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Claims  |
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What is claimed is:
1. A semiconductor light emitting device having a plurality of light
emitting diodes, each of which is driven separately, the device
comprising:
at least three light emitting diodes in which at least one pair of light
emitting diodes connected parallel in the reverse direction is included;
a common terminal in which each one of the electrodes of all the said light
emitting diodes is commonly connected with;
at least one first terminal in which the other electrodes of said diode
pair are commonly connected with;
at least one second terminal which is connected with the rest electrode of
said light emitting diode, which is not included in said diode pair;
a power source whose voltage is enough for driving said light emitting
diodes;
a low electric power source;
at least three switching means, each of which is respectively connected
with one of said first, second, and common terminal so as to connect
either one of said two power sources with said diodes; and
means for controlling said switching means such that the power sources
connected with said first terminal and said common terminal are different
for each other and the power sources connected with said second terminal
and said common terminal are different for each other.
2. The semiconductor light emitting device as claimed in claim 1, wherein
said switching means is comprised of a plurality of transistors in which
their on-off is controlled by control signals obtained from said control
means.
3. The semiconductor light emitting device as claimed in claim 1, wherein
said low electric power source is the earth.
4. The semiconductor light emitting device as claimed in claim 1, wherein
said control means controls said switching means so as to supply time
sharing current for said diode pair.
5. The semiconductor light emitting device as claimed in claim 1, wherein
said control means is comprised of the following:
a pulse generator for producing pulse signals whose pulse width can be
changed by a variable register;
a divider for producing three kind of pulse signals by dividing a generated
pulse from said generator into three parts in order to drive said three
light emitting diodes respectively;
three one-shot multivibrators, each of which produces one-shot signals from
the corresponding one of said three pulse signals produced in said
divider;
three AND gates, each of which performs an AND operation between a pulse
signal from said divider and an output signal from one of said
multivibrators corresponding to said pulse signal; and
an OR gate which performs an OR operation between two outputs from said AND
gates.
6. A multi-color light emitting device comprising:
a first light emitting diode capable of emitting a first color light, said
first color light being emitted in a first direction;
a second light emitting diode capable of emitting a second color light
different than said first color light, said second color light being
emitted in the first direction;
a first terminal connected to an anode of said first light emitting diode
and a cathode of said second light emitting diode, said first terminal
being connected to a first lead;
a second terminal connected to a cathode of said first light emitting diode
and an anode of said second light emitting diode, said second terminal
being connected to second lead;
a first switching device coupled between said first terminal and a first
voltage source and a second voltage source, said first voltage source
generating a voltage that is higher than a voltage generated by said
second voltage source, said first switching device for electrically
connecting said first terminal to said first voltage source in accordance
with a first control signal, and for electrically connecting said first
terminal to said second voltage source in accordance with a second control
signal; and
a second switching device coupled between said second terminal and said
first voltage source and said second voltage source, said second switching
device for electrically connecting said second terminal to said first
voltage source in accordance with a third control signal, and for
electrically connecting said second terminal to said second voltage source
in accordance with a fourth control signal,
a third light emitting diode capable of emitting a third color light
different than said first and second color lights, said third light
emitting diode having an anode and a cathode;
a third terminal connected to said anode of said third light emitting
diode, said cathode coupled to said second terminal; and
a third switching device coupled between said third terminal and said first
voltage source in order to selectively electrically connect said third
terminal to said first voltage source in accordance with a fifth control
signal,
wherein the first and second light emitting diodes are provided in a molded
package, said first and second leads extending from the package in a
second direction opposite the first direction.
7. The device of claim 6, wherein said first, second and third switching
devices include transistors.
8. A semiconductor light emitting device having a plurality of light
emitting diodes which emit different colored light when an electric
current is passed therethrough in a forward direction, comprising:
first, second and third light emitting diodes, each of said first, second
and third light emitting diodes having first and second electrodes, said
first and second light emitting diodes being connected in parallel in the
reverse direction;
a common terminal for providing a common electrical connection to each of
said first electrodes of said first, second and third light emitting
diodes;
a first terminal for providing a common electrical connection to the second
electrodes of said first and second light emitting diodes;
a second terminal for providing electrical connection to the second
electrode of said third light emitting diode;
a power source generating a potential sufficient for driving either one of
said first, second and third light emitting diodes;
a low electric power source;
at least three switching means, each of which is respectively connected
with one of said first, second, and common terminal so as to connect
either one of said power source and said low electric power source with
said plurality of light emitting diodes; and
means for controlling said switching means such that the power sources
connected with said first terminal and said common terminal are different
for each other and the power sources connected with said second terminal
and said common terminal are different for each other.
9. The semiconductor light emitting device as claimed in claim 8, wherein
said switching means is comprised of a plurality of transistors in which
their on-off state is controlled by control signals obtained from said
control means.
10. The semiconductor light emitting device as claimed in claim 8, wherein
said low electric power source is the earth.
11. The semiconductor light emitting device as claimed in claim 8, wherein
said control means controls said switching means so as to supply a time
sharing current for said diode pair.
12. The semiconductor light emitting device as claimed in claim 8, wherein
said control means is comprised of the following:
a pulse generator for producing pulse signals whose pulse width can be
changed by a variable register;
a divider for producing first, second and third pulse signals by dividing a
generated pulse from said generator into three parts in order to drive
said first, second and third light emitting diodes, respectively;
three one-shot multivibrators, each of which produces one-shot signals from
the corresponding one of said first, second and third pulse signals
produced by said divider;
three AND gates, each of which performs an AND operation between a
corresponding one of said first, second and third pulse signals from said
divider and an output signal from one said multivibrators corresponding to
a respective one of said first, second and third pulse signals; and
an OR gate which performs an OR operation between two outputs from two of
said three AND gates. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor light emitting device in which
more than three light emitting diodes are equipped to emit various colors
of light.
2. Description of the Prior Arts
A prior art multi-color light emitting device is shown in FIG. 5. This
device is comprised of a plurality of light emitting diodes (LEDs), each
of which emits light having a different wave length.
As shown in FIG. 5a, a multi-color LED lamp includes three light emitting
diodes 1a, 1b, and 1c, each of which emits light having a different wave
length. These diodes are placed on a lead 2, and molded by plastics 5.
Actually, the cathode sides (N sides) of these diodes are electrically
connected with the top surface of lead 2. On the other hand, each anode
side (P side) of diodes 1a, 1b, or 1c is connected with a respective
bonding lead 4a, 4b, or 4c through a corresponding bonding wire 3a, 3b, or
3c.
As shown in FIG. 5b, those light emitting diodes 1a, 1b, and 1c are
parallel-connected with each other in the forward direction so as to
connect each cathode in common. As a result, each diode can be controlled
separately in order to emit a different color light. The lamp, thus, works
as a multi-color light emitting device.
In the multi-color LED lamp shown in FIG. 5a, each anode of light emitting
diodes 1a, 1b, and 1c should be controlled separately. To this end, the
same number of bonding wires as that of diodes placed on lead 2 are
required. This fact makes it difficult to reduce the number of parts which
compose of the lamp, thus causing a large problem to miniaturize the whole
structure of the lamp.
Further, the top surfaces of three bonding leads 4a, 4b, and 4c and the top
surface of lead 2 are arranged on a straight line. As a result, the
distance between light emitting diode 1b and the corresponding bonding
lead 4b in the most outside diameter becomes large, thus making bonding
wire 3b longer. This fact also makes bonding works difficult.
In order to solve the above mentioned problem, a structure, in which the
anode sides of two light emitting diodes are connected with one bonding
lead, can be invented to reduce one bonding lead.
In this structure, however, two light emitting diodes connected with one
bonding lead are parallel-connected in the forward direction between lead
2 and the bonding lead. Accordingly, these two diodes cannot be driven
separately by external means in order to control their emission
independently. Monochromic emission cannot, therefore, be obtained from
these two diodes, thus causing restriction on the color tone of the whole
LED lamp.
As explained above, in the prior art multi-color LED lamp shown in FIG. 5,
it is difficult to obtain a small-sized LED lamp, because each light
emitting diode should be driven independently. This fact also deteriorates
the efficiency of the assembly works of LED lamps.
SUMMARY OF THE INVENTION
This invention has been made to overcome the above mentioned problems of
the prior art LED lamp.
Therefore, the main objective of the present invention is to provide a
semiconductor light emitting device having a plurality of light emitting
diodes, the device which can be formed smaller without loosing the
independent control of individual diodes.
Another objective of the present invention is to provide a circuit device
for controlling a semiconductor light emitting device having a plurality
of light emitting diodes so as to drive individual diodes separately.
Therefore, the first feature of the present invention is to provide a
semiconductor light emitting device having a plurality of light emitting
diodes, the device which is comprised of the following: at least three
light emitting diodes in which at least one pair of light emitting diodes
connected parallel in the reverse direction is included; a common terminal
in which each one of the electrodes of all the said light emitting diodes
is commonly connected with; at least one first terminal in which the other
electrodes of said diode pair are commonly connected with; and at least
one second terminal which is connected with the rest electrode of said
light emitting diode, which is not included in said diode pair.
The second feature of the present invention is to provide a semiconductor
light emitting device having a plurality of light emitting diodes, each of
which is driven separately, the device is comprised of the following: at
least three light emitting diodes in which at least one pair of light
emitting diodes connected parallel in the reverse direction is included; a
common terminal in which each one of the electrodes of all the said light
emitting diodes is commonly connected with; at least one first terminal in
which the other electrodes of said diode pair are commonly connected with;
at least one second terminal which is connected with the rest electrode of
said light emitting diode, which is not included in said diode pair; a
power source whose voltage is enough for driving said light emitting
diodes; a low electric power source; at least three switching means, each
of which is connected to one of said first, second, or common terminal so
as to connect either one of said two power sources with said diodes; and
means for controlling said switching means such that the power sources
connected with said first terminal and said common terminal are different
for each other and the power sources connected with said second terminal
and said common terminal are different for each other.
Among said three light emitting diodes, two of them, which are connected
parallel in the reverse direction, can be driven by time sharing current
so as to cause alternate pulse emission.
According to said first and second features of the present invention, said
three light emitting diodes can be controlled separately to emit light
using only three terminals. So, the space of the fourth terminal, which
has been required in the prior art device, can be saved to reduce the
whole size of the device of this invention.
These and other objectives, features, and advantages of the present
invention will be more apparent from the following detailed description of
preferred embodiments in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a view showing the structure of a semiconductor light emitting
device according to one embodiment of the present invention;
FIG. 1b shows the equivalent circuit of the device shown in FIG. 1a;
FIG. 2a is a schematic diagram of the circuit to drive the device shown in
FIGS. 1a and 1b;
FIG. 2a is a schematic diagram of the circuit to generate control signals
for the driving circuit shown in FIGS. 2a;
FIG. 3 is a timing chart showing an example of driving timings of the
circuit shown in FIGS. 2a and 2b;
FIG. 4a is a view showing the structure of a semiconductor light emitting
device according to another embodiment of the present invention;
FIG. 4b shows the equivalent circuit of the device shown in FIG. 4a;
FIG. 5 a is a view showing the structure of a prior art semiconductor light
emitting device having a plurality of light emitting diodes; and
FIG. 5b shows the equivalent circuit of the device shown in FIG. 5a.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be explained below with
referring to figures.
FIG. 1a shows the structure of a semiconductor light emitting device
according to one embodiment of the present invention, and FIG. 1b shows
the equivalent circuit of the device shown in FIG. 1a.
As shown in FIG. 1a, the device of this embodiment is characterized by the
fact that it has only two bonding leads 14a and 14b, in spite of having
three light emitting diodes 11a, 11b, and 11c in the same manner as the
prior art device. Of course, the wave lengths of emission in these light
emitting diodes are different for each other.
For example, GaP light emitting diode 11a, which emits a green light, and
SiC light emitting diode 11b, which emits a blue light, are placed on the
top surface of lead 12. In this case, the cathode sides (N sides) of these
diodes are placed to face the top surface of lead 12 to have electric
connection with lead 12. On the other hand, for example, a GaAlAs light
emitting diode 11c, which emits a red light, is placed on the top surface
of lead 12 by facing its anode side (P side) to said surface, and so,
electrically connected with the lead 12. Both of diodes 11a and 11b are
connected with one bonding lead 14a through gold wires 13a and 13b
respectively. Light emitting diode 11c is connected with bonding lead 14b
through gold wire 13c. These diodes, bonding wires, and parts of leads
12a, 14a, and 14b are, then, molded by plastics 15, thus providing a
multi-color LED lamp which emit red (R), green (G), and blue (B) lights.
Among three light emitting diodes 11a, 11b, and 11c, as shown in FIG. 1b,
diodes 11a and 11b are parallel-connected in the reverse direction for
each other between leads 12 and 14a.
The driving procedure of the above mentioned multi-color LED lamp, which
includes a pair of light emitting diodes parallel-connected in the reverse
direction, will be explained next.
FIGS. 2a and 2b show the structure of a circuit to drive the multi-color
LED lamp shown in FIGS. 1a and 1b. Especially, FIG. 2a shows the structure
of a driving part in said driving circuit, and FIG. 2b shows the structure
of a control signal generation part to supply driving signals into said
driving part.
As shown in FIG. 2a, common lead 12 for light emitting diodes 11a, 11b, and
11c in multi-color LED lamp 21 is connected with first switching means 22.
This means 22 is comprised of an NPN transistor 23, in which the emitter
is grounded, and a PNP transistor 24, in which the emitter is connected to
a power source (V.sub.DD). These transistors 23 and 24 are made to be a
conductive state alternately, in order to connect lead 12 with either one
of said sources, that is, the power source V.sub.DD or the ground.
On the other hand, lead 14a, through which light emitting diodes 11a and
11b are parallel-connected with each other, is connected with a second
switching means 25. This means 25 is comprised of transistors 26 and 27,
and performs the switching of power supply, in the same manner as that of
the first switching means 22. These first and second switching means 22
and 25 are controlled to select different power supplies (V.sub.DD or the
ground) for each other alternately.
Lead 14b, in which the P side of light emitting diode 11c is connected
with, is connected to power source V.sub.DD through an NPN transistor 28.
The conduction of transistors 28, 24, 26, 27, and 28 in said driving
circuit are controlled according to signals A-D, which are generated in
the control signal generation part shown in FIG. 2b.
As shown in FIG. 2b, the control signal generation part is comprised of the
following: a pulse generator 32 for producing pulse signals whose pulse
width can be changed by a variable register 31; a divider 33 for producing
three kind of pulse signals by dividing a generated pulse from generator
32 into three parts in order to drive said three light emitting diodes
11a, 11b, and 11c respectively; one-shot multivibrators 34B, 34G, and 34R,
each of which produces one-shot signals from the corresponding one of said
three pulse signals produced in said divider 33; AND gates 35B, 35G, and
35R, each of which performs an AND operation between a pulse signal from
divider 33 and an output signal from the corresponding multivibrator; and
an OR gate 36 which performs an OR operation between the outputs from said
AND gates 35B and 35R.
In the above mentioned circuit, output signals R, G, and B from divider 33
are obtained by dividing a single pulse generated in pulse generator 32
into three parts, as shown in the timing chart in FIG. 3. These signals
are then input to one-shot multivibrators respectively. Signals A, B, and
C shown in FIG. 3 are obtained as the result of said AND operations. Also,
signal D is obtained as the result of said OR operation. Pulse width of
each one-shot pulse signal A, B, or C can be set by arranging the
respective one-shot multivibrator 34B, 346, or 34R.
Among signals A, B, C, and D obtained in said control signal generation
part, signal A is then given to transistor 26 in said driving part to be a
timing signal for driving red light emitting diode 11b. Signal B is
inverted and given to transistors 24 and 27 to be timing signals for
driving green light emitting diode 11a. Signal C is given to transistor 28
to be a timing signal for driving blue light emitting diode 11c. And
signal D is given to transistor 23 to be a timing signal to light red
emitting diode 11b and blue emitting diode 11c.
In the driving system mentioned above, as shown in FIG. 3, signals A and D
change their states, first, from a low level to a high level, thus
allowing transistors 23 and 26 to conduct. As a result, current is
supplied to light emitting diode 11b so as to cause pulse emission.
Next, signal B changes its state from a low level to a high level. In this
condition, if signal A and D change their states from the high level to
the low level, transistors 24 and 27 become conductive to supply current
on light emitting diode 11a. As a result, diode 11a is driven to cause a
pulse emission. On the other hand, diode lib stops lighting.
Still next, signal C and D change their states from a low level to a high
level. In this condition, if signal B changes its state from the high
level to the low level, transistors 23 and 28 become conductive to supply
current on light emitting diode 11c. As a result, diode 11c is driven to
cause a pulse emission. On the other hand, diode 11a stops lighting.
As mentioned above, said three light emitting diodes 11a, 11b, and 11c, two
of which are parallel connected with each other in the reverse direction,
can be driven to emit light one after another by said time sharing driving
circuit. The intensity of emission in each light emitting diode 11a, 11b,
or 11c can be varied by changing the degree of amplification of the
pulse-current-current for diode 11a, 11b, or 11c, or adjusting the pulse
width of the one shot signals which are output from one-shot
multi-vibrators.
As a result, in said multi-color LED lamp, it is possible to control from
outside separately the values of current, which will be supplied for light
emitting diode 11a, 11b, and 11c respectively. Also, the above mentioned
LED lamp is very advantageous in that it requires only two bonding leads.
So, a small-sized LED lamp can be obtained according to this embodiment.
Further, as the result of reducing the number of bonding leads into two,
the bonding distance between a light emitting diode and its leads becomes
shorter, thus facilitating the bonding and assembly works of the device.
It is, thus, possible to mass produce the device more easily.
This invention, however, is not limited to the above mentioned embodiments.
For example, as shown in FIG. 4a, two pairs of diodes 41, 42 and 43, 44,
in which each diode in each pair is connected parallel to the other in the
reverse direction, can be placed on a lead to construct a multi-color LED
lamp. The connectivity of this lamp is shown in FIG. 4b. The driving
circuit shown in FIGS. 2a and 2b can be expanded in order to drive the LED
lamp shown in FIGS. 4a and 4b. The same advantages as those obtained from
the device shown in FIG. 1 can, of course, be obtained from the device
shown in FIGS. 4a and 4b.
The basic idea of this invention can, also, be applied to a device having
more than five light emitting diodes so as to construct a multi-color LED
lamp having smaller number of leads than the number of diodes. The same
advantages as those obtained from the device shown in FIG. 1a can, also,
be obtained from this kind of LED lamp.
In summary, two light emitting diodes in the LED lamp of this invention are
connected parallel in the reverse direction for each other. One of the
common connecting points of these two diodes is still connected with one
electrode of the third diode to compose a common terminal. As a result,
these three light emitting diodes can be controlled separately to emit
light independently with smaller number of terminals than that of the
prior art device. It is, thus, possible to miniaturize the whole structure
of the LED lamp of this invention as well as to improve the efficiency of
its assembly work.
Various modifications will become possible for those skilled in the art
after receiving the teachings of the present disclosure without departing
from the scope thereof.
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