Illumination – Plural light sources – Combined
Reexamination Certificate
2001-06-18
2003-01-14
O'Shea, Sandra (Department: 2875)
Illumination
Plural light sources
Combined
C362S276000, C362S800000, C315S18500S, C315S18500S
Reexamination Certificate
active
06505954
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a light emitting device and more particularly, to a safe light emitting device that can avoid fire when either over voltage or over current occurs.
BACKGROUND OF THE INVENTION
A light emitting diode lamp meets the requirement of energy saving and is widely applied in replace of traditional incandescent lamps. A series light emitting device that includes a plurality of light emitting diode lamps in series used as Christmas light sets is one of the applications of the light emitting diodes.
FIG. 1
depicts a traditional series light emitting device
10
such as a series of decorative lights of a Christmas tree. The light emitting device
10
includes several light emitting diode lamps, i.e. lamps
11
to
14
, which are connected in series. Such a light emitting device
10
can be found in U.S. Pat. No. 5,931,570.
The traditional light emitting device
10
is susceptible to either over current or over voltage and may lead to explosion of light emitting diode lamp, if the light emitting diodes break down one by one. The situation could be very dangerous because the explosion and fire would harm people and even damage property. Such shortcomings of the traditional light emitting device
10
mainly come from the characteristics of the power source and the light emitting diode lamps.
The power source from such as a household socket provides a so-called line voltage that has about 15% of fluctuation in voltage and is current-unlimited. This often leads to over voltage and over current.
Furthermore, the characteristic of the light emitting diode lamps worsens the situation. Please refer to
FIGS. 2 and 3
for more detailed description of why the characteristic of the light emitting diode lamps would worsen the situation.
FIG. 2
depicts the light emitting diode lamp
11
that exemplifies all the light emitting diode lamps
12
to
14
of the traditional light emitting device
10
. The light emitting diode lamp
11
generally includes elements of a light emitting diode chip
111
, a bonding wire
112
and a lead frame
113
. The elements
111
,
112
and
113
are encapsulated in a lamp cap
116
made of epoxy material which may explode if over heated abruptly.
FIG. 3
depicts schematically a current to voltage characteristic chart of a light emitting diode lamp. In a normal operation region A, the current of the light emitting diode lamp increases linearly similar to Ohm's law as the voltage increases. However, in the region B when over voltage occurs, the current jumps dramatically to an unbearable high that increases the temperature of the lamp. If the temperature increasing rate is moderate, the light emitting diode chip will break down. The impedance of the light emitting diode chip will drop down as it broke down. As the light emitting diode break down, the lamp behaves as a conductor, which means the load of the voltage would be added to the unbroken-down LED lamp(s). The added load burdens the unbroken-down LED lamp(s) and even increases the current. Consequently, the other lamp(s) are more susceptible to break down. Accordingly, the driving current in light emitting device
10
will increase step by step when the light emitting diode lamps break down one by one. Finally, the last unbroken-down LED lamp will be subjected to almost all the voltage load of the device
10
. The lamp cap of the final LED lamp would explode and cause spark which may result in fire. That would be extremely dangerous.
Therefore, there exists a need to overcome the shortcomings of the traditional series light emitting device.
SUMMARY OF THE INVENTION
The present invention provides a safe series light emitting device that can avoid explosion and fire when either over voltage or over current occurs. The light emitting device of the present invention includes a plurality of light emitting diode lamps in series. In the light emitting device, at least one of the light emitting diode lamps is a safe light emitting diode lamp. The safe light emitting diode lamp results in an open circuit when either over current or over voltage in the light emitting device occurs. As a result, the light emitting device would automatically fail before danger of explosion and fire might occur.
Preferably, the safe light emitting diode lamp includes a chip type resistor or similar device that would result in a broken circuit and disconnect the series lamps when either over voltage or over current in the light emitting device occurs. The chip type resistor is preferably disposed between a light emitting diode chip and a lead frame of the safe light emitting diode lamp.
Advantages and spirit of the present invention can be further understood by the following detailed description of the invention and drawings.
REFERENCES:
patent: 4211955 (1980-07-01), Ray
patent: 4223248 (1980-09-01), Tong
patent: 5313289 (1994-05-01), Nagane et al.
patent: 5931570 (1999-08-01), Yamuro
patent: 5994845 (1999-11-01), Gibboney, Jr.
patent: WO 00/13469 (2000-03-01), None
Excellence Opto. Inc.
Greenblum & Bernstein P.L.C.
O'Shea Sandra
Sawhney Hargobind S.
LandOfFree
Safe light emitting device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Safe light emitting device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Safe light emitting device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3011790