NO178910B - Circuit arrangement and method of operation (and ignition) of a gas discharge lamp - Google Patents

Abstract

A process for controlling the brightness (dimming) of a gas-discharge lamp (GE) which is located in a series resonant circuit (L1, C1) connected to a rectifier-inverter combination (10, 20), by varying the frequency (f) and the duty ratio (D, d) of the output alternating variable (uw) generated by the inverter and supplied to the gas-discharge lamp and to the series-resonant circuit (X; L1, C1, GE). The lamp (GE) is operated in a frequency range in which the dependency of the lamp power (Pab) on the frequency (f) of the output alternating variable (uw) can be represented by the duty ratio (D, d) as a parameter as a family of characteristic curves (K1, K2, K3, ...), each of which runs in the manner of a bell-shaped curve starting from a maximum value and reducing to form a point of inversion. The maximum value of the individual characteristic curves (K1, K2, K3, ...) of the family becomes smaller as the duty ratio (d1, d2, d3, ...) associated with these characteristic curves (K1, K2, K3, ...) as a parameter becomes smaller. The process is intended to be designed such that the brightness of a gas-discharge lamp can be varied in a stable manner without flicker. This is achieved in that the frequency (f) and the duty ratio (D, d) are in each case selected such that the operating point (B1, B2, B3, ...), with at least two characteristic curves selected or available for a specific lamp power (Pab), in each case coming to rest on that characteristic curve which has the lower gradient at this lamp power (brightness). <IMAGE>

Description

The invention relates to a circuit device for operation, and in particular for ignition, of a gas discharge lamp as stated in the preamble to patent claim 1. It also relates to a homonymous method as stated in the preamble to patent claim 13.

It is known to use a so-called electronic drive circuit (EVG) which emits a high-frequency alternating voltage to the gas discharge lamps or fluorescent tubes. With the help of electronic ballasts, it is possible to preheat, operate and light the fluorescent lamps in a gentle way. The lamps' efficiency is increased and operation with reduced lamp power (dimming) becomes possible.

From EP 0059064, a method and an electronic drive circuit for operating and lighting gas discharge lamps are known. An externally controlled transistorised inverter is inserted there which feeds a directly heated gas discharge lamp via a series resonant circuit. Every now and then one of the connections on the oppositely arranged heating coils or filaments is connected to the inverter by means of a parallel heating capacitor. The load voltage, respectively the inverter output voltage u,^, is supplied to the remaining filament connections across the series resonant circuit. When shifting the output frequency of the self-controlled inverter to a so-called glow frequency of approx. 50 kHz, the resistance of the parallel heating capacitor becomes so low-resistive that sufficient pre-heating of the filaments which are to dampen the fluorescent lamp's load circuit becomes possible. If the output frequency of the remote-controlled inverter is now shifted in the direction of the resonant frequency of the series-oscillating circuit located in the load circuit, which output frequency in the above-mentioned literature site is 28kHz, then both ignition of the preheated gas discharge lamp and after ignition, its nominal operation (with nominal power) and dimming effect possible (with reduced light power).

Also from EP 127,101 it is known to supply a discharge lamp with a higher frequency during ignition than during subsequent operation.

From DE-OS 33 38 464, an electronic drive circuit with firstly a self-oscillating inverter, and secondly an externally controlled inverter is known. An output branch of the inverter having MOS-FET transistors feeds in both cases a series resonant load circuit which is formed by a capacitance and a parallel connection where each branch has a gas discharge lamp and inductance connected in series. The filaments of the parallel-connected gas discharge lamps are each connected via a parallel heating capacitor so that by variation of the output frequency and/or of the pulse ratio or duty cycle of the output alternating voltage from the inverter arranged in the ECG, a preheating of the filaments becomes possible. The variation of the pulse conditions also gives the advantage that the frequency spectrum of the output alternating voltage is shifted up towards higher frequency portions, so that a better heating (less reactance in the parallel heating capacitor) of the gas discharge lamp in dimming mode is achieved.

It is an object of the invention to provide an improved circuit arrangement for operation, in particular for ignition, of a gas discharge lamp according to the introductory part of patent claim 1 (cold start). Likewise, it is an object of the invention to specify a method for operating, and in particular for lighting, an unheated gas discharge lamp according to the introductory part of patent claim 13, which method makes gentle operation, as well as safe and regulated lighting of the lamp possible - despite a cold start .

The first-mentioned purpose is solved by means of the combination of features specified in the characterizing part of patent claim 1. Likewise, the second purpose is solved by means of the combination of features specified in the characterizing part of patent claim 13.

A first purpose of the invention is to make it possible to use gas discharge lamps also in special applications such as e.g. in explosion-protected areas (EX areas).

For this purpose, pre-heating of the electrodes or windings must be waived, because in such working areas heat sources or especially incandescent lamps such as e.g. could trigger explosions, is used. Likewise, spark formations and electric arcs when switching with e.g. mechanical switches are also excluded. Because of regulations, it is therefore necessary - precisely because of the risk of sparking - to limit the maximum ignition voltage for gas discharge lamps with an unheated start. On the other hand, there are regulations that an initiated glow discharge that occurs due to ignition voltage in an unheated gas discharge lamp (tube) must not exceed a prescribed duration.

For this reason, edge values (maximum values) are currently set, i.e. <U>Zmax=1.5kV for the ignition voltage and T2=100ms as ignition duration. Both of these edge values form limit values that must not be exceeded under any circumstances. But in each case a safe ignition (start) must be guaranteed. This could be achieved with arbitrarily higher and arbitrarily longer applied ignition voltage Uz. On the other hand, cold-start gas discharge lamps must be able to be started and operated as gently as gas discharge lamps with incandescent cathodes. An arbitrarily long imposed and arbitrarily high ignition voltage is thus firstly against the regulations and secondly unfavorable for the tube.

The effect according to the invention is now that both of these edge values are fully utilized, i.e. that the function of the ignition alternating voltage's maximum values (effective values) proceeds for 100 ms approximately constantly at the maximum value of 1.5kv, and then, after ignition has occurred, the voltage drops steeply to the required operating voltage. It is clear that the edge values cannot be exceeded, but according to the invention it is both possible and reasonable to shorten the ignition duration (ignition phase), i.e. that the ignition voltage is set back to the operating voltage value at the moment the glow discharge has developed into a normal discharge, before the discharge of the 100 ms.

The purpose, i.e. to limit the time and amplitude of the ignition voltage, is achieved by the method according to patent claim 13 and/or by a circuit device according to patent claim 1, by regulating the ignition voltage. Variation of the frequency and/or of the pulse conditions or duty cycle of an output alternating voltage makes it possible to "drive purposefully forward" to each of the two resonant frequencies f± and f0 of the series resonant circuit, and by means of the distance of the output frequency from the relevant resonant frequency to make both the ignition voltage and the operating voltage adjustable based on their amplitude (self-controlled inverter). At the same time, the tube voltage's amplitude progression over time can be freely predetermined using the frequency and operating cycle variation (external controlled inverter).

One frequency fx of the two resonance frequencies lies clearly above the other resonance frequency f0. For ignition, the resonant load circuit is operated in the vicinity of the first resonant frequency flt so that the ignition voltage which leads to the ignition of a glow discharge in the tube's gas content occurs on the capacitor which is connected in parallel with the tube. For rapid transmission of this initiated glow discharge, the output impedance of the inductive part of the series resonant circuit in series with the tube is chosen low. According to the invention, lowering the throttle value L2 leads to a very rapid increase in load current, the ignition phase is transferred to the operating phase in the shortest possible time. A greatly reduced throttle value now leads in the operating phase to an excessively high lamp current ILeff, the nominal current IN and thus the nominal power of the lamp is exceeded - -, the service life decreases. As the nominal operating frequency fN is largely predetermined due to the nominal loss effect of the feeding alternating voltage generator, there is only negligible leeway for changing the discharge lamp's operating current ILeff when changing fN. In other words, firstly, the throttle is selected as low as possible (faster current increase) and secondly, as high as necessary (limitation of the operating current).

According to a further advantageous further development, an equalization circuit device is arranged, which after a predetermined time varies the frequency and/or duty cycle of the output alternating voltage which is emitted from the alternating voltage generator in such a way that the tube in stationary operation is supplied with exactly the nominal power PN. This intervention, which is carried out after the ignition phase, is carried out by slightly increasing the frequency and/or lowering the alternating voltage generator's output alternating voltage. The main frequency components of the output alternating voltage are thereby removed (shifted) by a predetermined value from the second resonance frequency f0 which the nominal frequency fN is located near, so that the impedance of the load circuit is increased and both the load current ILeff and the lamp power are reduced.

Operation of the lamp in the stationary operating phase with reduced nominal power (dimming operation) is just as possible as operation at full brightness (nominal operation). The transition to dimming operation (from nominal operation) or the transition from short-term operation with increased power supply to nominal operation can intersect in time or can be clearly distant from each other in terms of time.

If a self-controlled inverter is arranged as an alternating voltage generator, then according to the invention the ignition voltage is adjustable by means of tuning the inverter (emitter resistors, feedback connections) and by tuning the load circuit, the steep rise of the load current after completion of the flash discharge is also adjustable.

If an externally controlled inverter is used as an AC voltage generator, the output frequency of this AC voltage generator can be set independently of the load current by means of a control value. The output frequency's pulse ratio or duty cycle can also be varied independently of the load current. The predetermined time-dependent frequency profile causes in the resonant load circuit with the two different resonant frequencies f0 and f2 both the ignition voltage increase and the nominal current IN which can now be set considerably more precisely. After complete ignition, the frequency profile can be shifted steeply from the ignition frequency fz («f2) in the direction towards the nominal operating frequency fN. The faster the frequency change occurs, the steeper the current rise in the inductance to be measured.

According to an appropriate further development, the frequency and/or duty cycle of the externally controlled inverter is varied depending on the lamp operating state. This corresponds to an automatic self-adjustment of the frequency and/or the alternating voltage generator's operating cycle or pulse ratio. In the following, the invention will be explained in more detail in connection with design examples.

The drawings show:

Fig. 1 an equivalent diagram with an EVG and an embodiment example of a resonant load circuit according to the invention and which contains a gas discharge lamp, Fig. 2 a detailed connection core of the output circuit of an embodiment example of an inverter in the EVG according to the invention, with the controllable element T4 which is explained in more detail in a previous application, Fig. 3 switch types that can be inserted as switches SltS2 on

Fig. 2,

Fig. 4a, 4b, and 4c

time-corresponding diagrams for frequency progression, load current progression and load voltage progression for a circuit arrangement according to Fig. 1 or 2, Fig. 4d section enlargement of Fig. 4c, with an ignition voltage progression for the gas discharge lamp in Fig. 1, when the frequency and load current progressions occur as shown in Fig. 4a ,4b. Fig. 1 shows an exemplary embodiment of a lamp-load circuit that can be connected to an EVG 20. The EVG 20, which contains an alternating voltage generator, is fed by a direct voltage source U0, which is either formed by a battery or a direct current source or by a rectified alternating voltage source with smoothing capacitor. The load circuit has a series circuit consisting of a cap capacitance Clf, a cap capacitance C0 and an inductance Lx. This series resonant circuit is connected to the two output connections of EVG 20. An ordinary gas discharge lamp GE is with its opposite filaments or electrodes connected in parallel with the resonant circuit L-^, C^, C2 capacitor C1. As no filament current occurs, the filaments are short-circuited. They serve as clean electrodes arranged at both ends of the GE lamp. Cold start lamps that only have electrodes without filaments can also be used.

When the gas discharge lamp GE is in the active state, the series connection of C0 and C-^ serves as the resonant load circuit capacitance. The inductance Lx is clearly reduced compared to normal inductance values, so that after lighting the tube GE, a faster current rise in the load circuit is possible. During operation of the tube, i.e. after it has been ignited and after a steady state of operation has been achieved, C2 is practically ineffective. The inherent negative voltage/current characteristic (arcing characteristic) in a

gas discharge tube, dampens the oscillating circuit so that when the tube is operated, the cover capacitance C0 now largely determines only together with the inductance L-^ the resonant frequency of the load circuit. In the design example, the two resonance frequencies f1 and f0 differ by approximately a factor of 2. fx (operating in the original state) is approx. 42kHz, f0 (the resonant frequency that is active in the tube's stationary operation) is approx. 23 kHz. To ignite the tube without preheating its electrodes or windings, the EVG emits an alternating voltage uw with a frequency that is slightly above f1=42kHz (in the present case at fz=45kHz). Thereby, a greatly increased resonance voltage Uz occurs on the capacitor C-1, which leads to the initiation of a glow discharge in the tube. The glow discharge, which develops into a stable normal discharge, loads the EVG more strongly and dampens the parallel capacitor Clt so that the resonance frequency of the now changed load circuit changes.

The design example was dimensioned with the following values: C1=15nF, C0=33nF and L1=1.4mH.

Here, a distinction must be made between two different cases. If a self-controlled inverter is inserted in the EVG 20, then the frequency uw of the output alternating voltage is independent of the load current, and the frequency either depends on time or depends on the recorded operating state in the tube, predetermined or controlled. The frequency is lowered so much that it is still above the second resonance frequency f0=23kHz and the tube simultaneously takes up nominal current/nominal voltage. In this way, a nominal operating frequency of fN=35kHz is set. Reducing the throttle value makes a rapid current increase possible by lowering the frequency and thereby a rapid transfer of the glow discharge to a stable normal discharge.

If, in the second case, a self-controlled inverter is inserted in the EVG 20, then the frequency with which the self-controlled inverter oscillates cannot be predetermined completely freely. IdR oscillates a self-controlled inverter at the resonant frequency predetermined by the load circuit. The oscillation frequency can still be set within certain limits, as internal parameters such as emitter resistors or feedback parameters (layout of the feedback amplifier) are adapted accordingly. In this case, the ignition of the tube also begins with a frequency that lies slightly above the upper resonance frequency F1=42kHz. Ignition of the tube leads to the change in the load circuit that is explained in more detail above, and then to a changed resonant frequency. The self-controlled inverter adapts the frequency to its output AC voltage uw accordingly. In addition, the self-controlled inverter is dependent on the load current, so that after the glow discharge's effort and at the reduced throttle value, the result is a faster achievement of current rise in the load circuit and at the same time a sharp lowering of the output alternating voltage uw frequency is achieved. The self-controlled inverter achieves a stationary operating state at a frequency of approx. 28 kHz. This is closer to the operating resonance frequency of f0=2 3kHz. In this operating state, the tube emits an increased power P2 in relation to the nominal lamp power PN. In the design example, the power increase is approximately +25%. For a short while, this increased output is tolerated; however, if operated over time, it can lead to a shortened service life for the pipe. As it is explained in more detail in Fig. 2, after a predetermined time T5, an equalizing circuit device intervenes, via a controllable device T4, in such a way into the output circuit of the self-controlled inverter, that the frequency of the output alternating voltage is corrected upwards, so that also the self-controlled inverter has the possibility of stationary operation of the tube with nominal power PN. From now on, the output is also

the alternating voltage frequency of fN=35kHz.

To this, it can be noted that the predetermined time span T5 can be regulated to a large extent, so that the frequency increase of the output alternating voltage can, for example, already occur during the transition from the flash discharge to the stationary discharge. Likewise, the frequency-correcting intervention can only take place at a clearly increased time span T5, when the tube has already been operated for a certain time with increased power output Px. This can be predetermined depending on the ambient temperature or the ambient conditions.

Fig. 2 shows a detailed diagram of the output circuit of the inverter in the EVG 20, and schematically the load circuit Llt Clf C0, GE as already explained in connection with Fig. 1. The output circuit of the inverter shows the series connection of the circuit breaker Sx and the circuit breaker S2, which are connected in series (row) between the two + connections of a direct voltage supply U0 (the one in Fig. 1). Between the two switches Sx, S2, the frequency and duty cycle variable output voltage uw is supplied to the resonant load circuit.

The term circuit breaker applies to all switch types that can be switched on and off with control inputs (gate, base, optical fiber control electrode). This happens with a significantly higher frequency than the mains frequency, e.g. higher than the hearing limit (F>20kHz). Switch types that can be inserted are shown in Fig. 3. SlfS2 can be power transistors, MOS-FETs or GT0s that can be turned off. Other switch types can also be used.

A resistor R1,R2 is connected in series with each switch SX,S2 in Fig. 2. These resistors R2,R2 have different resistance values. In the embodiment, the resistor R2 connected to the negative supply connection - from U0 is chosen larger.

The different resistances Rx and R2 are the reason for the lack of symmetry in the two branches of the inverter output branch. This asymmetry can also be found in different switch types Sx and S2. The design in the design example with different emitter resistors has the advantage that the swing ratio of the self-controlled inverter can be influenced by varying the resistors R1 and R2. Thereby, as described, it becomes possible to predetermine the oscillation frequency with which the self-controlled inverter changes (oscillates) in a predetermined resonant load circuit (its resonance frequency). In this way, due to the emitter resistances, a predetermined ignition frequency fz, which causes a predetermined ignition voltage Uz, can be set at known resonance frequencies for the load circuit.

In the design example, the resonant load circuit is connected between the positive connection + of the supply direct voltage U0 and the intermediate branch on the output branch of the inverter. Correspondingly, however, the output circuit can be connected between the inverter's intermediate branch output connection and the negative supply connection - from U0. This is important when changing the pulse ratio or duty cycle d from uw(t). Parallel to the larger resistance, here R2, is an adjustable element T4, here a MOS-FET, which can vary its resistance, connected with its drain and source connection. The dimensioning of R2 takes place in such a way that the resistance value of the parallel connection of R2 and the fully connected and adjustable element T4 which still works with its transistor-dependent switching resistance RDson' exactly corresponds to the resistance value R-^ (symmetry).

The adjustable element T4 is controlled by an equalization circuit device R5,C5,D1,R4,R3 with a control signal u-^ The equalization circuit device is connected to the supply direct voltage UQ. The equalization circuit device regulates the adjustable element T4 in a time-dependent manner from the conducting state (RDSon) to the blocking state (RDS very high). Thus, a frequency and duty cycle variation (switch-on duration to switch-off duration) occurs of the output voltage uw(t) to the inverter or to the ECG 20

If the upper and lower sub-branches of the inverter output branch in the tube's GE ignition moment are symmetrical or essentially symmetrical, i.e. the adjustable element T4 conducts, then the self-controlled inverter oscillates at its highest frequency. After ignition of the tube GE and after the glow discharge has transitioned into a stationary nominal discharge, the time-dependent adjustable element T4, controlled by the control signal u1, engages; into the existing symmetry condition. T4 is transferred to the blocked state. Thus a complete or partial asymmetry is produced by the preselected resistors and R2. Firstly, the already previously occurring change of the effective resonant frequency of the resonant load circuit C0, and GE, and secondly, the previously selectable asymmetry from Rx and R2 at blocking T4 also determines the effective oscillation frequency of the inverter. This frequency is called the nominal operating frequency fN and causes exactly the production of the nominal power PN in the tube GE. The adjustment of the frequency or the pulse ratio or the duty cycle by means of the regulating intervention of the element T4 thus lowers the accumulated increased lamp power Pi at the negligible choke inductance L, 1 and thus extends the life of the tube.

The oscillation frequency of the self-controlled inverter changes when T4 is switched on from approx. 28kHz (here approx. 1.2xlPN is emitted from the tube) to approx. 35kHz (here the nominal power PN is emitted from the tube).

Equalization of the symmetry or of the desired asymmetry can further be adjusted by limiting the intervention to T4. This is, on the one hand, possible by connecting an additional resistance in series to T4f so that the firing frequency of the self-oscillating inverter at through-connected element T4 is adjustable. Secondly, it is possible not to transfer T4 all the way to the blocking state, so that in the operating state of the GE tube there is an additional possibility of changing the frequency f and the output alternating voltage uw pulse ratio d. This results in a variation in the brightness of the lamp GE , consequently dimming the lamp is possible.

Out equalizing circuit device R5, C5, Dx, R4, <R>3 emits a control signal u1 to the controllable element T4. In the embodiment example, this control signal is mostly the differentiated supply voltage signal U0. The equalization circuit device has, on the one hand, the described differentiating character, for setting the time span T5 (over R5 and C5), and for controlling the controllable element T4. On the other hand, the equalizing circuit device has a limiting character, because only a predetermined part of the supply voltage is differentiated. The supply voltage is usually approx. 300V, the control signal u2 which is supplied to the controllable element T4, is of the order of magnitude approx. 5V...15V. A limitation or division of the supply voltage is therefore necessary for direct control of the controllable element. In the embodiment example, the differentiation of the supply voltage signal is the possible variant which performs a time-dependent preselection of the controlling and equalizing intervention in the symmetry condition of the inverter's output branch. It is still just as impossible to shape this intervention depending on the operating condition or the load current. In the same way as the arrangement of a self-controlled inverter in the design example in Figures 1 and 2, an externally controlled inverter can be arranged. The frequency f and the pulse ratio d to the output alternating voltage uw can be arbitrarily predetermined from such an inverter.

According to the invention, "arbitrary" can mean an arbitrary dependence, e.g. lamp type dependent or load current dependent, or a fixed time dependent preselected frequency profile. An arbitrary pre-selection can still just as well mean that the frequency and duty cycle variation can be pre-determined by means of a potentiometer whose variable output voltage controls the controllable element T4 so that dimming operation is possible. The superimposition of the dimming control signal by means of a potentiometer or control voltage and the control signal of the adjustment circuit device u2 can combine the manual (or automatic) brightness regulation with the automatic course of the ignition sequence in the tube.

The mode of action for the time-dependent frequency shift over the controllable element T4 is composed as follows: 1. After switching on the supply voltage U0, there is a constant voltage of, for example, 15V on zener diode Dl. The differentiation link C5, R5 controls for a predetermined time (T5«R5xC5) the gate connection to the control element T4 forward with positive voltage ulf so that this conducts and in the emitter respect. the source circuit of S2 works the parallel connection of R2 and RDson* The inverter is symmetrical and emits an output voltage with a frequency that is close to the resonant frequency f2 from L-^C-l and C2=C1xC0/C1+C0. Preferably, this resonant circuit is operated inductively, i.e. with a frequency that is negligible

above <f>1.

2. The glow discharge and the subsequent time-limited normal discharge are formed in the tube GE. This happens in

matching with the inverter setting.

3. After the time T5, the differentiation link controls the control element T4 to the blocking state, so that the emitter-enh. v. the source resistance from S2 is increased. This leads to a worse pulse ratio and to an increase in the frequency of the self-controlled (or externally controlled)

the inverter. The output frequency from uw is increased. 4. The frequency shift to a higher frequency than the lower resonance frequency f0 causes a lowering of the lamp current IL, and the inverter 20 is controlled towards a nominal resp. a dimming working point (operating point). The tube emits the nominal power PN or a correspondingly reduced power (dimming operation).

In the following, the time diagrams in Figures 4a-4d will be briefly explained in more detail. The diagrams according to figures 4a, 4b and 4c correspond in time, in the upper diagram the time-dependent frequency f(t) is shown, in the middle diagram the lamp current IL obtained in the load circuit depending on the time and the frequency shown in the upper diagram. The lower diagram shows the voltage progression on the tube GE.

Based on a predetermined ignition frequency fz (approx. 45kHz), the high ignition voltage Uz of a maximum of 1.5kV, which is shown in figure 4c, is formed due to the undamped resonant load circuit. then a glow discharge is initiated in the tube GE, which glow discharge due to the low selected choke inductance L2 very quickly further develops into a normal discharge. This can be read from the steep current rise in the diagram in Figure 4b. At the same time as the rapid current rise in the diagram on figure 4b, the frequency drops in the diagram on figure 4a. Due to the steep current rise and the rapid lowering of the frequency, the lamp is brought out of the glow discharge state as quickly as possible and then gently transferred to the stationary discharge state. The lamp voltage in the diagram in Figure 4c decreases in relation to the gas discharge lamp's hyperbolic current/voltage characteristic.

Due to the negligible inductance, the frequency of the inverter output voltage, which is below the nominal frequency fN, causes an increased lamp power of 1.2 times the nominal current, as can be seen in Figure 4b. In order to reduce the increased lamp current to IN (or to reduced lamp current in dimming mode), the frequency f of the output alternating voltage uw is increased by means of the equalizing circuit arrangement and the controllable element T4 (in figure 2). The duty cycle d of the same output alternating voltage uw is also reduced. This shows for the frequency f with a solid line to the right after the "saddle" the again ascending diagram section on figvir 4a. Thereby there is a lowering of the nominal current in Figure 4b and an increase in the lamp voltage in Figure 4c.

In the design example of the self-controlled inverter according to Figure 2, both the frequency f. and the operating cycle d change; when inserting a self-controlled inverter or when changing the circuit of the self-controlled inverter, it is also possible within the invention to change only the frequency or only the operating cycle.

The insertion point for the equalization circuit device is drawn with change options for T5 on diagrams 4a, 4b and 4c. T5 is determined by the differentiating part R5/C5 of the equalization circuit. By making R5 larger, i.e. increasing the time constant T5, the controlling switch-on T4 is shifted in time to the right, i.e. it happens later - the lamp is operated with increased lamp power for a longer time. This can be advantageous for certain lamp types or ambient conditions. On the other hand, an instantaneous input of the controlling switch T4 is possible at a reduced time constant T5 - even when no steady state of operation has been achieved. In this way, an increased lamp effect is immediately avoided.

The curved arrow drawn in Figures 4a, 4b and 4c to indicate the brightness reduction (dimming) shows the possibility achieved with a potentiometer connected in parallel with the equalizing circuit. The potentiometer outlet as well as the output of the differentiation link C5, R5 then become e.g. disconnected via diodes and connected together on the controllable element T4. In this way, the dimming shown with curved arrow directions in Figures 4a, 4b becomes possible.

With a solid line shown in Figure 4a, 4b and 4c, e.g. how a frequency lamp current flow and lamp voltage flow only when using the equalization circuit device and the controllable element T4 works in a circuit device according to figure 2.

Figure 4d shows a time section from figure 4c, where it can be seen that the high-frequency, varying lamp voltage in figure 4c, which in amplitude depends on the resonance conditions, was only drawn with its envelope curve (connection of maximum values). Likewise, figure 4c can be regarded as the time course for the rms value of the lamp voltage UL which varies in amplitude and rms respectively.

Claims (20)

1. Circuit arrangement for operation, in particular for ignition, of a gas discharge lamp (GE), with a resonant circuit (LlfCltC0) like the lamp (GE) with its two filaments or electrodes, can be connected to and with an alternating voltage generator (20) which emits a output alternating voltage (uw) with variable frequency and/or variable pulse ratio (d) to the resonant circuit (L1,C1,C0), characterized by that the gas discharge lamp (GE) is unheated, that the resonant circuit (L-^C-^Cq) has a first resonant frequency (f2) and a second resonance frequency (f0) which lies below the first resonance frequency (f2), that for the beginning of the lamp lighting lies the essential frequency component of the alternating voltage generator (20) output alternating voltage (uw) in the vicinity of the first resonance frequency (f2), and that after lighting the lamp (GE) lies the essential frequency component of the output alternating voltage (uw) in the vicinity of the second resonant frequency (f0) . 2. Circuit arrangement according to claim 1, characterized by that the alternating voltage generator (20) is designed as a self-controlled inverter, whose frequency (f) or pulse ratio (d) can be affected depending on the lamp current (=f(iL)) and depending on a control signal (ux). 3. Circuit arrangement according to claim 1 or 2, characterized in that the inductive component (L2) of the resonant circuit (L1,C1,C0) is dimensioned so that a) the lamp current (iL) after application of a glow discharge which leads to ignition in the lamp (GE ), in the shortest possible time rises to the nominal current level (IL<2IN) and b) that at predetermined nominal operating frequency (fN«f0) or at nominal pulse ratio (dN) , the alternating voltage generator's (20) output alternating voltage (uw) maintains the lamp current (iL ) through the lit lamp (GE) at nominal level (IL<2IN) . 4. Circuit arrangement according to claim 2 or 3, characterized by that an equalization circuit device is arranged (R3,<D>1,C5,R4,R5,T4) which over a controllable element (T4) to which the control signal (u2) can be applied, depending on time and/or supply voltage, affects the frequency (f) and/or the pulse ratio (d) of the output alternating voltage (uw) delivered from the alternating voltage generator (20). 5. Circuit arrangement according to claim 4, characterized by that the equalization circuit device (R3, DlrC5,R4,R5,T4) has a differentiation link (C5,R5) whose input can be connected to an intermediate circuit DC voltage (U0) that feeds the inverter (20), or with a part (R3,R4,D1) thereof, and that the differentiation link (R5,C5) emits the control signal ( u2) to the controllable element (T4) of the alternating voltage generator (20). 6. Circuit arrangement according to claim 1, characterized by that the resonant circuit (L1,C1,C0) has a series circuit of an induk tans (L2) and two capacitances (ClfC2) , and that the two resonant frequencies (flrf0) differ by approximately a factor of two. 7. Circuit arrangement according to claim 1, characterized by that the gas discharge lamp (GE) filaments from time to time can be short-circuited and each filament during cold start operation can be used as an electrode for supplying ignition voltage (Uz) and operating current (iL) in/on the gas content of the lamp (GE). 8. Circuit arrangement according to claim 1 or claim 3, characterized by that the alternating voltage generator (20) is designed as externally controlled inverter whose frequency (f) or pulse ratio (d) can be predetermined independently of lamp current, and that a circuit device is arranged which, depending on a lamp operating condition, such as true condition, glow discharge condition, normal discharge condition, nominal operating condition, or a reduced brightness operating condition, sets a predetermined frequency profile for the output alternating voltage (uw). 9. Circuit arrangement according to claim 1 or claim 3, characterized by that a foreign-controlled inverter is inserted as alternating voltage generator, which inverter's frequency (f) can be controlled by a circuit device (R5,C5,21) depending on time and/or lamp type (GE). 10. Circuit arrangement according to claim 2, characterized by that the autonomous inverter has an unsymmetrical output branch with upper (S^R-^ and lower (S2,R2T4) branch halves connected in series to the supply DC voltage (U0), and that an equalization circuit device (R3,C^D-^R^Rg) by means of a controllable element (T4) after a time span (T5) which can be predetermined, starting from essentially symmetrical branch halves produces a slight asymmetry in the two branch halves, so that the frequency (f) is simultaneously increased and the pulse ratio (d) of the emitted output the alternating voltage (uw) between the two branch halves is lowered to reduce the power (P2) that is supplied to the gas discharge lamp (GE). 11. Circuit arrangement according to claim 10, characterized by that both the upper and lower branch halves are formed by one series connection of a power semiconductor (Slf S2) which can be switched on and off, and a resistor (R1#R2) / and that the asymmetry in the two branch halves consists in different resistance values in the resistors (R2,R2), so that the controllable element (T4) is connected in parallel with the largest (R2) of the resistors (R1,R2). 12. Circuit arrangement according to claim 2, claim 10 or claim 11, characterized by that the control signal (u2) which controls the controllable element (T4) i the most important consists of the differentiated supply voltage (U0) which is supplied to the self-controlled inverter. 13. Method for operation, in particular ignition, of a gas discharge lamp (GE) connected to a resonant circuit (L1,C1,C0) dg fed by an alternating voltage generator (20), characterized by the following steps: a) initiation of a glow discharge in the unheated lamp's (GE) gas content between its unheated electrodes, or wires; b) transfer of the glow discharge to a stable normal discharge with a higher power input (Px) to the lamp's (GE) gas content in relation to the lamp's nominal power (PN); c) lowering the increased power input (Px) after a predetermined time span (T5) and transferring to a stationary operating point (PN,PD) by increasing the output frequency (f) or/and lowering the pulse ratio (d) of the output of the alternating voltage generator (20) - alternating voltage (mw) • 14. Method according to claim 13, characterized by that the inductance (L2) of the resonant circuit (L1,C1,C0) is chosen so that the following conditions are met: the lamp current (iL) achieves the lamp's (GE) stable normal discharge phase in the shortest possible time after ignition, and in nominal operation with a predetermined nominal operating frequency (fN) or with a nominal pulse ratio (dN), a predetermined nominal load current (IN) in the lamp (GE) is not exceeded, or it is exceeded by less than 25%). 15. Method according to claim 13, characterized by that depending on the lamp type (GE) the power input (P2) is lowered after a predetermined time span (T5), starting with the switching on of the lamp (GE). 16. Method according to claim 13 or 14, characterized by that the initiation of the glow discharge and the transfer to it the stationary normal discharge as well as the stationary operating point (PN,PD) are controlled by varying the frequency (f) and/or the pulse ratio (d) of the output voltage (uw) of the alternating voltage generator (20). 17. Method according to claim 16, characterized by that the frequency and/or pulse ratio variation (f,d) at transfer to the stationary normal discharge occurs automatically due to lamp operating state-dependent resonant frequency changes in the resonant circuit (L1,C0,C1) with a self-controlled inverter as alternating voltage generator (20) . 18. Method according to claim 16, characterized by that the frequency and/or pulse ratio variation (f,d), depending of the time or the relevant lamp operating state (GE), is predetermined in a remote-controlled inverter that serves as an alternating voltage generator (20). 19. Method or circuit arrangement according to claim 13 or claim 1, characterized by that the alternating voltage generator (20) upon ignition and at stationary operation of the lamp (GE) emits output alternating voltages (uw) to a resonant circuit (L1,C1,C0,GE) which includes the lamp (GE), the essential frequency component of which output alternating voltages is always above the resonance frequency which is close to the resonance frequency at all times (flrfQ) in the inductive region of the resonant circuit (L1,C1,C0fGE). 20. Method according to claim 13 or circuit device according to claim 1, characterized by that the resonant circuit (L1,C1,C0, GE) with unlit lamp (GE) not attenuated, or is only slightly attenuated.