EP1243165B1 - Circuit for operating a gas discharge lamp - Google Patents

Abstract

In a circuit configuration to operate a gas discharge lamp (LA) the lamp (LA) is arranged in a full bridge circuit. A control circuit in normal operation actuates the four switches (S1-S4) in such a way that it changes over with a first frequency (f1) alternately between a first and a second state (T1, T2), whereby in the first state (T1) the two switches (S2, S3) of a first bridge diagonal are opened, one switch (S1) of the second bridge diagonal is closed and the other switch (S4) with a second frequency (f2), which is higher than the first frequency (f1), is alternately opened and closed. In the second state (T2) the four switches (S1-S4) are actuated in such a way that the lamp (LA) is pole reversed. In a start phase (TS) on the contrary the switch connected to the DC voltage source (S4) of a half-bridge is opened, the second switch (S3) of this half-bridge is closed, and the two switches (S1, S2) of the other half-bridge are with a third frequency (f3) alternately opened and closed. As a result reliable lamp starting is rendered possible and at the same time the generation of high-frequent alternating fields in normal operation is reduced.

Description

The present invention relates to a circuit arrangement for operating a Gas discharge lamp, in particular a low-pressure discharge lamp, according to the Preamble of claim 1.

In the development of electronic ballasts for operating Gas discharge lamps have two main tasks. For one thing the electronic ballast ensures reliable and effective lamp operation On the other hand, the ballast and the lamp should allow others Submissions do not affect their function or affect the Environment.

In order to achieve the highest possible lamp efficiency, Gas discharge lamps usually with high frequencies in a range from 20 to 50 kHz operated. At these frequencies, the electron density in the plasma can Fluorescent lamp no longer follow the time course of the current, so that one in the sets a substantially constant average electron density over time. In this case If there is a zero crossing of the mains supply, there is no longer a current gap to reignite the lamp, so that compared to lamp operation in the usual mains frequency of 50 Hz with a constant luminous flux a reduction of the electrical power consumed can be achieved by 8 to 10%.

On the other hand, high-frequency operation results from the high-frequency operation of the lamp Alternating fields where environmental impact is not complete can be excluded. For example, these alternating fields could be too Complaints from people nearby, such as headaches or the like. Especially with gas discharge lamps, which have the shape Elongated tubes have measures to limit the radiated Field strength can be taken.

The easiest way to avoid the creation of high-frequency fields consists in lowering the operating frequency of the lamp again, ideally using it To operate direct current. However, lamp operation is with pure DC voltage practically not possible because gas discharge lamps have a negative characteristic. From an economic point of view, this can only be achieved by using a Throttle can be counteracted sensibly. Pure DC operation also has the disadvantage that the electrodes of the lamp are worn unevenly, which is in an uneven coloring or blackening of the glass around the electrodes manifests.

A circuit arrangement, on the one hand, high-frequency lamp operation realized and secondly to a relatively limited extent high-frequency Alternating fields generated is described in WO 86/04752. The lamp is in a full bridge circuit comprising four controllable switches arranged and such controlled that in a first operating phase, two diagonally opposite Switches are opened while one of the two switches is the second Bridge diagonal is permanently closed and the other is clocked at high frequency. During this time the lamp is essentially in the same direction from the current traversed. In order to remove the harmful deposits that occur over time Avoid electrodes, after some time in a second operating phase four switches controlled so that the two previously permanently open switches be closed or clocked at high frequency, while both the other switches are now open, which effectively corresponds to reversing the polarity of the lamp. In this way the lamp is operated with a low-frequency voltage signal with a high-frequency vibration is superimposed. However, since the amplitude of the high-frequency vibration is relatively small, high-frequency alternating fields are only generated and emitted to a relatively small extent.

Starting from such a full bridge circuit, it is the task of the present Invention, preferably a circuit arrangement for operating a gas discharge lamp a low pressure discharge lamp - to indicate through which the lamp is operated with a high degree of efficiency and the other is effective Lamp start enabled. At the same time, the radiation from high-frequency fields be reduced.

This task is accomplished by a circuit arrangement which has the characteristics of Has claim 1 solved. Analogous to the known prior art Lamp operated with a full bridge circuit such that in normal operation is switched between the two bridge diagonals at a first frequency, the switches of the one bridge diagonal open and the switches of the other diagonal bridge are closed or with a second frequency that is greater than the first frequency to be clocked. So here too Gas discharge lamp operated in normal operation with a voltage signal that itself from a first low-frequency signal with a relatively high amplitude as well a second high-frequency signal with low amplitude. According to the invention, however, to start the lamp with the DC power supply to the full bridge switch connected one Half bridge open while the second switch of this half bridge is closed and at the same time opened the two switches of the other half-bridge at a high frequency and getting closed. Thus, the lamp is started with an AC voltage operated, the amplitude of which is greater than the amplitude of the low-frequency Voltage signal in normal operation and its frequency less than or equal to the second Is high frequency. Thus, the lamp will start with a strong short-term Radio frequency signal operated while after ignition with a low frequency switched DC voltage is driven only by the high frequency is superimposed. In this way, a much better and gentler Lamp start achieved. At the same time, however, the values are very low adjustable radiation ensures that no health Impairment of people in the area, because that High frequency signal superimposed on the lamp direct current accordingly. Further is by periodically switching the lamp current with a low frequency for example in the mHz to Hz range, ensures that the electrodes Wear evenly and no uneven coloring or blackening of the lamps occurs at one end.

Developments of the invention are the subject of the dependent claims. Because through the circuit arrangement according to the invention enables reliable lamp operation and at the same time the radiation of high-frequency alternating fields is significantly reduced very high frequencies can be used for the switches clocked in normal operation be used. In particular, it is conceivable to switch the switches with one frequency above 1 MHz - preferably even in the range between 2.2 MHz and 3.0 MHz - to clock. This is about 20 to 100 times higher than the current ones Operating frequencies between 20 kHz and 50 kHz. In this way, the Possibility to increase lamp efficiency. The frequency range between 2.2 MHz and 3.0 MHz is particularly cheap because the European Norms in this frequency window have a somewhat increased interference radiation on the Allow power supply network in the form of harmonics.

Furthermore, it has surprisingly been found that low-pressure discharge lamps these maximum frequencies are extremely volatile. Here is the invention Clock scheme especially suitable for a lamp start in the megahertz range. Due to the high ignitability, it may even be possible to preheat the Lamp electrodes are dispensed with and the lamp is immediately started cold instead become. This in turn means that a relatively simple circuit structure is realized can be.

If lamp operation in the megahertz range is actually selected, the result is as further advantage that the capacitance and inductance values of some in the Circuitry used components can be reduced so that instead integration of these is possible using discrete components. In particular, passive components such as chokes and capacitors, for example Be part of a series resonance circuit arranged in the bridge branch can, or transformers lend themselves to integration, so that a clear Reduction in dimensions of the entire circuit can be achieved. The Integration of the components can, for example, in the context of a multilayer Printed circuit board. The multilayer circuit is preferably implemented by a LTCC (Low Temperature Cofired Ceramic) structure realized, which consists of several low-sintering ceramic layers or foils arranged one above the other, between which there are conductor tracks, capacitive dielectric layers or the like.

Fig. 1 ein Vorschaltgerät mit einer erfindungsgemäßen Schaltungsanordnung;

Fig. 2 ein Taktschema zum erfindungsgemäßen Ansteuern der vier Schalter der Vollbrückenschaltung; und

Fig. 3 den idealisierten zeitlichen Verlauf der an der Lampe anliegenden Spannung.

The invention will be explained in more detail below with reference to the accompanying drawings. Show it:

1 shows a ballast with a circuit arrangement according to the invention;

2 shows a timing diagram for driving the four switches of the full bridge circuit according to the invention; and

Fig. 3 shows the idealized time course of the voltage applied to the lamp.

A rectifier circuit 1, for example a bridge rectifier or the like, forms the input of the ballast shown in FIG. 1 connected to the AC line voltage u _n . For smoothing the rectified AC line voltage u _n, there is a storage capacitor between the positive output of the rectifier circuit 1 and the input of the full bridge circuit functioning electrolytic capacitor C _s .

The full bridge circuit comprises four controllable switches S1 to S4, which for example are formed by MOS field effect transistors. In the bridge branch between the The gas discharge lamp LA, is located at the center taps of the two half bridges which is, in particular, a low-pressure discharge lamp. Furthermore, in the bridge branch has a series resonance circuit consisting of an inductor L and one Resonance capacitor C1 arranged, the low pressure discharge lamp LA and the resonance capacitor C1 are connected in parallel. Activate the four switches S1 to S4 is carried out by a control circuit, not shown.

The circuit arrangement shown in Fig. 1 can by in a known manner Monitoring circuits, which lamp operating parameters - for example the Lamp voltage and lamp current - record and depending on the control influence the switch or the lamp. That would also be Detection of lamp defects or the like possible. Such circuit extensions However, are not the subject of the present invention and are therefore not intended to continue be taken into account.

The actuation of the four switches S1 to S4 of the full bridge circuit will now be described with reference to FIG. 2. According to the invention, only the switches of one of the two half bridges, in the example shown the switches S1 and S2 of the left half bridge, are to be clocked during a start phase T ₁ . To start the lamp LA, the switch S3 is therefore opened (0), the switch S4 is closed (I) and the switches S1 and S2 are alternately opened and closed at a high frequency. The resultant idealized lamp voltage U _LA applied to the discharge lamp _LA is shown in FIG. 3. As can be seen from the signal curve, there is a high-frequency AC voltage with a frequency f3 and a relatively large amplitude U ₃ . The frequency f3 is preferably above 1 MHz, particularly advantageously in the range between 2.2 MHz and 3.0 MHz. Since gas discharge lamps are extremely ignitable at these frequencies, the electrodes of the lamp LA may not need to be preheated. However, it can be advantageous if the frequency f3 of the clock signal for the switches S1 and S2 for starting the lamp LA is lowered in the direction of the resonance frequency of the series resonance circuit.

After the lamp LA has been ignited, the four switches S1 to S4 are activated in normal operation. In a first state T _1, the two switches S2 and S3 of the one bridge diagonal are permanently opened, while the switch S1 is permanently closed and the switch S4 is clocked at high frequency. The switching frequency f2 for the switch S4 is preferably between 2.2 MHz and 3.0 MHz, for example approximately 2.65 MHz, and is the same as or higher than the frequency f3. After a certain time, the control circuit then changes to a second state T ₂ , in which the two switches S1 and S4 of the previously clocked bridge diagonal are now opened, while switch S3 is now closed and switch S2 is also clocked at high frequency f2. The change between the two states T ₁ and T ₂ takes place at a very low frequency f1.

Correspondingly, in normal operation the lamp voltage U _LA also shown in FIG. 3 results. It should be noted that, for reasons of clarity, the relationship between the high frequency f2 and the low switching frequency f1 is not shown correctly. The high frequency f2 is preferably in the megahertz range, while the switching frequency f1 can be, for example, 50 Hz and even significantly less - up to a few mHz. Overall, however, there is a very low-frequency voltage with an amplitude U ₁ , which is superimposed on a high-frequency voltage with a very small amplitude U ₂ . U ₁ is lower than the ignition voltage U ₃ . However, since the high-frequency signal components for the environmental compatibility of the lamp ballast system must be observed in the first place, a health impairment can be excluded. Otherwise, the starting phase T _{s is} only very short, so that the cause of complaints can also be excluded here.

Due to the high-frequency components in the control voltages that occur both in the starting phase T _s and during normal operation T ₁ and T ₂ , chokes and capacitors with relatively low capacitance and inductance values can be used for the series resonant circuit. In this case, it is possible to integrate these components into a multilayer circuit, for example an LTCC multilayer circuit. Such multilayer circuits, which consist of a plurality of low-sintering ceramic layers arranged one above the other, are already used in a wide range. For the circuit arrangement according to the invention, however, this represents a particularly advantageous embodiment, since in this case the dimensions of the switching arrangement or of the entire ballast can be significantly reduced, which in turn has the consequence that further shielding devices can be attached to the ballast without great effort.

Claims (13)

1. Circuitry arrangement for the operation of a gas discharge lamp,
   having a full bridge circuit to which a d.c. voltage is applied and which includes four controllable switches (S1-S4),
   there being connected in series a first switch (S1) with a second switch (S2) and a third switch (S3) with a fourth switch (S4) and there being connected the first switch (S1) with the third switch (S3) and the second switch (S2) with the fourth switch (S4),
   and the gas discharge lamp (LA) being arranged in a bridge branch which connects a node point between the first switch (S1) and the second switch (S2) with a node point between the third switch (S3) and the fourth switch (S4),
   and having a control circuit which in normal operation of the gas discharge lamp (LA) so controls the four switches (S1 - S4) that it switches over, with a first frequency (f1), alternatingly between a first and a second condition (T₁, T₂),
   in the first condition (T₁) the second and third switches (S2, S3) being open, the first switch (S1) being closed and the fourth switch (S4) being alternatingly open and closed with a second frequency (f2) which is higher than the first frequency (f1),
   and in the second condition (T₂) the first and fourth switches (S1, S4) being open, the third switch (S3) being closed and the second switch (S2) being alternatingly opened and closed with the second frequency (f2),
   characterized in that,
   the control circuit so controls the four switches (S1 - S4) in a start phase (T_s) that the fourth switch (S4) is closed, the third switch (S3) is opened, and the first and second switches (S1, S2) are alternatingly opened and closed with a third frequency (f3).
2. Circuitry arrangement according to claim 1,
   characterized in that,
   the second frequency (f2) is greater than 1 MHz.
3. Circuitry arrangement according to claim 2,
   characterized in that,
   the second frequency (f2) lies in the range between 2.2 MHz and 3.0 MHz.
4. Circuitry arrangement according to any of claims 1 to 3,
   characterized in that,
   the third frequency (f3) is greater than 1 MHz.
5. Circuitry arrangement according to claim 4,
   characterized in that,
   the third frequency (f3) lies in the range between 2.2 MHz and 3.0 MHz.
6. Circuitry arrangement according to any of claims 1 to 5,
   characterized in that,
   a series resonance circuit (L, C1) is arranged in the bridge branch.
7. Circuitry arrangement according to claim 6,
   characterized in that,
   the series resonance circuit has a choke coil (L) and a resonance capacitor (C1), the discharge lamp (LA) lying parallel to the resonance capacitor (C1).
8. Circuitry arrangement according to any preceding claim,
   characterized in that,
   passive components of the circuitry arrangement are integrated in a multi-layer circuit.
9. Circuitry arrangement according to claim 8,
   characterized in that,
   the multi-layer circuit is a LTCC-structure which is of a plurality of low temperature sintering ceramic layers arranged above one another.
10. Circuitry arrangement according to any preceding claim,
    characterized in that,
    this is a component of an electronic ballast which has a rectifier circuit (1) connected with a mains voltage (u_n), which feeds the circuitry arrangement.
11. Method of operating a gas discharge lamp (LA),
    the gas discharge lamp (LA) being operated in normal operation with an a.c. voltage which is of a first signal having a first frequency (f1) and a first amplitude (U₁), on which is superposed a second signal having a second frequency (f2) and a second amplitude (U₂), the second frequency (f2) being greater than the first frequency (f1) and the first amplitude (U₁) greater than the second amplitude (U₂),
    characterized in that,
    the gas discharge lamp is operated in a start phase with an a.c. voltage the amplitude of which (U₃) is greater than the first amplitude (U₁) and the frequency of which (f3) is smaller than or the same as the second frequency (f2).
12. Method according to claim 11,
    characterized in that,
    the second frequency (f2) is greater than 1 MHz.
13. Method according to claim 12,
    characterized in that,
    the second frequency (f2) lies in a range between 2.2 MHz and 3.0 MHz.

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