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Патент USA US3027476

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March 27, 1962
Filed May 15, 1958
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United States, Patent
Patented Mar. 27, 1962
2 FIG. 27 illustrates waveforms for the circuits of FIGS.
FIG. 28 illustrates the use of circuits as shown in FIGS.
2, 10 and 15 for ripple ?ltering,
Robert R. Roalef, 321 Keniiworth Ave., Dayton 5, Ohio
Filed May 15, 1958, Ser. No. 735,651
2 Claims. (Cl. 307-885)
(Granted under Title 35, U.S. Code (1952), sec. 266)
FIGS. 29 and 30 illustrate the use of the limiting cir
cuits of FIGS. 2, 10 and 15 in producing constant cur
rent sources, and
FIG. 31 illustrates the characteristic of the circuits of
The invention described herein may be manufactured
FIGS. 29 and 30.
and used ‘by or for the United States Government for 10
FIG. 1 shows the E—I characteristic of a typical junc
governmental purposes without the payment to me of any
tion type germanium diode such as the General Electric
royalty thereon.
IN93. For current ?ow in the back direction, the im
This invention relates to current limiting devices and
pedance of the diode at 25° C. is seen to ‘be relatively low
is primarily concerned with the protection of delicate
in the vicinity of zero current, as indicated by the steep
current sensing apparatus, such as sensitive null meters 15 ness of the characteristic, and to increase abruptly to a
or the sensitive error signal sensing ampli?ers used in
relatively high value at about .1 volt and 23 microam~
servo systems, ‘against overloads and consequent burn out.
peres. At 40° C. this change in impedance occurs at be
The ideal protective device would otter no resistance,
tween .1 and .2 volts and 70—8() microamperes. The
or very little resistance, to current flow to the protected
points are representative and can be expected to vary
apparatus at low applied voltage, so as to preserve the 20 somewhat from sample to sample.
sensitivity of the apparatus to weak signals, and would
T'Wo diodes having characteristics of the type shown in
act automatically at higher applied voltages to limit the
FIG. 1 may be connected in oppositely poled series rela
current to the protected apparatus to a safe value. The
tionship to ‘form a simple current limiting device, as
current limiting devices described herein utilize the pecu
shown in FIG. 2. Here a current limiter having termi
liar properties of semiconductive diodes to approach this 25 nals 1 and 2 and consisting of oppositely poled germani
um diodes 3 and 4 is connected in series with coil M,
Although intended primarily as protective devices the
which, for example, may be the coil of a null meter or the
properties of the current limiting networks disclosed may
input coil of a magnetic ampli?er, and serves to protect
be utilized in other ways, several of which will be de
the coil against excessive current ?ow in either direction.
30 The characteristic of the circuit of FIG. 2 is as shown
A more detailed description of the invention will be
in FIG. 3. For current flow in the direction shown, diode
given with reference to the speci?c embodiments thereof
3 offers a constant relatively low impedance for all values
shown in the accompanying drawings in which
of e. Diode 4 offers a similar relatively low impedance
FIG. 1 illustrates the characteristic of a diode having
for values of 2 below the value, varying with tempera
low incremental impedance at zero voltage, such as a 35 ture, that brings the diode voltage to the point of in?ec
tion on the diode characteristic. When the current flow
germanium diode,
FIG. 2 is a current limiter employing diodes having
characteristics as shown in FIG. 1,
FIG. 3 shows the characteristic of the limiter of FIG. 2,
is in the opposite direction the roles of diodes 3 and 4
are reversed. For small values of e, therefore, the com
bined impedance of diodes 3 and 4 is relatively low and
FIG. 4 shows a limiter employing series diodes of the 40 is less than the impedance of coil M, so that the sensi
type illustrated in FIG. 1 and shunt diodes of the type
tivity of the protected apparatus to small voltages is not
illustrated in FIG. 5,
greatly reduced by the current limiting device. For
FIG. 5 illustrates the characteristic of a diode having
higher values of 2, above that at which in?ection occurs,
high incremental impedance at zero voltage, such as a
the greatly increased impedance of diode 3 or 4 presents
silicon diode,
any appreciable further increase in current through the
FIG. 6 illustrates the characteristic of FIG. 4,
coil M. This type of protective device is simple and can
FIGS, 7, 8 and 9 illustrate the principles involved in a
be installed within the case of a meter, thereby permit—
current limiter having an adjustable threshold and using
ting a sensitive meter to be used in circuits where over
diodes of either the type shown in FIG. 1 or in FIG. 5,
loading is likely to occur without the danger of meter
FIG. 10 is a limiter circuit employing the principles 50 burn out.
of FIGS. 7, 8 and 9,
FIG. 11 is the overall characteristic of the limiter in
As indicated, the protection afforded by the above de
scribed device is not independent of temperature, which
FIG. 10,
FIGS. 12a and 12b illustrate the operation of FIG. 10,
may possibly result in inadeqaute protection being pro-'
vided at higher temperatures. The arrangement of FIG.
FIGS. 13 and 14 are measured charcteristics of lim 55 4 is intended to alleviate this di?iculty through the use
iters of the type shown in FIG. 10,
of a pair of oppositely poled silicon diodes 5 and 6 in
shunt to coil M. The E—I characteristic of a typical
biasing voltage then the limiter of FIG. 10,
point contact silicon diode, such as the Hughes No. 6002,
FIG. 16 is the characteristic of the limiter in FIG. 15,
is shown in \FIG. 5 and is substantially independent of
FIGS. 17 and 18 illustrate alternating current biasing 60 temperature. It is seen that the diode has a very high im
in circuits of the type shown in FIGS. 10 and 15.
pedance, substantially an open circuit, in the back direc
FIGS. 19 and 2() illustrate limiters of the type shown in
tion and also a high impedance in the forward direction
FIG. 15 illustrates a current limiter requiring a smaller
FIGS. 10 and 15 used as phase detectors,
up to a voltage between .3 and .5 volt where there is a
FIG. 21 illustrates the phase characteristics of the cir
sharp in?ection of the curve representing an abrupt drop
cuits of FIGS. 19 and 20,
in impedance to a relatively low value. In the arrange
FIGS. 22 and 23 illustrate the uses of the circuits of
ment of FIG. 4, therefore, IM, as seen in FIG. 6, in
FIGS. 2, 10 and 15 in the generation of rectangular
creases as 2 increases up to a value e’ at which the volt
tage across the coil M and the silicon diodes is some
FIGS. 24, 25 and 26 illustrates modi?cations of FIG.
where between .4 and .5 volt and the impedance of the
22 or FIG. 23 to produce triangular waves, step functions 70 ‘forward connected diode starts changing to its lower
value. At this point the diode begins to conduct so that
sharp pulses, respectively,
the total current IT divides between coil M and the
shunting diode. The effect of this is to limit further in
creases in voltage across the coil and in IM, as shown in
‘ FIG. 6.
Sincev the silicon diode charcteristics are'sub
current so that it must ?ow through the battery and R,
as shown in FIG. 12b, and is limited to the value per
mitted by the magnitude of this resistance. Due to the
symmetry of the circuit, reversing the polarity of a merely ,
stantialy unaffected by temperature changes, the shunt
interchanges the roles of diodes 7 and 8.
ing diodes protect the coil against the increased current
permitted by the germanium diodes at the higher tempera
As may be seen by a comparison of FIGS. 8 and 9,
the effectiveness of the circuit of FIG. 10 as a current
limiter increases as R increases. For eiiective limiting,
as indicated by a low value of slope for that part of the
‘ Because of the fact that silicon'diodes require a for
ward voltage of about .5 volt to produce an abrupt fall in
impedance, as shownin FIG. 5, these diodes are not suit
e-—IS curve corresponding to values of e below the ?ex- '
ure region, a relatively large R is required. FIGS. 13
able for use in a simple limiting circuit of the type shown
and 14 show the measured characteristics of the circuit
in FIG. 2.. However, by the use of a direct biasing vol‘
age in circuit with a pair of silicon diodes, it is possible
of FIG. 10 for two values of R with the values of E
required to produce limiting in the 30-35 microampere
to construct a limiting circuit having a characteristic 15 region. FIG. 13 shows the effec'tgof the coil M or load
similar to the circuit of FIG. 2 and providing the advan
resistance on one of the characteristics for low values of
tage that, was a result of using silicon diodes, the limiter
en It is apparent that limiting takes place when the cur
characteristic is substantially independent of temperature.
rent reaches a value equal to the quiescent current I0
FIGS. 7-12 illustrate the principles underlying the design
which is directly related to E/R and, for large values of
of this circuit.
20 R, is substantially equal to E/R, as seen in FIGS. 8 and
Referring to FIG. 7, silicon diode 7 is connected in
9. Therefore, for any given value of R, the limiting
series with a source of direct voltage E and a resistance
R. A source 8 of low internal impedance relative to R
and providing a variable direct voltage a is connected
across the diode. It is apparent that IS=ID-IR. FIG.
8 shows the manner in which ID, in and their algebraic
difference Is vary with e.
As e decreases from a value
point can be controlled by changing E.v For quiescent
currents in the microampere range, as would occur when
protecting a very sensitive meter element, it is feasible
to use small batteries to supply the voltage E since at this
low current drain the battery life can be expected to
approximate shelf life. The voltage E can of course be
obtained from a conventional DC. power supply instead
above E0, which is the voltage that would exist across the
diode if source 8 were removed, IR increases and ID de
of a battery where complete portability is not required.
creases, becoming equal and reducing Is to zero at e=E0. 30
As seen from FIGS. 13 and 14, for effective limiting at‘
At this point IR=ID=I0 where is referred to as the quies
currents of 30 microamperes or greater relatively high
cent current.
As e decreases below E0, IS reverses its
direction and flows into source 8. This current begins to
limit as e enters the region of ?exu're of the ID curve.
‘ values of E are required, which may be undesirable where
7 batteries are used to supply the potential. The circuit of
Below this region the diode has a very high impedance,
FIG. 15 provides absolute limitation of the current
through coil M over a wide range without requiring high
as indicated by the ?atness of the ID curve, and the value
direct biasing voltages. Considering this circuit further
of Is is determined principally by R which, as stated
above, is assumed to ‘be much greater than the internal
impedance of source 8. In FIG. 8 the internal impedance
and assuming e=(), battery 9 causes a circulating current
I01 to ?ow in the loop circuit consisting of battery 9‘, re
sistor 10, diode D1 and coil M. Similarly, battery 11
of source 8 is assumed to be substantially zero so that 40 causes a circulating current I02 to flow in the loop circuit
consisting of battery 11, 1resistor 12, diode D2 and coil M.
If the ‘sources 9 and 11 provide equal voltages E, if re
sistors 10 and 12 have equal values R and if the diodm
D1 and D2 are matched, then Io1=I02 and, since the two
for values of 2 below the flexure region. The resistance
presented by the circuit to source 8 at e=Eo is very low 45 currents ?ow in opposite directions through coil M, the
current 1M is Zero. Diodes D1 and D2 may be of germa
as indicated ‘by the steepness of the e-Is characteristic
nium or silicon, but are preferably the latter in order to
at this point. By increasing R to a relatively high value
take advantage of the relative independence of tempera
and then increasing E1 as required to reestablish the same
ture exhibited by the silicon diode characteristic.
value of ID, the limiting action of the circuit for current
The voltages E bias diodes D1 and D2 in their conduc
?ow into source 8 can be improved, as indicated in FIG.
tive regions at a voltage at which the incremental imped
9 where that part of the IS curve below the ?exure region
ance is low. This biasing voltage across the diode termi
is much ?atter than in FIG. 8.
nals may be designated E0 and may have, ‘for silicon, a
It will be ‘seen that the shape of the e~IS characteristic
of ‘FIG. 9 is very similar to that of the E-I character 55 value of .51 volt, for example, giving a diode current of
about 35 microamperes as seen in FIG. 5. The value of
istic of silicon shown in FIG. 5. Also, if the point E0
R is determined by the relationship
is considered the origin, the characteristic is very similar
to that of germanium shown in FIG. 1. By using a sec
ond diode 8 and’ duplicating the circuit of FIG. ‘7, as
shown in FIG. 10, E, can eifectively be made the origin
60 and for the above speci?c case, using a small low voltage
with respect to an applied voltage e of either polarity.
battery such, for example, as the Mallory PR-l mercury
Therefore, the circuit between terminals 1 and 2 acts as
cell having a potential of 2.6 volts,
a current limiting device for coil M and, as shown in
FIG. 11, has a characteristic which is similar to the char
acteristic of the circuit of FIG. 2. FIGS. 12a and 12b 65
illustrate the operation of the circuit of FIG. 10. For
As e increases above zero, assuming the polarity shown, .
small values of e, of the polarity shown, the current 1M
travels through diode 7 in the forward direction and
the resulting source current IS flows through D1, M' and
D2 in succession. The current takes this path because
' through diode 8 in the backward ‘direction, the impedance
the incremental impedance of D1 and D2 at E0 (FIG. 5)
of the diodes being very low relative to R for voltages in 70 is much less than R and therefore substantiallynone of
the vicinity of EU as indicated in FIG. 9 by the steepness
of the characteristic at this point. For values of e causing
the voltage across diode 8, as measured from E0 in FIG.
IS ?ows through resistors 10 and 12. V'Ihe current 15'
?ows through D2v in opposition to ‘I02 and, therefore re;
duces the total forward current flow through this diode ’
9, to go beyond the ?exute region of its characteristic,
and the voltage across it. For values‘of e from zero up
the diode presents substantially an open circuit to the 75 to a certain value E1 the voltage across D2 is' such that its 1
incremental impedance is low. For the diode of FIG. 5,
‘the output magnitude is not indicative of error signal mag
E1 would be that value of e for which the voltage across
the diode is reduced to about .48 volt. Over this range
of e, IM=IS. As e increases above E1 the incremental
impedance of D2 begins to increase, as indicated by the
nitude; however, the output polarity is still indicative of
phase relation, in this case indicating the direction of de
parture of one voltage from a'quadrature relation to the
decreasing slope of the characteristic in FIG. 5, and in
The circuits of FIGS. 17 and 18 also may be used to
give a direct current indication of the phase relation
between two alternating voltages of the same frequency
creases rapidly until the potential across the diode is re
duced to about .3 volt at which point D2 represents sub
which is substantially independent of the‘relative magni~
stantially an open circuit. .As the impedance of D2 in
creases an increasing portion of the increment in IS ?ows 10 tudes of the two alternating voltages. FIGS. 19 and 20
illustrate such use of the circuits of FIGS. 17 and 18,
through resistor 12 until eventually any signi?cant fur
respectively. Referring to FIG. 19, this circuit com
ther increase in the current through D2, and therefore
through M, is impossible. Since the current through D;
equals log-1M, when this current becomes zero 1M=Io2
so that the current in coil M positively limits at a value
equal to the quiescent current. As 2 increases still further
IM remains constant at the quiescent value while IS con
tinues 'to increase at a rate determined by R. This is
illustrated in FIG. 16. Due to the symmetry of the cir
pares the phase of e1 with that of E2, which may he
considered the reference phase, and produces a positive
potential at terminal 13 when the phase difference is in
the range 0°—90° and a negative potential when in the
range 90°-180°, the potential being zero at 90°. The
characteristic is illustrated in FIG. 21. E2 corresponds to
the biasing voltage E of FIG. 10 and is selected in ac
cuit, reversing the polarity of e simply interchanges the 20 cordance with the maximum voltage desired at terminal
13. The signal e1 must have su?icient magnitude in this
roles of D1 and D2 and reverses the direction of IM.
case to drive the circuit into its limiting range. In other
As stated above, the current at which the circuit of
words, 21 must exceed the magnitude required at phase
FIG. 15 limits is equal to the quiescent current 10. Since
this current is determined by E and R in accordance with
the relation
I0: E-Eo
angles 0° or 180'’ to reduce the potential across the diode
where it opposes the biasing potential sufficiently to drive
that diode into its high impedance range. If the diodes
are biased at about the point indicated in FIG. 5 the
required minimum potential reduction would be about .1
volt or slightly more.
the limiting value can be varied by appropriate changes
The operating principle of the circuit of FIG. 19 is no
in E or R. For limiting in the range of 30-80 micro— 30
different from that of the circuit of FIG. 10. If the phase
amperes with a low value of E, the values of R are rela
difference between el and E2 is 0° these two voltages have
tively low and the circuit, when in the limiting state, does
the same phase at diode 7 and opposite phases at diode 8.
not present as high an impedance to the source of e as
Therefore, on the positive half-cycles of E2, diode 7 has
is presented by the circuit of FIG. 10. However, by in
creasing E and R in proportion any desired circuit im 35 ‘a low impedance and diode 8 a very high impedance so
that current flows from the secondary of transformer 14
pedance may be obtained for any given limiting current.
through diode 7, the secondary of transformer 15, resistor
E0 is nearly a constant quantity as may be seen in FIG. 5
16 and resistor 17 causing terminal '13 to be positive rela—
where over a current range of l0-80 microamperes it
tive to ground. If the phase difference is 180° the two
varies less than .1 volt. As in FIG. 10, the small current
drain permits the life of the batteries supplying E to 40 voltages are in phase on diode 8 and of opposite phase on
approximate their shelf life. E can, of course, be ob
tained from a conventional DC. power supply if desired.
It isnot necessary that the circuits of FIGS. 10 and
diode 7.
Consequently the previous conditions are re
versed with current ?owing from the secondary of trans
former 14 upward through resistor 17,and thence through
15' be biased with direct current. Alternating biasing » diode 8, the secondary of transformer 15 and resistor 18,
voltages may be used as shown in FIGS. 17 and 18. In 45 causing terminal 13 to be negative. When the phase differ
ence is 90", equal currents ?ow in opposite directions
FIG. 18, the phasing of the transformer secondary wind
through resistor 17 during each positive half-cycle of E2
ings must be as indicated and the secondary voltages must
so that the net current and the voltage at terminal 13 are
be equal. The operation is similar to the direct current
zero. As in FIG. 10,,the limiting action of the circuit, re
biased condition except that a pulsing rather than a con
50 sulting from the high value of R, makes the voltage at ter
tinuous direct current passes through coil M.
minal 13 substantially independent of the magnitude of e1.
The signal e in the above case may be alternating as
When operated under the conditions speci?ed above
well as direct provided it has the same frequency as E;
for FIG. 19, the circuit of FIG. 20 operates to produce
the same result, the basic operating principle being the
0° to 180°, between e and E2. The smallest alternating
voltages may be measured since the diodes are forced 55 same as for FIG. 15. When el and E2 have a phase di?er
ence of zero, the two voltages at D1 due to e1 and E2
into conduction by the biasing voltage once in each cycle
‘have the same phase. whereas the two voltages at D2 have
and while conductive the smallest departure of e from
and provided there is a ?xed phase di?’erence, preferably
zero can cause a current ?ow through M. It is therefore
opposite phases. D2 therefore has a very high impedance,
coil M which may be the input to a sensitive servo con
ing each positive half-cycle of E2 with the result that the
trol system. In this case also, the limiting action of the
circuit protects coil M against high values of the error
signal e. Where the above 0°—180° relationship between
net current and the voltage of terminal 13 are zero. Since
the current through resistor 17 can never exceed the
provided e1 exceeds the minimum value speci?ed above
not necessary for the signal being measured to provide the
initial voltage required to cause diode conduction. It is 60 as required, and the current from transformer 14 ?ows
through D1 and then divides, part ?owing through resistor
evident that changing the phase relation between e and
17 and D2 to the extent required to cancel the opposite
E2 by 180° reverses the direction of current ?ow through
?ow through D2 due to transformer 15", and the re
M. The circuit may therefore be used as a phase sensi
mainder flowing through the secondary of transformer
tive recti?er in servo systems in which the error signal
is an alternating voltage having one of two opposite phases 65 15" and resistor 12. Terminal 13 is therefore positive.
If the phase difference is 180°, conditions are exactly re
depending upon the direction of the error. In this appli
versed so that current ?ows upward through resistor 17
cation, e would represent the error signal and E2 would
toward terminal 13 with the result that this terminal is
supply the reference phase. A reversal in phase of e, in
negative. When the phase diiference is 90", equal cur
dicating a change in the direction or sign of the error,
results in a change in direction of the direct current in 70 rents ?ow in opposite directions through resistor 17 dur
quiescent current through D1 or D2 resulting from the
the two applied alternating voltages is not maintained, 76 biasing voltages from transformers 15' and 15", the po
tential ‘at terminal :13 is independent of the magnitude of
e1 in the range above the speci?ed minimum. The maxi
mum voltage at terminal 13 can be adjusted by changing
R or the equal secondary voltages of transformers 15'
and 15".
rent limiters ofthe type shown in FIGS. 10‘ and 15 are ,
used, the value of I may be adjusted by varying the E
or R of these'?gures.
I claim:
1. A current limiting device having a pair of input ter
FIGS. 22-31 illustrate examples of various additional
minals “a” and “b” for connection to a source of current
and a pair of output terminals “c” and “d” for connection
uses to which the limiting and constant current character
to a load, said device comprising: a diode connected be
istics of the circuits of FIGS. 2, 10 and _15 may be put.
tween terminals “a” and “c,” a like diode connected be
FIG. 22 illustrates a circuit having input terminals 18-19
and output terminals 20-21, and containing a current 10 tween’terminals “b” and “d,” said diodes having like
limiting circuit 22 of either the type shown in FIG. 2
poles connected to terminals “1;” and “d,” a source of
voltage andan impedance connected in series between
or the type shown in FIG. _10. FIG. 23 illustrates sim
ilar circuit containing a limiter 22’ of the type shown in
terminals “a” and “d” and a like source of voltage and
FIG. 15 and having corresponding reference terminals.
a like impedance connected between terminals ‘v‘b” andv
With an alternating voltage asshown at (1) in FIG. 27
applied to input terminals 18-19 of either circuit, the
currents through said diodes in the forward direction, - I
“c,” said voltage sources being poled to send equal biasing '
maximum amplitude of this voltage being much greater
said diodes being of the type having a high impedance in
than the voltageEl, illustrated in FIGS. 3, 11 and 16, at
which limiting occurs, various waveforms may be gener
ated. If'the impedance between terminals 20-21 is a
resistance, as in FIGS. 22 and 23, a substantially rec
_ tangular alternating wave as shown at (2) in FIG. 27 is
produced. If the impedance is a condenser, as shown in
FIG. 24, the resulting constant current charging and dis
the reverse direction and also in the forward direction
up to a predetermined'forward voltage at which the irn- ’
pedance changes sharply to a low value.
2. A current limiting device for connection between a
two-terminal source of current and a two-terminal load
for abruptly limiting the current ?ow through said load
at a predetermined value, said device comprising a diode
charging of this condenser produces a linear triangular
P connected between one of the source terminals and one of
alternating voltage at terminals 20-21 as shown at 3
the load terminals, a like diode connected between the
other source terminal and the other load terminal, said
in FIG.‘ 27. If_ the circuit of FIG. 25 is substituted in
FIGS. 22 and 23, the recti?er prevents the condenser
diodes having like poles connected to said load terminals,
from discharging so that the resulting direct voltage at
a source of voltage and an impedance connected in series
terminals 20-21, increases by one step for each cycle of 30 between said one current source terminal and said other
load terminal, a source of voltage and an impedance con~
the applied alternating voltage as shown at (,4) in FIG.
27. Finally, if the circuit of FIG. 26 is substituted in
nected in series between said other current source terminal
FIGS. 22 and 23, a substantiallyrectangular wave of cur
and said one load terminal, said impedances having equal
rent ?ows through the primary of the transformer produc
values and said voltage sources having equal voltages
ing sharp voltage pulses at the secondary terminals 20
; poled to send current through said diodes in the forward
21, as shown at (5) in FIG. 27.
direction, said diodes being of the type having a high
The circuits of FIGS. 22 and 23 are capable of acting
impedance in the reverse direction and also in the forward
as a ripple ?lter for a direct voltage applied to input ter
.minals 18-19. Such a voltage is illustrated at (1) in
FIG. 28. If its minimum amplitude always exceeds E1 40
the voltage at which limiting occurs, the output voltage is
ripple free as shown at (2).
Limiting circuits of the type described in FIGS. 2, 10
vdirection up to a predetermined forward voltage at which
the impedance changes sharply to a low value.
‘References Cited’ in the ?le of this patent
and 15 may also be used as a constant direct current
source fora variable‘impedance load, as illustrated in 45
Mayer ___________ __Y___ July 5, 1938
FIGS. 29 and 30. The operating characteristic is shown
in FIG. 31.‘ For any value of R1, the impedance of the
Sivers et al. ___ _______ __ Feb. 19, 1957
Hughes ______________ .._ Apr. 1, 1958
load, forwhich ES—-IR1 is greater thanE1, the voltage
at which the limiting actions of circuits 22 and 22' be
come elfec'tive, the current I remains-constant. If our
Devol _______ __-_ ____ __ Oct. 18, 1932
Radcliffe ______ h _____ __
1, 1958
\ 2,843,745
Smith ________________ __ July 15, 1958
Kircher _____________ __ Sept. 30, 1958
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