Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Plural periodic switches or multiple contact periodic switch
Patent
1995-02-13
1997-03-11
Pascal, Robert
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Plural periodic switches or multiple contact periodic switch
315209R, 315224, 315244, 315DIG7, H05B 3702
Patent
active
056104790
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The-invention relates to a circuit arrangement for high-frequency operation of one or more parallel- or serially-connected low-pressure discharge lamps.
BACKGROUND
A circuit arrangement to operate low-pressure discharge lamps is described in European Patent Application 0 395 776, Krummel. However, it has the disadvantage, first, that higher costs and a greater space requirement are created as a result of additional limiter diodes at the lamp base point, along with a necessarily fast bridge rectifier and an expensive radio interference suppressor filter on the alternating voltage side. Secondly, the circuit is also less suitable for relatively low mains voltages combined with high lamp burning and igniting voltages, since the full resonant capacitance is parallel to the lamp and consequently the converted idle output--which is necessary to generate the high burning and igniting voltages--undergoes a very major modulation as a function of the instantaneous value of the rectified mains voltage.
THE INVENTION
It is an object of the present invention to provide a circuit arrangement of the type described at the outset, which, with technically simple means, without increased interfering radiation and at low additional power losses, assures both an increase in the power factor of the circuit arrangement and reliable operation without a protective circuit.
The circuit according to the invention includes a pump circuit, in which the positive terminal of the rectified alternating mains voltage, on the output side of a radio interference suppression filter, is connected to the base point of the lamp via a first fast diode polarized in the forward direction. This point is connected to the positive terminal of the filter capacitor via a second diode also polarized in the forward direction.
The modulation of the lamp current and the generation of the harmonics is reduced by the capacitor being located parallel to the second diode of the diode series circuit.
Further radio interference suppression is achieved by means of a further capacitor, which is connected parallel to the first diode.
Preferably, the capacitance of the series resonant circuit assigned to each low-pressure discharge lamp is formed by two parallel-connected capacitors; the following inequality is desirable for the ratio between the capacitances of the two capacitors C.sub.R1 and C.sub.R2 (connected to the filter capacitor):
In a further embodiment, the other of the two capacitors, given suitable filaments, can be replaced by suitably modified preheating capacitors.
According to the invention, a current takeup from the mains during one-half of a period of the RF inverter results, and then charging (pumping) of the filter capacitor during the other half period. By placing a choke before the first diode and connecting a capacitor parallel to the second diode, it is assured that the charging process will not be interrupted at the time periods when the mains voltage drops below half the filter capacitor voltage. Overpumping or a voltage overload especially during ignition is prevented in this circuit arrangement due to attenuation of the pump process, by providing that the resonant capacitance parallel to the lamp is split into at least two capacitors, and one of the at least two capacitors is connected directly to the positive or negative terminal, respectively, of the filter capacitor. This not only prevents an overvoltage at this capacitor but also reduces the modulation of the lamp current, without also markedly worsening the ignitability of the circuit.
A further improvement is obtained by connecting a capacitor parallel to the first diode. The current across this first diode is very rich in harmonics and causes major radio interference, especially in the range above 1 MHz. The capacitor having a capacitance of approximately 1 to 5 nF brings about a pronounced reduction in harmonics of the operating frequency (50 kHz) and thus a drastic reduction in radio interference.
DRAWINGS
Further advantages and characteristics of
REFERENCES:
patent: 4547706 (1985-10-01), Krummel
patent: 4553070 (1985-11-01), Sairanen et al.
patent: 4572989 (1986-02-01), Zuchtriegel
patent: 4782268 (1988-11-01), Fahnrich et al.
Pascal Robert
Patent-Treuhand-Gesellschaft fur elektrische Gluhlampen mbH
Philogene Haissa
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