Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
2000-11-03
2002-08-06
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S224000, C315S20000A, C315SDIG007, C315S291000
Reexamination Certificate
active
06429602
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a fluorescent lamp operating apparatus containing an inverter circuit.
As a conventional fluorescent lamp operating apparatus, such a series inverter as disclosed in Japanese Laid-Open Patent Application No. 10-162983 is known. The applicant of the present invention presented a fluorescent lamp operating apparatus as shown in
FIG. 9
in Japanese Patent Application No. 11-161874.
The fluorescent lamp operating apparatus shown in
FIG. 9
comprises an AC power supply
1
, a noise-proof capacitor
2
, a rectifier circuit
3
, a smoothing capacitor
4
, FETs
5
,
6
, a first resonance capacitor
7
, a fluorescent lamp
8
, a preheat capacitor
9
, a choke coil
10
, a trigger capacitor
14
, Zener diodes
15
,
16
, a second resonance capacitor
17
and a resistance
19
. In the structure shown in
FIG. 9
, the resonance capacitor
7
, the fluorescent lamp
8
, the choke coil
10
and the source and drain terminals of the P-type FET
6
as the first switching element are connected in series in that order.
The smoothing capacitor
4
is connected between one end of the resonance capacitor
7
and the drain terminal of the FET
6
so as to form a closed circuit. The N-type FET
5
, which is the second switching element, is connected between the junction of the choke coil
10
and the FET
6
and the junction of the resonance capacitor
7
and the smoothing capacitor
4
. The input terminals of the rectifier circuit
3
are connected to the AC power supply
1
via the noise-proof capacitor
2
. The preheat capacitor
9
is connected between a pair of electrodes
8
A and
8
B of the fluorescent lamp
8
on the side opposite to the power supply
1
. All these components together form a high-frequency inverter circuit.
The high-frequency inverter circuit first obtains a direct current by rectifying and smoothing commercial AC power supplied from the AC power supply
1
. In this circuit structure, the AC power supply
1
, the noise-proof capacitor
2
, the rectifier circuit
3
and the smoothing capacitor
4
together compose a DC power supply
22
. Then, the obtained direct current is entered into a serial circuit of the switching elements (N-type FET
5
and P-type FET
6
) which are connected in parallel between the smoothing capacitor
4
and the fluorescent lamp
8
and oscillate at radio frequencies. After this, the current is entered into an LC resonance circuit composed of the choke coil
10
and the resonance capacitor
7
which is connected to the N-type FET
5
and further to the fluorescent lamp
8
in series. Thus, the inverter circuit shown in
FIG. 9
generates high-frequency electric power.
As means for starting the high-frequency inverter circuit, the N-type FET
5
and the P-type FET
6
each have a closed loop between the gate and source terminals. The closed loop is composed of a second choke coil
11
, the secondary winding
10
A of the choke coil
10
and the trigger capacitor
14
connected in series, and one side of the trigger capacitor
14
is connected to the source terminals of the FETs
5
,
6
. Furthermore, resistances
12
,
13
and
19
, the Zener diodes
15
,
16
, the second choke coil
11
, the secondary winding
10
A of the choke coil
10
and the second resonance capacitor
17
together compose a gate driving circuit
23
. The junction of the resistance
12
, the second choke coil
11
and the Zener diode
15
is the output terminal of the gate driving circuit
23
.
In the fluorescent lamp operating apparatus structured as described above, before the fluorescent lamp
8
is initiated, the AC power supply
1
supplies the noise-proof capacitor
2
with utility AC power to generate a pulsing voltage via the rectifier circuit
3
. The current resulting from the pulsing voltage makes the smoothing capacitor
4
be charged until it reaches the power-supply voltage. In addition, the resonance capacitor
7
and the preheat capacitor
9
are charged via the resistance
19
, and at the same time, the trigger capacitor
14
is charged via the resistance
12
, the second choke coil
11
and the secondary winding
10
A of the choke coil
10
.
When the charging voltage of the trigger capacitor
14
reaches the threshold voltage in the Zener diode
15
, the electric charge of the trigger capacitor
14
is supplied to the gate terminal of the FET
5
so as to turn the FET
5
on. When the FET
5
is thus placed in the ON state, the electric charges of the resonance capacitor
7
and the preheat capacitor
9
flow into the primary winding
10
B of the choke coil
10
via the FET
5
.
Then, the current flowing through the primary winding
10
B of the choke coil
10
develops an inductive voltage in the secondary winding
10
A of the choke coil
10
. This causes the second choke coil
11
and the capacitor
17
to resonate, thereby making the capacitor
17
have a voltage opposite in direction to the trigger capacitor
14
. Then, a reverse-biased voltage is supplied between the gate and the source of the FET
5
so as to turn the FET
5
off. At the same time, a forward-biased voltage is supplied between the gate and the source of the FET
6
to turn the FET
6
on.
When the FET
6
is thus placed in the ON state, the current flows from the smoothing capacitor
4
through the closed circuit composed of the resonance capacitor
7
, the fluorescent lamp
8
, the choke coil
10
and the FET
6
so as to resonate the primary winding
10
B of the choke coil
10
, the resonance capacitor
7
and the preheat capacitor
9
. At this moment, the current flowing in the reverse direction through the primary winding
10
B of the choke coil
10
develops an inverse inductive voltage at the secondary winding
10
A of the choke coil
10
, which resonates the second choke coil
11
and the capacitor
17
, thereby making the capacitor
17
have a voltage in the opposite direction. As a result, a reverse-biased voltage is supplied between the gate and the source of the FET
6
to turn the FET
6
off. Later, a forward-biased voltage is supplied between the gate and the source of the FET
5
to turn the FET
5
back on. Hereafter, the above-described operations are repeated to turn on and off the FET
5
and the FET
6
alternately.
The above-mentioned current heats the electrodes
8
A,
8
B while flowing through the preheat electrode of the fluorescent lamp
8
. At the same time, a large voltage is placed by resonance between the electrodes of the fluorescent lamp
8
, which increases the temperature of the electrodes so as to start a discharge from the state where the impedance between the electrodes of the fluorescent lamp
8
is infinity. Once the discharge is started, the impedance between the electrodes of the fluorescent lamp
8
drops suddenly, so that an abrupt large current flows from the power line through the fluorescent lamp
8
(this phenomenon is hereinafter referred to as a breakdown, and the large current is referred to as a breakdown current). When a breakdown occurs, the impedance decreases enough to be in a normal stable lighting condition.
The inventors of the present invention have found through experiments that in a fluorescent lamp operating apparatus like this, there are cases where a sudden drop in the lamp impedance at a breakdown causes an extremely large and abrupt breakdown current to flow through the power switching elements, and this inrush current breaks the power switching elements. Furthermore, in the electrodes
8
A and
8
B of the fluorescent lamp
8
, an abrupt and large breakdown current at start-up causes electrons to be concentrated to form a heat spot, thereby to increase local heating. This becomes an issue because it may lead to a disconnection of the electrodes to seriously damage the flashing life characteristics of the fluorescent lamp.
The present invention has been contrived in view of these aspects, with a main object of providing a fluorescent lamp operating apparatus having a fluorescent lamp whose flashing life characteristics have been improved in a simple circuit structur
Imai Takayuki
Ito Kazuhiko
Takahashi Kenichiro
Takeda Mamoru
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Studebaker Donald R.
Vo Tuyet T.
Wong Don
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