U.S. patent application number 15/370723 was filed with the patent office on 2017-04-13 for led lamp.
The applicant listed for this patent is Feit Electric Company, Inc.. Invention is credited to Raymond G. Janik, Carlo Scianna.
Application Number | 20170102112 15/370723 |
Document ID | / |
Family ID | 40853489 |
Filed Date | 2017-04-13 |
United States Patent
Application |
20170102112 |
Kind Code |
A1 |
Janik; Raymond G. ; et
al. |
April 13, 2017 |
LED LAMP
Abstract
An LED lamp that can take the place of incandescent lamps. An
elevated light source is positioned above a screw-type base. A
first plurality of LEDs is connected in a series on one side of a
flat substrate and a second plurality of LEDs, equal in number to
the first, is connected in series on an opposite side of the
substrate. Each LED of the first and second plurality of LEDs is
mounted proximate a heat sink and a drive circuit is provided for
the LEDs, with the drive circuit being located proximate and
electrically connected to the screw base.
Inventors: |
Janik; Raymond G.; (Wheaton,
IL) ; Scianna; Carlo; (Des Plaines, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Feit Electric Company, Inc. |
Pico Rivera |
CA |
US |
|
|
Family ID: |
40853489 |
Appl. No.: |
15/370723 |
Filed: |
December 6, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15015834 |
Feb 4, 2016 |
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15370723 |
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14638406 |
Mar 4, 2015 |
9267649 |
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15015834 |
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13855391 |
Apr 2, 2013 |
9016901 |
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14638406 |
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12826774 |
Jun 30, 2010 |
8408748 |
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13855391 |
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PCT/US2009/030741 |
Jan 12, 2009 |
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12826774 |
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61020326 |
Jan 10, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F21K 9/238 20160801;
F21Y 2115/10 20160801; F21K 9/232 20160801; H05B 45/10 20200101;
F21V 19/006 20130101; F21V 29/70 20150115; F21K 9/237 20160801;
F21K 9/23 20160801; F21K 9/235 20160801; F21V 19/005 20130101; F21V
3/02 20130101; H05K 1/0207 20130101; F21V 23/005 20130101; F21Y
2101/00 20130101; F21V 29/80 20150115; F21Y 2107/90 20160801; F21V
29/83 20150115 |
International
Class: |
F21K 9/232 20060101
F21K009/232; F21V 23/00 20060101 F21V023/00; F21K 9/235 20060101
F21K009/235; F21K 9/238 20060101 F21K009/238; F21K 9/237 20060101
F21K009/237; F21V 29/83 20060101 F21V029/83; F21V 3/02 20060101
F21V003/02 |
Claims
1. An LED lamp comprising a. a base, b. an elevated light source,
comprising i. a first plurality of LEDs connected in series and
mounted on one side of a generally flat substrate, said substrate
being spaced from said base, and ii. a second plurality of LEDs,
equal in number to said first plurality of LEDs, connected in
series and mounted on an opposite side of said generally flat
substrate, said second plurality of LEDs being located on said
opposite side of said generally flat substrate generally in
alignment with said first plurality of LEDs, c a heat sink in said
substrate, each LED of said first and second plurality of LEDs
being mounted proximate said heat sink, and d a drive circuit for
said LEDs, said drive circuit being located proximate and
electrically connected to said base.
2. The LED lamp according to claim 1, in which said base is a
screw-type base.
3. The LED lamp according to claim 1, in which said drive circuit
is mounted on a circuit board extending from said flat substrate,
said circuit board extending into said base.
4. The LED lamp according to claim 1, in which said heat sink
comprises at least one conductive heat island on each side of said
substrate, each LED of said first plurality of LEDs being proximate
a heat island on said one side, and each LED of said second
plurality of LEDs being proximate a heat island on said opposite
side.
5. The LED lamp according to claim 4, in which said heat sink
includes at least one conductive heat spreader, each heat island
being connected to said heat spreader.
6. The LED lamp according to claim 5, in which said heat spreader
is located in said substrate, said heat spreader extending to said
base.
7. The LED lamp according to claim 5, including first and second
heat spreaders, each heat island on said one side of said substrate
being connected to said first heat spreader and each heat island on
said opposite side being connected to said second heat
spreader.
8. The LED lamp according to claim 7, in which said heat spreaders
are unitary.
9. The LED lamp according to claim 1, including a globe connected
to said base.
10. The LED lamp according to claim 1, in which said first and
second plurality of LEDs are oriented generally in an arc.
11. The LED lamp according to claim 1, in which said drive circuit
comprises a surge suppressor, a rectifier, a smoothing capacitor
and resistor, said first plurality of LEDs and said second
plurality of LEDs being connected in parallel to said resistor.
12. The LED lamp according to claim 1, in which said substrate is
oriented parallel to a line extending from said base.
13. The LED lamp according to claim 1, in which said substrate is
oriented perpendicular to a line extending from said base.
14. The LED lamp according to claim 13, in which said heat sink
comprises a plurality of conductive heat spreader rods extending
from proximate said base to said substrate.
15. The LED lamp according to claim 14, in which said heat sink
includes at least one conductive heat island on each side of said
substrate, each LED of said first plurality of LEDs being proximate
a heat island on said one side, and each LED of said second
plurality of LEDs being proximate a heat island on said opposite
side.
16. An LED lamp comprising: a base, an elevated light source,
comprising: a first set of LEDs connected in series and mounted on
one side of a generally flat substrate, said substrate being spaced
from said base, and a second set of LEDs, equal in number to said
first plurality of LEDs, connected in series and mounted on an
opposite side of said generally flat substrate, said second
plurality of LEDs being located on said opposite side of said
generally flat substrate generally in alignment with said first
plurality of LEDs, and a set of electrically isolated heat sinks
defined in a first portion of said substrate, each LED of said
first and second sets of LEDs being mounted proximate at least one
electrically isolated heat sink of said set of electrically
isolated heat sinks.
17. The LED lamp according to claim 16, wherein said first portion
of said substrate comprises at least one conductive heat island on
each side of said substrate, each LED of said first set of LEDs
being proximate a heat island on said one side, and each LED of
said second set of LEDs being proximate a heat island on said
opposite side.
18. The LED lamp according to claim 16, wherein: said LED lamp
further comprises a drive circuit for said LEDs, said drive circuit
is located proximate and electrically connected to said base, and
each LED of said first and second sets of LEDs is further mounted
proximate a second portion of said substrate so as to provide
electrical connection between said drive circuit and each LED.
19. The LED lamp according to claim 18, in which said drive circuit
comprises a surge suppressor, a rectifier, a smoothing capacitor
and resistor, said first plurality of LEDs and said second
plurality of LEDs being connected in parallel to said resistor.
20. The LED lamp according to claim 16, wherein: said base is
oriented about a central axis extending there-through; and said
substrate extends along and parallel to said central axis.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S.
application Ser. No. 15/015,834, filed Feb. 4, 2016, which
application is a continuation of U.S. patent application Ser. No.
14/638,406, filed Mar. 4, 2015 and now U.S. Pat. No. 9,267,649;
which application is a continuation of U.S. patent application Ser.
No. 13/855,391, filed Apr. 2, 2013 and now U.S. Pat. No. 9,016,901;
which application is a continuation of U.S. patent application Ser.
No. 12/826,774, filed Jun. 30, 2010 and now U.S. Pat. No.
8,408,748; which application is a continuation-in-part of
International Application No. PCT/US2009/030741, filed Jan. 12,
2009; which application claims priority from U.S. Provisional
Application No. 61/020,326, filed Jan. 10, 2008; the contents of
all of which as are hereby incorporated herein by reference in
their entirety.
BACKGROUND
[0002] Technical Field
[0003] This application relates to LED (light-emitting diode)
lamps, and in particular to an LED lamp to replace standard
incandescent lamps.
[0004] Incandescent lamps have existed for over a hundred years.
They are attractive and aesthetically pleasing for their high Color
Rendering Index (CRI) and warm color temperature. However, low
efficiency, short life and energy waste have been major drawbacks
that forced consumers to switch to more efficient sources of light,
such as the fluorescent lamp.
[0005] The incandescent lamp would have become obsolete many
decades ago had it not been for the fact that fluorescent lamps
have low CRI, are physically large, exhibit flicker effect and
include hazardous materials such as mercury.
[0006] Until the late 1980s, LEDs had been primarily used as an
indicator light in electronic equipment. Their high efficiency
compared to incandescent made them very popular. Towards the late
1990s, high intensity LEDs started emerging, including the white
LED. Today, the advancement in LED chip design and manufacturing
makes it more feasible than ever to replace the incandescent
lamp.
[0007] However there remain several challenges that slow the spread
of LED lamps:
[0008] 1. Low Maximum LED Junction Temperature and Heat
Dissipation.
[0009] LEDs generate heat at a rate equal to the product of the
voltage drop V.sub.D and the drive current I.sub.D,
P ( Watts ) = I D ( Amp ) .times. V D ( Volt ) = .DELTA. Q ( JOULES
) .DELTA. t ( Sec ) ##EQU00001##
where P is the power and Q the heat energy produced by the LED. The
LED junction temperature rise is a function of the difference
between heat generated and heat dissipated. Heat dissipation is a
function of the heat sink surface area, the thermal conductivity of
the different media and interfaces and the temperature difference
between the heat sink and ambient temperature. Most LEDs have a
maximum junction temperature of 125.degree. C. and a few
manufacturers advertise up to 180.degree. C. Light output from LEDs
is limited by how fast heat can be dissipated away from the die.
The luminous output of LEDs is reduced as the junction temperature
elevates. FIG. 1 is a plot of the luminous output vs. junction
temperature of a typical LED.
[0010] 2. Luminous Output and Efficacy.
[0011] Luminous Efficacy is the ratio of luminous flux (Lm) to
applied power (Watts). Typical values of low power incandescent
lamp efficacy are:
TABLE-US-00001 Luminous Efficacy LM/W Combustion Candle 0.3 5 W
Incandescent 5 40 W Incandescent 12
[0012] LED efficacy has improved over the last few years and has
exceeded 100 Lm/W. Commonly available power LEDs can measure up to
85 Lm/W. However, it should be noted that these measurements are
taken at 25.degree. C. junction temperature and reduced drive
current.
[0013] As noted earlier, the luminous output decreases when the die
temperature increases. Increasing the drive current has an even
greater effect on reducing efficacy. As the current increases, the
light output increases in a non-linear fashion, as shown in FIG. 2,
but as FIG. 3 shows, the voltage increases as well.
[0014] In other words, if the current I is increased by a factor
(1+K, where 0<K<1), not only will the luminous output be
increased by a factor (k+1, where 0<k<K), but the LED voltage
V will also increase by a factor (1+v). The new LED power
consumption will become:
P=(I+K).times.(V+v)=(I+K).times.V+(I+K).times.v
where the first term represents the increase in power due to
increase in current only, and the second term represents the
increase in power due to increase in current and voltage.
[0015] Thus, increasing the LED current will increase the LED
output at the expense of reducing its efficacy. The percentage
increase in lumens is lower than that of the increase in current,
which will reduce efficacy at a much higher rate.
[0016] 3. An LED is a Unidirectional Light Source.
[0017] LEDs emit light in a cone that is less than a half space,
making it difficult to be used in a traditional "A" type lamp, as
FIG. 4 shows. When mounted on a heat sink and placed in a bulb-like
shell, some of the light will be absorbed by the package and lens
material which will reduce the system efficacy, For a successful
implementation of the LED in an `A` type lamp, the LED needs to be
elevated to the center of the bulb, but this reduces the thermal
dissipation capabilities.
[0018] 4. Need for Power Conversion.
[0019] LEDs are current driven devices that require a constant
current source power supply (FIG. 5). As FIG. 3 indicates, the
voltage reflected by an LED is an exponential function of the drive
current. An LED cannot be driven by a voltage source, since the
source voltage must match the LED voltage. Otherwise, the
difference in voltage divided by the total circuit resistance will
result in a current that would easily exceed the maximum LED rating
and cause the device to fail.
[0020] A constant current source power supply adds cost and reduces
the reliability and efficiency of the LED lamp system. A fly-back
power supply under 5 watts has a typical efficiency of less than
80% which will reduce the luminous efficacy of the whole lamp
system.
[0021] Power supplies occupy valuable real estate in a lamp system,
and special measures need to be taken in order to isolate a power
supply from the heat generated by the LED.
[0022] 5. Dimmability.
[0023] A dimmer controls the light output by phase controlling the
AC input voltage. However, a constant current power supply will
compensate for any change in input voltage in order to keep the
output current constant. There are specialty power supplies that
permit dimmability. These power supplies are designed to produce an
output current that is proportional to the RMS input voltage. Such
power supplies are generally more complex and exhibit lower
efficiency.
[0024] FIG. 5 is a block diagram of an off-line switch mode power
supply. A switch mode power supply is required to convert the 120
Vac line voltage to a low DC current (10 mA-350 mA). Power supplies
of 5 Watts output power or less are almost always fly-back type,
and have a typical efficiency of less than 80%. They are also prone
to failure if they encounter a surge, where a spike of high voltage
could damage the MOSFET switch, especially if a surge suppressor,
such as an MOV (metal oxide varistor), is not incorporated.
[0025] Another common method of driving low voltage LEDs is by
using an impedance in series with AC line to limit the current and
drop the excess voltage across it. This impedance may be a
resistor, a capacitor or an inductor. A resistor is the cheapest
and most available, but the energy E=I.sup.2R.DELTA.t it dissipates
is lost and cannot be recovered. The losses increase with the
increase in the difference in voltage between the source voltage
and the LED voltage, as demonstrated in FIG. 6.
[0026] Assume V.sub.s=166V, V=36V, and I=20 mA. Then,
R = V s - V I = 166 - 36 0.02 = 6.5 k .OMEGA. ##EQU00002##
[0027] The power dissipation across the resistor is
P.sub.R=I.sup.2.times.R=2.6 W
[0028] The efficiency of the system becomes:
P OUT P IN = I .times. V ( I .times. V ) + P R = 0.02 .times. 36 (
0.02 .times. 36 ) + 2.6 = 0.72 3.32 = 22 % ##EQU00003##
[0029] Obviously this system is not feasible.
[0030] Another solution is to replace R by an impedance that does
not dissipate energy, such as an inductor or a capacitor. A
capacitor is more available in size and value than an inductor. The
only limiting factor is the maximum allowable voltage drop across
the capacitor. However, this solution renders the LED non-dimmable
and increases the size of the circuit board due to the large size
of the AC capacitor which needs to be rated to the line voltage
plus a margin.
[0031] The resistor impedance solution would be feasible if the
power dissipation is reduced, which is accomplished if the voltage
difference (Vs-V) is reduced. This is done by increasing the number
of LEDs in series until the total LED voltage drop approaches the
source voltage Vs which will reduce the voltage difference (Vs-V)
as well as the value of R required to limit the current.
[0032] For example, assume several LEDs are connected in series to
produce a total load voltage V=136V. The new value for R is:
R = V s - V I = 166 - 36 0.02 = 1.5 k .OMEGA. ##EQU00004##
[0033] The new power dissipation is
P.sub.R=I.sup.2.sub.LOADR=0.6 W
[0034] The new system efficiency becomes
P OUT P IN = I .times. V ( I .times. V ) + P R = 0.02 .times. 136 (
0.02 .times. 116 ) + 0.6 = 2.72 3.32 = 82 % ##EQU00005##
[0035] Clearly, this is well within the acceptable range for power
supply efficiency, which is accomplished by shifting more of the
wasted power to useful power.
BRIEF SUMMARY
[0036] The invention is directed to an LED lamp comprising a base
and an elevated light source. The light source is composed of a
first plurality of LEDs connected in series and mounted on one side
of a generally flat substrate, the substrate being spaced from the
base, and a second plurality of LEDs, connected in series and
mounted on an opposite side of the substrate, with the second
plurality of LEDs being located generally in registration with the
first plurality of LEDs. A heat sink is in the substrate, with each
LED of the first and second plurality of LEDs being mounted
proximate the heat sink. A drive circuit is provided for the LEDs,
the drive circuit being located proximate and electrically
connected to the base.
[0037] In accordance with the preferred form of the invention, the
base is a screw-type base. The drive circuit is mounted on a
circuit board extending from the flat substrate, the circuit board
extending into the base.
[0038] In one form of the invention, the heat sink comprises at
least one conductive heat island on each side of the substrate,
each LED of the first plurality of LEDs being proximate a heat
island on the one side of the substrate, and each LED of the second
plurality of LEDs being proximate a heat island on the opposite
side of the substrate. The heat sink also includes at least one
conductive heat spreader, each heat island being connected to the
heat spreader. The heat spreader is located in the substrate, and
extends to the base. Preferably, there are first and second heat
spreaders, with each heat island on one side of the substrate being
connected to the first heat spreader and each heat island on the
opposite side being connected to the second heat spreader. Each
heat spreader is preferably a unitary structure, although the heat
spreaders can be a series of conductive elements connected to one
another.
[0039] Preferably, the invention is in the shape of a conventional
light bulb. It therefore includes a globe which is connected to the
base. The first and second plurality of LEDs are oriented generally
in an arc inside the globe.
[0040] The drive circuit comprises a surge suppressor, a rectifier,
a smoothing capacitor and a resistor, with the first plurality of
LEDs and the second plurality of LEDs being connected in parallel
and their parallel connection being to the resistor.
[0041] In one form of the invention, the substrate is oriented
parallel to a line extending from the base. In a second form of the
invention, the substrate is oriented perpendicular to the line
extending from the base. In this form of the invention, the heat
sink comprises a plurality of conductive heat spreader rods
extending from proximate the base to the substrate.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0042] The invention is described in greater detail in the
following description of examples embodying the best mode of the
invention, taken in conjunction with the drawing figures, in
which:
[0043] FIG. 1 is a plot of the luminous output versus junction
temperature of a typical LED,
[0044] FIG. 2 is a plot of the light output versus current drive of
a LED, FIG. 3 is a plot of LED voltage versus LED current,
[0045] FIG. 4 is a plot of the cone of light emission of an
LED,
[0046] FIG. 5 is an off-line switch mode power supply for an
LED,
[0047] FIG. 6 demonstrates how losses increase with the increase in
the difference between voltage between a source voltage and the LED
voltage,
[0048] FIG. 7 is an elevational illustration of a circuit board
according to the invention,
[0049] FIG. 8 illustrates a simple circuit for connecting LEDs in
series,
[0050] FIG. 9 is a typical circuit used in connection with the
present invention,
[0051] FIG. 10 represents the waveforms for the input alternating
current voltage, the rectified voltage and the LED current of the
circuit of FIG. 9,
[0052] FIG. 11A is an elevational view, similar to FIG. 7, of one
form of the invention,
[0053] FIG. 11B is a side elevational illustration of FIG. 11A,
[0054] FIG. 11C is the substrate of FIGS. 11A and 11B showing the
heat spreader,
[0055] FIG. 12A is an elevational illustration of another form of
the invention, FIG. 12B is an elevational view of another form of
the invention,
[0056] FIG. 12C is an elevational view of yet another form of the
invention,
[0057] FIG. 13A is a perspective schematic illustration of another
form of the invention with the LEDs oriented perpendicular to the
earlier embodiments of the invention,
[0058] FIG. 13B is a perspective view of the form of the invention
shown in FIG. 13A, as a completed lamp,
[0059] FIG. 14 is an exploded view of the lamp shown in FIG.
13B,
[0060] FIG. 14A is a plan view of another form of the invention for
fluorescent lamp replacement,
[0061] FIG. 14B is a side elevational view thereof,
[0062] FIG. 140 is an enlarged partial top plan view of area A of
FIG. 14A,
[0063] FIG. 14D is a second version of the embodiment of FIG.
14A,
[0064] FIG. 14E is a side elevational view thereof,
[0065] FIG. 14F is an enlarged partial top plan view of area A of
FIG. 14D, and
[0066] FIG. 15 illustrates a slightly modified version of the
invention shown in FIG. 11, with FIG. 15A showing the base, FIG.
15B showing the circuitry and light source, and FIG. 15C showing
the globe.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS
[0067] The invention produces an LED based lamp that overcomes the
above-described limitations of the prior art, namely: [0068] Simple
robust power converter [0069] High system luminous efficacy [0070]
Dimmable [0071] Efficient 360.degree. light output [0072] Efficient
thermal management system [0073] Direct replacement for any low
power incandescent lamp [0074] Designed for manufacturability
[0075] The invention utilizes multiple low cost surface mount LEDs
connected in series on a surface board thereby increasing the load
voltage drop as well as the useful light output and the system
efficiency (FIGS. 7 and 8). This may also be accomplished by
assembling LED dies directly on the printed circuit board (Chip On
Board) in the same series combination.
[0076] An LED emitter can be packaged by combining LED dies in
series to produce a high combined LED voltage at the rated current.
Such an LED series will draw the same current as a single LED, but
will reflect a voltage that is very close to the rectified source
voltage. This is different from the Seoul Semiconductor "Acriche"
LED where the dies are connected in antiparallel, thereby
eliminating the need for a rectifier and transforming the LED into
a high voltage AC LED. Combining LEDs in series results in a high
voltage DC LED, which will require a rectifier when operated from
an AC source. The advantage is the ability to add a smoothing
capacitor to reduce current ripple and attain a steady light source
with no flicker. The Acriche LED does not allow for a smoothing
capacitor to be installed since the rectification process is
internal to the package.
[0077] The assembly of surface-mount devices (SMD) is an automated
and low cost process. It is therefore critical that all components
are SMD type. This is another reason a high voltage AC capacitor is
not feasible since they are hard to find in SMD.
[0078] FIG. 9 is a schematic of a typical circuit according to the
invention, designated generally at 10. The invention is described
in relation to an alternating current source 12 although obviously
if direct current is available, then a rectifier is unnecessary.
The alternating current source 12 is supplied through a fuse to a
rectifier 16. The rectifier 16 rectifies the alternating current to
produce a voltage source, illustrated schematically at 18. A series
resistor 20, described above, is followed by two parallel
combinations of LEDs 22 in series and LEDs 24 in series. To
increase the reliability of the circuit 10, a surface mounted MOV
(metal oxide varistor) surge suppressor 26 is also included. A
smoothing capacitor 28 reduces current ripple and eliminates
flicker.
[0079] The efficiency may be further improved by adding more LEDs
in series, thus increasing the total voltage drop.
[0080] In general, let .DELTA.V=Vs-V which is the voltage across
the resistor 20. For a given load current I,
R = .DELTA. V I and P R = I .times. .DELTA. V . ##EQU00006##
[0081] An adverse effect of a low .DELTA.V is poor regulation.
Since the LED voltage drop is not sensitive to current (FIG. 3), a
change in the input voltage will be applied to .DELTA.V only, which
will cause the current to change in a proportional manner.
[0082] If .delta.V is the change in the source voltage Vs, the same
change will be applied to R, which is now constant. The new current
will become:
I = .DELTA. V + .delta. V R ##EQU00007##
where .delta.V may be positive or negative. Let .delta.I represent
the change in load current. Then
Reg . = .delta. I I = .delta. V R .DELTA. V R = .delta. V .DELTA. V
##EQU00008##
[0083] Regulation will be defined as the percentage change in
output:
[0084] Regulation is to be made as small as possible in order to
minimize the change in output as the input changes. But a low value
for regulation means a large value for .DELTA.V, which increases
the losses and reduces the efficiency, as described earlier.
P R = I .times. .DELTA. V = ( .DELTA. V ) 2 R , and efficiency
##EQU00009## P OUT P IN = I .times. V ( I .times. V ) + P R .
##EQU00009.2##
[0085] One aim of the invention is to specify the largest
acceptable regulation for a given change .delta.V in source voltage
Vs. This will define the smallest .DELTA.V, which will be used to
determine R and the efficiency of the system.
[0086] FIG. 10 represents the waveforms of the input AC voltage,
the rectified voltage, and the LED current.
[0087] LEDs are most efficient when driven at a relatively low
current where the losses are the lowest. However, this also means
that the total lumen is low. For example, if an LED has an
efficiency of 100 Lm/W at 0.03 W, then its output will be 3 lumens.
An efficient LED does not necessarily mean a bright LED. On the
contrary, the most efficient LED may be so dim that it will be
rendered unusable as a light source for illumination.
[0088] Some prior LEDs have been made up of multiple smaller LEDs,
mounted on an insulated aluminum substrate, but they are arranged
in series and parallel combination which keeps the total LED
voltage low, and its current high. Because the LEDs are packed
close to one another, it may be inefficient for all the light to
exit, part of which could be absorbed by adjacent LEDs. Driving
LEDs at a high current will further reduce efficacy.
[0089] In the present invention, the low cost efficient LEDs 22 and
24 are arranged in series, on both layers of a printed circuit
board or substrate so as to maximize the total lumen output and
reduce absorption. The LEDs are driven at a low current to keep the
efficacy high. The low lumen output is compensated by increasing
the number of LEDs. Since LED size is miniature and the PCB
placement cost of surface mount components is low, the only penalty
is LED cost.
[0090] Consider two luminous intensities, a 15 Watt/75 Lm, and a 25
Watt/200 Lm incandescent equivalent LED lamp.
[0091] For the 75 Lm system, 36 LEDs are arranged in series, 18 on
either side of the circuit board in identical locations. The system
is shown in FIG. 7 and is driven according to the schematic in FIG.
9, at an LED current of 10 mA. The lumen output per LED at that
current is 2 lumens, yielding a total of 75 lumens at a total input
power of 1.2 W, and a total system luminous efficacy of 60
Lm/W.
[0092] The high output version has two parallel circuits of 36 LEDs
each on either sides of the PCB, as shown in FIGS. 11A-11C. The LED
current for each series circuit is increased to 30 mA.
[0093] Due to the method in which the LEDs are arranged and mounted
inside the lamp, more lumens leave the lamp due to less absorption
and obstruction.
[0094] Even though the large number of LEDs in each circuit will
ensure equal current sharing, series resistors 30 are added for
each circuit 10 to help dissipate the increase in losses due to the
higher output, as well as improve current sharing, The surface
mount MOV surge suppressor 26 and fuse 14 can also be added to
increase reliability.
[0095] Even though the previous discussion was limited to two power
levels, the same principle can be applied to achieve a higher power
of 40 Watts equivalent or higher. The total system efficacy can be
increased by utilizing more LEDs and reducing the drive
current.
[0096] The brightness of an LED is limited by the maximum junction
temperature. In most cases, the junction temperature is 125.degree.
C. Assuming a temperature difference of 10.degree. C. between
junction and case, a rule of thumb is to maintain a case
temperature of no more than 95.degree. C. with a 15.degree. C.
margin. The more heat dissipated from the LED junction, the higher
the attainable light output.
[0097] For prior art power LED lamps of 6 Watts or higher, an
external heat sink is usually implemented, which places the LED
directly on the heat sink, reducing its affectivity and increasing
cost.
[0098] The present invention offers an alternate method of LED heat
dissipation. Rather than dissipating heat from one power LED
through an external heat sink, multiple low power LEDs 24 and 26
dissipate their heat through heat spreader copper islands 32 and 34
on top and bottom layers of a multi-layered PCB board or substrate
36. The islands 32 and 34 transfer the heat to two inner layers of
copper heat spreaders 38 and 40. Each is located very close to the
heat islands 32 and 34 on the outer layers. The inner spreaders 38
and 40 conduct heat internally to a screw base 42 of the lamp,
which in turn will dissipate it away through the fixture and
electrical wiring (not illustrated). Since the screw base 42 is
connected to AC line, it needs to be fully isolated from the rest
of the circuit 10. The core thickness of the substrate 36 between
the outer islands 32 and 34 and the inner heat spreaders 38 and 40
should have the minimum thickness that the safety standards will
allow to reduce thermal resistance to a minimum and maximize heat
transfer.
[0099] Since in this invention heat is dissipated through
conduction to the screw base, the lamp can be placed inside a
sealed globe 44 (FIG. 12A, etc.) with no air circulation. It will
also allow for more light to radiate, since the LEDs are elevated
and more visible.
[0100] At the bottom of the LED substrate 36, the heat spreaders 38
and 40 are thermally bonded together by printed circuit board vias,
which are means to provide electrical connection between traces on
different layers of a circuit board, in order to maximize power
dissipation to the screw base by thermally conducting heat from one
layer to another.
[0101] The LEDs 22 and 24 are positioned on the substrate 36 in an
arrangement of an arc that resembles the filament of an
incandescent light bulb, with the intention of maintaining its
classic look. The power conversion part of the system is installed
on a circuit board portion of the substrate 36 in order to minimize
cost and simplify assembly. All the components are surface-mount
devices which allows for automation.
[0102] The LEDs 22 and 24 are placed in registration on either side
of the substrate 36 in preferably exactly the same relative
location which gives the impression of transparency. Since no
external heat sink is used, the lamp globe 24 can be made entirely
of transparent material with the LEDs 22 and 24 elevated to maximum
lumen efficacy. To better resemble the incandescent lamp, the LED
Correlated Color Temperature (CCT) should be 2800.degree. K, which
is close to that of an incandescent lamp, and the Color Rendering
Index (CRI) should be typically 95. The effect will be to create an
identical application, effect and look of an incandescent light
bulb.
[0103] The LEDs are precisely placed on either side of the
substrate 36 to make the substrate look invisible. The effect is
for the observer to see only the trace of light. The shapes and
arrangement of the LEDs may vary depending on the effect
required.
[0104] FIG. 12A depicts an A19 and FIGS. 12B and 12C depict B10
type lamps. This invention allows the use of this arrangement of
LEDs in any low power incandescent application, including
decorative lamps. The pattern in which the LEDs are arranged is not
limited to those shown in FIG. 12, and may extend to any
arrangement to produce any desired effect.
[0105] FIGS. 13A, 13B and 14 are other embodiments of the invention
where the heat collectors are solid rods 46 bonded to the heat
islands. In this case, the lamp will retain more resemblance to the
classical incandescent lamp. The elements are the same as the first
form of the invention, but since the substrate is horizontal, all
elements have the identifier "a". The power supply circuit 10 is
located in the screw base 42 of the lamp.
[0106] The LEDs 22 and 24 may be incorporated in a plastic polymer
shaped as a filament. The LEDs 22 and 24 may be arranged to
illuminate the polymer which will efficiently conduct light and
give the impression of continuous filament glow.
[0107] Another embodiment is to mount LED dies directly on the
substrate 36 in the same pattern (Chip on Board), and apply
phosphor on all the dies at once. This will make the group of LED
dies glow as one. It can also reduce the LED cost since they are
not packaged individually.
[0108] The choice of resistive impedance R makes it possible to use
with conventional Triac dimmers in a manner similar to incandescent
lamps. The only limitation is the LED current which must be higher
than the Triac Holding current, which is usually the case since the
low intensity B10 type lamps are usually arranged in groups of 5 or
more in chandeliers.
[0109] The LEDs 22 can also be arranged in a linear fashion to
replace a fluorescent lamp, as shown in FIGS. 14A through 14F. In
this form of the invention, the LEDs 22 are on one side of a PCB
board or substrate 36b, while the circuit 10 is located on the
opposite side of the board 36b.
[0110] Just as in the earlier forms of the invention in relation to
replacement of an incandescent lamp, the lamp of FIGS. 14A-14F can
be completely enclosed in a tube or fixture (not illustrated), due
to the low amount of generated heat that needs to be dissipated.
The LED correlated color temperature (COT) can be anywhere between
3,000.degree. K to 5,000.degree. K for replicating and replacing
bulbs in current fluorescent light systems.
[0111] The invention consists of 3 main parts (FIG. 15), screw base
42, LED circuit 10, and lamp globe 44. The LED-bearing substrate 36
is installed in the screw base 42 by first soldering the middle
terminal, then by bonding the plated sides to the barrel of the
screw base 42. This will ensure electrical contact as well as
provide a thermal passage to conduct the heat generated by LEDs 22
and 24 to the screw base 42 and the electrical wiring (not
illustrated) which will act as an extended heat sink.
[0112] Various changes can be made to the invention without
departing from the spirit thereof or scope of the following
claims.
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