Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-12-29
2004-02-24
Patidar, Jay (Department: 2862)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S500000, C362S800000
Reexamination Certificate
active
06696784
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light emitting diode module as a compact light source for a lighting unit incorporated in a contact image sensor type of image reader. More specifically, this invention relates to a light emitting diode module having the configuration capable of preventing destruction by static electricity.
BACKGROUND OF THE INVENTION
In a contact image sensor type of image reader used, for instance, in a facsimile terminal equipment, a copying machine, or a scanner, a light emitting diode (described as LED hereinafter) is used as a compact light source for a linear lighting unit to emit light in a linear state to a surface of a document. An example of the linear lighting unit based on the conventional technology is disclosed in Japanese Patent Laid-open Publication No. 8-163320. As shown in
FIG. 1
, the linear lighting unit described in this publication incorporates therein a light conductor
14
within a white casing
12
for a linear lighting unit
10
, and an LED module
16
comprising a plurality of LEDs is attached to a package having a form like a flat plate at one edge of the light conductor
14
.
A full-color image reader often uses, as a linear lighting unit thereof, an LED module in which LEDS for three colors of red, green, and blue (R, G, B) are sequentially lighted up. Generally the LED module is a 4-terminal module in which a cathode and an anode of each LED are connected to individual terminals respectively and at the same time the anode and cathode are commonly connected to the respective common terminals.
FIG. 2
shows a connection diagram of a 4-terminal module. In the figure, designated at the reference numeral
20
is a red LED, at
22
a green LED, and at
24
a blue LED, and anodes of the LEDs are connected to terminals
26
,
28
,
30
respectively, while cathodes of the LEDs are commonly connected to a terminal
32
.
Typically the red LED
20
has a conductive substrate, and a cathode or anode electrode is provided on a rear surface of the substrate, namely on a rear surface of the chip, while the anode or cathode electrode is provided on a top surface of the chip. The green LED and blue LED have an insulating substrate, and in many cases an node electrode and a cathode electrode are provided on a top surface of the chip. Because of the configuration described above, the connection with the anode connected to a common terminal as shown in
FIG. 2
is implemented as shown in
FIG. 3
in actual wiring.
In
FIG. 3
, packaged in a flat plate-formed package
34
(indicated by the dotted line) are lead frames
36
,
38
,
40
having individual terminals
26
,
28
,
30
shown in
FIG. 2
at one edges respectively and a lead frame
42
having a common terminal
32
at one edge thereof. The red LED
20
is provided on the lead frame
36
, the greed LED
22
on the lead frame
38
, and the blue LED
24
on the lead frame
40
.
The red LED
20
has an anode electrode
20
A provided on a top surface of the chip and a cathode electrode (not shown) on a rear surface of the chip; the green LED
22
has an anode electrode
22
A and a cathode electrode
22
K both provided on a top surface of the chip; and the blue LED
22
has an anode electrode
24
A and a cathode electrode
24
K both provided on a top surface of the chip.
A cathode electrode of the read LED
20
is directly connected to the lead frame
36
; the cathode electrode
22
K of the green LED
22
is connected via a bonding wire
48
to the lead frame
38
; and the cathode electrode
24
K of the blue LED
24
is connected via a bonding wire
50
to the read frame
40
.
The anode electrode
20
A of the red LED
20
, anode electrode
22
A of the green LED
22
, and anode electrode
24
A of the blue LED
24
are connected via bonding wires
52
,
54
, and
56
respectively to the common lead frame
42
.
It is generally known that an LED is disadvantageously vulnerable to a surge voltage caused by discharge of static electricity. When the terminal is connected, the LED may be destructed by a current higher than the rated one flowing in the reverse direction even for a very short period of time. It is generally recognized that especially the green LED and blue LED based on the conventional technology are more vulnerable to destruction caused by static electricity as compared to the red LED. For the purpose to prevent destruction by a surge voltage, load of a high voltage to an LED due to electrostatic discharge, generally a Zener diode is connected in parallel as shown in
FIG. 4
to the LED or a Zener diode is provided on a substrate to which the LED module is connected to prevent a high voltage due to electrostatic discharge from being loaded to the LED.
However, when it is tried to incorporate a Zener diode in an LED module, a number of steps for packaging the chip not directly relating to the light emitting function into the module increases, which in turn causes disadvantageous problems such as the difficulty in size reduction of the module and increase in the production cost. Further, when a Zener diode is to be packaged on a substrate, the LED module may directly be affected by electrostatic discharge in the state where the terminal is connected until the LED module is packaged on the substrate, and it is required to take appropriate countermeasures for suppressing generation of static electricity in the peripheral environment.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a compact LED module capable of preventing destruction due to static electricity without using a Zener diode and requiring few countermeasures against static electricity in the peripheral environment.
In a first aspect of the present invention, the light emitting diode as a compact light source for a lighting unit has first, second, and third terminals; first and second light emitting diodes connected between the first and second terminals and also connected in inverse parallel to each other; and a third light emitting diode connected between the first or second terminal and the third terminal.
In this LED module, it is preferable that the first light emitting diode is a green light emitting diode, the second light emitting diode is a blue light emitting diode, and the third light emitting diode is a red light emitting diode.
In a second aspect of the present invention, the light emitting diode as a compact light source for a lighting unit has first, second, and third terminals; first and second light emitting diodes connected between the first and second terminals and also connected in parallelism to each other; and third and fourth light emitting diodes connected between the second and third terminals and also connected in inverse parallel to each other.
In this LED module, it is preferable that the first light emitting diode is a green light emitting diode, the third light emitting diode is a blue light emitting diode, and the second and fourth light emitting diodes are red light emitting diodes.
REFERENCES:
patent: 6069365 (2000-05-01), Chow et al.
patent: 6297598 (2001-10-01), Wang et al.
Matsumoto Haruo
Yoshida Minoru
Nippon Sheet Glass Co. Ltd.
Patidar Jay
RatnerPrestia
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