Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch in the primary circuit of the supply...
Reexamination Certificate
2001-03-19
2002-07-30
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch in the primary circuit of the supply...
C315S224000, C315S243000
Reexamination Certificate
active
06426597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit arrangement for operating gas discharge lamps, in particular high-pressure gas discharge lamps, that is used in electronic ballasts for corresponding gas discharge lamps.
High-pressure gas discharge lamps differ from low-pressure gas discharge lamps inter alia in that they require higher ignition voltages, and their colour temperature changes with the respective lamp power that is supplied. The consequence of the last-mentioned property is that high-pressure gas discharge lamps can only be dimmed with difficulty or cannot be dimmed. On the contrary, in order to maintain the colour temperature of the high-pressure gas discharge lamp, the energy that is supplied to the respective lamp must be kept constant by means of corresponding control. Accordingly, an electronic ballast for high-pressure gas discharge lamps, on the one hand, must generate a high ignition voltage and, on the other hand, must present the possibility of keeping the power supplied to the lamp constant.
2. Description of the Related Art
Known electronic ballasts for high-pressure gas discharge lamps are based on a full-bridge circuit that comprises four controllable electronic switches. This principle shall be explained in the following with reference to
FIG. 4
, with the circuit that is shown in
FIG. 4
being known, for example, from WO-A-86/04752.
As has already been mentioned, this known circuit, for the purpose of activating a gas discharge lamp EL, in particular a high-pressure gas discharge lamp, comprises a full bridge that has four controllable switches S
1
-S
4
which are formed, in accordance with the previously mentioned printed specification, in particular by means of bipolar transistors. Connected in the bridge branch of this full bridge there is a series resonant circuit consisting of a coil L
1
and a capacitor C
1
, with the gas discharge lamp EL that is to be activated being arranged in parallel with the capacitor C
1
. The full bridge is fed with a direct voltage U
0
. Connected in parallel with the switches or transistors S
1
-S
4
there are free-wheeling diodes, although these are not shown in
FIG. 4
for the sake of simplicity. In order to operate the gas discharge lamp EL, in WO-A-86/04752 it is proposed that during a first operating phase the switch S
4
be closed and the switches S
2
and S
3
be opened. Furthermore, during this first operating phase the switch S
1
is switched on and off alternately at a high clock frequency. During the on-period of the switch S
1
a direct current flows by way of the switch S
1
, the coil or inductor L
1
, the gas discharge lamp EL and the switch S
4
which is continuously closed during this operating phase. By opening the transistor S
1
the flow of current is interrupted and the magnetic energy previously built up in the coil L
1
as a result of the flow of current is converted into electrical energy that supplies a counter-voltage which maintains the flow of current through the gas discharge lamp EL in the same direction until the next time the switch S
1
is switched on, with the energy that is stored in the coil L
1
thereby being reduced. By switching on the switch S
1
again, the electric circuit previously described is closed again so that the process mentioned above is repeated. During this first operating phase in which the switches S
2
and S
3
are permanently open and the switch S
4
is permanently closed and the switch S
1
is opened and closed alternately at a high frequency, the current flows through the gas discharge lamp EL continuously in the same direction. This results in the gas discharge lamp EL flickering less during the operation thereof and a higher level of luminous efficiency is possible. During permanent operation with the direct voltage U
0
, however, it is possible that deposits will accumulate in the electrode region of the gas discharge lamp EL, caused by the flow of electrons flowing continuously in the same direction. In order to avoid these deposits, the polarity of the gas discharge lamp EL is repeatedly reversed at a low frequency. This is effected in that during a second operating phase the switches or transistors S
1
and S
4
are now permanently open and the switch S
3
is permanently closed. Furthermore, during this second operating phase the switch S
2
is switched on and off alternately at a high frequency so that in principle the same mode of operation ensues as that which ensues during the first operating phase previously described, although during the second operating phase the flow of current through the gas discharge lamp EL is reversed.
In summary it can accordingly be established that the full bridge shown in
FIG. 4
in principle is operated with the direct voltage U
0
, although as a result of the low-frequency polarity-reversal between the bridge diagonals S
1
-S
4
or S
2
-S
3
respectively, that is, as a result of the low-frequency switch-over between the two first and second operating phases previously described, a low-frequency alternating current, the frequency of which current corresponds to the frequency of polarity-reversal, is supplied to the gas discharge lamp EL and the inductor L
1
. During the two operating phases, either the switch S
1
or the switch S
2
is switched on and off alternately at a high frequency.
The ratio of magnitudes between the clock frequency, with which the switches S
1
or S
2
are alternately switched on and off, and the clearly lower frequency of polarity-reversal should be selected so as to be as large as possible and can amount, for example, to 1000:1. The greater this ratio is, the smaller the dimensions of the inductor or coil L
1
can be. On account of the high-frequency switch-over of the switches S
1
or S
2
respectively, a correspondingly high-frequency current is generated that flows through the inductor L
1
. The inductor serving to limit the lamp current can therefore have smaller dimensions than in the case where a low-frequency current flows through
The ignition of the gas discharge lamp EL that is shown in
FIG. 4
is effected with the aid of the series resonant circuit that is formed by the inductor L
1
and the capacitor C
1
, in which case for ignition purposes it is necessary to operate the gas discharge lamp EL at a frequency that lies close to the resonant frequency of the series resonant circuit. If this is the case, a voltage overshoot occurs at the gas discharge lamp EL leading to the ignition of the gas discharge lamp.
A similar circuit arrangement for igniting and operating a gas discharge lamp, in particular a high-pressure gas discharge lamp, is known from EP-A2-0740 492. For the purpose of igniting or operating the gas discharge lamp it is proposed in this printed specification that with the aid of a corresponding control circuit the switches S
1
, S
4
or S
2
, S
3
of the full bridge that are arranged in the bridge diagonals be controlled during a first operating phase in a complementary manner at a comparatively high frequency until the gas discharge lamp ignites. Subsequently, the control circuit switches over into a second operating phase (nominal operating phase) in which the control circuit activates the switches S
1
-S
4
of the full-bridge arrangement in a complementary manner at a comparatively low frequency. Moreover, according to this printed specification a regulating device is used that is coupled on the output side by way of a capacitor to the full bridge in such a way that the full bridge is arranged parallel to the capacitor. The regulating device is used, moreover, to supply voltage to the full bridge and regulates in particular the power that is supplied to the gas discharge lamp. To this end, the voltage that is applied to the output terminals of the regulating device and also the instantaneously flowing current are measured, the corresponding values are multiplied and the actual value formed is supplied as the actual value of the lamp power of the regulating device. The control circuit previously mentioned is connec
Huber Martin
Rast Urs
Tobler Felix
Fitzpatrick ,Cella, Harper & Scinto
Knobel AG Lichttechnische Komponenten
Vu David
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