Circuitry arrangement for the operation of a plurality of...

Details Circuitry arrangement for the operation of a plurality of... Circuitry arrangement for the operation of a plurality of...

2003-04-08

2004-07-20

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

C315S224000, C315S297000

Reexamination Certificate

active

06765354

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
This is a Continuation of International Application PCT/EP01/11073 filed Sep. 25, 2001 which in turn claims priority of German application DE 100 49 842.6 filed Oct. 9, 2000, the priorities of which are hereby claimed, said International Application having been published in German, but not in English, as WO 02/32196 A1 on Apr. 18, 2002. International Application PCT/EP01/11073 is incorporated by reference herein in its entirety, as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuitry arrangement for the operation of at least two gas discharge lamps.
2. Description of the Related Art
Through the employment of so called double-lamp or multiple-lamp ballasts to a certain extent a reduction of the outlay in terms of circuitry can be achieved. The advantage in comparison with the employment of ballasts which in each case control only a single gas discharge lamp consists in that a greater part of the components of the ballast, for example the rectifier, the harmonics filter, the control circuit and the inverter, can be simultaneously employed for the operation of a plurality of lamps.
The inverter and the load circuit of a known double-lamp ballast, which is disclosed in EP 0 490 329 A1, are schematically illustrated in FIG.
4
and will be briefly explained below. The inverter is formed by means of two controllable switches S
1
and S
2
which are arranged in a half-bridge arrangement to the input of which a supply d.c. voltage V
BUS
is applied. The two switches S
1
and S
2
are so controlled by a control circuit
1
that they alternatingly open and close so that at the middle point of the half-bridge there is yielded a high frequency a.c. voltage U
ac
. This a. c. voltage is delivered to the load circuit, which initially on the input side has a series resonant circuit of an inductance L
a
and a capacitance C
r
. To the common node point between the inductance L
a
and the capacitance C
r
, the two gas discharge lamps LA
1
and LA
2
are connected in parallel in each case via a coupling capacitor C
k1
and C
k2
.
Further, there is connected upstream of two gas discharge lamps LA
1
and LA
2
a balancing transformer L
bal
, the windings of which are flowed through by the two lamp currents. This happens in opposite senses so that upon deviations of the current amplitudes a magnetization arises which induces a voltage in the windings, which in turn works in a balancing manner. By means of the balancing transformer L
bal
component tolerances and lamp tolerances, and different temperature conditions, which could have the consequence that the two lamps LA
1
and LA
2
burn with different brightnesses, can be compensated to a certain degree.
The balancing effect of the transformer L
bal
is however restricted and does not ensure a complete equalization of the lamp currents. For example at low currents, which occur with small dimming levels, the lamps are practically parallel connected, since the voltage drop at the balancing transformer can amount only to a fraction of the arc drop voltage of the lamps. This is manifest particularly at lower temperatures, where the arc drop voltage at small lamp currents reaches a maximum.
This case is illustrated in FIG.
5
. Thereby, the two lamps are to be operated at a brightness which corresponds to a certain desired current I
SOLL
. However, due to tolerances, the two lamps are not identical but manifest characteristic lines U
arc1
and U
arc2
which are slightly displaced with respect to one another, as they are illustrated in FIG.
5
. Thus, for example, with a predetermined current, the second lamp requires in principle a somewhat greater arc drop voltage U
arc2
than the first lamp. In order then to be able to operate both lamps with the desired current, I
SOLL
, two different arc drop voltages U
SOLL1
and U
SOLL2
would be necessary. Since, however, the ballast with the inverter makes available only one voltage value U
SOLL1
, which in the illustrated example is determined by the lamp having the lower arc drop voltage, that is by the first lamp having the characteristic line U
arc1
, this voltage U
SOLL1
is also applied to the second lamp. As a consequence thereof the second lamp does not take up the desired current value I
SOLL
but possibly forms a second working point with a different current value I
arc2
and therewith naturally also has a different brightness. There exists, however, also the danger that the second lamp having the higher arc drop voltage possibly may be able to find no fixed working point and as a consequence extinguishes.
In order therefore, in the case of lower brightness values, to avoid the extinguishing of one of the two lamps LA
1
or LA
2
, there is effected with the ballast illustrated in
FIG. 4
the regulation of the inverter always in accordance with that lamp LA
1
or LA
2
which has the lower lamp current at the time. For this purpose, the ballast has two detection circuits
2
1
and
2
2
which in each case detect the current flowing through a lamp LA
1
or LA
2
, in that they determined the voltage dropped across a measurement resistance R
SENS1
or R
SENS2
. The actual values V
IST1
and V
IST2
generated by the two detection circuits
2
1
and
2
2
are then delivered to a comparator circuit
3
which selects the corresponding lower value and passes this as the final actual value V
IST
to the control circuit
1
for the control of the inverter.
Thus, there is needed for each lamp its own detection circuit, in order to be able reliably to ensure that neither of the two lamps extinguishes. The outlay in terms of circuitry is, however, again increased through this. Further, it is to be taken into consideration that depending upon the switching capacitances of the lamps or the wiring, a capacitive current always also flows through the lamps. A satisfactory control is, however, only then ensured if the actual effective component of the lamp current is determined. For this purpose complex and expensive circuits are necessary. Finally with the multiple lamp systems, with which more than two lamps are connected to a single inverter, there is needed a complex selection circuit for selecting the lowest actual value in each case.
SUMMARY OF THE INVENTION
It is thus the object of the present invention to indicate a simplified circuitry arrangement for the operation of at least two gas discharge lamps, with which the extinguishing of one of the lamps can be reliably avoided.
This object is achieved by means of a circuitry arrangement in accordance with the present invention. In accordance with the invention, n (n is a whole number and greater than 1) gas discharge lamps are operated with a single inverter, which is supplied with a d.c. voltage and generates an a.c. voltage which is alterable in its frequency, which is delivered to a load circuit arrangement at the output of the inverter. Thereby, the load circuit includes a series resonant circuit of an inductance and a capacitance, and the n gas discharge lamps connected to the common node point between the inductance and the capacitance. Further, the load circuit contains (n−1) balancing transformers for the balancing of the currents of in each case two gas discharge lamps.
In order to prevent that one of the lamps extinguishes, in accordance with the invention the load circuit has for each gas discharge lamp a d.c. current supply line which in each case taps between the output side terminal of the winding of the balancing transformer and the gas discharge lamp and via which a d.c. current is delivered to each gas discharge lamp. Thus, each gas discharge lamp receives, along with the a.c. voltage delivered via the resonant circuit and the rectifier, additionally an independent current source which supplies the lamp with a d.c. current. This additional d.c. current corresponds advantageously approximately to the half of the nominal 1% current at 25° C. to 35° C. It has the effect that even for the case that due to the predetermined a.c. voltage

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