Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
2000-04-27
2002-08-06
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S244000, C315S2090SC, C315S308000, C315SDIG004, C315SDIG007
Reexamination Certificate
active
06429603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a discharge lamp lighting apparatus which lights a discharge lamp by a high frequency current generated by a switching element.
2. Prior Art
FIG. 34
is a circuit diagram showing a construction of a conventional discharge lamp lighting apparatus. In
FIG. 34
, a reference symbol IV denotes an inverter circuit which is connected to a direct current power supply E, and switches a direct current of the direct current power supply E so that the direct current is converted into a high frequency current, an LAC
1
denotes a discharge lamp load circuit for lighting a discharge lamp LA by a high frequency current generated by the inverter circuit IV, and an NP
1
denotes a protective circuit which detects a fault of the discharge lamp load circuit LAC
1
, and outputs a control signal for stopping an operation of the inverter circuit IV.
The following is a detailed description on each of the above circuits.
The inverter circuit IV includes a starting circuit, a pair of MOS-FETs Q
1
and Q
2
(hereinafter, referred to as switching element Q
1
and Q
2
), an inverter control circuit IC
1
(hereinafter, referred to as IV control circuit IC
1
), and a frequency control circuit FC
1
. More specifically, the starting circuit is constructed in a manner that a starting resistor R
1
and a control power supply capacitor C
1
are connected in series and a constant voltage diode DZ
1
is connected in parallel with the control power supply capacitor C
1
. The pair of switching elements Q
1
and Q
2
are connected in series between both electrodes of the direct current power supply E. The inverter control circuit IC
1
controls the switching elements Q
1
and Q
2
. The frequency control circuit FC
1
sets a switching frequency of the switching elements Q
1
and Q
2
via the IV control circuit IC
1
. The IV control circuit IC
1
has terminals; more specifically, a power supply terminal
1
(hereinafter, referred to as terminal
1
) is connected to the control power supply capacitor C
1
, output terminals
2
,
3
and
4
(hereinafter, referred to as terminals
2
,
3
and
4
) are connected to the switching elements Q
1
and Q
2
, and oscillation control terminals
6
and
7
(hereinafter, referred to as terminals
6
and
7
) are connected to the frequency control circuit FC
1
. Moreover, the frequency control circuit FC
1
is composed of a main oscillation resistor R
2
and an oscillation capacitor C
2
which are connected between a negative electrode of the direct current power supply E and the terminals
6
and
7
of the IV control circuit IC
1
, respectively. In this manner, the IV control circuit IC
1
oscillates at a frequency f=K* (current flowing from the terminal
6
of the IV control circuit, which has a constant direct current potential) with respect to a constant K determined by a capacitance of the oscillation capacitor C
2
, and thereby, the switching elements Q
1
and Q
2
make a switching operation at the frequency f.
Next, the following is a description on the discharge lamp load circuit LAC
1
.
As shown in
FIG. 34
, the discharge lamp load circuit LAC
1
is composed of a ballast chock T
1
, a discharge lamp LA having electrodes F
1
and F
2
, and a coupling capacitor C
4
which are connected in series between both terminals of the switching element Q
2
, and further of a starting capacitor C
3
connected in parallel with the discharge lamp LA.
On the other hand, the protective circuit NP
1
is so constructed that the protective circuit NP
1
detects a peak-to-peak voltage (Vmax−Vmin) of a waveform of high frequency voltage between the electrode F
1
side terminal of the ballast chock T
1
and a negative electrode of the direct current power supply E by detection capacitors C
5
and C
6
connected to the discharge lamp load circuit LAC
1
, diodes D
1
and D
2
and a capacitor C
7
. Then, when a direct current voltage generated in both terminals of the capacitor C
7
exceeds a Zener voltage of a constant voltage diode DZ
2
, the protective circuit NP
1
outputs a signal to an oscillation stop terminal
5
(hereinafter, referred to as terminal
5
) of the IV control circuit IC
1
connected to the protective circuit NP
1
so that a switching operation of the switching elements Q
1
and Q
2
is stopped. In this case, when the discharge lamp LA is normally lighting, the direct current voltage of the capacitor C
7
is set so as to become lower than a Zener voltage of the constant voltage diode DZ
2
. Therefor, the protective circuit NP
1
is not operated. Moreover, a resistor R
4
is used for discharging a charge stored in the capacitor C
7
when a power supply is turned off, and a resistor R
16
and a capacitor C
11
divide and control a voltage inputted to the terminal
5
, and smooth an external high frequency noise, to prevent a malfunction of the IV control circuit IC
1
.
Next, the following is a description on an operation of a conventional discharge lamp lighting apparatus.
The discharge lamp is started up, and then, when a current is supplied to the inverter circuit IV from the direct current power supply E, the control power supply capacitor C
1
is charged by a starting current flowing through the starting resistor R
1
from the direct current power supply E. When a voltage of the terminal
1
of the IV control circuit IC reaches a predetermined operating voltage, the IV control circuit IC
1
oscillates at a frequency f determined by the frequency control circuit FC
1
so that a high frequency signal is outputted to the switching elements Q
1
and Q
2
from its terminals
2
and
4
. Then, the switching elements Q
1
and Q
2
are alternately turned on and off, and thereby, a high frequency current is supplied to the discharge lamp load circuit LAC
1
. By the high frequency current, a series circuit comprising the ballast chock T
1
and the starting capacitor C
3
(for the coupling capacitor C
4
is designed so as to have a capacitance several times as much as that of the starting capacitor C
3
, the coupling capacitor C
4
has no influence on the following resonance phenomenon) generates an LC resonance. Subsequently, a high voltage is generated in the starting capacitor C
3
, that is, between both terminals of the discharge lamp LA. Thus, the discharge lamp LA is started, and continues to light at a frequency f. In this case, the control power supply capacitor C
1
is connected in parallel with the constant voltage diode DZ
1
, so that a voltage applied to the terminals
1
of the IV control circuit IC
1
is limited by a Zener voltage of the constant voltage diode DZ
1
.
Next, the following is a description on an operation of a conventional protective circuit NP
1
.
When the discharge lamp LA is lighting, a high frequency voltage as shown in
FIG. 35
is generated between the electrode F
1
side terminal of the ballast chock T
1
and a negative electrode of the direct current power supply E. The high frequency voltage is generated so as to be overlapped with a constant direct current voltage. In the protective circuit NP
1
, a peak-to-peak voltage (Vmax—Vmin) is detected by the detection capacitors C
5
and C
6
and the diodes D
1
and D
2
which are connected between the ballast chock T
1
and the direct current power supply E, and further, is converted into a direct current voltage by the capacitor C
7
, and thus, is inputted to the constant voltage diode DZ
2
. In this case, when the discharge lamp LA is normally lighting, the direct current voltage of the capacitor C
7
is set so as to become less than a Zener voltage of the constant voltage diode DZ
2
; therefore, no oscillation stop signal is outputted to the IV control circuit IC
1
from the protective circuit NP
1
.
However, for example, in the case where the discharge lamp LA is rectified and lighting in the end of its file, a high frequency lamp voltage of the discharge lamp LA rises up; for this reason, a voltage of the capacitor C
7
becomes higher than the Zener voltage of the constant voltage diode DZ
2
. Whereu
Hamazaki Kenji
Ieki Yasunori
Ishikawa Osamu
Kobayashi Tetsuya
Nishikawa Hiroaki
Mitsubishi Denki & Kabushiki Kaisha
Philogene Haissa
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