Electric lamp and discharge devices: systems – With cathode or cathode heater supply circuit
Reexamination Certificate
2001-10-25
2004-09-07
Vannucci, James (Department: 2821)
Electric lamp and discharge devices: systems
With cathode or cathode heater supply circuit
C315S291000, C315S307000
Reexamination Certificate
active
06788001
ABSTRACT:
TECHNICAL FIELD
The invention relates to a lighting system which comprises an electronic operating device and at least one gas discharge lamp with filaments. In particular, the preheating operation of the gas discharge lamps is intended to be improved.
PRIOR ART
In an electronic operating device for gas discharge lamps, an AC voltage generator G which operates at a frequency which is substantially higher than the line frequency feeds energy into a load circuit. This state of affairs is illustrated in a block diagram in FIG.
1
. The AC voltage generator G is connected to a load circuit comprising a lamp inductor L
1
, a resonance capacitor C
1
and a gas discharge lamp Lp. The gas discharge lamp will be called a lamp for short in what follows. As illustrated in
FIG. 1
, the lamp inductor L
1
and the resonance capacitor C
1
mostly form a series resonant circuit which is connected to the AC voltage generator G. The lamp Lp is connected in parallel with the resonance capacitor C
1
. Not only is this configuration suitable for operating the lamp Lp, but it also permits the lamp to be started. Before the starting of the lamp, the load circuit constitutes a series resonant circuit of high quality. If this resonant circuit is excited with its resonant frequency, there is produced across the lamp Lp a high voltage which leads to the starting of the lamp. In order to lengthen the lifetime of the lamp, the filaments W
1
and W
2
of the lamp Lp must be preheated before the starting. The circuit illustrated in
FIG. 1
has proved itself for the purpose of implementing preheating. The resonance capacitor C
1
is not connected directly to the lamp inductor L
1
and the AC voltage generator G. Rather, connection to the lamp inductor L
1
is performed via the filament W
1
, and connection to the AC voltage generator G is performed by the filament W
2
. For preheating purposes, the AC voltage generator G outputs a voltage whose frequency is substantially above the resonant frequency of the series resonant circuit comprising the lamp inductor L
1
and the resonance capacitor C
1
. The filaments W
1
, W
2
therefore already conduct current before the starting, and are preheated. This preheating operation leads, however, to a dilemma: firstly, the preheating current must be strong enough to heat up the filaments to the required temperature in a time which is to be in the range of a second. For this purpose, the frequency of the voltage which the AC voltage generator G outputs during preheating may not be selected to be too high. Secondly, during the preheating the voltage across the lamp Lp may not be too high, since glow discharges harmful to the filaments otherwise occur. For this purpose, the frequency of the voltage which is output by the AC generator G during the preheating may not be selected to be too low. The decisive factor for this is the non-starting voltage specified by the lamp manufacturer. It may not be exceeded during preheating. For many lamps, there is no frequency for the voltage output by the AC voltage generator G during preheating for which both conditions named above are fulfilled. All possible frequencies are either too close to the resonant frequency of the series resonant circuit, comprising the lamp inductor L
1
and resonance capacitor C
1
, and therefore produce too high a voltage across the lamp Lp, or they are too far removed from the resonant frequency and therefore produce an excessively low preheating current.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a lighting system in which the lamps can be preheated in a short time without the non-starting voltage specified for the lamps being exceeded.
According to the invention, the above-described resonance capacitor C
1
is replaced by an impedance network which has the following properties: the impedance function of the impedance network has a zero point at the frequency f
1
. In accordance with the above statements relating to the prior art, the impedance network is connected in series to the lamp inductor L
1
via the filaments W
1
, W
2
. The series circuit of the impedance network with the lamp inductor L
1
has an impedance function with a zero point at the frequency f
2
. For preheating purposes, the AC voltage generator G now outputs a voltage whose essential spectral component is at a frequency which is near the frequency f
1
for the zero point of the impedance function of the impedance network. “Near the frequency f
1
” describes in this context a frequency band from 0.8*f
1
to 1.2*f
1
. The voltage across the lamp is thereby low (below the non-starting voltage) and at the same time it is possible to implement a sufficiently high current through the filaments W
1
, W
2
which permits a preheating time of less than a second. For starting purposes, the AC voltage generator G outputs a voltage whose essential spectral component is at a frequency which is near the frequency f
2
for the zero point of the impedance function of the series circuit comprising the lamp inductor L
1
and the impedance network.
A simple configuration of the impedance network consists of the series circuit of a capacitor and an inductor. If the capacitor has the capacitance C and the inductor the inductance L, the zero point of the impedance function is at a frequency ƒ
1
=1/2&pgr;{square root over (LC)}.
A preheating circuit according to the invention can also be used for lighting systems with a plurality of lamps. All combinations of parallel and series connection are possible in this case. In the case of parallel connection, a plurality of lamp circuits which contain an impedance network according to the invention, a lamp inductor and a lamp are connected in parallel. In the case of series connection, only the lamps are connected in series. It then suffices to connect the impedance network according to the invention with in each case one filament terminal of the first and last lamp of the series circuit of lamps.
REFERENCES:
patent: 3619716 (1971-11-01), Spira et al.
patent: 3869639 (1975-03-01), Herzog
patent: 4238708 (1980-12-01), Kaneda
patent: 4350935 (1982-09-01), Spira et al.
patent: 5404082 (1995-04-01), Hernandez et al.
patent: 5424614 (1995-06-01), Maheshwari
Bessone Carlo S.
Pätent-Treuhand-Gesellschaft fuer elektrische Gluehlampen mbH
Vannucci James
Vu Jimmy T.
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