EP1443807B1 - Circuit and method for starting and operating discharge lamps - Google Patents

Abstract

The gas discharge lamps [LP1,LP2] are supplied by a system with a rectifier [D1-4] having an output coupled to an electronic pumping circuit [UN1,D7,D8] and a capacitor [C31]. An AC inverter [INV] connects with a resonator circuit [L3,C6,C7] having a regulator [CONT]. This operates to limit values from a switch.

Description

Technical area

The invention relates to a circuit arrangement according to the preamble of claim 1. It is in particular a circuit arrangement for the operation of discharge lamps, the so-called. Charge pumps for reducing mains harmonics.

State of the art

Circuit arrangements for starting and operating discharge lamps are used in electronic control gear for discharge lamps. The start of the discharge lamp is understood below to mean at least the ignition during an ignition phase. However, preheating of electrode filaments during a preheating phase of the ignition phase may also precede. If the operating devices are operated at a mains voltage, they are subject to relevant regulations regarding mains harmonics, eg. Eg IEC 1000-3-2. To comply with these regulations, circuit measures are required to reduce line harmonics. One such measure is the installation of so-called charge pumps. The advantage of charge pumps is the low circuit complexity, which is necessary for their realization.

• einen Gleichrichter zur Gleichrichtung der Netzspannung
• einen Hauptenergiespeicher
• einen Wechselrichter, der Energie aus dem Hauptenergiespeicher bezieht und an einem Wechselrichterausgang eine Wechselrichterspannung zur Verfügung stellt, die eine Wechselrichterfrequenz aufweist, die wesentlich höher ist als die Netzfrequenz
• ein Anpassnetzwerk, über das Entladungslampen mit dem Wechselrichterausgang gekoppelt werden können

Circuit arrangements for operating discharge lamps which are operated at a mains voltage generally contain the following elements:

• a rectifier for rectifying the mains voltage
• a main energy store
• an inverter that draws energy from the main energy storage and at an inverter output provides an inverter voltage having an inverter frequency that is substantially higher than the grid frequency
• a matching network, via which discharge lamps can be coupled to the inverter output

If the main energy store is charged directly from the rectifier, charge current peaks occur which lead to a violation of said regulations.

The topology of a charge pump includes that the rectifier is coupled to the main energy storage via an electronic pump switch. This creates a pump node between the rectifier and the electronic pump switch. The pump node is coupled to the changer output via a pump network. The pump network may include components that can be assigned to the matching network at the same time. The principle of the charge pump is that energy is taken from the mains voltage via the pump node during a period of use of the variable frequency converter and intermediately stored in the pump network. In the following half-period of the inverter frequency, the cached energy is supplied to the main energy storage via the electronic pump switch.

The mains voltage is therefore taken from energy in time with the inverter frequency. In general, the electronic ballast includes filter circuits that suppress spectral components of the mains current that are at or above the inverter frequency. The charge pump can be designed so that the harmonics of the mains current are so low that said regulations are met. The following documents describe in detail charge pumps for electronic control gear for discharge lamps:

Qian J., Lee F.C., Yamauchi T., "Analysis, Design and Experiments of High-Power-Factor Electronic Ballast", IEEE Transactions on Industry Applications, Vol. 3, May / June 1998

Qian J., Lee F.C., Yamauchi T.: "New Continuous Current Charge Pump Power Factor Correlation Electronic Ballast", IEEE Transactions on Industry Applications, Vol. 2, March / April 1999

In the document US Pat. No. 5,747,942 (Ranganath) an inverter for the operation of a discharge lamp is described. To ignite the discharge lamp is not used, the resonant circuit, which is used for coupling the discharge lamp to the inverter. Rather, the inverter includes a transformer that transforms the output voltage of the inverter to a value that is sufficient for the ignition of the discharge lamp. The voltage at the lamp before the ignition is independent of the inverter frequency for the described inverter.

Document EP 0 621 743 (Mattas) describes a circuit arrangement for operating a discharge lamp which contains a charge pump. In addition, it has a controller which effects a modulation of the inverter frequency with twice the mains frequency. Thus, the problem is solved to improve the crest factor of the lamp current, which is applied to the discharge lamp. This increases the life of the lamps.

The o. G. Matching network includes a resonant circuit, which essentially contains a resonant capacitor and a lamp choke. The resonant circuit has a resonant frequency which is at a natural frequency of the resonant circuit without attenuation of the resonant circuit.

To ignite the discharge lamp, the inverter is first operated at an inverter frequency that is above the natural frequency. In an ignition phase, the inverter frequency is lowered until, in the vicinity of the natural frequency, the resonant circuit generates a high voltage on the discharge lamp and ignites the discharge lamp.

The following problem occurs: Before the ignition of the discharge lamp, there is on the one hand in the circuit arrangement no significant energy consumers. On the other hand, the charge pump works and constantly deposits energy in the main energy storage. This creates an imbalance between absorbed and emitted energy of the circuitry. If the discharge lamp fails to ignite in time, this leads either to the destruction of the main energy storage or to the shutdown of the circuitry, if shutdown means are provided for it.

In the prior art, this leads to an optimization problem for the choice of the inverter frequency during the ignition phase: on the one hand, the time in which the said energy imbalance prevails should be short. This achieves a high ignition voltage, which requires an inverter frequency close to the natural frequency. On the other hand, the energy imbalance should be as low as possible so that the time to overload the main energy storage and thus the ignition phase can be as long as possible. This is desirable for a reliable ignition of the discharge lamp, but requires an inverter frequency that is as far above the natural frequency. The optimization task is complicated by the fact that external circumstances such. B. the ignition properties of the discharge lamp, ambient temperature and component tolerances have influence on it.

In the prior art there are two solutions to the problem: Either an unreliable ignition of the discharge lamp is accepted, or components such as main energy storage and lamp choke are oversized and thus expensive and bulky.

Presentation of the invention

It is an object of the present invention to provide a circuit arrangement for starting and operating discharge lamps according to the preamble of claim 1, which accomplishes a reliable and cost-effective ignition of the lamp.

This object is achieved by a circuit arrangement for starting and operating discharge lamps with the features of the preamble of claim 1 by the features of the characterizing part of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

Prior art EP 0 621 743 (Mattas) describes a regulator which has a first regulator input. This first regulator input is supplied with an electrical quantity which corresponds to a first operating variable of a discharge lamp operated on lamp terminals.

According to the invention, the controller has a second regulator input. The second regulator input is supplied with a second electrical quantity that corresponds to a second operating variable, which is a measure of the reactive energy oscillating in the resonant circuit. According to the invention, the second electrical variable is supplied to the second regulator input via a threshold value switch. In the event that the value of the second electrical quantity exceeds the threshold value of the threshold value, the inverter frequency is increased.

By selecting the threshold value and increasing the frequency, it is possible to set the maximum energy imbalance in the charge pump. According to the invention, a maximum ignition voltage can thus be achieved with optimum utilization of the components. For a reliable ignition of discharge lamps is also possible with low-cost components.

Brief description of the drawings

Figur 1

ein Blockschaltbild für eine crfindungsgcmäßc Schaltungsanordnung zum Start und Betrieb von Entladtingslampen,

Figur 2

ein Ausführungsbeispiel für eine erfindungsgemäße Schaltungsanordnung zum Start und Betrieb von Entladungslampen.

In the following, the invention will be explained in more detail with reference to Ausführungsbcispiclen with reference to drawings. Show it:

FIG. 1

1 is a block diagram of a circuit arrangement for starting and operating discharge lamps;

FIG. 2

An embodiment of a circuit arrangement according to the invention for the start and operation of discharge lamps.

In the following, resistors are denoted by the letter R, transistors by the letter T, coils by the letter L, amplifiers by the letter A, diodes by the letter D, node potentials by the letter N and capacitors by the letter C respectively followed by a number , Also, the same reference numerals are used throughout for the same and equivalent elements of the various embodiments.

Preferred embodiment of the invention

FIG. 1 shows a block diagram of a circuit arrangement according to the invention for starting and operating discharge lamps. At terminals J, a mains voltage from a mains voltage source of the circuit arrangement can be supplied. The mains voltage is first fed into a block FR. On the one hand, this block contains known means for filtering disturbances. On the other hand, this block contains a rectifier, which rectifies the mains voltage, which is an AC voltage. Usually, a full-wave rectifier is used in bridge circuit for this purpose. Important for the function of a charge pump realized in the circuit arrangement is the property of the rectifier that it does not allow any current that allows a flow of energy from the circuit arrangement to the mains voltage source.

The rectified mains voltage is supplied to an electronic pump switch UNI, wherein at the Verbindutigsstelle between rectifier FR and electronic pump switch UNI a pump node N1 is formed. In the simplest case, the electronic pump switch UNI consists of a pumping diode, which allows only one current flow, which flows from the pump node N1 to the pumping diode. But it is also possible any electronic switch, such. As a MOSFET to use for the electronic pump switch UNI, which fulfills the function of the pump diode.

The current through which the electronic pump switch UNI passes feeds a main photocycle storage STO. Most of the main energy storage STO is designed as an electrolytic capacitor. However, other types of capacitors are possible. In principle, the form of energy storage that is dual to the capacitor is also possible. In the dual case, the main energy storage STO is designed as a coil. Because of the lower cost and better efficiency, a capacitor is preferred as the main energy storage STO.

There are also versions of charge pumps with several so-called pumping branches. Several electronic pump switches UNI are connected in parallel. This results in several pump nodes N1. For mutual decoupling of Pump node, a diode is connected between each rectifier and pump node. An embodiment with two pump branches is shown in FIG.

The main energy storage STO provides its energy to an inverter INV. The inverter INV generates a variable, usually an AC voltage, which is supplied to a block designated MN and PN. MN denotes the function of the block as a matching network. With regard to this function, the block MN / PN can be connected to a discharge lamp L. PN denotes the function of the block as a pumping network. Regarding this function, the block MN / PN is connected to the pump node N1. The connecting line between the pump node N1 and the block MN / PN is provided in Figure 1 at both ends with an arrow. This is intended to indicate that energy flows alternately from the pump node N1 to the block MN / PN and back. The functions of the matching network and the pump network are summarized in the block MN / PN because embodiments of the invention are possible in which individual components can be assigned to both the one and the other function.

To control a desired first operating variable, a controller CONT is provided which acts on the inverter INV via a manipulated variable. This is a parameter of the output from the inverter change size, eg. As the operating frequency or the pulse width, so changed that a change of the first operating variable is counteracted. The first operating variable is supplied to a first input of the regulator via the connection B 1. The first operating size is a quantity that determines the operation of the lamp. Therefore, in FIG. 1, the connection B1 originates from the block for the discharge lamp L. For example, the first operating quantity is the lamp current or the lamp power. These quantities need not be detected directly on the discharge lamp L, but can also be found in the block MN / PN.

According to the controller CONT has a second input. A second operating variable is supplied to the second input via a threshold value switch TH. The second operating variable according to the invention is a measure of the reactive energy oscillating in a resonant circuit contained in the block MN / PN. The tap The second operating variable by means of the connection B2 therefore takes place at the block MN / PN. But it is also possible a measure of the said reactive energy from lamp operating variables, such. B. to win the lamp voltage.

To ignite the discharge lamp L reactive energy is built up in the resonant circuit. The reactive energy provides information about the energy imbalance of the charge pump and the load on components. If the second operating variable exceeds the threshold of the threshold switch, according to the invention the inverter CONT is influenced in such a way that the reactive energy does not increase any further. This can be done by raising the operating frequency of the inverter INV. The controller CONT may include an adder which adds the signals applied to the controller inputs. It must be ensured that the signal at the first controller input does not jam the signal at the second controller input. If the signal at the second controller input exceeds the signal at the first controller input, the signal at the second controller input must be the relevant controller signal.

FIG. 2 shows an exemplary embodiment of a switching gear arrangement according to the invention for starting and operating discharge lamps.

At the terminals J 1 and J2 a mains voltage can be connected. Via a filter consisting of two capacitors C1, C2 and two coils L1, L2, the mains voltage is fed to a full-bridge rectifier consisting of the diodes D1, D2, D3, D4. The full-bridge rectifier provides at its positive output, a node N21, the rectified mains voltage with respect to a reference node N0.

Via the diodes D5 and D6, the rectified mains voltage is fed to two pump nodes N22 and N23. The embodiment in Figure 2 therefore has two pump branches. In order to decouple the pump branches against each other, the diodes D5 and D6 are necessary. With only one pump branch, a pump node can be connected directly to the rectifier output, node 21. It should be noted, however, that the diodes used in the rectifier can switch fast enough to follow the inverter frequency. If this is not the case, must even with only one pump branch, a fast diode can be connected between rectifier output and pump node. In the exemplary embodiment in FIG. 2, the pump nodes are coupled to the positive output of the rectifier. The literature also discloses charge pump topologies in which pump nodes are coupled to the negative output of the rectifier.

From the pumping nodes N22 and N23, an electronic pump switch, which are implemented as diodes D7 and D8, respectively, leads to the node N24. Between N24 and N0 is the main energy storage, which is designed as an electrolytic capacitor C3, connected.

C3 feeds the inverter, which is designed as a half-bridge. However, there are also other transducer topologies such. B. flyback converter or full bridge used. Advantageously, a half-bridge is used for lamp powers between 5W and 300W, as it represents the most cost-effective topology.

In essence, the half-bridge consists of a series connection of two half-bridge transistors T1 and T2 and a series connection of two coupling capacitors C4 and C5. Both Scrienschaltungen are connected in parallel to C3. A connection node N25 of the half-bridge transistors and a connection node N26 of the coupling capacitors form the inverter output to which a rectangular wave converter voltage with an inverter frequency is applied.

Between N25 and a lamp voltage node N27, a lamp inductor L3 is connected. At N27, the terminal J3 is connected, to which in the exemplary embodiment, the series connection of two discharge lamps Lp1 and Lp2 is connected. However, the present invention is also practicable with one or more lamps. The current through the discharge lamps Lp1 and Lp2 flows through a terminal J8 through a winding W1 of a measuring transformer to the node N26. In essence, the inverter voltage is thus applied to a series connection of two discharge lamps Lp 1, Lp 2 and the lamp inductor L 3.

The current fed in J3 flows not only by the gas discharge of the discharge lamps Lp1, Lp2 but also by an outer coil of the first discharge lamp Lp1 to a port J4. From there, continue through a winding W4 of a heating transformer, further through a variable resistor R 1, further through a winding W3 of the measuring transformer to the terminal J7. At terminal J7, an outer coil of the second discharge lamp Lp2 is connected, the other end of which leads to terminal J8. Two inner coils of the discharge lamps Lp1 and Lp2 are connected to the winding W5 of the heating transformer through the terminals J5 and J6, respectively. By the arrangement described in this paragraph, the inverter voltage causes not only a current through the gas discharge of the discharge lamps Lp1, Lp2 but also a heating current through the outer coils and via the heating transformer also a heating current through the inner coils of the discharge lamps Lp1, Lp2. If only one discharge lamp is to be operated, then the heating transformer can be dispensed with.

The heating current is essentially required before the ignition of the discharge lamps Lp1, Lp2 during a preheating as preheating current for the preheating of the helices. The value of the heating current is essentially determined by the variable resistor R1. During the preheating phase, the value of R 1 is so low that a heating current predetermined by the lamp data is achieved. After the preheating phase, the value of R1 increases, so that in comparison to the current through the gas discharge of the discharge lamps Lp1, Lp2 negligible heating current flows. In the exemplary embodiment, R1 is implemented by a so-called PTC or PTC thermistor. This is a resistor which has a low resistance when cold. The heating current heats the PTC thermistor, increasing its resistance. R1 can also be realized by an electronic switch, which is closed in the preheat phase and then opened. In series with this switch, a resistor with a constant resistance value can be switched. This allows a quick transition from the preheating phase to the ignition phase.

As a result of the described arrangement for preheating the filaments, the resonant frequency of a resonant circuit described in the next section is lower than its natural frequency during the preheating phase due to damping. Advantageously, an inverter frequency is chosen during the preheating phase, which is below the natural frequency is located, so that there is a high heating current and thus a short preheating.

The lamp voltage node N27 is connected to the pump node N23 via a first resonance capacitor C6. Between N23 and N0 a second resonant capacitor C7 is connected. C6 and C7 form a resonant circuit with the lamp inductor L3. To determine the natural frequency of the resonant circuit, C6 and C7 are considered connected in series. The effective capacitance value of C6 and C7 with respect to the natural frequency is thus the quotient of the product and the sum of the capacitance values of C6 and C7. If the resonant circuit is excited near its natural frequency, an ignition voltage is produced across the lamps which leads to the ignition of the discharge lamps. After ignition, L3 acts together with C6 and C7 as a matching network, which transforms an output impedance of the inverter into an impedance necessary to operate the discharge lamps.

However, by combining C6 and C7 with pump node N23, the combination of L3, C6, and C7 not only acts as a resonant circuit and matching network, but also as a pumping network. If the potential at N23 is lower than the instantaneous mains voltage, the pumping network L3, C6, C7 draws energy from the mains voltage. If the potential at N23 exceeds the voltage at the main memory C3, the power absorbed by the mains voltage is output at C3. By choosing the ratio of the capacitance values of C6 and C7, the effect of network L3, C6, C7 as pumping network can be adjusted. The larger the capacitance value of C7, the lower the effect of the network L3, C6, C7 as the pump network.

Another pumping action starts from a capacitor C8, which is connected between N23 and the connection node N25 of the half-bridge transistors T1, T2. C8 not only acts as a pump network, but also fulfills the role of a snubber capacitor. Snubber capacitors are commonly known as a measure of switch relieving in inverters.

The pumping network for the second pump branch consists of the series connection of a pumping inductor L4 and a pumping capacitor C9. This pump network is connected between the connection node N25 of the half-bridge transistors T1, T2 and the pump node N22. In the present embodiment, two pump branches are used to divide the pumped energy among several components. For a more cost-effective dimensioning of the components is possible. This also gives a degree of freedom in the design of the dependence of the pumped energy on the operating parameters of the discharge lamps. However, the invention can also be realized with only one pump branch.

The half-bridge transistors T1, T2 are designed as a MOSFET. Other electronic switches can be used for this purpose. For driving the gates of T1 and T2, an integrated circuit IC1 is provided in the exemplary embodiment. IC1 in the present example is a circuit of International Rectifier type IR2153. Alternative circuits of this type are also available on the market; z. B. L6571 the company STM. The circuit IR2153 contains a so-called high-side driver with which the half-bridge transistor T1 can also be driven, although it has no connection at the reference potential N0. This requires a diode D10 and a capacitor C10.

The operating voltage supply of the ICl via the connection 1 of the ICl. In FIG. 2, a voltage source VCC is provided between terminal 1 of the IC1 and N0. There are generally several ways known how this voltage source VCC can be realized. In the simplest case, the IC can be supplied via a resistor from the rectified mains voltage.

In addition to the driver circuits for the half-bridge transistors, the IC1 includes an oscillator whose oscillation frequency can be adjusted via the terminals 2 and 3. The oscillation frequency of the oscillator corresponds to the inverter frequency. Between the terminals 2 and 3, a frequency-determining resistor R3 is connected. Between terminal 3 and N0, the series connection of a frequency-determining capacitor C11 and the emitter-collector path of a bipolar transistor T3 is connected. Parallel to the emitter-collector path of T3 is a diode D9 switched to allow C11 to be charged and discharged. A voltage between the base terminal of T3 and N0 can be used to set the inverter frequency and thus form a control loop variable. The base terminal of T3 is connected to a manipulated variable node N28. T3, ICl and their wiring can thus be understood as a regulator.

The functions of the IC 1 and its wiring can also be realized by any voltage or current controlled oscillator, which accomplishes the driving of the half-bridge transistors via driver circuits.

The control loop in the embodiment detects the controlled current as the flow through the gas discharge of the discharge lamps Lp1, Lp2. For this purpose, the measuring transformer has a winding W2. The winding sense in the measuring transformer is designed in such a way that the heating current in winding W3 is subtracted from a total current in winding W1, so that a current flows in winding W2 which is proportional to the current through the gas discharge of the discharge lamps Lp1, Lp2. A Vollbrückenglcichriclter formed by diodes D11, D12, D13 and D 14 rectifies the current through winding W2 and leads him via a low-impedance measuring resistor R4 to NO. The voltage drop across R4 is thus a measure of the current through the gas discharge of the discharge lamps Lp1, Lp2. Via a low pass for averaging, which is formed by a resistor R5 and a capacitor C13, the voltage drop at R4 reaches the input of a non-inverting measuring amplifier.

The measuring amplifier is realized in a known manner by an operational amplifier AMP and the resistors R6, R7 and R8. In the exemplary embodiment, a gain of the measuring amplifier of about 10 is set. In the event that the voltage drop at R4 has values that can be used directly as a manipulated variable, the amplifier can be omitted or by an impedance converter, such. As an emitter follower to be replaced.

The output of the measuring amplifier is connected via a diode D15 to the Stcllgrößcnknoten N28. Thus, the control circuit for controlling the current through the gas discharge of the discharge lamps Lp1, Lp2 is closed. Diode D15 is necessary so that the potential of N28 can be increased to a value that is above the value specified by the measuring amplifier. The anode of D15 represents a first regulator input.

The threshold value switch according to the invention is implemented in FIG. 2 by a varistor MOV. It is connected in series with a capacitor C12, a resistor R2 and a diode D17, which connects the lamp voltage node N27 to the manipulated variable node N28. The anode of D17 represents a second regulator input. N28 is connected to N0 via the parallel connection of a resistor R9 and a capacitor C14.

At N27 there is a voltage opposite N0, which is a measure of the reactive energy oscillating in the resonant circuit formed by L3, C6 and C7. If this voltage exceeds the threshold voltage of the varistor MOV, a current flows through R9 and C14 is charged. This raises the voltage at the manipulated variable node N28. This causes an increase in the Wechsehichterfrequenz and the resonant circuit oscillating reactive energy is reduced because the Wechsclrichterfrequenz further from the natural frequency of the resonant circuit.

Between N0 and the junction of R2 and D17, diode D16 is connected. This is used in conjunction with C12 to N28, the sum of positive and negative amplitude of the voltage applied, which allows the varistor MOV. Instead of the varistor MOV can find any other threshold value use, as it is z. B. can be constructed by zener diodes or suppressor diodes. The threshold value of the varistor MOV is 250Veff in the application example. A higher value allows more reactive energy in the resonant circuit, which leads to a higher ignition voltage at the discharge lamps Lp1, Lp2, but also to a higher load on components. A desired optimum can thus be set via the threshold value of the varistor MOV.

The value of the resistor R2 influences the strength of the effect of the intervention according to the invention on the control loop at the manipulated variable node N28. It is also advantageous a non-linear relationship between the voltage at the manipulated variable node N28 and the inverter frequency. This non-linear relationship is realized in the application example by the non-linear characteristic of T3. In addition, it is influenced by the dependence of the frequency of the oscillator in IC1 on the voltage at terminal 3 of the ICl. A strong increase in the voltage at N27 leads to a disproportionate increase in the inverter frequency due to the non-linearity, whereby an overload of components such. B. the voltage load of C3 or the current load of T 1 and T2, is prevented.

Instead of the voltage and the current in the resonant circuit could be used as a measure of the reactive energy oscillating in the resonant circuit. For example, an additional winding on L3 could serve this purpose.

Claims (16)

1. Circuit arrangement for starting and operating discharge lamps (L, Lp1, Lp2), with the following features:

   • a first and a second line terminal (J1, J2) for the connection of a line voltage,

   • a rectifier (D1, D2, D3, D4), the rectifier input of which is coupled to the line terminals and at the rectifier output (N21) of which the rectified line voltage is present,

   • the rectifier output (N21) is coupled to an electronic pumping switch (UNI, D7, D8), with the effect of forming a first pumping node (N1, N23) at the electronic pumping switch (UNI, D7, D8),

   • the side of the electronic pumping switch facing away from the rectifier output (N21) is coupled to a main energy store (C3),

   • the main energy store (C3) supplies energy to an inverter (INV), which produces at an inverter output (N25, N26) an inverter voltage which has an inverter frequency that is much higher than the frequency of the line voltage,

   • the inverter output (N25) is coupled to the first pumping node (N1, N23) via a pumping network (PN, L3, C6, C7),

   • discharge lamps (L, Lp1, Lp2) can be connected by lamp terminals (J3-J6) to the inverter output (N25) via a matching network (MN, L3, C6, C7), which has a resonant circuit (L3, C6, C7) with a natural frequency,

   • a controller (CONT), the controller output of which outputs an actuating signal, the controller output being coupled to the inverter (INV) in such a way that the actuating signal influences the inverter frequency,

   • a first controller input (B1), into which there is fed a first electrical variable, which corresponds to a first operating variable,

   characterized in that
   the controller has a second controller input, into which there is fed via a threshold switch (TH, MOV), a second electrical variable, which corresponds to a second operating variable (B2), which is a measure of the reactive energy that resonates in the resonant circuit (L3, C6, C7), the value of the second electrical variable bringing about a greater value of the inverter frequency if the threshold value of the threshold switch (TH, MOV) is exceeded.
2. Circuit arrangement according to claim 1, characterized in that the controller includes an adder, which adds the electrical variables from the first and second controller inputs.
3. Circuit arrangement according to claim 1, characterized in that the electronic pumping switch (UNI) is realized by a first pumping diode (D7), which is polarized in such a way that energy can be fed via the first pumping diode (D7) to the main energy store (C3).
4. Circuit arrangement according to claim 3, characterized in that the rectifier output (N21) is connected via a second pumping diode (D5) to the first pumping node (N23), the second pumping diode (D5) being polarized in such a way that energy can be drawn from the rectifier via the second pumping diode.
5. Circuit arrangement according to claim 4, characterized in that the rectifier output (N21) is coupled via the series connection of a third pumping diode (D6) and a fourth pumping diode (D8) to the main energy store (C3), with the effect of forming at the connecting point of the third pumping diode (D6) and the fourth pumping diode (D8) a second pumping node (N22), into which part of the energy which the rectifier output (N25) delivers is fed.
6. Circuit arrangement according to claim 1 or 5, characterized in that the first pumping node (N23) or the second pumping (N22) is connected via a series connection of a pumping inductor (L4) and a pumping capacitor (C9) to the inverter output (N25).
7. Circuit arrangement according to claim 1 or 5, characterized in that the inverter output (N25) is connected via a lamp inductor (L3) to a terminal (J3) for a discharge lamp (Lp1), with the effect of forming at this terminal a lamp voltage node (N27), which is connected via a resonant capacitor (C6) to the first pumping node (N23) or the second pumping node (N22).
8. Circuit arrangement according to claim 1 or 5, characterized in that the current is fed through a discharge lamp into the first or the second pumping node.
9. Circuit arrangement according to claim 1, characterized in that the inverter output (N25) is connected via a lamp inductor (L3) to a terminal for a discharge lamp (J3), with the effect of forming at this terminal a lamp voltage node (N27), at which the second electrical operating variable (B2) is tapped.
10. Circuit arrangement according to claim 9, characterized in that the threshold switch (TH) is realized by a varistor (MOV) and is connected in series with a capacitor (C12) and a resistor (R2).
11. Circuit arrangement according to claim 1, characterized in that the first operating variable (B1) is the current through an operated discharge lamp (Lp1, Lp2).
12. Circuit arrangement according to claim 11, characterized in that a variable resistor (R1) closes a heating circuit, which brings about a heating current, driven by the inverter voltage, through electrode filaments of a connected discharge lamp (Lp1, Lp2).
13. Circuit arrangement according to claim 12, characterized in that the variable resistor (R1) is a PTC thermistor.
14. Circuit arrangement according to claim 12, characterized in that the variable resistor (R1) is an electronic switch.
15. Circuit arrangement according to claim 1, characterized in that the controller has a nonlinear characteristic.
16. Method for starting and operating discharge lamps with a circuit arrangement according to claim 1, characterized by the following steps:

    • damping the resonant circuit (L3, C6, C7) via filaments of connected discharge lamps,

    • setting an inverter frequency that lies below the natural frequency,

    • removal of the damping of the resonant circuit,

    • recording of the second operating variable (B2),

    • comparison of the second operating variable (B2) with a prescribed threshold value,

    • increasing the inverter frequency in the event that the second operating variable (B2) exceeds the threshold value.

Images