Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Transformer in the supply circuit
Reexamination Certificate
2000-03-24
2001-02-06
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Transformer in the supply circuit
C315S224000, C315SDIG005
Reexamination Certificate
active
06184634
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a circuit arrangement for igniting and operating a lamp, comprising
supply terminals for connection to a supply voltage source,
a piezotransformer equipped with two input terminals and two output terminals,
an oscillator, coupled with the supply terminals and the input terminals of the piezotransformer, for generating a periodical voltage,
a load circuit equipped with terminals for lamp connection and coupled between the output terminals of the piezotransformer.
Such a circuit arrangement is known from EP 0665600. The piezotransformer is only very small, so that the known circuit arrangement is very suitable for use in for instance a flat panel display. In the known circuit arrangement both the ignition voltage as well as the voltage present over the lamp during stationary operation are both generated by the piezotransformer. In practice this means that the circuit arrangement can only be used in combination with lamps that have a relatively low ingnition voltage while a relatively high voltage is present over the lamp during stationary operation. The possible applications of the known circuit arrangement are therefore limited. In practice only low pressure discharge lamps can be ignited and operated by means of the known circuit arrangement. High pressure discharge lamps, however, are characterized by a very high ignition voltage while the voltage that is present over the lamp during stationary operation is relatively low. Circuit arrangements for igniting and operating high pressure discharge lamps are typically equipped with either a series- or a parallel igniter for generating an ignition pulse with a relatively high voltage. These igniters tend to be bulky, increasing the size and the cost of the circuit arrangement In case of a series igniter the igniter is arranged in series with the lamp, so that at least part of the series igniter carries a current not only during ignition but also after ignition of the lamp during stationary operation, which leads to power dissipation and therefore a relatively low efficiency of the circuit arrangement. On the other hand, in case use is made of a parallel igniter (arranged in parallel with the lamp), part of the circuit arrangement needs to be protected against the ignition pulse by means of a filter. This filter, however, not only functions during ignition but also carries a current during stationary operation and therefore decreases the efficiency of the circuit arrangement.
SUMMARY OF THE INVENTION
The invention aims to provide a circuit arrangement for igniting and operating a lamp that comprises a piezotransformer and can therefore be relatively small and simple and that additionally is capable of operating lamps having an ignition voltage that differs substantially from the voltage present over the lamp during stationary operation, while the circuit arrangement also does not contain bulky components that dissipate power during stationary operation.
A circuit arrangement as mentioned in the opening paragraph is therefore in accordance with the invention characterized in that the circuit arrangement further comprises an igniter, coupled between the output terminals of the piezotransformer, for generating during ignition a DC voltage with an amplitude that is higher than the voltage that is present between the output terminals of the piezotransformer during stationary lamp operation.
During ignition the secondary side of the piezotransformer functions as a capacitor that is charged by the igniter to a DC voltage with an amplitude that is higher than the voltage that is present between the output terminals of the piezotransformer during stationary lamp operation. The lamp connected to the circuit arrangement is ignited by means of this DC voltage. After the ignition of the lamp the igniter is disabled and the stationary operation of the lamp is started. During this stationary operation a periodical voltage is generated by the oscillator and amplified by the piezotransformer. The amplified periodical voltage is present over the load circuit coupled between the output terminals the piezotransformer. Since the lamp is ignited by means of a DC voltage, the igniter can be of a relatively simple construction and need not comprise parts that dissipate a relatively large amount of power during stationary operation. Furthermore the circuit arrangement needs not comprise a filter. A circuit arrangement according to the invention can be relatively small, can operate with a high efficiency and is capable of igniting and operating lamps that have a relatively high ignition voltage while the voltage present over the lamp during stationary operation is much smaller.
Good results have been obtained for embodiments of a circuit arrangement according to the invention in which the igniter comprises a voltage multiplier. Preferably the oscillator and the piezotransformer can be part of the igniter.
Good results have also been obtained for embodiments of a circuit arrangement according to the invention, wherein the piezotransformer is of the Rosen type.
REFERENCES:
patent: 6091209 (2000-07-01), Hilgers
patent: 0665600A1 (1995-08-01), None
Leers Dieter
Ossmann Martin
Kraus Robert J.
U.S. Philips Corporation
Vu David
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