Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Transformer in the supply circuit
Reexamination Certificate
2000-03-06
2001-11-27
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Transformer in the supply circuit
C323S355000, C336S012000, C336S015000, C336S020000, C336S170000
Reexamination Certificate
active
06323602
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a circuit arrangement for operating two or more lamps in parallel, equipped with
an equalizer transformer comprising a main core of magnetizable material around which a first winding and a second winding are provided, the first and second winding each comprising a number of turns substantially equal to N, said first and second winding during operation being connected in series with respective lamps,
inductive ballast means.
The invention also relates to an inductive component.
A circuit arrangement as mentioned in the first paragraph is known from EP 0766500-A1. The known circuit arrangement is widely used for supplying low-pressure mercury discharge lamps. In the known circuit arrangement the equalizer transformer fulfils two functions. First of all, during ignition, after the first lamp has ignited, the equalizer transformer makes sure that the voltage over the lamp that has not yet ignited is high enough to realize the ignition of that lamp. In the second place, during steady state operation the equalizer transformer makes sure that the currents flowing through the lamps are substantially equal. The inductive ballast means is normally formed by a single choke that is in series with both lamps. The function of the inductive ballast means is to limit the current flowing through the lamps. A disadvantage of the known circuit arrangement is that the total number of components comprised in the circuit arrangement is comparatively high so that it is relatively complicated and therefore expensive to manufacture the circuit arrangement.
BRIEF SUMMARY OF THE INVENTION
The invention aims to provide a circuit arrangement that comprises only a comparatively small number of components.
A circuit arrangement as mentioned in the opening paragraph is therefor according to the invention characterized in that the inductive ballast means comprise a third winding and a fourth winding around the core of magnetizable material, said third and said fourth winding each comprising a number of turns substantially equal to M, and in that the third and the fourth winding are arranged symmetrically with respect to the first and second winding.
The equalizer transformer and the inductive ballast means have been integrated into a single inductive component in a circuit arrangement according to the invention. The process of assembling a circuit arrangement according to the invention and its integration in a compact lamp are comparatively simple as a result of this.
Since the third and fourth winding comprise a substantially equal number of turns and they are arranged symmetrically with respect to the first and second winding, the magnetic fluxes through the third and fourth winding hardly interfere with the functioning of the first and the second winding during operation. In other words there is hardly any interaction between the inductive ballast means and the equalizer transformer. The third and the fourth winding are so arranged that during operation there is only a relatively small magnetic coupling between them; that is, they are loosely coupled magnetically. Because of this relatively small magnetic coupling the third and fourth winding can together form an inductor. The first and the second winding, however, are so arranged that during operation, there exists a good magnetic coupling between them; that is, they are loosely coupled magnetically. This good coupling is necessary for the first and second winding to form an equalizer transformer. The magnetic coupling between the first and the second winding is good when the two windings are close together on the main core. The magnetic coupling can be further improved by forming the first and second winding as a bifilar winding. In this case the first and the second winding are not just close to each other but occupy the same space.
Preferably the first winding and the second winding are arranged between the third and the fourth winding. In such an arrangement the coupling between the first and second winding can be good since they can be close together. At the same time the third and fourth winding are separated from each other by the first and second winding so that the coupling between the third and fourth winding is relatively small.
A circuit arrangement according to the invention preferably comprises a first E-core and a second E-core formed out of magnetizable material, wherein the end surfaces of the transverse legs of the first E-core are facing the end surfaces of the second E-core, and wherein the first winding and the third winding surround the middle transverse leg of the first E-core, while the second and the fourth winding surround the middle transverse leg of the second E-core.
In another preferred embodiment of a circuit arrangement according to the invention, the main core comprises a first U-core and a second U-core formed out of magnetizable material, wherein the end surfaces of the transverse legs of the first U-core are facing the end surfaces of the transverse legs of the second U-core and wherein the first winding and the third winding surround a first transverse leg of the first U-core, while the second and the fourth winding surround a first transverse leg of the second U-core, the end surface of the first transverse leg of the first U-core facing the end surface of the first transverse leg of the second U-core. In practice it has been found that the performance of a main core comprising two U-cores is not as good as the performance of a main core comprising two E-cores, but in the first case less magnetizable material needs to be used, so that the circuit arrangement can be smaller and cheaper.
It be mentioned that, for instance in U.S. Pat. No. 5,313,176, an inductive component is disclosed in which the functions of two chokes and a transformer are integrated. This inductive component comprises only two windings and is very suitable for use e.g. in an EMI/RFI filter. However, since both functions of the component strongly influence each other, the chokes and the transformer cannot be used independently, or more particularly conduct different currents. For these reasons the inductive component disclosed in U.S. Pat. No. 5,313,176 is not suitable for use as an integrated equalizer transformer plus inductive ballast means in a circuit arrangement according to the present invention.
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patent: 4613841 (1986-09-01), Roberts
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patent: 5568018 (1996-10-01), Muzic
De Groot Hendrik W. J.
Laros Petrus C. J.
Tran Thuy Vinh
U.S. Philips Corporation
Wong Don
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