EP2526741B1 - Circuit arrangement and method for rapid commutation during square wave operation of high-pressure discharge lamps - Google Patents

Description

Technical area

The invention relates to a circuit arrangement and method for rapid commutation in the rectangular operation of high-pressure discharge lamps. In particular, the invention relates to an electronically controlled operation of high pressure discharge lamps with fast commutation sequence.

background

The invention relates to a circuit arrangement for rapid commutation in the rectangular operation of high-pressure discharge lamps according to the preamble of the main claim.

For the operation of high-pressure discharge lamps, in particular high-pressure discharge lamps with a ceramic discharge vessel, a relatively low-frequency rectangular lamp power supply with fast commutation is usually used. High-pressure discharge lamps generally have two rod-shaped electrodes mounted in the discharge vessel, which are often equipped with coiled attachments for conditioning the sheet approach. The current commutation serves to prevent the one-sided electrode wear and must be accomplished with sufficiently fast polarity reversal, so that the lamp does not go out during commutation.

From the DE 10 2009 016 579 A1 a circuit arrangement for operating a high-pressure discharge lamp is known, which has a half-bridge, in which the upper and the lower Switch for the purpose of straightening the discharge arc are independently controllable.

From the DE 10 2008 016 888 A1 a circuit arrangement for operating a high-pressure discharge lamp is known, which has a storage capacitor for increasing the commutation of the inverter of the circuit arrangement.

From the WO 2007/00 31 71 A1 a circuit arrangement for operating a high-pressure discharge lamp is known, which has a control circuit which forms current pulses in the vicinity of the zero crossing of the supply voltage in order to stabilize the operation of the high-pressure discharge lamp.

For standard high-pressure discharge lamps, the commutation time is typically in the range of less than 100 μs.

The commutation frequency is generally chosen so that, on the one hand, the short-term discontinuities during the commutation process do not manifest as flickering in the light and, on the other hand, the acoustic emissions from both the hot lamp and the operating equipment do not fall within the audible range.

This requirement can best be achieved with a commutation frequency in the range between 50 Hz and 200 Hz.

The best results are achieved by synchronizing the commutation frequency at 100 Hz (European) or at 120 Hz (American) to the mains and thus the low-frequency and easily visible mixing modes between the 100 Hz ripple or 120 Hz ripple of the mains supply and the Suppress fluctuations in the commutation transitions.

However, the commutation frequency should not be set above the audio hearing range at more than 20 kHz, so that the operation of the lamp, the acoustic resonances of the discharge arc, which are in common lamp geometries in the range between 20 kHz and 150 kHz, not be arbitrarily excited.

A resonant excitation of the arc would in most cases lead to arc fluctuation and arc instabilities, which can lead to flickering, ultimately extinction or even destruction of the lamp.

A further boundary condition for the rectangular operation of a high-pressure discharge lamp is the minimization of the high-frequency ripples on the rectangular lamp current, so that thereby the acoustic modes in the discharge arc of the Lamp can not be arbitrarily excited, which, as already mentioned, can lead to arc instabilities.

The limit value for the high-frequency residual ripple which is permissible for standard rectangular operation of a high-pressure discharge lamp is less than 2%.

The high frequency ripple of a standard rectangular lamp current form driver is essentially the remaining residual ripple resulting from the internal high frequency operating method of the switching converter.

The visible remaining residual ripple depends directly on the time constant of the smoothing devices, which depends essentially on the size of the smoothing capacitor used at the output of the lamp circuit.

At this point, the fact that in a standard operating device with rectangular lamp current form for operating a high-pressure discharge lamp the implementation of a sufficiently strong lamp current smoothing counteracts the requirement of a sufficiently fast current commutation becomes clear.

A high time constant for smoothing the lamp current leads in the same way to slowing down the natural commutation time or to increase the circuit complexity for the implementation of an actively controlled commutation process.

In the case of a standard operating device with a rectangular lamp current form for the operation of standard high-pressure discharge lamps, a compensation between the smoothing requirement (residual ripple less than 2%) and the commutation time (commutation time t_com less than 100 μs) is therefore generally aimed for.

In Fig. 1 A schematic circuit topology of an electronic control gear for operating a standard high pressure discharge lamp according to the prior art is shown in which the amount of residual ripple of the lamp current has been reconciled with the achievable commutation time.

The intermediate circuit voltage U _ZK of 400 VDC is provided by a network power factor correction unit (not shown) via a DC link capacitor C _ZK .

The half-bridge circuit is designed as a deep-set half-bridge with the transistors Q1_HIGH and Q2_LOW. In the case of a deep-setting half-bridge, high-frequency pulse-width modulation is superimposed on the low-frequency operation at approximately 100 Hz in order to be able to reduce the input voltage of the half-bridge to the required lamp voltage. This operation is well known in the art and will therefore not be discussed further here. At the half-bridge, at its output, alternatively, in 100 Hz clock for forward operation (switch Q1_High is clocked with long pulse widths, switch Q2_Low is clocked with short pulse widths) a voltage of + 300V and for the reverse operation (switch Q2_LOW is clocked with long pulse widths, Switch Q1_High is clocked with short pulse widths) a voltage of + 100V is provided.

The high-pressure discharge lamp 5, hereinafter also referred to as a lamp, is operated in the two phases, the forward phase and the reverse phase, to the average voltage U _CB , which adjusts itself constant at the blocking capacitor C _B in the amount of 200VDC. The differential voltage U _L occurring at the lamp is + 100V in forward operation and -100V in reverse operation. The current I _L occurring at the lamp is in the two operating phases corresponding to Lamp voltage also inverted in each case. The smoothing of the generated operating voltage at the output of the switching converter depends on the operating frequency and the LC time constant of the switching converter.

To minimize the remaining high-frequency Schaltripples on the lamp voltage U _L , the time constant (or derived from this time constant frequency fo) of Schaltkonverterbauteile compared to the operating frequency f _operation should be as large as possible: $$\mathrm{fo}:=\frac{\mathrm{1}}{\mathrm{2}\cdot \mathrm{\pi }}\cdot \sqrt{\frac{\mathrm{1}}{\mathrm{L}\cdot \mathrm{C}}}=\frac{\mathrm{1}}{\mathrm{2}\cdot \mathrm{\pi }}\cdot \sqrt{\frac{\mathrm{1}}{\mathrm{0.5}\cdot \mathrm{mH}\cdot \mathrm{nF}}}=\mathrm{10}\cdot \mathrm{KHz}<<\mathrm{foperation}:=\mathrm{60}\mathrm{kHz}\mathrm{,}$$

During the forward commutation, the state of charge of the converter capacitor C is charged from the intermediate circuit capacitor C _ZK via the inductance L resonantly to the voltage value 300V.

In Rückwätskommutierung the state of charge of the converter capacitor C is reversibly charged via the inductance L resonant to the voltage value 100V in the DC link capacitor C _ZK . Ideally, the resonant transshipment process takes place without sufficient dissipation when there are sufficiently high structural components. The commutation times for the resonant recharging processes depend essentially on the LC time constant of the switching converter.

A large LC time constant results in a long resonant recharging time and thus a correspondingly slow commutation time.

$\frac{\mathrm{1}}{\mathrm{2}\cdot \mathrm{\pi }}\cdot \sqrt{\frac{\mathrm{1}}{0.5\cdot \mathrm{mH}\cdot 500\mathrm{nF}}}=10\cdot \mathrm{KHz}$

entspricht einer Umlade- bzw. Kommutierungszeit von 100 µs.The resonant frequency of the LC circuit of $\mathrm{fo}:=\frac{\mathrm{1}}{\mathrm{2}\cdot \mathrm{\pi }}\cdot \sqrt{\frac{\mathrm{1}}{\mathrm{L}\cdot \mathrm{C}}}=$

$\frac{\mathrm{1}}{\mathrm{2}\cdot \mathrm{\pi }}\cdot \sqrt{\frac{\mathrm{1}}{0.5\cdot \mathrm{mH}\cdot 500\mathrm{nF}}}=10\cdot \mathrm{KHz}$

corresponds to a recharge or commutation time of 100 μs.

The time constant of fo = 10kHz results in a ripple of less than 2% at an operating frequency of approx. The smoothing requirements and the commutation times conflict with this switching arrangement and must be compensated appropriately.

To generate the ignition voltage, an ignition transformer with a switching transistor for generating one or more ignition pulses is inserted in series into the lamp circuit.

With the simple rectangular operation described above, it is usually possible to operate most standardized high-pressure discharge lamps without significant arc instabilities and arc deflections occurring.

On the other hand, it is different in the operation of mercury-free molecular-dominated high-pressure discharge lamps or saturated capillary-free high-pressure discharge lamps, in which the lamp fillings used often have high thermal conductivity, resulting in rapid cooling of the electrodes and the lamp plasma during the current commutation and thus the spontaneous extinction of the lamps at this Can lead place.

The requirement for the current commutation time during operation of these novel lamps is thus high and is in the range of less than 40 μs.

In addition to the requirement of fast current commutation, the fillings of these novel lamps usually show one Increased sensitivity for excitation arc-stabilizing acoustic eigenmodes, which increases the requirements for the smoothing capacity of the output circuit (Ripplegrenzwerte less than 1%), but this, as already mentioned, from a technical point of view, the rapid commutation.

Furthermore, in order to stabilize the discharge arc, special modulation operating methods are usually required in the operation of such lamps, which, from a circuit engineering point of view, represents additional defined boundary conditions with respect to the size of the time constants of the internal switching converter or the smoothing properties of the output circuit Commutation are difficult to reconcile.

task

It is an object of the invention to provide a circuit arrangement for fast commutation in the rectangular operation of high-pressure discharge lamps, with the smoothing of the lamp current from the buck converter is arbitrarily adjustable, but the current commutation can be done independently of it at high speed.

Presentation of the invention

The solution of the problem with respect to the circuit arrangement according to the invention with a circuit arrangement according to claim 1 for rapid commutation in the rectangular operation of high-pressure discharge lamps, comprising a Tiefsetzende half-bridge arrangement with a half-bridge, a lamp inductor, a converter capacitor, a blocking capacitor, a first switch for coupling the half-bridge arrangement with the Lamp, a second switch for performing the Vorwärtsstromkommutierung and for initiating a forward phase, a third switch for performing the Rückwärtsstromkommutierung and for initiating a reverse phase. By this measure, the half-bridge can be slowly reloaded as in the prior art, since the lamp circuit is coupled away via the first switch of the half-bridge. When the slow transfer at the half-bridge is completed, the lamp circuit can be reconnected. By the second switch, the lamp according to the invention is subjected to a very fast commutation.

Preferably, the circuit arrangement further comprises a starting inductance and a starting capacitor. With this, a simplified ignition of the high-pressure discharge lamp can be realized in conjunction with the circuit arrangement according to the invention.

In a further preferred embodiment, the circuit arrangement further comprises a power factor correction circuit. It can also be used to operate lamps of higher power in compliance with all prescribed regulations on a public supply network.

• vor dem Einleiten einer Kommutierung abkoppeln der Halbbrückenanordnung von der Hochdruckentladungslampe durch Öffnen eines ersten Schalters,
• Vollzug der Vorwärtskommutierung durch Schließen eines zweiten Schalters zur Einleitung einer Vorwärtsphase und durch Öffnen eines dritten Schalters, oder Vollzug der Rückwärtskommutierung durch Schließen eines dritten Schalters zur Einleitung einer Rückwärtsphase und durch Öffnen eines zweiten Schalters,
• Ankoppeln der Halbbrückenanordnung an die Hochdruckentladungslampe durch Schließen des ersten Schalters,
• Öffnen des zweiten Schalters und des dritten Schalters.

The object is achieved with respect to the method according to the invention with a method according to claim 4 for operating a high-pressure discharge lamp by means of a circuit arrangement with a half-bridge arrangement with a half-bridge and a lamp inductor, a converter capacitor and a blocking capacitor, with the following steps:

• before initiating a commutation decoupling of the half-bridge arrangement from the high-pressure discharge lamp by opening a first switch,
• Performing forward commutation by closing a second switch to initiate a forward phase and opening a third switch, or performing reverse commutation by closing a third switch to initiate a reverse phase and opening a second switch,
• Coupling the half-bridge arrangement to the high-pressure discharge lamp by closing the first switch,
• Opening the second switch and the third switch.

Further advantageous developments and refinements of the circuit arrangement according to the invention for rapid commutation in the rectangular operation of high-pressure discharge lamps will become apparent from the dependent claims and from the following description.

Brief description of the drawings

Fig.1

eine Schaltungstopologie nach dem Stand der Technik dargestellt, bei der der Betrag der Restwelligkeit des Lampenstroms mit der erreichbaren Kommutierungszeit in Einklang gebracht wurde,

Fig. 2

eine erfindungsgemäße Schaltungsanordnung in einer ersten Ausführungsform, bei der die tiefsetzende Halbbrücke von der Glättungseigenschaft des internen Schaltkonverters entkoppelt wird und beide Charakteristika unabhängig voneinander eingestellt werden können,

Fig. 3a

eine Gesamtansicht zur Funktionalität der Schaltanordnung für den Rechteckbetrieb,

Fig. 3b

eine detaillierte Schaltsequenz der Kommutierung in den Vorwärtsbetrieb,

Fig. 3c

eine detaillierte Schaltsequenz der Kommutierung in den Rückwärtsbetrieb,

Fig. 4

eine erfindungsgemäße Schaltungsanordnung in einer zweiten Ausführungsform zur Erzielung einer schnellen Lampenstromkommutation ausschließlich für die Rückwärtskommutierung zur Einleitung der stationären Rückwärtsphase bei einem EVG für Rechteckbetrieb.

Further advantages, features and details of the invention will become apparent from the following description of exemplary embodiments and with reference to the drawings, in which the same or functionally identical elements are provided with identical reference numerals. Showing:

Fig.1

a prior art circuit topology in which the amount of residual ripple of the lamp current has been reconciled with the achievable commutation time,

Fig. 2

a circuit arrangement according to the invention in a first embodiment, in which the deep-setting half-bridge is decoupled from the smoothing property of the internal switching converter and both characteristics can be adjusted independently of each other,

Fig. 3a

an overall view of the functionality of the circuit arrangement for the rectangular operation,

Fig. 3b

a detailed switching sequence of commutation in the forward mode,

Fig. 3c

a detailed switching sequence of the commutation in reverse operation,

Fig. 4

a circuit arrangement according to the invention in a second embodiment to achieve a fast Lampenstromkommutation exclusively for the Rückwärtskommutierung to initiate the stationary backward phase at a ballast for rectangular operation.

Preferred embodiment of the invention

Fig. 2 shows a circuit arrangement according to the invention, in which the deep-setting half-bridge from the smoothing property of the internal switching converter is decoupled and both characteristics can be set independently.

The buck converter switching device arrangement, supplied by the intermediate circuit voltage, provides the two different voltage values of 300V and 100V respectively for the forward operation and the reverse operation on the converter capacitor C as in the prior art.

The reloading of the converter capacitor C to the two voltage values takes place, as in the prior art, resonantly over the time constants of the LC circuit, which are as large as possible can be selected to ensure a sufficiently good smoothing of the lamp operating current at the end.

The lamp itself is operated to the intermediate voltage level at 200VDC at blocking capacitor C _B.

In particular, by means of the switch Q_TRANS the lamp circuit and thus the lamp can be temporarily disconnected during the relatively long recharging processes of the converter capacitor C of the switching converter (more than 100 μs).

During the time of decoupling, the lamp can now either bypassing the slow time constant of the converter either to initiate the forward phase directly via the switch Q_COM_FW be placed on the DC link voltage of 400V, or be placed to initiate the reverse phase directly through the switch Q_COM_BW to GND.

At the initiation of the forward phase, in which the switch Q_COM_FW is switched to U _ZK = 400VDC, a strong lamp current in the forward direction is set in motion via the introduced ignition choke L_Zünd, whose height in addition to the prevailing lamp impedance of the size of the inductance of the ignition choke L_zünd and the duty cycle depends.

The forward commutation is understood to mean the commutation from the reverse phase to the forward phase, during which the lamp current has to be changed from a negative value to a positive value.

In the forward phase, in the present circuit arrangement, a positive current I _{L is conducted} via the switch Q_COM_FW starting from the intermediate circuit voltage U _ZK through the lamp 5 to U _CB at the blocking capacitor C _B

The switch-on duration of the forward commutation is selected such that the commutation current that arises is the For a short time the lamp heats up sufficiently so that the subsequent coupling back of the lamp to a converter capacitor C of the switching converter can be accomplished without danger of extinction.

Similarly, for the initiation of the reverse phase, in which the switch Q_COM_BW is turned on GND, also set via the introduced ignition choke a strong lamp current in the reverse direction in motion, whose height also in addition to the prevailing lamp impedance of the inductance of the ignition choke L_ZÜND and the Duty cycle depends.

Backward commutation is understood to mean the commutation from the forward phase to the backward phase at which the lamp current must be changed from a positive value to a negative value.

In the reverse phase in the present circuit arrangement via the switch Q_COM_BW a negative current I _L, starting from U _CB directed at blocking capacitor through the lamp 5 to ground.

Again, the switching duration of the Rückwärtskommutierung is chosen so that the adjusting commutation current heats the lamp sufficiently so that the subsequent feedback of the lamp to a converter capacitor C of the switching converter can be accomplished without a lamp extinguishing.

The duty cycle of the impressed current for the forward and backward commutation is chosen so that the adjusting commutation current sufficiently heats the electrodes of the lamp for a short time so that the subsequent feeding back of the lamp to a converter capacitor C of the switching converter can be accomplished without risking a lamp extinguishing.

If an ignition inductance of typically 1 mH is taken as a basis, the typical current run times for the lamp current commutation are approximately 20 μs and the switch-off or the reconnecting lamp to the switching converter output for the continuation of the stationary forward operation or reverse operation can take place after approximately 50 μs to 70 μs ,

Another advantage of the circuit arrangement according to the invention is that with the three decoupling switches Q_TRANS, Q_COM_FW and Q_COM_BW together with L_ZÜND for the lamp start also a resonant ignition sequence can continue to be realized.

For this purpose, to ignite the lamp, the lamp circuit via Q_TRANS decoupled from the Tiefsetzerschaltkonverter which can be realized with the two switches Q_COM_FW and Q_COM_BW via the Zünddrossel L_ZÜND and the ignition capacitor C_ZÜND a half-bridge operation for a resonant ignition sequence. Such circuit arrangements for the ignition of high-pressure discharge lamps are known in the prior art and are therefore not explained here.

After the lamp has ignited, the lamp can still continue to drive high-frequency via the half-bridge still disconnected in a warm-up phase as needed until coupling to the switching converter to record the rectangular operation is indicated.

Fig. 3a shows the relevant signals to explain the operation of the circuit arrangement according to the invention.

The top curve 1 shows the constant intermediate circuit voltage U _ZK in the amount of 400VDC, which is provided by the power factor correction circuit via C_PFC. Curve 2 shows the constant average voltage U _CB of 200VDC, which adjusts to the blocking capacitor C _B , towards which the lamp is operated.

About the buck converter switching converter C are alternately generated at intervals of 100Hz, the voltage values of 300V and 100V and provided at its converter capacitor C, with which the lamp is fed in the two phases of operation phase, forward operation and reverse operation.

The curve 3 shows this alternating voltage U _C on the capacitor C.

The coupled to the output of the switching converter lamp is operated to the constant 200V voltage across the blocking capacitor C _B and thus experiences the difference voltage U _L between C _B and C, which is inverted in each case at 100V in each phase of operation.

The curve 5 shows the self-adjusting lamp current I _L analog to the lamp voltage U _L at curve. 4

Fig. 3b shows a detailed switching sequence of the circuit arrangement according to the invention in the commutation in the forward mode. The curve 1 shows the switching state or the gate voltage UQ_TRANS of the coupling transistor Q_TRANS. At the beginning of the commutation process, the lamp circuit is disconnected via the coupling transistor Q_TRANS from the output of the switching converter for about 70 μs.

Curve 2 shows the switching state or the gate voltage UQ_COM_FW of the switching transistor Q_COM_FW. During commutation in forward mode, the lamp circuit is coupled via the switching transistor Q_COM_FW for approx. 70 μs to the intermediate circuit voltage of 400VDC, thus enabling a fast and strong lamp current in the forward direction.

The curve 3 shows the switching state or the gate voltage UQ_COM_BW of the switching transistor Q_COM_BW. During commutation in the forward mode, the switching transistor Q_COM_BW remains closed.

The curve 4 shows the pulsed lamp current I _L on the lamp for initiating the forward operation. The self-adjusting current pulse at the lamp is due to the coupling of the lamp circuit via the switching transistor Q_COM_FW to the positive intermediate circuit voltage of 400VDC, bypassing the current-braking lamp inductor L.

The curve 5 shows the pulse-shaped lamp current I _L in the forward commutation in higher temporal resolution.

The current direction at the lamp changes from -1A to + 2.5A within 20usec, which corresponds to a current commutation time of less than 20 μs.

The curve 6 shows the switching state or the gate voltage UQ_COM_FW of the switching transistor Q_COM_FW in higher temporal resolution.

The forward commutation process is terminated after 70 μs in which the switch Q_COM_FW is reopened, the lamp circuit is again coupled to the output capacitor C of the buck converter by the switch Q_COM_FW is closed again.

Fig. 3c shows a detailed switching sequence of the circuit arrangement according to the invention in the commutation in the reverse mode. The curve 1 shows the switching state or the gate voltage UQ_TRANS of the coupling transistor Q_TRANS. At the beginning of the commutation process, the lamp circuit is disconnected via the coupling transistor Q_TRANS from the output of the switching converter for about 70 μs.

Curve 2 shows the switching state or the gate voltage UQ_COM_FW of the switching transistor Q_COM_FW. During commutation in reverse operation, the switching transistor Q_COM_FW remains closed.

The curve 3 shows the switching state or the gate voltage UQ_COM_BW of the switching transistor Q_COM_BW. During the commutation in reverse operation, the lamp circuit is coupled via the switching transistor Q_COM_BW for about 70 microseconds to 0V = GND and thus allows a fast and strong lamp current in the reverse direction.

The curve 4 shows the pulse-shaped lamp current I _L for initiating the reverse operation. The current pulse to the lamp, which sets itself up to initiate the reverse operation, arises as a result of the coupling of the lamp circuit via the switching transistor Q_COM_BW to 0V = GND.

The curve 5 shows the pulse-shaped lamp current I _L in the reverse commutation in higher temporal resolution.

The current direction at the lamp changes from + 1A to -2.5A within 20usec, which corresponds to a current commutation time of less than 20 μs.

The curve 6 shows the switching state or the gate voltage UQ_COM_BW of the switching transistor Q_COM_BW in higher temporal resolution.

The backward commutation process is terminated after 70 μs in which the switch Q_COM_BW is reopened, with the lamp circuit again being coupled to the output capacitor C of the buck converter by closing the switch Q_COM_FW again.

Fig. 4 shows a simplified circuit arrangement, which in a ballast for rectangular operation only the fast backward commutation to initiate the stationary reverse phase is possible.

With the missing switch Q_COM_FW, this switching arrangement thus has one less switch and is less expensive to manufacture.

Claims (4)

1. Circuit arrangement for rapid commutation during squarewave operation of high-pressure discharge lamps, having:

   - a first half-bridge arrangement comprising a half-bridge (Q1_HIGH, Q2_LOW), which is connected to an intermediate-circuit voltage,

   - a lamp inductor (L), whose first connection is coupled to the centre point of the half-bridge,

   - a converter capacitor (C), whose first connection is coupled to the second connection of the lamp inductor and whose second connection is coupled to the reference potential of the first half-bridge arrangement,

   - a first switch (UQ_TRANS) for coupling the half-bridge arrangement to the lamp, wherein the second connection of the lamp inductor is coupled to a first connection of the first switch, and wherein the lamp can be uncoupled during the recharging operations of the converter capacitor by means of the first switch,

   - a block capacitor (C_B), which couples the lamp to the reference potential of the first half-bridge arrangement, characterized in that the circuit arrangement further has:

   - a second switch (Q_COM_FW) for performing a forward commutation, i.e. commutation from the reverse phase to the forward phase, in which the lamp current is changed from a negative value to a positive value, and for introducing a forward phase, wherein, in the forward phase, a positive current, starting from the intermediate-circuit voltage, is conducted through the lamp to the block capacitor,

   - a third switch (Q_COM_BW) for performing a reverse commutation, i.e. commutation from the forward phase to the reverse phase, in which the lamp current is changed from a positive value to a negative value, and for introducing a reverse phase, wherein, in the reverse phase, a negative current, starting from the voltage at the block capacitor, is conducted through the lamp to the reference potential of the first half-bridge arrangement, wherein the second switch (Q_COM_FW) and the third switch (Q_COM_BW) form a second half-bridge arrangement, which is connected in parallel with the first half-bridge arrangement, wherein the centre point of the second half-bridge arrangement is coupled to the centre point of the half-bridge of the first half-bridge arrangement by the circuit comprising the lamp inductor and the first switch, and wherein a second connection of the first switch is coupled to the centre point of the second half-bridge arrangement.
2. Circuit arrangement according to Claim 1, characterized in that the circuit arrangement furthermore has a starting inductance (L_START) and a starting capacitor (C_START).
3. Circuit arrangement according to Claim 1 or 2, characterized in that the circuit arrangement furthermore has a power factor correction circuit.
4. Method for operating a high-pressure discharge lamp (5) by means of a circuit arrangement according to one of Claims 1 to 3, characterized by the following steps:

   - decoupling the first half-bridge arrangement from the high-pressure discharge lamp (5) by opening the first switch (UQ_TRANS) prior to the introduction of commutation,

   - performing forward commutation by opening the third switch (Q_COM_BW) and by closing the second switch (Q_COM_FW) for introducing a forward phase, or performing reverse commutation by opening the second switch (Q_COM_FW) and by closing the third switch (Q_COM_BW) for introducing a reverse phase,

   - coupling the first half-bridge arrangement to the high-pressure discharge lamp (5) by closing the first switch (UQ_TRANS),

   - opening the second switch (Q_COM_FW) and the third switch (Q_COM_BW).

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