U.S. patent application number 12/268439 was filed with the patent office on 2009-03-12 for pcb contact arrangement.
Invention is credited to JAMES K. NG.
Application Number | 20090066208 12/268439 |
Document ID | / |
Family ID | 34619893 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090066208 |
Kind Code |
A1 |
NG; JAMES K. |
March 12, 2009 |
PCB CONTACT ARRANGEMENT
Abstract
A printed circuit board (PCB) for mounting electrical components
such as LEDs has either contact traces leading to an edge of the
PCB, or outward edge protrusions on which an electrically
conductive material is deposited, such that the board itself can be
used to make electrical contact in a pre-existing, commercially
available fitting, such as a wedge or screw-in or bayonet-base
fitting designed to receive incandescent light bulbs.
Inventors: |
NG; JAMES K.; (Seattle,
WA) |
Correspondence
Address: |
Jeffrey Pearce
34825 Sultan-Startup Rd.
Sultan
WA
98294
US
|
Family ID: |
34619893 |
Appl. No.: |
12/268439 |
Filed: |
November 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11418919 |
May 5, 2006 |
7450394 |
|
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12268439 |
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10714761 |
Nov 17, 2003 |
7053560 |
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11418919 |
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Current U.S.
Class: |
313/1 |
Current CPC
Class: |
F21Y 2107/90 20160801;
F21Y 2115/10 20160801; Y10S 362/80 20130101; F21K 9/23 20160801;
H05B 45/42 20200101; H05B 45/40 20200101; H01L 2224/48257 20130101;
H05B 45/10 20200101; H01L 2224/48247 20130101; H05B 45/00 20200101;
H05B 45/3574 20200101; F21Y 2113/13 20160801; Y02B 20/30
20130101 |
Class at
Publication: |
313/1 |
International
Class: |
H01J 61/92 20060101
H01J061/92 |
Claims
1. A lighting arrangement comprising: a source of electrical power;
a printed circuit board (PCB) base having front and rear surfaces;
a plurality of light-emitting diodes (LEDs) driven by the power
source and mounted on the PCB base; at least two electrically
conductive traces on a planar surface of the PCB base leading
electrical current between the source of electrical power and the
LEDs; electrical trace contacts formed on the PCB base in
electrical contact with respective ones of the traces and extending
to a contact edge of the PCB base such that when the PCB base is
inserted into a standard, pre-existing, commercially available
wedge-based light fitting designed to receive an incandescent light
bulb, each electrical trace contact is pressed into electrical
contact with a mating contact element in the wedge-based light
fitting, the LEDs thereby replacing the incandescent light
bulb.
2. A contact surface arrangement for a printed circuit board (PCB)
for mounting at least one electrical component comprising: a base
cut from a PCB substrate; at least one lateral base protrusion
mating with at least a first internal, at least partially
electrically conductive, surface of a pre-existing, commercially
available fitting; an electrically conductive material deposited on
an outer edge of the lateral base protrusion; at least one
electrically conductive trace on a planar surface of the base, the
trace being in electrical contact with the electrically conductive
material deposited on the lateral base protrusion so as to create a
first electrical path to at least one of the electrical components;
and at least one slot in the base extending in an axial direction
of the fitting, each slot comprising a physical opening in the PCB
board itself; in which the base is wider than an internal diameter
of the fitting, but by no more than a total width of the slot(s),
such that the base, upon installation in the fitting, biases the
lateral base protrusions outward and into contact with the first
internal surface of the fitting.
3. An arrangement as in claim 2, in which the electrical component
is a light-emitting diode and the fitting is a standard fitting
designed to receive an incandescent light bulb by insertion of the
bulb in an axial direction.
4. An arrangement as in claim 2, in which: the fitting is a
standard bayonet fitting and the internal surface has indexed
indentations; and the lateral base protrusions have the same
indexing as the indentations.
5. An arrangement as in claim 2, in which: the standard fitting is
a screw-in fitting and the internal surface has threading with a
pitch; and on either side of the base portion, the lateral base
protrusions have the same pitch as the pitch of the threading.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/418,919, "PCB Contact Arrangement," filed 5
May 2006 (which will issue on 11 Nov. 2008 as U.S. Pat. No.
7,450,394), which in turn is a divisional of U.S. patent
application Ser. No. 10/714,761, "Bi-Directional LED-Based Light,"
filed 17 Nov. 2003 (which issued on 30 May 2006 as U.S. Pat. No.
7,053,560). This application claims priority of and incorporates by
reference both of these previous U.S. Patent Applications.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to lights that use multiple
light-emitting diodes, as well as to fixtures for mounting such
lights.
[0004] 2. Description of the Related Art
[0005] Incandescent light bulbs are commonly used for indicator
lamps, task lamps, general lighting, decorative lamps, warning
lamps, traffic lamps and the like. However, incandescent bulbs, and
to a lesser extent even plasma-based fluorescent and halogen
lights, are generally inefficient in terms of energy use and are
subject to frequent replacement due to their limited lifetime.
Significant savings can be made by the use light bulbs where the
source of light is light-emitting diodes (LED).
[0006] LEDs are much more efficient (in terms of lumens per watt)
than incandescent and fluorescent lights; moreover, LEDs generally
last much longer. This is particularly true of the class of LEDs
known as "super-luminescent" or "super-bright," which have already
found uses in such applications as automobile tail lights and
traffic signal lights.
[0007] Being diodes, one problem with LEDs is that they are
direct-current (DC) devices that are easily damaged by too high
reverse voltage, whereas the power supplies for many devices that
would benefit from the advantages of LEDs deliver alternating
current (AC). Even low-voltage light fixtures typically use a 12V
AC power source, which is transformed from, for example, 120V AC at
60 Hz.
[0008] One common way to provide direct current to LEDs from an AC
source is to include in the power-supply circuit a full-wave
rectifier and a current-limiting device such as a power resistor.
One drawback of this approach is that four rectifying diodes are
typically needed and each of these rectifying diodes must carry
half the full current load of all the LEDs.
[0009] Another known way to provide DC current to LEDs is to
include in the power-supply circuit a half-wave rectifier and,
again, a current-limiting device such as a power resistor. This is
a much simpler circuit than is needed for full-wave rectification,
but even it has at least three major drawbacks: First, the light
emitted from the LEDs will flicker, for example, at 120 Hz in case
the AC power source frequency is 60 Hz. Second, when the supplied
voltage is negative, this circuit assumes that the LEDs will evenly
divide the reverse voltage among themselves. Failure to do so can
lead to a cascade failure of the LEDs; this failure is most
prominent in transient conditions. Third, the rectifying diode must
carry the full current load of the LEDs.
[0010] Even assuming that the power supply problems of the LEDs are
overcome, there must still be some convenient way to mount and
install the lights themselves. There are of course many different
types of light fixtures for the many different common types of
incandescent light bulbs. These fixtures feature an array of
different types of physical connections with wedge, screw-in,
bayonet, flange, bi-pin and other bases. This means that any
after-market LED-based light bulb replacement must be able to
correctly connect to the different types of existing sockets of the
bulbs it is intended to replace. It would be possible to mount LED
units within the casings--usually bulbs--of the original lights,
but this complicates the manufacture of such LED replacements.
[0011] Yet another concern is that incandescent elements can
typically be mounted without regard to polarity, whereas existing
LED arrangements cannot. When installing an LED replacement in a DC
system such as an automobile tail light, there is therefore a risk
of incorrect installation because even with a given fitting, the
polarity of the wiring is not always the same from one car
manufacturer to another.
[0012] What is needed is an LED lighting arrangement that
eliminates or at least reduces the problems mentioned above. In
particular, some fitting is needed to enable easy after-market LED
replacement.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a circuit drawing of the simplest embodiment of an
"AC LED" according to the invention.
[0014] FIG. 2 is a circuit drawing of a generalized embodiment of
the invention, including an LED array.
[0015] FIG. 3 is a plan view of a printed circuit board (PCB) from
which several PCB bases are manufactured for an embodiment of the
invention suitable for use as an after-market replacement for light
with a typical screw-in fitting.
[0016] FIG. 4 is plan view of a single PCB base separated from the
PCB shown in FIG. 3.
[0017] FIG. 5 illustrates an example of a trace pattern used in the
embodiment of the invention that provides an AC LED for screw-in
fittings.
[0018] FIG. 6 shows an example of component layout on the PCB base
illustrated in FIGS. 4 and 5, as well as how this PCB base can be
screwed into a typical socket.
[0019] FIG. 7 is a side view of the arrangement shown in FIG.
6.
[0020] FIG. 8 illustrates a preferred way to spring-bias the PCB
base of FIGS. 4-7 so as to improve electrical contact between the
base and the screw-in socket.
[0021] FIG. 9 illustrates an embodiment of the invention suitable
for after-market installation in a wedge-type fitting.
[0022] FIG. 10 illustrates an embodiment of the invention in which
two AC LEDs according to the invention are provided on a single PCB
substrate.
[0023] FIG. 11 illustrates one example of how several LEDs of
different colors may be mounted on a PCB base and electrically
connected as in FIG. 2 so as to approximate a full-spectrum light
source.
[0024] FIG. 12 is a side view of the arrangement shown in FIG.
11.
[0025] FIGS. 13 and 14 are side and top views, respectively, of a
dual-element AC LED according to the invention in a single
capsule.
[0026] FIG. 15 illustrates an alternative layout of connectors and
LED elements for the dual-element AC LED.
DETAILED DESCRIPTION
[0027] FIG. 1 is a circuit diagram that illustrates the fundamental
embodiment of the invention: A pair of LEDs D.sup.+ and D.sup.- are
connected in parallel, with reverse polarity (with the anode of
D.sup.+ connected to the cathode D.sup.- and the anode of D.sup.-
connected to the cathode of D.sup.+) in series with a
current-limiting device, R, typically a resistor, and driven via
contacts k1, k2 by a power (or, equivalently, voltage or current)
source S that delivers either alternating or direct current.
[0028] In applications that require illumination (such as reading
lights) as opposed to simple indication (such as on/off), the LEDs
D.sup.+ and D.sup.- are preferably of the super-luminescent type,
for obvious reasons. Even a minimally skillful electrical engineer
will be able to choose the actual type of LEDs used, as well as the
type and value of the resistor R, to fit the needs of a given
application given the specifications of the power source S, in
particular, its peak delivered voltage.
[0029] Assume for the sake of illustration that when the source S
supplies positive voltage, current is flowing in the clockwise
direction (viewed as in FIG. 1); negative output voltage therefore
gives a counter-clockwise current flow. The operation of the LED
pair D.sup.+ and D.sup.- then follows from the known properties of
diodes: When the source S is producing positive voltage, LED
D.sup.+ will be forward biased and will light up, whereas LED
D.sup.- will be reverse biased at the forward bias voltage of D+
and will not give off light. The reverse voltage over D.sup.- will
be kept within safe limits (typically less than 4.0V for a white
color LED and less than 2.0V for a red LED), at the forward bias
voltage of D.sup.+, as D+ will be conductive. Current through
D.sup.+ will be limited by the resistor R. When the source voltage
polarity switches, so too does the conductive LED in the pair:
D.sup.- will become conductive and D.sup.+ will be reverse biased
at the forward bias voltage of D.sup.-. The two paired LEDs D.sup.+
and D.sup.- thus operate as a single "AC LED" in that, as long as
the supply voltage is above the minimum forward turn-on voltage,
one LED of the pair will always be producing light.
[0030] Some of the advantages even of the basic embodiment of the
invention shown in FIG. 1 are:
[0031] The only diodes required are those that actually produce
light--no rectifying elements are needed at all.
[0032] The invention will work whether the voltage source S
delivers alternating or direct current. When operating with a DC
voltage source, only one of the LEDs will be active, but on the
other hand, the assembly of only three components R, D.sup.+ and
D.sup.- will work equally well regardless of the polarity of the
voltage source S.
[0033] Each LED D.sup.+ and D.sup.- is protected from reverse
voltage breakdown by the other LED in the pair.
[0034] When operating with an AC voltage source, flicker is greatly
reduced. In fact, at typical supply frequencies, for example, 60
Hz, D.sup.+ and D.sup.- will both appear as 120 Hz but totally out
of phase with each other; therefore, little flicker will be
apparent to a viewer at all.
[0035] When powered from an AC source, the peak current of each LED
may reach a value higher than the allowed continuous DC current. In
such case, the LEDs will emit a higher peak brightness intensity
while maintaining lower temperature than when driven at the maximum
allowable DC current, which reduces the risk of damage and
premature failure.
[0036] FIG. 2 illustrates a generalized embodiment of the
invention: Rather than a single LED pair D.sup.+ and D.sup.- being
connected in parallel with reverse polarity, an m-by-n array 200 of
such LED pairs D.sub.ij.sup.+ and D.sub.ij.sup.- is provided (i=1,
. . . , m; j=1, . . . , n), with m LED pairs connected in series in
each of n parallel paths.
[0037] A separate current-limiting device, R.sub.j, again, usually
a resistor, is preferably included in each parallel path in series
with the LED pairs. Although not strictly necessary to the
invention (a single current-limiting device could be used as shown
in FIG. 1), this reduces the load through any given resistor (for
example) and allows for variation in the number or characteristics
of the diodes in each parallel path. The value(s) of R.sub.j may be
chosen using normal design methods, taking into account the number
and characteristics of the LEDs and the properties of the voltage
source S.
[0038] Each LED pair in the array may use the same diode type
(and/or color) and be arranged the same as all other pairs,
although this is not strictly necessary as long as standard
measures (such as adjusting the appropriate resistor values) are
taken to ensure proper voltage and current supply to the LEDs. In
FIG. 2, the same number (m) of LED pairs is shown in each of the n
parallel LED paths. This is not necessary to the invention; rather,
unequal numbers of LED pairs may be included in different
paths--again, using separate resistors R.sub.j in each path
facilitates this option.
[0039] The operation of each pair of LEDs in the array will be the
same as described above for the single pair D.sup.+ and D.sup.-
shown in FIG. 1: At any given time, at most one LED in each pair
will be forward biased and therefore giving off light, the other
being reverse biased and therefore turned off.
[0040] FIG. 3 illustrates a standard printed circuit board (PCB)
100, from which a plurality of bases are to be manufactured. For
the sake of simplicity, only a single base 300 is described in
detail. Any number (including a single one) of identical bases may
be made from the PCB 100.
[0041] As FIG. 3 shows, a plurality of through-holes or routes
(illustrated using a heavier lines 310-315, 330) are cut or bored
through the PCB, preferably by conventional 1 mm routing, so as to
form a plurality of laterally extending protrusions 410-415, and
preferably a bottom protrusion 430, which extends out from the
outer edge of the base 300. In the preferred embodiment of the
invention, the routes are curved, at least substantially
semi-circular, although this is not essential and will depend on
the cross-sectional geometry of the threaded or slotted contact
surface of the fitting the base 300 is to be installed in (see
below); thus, the protrusions could be right-angled or other have
some other shape.
[0042] After routing, the routes 410-415, 430 are treated,
preferably using a standard PCB plating process, to deposit an
electrically conductive material such as copper on the inside,
upper, and lower surfaces of the routes. The PCB base 300 is then
either punched out of the larger PCB 100 by using a pre-designed
punch-and-die set or scored and broken along the lines defining the
rest (other than the protrusions) of the periphery of the base 300.
FIG. 4 illustrates the base 300 after separation from the PCB 100.
In the figures, six side-edge protrusions 410-415 are shown merely
by way of example; the actual number used may vary and in any given
implementation of the invention will depend on the needs of that
implementation.
[0043] FIG. 5 illustrates one example of a pattern of traces T1,
T2, T3 used to create the electrical connections symbolized in FIG.
1, with the traces corresponding to the similarly numbered leads in
FIG. 1. The dark dots represent solder pads used to electrically
connect component leads to the traces. As part of plating the
protrusions 410-415 some of the conductive plating material will be
deposited on the inside, upper and lower surfaces of the base 300
as well so as to join with adjacent portions of the trace T3. The
trace T3 will therefore be in electrical contact with the inner
surfaces of the protrusions. Similarly, the conductive material
deposited on the bottom edge protrusion 430 will be electrically
connected to the trace T1.
[0044] FIGS. 6 and 7 illustrate one example of how the LEDs
D.sup.+, D.sup.- and the current-limiting element (here, resistor)
R can be mounted on the base 300. In FIG. 6, the distance between
the centers of the LEDs is indicated as d. This distance d should
be kept as small as possible so as to reduce any parallactic
optical effects when the user views the light and thus to increase
the impression that the LED pair is a single AC LED. For example,
when using standard 5 mm LEDs, which have a diameter of
approximately 5 mm, d should be from five to eight millimeters, and
preferably from five to six millimeters; in other words, the LEDs
should either just touch, or be no more than 3 mm apart, and
preferably no more than 1 mm. FIG. 7 is a side view of the PCB 300
with the components D.sup.+, D.sup.- and R mounted.
[0045] Even though LEDs will typically generate less than 0.1 W of
power each, applications such as those that have limited space but
require high light intensity also require very close packing of
multiple LEDs. In existing arrangements, this leads to severe
problems of heat dissipation. One advantage of connecting the LEDs
in pairs (especially in the multi-LED embodiments of the invention
shown below) to form an "AC LED" is that each LED is only "on"
about half the time; this reduces generated heat and gives better
opportunity for effective heat dissipation. Even disregarding the
thermal advantages of the LEDs' 50% duty cycles, the invention
still will operate much cooler than a typically halogen bulb, whose
operating temperature is as high and potentially dangerous as
200.degree. C.
[0046] FIG. 6 also illustrates a screw-in fitting 600 typically
used to receive incandescent bulbs. Inner and outer dimensions
(usually, diameters) of the fitting 600 are shown as wi and wo,
respectively. The vertical separation (viewed as in FIGS. 4-6),
that is, the pitch p, of the protrusions 410-415 is then chosen to
match the pitch p of the internal contact threading 610 of the
screw-in fitting 600 the light is to be installed in.
[0047] The width w of the main portion (without the protrusions
410-415) of the base 300 is preferably chosen to be the same or
slightly less than the inner diameter of the screw-in fitting 600.
When the base 300 is screwed into the fitting 600, the helical
inner contact surface 610 of the fitting will electrically contact
at least one (and usually all) of the plated protrusions 410-413;
the trace T1 will be electrically connected with the other contact
632 of the fitting via the protrusion contact 430. In a different
but preferred embodiment of the base 300, the width w is preferably
slightly greater than wi; this is described below in conjunction
with FIG. 8.
[0048] FIG. 8 shows the preferred method according to the invention
for providing a lateral biasing force to increase the contact
between the plated protrusions 410-413 and the inner contact
surface(s) 610 of a fitting: Using conventional techniques, slots
701, 702 are cut or punched into the base 300 so as to preferably
extend in the direction in which the base is installed in the
fitting. In the illustrated example, the slots are therefore
vertical. The illustrated slots are straight, but this is not
required by the invention and will in many cases depend on the
layout of traces. Curved slots are also possible, or slots with a
more complicated geometry.
[0049] The width w of the main portion of the base 300 (not
including the protrusions) may then be slightly greater than the
inner diameter wi of the fitting 600. When the base 300 is
installed, for example, screwed in, it will therefore compress
laterally, squeezing together the slots 701, 702. The flexibility
of the PCB material itself will bias the protrusions 410-415
outward against the inner contact surfaces 610 of the fitting
600.
[0050] Another way to bias the base against the inner contact
surface(s) 610 of the fitting 600 would be to mount an electrically
conductive compression spring (not shown) on the bottom protrusion
430 and to connect this spring to the trace T1. The biasing force
would then be vertical, which would tend to force the upper plated
edges of the edges of the protrusions 410-415 into physical and
thus electrical contact with the inner contact surface (s) 610 of
the fitting 600.
[0051] The invention is easily adapted for use in other types of
fittings besides the screw-in fitting shown in FIG. 6. For example,
using only two plated protrusions, one on either side, the base 300
could be used to fit into a standard bayonet fitting. By adjusting
the vertical separation (from zero upward) of the protrusions, and
the base width, most standard bayonet fittings could be
accommodated, regardless of their degree of indexing. A flanged
base can also be created using a similar technique.
[0052] The "AC LED" according to the invention may of course also
be used in fittings that do not require screwing in or rotation at
all. FIG. 9 illustrates, for example, how the base 300 may be
formed so as to fit into a standard wedge-type fitting. In this
case, no special protrusions are required at all. Rather, standard
contacts 901, 902 are bonded onto the PCB so as to contact the
traces leading current from the two different poles of the voltage
source. The lateral separation of the contacts 901, 902 will of
course be chosen to match the positions of the female contacts
(usually, spring-biased contacts in slots) into which the base 300
is to be fitted. Note that this embodiment of the base 300 may be
made exceptionally compact, in most cases little larger (and
possibly even smaller) than the incandescent bulb it replaces.
[0053] FIG. 10 illustrates just one of many different ways in which
more than one LED pair, in this case D.sub.11.sup.+, D.sub.11.sup.-
and D.sub.21.sup.+, D.sub.21.sup.- may be mounted on a single base
300. Depending on the needs of the particular implementation, the
two pairs may be connected either in series (comparing with FIG. 2,
m=2 and n=1) or in parallel (m=1 and n=2). If the LED pairs are
connected in parallel, then separate resistors R.sub.1 and R.sub.2
are preferably included, one in each path. Traces to supply current
to the LEDs may then be routed in any known manner, also depending
on the type of fitting the light is to be used in.
[0054] The usefulness of the configuration shown in FIG. 9 is more
than simply the doubling the number of LEDs active at any one time.
One additional advantage is that it allows for front-and-back
illumination coverage. Most common LEDs have up to approximately
50-degree illumination coverage; front-and-back mounting would
therefore provide roughly 100-degree coverage. The degree of
coverage in any given implementation of the illustrated embodiment
of the invention will of course depend on the degree of coverage of
the chosen LEDs.
[0055] It would also be possible to bend the leads of the LEDs, or
to mount them differently, so that they extend laterally out from
the base 300 rather than perpendicularly away from its surface.
[0056] Still another advantage arises in industries such as the
automotive industry. Tail lights in a car are DC devices, but the
fittings are usually polarized nonetheless, such that the
invention, in particular, the base 300, would be able to fit in the
fitting in only one orientation. Because the invention provides an
"AC LED," polarity will not make any difference. On the other hand,
the "correct" orientation of the invention for a given car model,
or in a given fitting (left as opposed to right, for example) might
be such that a single LED pair, as shown in FIGS. 6 and 7, would be
facing backwards. The twin-pair LED arrangement of FIG. 10 would
eliminate this concern.
[0057] Note that LEDs are typically so cheap that it would in most
cases be better simply to have "idle" LEDs rather than having
separate "left-handed" or "right-handed" bases. Rather than allow
an LED pair to illuminate to no purpose (for example, the pair
facing away from any potential viewers), it would also be possible
to route current to the two LED pairs through a switch (double-pole
double-throw) so that only one pair is activated at any time; if
the PCB is mounted "backwards" then the user can flip the switch
and activate the other LED pair.
[0058] FIGS. 11 and 12 illustrate, respectively, top and side views
of an embodiment of a multi-element, multi-path AC LED
configuration that provides substantially full-spectrum light, at
least at distances from the light assembly that users will normally
be located for reading, working, etc. In this embodiment, several
LEDs are mounted in any known manner so as to extend at least
substantially perpendicular from a PCB base 1100. Again, the LEDs
are preferably mounted close together; as before, the LEDs should
either just touch, or be no more than 3 mm apart, and preferably no
more than 1 mm apart. LEDs are included that emit three different
wavelengths, that is, colors, preferably red, blue and green, (or
any other combination of colors) which, when mixed, are perceived
by a viewer as being full spectrum white. The LEDs are preferably
distributed so that no color clearly predominates in any particular
region of the layout.
[0059] In this multi-color embodiment of the invention, the LEDs
are preferably connected as reversed-polarity pairs as shown in
FIG. 2, with a resistive element (labeled "R") for each
electrically parallel branch. Thus, the LEDs will be of six "types"
D.sup.+.sub.r, D.sup.-.sub.r, D.sup.+.sub.g, D.sup.-.sub.g,
D.sup.+.sub.b, and D.sup.-.sub.b, that is, permutations of color
(indicated by subscripts r, g, and b for red, blue and green) and
polarity.
[0060] All LED pairs emitting the same color may comprise one
parallel branch of the configuration shown in FIG. 2, but this is
not necessary. Rather, LED pairs of different colors may instead be
connected in the same parallel path; this would enable the
full-spectrum light effect even in the very unlikely event that one
or more parallel paths were to fail. It would also be possible to
include different numbers of LED pairs for different colors so as
to properly balance the luminance for each color to create the most
white effect; in this case, it is advantageous to series-connect
the LEDs of each color so that proper resistance values can be
chosen in each parallel path.
[0061] At a typical user's normal reading or working distance from
the assembly, the light from the LEDs will be so "mixed" that the
user will not be able to distinguish any red, green, or blue hues
unless he is looking directly at the assembly. When looking at an
illuminated object located at distances beyond about 20 cm from the
assembly, and possibly even closer, the user will perceive the
mixture of red, green, and blue as pure white, or, rather,
full-spectrum light illuminating the object. Contrast this with a
conventional "white" LED, which is simply a blue-light LED coated
with phosphorous so as to introduce a yellow component to the
spectrum and produce a "pseudo-white" color.
[0062] In one prototype of the multi-element embodiment of the
invention illustrated in FIGS. 11 and 12, the base 1100 was
substantially round, with a diameter chosen so the base would fit
and could be used as an aftermarket insert into common halogen
fixtures. The illustrated embodiment is particularly advantageous
for mounting within existing MR11 or MR16 fixtures with a bi-pin
base and mirror reflector (hence the "MR"), or the smaller G4
fixture. The structures used to connect the LEDs electrically to
the power supply will be chosen depending on which type of
conventional lighting assembly is to be replaced.
[0063] It is of course not necessary for the LEDs in the
multi-element embodiment shown in FIGS. 11 and 12 to have different
colors. Rather, all the elements could be of one color, such as
white (for example, conventional "pseudo-white" LEDs), red (for
example, for cockpits or boats or other environments where good
night vision is important), or any other wavelength, including
non-visible wavelengths. A simple switching mechanism could also be
included to allow the user to switch between colors, for example,
between white and red. Because the AC-coupling of LED pairs
according to the invention enables them to operate much cooler than
standard DC LEDs and in general much cooler than standard
incandescent and halogen bulbs, even dozens of LEDs (single or
multi-color) can be densely mounted on a single base 1100 and
provide light as bright or brighter than the bulbs being replaced,
yet at lower temperature.
[0064] FIGS. 13 and 14 are side and top illustrations of an
embodiment of the invention in which reverse-polarity LED elements
(dies) 1301, 1302 are encapsulated in a single casing 1300. In FIG.
14, the standard diode symbols are included on the dies 1301, 1302
merely to show that these semi-conductive elements are connected
with reverse polarity. Electrically conductive legs/leads 1320,
1322 extend into the casing, on one of which (leg 1320) the LED
dies are mounted by conventional bonding methods. Two connecting
wires are included for each element to connect it electrically to
legs 1320 and 1322 and to complete the electric circuit from the
power supply (not shown here) through the LEDs. Connecting wires
1312, 1313 are labeled in FIG. 13 for the element 1302; four
connecting wires are shown in FIG. 14, two for each element 1301,
1302.
[0065] By including the two parallel connected, reverse-polarity
LED dies within a single casing, a single component is provided
that implements the AC LED according to the invention. Such a
component could be used to implement any LED pair described in any
embodiment of this invention.
[0066] FIG. 15 shows an alternate configuration of the
common-casing, AC LED, in which each element in the pair is mounted
on a different one of the legs, with a respective connecting wire
connecting the element to the opposite leg. One advantage of this
structure is that the leg/die/wire configuration for each "side" is
identical to the other, differing only in its mounted orientation
within the casing. This simplifies manufacture, since only one
arrangement is needed.
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