Note: Descriptions are shown in the official language in which they were submitted.
'~ 4
1 47,71912
HIGH FREQUENCY ELECTRODELESS LAMP
HAVING A GAPPED MAGNETIC CORE AND METHOD
CROSS-REFERENCE TO RELATED PATENT
.
In U.S. Patent No. 4,245,178, issued January
13, 1981 by James W. H. Justice, one of the present appli-
cants, and owned by the present assignee is disclosed an
improved circuit for energizing the present lamps wherein
a simplified oscillator is operated in Class E mode.
BACKGROUND OF THE INVENTION
_
This invention generally relates to high fre-
quency electrodeless lamps and, more particularly, to such
lamps which are specially designed to have a relatively
constant predetermined operating frequency with a minimum
of output harmonics of the operating frequency.
High frequency electrodeless (HFE) lamps have
received considerable attention in recent years as a pos
sible replacement for the standard household incandescent
lamps which convert electricit~ into light in a relatively
inef~icient manner. Fluorescent lamps are efficient con-
verters of electricity into light, but their cum~ersome
size and their need for ballasting has limited their
application in the household. HFE lamps, in contrast to
-
~$
2 ~7,71912
the starldard fluorescent lamps, can be fabricated in a
relatively compact size.
U.S. Patent No. 4,017,764, dated April 12, 1977
to Anderson, discloses an HFE lamp of the fluorescent type
wherein a ferrite core is entirely contained within a
phosphor-coated envelope. At column 5, lines 38-43 there-
of, it is suggested to admix with powdered ferri.te a
polyimide resin to lower the permeability of the core.
U.S. Patent No. 4,010,400, dated March 1, 1977
0 to Hollister, disclos~s an HFE lamp which utilizes a
ferrite core as a part of a tuned circuit output for a
radio frequency energizing source.
U.S. Patent No. 4,005,330 dated January 25, 1977
to Glascock et al discloses an HFE lamp wherein a closed
magnetic core is positioned exteriorly of the environment
of the envelope, but in energy transferring relationship
with respect to the environment within the envelope.
U.S. Patent No. 3,987,335, dated October 19,
1976 to Anderson, discloses an HFE lamp of the fluorescent
type wherein a ferrite core is only partially contained
within the phosphor coated envelope.
U.S. Patent No. 3,908,264, dated September 30,
1975 to Frieberg et al., discloses a high permeability
core which constitutes a part of a tuped circuit wherein
the resonant frequency of the circuit is calibrated by
removing a portion of the core.
U.S. Patent No. 3,150,340, dated September 22,
1964 to Kalbfell, discloses a toroida] core for a high Q
coil which includes an air gap in order to obtain a high
value of Q for the coil.
An early design of electrodeless discharge lamp
wherein the discharge is maintained by the fields estab-
lished by a magnetic coil is disclosed in U.S. Patent No.
1,&13,580, dated July 7, 1931 to Morrison.
SUMMARY OF THE INVENTION
There is provided an electrodeless discharge
device designed to operate with a rated power consumption
when energized with predetermined radio frequency energy
3 47,719I2
as generated by a radio frequency power source. The power
source has an output portion comprising a tuned circuit
having a resonanl frequency which approximates the prede-
termined radio frequency at which the device is to be
operated. The device comprises a sealed, light-transmitt-
ing envelope of predetermined dimensions, preferably of
rounded or globular shape, and containing a dlscharge-
sustaining medium with a layer comprising phosphor carried
on the envelope interior surface. A magnetic core such as
ferrite is operatively positioned in energy transferring
relationship with respect to the environment within the
envelope and the ferrite material which principally com-
prises the core h~s a very high permeability. The core
has a generally looped configuration, and in accordance
with the present invention, the basic core is interrupted
to include narrow gap means comprising low-permeability
substance which traverses the cross section of the core.
A winding having a predetermined number of turns is wrap-
ped about the core and the winding is connected to a radio
frequency power source by means of lead-in members. The
core comprises a part of the tuned circuit output portion
of the radio frequency power source and the magnetic
permeability of the core constitutes a principal variable
factor which can caùse the resonant freqùency of the tuned
circuit output portion to vary. During operation of the
device, the gap means in the core stabilizes the effective
permeability of the core so that substantial changes in
the permeability of the principal material comprising the
core reflect only as minor changes in the overall effect-
ive permeability of the gapped core. This stabilizes theoperating resonant frequency of the tuned circuit output
portion and the gap means in the core also substantially
increases the Q of the tuned circuit, as compared to the Q
of an otherwise similar tuned circuit which does not
utilize a gap, in order to substantially increase the
selectivity of the tuned circuit output portion and sup-
press output harmonics of the resonant frequency.
There is also provided a method for fabricating
Z4
4 l~7,719I2
s~lch devices as well as the resulting devices wherein the
core portions thereof are not exposed to the temperature
extremes required for processing the envelopes.
B EF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention,
reference may be had to the preferred embodiments, exem-
plary of the invention, shown in the accompanying draw-
ings, in which:
Figure l is a diagrammatic view, shown partly in
section, of the basie components comprising the present
lamp;
Fig. 2A is a simplified circuit diagram for the
present HFE lamp and the circuit shown in Fig. 2B is
equivalent to that shown in Fig. 2A;
Fig. 3 is an elevational view, shown partly in
section, of a practical embodiment of an HFE lamp, wherein
the gapped core is entirely contained with the lamp enve-
lope;
Fig. ~ is a detailed diagram of an A.C. to D.C.
power supply together with the high frequency driver and
oscillator used to energize the lamp shown in Fig. 3;
Fig. 5 is an elevational view, shown partly in
section, of an alternative lamp embodiment wherein the
gapped ferrite core is only partially contained within the
lamp envelope;
Fig. 6 is an alternative circuit diagram for the
A.C. to ~.C. power supply together with the high frequency
driver and oscillator for energizing the lamp embodiment
as shown in Fig. 5;
In Fig. 7 is set forth an elevational view,
partly in section, of still another alternative lamp
embodiment wherein a heat-conductive metallic member is
affixed to the core, with an additional heat-conducting
member to transfer heat from the core to an external
radiator, and a second heat transferring member is pro-
vided to transfer heat from the casing of the power source
to an external radiator;
Fig. 8 is an isometric view, partly broken away,
ZZ4
47,719I2
of the enve~ope and core portion of yet another alterna-
tive lamp embodiment wherein the wound core is isolated
from the discharge-sustaining environment within the
envelope, with ~he core being in energy transferring
relationship with respect to the environment within the
envelope;
Fig. 9 is an elevational view, partly broken
away, showing the alternative lamp embodiment which incor-
porates the envelope and core as shown in Fig. 8;
Fig. 10 is an isometric view, partly broken
away, of the envelope and core portion of still another
alternative lamp embodiment whereln the wound core is
isolated from the environment within the envelope;
Fig. ll is an elevational view, partly broken
away, of the lamp embodiment which incorporates the enve-
lope and core as shown in Fig. lO;
Fig. 12 is an isometric view, partly broken
away, of the envelope and core portion of still another
alternative embodiment wherein the core is isolated from
the discharge-sustaining environment within the envelope;
Fig. 13 is an elevational view, shown partly in
section, of the alternative lamp embodiment which incor-
porates the envelope and core portion as shown in Fig. 12;
Fig. 14 is an isometric view, shown partly in
section, of yet another alternative embodiment of a core
mounting structure wherein the core is mounted within an
envelope reentrant portion;
Fig. 15 is an elevational view, shown partly in
section, of a lamp which incorporates the envelope re-
entrant portion which in turn incorporates the wound coreas shown in Fig. 14;
Fig. 16 is an isometric view, partly broken away
and shown partly in section, of yet another lamp embodi-
ment wherein the envelope is provided with a single pas-
sageway therethrough which receives a segment portion ofthe ferrite core, with the remainder of the core formed
with a looped configuration and retained outside the
sealed envelope;
~4ZZ4
6 47,719I2
Fig. 17 is an elevation view, shown partly in
section, of still another lamp embodiment wherein the
envelope is provided with a single passageway therethrough
which is offset toward one end of the envelope, with the
single passageway enclosing a segment portion of the
ferrite core, and with the remainder of the core formed
with a looped configuration outside the envelope and
positioned within the base portion of the lamp; and
Fig. 18 is a side elevational view, shown partly
o in section, of the lamp embodiment a~ shown in Fig. 17.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the diagrammatic showing of Fig. 1,
the lamp 10 generally comprises a sealed light-transmitt-
ing globular-shaped envelope 12 of predetermined dimen-
sions and enclosing a discharge-sustaining medium such as
a few torrs of argon and a small amount of mercury 14,
similar to conventional fluorescent lamps. Carried on the
internal surface of the envelope is a layer 16 comprising
luminescent phosphor material. Included within the envel-
ope is a core 18 which principally comprises magneticmaterial of high permeability and having a looped config-
uration of predetermined dimensions. As a specific exam-
ple, the core has a toroidal configuration and in accor-
dance with the present invention, it also includes a
narrow gap 20 comprising low-permeability substance such
as mica traversing the cross section of the core. A
winding 22 having a predetermined number of turns is
wrapped about the core and lead-in members 24 connect the
winding 22 to the radio frequency power source 25 which
3 comprises an HF drive and oscillator section 26 together
with an A.C. to D.C. power supply 28 designed to operate
from a standard 115 volt A.C., 60 Hz line. In the opera-
tion of the lamp as shown in Fig. 1, when the lamp is
energized, the radio frequency electromagnetic fields set
up through and about the core and within the envelope
excite the discharge-sustaining medium to emit short
wavelength radiations which in turn excite the phosphor
layer to emit visible radiations which pass through the
4~24
7 47,719I2
envelope.
The ferrite core can be considered, electrical-
ly, as a tr~nsformer with "N" turns of winding 22 on its
primary and one turn on its secondary, namely the dis-
charge, loaded by the equivalent lamp resistance, RL
Fig. 2A shows this equivalent circuit with the lamp volt-
age, VL, also indicated and Fig. 2B shows a further sim-
plification of this equivalent circuit. In operation,
lamp load is reflected in the coil 22 as approximately
N2RL ohms.
In Figs. 4 and 6 are shown two of many possible
circuit configurations suitable for driving an HFE lamp.
The circuits are self-oscillatory and operate in a class
A, B or C mode, with class B or C providing both good
efficiency and power output. The frequency of operation
of these circuits is determined by thq inductance, L, and
the capacitance, C, values of the tank circuits. An
improved circuit is shown in the cros~-referenced ee~e~-
Y~ ~. ~ ~ ~0~ ~5
ing application ~.N. ~3,703, filcd Fcbruary 21, 1-9
wherein the circuit can be made very compact and operates
with excellent efficiency in Class E Mode.
For a given lamp-core-gas configuration and
composition, the operating voltage of the lamp, VL, is
fixed within fairly close limits. Under class B or C
operation, the RMS voltage Vc across the primary winding
for specific lamps as considered hereinafter will be
approximately 0.707 VDc or in this case, 113 VRMs. The
number of turns of the primary winding 22 on the ferrite
core will be N = Vc/VL = 0.707 VDc/VL.
EFFECTS OF CHANGES IN PERMEABILITY OF THE CORE
Temperature variations in the operating lamp and
also manufacturing variations in the fabrication of the
ferrite cores can cause the permeability of the core to
vary. With reference to the equivalent circuit as shown
in Fig. 2B, the resonant frequency, fo, of the circuit is
given by:
t.Z4
8 47,719I2
fo _ 1 _ }Iz (I)
2~ J~-C
where 1. is the inductance of the coil 22 in Henries and C
is the tank capacitance in Farads. L can be determined as
follows:
~N ~' A
LCoil ~ C Henries, (II)
where N is the number of turns, ~' is the effective perm-
eability, AC is the cross sectional ~rea of the core in
square centimeters and lC is the len~th of the magnetic
path in the core in centimeters.
In order to determine the effects of changes in
permeability of the principal material comprising the
core, the permeability of the core formed as a completely
closed loop of ferrite can be defined as ~C If there is
introduced into the core a narrow gap comprising low
permeability, ~A~ substance such as mica, which traverses
the cross section of the core, the effective permeability
of the core changes to ~' where ~C and ~' are related as
follows:
~C
+~ClA (111)
~ALc
Considering a practical case, for a commercial
ferrite core having a torroidal configuration with an
outer diameter of 6.096 centimeters, an inner diameter of
3.556 centimeters and a thickness of 1.27 centimeters, a
representative value of permeability for the ferrite, ~C'
is 5,000, the effective cross sectional diameter area, Ac,
is 1.57 sq cm, and the mean core length, lc, is 14.43 cm.
When a mica gap, for which ~A = 1, having a thickness of
0.015 cm is included in the core, the effective permeabil-
ity of the core is decreased from 5,000 to 806.8 as deter-
mined by substituting the foregoing values into the perme-
ability formula (III).
.2~
9 47 ,719I2
Consider the effects o~ a 20% change or decrease
in actual permeability of the principal material compris-
ing the core, i.e., the ferrite, upon the effective perme-
ability of a gapped core. If the actual permeability of
the ferrite decreases 20%, i.e., from 5,000 to 4,000, by
substituting the modified values into the foregoing effec-
tive permeability formula (III), it is seen that the
effective permeability for the gapped core will be 775.5.
From the foregoing, it can be seen that a 20% change in
the actual permeability of the ferrite material introduces
a change in ~', namely the effective permeability of the
core, of only 3.9%. Thus by including the narrow gap in
the core, changes in the permeability of the ferrite
material due to manufacturing variability, or temperature,
or both, will have very much less effect upon the actual
or effective permeability of the gapped core.
EFFECTS OF STABILIZED PERMEABILITY OF CORE
ON RESONANT FREQUENCY OF TUNED CI~CUIT
As indicated hereinbefore, the core comprises a
part of the tuned circuit output portion of the radio
frequency power source, with the resonant frequency being
determined in accordance with the previously recited form-
ula. For a core having 22 turns wrapped thereabout and an
effective permeability of 806.8, the core inductance can
be calculated as 534 microhenries. A representative value
of a capacitance used with the tuned circuit is 5,000
picofarads, which provide a resonant frequency for the
tuned circuit of 97.4 kilohertz, see formula (I). As a
matter of practicality, for good power transfer to the
discharge with only limited electrical losses in the core,
this is a very desirable operating frequency. Using the
foregoing example wherein the effective permeability of
the gapped core is decreased to 775.5, the effect upon the
resonant frequency will be to increase same by 1.99%. If
the gap were not included in the core, however, a 20%
decrease in the permeability of the core would increase
the resonant frequency of the tuned circuit by over 10%.
From the foregoing, it can be seen that inclusion of the
~442Z4
10 47,719I2
gap in the core stabilizes the resonant frequency of the
tuned circuit of which the core is a part and from a
practical lamp design standpoint, this is highly desir-
able.
It should be understood that the predetermined
frequency at which the lamp is adapted to be operated can
vary considerably within the low freq~ency radio frequency
range and, as a practical matter, oper~ting frequencies in
the order of 70 to 110 kilohertz have been found to be
very acceptable from the standpoint of minimized core
losses and radiation levels.
EFFECT OF GAPPED CORE IN SUPPRESSING
OUTPUT HARMONICS OF RESONANT FREQUENCY
The inductance, Lc, for a core and coil without
a gap is determined by the foregoing formula (II), re-
peated as follows:
477N2llCAC
LC = 9 Henries, (II)
10 lc
wherein the number of turns is 22, ~C = 5~000, AC = 1.57,
and lC = 14.43. ~nder these conditions, LC = 3309 micro-
henries.
If an air gap is included, as before, wherein
the effective permeability of the gapped core is 806.8,
the resulting inductance, LA, of the gapped core and coil
can be calculated as 534 microhenries, using formula (II).
Referring now to the equivalent circuit as shown
in Fig. 2B, the effective Q for the tuned circuit is given
by the following formula:
N2R~
Q = ~ (IV)
For a 40 watt lamp, a representative value of VL is 5
volts and RL is 0.625 ohm. Substituting the values of
LC = 3309 microhenries and LA = 534 microhenries into the
foregoing formula, the Q of the circuit without the air
gap is 0.149 and with the air gap the Q is approximately
0.93.
;24
11 47,71912
With a lower value of Q, the selectivity of thetuned circuit against harmonics is quite poor whereas if Q
approximates a valwe of about 1, the se].ectivlty is much
improved, as shown in the following Table A:
TABLE A
Q f = fo f = 2fo f = 3fo f = 4_
.162 0 dB -.24 dB -.716 dB -1.32 dB
.5 0 dB -1.9 dB -4.4 dB -6.55 dB
1.0 0 dB -5.1 dB -8.~ dB -11.77 dB
2 0 dB -10 dB -4.65 dB -17.6 dB
3 0 dB -13 dB -18.13 dB -21 dB
The efficiency of the output circuit can be de-
fined in terms of the Q of the circuit with the load re-
moved, QU' and the Q with the load applied, QL, as fol-
lows:
n = ~ - QL)x 100% (V)
For a practical case, QU approximates 20, and
the following Table B can be made:
TABLE B
QL n
.162 99.2%
.5 97.5%
1 95
2 90
4 80
As can be seen from the foregoing Table B, for a
value of QL in the order of about 1, there is about a 5%
loss in efficiency, but selectivity is substantially im-
proved over those coils having a substantially lower QL.
Since it is highly desirable to minimize harmonics while
maintaining the efficiency relatively high, it is also
desirable to obtain values of Q for the tuned circuit in
the order of about 1.
PRACTICAL LAMP EMBODIMENTS
Referring to Fig. 3, the lamp 10 comprises a
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12 47,719I2
sealed li~ht-transmitting ~lobular or pear-shapecl envelope
12 of predetermined dimensions. As an example, the enve-
lope 12 has a height of 6 inches and an outer diameter of
4 inches. The envelope 12 is evacuated via the tip 30 at
the top thereof and is provided with a discharge-sustain-
ing filling comprising 1.5 torrs of argon and a small
charge of mercury 14 or a mercury amalgam. A layer com-
prising phosphor material 16 is carried on the interior
surface of the envelope and as a specific example, any of
the standard halophosphates can be used. Alternatively,
for better temperature-dependence characteristics, a three
component blend of rare-earth activated phosphors can be
used and such a phosphor mixture is disclosed in U.S.
Patent No. 3,937,998, dated February 10, 1976 to Verstegen
et al.
A core 18, such as previously described in
detail, is operatively positioned within the envelope 12
and the core principally comprises magnetic material of
high permeability and having a looped configuration of
predetermined dimensions and a cross sectional area, such
as previously described in detail. Preferably the core
has a toroidal configuration for convenience of manufac-
turing, but this configuration can be varied considerably.
As described hereinbefore, the core also includes a narrow
gap 20 which traverses the cross secti~n of the core and a
winding 22 of twenty-two turns is wrapped about the core
18.
The preferred principal material comprising the
core 18 is ferrite, although other magnetic materials can
be substituted therefor. As is well known, and using 2
dictionary definition, ferrite is any of several compounds
formed usually by treating hydrated ferric oxide with an
alkali or by heating ferric oxide with a metallic oxide
and regarded in some cases as spinels such as NaFeO2 or
ZnFe~O4. The ferrite core specifically considered herein-
before is marketed as the 8000 Series by Indiana General,
a Division of Electronic Memories ~ Magnetics Corp.,
Keasbey, NJ and is commercially available in a form which
~g9~ZZ4
13 47,719I2
is not provided wi~h the gap as described hereinbefore.
~uch ferrites are normally prepared with a sintering
lecllni(luc. As sintered in a torroidal Eorm, ttle errite
has a high permeability such as 5,000 and a low electrical
resistivity such as 100 ohm-cm.
Lead-in members 24 connect the winding 22 to the
radio frequency power source 25 comprising the combined
driver 26 and A.C. to D.C. power supply ~8 (shown in block
form in Fig. 1) and positioned within the elongated neck
portion 32 of the lamp 10. As previously described, the
core 18 comprises a part of the tuned circuit output
portion for the radio frequency power source and the
magnetic permeability of the core constitutes a principal
variable factor which can cause this resonant frequency of
the tuned circuit output portion to vary. Other details
of the lamp 10 are of generally conventional construction
and three leads to the coil 18 are sealed through a stem
34 to connect to the power source 25 within the elongated
stem and neck, which in turn connects to a conventional
screw type base 36 which is affixed to the lamp neck by
means of a base adaptor member 38 formed of suitable
plastic such as phenolic resin. Preferably, the phosphor
material is also coated over the core 18 for most effic-
ient utilization of the 254nm radiations generated by the
low-pressure mercury discharge. Alternatively, a reflect-
ing coating can be provided over the core and the phosphor
layer 16 applied thereover.
The operation of the lamp 10 is initiated by
means of an additional winding 40 comprising a relatively
large number of turns carried on the core 18 and the
winding 40 terminates in end portions 42 spaced apart a
predetermined distance within the envelope 12. In the
operation of the device, when the tuned circuit is ini-
tially energized, the additional winding 40 has generated
between the spaced end portions 42 a relatively high
voltage and the capacitive coupling therebetween ionizes
the discharge-sustaining medium within the envelope 12 to
initiate the operation of the device. Once the device is
l~f~4224
14 47,71912
operating, the winding 40 in ef~ect is out o~ the circuit.
As a specific example, the winding 40 comprises eighty-
eight turns and the end portions 42 are spaced apart by
more than one centimeter, and example being two cm.
In Fig. 4 is shown the circuit which is used to
energize the lamp embodiment as shown in Fig. 3 and the
circuit comprises the A.C. to D.C. power supply section 28
comprising a full wave diode rectifier 44 and filter
capacitor 46 and the HF driver and oscillator section 26
comprising the core section 18, tuned circuit capacitor
48, and feedback coil 50 which comprises one or two turns
carried on the core 18. The additional starting winding
40 is shown as connected to one of the leads, although it
need not be. The three terminal connections at the lamp
stem 34 are shown as 52. To complete the circuit, a
transistor 54, capacitor 55 and blocking diode 56 provide
the necessary oscillation. The capacitor 55 and resistor
57 provide proper bias for the transistor 54. In the
circuit shown in Fig. 4, 160 volts D.C. are developed by
the full wave rectifier. With a turns ratio of 22:1, this
provides 5 volts A.C. drop across the operating discharge
and with a load resistance of 0.625 ohm, the lamp operates
with a wattage consumption in the discharge of 40 watts.
~ith this type of lamp and using a cool white halophos-
phate phosphor, representative efficacies of sixty lumens
per watt have been obtained with an additional loss of
seventeen watts in the power source. Substantially higher
efficacies are contemplated by the use of rare-earth
activated phosphors.
An alternative lamp embodiment lOa is disclosed
in Fig. 5 wherein only a portion of the core 18a is con-
tained within the envelope 12a. The twenty-two turns of
the winding 22 are wrapped about that portion of the core
18a which is positioned exteriorly of the sealed envelope
12a. The eighty-eight turns of the starting winding 40,
however, have the end portions 42 thereof positioned
within the envelope to initiate the discharge. In this
embodiment, four leads 24a connect the RF power source 25
47,719I2
to the main winding 22 and Eeedback coil 50. A circuit
for energizing the lamp embodiment of Fig. 5 is shown in
Fig. 6 and the terminal connections between the coils 22
and 50 and the power source are indioated as 58. The
circuit is otherwise the same as shown in Fig. 4. In this
lamp embodiment, the gap means are provided as two indi-
vidual gaps 20a, each having a thickness of 0.0075 cm. and
they are positioned at those portions of the core 18a
which pass through the envelope 12a.
In Fig. 7 is shown yet another lamp embodiment
10b which generally corresponds to the embodiment 10 shown
in Fig. 3 except that a heat conductive metallic member
such as a band of copper 60 is positioned about the fer-
rite core 18 in heat transfer relationship therewith. An
additional heat sink member 62 such as a radiator is
affixed to the exterior of the lamp base member 38b. The
copper strip 60 which encases the exterior of the core is
maintained in heat transferring relationship with the
radiator 62 by means of an additional copper conductor
member 64. As another possible embodiment, a metallic
casing 65 provided for the power source 25 is maintained
in heat transfer relationship with a second radiator
member 66 by means of an additional conductor 68.
In any of the foregoing embodiments, it is
desirable to insulate the winding 22 from the ferrite core
and this is readily accomplished by providing the core
with a layer 70 of a refractory-type inorganic cement such
as that marketed by Sauereisen Cement Co., Pittsburgh, PA,
and sold under the trademark "Sauereisen Cement", which is
a zirconia-based cement. A typical thickness for the
layer 70 is 0.05 to 0.1 mm. Other materials which can be
used to coat the ferrite core to insulate the same from
the winding are a devitrifying glass such as that marketed
by Corning Glass Co. under -the trademark "Pyroceram".
Alternatively, the winding 22 can be provided with a layer
of glass or fiberglass insulation thereabout.
In the preferred embodiment, the gap means has
been described as fabricated of a mica spacer. Other
16 47,719I2
materials can be substituted therefor such as a disc of
alumina, zirconia, magnesia, or strontium oxide, for
e~ample. Alternatively, the gap need not have a filler
and the atmosphere of the lamp can constitute the low-per-
meability substance.
While the gap lowers the effective permeabilityof the core, for lamp embodiments such as described here-
inbefore, it is desirable that the effective permeability
of the core should not be decreased to less than about
200, and this of course is a substantial reduction from
the permeability which is normally obtained with ferrite
per se.
Many different energizing type circuits can be
used to replace the specific examples described herein-
before. It is highly desirable, however, to use an ener-
gizing circuit which incorporates a tuned circuit output
with the core comprising a part of the tuned circuit and
in such cases, the gap which i5 provided in accordance
with the present invention provides the dual benefits of a
stabilized frequency of operation and suppression of
harmonics.
The lamp embodiments as described hereinbefore
can be modified substanti,ally. For example, the power
source need not be mounted in the envelope neck, but can
be separately mounted, such as by a standard screw-type
base member which fits into a standard incandescent sock-
et. The lamp per se can then be plugged into or otherwise
affixed to the power source, so that either the lamp or
the power source can be separately replaced.
The incorporation of the low permeability,
narrow gap or gaps in the cores provides additional advan-
tages with respect to lamp assembly. For example, if the
core is to be physically isolated from the environment
within the sealed envelope, but operatively positioned in
energy transferring relationship with respect to the
environment within the envelope, and the core also is
formed as a closed loop of magnetic material, fabrication
problems may be presented, such as outlined in the refer-
l~g~Z4
17 47,719I2
enced Patent No. 4,005,330. More specifically, referring
to Fig. 4 of this patent, the totally fabricated core has
inserted therein a glass sleeve which is then fused onto
the glass reentrant member, with the mounted core and
reentrant portion thereafter sealed into the lamp enve-
lope.
In accordance with the present invention, when
providing the gap means of low permeability, the cores can
be initially fabricated as separate portions and there-
after assembled by using a cement or adhesive. In addi-
tion, since the core can be isolated from the discharge-
sustaining environment within the lamp envelope, for some
embodiments the core segments can be joined together by
the use of relatively easy-to-handle adhesives, such as
conventional epoxy cement. If such cements were to be
used with a core which was exposed to the operating en-
vironment within the lamp envelope, the ultraviolet radia-
tions generated would normally cause the epoxy cements to
degrade, with the products of decomposition deleteriously
affecting lamp performance.
A variety of embodiments wherein the core is
physically isolated from the environment within the sealed
envelope, but also operatively positioned in energy trans-
ferring relationship with respect to the environment
within the sealed envelope are shown in Figs. 8 through 18
and these embodiments are representative of the lamp
design flexibility which is provided by making the core in
separate sections and thereafter assembling these sec-
tions, preferably with the low permeability gaps included
as a part of the jointures between the core sections.
In the lamp embodiment l~c as shown in Figs. 8
and 9, the envelope 12c has a generally cylindrical con-
figuration and is provided with two vitreous passageways
70 which have a hollow, elongated configuration and extend
through the envelope 12c in the same direction, with the
terminal ends 72 of the passageways being open. After the
envelope is phosphor coated and lehred to drive out the
products of decomposition of the binder material, as is
4 22~
18 47,719I2
conventional, to deposit the phosphor coating 16, the
envelope processing is completed by baking, evacuating,
and dosing with the discharge-sustaining filling through a
tip-off 73. Thereafter, the core is inserted through the
elongated passageways 70 for mounting in energy-transfer-
ring relationship with respect to the environment within
the processed envelope 12c. In such an embodiment, the
core 18c is formed of at least two separate portions, one
of which portions 74 has a ~-shaped configuration with the
other portion 76 conformed to be adhered proximate the
ends of the U-shaped portion 74. The two core portions
are affixed to one another by the simple expedient of a
suitable cement, such as a conventional epoxy cement, and
the spacing of low permeability material, which provides
the gap means 78 can be formed of a thin disk of mica
cemented to join together the separate core portions. In
such an embodiment, the gap 78 can be formed of a single
mica disk or two disks can be used. In other respects,
the winding 22c is generally as described hereinbefore and
starting is provided by the winding 40c which is capaci-
tively coupled through the vitreous wall of the passageway
70. In other respects the lamp lOc is similar to the
previous embodiments including the phosphor coating 16 and
discharge-sustaining filling such as a small amount of
mercury 14. For purposes of illustration, only a portion
of the phosphor coating 16 is shown.
A practical lamp embodiment lOc is shown in Fig.
9 wherein the modified envelope 12c is affixed to a modi-
fied hollow base adaptor 38c, which contains the energiz-
3 ing circuitry 25 and which in turn is connected to theconventional screw-type base 36. Such a construction has
additional advantages since the lamp or device lOc can be
designed for operation in such an orientation that the
passageways 70 are vertically disposed, in order to pro-
vide a chimney effect through the passageways 70 andpermit cooling of the fabricated core 18c during lamp
operation. To facilitate such cooling, the hollow base
adaptor 38c is provided with apertures 80 therethrough and
19 47,719I2
the lamp is also provided with a :light transmitting top
cap 82 which also has apertures 84 provided therethrough
to complete the chimney effect. To protect the epoxy
cement portion of ~he gaps 78 from being exposed to the
ultraviolet radiations which are generated within the
envelope 12c during lamp operation, the passageways can be
formed of glass which transmits substantially no ultra-
violet radiations, such as the conventional soda-lime-
silica glass. Alternatively, conventional ultraviolet
reflecting materials can be coated over the envelope-
interior surfaces of the passageways 70 and such coatings
are well known.
In Figs. 10 and 11 are shown another device
embodiment lOd wherein the modified envelope 12d is pro-
vided with a hollow, elongated curved passageway 86 whichis sealed from the discharge-sustaining medium within the
envelope and which may be formed of vitreous substance
such as soft or hard glass. The ends 88 of the hollow
curved passageway 86 open through the wall of the envelope
12d and after the envelope interior is coated with phos-
phor 16 and lehred, and thereafter completely processed by
baking, evacuating and dosing with the mercury discharge-
sustaining filling 14, the core 18d is assembled therein
by joining together three core pieces 90, 92 and 94 with a
suitable cement such as epoxy, with suitable low perme-
ability spacers included at least at one of the jointures
96. For purposes of illustration, only a portion of the
phosphor coating 16 is shown. The starting winding 40d in
this embodiment is wrapped on the exterior portion of the
curved tubular member 86 so that it is magnetically cou-
pled to the core 18d after it is assembled, in order to
facilitate starting of the device lOd. The device lOd as
assembled in a practical form is shown in Fig. 11 wherein
the envelope 12d is sealed to a hollow base adaptor means
38d which has the energizing circuitry 25 contained there-
in and which connects to a winding 22d and base 36 in the
manner as described hereinbefore.
In device embodiments as shown in Figures 8-11
4'~;~4
20 ~7,719I2
and also Figs. 16-18, the envelopes can be totally fabri-
cated and processed without exposing ~he core portions ot
the devices to the temperature extremes which are required
for envelope processing. In explanation, and referring to
Figures 8-11, the envelopes 12c and 12d are fabricated of
light-transmitting material such as glass and are adapted
to be evacuated and sealed. Enclosed within the envelopes
are hollow conduit-type passageway means (70 in Fig. 8 and
86 in Fig. 10), with the terminal portions of the passage-
way means 72 in Fig. 8 and 88 in Fig 10 sealed to and
opening through different portions of the walls of the
respective envelopes. The respective terminal portions of
the passageways remain open to permit the later insertion
therein of segment portions of the cores of the devices.
In processing the fabricated envelopes 12c and
12d for these device embodiments, there is first applied
to the interior surfaces of the envelopes a phosphor
coating composition. Such phosphor coating compositions
are well known in the art and a typical composition is
described in U.S. Patent No. 3,833,392, dated September 3,
1974 to Repsher et al. Such a composition incorporates a
viscosity-imparting organic binder and after the composi-
tion is applied, it is necessary to lehr the envelopes at
a relatively high temperature in order to decompose and
burn out the organic binder. As an example, temperatures
in the order of 525C and over are required.
After the envelopes are lehred to complete the
phosphor coating processing, the envelopes are allowed to
cool and then baked and evacuated to remove occluded gases
and other impurities, and a typical baking temperature is
450C. Alternatively, the lehring and baking can be
performed as one step. The heated envelopes are then
evacuated and dosed with a discharge-sustaining filling
such as the small charge of mercury 14 and a low pressure
of inert ionizable starting gas such as the 1.5 torrs of
argon. The envelopes are then hermetically sealed by
tipping off the filling tubulation, such as 73 as shown in
Figures 8 and 9.
~4f~2~
~1 47,719I2
Ln the steps as descr:ibe(l here:inbefore, the
en~elopes are essentia1ly completely processed without
e~posing the core portions of l:he (leviccs lo ~he telnpera-
ture extremes required for proper envelope processing.
Thereafter, there is inserted into the hollow passageway
means an elongated segment of the core which principally
comprises the magnetic material of high permeability. In
the embodiment lOc as shown in Figure 8 this is the core
portion 74, and in the embodiment lOd as shown in Figure
10, this is the joined core portion formed by the cemented
segments 92 and 94. There is then cemented to the ends of
the inserted core segment an additional elongated segment
of the core, such as the segment 76 as shown in Figure 8
or the segment 90 as shown in Figure 10. The inserted
core segment and the additional core segment, as cemented
together, have a looped configuration with at least a
portion of the additional core segment projecting exter-
iorly of the fabricated envelope. In this manner, neither
the core nor the segmented jointures thereof are exposed
to any of the high temperatures required for envelope
processing with the additional advantages that temperature
degradable cements, such as some epoxies, can be used. In
the preferred embodiments, at least one of the cemented
jointures between the core segments includes as a part
~5 thereof a thin spacing comprising the lGw-magnetic-permea-
bility material, with the preferred material comprising
mica included in the jointure or jointures between the
elongated core segments.
Still another lamp embodiment lOe is shown in
Figs. 12 and 13 wherein a hollow, elongated, closed-loop
passageway 98, which is formed of suitable material such
as glass, is provided within the envelope and a glass
conduit member 100 is sealed through the envelope 12e and
opens into the passageway 98. In this manner, the inter-
ior of the passageway is isolated from the discharge-
sustaining medium which is enclosed by the envelope 12e.
To fabricate such an embodiment, the separate core sec-
tions 102 and 104 are first inserted into two semicircular
~4'~'~
22 ~7,71912
glass t:ubes l06 ~nd 108, one of which has the conduit 100
affi~ed thereto. I`he sep~lrate core ~nembers are then
cementecl together with the low permeability material gap
means 109 included at the jointure and the separate glass
members are then fused together at their jointure 1]0.
Prior to mounting the core 18e in these glass members, it
is desirable to phosphor coat the exterior of the glass
tubes so that the core 18e is not subject to the lehring
temperatures. Thereafter, the core is inserted into the
semicircular tubes. To facilitate lamp bake-out during
final fabrication, it is desirable to affi~ the separate
core pieces 102 and 104 together with a relativel~ high
temperature cement, such as the previously described
refractory-type zirconia-based cement sold under the
trademark "Sauereisen Cement". As in the previous embodi-
ments, only a portion of the phosphor coating 16 is shown.
A practical embodiment of the lamp lOe is shown
in in Fig. 13 wherein the envelope 12e is sealed at its
neck portion to a hollow base-adaptor means 38e. As in
the previous embodiments, the inner surface of the enve-
lope 12e carries the phosphor coating 16 and is provided
with the discharge-sustaining filling of mercury 14. The
winding 22e, starting winding 40e, power so-urce 25 and
base 36 are generally similar to the previous embodiments.
In Figs. 14 and 15 are shown a modified device
lOf which generally conforms to the construction as shown
in U.S. Patent No. 4,005~330 referred to hereinbefore,
except that the magnetic core is not formed as a closed
loop but is formed as separable core portions 112 and 114
which together form the composite core 18f after being
cemented together at their jointure to form the low-perme-
abili-ty gaps 116. The winding 22f is carried on the core
portion 114. Again, in such an embodiment it is desirable
to cement the separate core portions together with the
hereinbefore referenced refractory-type zirconia-based
cement, in order to insure the core cemented portions are
not damaged d-uring lamp baking. The use of the separate
core portions facilitates lamp fabrication since the glass
Z4
23 47,719I2
conduit 118 which passes through the center o the core
18f may be sealed to the sides of the envelope reentrant
portion 120 before the core sections are fitted thereover
and cemented together. In the lamp as assembled the
reentrant portion 120 has a phosphor coating 16 applied
thereover.
The fabricated lamp lOf is shown in Fig. 15
wherein the reentrant portion 120 with the core 18f mount-
ed therein is sealed into the neck portion of the envelope
12f. As in the previous embodiments, a hollow base adapt-
or 38f is sealed to the neck of the envelope 12f and
contains the power source 25 which connects to the conven-
tional screw-type base 36. The inner surface of envelope
12f is provided with the phosphor coating 16 and a small
charge of mercury 14 is included.
In all of the embodiments as shown in Figs. 8-18
and as described, any out-gassing problems which may be
encountered with the cores during lamp operation are
eliminated. Also, in those embodiments where core expo-
sure to lamp baking temperatures and phosphor lehringtemperatures can be eliminated, the low permeability gap
means which are provided in accordance with the present
invention can be included simply by cementing low perme-
ability disc means in place between separate core portions
by use of a conventional cement, such as epoxy cement,
since the jointures between the separate core portions are
not exposed to ultraviolet radiations which can degrade
organic-type cements or to the temperatures required for
lamp processing. Thus, by fabricating the cores as sepa-
rate pieces, which can then be affixed together as unitarymembers with the low permeability gap or gaps included
therein, the performance of the devices can be substan-
tially improved.
In any of the embodiments as described hereinbe-
fore, the dimensions of the low permeability gap or gapscan be very carefully controlled, and the permeability of
the gap or gaps is very stable. Since these low-perme-
ability gap members are the primary factor in determining
42Z~
2~l 47,719I2
the effective permeability of the composite core, the
devices can be made readily reproducible and their per-
formance under varying conditions of operation is improved
with respect to stability, as compared to an otherwise
similar device which incorporates a closed loop magnetic
core.
While mercury is the prèferred discharge-sus-
taining substance, other discharge-sustaining substances
can be substituted therefor, an example being cadmium plus
the inert, ionizable starting gas.
In Fig. 16 is shown in isometric view still
another lamp embodiment lOg wherein the envelope portion
12g is provided with a generally cylindrical configuration
and with a hollow, elongated, conduit-like passageway
means 122 e~tending axially through the envelope 12g, with
the end portions 124 of the passageway 122 sealed to and
opening through the end walls 125 of the cylindrical
envelope 12g. In such a construction, the environment
within the passageway 122 is sealed from the environment
within the envelope 12g. As in the previous embodiments,
the interior surface of the envelope 12g is coated with a
layer of phosphor material 16 and the environment within
the envelope includes a small charge of mercury 14 and a
small pressure of inert, ionizable, starting gas, in order
to provide a discharge-sustaining environment when the
device lOg is energized. In such a construction, the
envelope portion 12g of the device is fabricated by phos-
phor coating through a suitable tubulation member 126,
lehring, evacuating and dosing with the discharge-sustain-
ing medium, after which the tubulation 126 is tipped off
to provide a sealed and completely fabricated envelope.
In the showing of Fig. 16, only a small portion of the
phosphor layer 16 has been shown for purposes of illustra-
tion.
After the envelope is fabricated, the lamp
assembly is completed by inserting through the passageway
122 a segment portion 128 of:the modified ferrite core
18g. The remaining portion 130 of the core is then af-
l~4~æ4
47,719I2
fixed to the inserted core portion 128, either by suitable
cement such as epoxy resin or by other ret:aining ~leans
such as a mechanical clamp mechanism. ~s in the previous
embodiments, a starting winding 40g is wrapped about the
segment 128 of the core which projects through the pas-
sageway 122 and the power winding 22g for the core con-
nects through suitable lead-in members 24g to a radio
frequency power source 25. A suitable base member 38g
which can be fabricated of plastic is affixed to the
envelope 12g and in turn has a suitable base adapter 36
affixed thereto for energizing the lamp.
In the embodiment as shown, the core 18g is
formed of four separate segments affixed to one another by
a suitable retaining means or cement at the jointures 132.
As in the previous embodiments, for best performance of
the device, it is desirable to include a low permeability
spacer or gap 133 at least at one of the jointures 132
which traverses the cross section of the core, in order to
realize the attendant advantages as described hereinbe-
fore. In the case of some oscillators, however, with aClass D oscillator being an example, the gap means 133
comprising low permeability material can be dispensed with
and the individual core segments affixed directly to one
another. In such an embodiment, the envelope is complete-
ly fabricated without exposing the core to the high envel-
ope processing temperatures and if it is desired to util-
ize a degradable type adhesive to join the core segments
together, this adhesive can readily be protected from the
deleterious effects of the ultraviolet radiations gener-
ated within the operating envelope. The portion of thecore 18g which is exterior to the envelope 12g is prefer-
ably provided with a reflecting coating 13~ to minimize
light absorption.
In Figs. 17 and 18 are shown still another lamp
embodiment lOh wherein the single conduit-type passageway
122h extends through the envelope 12h in such a fashion as
to provide a relatively constricted spacing between the
single passageway 122h and a proximate wall portion 135 of
4ZZ4
26 47,719I2
the envelope 12h. ~he looped core l~h is conformed to
extend through the passageway 122h and to loop about the
exterior of the envelope wall portion 135 which is proxi-
mate the passageway 122h. In this fashion, the core is
physically isolated from the environment within the sealed
envelope, but is operatively positioned in energy trans-
ferring relationship with respect to the discharge-sus-
taining environment within the envelope 12h. As in the
previous embodiment, the core is formed of at least two
separate segments 136 and 138 held together by suitable
retaining means, either a mechanical clamp or some suit-
able adhesive such as epoxy cement at the core jointures
139. As in the previous embodiment, a starting winding
40h is provided within the passageway 122h wrapped about
the core segment 136 and a power winding 22h is wrapped
about the core segment 138 and connects through lead-in
conductors 24h to a radio frequency power source 25. A
suitable base member adapter 38h is affixed to the envel-
ope and has projecting therefrom a suitable screw-type
base adapter 36 to connect the lamp to a power source.
Only a portion of the phosphor layer 16 is shown for
purposes of illustration with the discharge-sustaining
medium comprising a small charge of mercury 14 and the
usual inert, ionizable starting gas. As in the previous
embodiment, the envelope is first totally fabricated and
sealed at the top tip off 140, with the ferrite core
thereafter inserted through the passageway 122h and the
lamp fabrication completed so that the core is not exposed
to the operating environment within the envelope and the
relatively high processing temperatures which are required
to complete the envelope fabrication. Preferably at least
one of the core jointures 139 includes the gap means 142
comprising the low-permeability material, such as a mica
spacer.
