DE3943350A1 - Gas discharge lamp operating circuit - Google Patents

Abstract

The lamp operating circuit has a resonance stage (L1, C1, Co) to which the 2 heating coils or electrodes of the lamp (GE) are coupled, supplied via an AC generator (20) with a variable frequency and/or variable pulse ratio signal. The resonance stage (L1, C1, Co) has 2 different resonance frequencies, the AC generator providing an output with frequency components at the lower resonance frequency for ignition of the lamp (GE), before switching to the second frequency for maintaining the lamp in operation. Pref. a dimmer stage can be incorporated in the lamp operating circuit.

Description

The invention relates to a method for operating the Brightness (dimming) of gas discharge lamps according to the Preamble of claim 1. It also relates to a electronic ballast, especially for implementation of the method according to claim 1.

Process for adjusting the brightness of fluorescent lamps or Gas discharge lamps and circuit arrangements for Carrying out such procedures allow, so far, only Fluorescent lamps that can be operated with constant nominal brightness to dim like ordinary light bulbs (in their brightness adjust). Conventional mechanical starter circuits are unable to adjust the brightness of fluorescent lamps To ensure, too, are conventional dimmers as they are for Incandescent lamps are used, but not for fluorescent lamps usable. So there are so-called electronic Ballasts (EVG) used that have a high frequency Output AC voltage to the fluorescent tubes and on them Way both a frequency controlled starting process (Ignition process) of the gas discharge lamp as well enable frequency-controlled dimming.

A method and an electronic ballast of the type mentioned is known for example from EP 00 59 064. An externally operated transistorized inverter is used there, which feeds a directly heated gas discharge lamp via a series resonance circuit. The two heating filaments of the gas discharge lamp are connected via a parallel heating capacitor connected in parallel with the gas discharge lamp. In the series resonance circuit, an inductive current detection is also switched on, which measures the lamp current. By shifting the output frequency of the self-commutated inverter from a heating frequency of 50 kHz towards the operating frequency of 28 kHz, which is close to the resonance frequency of the series resonant circuit, the lamp can be preheated (50 kHz) as well as ignited by resonance voltage increase above the resonance frequency (f _ignition <28 kHz). After the lamp has been ignited, the series resonant circuit, now damped with the lamp, is operated at the nominal operating frequency of 28 kHz. To change the brightness, ie to dim the gas discharge lamp, the output frequency of the self-commutated inverter can now be increased again. Simultaneously with the increase in the output frequency, the heating current in the heating coils increases due to the apparent resistance of the parallel heating capacitor, which decreases at a higher frequency. The desired increase in the output frequency of the inverter in order to change the brightness takes place via a comparator (as a controller), the output signal of which shifts the frequency of a frequency generator which drives the inverter. One input connection of the comparator is connected to a dimming potentiometer, the other input connection is supplied with the current measurement signal from the inductive lamp current sensor. In this way, a stable change in brightness is achieved by regulating the lamp current by simply changing the frequency of the self-commutated inverter.

From DE-OS 33 38 464 is both an electronic Ballast with self-oscillating inverter as well one with an externally controlled inverter is known. Here feeds an output branch of the MOS-FET transistor Inverter has a series resonance circuit that consists of a Capacity and a parallel connection of one in series switched gas discharge lamp and inductance is formed. On the one hand, it is now possible to change the duty cycle from 50%, or 1: 1, always unchanged and only that Output frequency f of the inverter for the  To increase the reduction in brightness, this corresponds to the above mentioned example. On the other hand, it is for brightness control a gas discharge lamp, especially one self-commutated inverters, possible and known that Pulse / pause ratio, i.e. H. the duty cycle of that Center tap of the output branch of the inverter to reduce emitted high-frequency AC voltage. This is based on a symmetrical 1: 1 ratio about 1:10, i.e. H. 10%, which reduces the light intensity of the Fluorescent lamp decreases by more than a factor of 10. The Reduction of the duty cycle works with rectangular, non-sinusoidal AC output voltage as one Amplitude increase of the harmonics with simultaneous Reduction in amplitude of the fundamental wave. This does the same Effect, like pure frequency variation, only becomes with pure Duty cycle change maintain the frequency of the fundamental and the amplitudes (Fourier coefficients) of the harmonics postponed.

The latter is more casual Combination of frequency and pulse width control mentioned, this reduces the power consumption of the inverter and increases its output frequency, which increases the lamp brightness can be reduced.

It is an object of the invention to provide an improved method and / or a suitable device for controlling the To create brightness of a gas discharge lamp.

The task is in a method according to the preamble of Claim 1 according to the invention in the characterizing of Features specified claim 1 solved.

As an alternative to this, the task is performed according to a method Preamble of claim 13 by its characterizing Features solved. The solution to the same problem lies with one Circuit according to the preamble of claim 6 in the characterizing features of claim 6.  

An essential purpose of the invention is that Dimming operation, d. H. the operation of the lamp at reduced Brightness, stabilize. The characteristic of the Features specified claim 1 act in that the Lamp brightness characteristic curve of the one containing the lamp Series resonance circuit is changed in shape. Through this The change is simultaneous with decreasing brightness of the lamp their lamp brightness characteristic changed. This change levels the steep area in the currently valid Brightness characteristic and enables clearly defined, stable operating points even for heavily dimmed operation.

By the features specified in the characterizing part of claim 1 it is avoided that the mentioned operating points or Working points in the steep section one for each Frequency or a respective duty cycle valid Lamp brightness function come to rest. Especially at a free-swinging (self-guided) inverter, at which the oscillation frequency u. a. on the level of the mains voltage or the level of the DC voltage feeding the inverter depends, is the stabilization of the invention Dimming operation without additional controller is particularly effective.

The advantageous increase in heating current for dimming is due to the combined frequency increase and Reduced duty cycle reduction achieved this effect works for the gas discharge lamp, which is reduced in brightness additionally stabilizing.

According to an advantageous development of the invention The method can be set by any nonlinear Control curve the dependence of the brightness of one of these controlling control voltage or potentiometer setting be linearized.  

The methods according to the invention according to claim 1 and claim 13 can work on the one hand with two-dimensional characteristic curves or with three-dimensional characteristic surface. The independent variable for a characteristic is either the frequency f or the duty cycle T, the dependent parameter is given in both cases, the lamp power P and _from the lamp brightness. The further variable which is not used as the abscissa variable in each case in the two-dimensional case forms a parameter with which the family of bell-shaped characteristic curves explained in the preamble of claim 1 are formed. A respective pair of a pulse duty factor d ₁ and a frequency f ₁ results in a clear lamp brightness, since both the characteristic curve and the abscissa value are fixed, with which the ordinate value can be read. Means according to the invention function generator it is possible, depending on a command which either P _soll (desired lamp power) or the frequency f or the duty cycle may be d to specify one or both of parameters (frequency and duty cycle) in a desired manner the inverter of the ballast. The respective specification can be made individually for the lamp, accordingly depending on the type of lamp, for example krypton or argon, or depending on the nominal lamp power P _{N used} . The connection of all operating points forms, according to the invention, a control curve which can be both linear and deliberately distorted, ie non-linear.

In addition to the possibility of controlling the brightness of the gas discharge lamp using two-dimensional characteristics, there is also the alternative of controlling using a three-dimensional characteristic field, ie a lamp-specific characteristic surface. The control curve is formed in space, on the surface of the characteristic surface. The respective projection of this control curve lying in space onto the plane spanned by the axes P _ab and f or the plane spanned by the axes P _ab and d forms the previously explained two-dimensional control curve. The advantage of a three-dimensional specification lies in a single function generator, which also selects a respective pair of frequency and duty cycle as a function of a reference variable, for example P _should . Equating setpoint (reference variable P _set), and the actual value, ie given lamp power P, this allows you to set a desired brightness without using a controller. The control curve according to the invention is placed on the characteristic surface, whereby any desired lamp brightness, ie each lamp power P _ab , for P _soll = P _ab a definable pair of values from the duty cycle and frequency can be assigned.

The desired brightness, and the desired output light power P _should, in accordance with an advantageous further development may be achieved either by means of a potentiometer or an externally supplied control voltage U _ST.

Another purpose of the invention is to provide a electronic ballast with preferably cantilevered inverter that is simple and modular for the dimming operation, in particular according to claim 1 or claim 13, is customizable. The modulation of the asymmetry in one Inverter output branch allowed, according to the label of claim 6 having its own inventive content, which simultaneous change in the duty cycle d and the Frequency f of an AC output voltage or current. The Control circuit arrangement according to the invention modulates here the existing asymmetry such that starting from an im Duty cycle symmetrical nominal operating frequency Dimming operation by simultaneously increasing the output frequency as well as lowering the duty cycle is made possible. The The control circuit arrangement according to the invention is modular here can be added to a finished electronic ballast so that one and the same electronic ballast for both nominal operation and - with the addition of Control circuit arrangement - can be used for dimming.  

The asymmetry is advantageously of unequal ohmic Resistors formed and one of the larger of the two Resistors connected in parallel controllable resistor, preferably a MOS-FET, can be between full symmetry (50% duty cycle) and by resistance difference conditional asymmetry can be varied. The differences in the According to the invention, resistances act back on the Saturation times of the to control the self-guided Inverter with its primary winding in the Series resonance circuit inserted control transmitter. His Secondary windings control the control connections of the output Power semiconductor of the inverter.

Embodiments of the known circuit and the circuit according to the invention and a circuit according to the invention Processes are described below with reference to the drawing. Show it

Fig. 1 is a power-frequency diagram with a lamp brightness characteristic curve for a 50% duty cycle and an exemplary set operating point B 4,

Fig. 2 shows three time diagrams of a tastfrequenzvariablen square wave as fremdgeführen of one or self-commutated inverter are submitted,

Fig. 3 is a FIG. 1, similar diagram, where the change of the present invention Lampenhelligkeits- characteristic and a linear exemplary control curve 1 is explained,

Fig. 4 an inventive electronic ballast in embodiments with selbstschwingendem inverter,

FIG. 5a is a detail circuit diagram of a control circuit of the invention for modulating the unbalance of the inverter of Fig. 4,

Fig. 5b is a detailed circuit diagram for explaining the saturation-controlled frequency / duty-cycle modulation by means of the lower part of the branch of the inverter output branch,

Fig. 6 is a three-dimensional characteristic field (area) formed by the independent parameters f (frequency) and d (duty cycle) and the characteristic area forming in z-direction dependent variables P _from (lamp brightness), wherein P _ab as a function of d and f is shown

Fig. 7 is a lamp brightness characteristic as a function of the duty cycle with the "frequency" for explaining a pure frequency control,

Fig. 8 is a lamp brightness characteristic as a function of the frequency with the parameter "duty cycle" for explaining a pure duty ratio,

FIG. 9 shows a diagram corresponding to FIG. 3 with an explanation of a non-linear control curve II with a view to the linearization of the lamp brightness function, depending on a control voltage or a change in the potentiometer.

FIG. 10a function generator which, starting in Fig. Characteristic surface depicted 6 F depending on a reference variable, P _{is intended} here emits from the corresponding to a desired brightness lamp individual pair of values of a frequency (f) and a duty cycle (d) to the inverter 20 ,

Fig. 10b alternative specification of the respective frequency and duty cycle associated with a simple additional function generator which, an associated duty cycle outputs depending on a frequency which is used here as a reference variable,

Fig. 11 implementation example for an inventive electronic ballast, which feeds the lamp load circuit X, and the inverter 20 in accordance with Fig. 10a and 10b generated pairs of values of pulse duty factor and frequency can be fed.

Fig. 1 shows a lamp brightness characteristic or the function of the output power P _from which corresponds to the brightness, supplied in dependence on the frequency of a series resonant circuit with a gas discharge lamp GE AC voltage. There is shown an exemplary operating point B 4, the f at a set frequency ₄ is an output power P due _4. This output power P ₄ corresponds to a certain brightness H ₄ .

First of all, it can be seen from the lamp brightness characteristic curve that the lamp brightness can basically be achieved by changing the frequency. The lamp brightness characteristic curve is relatively flat at low frequencies and at high frequencies, ie the power change ΔP _ab for a given Δf is small, and has a steep area connecting these two flat areas with a high degree of power change for the same predetermined frequency change. The property of this lamp brightness function, which is shown here for example for a symmetrical pulse duty factor of d ₁ = 50% or 1: 1, is dependent on the properties of the series resonant circuit L 1 / C 1 and on gas discharge lamps. A similar lamp brightness characteristic curve results for a constant frequency with a variable duty cycle.

The difference Δ is referred to below as "DELTA".

If a predetermined frequency f _{4 is} set by means of an electronic ballast (EVG) or the inverter 20 contained therein (see FIG. 11) and this is fed to the series resonance circuit containing the gas discharge lamp GE, then for a certain type of lamp this results in the duty cycle mentioned of d ₁ = 50% an operating point B 4 , which corresponds to a power output P ₄ or H₄. A slight frequency fluctuation, denoted by DELTA f ₄ in FIG. 1, which is, for example, symmetrical to f ₄ , now leads to a comparatively high change in power DELTA P ₄ due to the steep characteristic. If the frequency is not constant, this relatively high change in output manifests itself in a flickering of the lamp, which is perceived as unpleasant and annoying for the human eye. A slight shift in the frequency f ₄ accordingly causes a strong stationary change in brightness on the one hand, but on the other hand the undesirable flickering property. A parasitic slight change in frequency DELTA f ₄ can be caused by a non-constant (fluctuating) mains voltage, especially when using self-commutated inverters.

The operating point (operating point) B 4 can now be compared, for example, with the nominal operating point BN, which is established at a nominal operating frequency f _N. Here the lamp emits the nominal power P _N , which corresponds to the nominal brightness. The nominal frequency is usually slightly above the resonant circuit resonance frequency, for example approximately 20 kHz, preferably above the hearing frequency. The change in the power output occurring at the named nominal operating point BN for a predetermined slight frequency change DELTA f ₅ is only DELTA P₅. This change in lamp brightness is many times smaller than the change in lamp brightness caused by the same frequency change at dimming operating point B 4 (with DELTA f ₄ = DELTA f ₅ ). It can thus be seen that, starting from the nominal operation, where a gas discharge lamp does not or only flickers slightly, dimming the lamp with an electronic ballast by increasing the frequency alone (with a constant pulse duty factor d ₁ ) leads to increased flickering, ie to instability.

This is where the idea of the invention comes in; it enables the lamp brightness characteristic curve according to FIG. 3 to be changed by varying the duty cycle d. The duty cycle (relative duty cycle d, absolute duty cycle D) is defined as the ratio of the on-time to the off-time of the high-frequency AC voltage emitted by the electronic ballast u _W. A symmetrical key ratio means that the switch-on time and the switch-off time of the AC voltage are identical, i.e. d _SYMM = 50% or D = 50: 50 or 1: 1. Shifting the pulse ratio to lower relative pulse duty factors d <50% means a reduction in Switch-on time while increasing the switch-off time. The same time T remains as a sum, so that the frequency f = 1 / T is unchanged ( FIG. 2).

According to FIG. 3, the lamp brightness characteristic curve becomes flatter by lowering the duty cycle or lowering the relative duty cycle d. The steep area loses slope, the risk of frequency change-induced flickering of the gas discharge lamp decreases.

A control curve I can be defined, which is formed by all the resulting operating points B 1 , B 2 , B 3 . . ., which apply to the respective frequency / duty cycle combinations. The control curve 1 forms the connection of all operating points. This can have any shape. B 1 , B 2 , B 3 are exemplary operating points. The 3 characteristic curves K 1 ; K 2 , K 3 are exemplary characteristic curves. There are an infinite number of bell-shaped characteristic curves for continuously changeable duty cycle, these are continuously shifted with continuous tuning of the duty cycle d (or the frequency f) and their slopes are changed. The control curve, labeled I in FIG. 3 and labeled II in FIG. 9, can be selected to be non-linear. This depends on the desired control function and the type of lamp used. On the other hand, a control curve can also be defined by the fact that for many respective combinations of a frequency, for example f ₂ , and a pulse duty factor, for example d ₂ = 25%, there is in each case a clear operating point (operating point), here B 2 . The frequency specifies the abscissa coordinate, while the duty cycle selects the currently valid lamp brightness function on which the operating point for the selected frequency is located. In the same way, a control curve can be defined, in which the pulse duty factor is plotted in the abscissa direction, while the frequency f is used as the parameter of the pair of lamp brightness characteristics ( FIG. 7).

For the flicker-free operation of a GE gas discharge lamp it is now relevant to run the tax curve in such a way to let all of the operating points in the initial flat Range or above the turning point of the applicable one Lamp brightness characteristics come to rest.

The control curve I shown by way of example in FIG. 3 enables the flicker-free dimming operation of a fluorescent lamp. The control curve is defined, for example, by three operating points (operating points) B 1 , B 2 and B 3 , each of which lies on a characteristic curve that applies to a fixed duty cycle. The three entered characteristic curves K 1 , K 2 and K 3 , which correspond to the duty ratios d ₁ , d ₂ and d ₃ , form only an exemplary selection from an infinite number of characteristic curves. The infinite number of characteristic curves arises with a continuously variable duty cycle. Each adjustable operating point on each characteristic curve forms a point on the control curve I. The operating points are selected by selecting the duty cycle and the frequency such that each operating point is as far as possible from the turning point of its associated characteristic curve. In this way, the operating points come to lie in those characteristic curve areas that have a slight or minimal slope. If only certain characteristic curves are available, for example when the duty cycle is not continuously changing, each operating point must be selected such that it comes to lie on a characteristic curve which has a minimal gradient for the desired lamp output.

The lower the duty cycle, the flatter they become Maxima of the characteristic curves and the less steep they become at the beginning steep areas around the turning point. The on these characteristics lying operating points can be closer to the turning point because here too a comparatively small slope of the characteristic given is.

The independent frequency and duty cycle control is both for the self-commutated inverter of an electronic ballast and can also be used for an externally managed inverter. In an externally managed inverter can do this Frequency change and duty cycle change independent from each other. A control curve and Lamp brightness can thus be controlled independently by two selectable influencing variables can be freely determined or specified will.

Either an externally supplied control voltage u _{St is used} as the input variable for a combined (common) frequency and duty cycle control, or the frequency and duty cycle control is based on a potentiometer setting.

In the case of a self-commutated inverter, the combined change in frequency and duty cycle already takes place by changing the duty cycle of the alternating voltage u _W supplied to the load circuit X. As a result, the duty cycle and frequency change with a constant switch-off time.

FIGS. 7 and 8 show lamp brightness characteristic curves once again, once as a function of the pulse duty factor d and in the second case as a function of the frequency f (as already in FIG. 3). The respective other value is used as a parameter, ie the lamp brightness characteristics, which are shown as a function of the pulse duty factor d in FIG. 7, show the frequency f as parameters for the different characteristics.

The output power P _ab , which corresponds to the lamp brightness, is plotted on the ordinate for both cases. A pure frequency control and a pure duty cycle control, both of which have a brightness-varying effect, are to be represented in their respective diagrams by a vertical line. Here, with a constant pulse duty factor of 50% in FIG. 7, a brightness variation is achieved by changing the frequency, the control curve runs vertically, different frequencies lead to different intersection points (operating points) and different lamp brightnesses. In the same way, at a constant frequency f ₁ in FIG. 8, a different lamp brightness is set in each case by choosing different duty cycles. The inclination according to the invention or the free specification of the control curve corresponds to a simultaneous change in the frequency f and the duty cycle d and enables the stationary flicker-free dimming operation of fluorescent lamps.

The usually non-linear dependence of the lamp brightness on the frequency change and / or change in the duty cycle can be linearized by any curvature of the control curve, as is identified, for example, as control curve II on the basis of FIG. 9. This is particularly advantageous in the case of brightness controls via control voltage change u _St ; a separate regulation for the brightness stabilization is unnecessary.

The two-dimensional characteristics shown in FIGS. 7, 8 and 9, each showing P _ab as a dependent variable on the ordinate, can be represented together in a three-dimensional coordinate system. This is shown in FIG. 6. The lamp-specific characteristic curves are shown as an isometric network in the characteristic surface F, the control curve II or III are shown spatially. The two independent variables duty cycle d and frequency f run in the x and y directions. The dependent variable, the output power P _{ab, is} plotted in the z direction. The dependent and the independent variables are interchangeable, for example for the described case in which P _ab = P _{should be} specified (above u _St ) and, according to the control curve 2 lying on the characteristic surface F formed in space, a unique pair of frequency and duty cycle for a respective desired lamp brightness is specified. Each operating point is defined as the point of intersection of the control curve II or III through the plane which is parallel to the plane spanned by the axes d and f and which is at the level of the desired output P _ab .

Fig. 7 and Fig. 8 can be derived from the characteristic area F. For example, FIG. 8 is formed by all intersection curves that exist between the characteristic surface F and planes that run parallel to the plane that are formed by the axes f and P _ab . A parallel displacement of these planes in the direction of the d-axis forms the characteristic curves shown in FIG. 8 as a respective intersection curve with the characteristic surface F from FIG. 6. The same applies to planes that run parallel to the plane that are spanned by the d and P _ab axes and that also form intersection curves with the characteristic surface F when the plane is shifted in the direction of the frequency axis f. This results in FIG. 7.

The intersection curve of a plane, which runs parallel to the plane spanned by the axes d and f, indicates all those operating points that are possible for a specific power P _ab with a predetermined characteristic surface F. One of these possible points is selected for control curve II. For example, the plane E ₂ runs parallel to the plane spanned by the axes f and d and lies at the height of P ₂ . The intersection curve of this plane E ₂ with the characteristic surface F represents all those operating points that are possible to achieve the power P ₂ . One of these operating points is selected in order to grant minimal flicker properties, whereby a point of the control curve II is defined. In this way it is possible to proceed in the range O <P _from <P _N (nominal lamp power) to form a complete control curve II.

Fig. 4 shows an inverter output branch of a self-commutated inverter in an electronic ballast for the lamp brightness change by combined varying the duty cycle d and the frequency f of the output voltage u _W (t). The use in a self-commutated inverter is to be understood as an example; the invention, as described, can also be used for other types of inverters, for example externally managed inverters. Self-commutated inverters have the advantage that they can be constructed simply and robustly and inexpensively; externally-guided inverters are more flexible, ie easier to regulate, but more expensive to build.

The series resonance circuit already mentioned in Fig. 1 first has the series connection of an inductor L ₁ , a capacitance C ₁ and the series connection of both heating filaments of the GE lamp and a parallel heating capacitor C₀. The heating capacitor C ₀ is connected in parallel to the gas discharge lamp GE, this is referred to as a parallel heating circuit. The primary winding T are turned on in the series resonant circuit in FIG. 4 further _2-D a Steuerübertragers T ₂ and the two primary windings of T ₁ and T -A ₁ -B an additional detonator identification transformer T _1. The latter forms an advantageous addition to the output circuit according to the invention, but is not necessary for its basic function.

The two input connections of the series resonance circuit are connected to two output connections of an inverter branch S ₁ , R ₁ , S ₂ , R ₂ . In the exemplary embodiment, the output inverter branch is formed by the series connection of a first electronic switch S ₁ , a first resistor R ₁ , a second electronic switch S ₂ and a second resistor R ₂ . This output branch is connected with its upper and with its lower connection to a DC supply voltage +, -. It contains the two branches S ₁ and R ₁ as well as S ₂ and R ₂ . The two connections of the series resonance circuit are now to be connected either in parallel to the one branch or in parallel to the second branch. In the exemplary embodiment, they are connected in parallel to the upper branch S ₁ , R ₁ .

The two resistors R ₁ and R ₂ have different resistance values, the difference in resistance is a measure of the selected asymmetry of the two sub-branches of the inverter output branch. In the exemplary embodiment, a control circuit arrangement 10 is also connected in parallel with the resistor R ₂ , which is to be assumed to be a larger resistor. However, it is also possible to connect the control circuit arrangement in parallel with resistor R ₁ if this has the larger value of the two resistors R ₁ and R ₂ . It is also possible to connect the control circuit arrangement 10 in series to one of the sub-branches, in this case the asymmetry is determined solely by the volume resistance (series resistance) R _{DS of} the circuit arrangement 10 .

The control circuit arrangement 10 is optionally controlled via a control voltage u _St or via a potentiometer position, FIG. 5a shows the potentiometer POT used for this. The control voltage u _St or the potentiometer position determine the forward resistance of the circuit arrangement 10 , and consequently the resistance connected in parallel with the resistor R _DS . A symmetry of the two sub-branches is achieved when the parallel connection of larger resistor R ₂ and _contact resistance R _DSon of control _{circuit arrangement} 10 corresponds to resistor R ₁ . The highest degree of asymmetry and therefore the lowest duty cycle at the highest frequency is achieved when the control circuit 10 blocks or has its highest series resistance. The asymmetry is then essentially determined by the ratio of the two resistors R ₁ and R ₂ . This makes it adjustable and the operating range of the inverter can be adjusted or predetermined.

The control transformer T ₂ -D inserted in the series resonance circuit has at least two secondary windings for the self-commutated inverter, T ₂ -A and T ₂ -C. These control the two electronic switches S ₁ and S _{2 of} the inverter branch crosswise in opposite directions. The saturation property of this transformer T ₂ is predetermined on the basis of the core and the number of windings of the windings. Saturation occurs after a predetermined voltage time area has been reached. By varying the resistance R ₂ , the time required to reach the saturation-generating voltage time area can be shortened when the secondary voltage is increased.

Fig. 5b shows an example of the driving scheme of the second electronic switch S ₂ with its associated secondary winding T ₂ -C of the control transformer. It is assumed that negative load current i _w (t) flows through the primary winding of the control transformer, so that the control voltage u ₂ applied to the second secondary winding is positive, whereby the power transistor forming the second electronic switch S ₂ in this exemplary embodiment is turned on in an emitter circuit . For a given load current i _w (t), the voltage u _{2 can be} influenced by variation (modulation) of the effective emitter resistance R ₂ || LR _DS (parallel connection of R ₂ and forward resistance R _{DS of} the control circuit arrangement 10 ) - which is just happening through the control circuit arrangement 10 will. If this is increased with a larger effective emitter resistance R ₂ || LR _DS , the control transformer T ₂ is saturated more quickly. After saturation occurs, the second power semiconductor S ₂ begins to block, the first power semiconductor S ₁ begins to conduct. This principle shows that an unchanged resistor R ₁ and a modulated second emitter resistor R ₂ || LR _DS simultaneously effect a change in frequency and duty cycle.

A MOS-FET is preferably used as the controllable resistor for the control circuit arrangement. Power transistors are also preferably used as electronic switches S ₁ and S ₂ . It goes without saying that any type of power semiconductors can be connected into the two branches and that any type of controllable resistor R _DS including a switch element for the control circuit arrangement 10 can also be used in parallel or series connection.

Fig. 5a shows the detail circuit diagram of a control circuitry 10, in which the controllable resistor formed by a MOS-FET V4. To change its forward resistance R _DS , a potentiometer POT is changed in such a way that the GATE voltage of the V4 is varied, as a result of which its forward resistance R _{DS is} changed. This applies to through-connected transistor V ₃ and supply of a positive gate supply voltage for V4 via a bias resistor R ₅ . FIG. 5 a further shows how, with the one secondary winding of the ignition detection transmitter T _1, the dimming control circuit arrangement 10 is activated depending on the ignition of the gas discharge lamp, via a further MOS-FET V3. The two oppositely wound primary windings T ₁ -A, T ₁ -B, one of which is connected to the load circuit and the other to the heating circuit of the GE lamp, only generate a positive voltage u _e () in the secondary winding T ₁ -C t) if the GE lamp has already ignited. Due to a positive voltage u _e (t), V3, POT, V4 and thus the control circuit arrangement 10 are now activated, dimming operation is made possible. In this way it can be ensured that brightness control of the GE lamp can only take place if it has already ignited (see also FIG. 4).

The bias voltage for the MOS-FET V4 influencing the degree of asymmetry can be taken from the load circuit or from the DC supply circuit +, and the controllable MOS-FET V4 can also be assigned a time-dependent circuit at its gate connection for controlling the preheating and ignition of the lamp will. This changes the frequency and duty cycle of the inverter output voltage u _W (t) at the beginning before the GE lamp is ignited.

Fig. 11 shows one exemplary implementation of an electronic ballast having a rectifier 19 for rectifying an AC voltage supply. An inverter 20 , which outputs an alternating output variable u _W (t) to the lamp load circuit X (see FIG. 1), can be controlled in such a way that the alternating output variable u _W (t) is adjustable in frequency and duty cycle. The rectifier 19 can be omitted if the lamp GE (in the load circuit X) is fed from a battery or a direct current network. The detailed circuit diagram of the output branch of the inverter 20 is shown in FIG. 4, which has already been described.

FIG. 10a shows the characteristic surface F explained in FIG. 6 in a function generator 11 , which outputs two output variables for the inverter 20 depending on an input variable. The function generator 11 is constructed, for example, by a ROM or by means of non-linear characteristic curves. P _should or u _St form its input variable, depending on this, only a valid pair of output variables (duty cycle d and frequency f) are output to the inverter 20 in accordance with the set control curve II (or a similar one).

Fig. 10b shows an alternative form of the frequency and duty setting of the output AC size & _W (t) of the inverter 20. Here, a respective pair of frequency and duty cycle is formed via a reference variable f (frequency) and a non-linear function generator 12 . These are fed to the inverter 20 . The brightness specification of the lamp GE via frequency specification f according to FIG. 10 b and a pulse duty factor d dependent on the frequency f (corresponding to the control curve / characteristic curve determined by function generator 12 ) can also be modified in such a way that the pulse duty factor d and the function generator 12 are used as reference variables depending on this, a specific course of the frequency f is generated.

Claims (16)

1. A method for controlling the brightness (dimming) of a gas discharge lamp (GE), which lies in a series resonant circuit (L ₁ , C ₁ ) connected to a rectifier-inverter combination ( 10 , 20 ), by changing the frequency (f) and the pulse duty factor (D, d) of the output alternating variable (u _W ) generated by the inverter and supplied to the gas discharge lamp and the series resonant circuit (X; L ₁ , C ₁ , GE), the lamp (GE) being operated in a frequency range, in which the dependence of the lamp power (P _ab ) on the frequency (f) of the output variable (u _W ) with the pulse duty factor (D, d) as a parameter as a family of characteristics (K 1 , K 2 , K 3 ,. .), each of which runs in the manner of a bell curve starting from a maximum value and falling to form a turning point, the maximum value of the individual characteristic curves (K 1 , K 2 , K 3 ,...) the lower the lower this characteristic nien (K 1 , K 2 , K 3 ,. . .) as a parameter assigned duty cycle (d ₁ , d ₂ , d ₃ ,...), characterized in that the frequency (f) and the duty cycle (D, d) are each selected so that the operating point (B 1 , B 2 , B 3 ,...) With at least two characteristic curves available or selected for a certain lamp power (P _ab ), each comes to lie on the characteristic curve which has the lower slope at this lamp power (brightness). 2. The method according to claim 1, characterized in that the maximum value of the monotonically falling bell curves (characteristic curves) is the respective maximum and that the operating points (B 1 , B 2 , B 3 ,...) Are selected such that the lamp power (P _ab ) depends linearly on a reference variable (u _St , P _soll , f) which specifies the brightness of the gas discharge lamp (GE). 3. The method according to claim 1, characterized in that the respective selection of the operating points (B 1 , B 2 , B 3 ,...) By independent specification of a pair of frequency (f ₁ , f ₂ , f ₃ ,... .) and duty cycle (d ₁ , d ₂ , d ₃ ,...) for the output variable (u _W ) of the inverter ( 20 ), which means that any lamp power (P ₁ , P ₂ , P ₃ ,. .) is adjustable. 4. The method according to claim 1 or claim 2, characterized in that both a frequency (f ₁ , f ₂ , f ₃ ,...) And a pulse duty factor (u ₁ , P set) are respectively via one or the common reference variable (u _St , P _should ) d ₁ , d ₂ , d ₃ ,...) of the alternating output variable (u _W ) is jointly predetermined, whereby any lamp power (P ₁ , P ₂ , P ₃ ,...) can be set. 5. The method according to any one of the preceding claims, characterized in that a lamp-specific (argon, krypton, neon, PN) control curve (I, II, III) on a three-dimensional map surface (P _ab = F (d, f)) as connection of all lamp specifically desired operating points (B 1, B 2,.. B 3,.) is set, and depending on a or the command variable _(to P, u _St) for the purpose of dimming is by mobile and in that the lamp-specific control curve (I, II ) is so non-linear that the dependence of the lamp power (P _ab ) on the reference variable (P _soll , u _St ) is linearized. 6. Electronic ballast, in particular for performing the method according to one of the preceding claims, characterized by an asymmetrical output branch connected between a supply constant (+) and the reference potential (-), which has an upper and lower branch half connected in series and a control circuit arrangement ( 10 ), by means of which the degree of asymmetry of the two halves of the half for simultaneous variation of the frequency (f) and the duty cycle (d, D) of the output alternating variable (u _W ) delivered between the two halves can be changed. 7. Electronic ballast according to claim 6, characterized in that the upper and the lower half are each formed from the series connection of a power semiconductor which can be switched on and off (S ₁ , S ₂ ) and a resistor (R ₁ , R ₂ ) and that Asymmetry of the two halves in different resistance values of the resistors (R ₁ , R ₂ ). 8. Electronic ballast according to claim 7, characterized in that the control circuit _arrangement ( 10 ) is connected in parallel to the larger of the two resistors (R ₂ ), and in completely conductive state (R _DSon ) of the control _{circuit arrangement} ( 10 ) the resulting half-half resistors (R ₁ , R ₂ // R _DSon ) are essentially the same, making the output _branch symmetrical. 9. Electronic ballast according to claim 6 or 7, characterized in that the control circuit arrangement ( 10 ) has a symmetrizing control element (V 4 ), which can produce both symmetry and predeterminable asymmetry of the two halves by controllably changing its forward resistance (R _DS ). 10. Electronic ballast according to claim 6, characterized in that a primary winding (T ₁ -A) of a transformer (T ₁ ) the series resonant circuit (L ₁ , C ₁ ) is connected in series and a second primary winding (T ₁ -B) Transmitter (T ₁ ) is connected in series with the parallel heating circuit (C ₀ ), that the first and second primary windings (T ₁ -A, T ₁ -B) have opposite sense of winding and that the secondary winding (T ₁ -C) of the transfer (T ₁ ) the control circuit arrangement ( 10 ) stops until a voltage is induced in the secondary winding (T ₁ -C). 11. Electronic ballast according to one of claims 6 to 10, characterized in that the forward resistance (R _DS ) of the control circuit arrangement ( 10 ), or of the control element (V ₄ ), via a potentiometer (POT) or via a variable control DC voltage (u _St ) can be changed for powerless control of the lamp brightness. 12. Electronic ballast according to claim 11, characterized in that a linearization circuit is provided which produces a linear dependency between the variable control DC voltage (u _St ) and the GE lamp brightness. 13.Procedure for operating a directly heatable gas discharge lamp (GE), in particular for the purpose of changing the brightness, which is part of a series resonance circuit (L ₁ , C ₁ ) and whose heating coil can be heated via a parallel heating reactance (C ₀ ), in which method both the frequency (f) as well as the duty cycle (D, d) of an output ballast (u _W ) generated by an electronic ballast (EVG) and supplied to the series resonance circuit (L ₁ , C ₁ ) is changed, characterized in that a Control curve (I, II, III) through which the change in brightness can be selected is such that the output signals for the respective combinations of pulse duty factor and frequency (f ₁ , d ₁ ; f ₂ , d ₂ ; f ₃ , d ₃ ,...) Alternating variable (u _W ) setting, stationary operating points (B 1 , B 2 , B 3 ), which correspond to certain lamp brightnesses (P ₁ , P ₂ , P ₃ ,...), In the convexly curved area of a lamp-specific of the Frequency (f) and the duty cycle (d, D) dependent lamp brightness characteristic area (F). 14. The method according to claim 13, characterized in that for lowering the brightness of the gas discharge lamp (GE), the frequency (f) is increased starting from the nominal operating frequency (f _N ) of the output variable (u _W ) and at the same time its duty cycle symmetrical for nominal operation (d _N , D _N ) is reduced. 15. The method according to claim 13 or claim 14, characterized in that the course of the control curves (I, II) is adapted so that a linear change in brightness depending on a potentiometer position (POT) or a control voltage (u _St ) is adjustable. 16. The method according to any one of claims 13 to 15, characterized, that the change in the brightness of the lamp (GE) only after its Ignition can be done.