Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
2001-08-20
2003-07-29
Le, Hoanganh (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S046000, C315S050000
Reexamination Certificate
active
06600272
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fluorescent lamp, and particularly to a bulb-shaped fluorescent lamp.
2. Related Background Art
In the last few years, the consciousness for saving energy has increased, and as an alternative low power light source that takes the place of low efficiency bulbs, fluorescent lamps, in particular, bulb-shaped fluorescent lamps, have been developed and used actively.
The bulb-shaped fluorescent lamp basically has an integrated structure, as shown in FIG.
4
. The bulb-shaped fluorescent lamp includes a combination of a fluorescent arc tube
18
in which glass tubes each having coiled electrodes
19
and
20
on end portions are bent or jointed to form a series of discharge paths, and an electronic ballast
21
that is a circuit for lighting the fluorescent arc tube
18
stably. The bulb-shaped fluorescent lamp further is provided with a bulb base
22
. Typically, the fluorescent arc tube
18
is disposed in an outer tube glass bulb
23
, and the electronic ballast
21
is disposed in a resin case
24
.
A conventional bulb-shaped fluorescent lamp has addressed important issues such as improvement in characteristics (e.g., lamp efficiency and its life). In addition, it has been attempted to reduce the conventional bulb-shaped fluorescent lamp in its size and weight so as to use it as an alternative to a bulb. As a result, as shown in
FIG. 4
, the electronic ballast
21
for high frequency lighting is employed currently as a main ballast in the bulb-shaped fluorescent lamp, because it is superior in both aspects such as the improvement in lamp characteristics and reduction in its size and weight.
As shown in
FIG. 5
, the general purpose lighting circuit of the above-described conventional electronic ballast
21
includes an inverter circuit portion
25
, an inductor
26
connected in series to the fluorescent arc tube
18
and a capacitor
27
connected in parallel to the fluorescent arc tube
18
. In addition, a positive temperature characteristic resistive element (PTC)
28
connected in parallel to the fluorescent arc tube
18
is installed as in almost all circuits.
Hereinafter, an operation of lighting a lamp by the conventional lighting circuit will be described.
(a) First, when a power supply
29
is turned on, a preheat current sufficient for starting the arc tube flows through the coiled electrodes
19
and
20
via the capacitor
27
and the positive temperature characteristic resistive element
28
.
(b) Next, when the resistance of the positive temperature characteristic resistive element
28
becomes high due to a rise in temperature, a so-called resonant voltage (peak value: 700 V to 1000V) of the inductor
26
and the capacitor
27
is applied to the fluorescent arc tube
18
, whereby the fluorescent arc tube
18
starts.
(c) Thereafter a predetermined lamp current flows through the fluorescent arc tube
18
, and the lamp starts to light steadily. During steady lighting of the lamp, a current also continuously flows through the capacitor
27
via the coiled electrodes
19
and
20
.
As described above, the conventional lighting circuit in which the capacitor
27
is connected in parallel to the fluorescent arc tube
18
has a relatively simple configuration. In addition, it is characterized in that the coiled electrodes
19
and
20
are preheated sufficiently and supplied with a predetermined starting voltage when the lamp starts. In this respect, it is considered to be an inexpensive and reliable circuit.
Moreover, as shown in
FIG. 4
, during assembly of the circuit parts of the electronic ballast
21
, main parts including the capacitor
27
are disposed and mounted on the surface of a printed circuit board
30
on the base
22
side. This allows the printed circuit board
30
to thermally insulate the main parts from a heat source or the fluorescent arc tube
18
during lighting of the lamp, thereby suppressing a temperature rise in the main parts.
As a recent trend of a bulb-shaped fluorescent lamp, a high watt-type lamp of 20 W or more (e.g., 22 W to 25 W) has been developed as an alternative to a 100 W bulb, along with a low watt-type lamp of 13 W as an alternative to a 60 W bulb. Since a 60 W bulb is the same as a 100 W bulb in shape, in the development of this high watt-type lamp, it also has been attempted to miniaturize the lamp as an alternative to a bulb. That is to say, a high watt-type lamp is required while it is kept as small as possible.
The present inventors employed the electronic ballast
21
composed of a basic characteristic circuit of the prior art, as shown in FIG.
4
and worked toward the development of a similar small high watt-type lamp. As a result, it was found that a temperature rise particularly in the circuit parts of the electronic ballast cannot be avoided, which results in an occurrence of circuit failure and a short life of the lamp. Further, the analysis of the lamp with a short life revealed that the circuit failure is caused mainly by the damage of the capacitor
27
connected in parallel to the fluorescent arc tube
18
in
FIG. 4
due to its temperature rise.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-described problems by providing a bulb-shaped fluorescent lamp adopting an inexpensive and reliable electronic ballast.
To achieve the above object, the bulb-shaped fluorescent lamp of the present invention includes a fluorescent arc tube, an electronic ballast for lighting and driving the fluorescent arc lamp, and a base for providing power to the electronic ballast, which are arranged in this order. The electronic ballast includes an inductor connected in series to the fluorescent arc tube and at least two capacitors constituting a resonant circuit with the inductor and connected in parallel to the fluorescent arc tube.
In this bulb-shaped fluorescent lamp, it is preferable that at least two capacitors are disposed on the surface of a printed board constituting the electronic ballast on the base side, and their bodies are disposed stepwise without being opposed to each other. In this case, it also is preferable that as the capacitance of at least two capacitors becomes larger, their bodies are spaced further from the fluorescent arc tube and disposed stepwise.
According to the above-described constitution, the bulb-shaped fluorescent lamp adopting an inexpensive and reliable electronic ballast can be realized, in which the surface temperature of at least two capacitors during steady lighting of the lamp is kept at not more than a guaranteed upper limit operating temperature, resulting in reduction of damage to the at least two capacitors during the use of the lamp.
REFERENCES:
patent: 5714846 (1998-02-01), Rasch et al.
patent: 6177768 (2001-01-01), Kamata et al.
patent: 6274988 (2001-08-01), De Vries
patent: 6469447 (2002-10-01), Nakagawa et al.
patent: 2000-286088 (2000-10-01), None
patent: 2001-035675 (2001-09-01), None
Matsui Nobuyuki
Nakagawa Hiroki
Tahara Tetsuya
Le Hoang-anh
Merchant & Gould P.C.
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