiting both positive across the conductors of said line, a gas-filled
and negative voltage peaks of alternating cur
space-discharge, device, an anode and a cathode
rent transmitted over a line, said arrangement for said device, a source of potential connected
comprising a three-element gas-?lled discharge to said anode and cathodeand having a voltage
device having an anode and two similar cold elec
su?icient'to maintain a constant glow discharge
- trodes, said cold electrodes being connected‘ to between said anode and cathode, a control elec
opposite sides of the line, a multivolta'wge source trode forming with said cathode a discharge gap
of direct currem independent’ 01' the line and having an impedance which varies with the volt
, means connecting said source to said anode and
age ‘impressed across said gap, a, second source
cold electrodes in such a manner that a continu
for impressing across said cathode and control
electrodev a biasing voltage corresponding to a
ous glow discharge will be maintained between
the anode and one of said cold electrodes and relatively high impedance value for said discharge
that a positive potential- will be applied 'to the gap, circuit connections for said cathode and
other cold electrode with respect to the ?rst cold ,control electrode for including said discharge gap 40
electrode or substantially half‘ the voltage neces
in a circuit across said line to limit the voltage
sary to maintain a glow discharge therebetween. on said line, and circuit means for applying the
3. In a peak voltage limiter for alternating voltages of one polarity present-on said line to .
current transmission circuitsv a three-element said gap in aiding relation to the biasing voltage
gas-?lled discharge device having an anode and *thereon and for applying the voltages of the op 45
two cold similar electrodes, said two, electrodes posite polarity in opposing relation to said biasing
being connected to opposite sides‘ of thecircuit _ voltage, the resulting increase or decrease in the
in which the peak voltages are to be limited-a ‘ voltage across the discharge gap serving in either
source 01' direct current connected ‘across said case to reduce the impedance of said gap to a
50
anode and a ?rst one 01' said cold electrodes for relatively low value.
_
»
I
initiating and maintaining a ‘continuous glow
6. The combination in a voltage limiting sys
discharge therebetween, a'second source of di vtem of a transmission line, means for impressing
rect current connected across said two cold elec-. voltages" of alternating polarity and of varying I
trodes for maintaining the second cold‘electr'ode magnitude across the conductors of said line, a
at a positive potential with respect to the ?rst gas-?lled space-discharge device,"an anode and 55
electrode less than that required to maintain a
glow discharge therebetween, the- gap between
vsaid cold electrodes forming an impedance bridge
a cathode for said device, a source of direct cur- .
_
rent potential connected to said anode and cath
ode and having a voltage su?icient to initiate and
across‘ said transmission circuit which varies with
the line voltage, the value of said second source vmaintains.‘continuous glow discharge between
being so chosen with respect to the, sustaining; said anode and cathode, a third electrode, a con
potential of said gap, and to vthe line voltage nection/‘between said third electrode and one side
of the -line,_a connection between-the other ‘side
peaks to‘ be'limited, that for all line potentials of
the line and said cathode, said thlrd’e'lectrode
below a- predetermined critical value the imped . andkcathode
thereby-forming a "discharge gap
ance of said gap will be relatively high and‘ when
across
the
line
which varies in impedance with
‘ . said line potential of either polarity exceeds said
the-\ voltage impressed thereacross, a second
critical value, the impedance of said gap, will source of-direct current and connections therefor ‘
rapidly fall to a relatively low value;
_10
'
4. In a peak voltage limiter for alternating
current transmission circuits,‘ a three-element
for impressing across'saidcathode and ‘third elec-'‘
trode a biasing voltage of such value thatybelow a
predetermined line voltage of either polarity the
' gas-?lled discharge device having an anode and ' impedance of said gap-will be relatively high and
two cold similar electrodes, said two electrodes
being ‘connected to'opposite sides of the circuit
" in which the’peak voltages are to be limited, 9.
as the line" voltage oi’ either polarity'rise's above
to
said predetermined value the impedance" of said
gap will be reduced to a relatively low value;
75
4
2,155,930
'7. In a peak voltage limiter for alternating cur
rent transmission circuits, a three-element cold
cathode gas-?lled space discharge device having
a cathode and a control electrode connected to
opposite sides of the circuit in which the peak
' voltage is to be limited, a multivoltage source of
direct current independent of the line and con
nections therefrom to all three electrodes of said
device for maintaining a continuous glow dis
10 charge between the anode and cathode and for
maintaining a predetermined positive potential
on said control electrode with respect to the
cathode substantially one-half that necessary to
maintain a discharge therebetween, the gap be
15 tween said cathode and control electrode form
ing an impedance bridge across the line which
varies with ,the- line voltage’ impressed there
across, the value of said direct current voltage
across said gap being so chosen with respect to
the breakdown potential thereof, and the line
potential to be limited, that when the potential
di?erence across said gap is substantially zero,
due to the combined action of said direct current
voltage and said line voltage, the impedance of
said gap becomes relatively low and when the
potential di?erence across said gap is equal to 10
the voltage required to maintain a discharge
'thereacroas the impedance thereof likewise be
comes low, said gap impedance, at all other poten
tial di?erences between zero and the arc sus
taining voltage, being relatively high.
7/
WILLIAM H. T. HOLDEN.
15