EP0461441B1 - Process and circuit for varying the light intensity (dimming) of gas discharge lamps - Google Patents

Abstract

A process and electronic ballast allow the brightness (dimming) of gas-discharge lamps (GE) to be controlled, especially in the case of gas-discharge lamps of a different type, such as argon or krypton lamps, and gas-discharge lamps of different rated power (PN). In this case, an invertor (20) is provided which emits an AC output voltage (uw) of variable frequency (f) and/or of variable duty cycle (d) to a load circuit (10) containing a gas-discharge lamp (GE). Furthermore, a first and a second current measuring element (25, 26) are provided for detecting a lamp current (IWrms, Ilamp) and a DC current (Idc) taken by the invertor (20) or intermediate-circuit smoothing capacitor (C0), and a first voltage measuring element (27) for detecting intermediate-circuit DC voltage (U0, Udc) for the invertor (20). The circuit arrangement and the specified process are intended to achieve an improved brightness control, particularly in a small brightness range. In addition, it is intended to achieve independence from the lamp type. To this end, the current measurement variables (IWrms, Idc) are combined in a synthetic current measurement variable (Iq), and the synthetic measurement variable (Iq) thus formed is multiplied by, or quasi-multiplied by, the DC voltage measurement variable (Udc), as a result of which an actual power variable (Pmess) which essentially represents the absorbed or emitted lamp power (Pout, Pin) can be formed for a power control loop (40, 20, p, Pdes, GE, 10). <IMAGE>

Description

The invention relates both to a method for regulating the brightness of gas discharge lamps acc. The preamble of claim 1 and an electronic ballast for a purpose of the same name, the latter being used in particular to carry out a method according to claim 1.

Electronic ballasts and methods for operating gas discharge lamps are known in many variants. The electronic ballasts used offer advantageous operating modes for the tubes mentioned. Efficiency increases, flicker-free and gentle operation, comfortable (re) ignition options and improved dimming behavior are considered. In particular, the last-mentioned operating option, that which also allows gas discharge lamps to be controlled in terms of brightness over a wide range, continues to present technical difficulties despite advanced circuit technology and increased output frequencies of the electronic ballasts.

For example, EP-A-0 338 109 from the applicant discloses an electronic ballast in which a line rectifier is connected to a line supply voltage. It supplies a DC link voltage for a downstream inverter. This outputs an AC output voltage to a load circuit containing the gas discharge lamp. A large number of circuit parts are provided for controlling the inverter, for monitoring the operating state and for recording measured variables. Among other things, a first smoothing filter is provided, by means of which the direct current flowing in the intermediate circuit can be fed to a multiplier. The output of a second measuring element, which is connected to the intermediate circuit voltage, is fed to the second input of the multiplier. DC voltage / current are thus detected on the input side and fed to a control and monitoring unit. Both lamp current and the Lamp voltage detected and fed via comparators to the control and monitoring unit mentioned.

The circuit arrangement described now allows extensive monitoring and checking of all operating parameters, but there is no possibility for setting and varying the brightness of connected gas discharge lamp (s). This is not least because the input power on the DC side is regulated to a constant value by means of the multiplier mentioned and a corresponding frequency control of the inverter. This value is defined by the nominal power of the connected gas discharge tube and with (in nominal operation) negligible power loss of the inverter, a constant direct current input power results in a constant (nominal) light output power of the alternating current power.

The invention is based on the object , inter alia, of creating an improved brightness control by specifying both an improved device and an improved method for the stated purpose.

Last but not least, this object is achieved in a method for regulating the brightness according to the preamble of claim 1 by the features specified in the characterizing part of this claim. The solution to the same problem is solved in an electronic ballast according to the preamble of claim 11 by the characterizing features of this claim.

A first essential basic idea of the invention is to form the current measured value / size of the system used for the power measurement or for the power calculation of the lamp (s) as a combination of DC-side and AC-side current value.

Already on the basis of this measure according to the invention, it is now possible to adjust the lamp brightness of the gas discharge lamp to vary particularly wide limits flicker-free and evenly. Here, the invention makes use of the knowledge that - within the permitted tolerance - the aforementioned correspondence of direct current power and alternating current power is only valid for the higher (up to nominal power and above) power range.

A significant reduction in brightness down to the lowest brightness is made possible according to the invention in that the combined (synthetic) current measurement quantity has no or only a small proportion of the direct current on the input side of the inverter. An effect according to the invention is thus essentially based on the fact that a redistribution of the current components in the synthetic current measured value I _{q takes place} from the direct current input side I _dc (with high light output of the tube) to the alternating current output side I _q (with low lamp brightnesses). This idea is also applicable to a redistribution of power quantities calculated by means of two multipliers in a synthetic power quantity P _q .

It is known to vary the frequencies and / or the pulse duty factor of an alternating voltage supplied to the gas discharge lamps. This is used on the one hand to cause the tube to ignite or preheat, and on the other hand such a frequency shift can also be used to change the brightness. The resonance circuit in which the gas discharge lamp is connected is fed with a frequency which, depending on the desired degree of brightness, is closer or farther from the resonance frequency of the load circuit. A frequency shift "away" from the resonance frequency reduces the lamp current, at the same time increases the lamp voltage (negative arc characteristic) and makes it possible to reduce the light output. However, a frequency-controlled arrangement selected in this way is not able to ensure a brightness that is independent of the lamp type, ie when using several or different gas discharge lamps. If a large number of gas discharge lamps are used in large rooms, same type, for example in light band structures, a uniform brightness / brightness variation of this large number of lamps cannot be guaranteed with a conventional circuit arrangement.

Another essential purpose of the invention is thus to ensure the lamp brightness independently of the lamps chosen and used in practice (regardless of lamp type). This has significant advantages in that lamps of different designs, different nominal powers or different gas fillings, such as argon lamps or krypton lamps, can now be fed from the same ballast - without circuit adaptation. According to the invention, all of these lamp types can be operated uniformly in a wide range of brightness, which includes the nominal load P _N down to regions which are below 1% of this nominal load. Short-term powers above the nominal load P _N can also be permitted.

The effect of the lamp power control according to the invention , via the formation of a combined synthetic current value I _q , lies in the now existing independence from the lamp lamp voltage, from the load circuit impedance into which the gas discharge lamp is switched, from the signal characteristic and from the phase position in the load circuit. The same tubes operated side by side via separate electronic ballasts give the same (adjustable) power, in particular the nominal power P _N , in the circuit arrangement and method in accordance with the invention.

The brightness control according to the invention can be achieved via a power controller which controls the inverter in a wide frequency range. The feedback is formed via the power determination using the synthetic measured value I _q . The closed control loop in this way is temperature-resistant, independent of the load circuit and independent of the lamp type. The setpoint for a desired performance is freely and freely definable. The The manipulated variable in the control loop is formed by the frequency of the AC output voltage, which is fed to the lamp load circuit. Equivalent to the frequency or in a particularly advantageous manner combined with the frequency, the pulse duty factor d of the AC output voltage can be used as a manipulated variable of the control loop. For the purposes of the invention, both pulse width modulation and pulse train modulation and a combination of the aforementioned types of modulation can be used for the AC output voltage u _W.

In addition to the possibility of wide and stable brightness variation, a further central purpose of the invention is to meet the specifications on the nameplate of any gas discharge lamp. This applies in particular to the nominal operation.

Assuming that the efficiency of similar tubes of different power is identical, it can be assumed that the electrical power P _up absorbed by the tube is in a fixed ratio to the light output P _from the tube. This (ratio) value is known for commercially available tubes; it is thus possible according to the invention to simulate the power consumed by the lamp in the ballast and to compare it with a predetermined target power. The power consumed and indirectly the power emitted by the tube are regulated directly via frequency variation of the inverter.

The calculation of the power _consumed by multiplication with the intermediate circuit DC voltage variable U₀ and the AC rms value I _{Weff consumed} by the tube proves to be particularly advantageous. This is the subject of claim 5.

The DC link DC voltage value for multiplication by the stated current variable changes depending on the load state and depending on the effective value of the mains voltage only to a comparatively small extent. This enables one simplified multiplication, for example through digital / analog converter. Experience has shown that the DC link voltage fluctuation, which can be replaced by any battery voltage, is ± 20% (e.g. 60V) of the nominal value (e.g. 300V). Higher voltages can also be used with changed mains supply voltages.

The dependence of the efficiency of the tube can be taken into account in terms of circuitry or program technology, so that program-wise, depending on system sizes, it can be detected which lamp is currently being connected and operated, or a predetermined efficiency level can be assumed in terms of circuitry. In the event that different types of (argon, krypton) tubes with their efficiency deviations lie within the permitted tolerance, different types of tubes can also be operated according to the invention with one and the same electronic ballast without modification.

Another essential purpose was already mentioned when the state of the art was presented. This is the uniform brightness of several electronic ballasts operated next to each other, to which one or more gas discharge lamps are connected. One area of application here is in large offices or open-plan offices in which uniform illumination is required or desired. The inaccuracy (the brightness) should be below 10%; the subjective feeling does not perceive differences in brightness within this inaccuracy range. At the same time, the set brightness for areas of the room or the entire room should be able to be varied in a simultaneous and uniform manner depending on several area setpoints or an overall setpoint. The specification of, for example, 5% of the nominal power must set a brightness in all of the luminaries concerned which satisfies the aforementioned margin of error.

The effect according to the invention here lies in the elimination of all factors influencing the output, such as Component tolerances for load inductance and / or load capacitance and / or preheating capacitance as well as frequency variations in the inverter and mains voltage fluctuations due to a superimposed power control. A power control loop formed via the synthetic combination current I _{q also} allows inexpensive implementation, since no high-frequency multiplier is used to obtain a power measurement variable P _mess . The multiplication can be carried out with two direct variables, the DC input power of the inverter results from the DC link supply voltage and input DC current, the inverter output power from the DC link supply voltage and the inverter (RMS value) output current. In the vicinity of the nominal power, the inverter losses can be neglected to a good approximation on the one hand, on the other hand they are essentially the same size - even for different devices. In this respect, the power output is essentially the power input minus the (fixed) inverter losses. In the example, a 50W lamp could be operated, the inverter losses would be in the range of approx. 5W, ie approx. 10%.

If one starts from the above-mentioned example, according to the invention a gas discharge lamp can also be operated with 1% of its brightness, this would be 0.5W in the example mentioned, with the same advantageous properties that are achieved above in the range of the nominal operation. The particular difficulty of the underlying problem is clearly recognizable if a given power of 0.5W with 10% tolerance must be given in different devices and the inverter has losses that exceed the given power by a factor of 10. This is in turn achieved according to the invention by the formation of the synthetic measuring current I _q , which takes into account both currents in combination, the input direct current (at high power) and the output alternating current (in the present case at low power). The For power calculation, multiplication takes place only with a constant, the intermediate circuit voltage U _dc and a variable I _Weff corresponding to the alternating current. This variable corresponding to the alternating current can also be obtained from the maximum value, in particular in the case of a sinusoidal shape. The use of the effective value of the output alternating current is particularly advantageous.

In other words, the effect according to the invention can be described in such a way that in the lower power range, where the inverter losses are above the lamp power to be output, the power calculation is based on the multiplication of an intermediate circuit variable and an AC output variable, whereas in the power range in which the output Light output is significantly or significantly above the inverter power loss, the power calculation is based on two DC variables taken from the DC voltage intermediate circuit. In the intermediate area there are different cross-fading or redistribution possibilities, these are advantageously a linear redistribution according to claim 3, a hysteresis-based switchover according to claim 16 or a limited continuous (section linear) continuous redistribution according to claim 9.

It is particularly advantageous to design the redistribution on the basis of the power setpoint p or P _SET . This is the subject of claim 3 and claim 8. The dependence on a constant, performance-proportional system size, which is not the predetermined target power, is specified in claim 15.

The implementation of a digital command setpoint has proven to be advantageous in the implementation, but the analog setpoint specification also has advantages. This can be decided depending on the application of the invention.

An advantageous method for calculating the absorbed or emitted lamp power is specified in claim 5.

A control technology equivalent implementation is specified in claim 10. An advantageous implementation of an inexpensive multiplier is the subject of claim 6.

A non-linear combination is possible equivalent to the aforementioned linear combinations. In this way, known lamp characteristics can advantageously be compensated for. Likewise, within the meaning of the invention, it is possible to convert the explained equivalent control circuit diagram (block diagram) according to control engineering aspects without changing its mode of operation and function. Such a change lies, for example, in the replacement of one multiplier by two multipliers, with power values being calculated in both cases, on the one hand the DC input power and on the other hand the lamp power output. The resulting two power quantities are then combined in accordance with the combination of the current values according to claim 1 to form a new synthetic power value. Such an independent realization of the idea of the invention is the subject of independent claim 17.

The synchronism of parallel operated ECGs with identical / dissimilar tubes with identical / unequal nameplate information (with large area lighting) can be ensured according to the invention in the entire dimming range. As a result , with the invention, any type of tube with any type plate specification, in particular in parallel operation of various electronic ballasts, can be operated with the stated requirements.

The invention is explained in more detail below on the basis of exemplary embodiments which describe both an electronic ballast and a method for brightness control.

• Fig.1 ein elektronisches Vorschaltgerät 1,EVG mit einem Wechselrichter 20, welches einen Lastkreis 10, der die Gasentladungslampe GE enthält, mit einer Ausgangs-Wechselspannung u_W speist;
• Fig.2 ein regelungstechnisches Ersatzschaltbild der erfindungsgemäßen Stromkombination gemeinsam mit einer anwendbaren Leistungsberechnung und einem Regler 40 eines Helligkeits-Regelkreises;
• Fig.3 ein Detail-Blockschaltbild des EVG gemäß Fig.1 mit seinen wesentlichen Komponenten und System-Meßgrößen;
• Fig.4a,4b,4c erfindungsgemäße Realisierungsbeispiele der Stromkombination zur Bildung der synthetischen Stromgröße I_q;
• Fig.5 ein Dimmensionierungsbeispiel für die Bestimmung des erfindungsgemäß zur Leistungsberechnung heranzuziehenden synthetischen Stromwertes I_q.

Show it:

• 1 shows an electronic ballast 1, electronic ballast with an inverter 20, which feeds a load circuit 10, which contains the gas discharge lamp GE, with an output AC voltage u _W ;
• 2 shows a control equivalent circuit diagram of the current combination according to the invention together with an applicable power calculation and a controller 40 of a brightness control circuit;
• 3 shows a detailed block diagram of the electronic ballast according to FIG. 1 with its essential components and system measured variables;
• 4a, 4b, 4c implementation examples according to the invention of the current combination for forming the synthetic current quantity I _q ;
• 5 shows a dimensioning example for the determination of the synthetic current value I _q to be used according to the invention for the power calculation.

An electronic ballast with which the invention is realized, shows the Fig.1. The ballast 1 can be supplied with a mains supply voltage which can be taken from the 220V or 380V mains. The inverter 20 provided in the electronic ballast can be controlled via one or more control inputs by a control circuit arrangement, as is shown, for example, in FIG. The control input effects a frequency and / or duty cycle variation of the output AC voltage u _W output by the inverter 20 to a load circuit 10. The load circuit can, as usual, consist of the series connection of a capacitance C _L, an inductor L _L and the gas discharge lamp (s) GE. In the case of a lamp which is started "warm", the heating filaments are bridged via a heating capacitor C _H. However, a cold start can be equivalent with the electronic ballast of the invention Gas discharge lamp, here the capacitor C _{H is} omitted. An ignition capacitor C _{Z is} connected in parallel to the lamp GE for the cold start. This avoids heating current. When the inverter 20 is implemented in a full-bridge circuit, the DC coupling-out capacitor C _{L can be} omitted, the load circuit then consists only of the series connection of the inductor L _L and one or more gas discharge lamps GE, and C _H or C _Z may be provided.

As already mentioned, FIG. 2 shows an exemplary embodiment for the formation of a combination current I _q and the subsequent power calculation P _mess . A combination device 22, 23, 24 is provided for this purpose, which combines the two current quantities I _W and I _dc to form the synthetic combination current I _q . The combining means is further p the reference variable, P _SOLL fed, which controls the proportions of the two input currents into the output current I _q. p represents a standardized power quantity, $${\text{p = P}}_{\text{SHOULD}}{\text{/ P}}_{\text{N}}$$

In the combination arrangement, a summing point 14 is also provided for receiving the weighted portions of the two current measured values formed in the two functional elements 22 and 23. The dependence of the function elements in the combining means of the reference variable p or P _SOLL will be explained in more detail with reference to the 4a to 4c. Replicated in the exemplary embodiment of the addition point 24 is a multiplying D / A converter 30. This can be supplied with a third measured variable at its reference input, the measured intermediate circuit supply voltage U _dc , which feeds the inverter 20 in FIG. The intermediate circuit supply voltage can be made available either from a battery voltage or from a rectified mains voltage smoothed by means of an intermediate circuit capacitor.

In the exemplary embodiment, the D / A converter is supplied with the synthetic combination current I _q in the form of a digital variable. For example, it can have 8 bits. Others too Data widths are applicable. The advantage of digital processing of I _q lies in the combination circuit or unit 22, 23, 24, which can also be implemented programmatically or digitally. For this purpose, the current measured variables I _W , I _dc are followed by analog-to-digital converters, not shown. In this way, any redistribution characteristics can be realized in the guide members 22 and 23 depending on the digitally specified command variable p. The subsequent conversion into an again analog quantity P _mess is done by the digital / analog converter 30. Such a can be used cost-effectively because the measured intermediate _circuit voltage U _dc varies only to a small extent, for example ± 20% based on the intermediate circuit voltage rating . The power P _mess determined in this way is fed analogously to a controller 40 via a subtraction point 31. This setpoint / actual value comparison enables precise light output control. The output variable of the controller 40, the manipulated variable f or d (frequency and / or duty cycle) now controls the inverter 20 shown in detail in FIG. 3 and globally in FIG.

The mixed form digital / analog shown in the exemplary embodiment of FIG. 2 can be modified in both ways. A completely digital solution can be chosen in which the multiplication 30 is also implemented in terms of program technology. The controller 40 would also be implementable in terms of program technology, its output variable can then either be digitally specified to a frequency / duty cycle generator (VCO) or the switching pulses for the inverter control can be derived directly from the digital implementation of FIG. 2. A completely analog implementation can also be selected, the functional elements 22, 23 are thus formed by linear or non-linear transmission elements. There may be a p-dependency here. However, the idea according to the invention can also be implemented with p-independent (then non-linear) function elements 22, 23.

A gain-controlled is equivalent for the digital / analog converter 30 in the case of analog implementation Operational amplifiers (OTA) or a real analog multiplier (simple, since only constant values are available) can be provided.

3 shows a basic circuit diagram of the inverter 20, as is shown schematically in FIG. The measuring elements 25, 26, 27 used to measure the system sizes are only shown in principle. First, the intermediate circuit voltage U₀, U _{dc is} measured by means of the voltage measuring element 27 and, if appropriate, is supplied to the multiplier 30 in a correspondingly amplified or potential-shifted manner.

The load circuit 10 connected to the inverter output branch is connected in the exemplary embodiment in parallel to the upper power semiconductor switch S 2. Equally, this load circuit can be connected in parallel to the lower power semiconductor switch S 1 of the inverter output branch. The control of the two power semiconductor switches is shown only schematically, it responds to control signals from the controller 40 or a VCO (voltage controlled oscillator) and controls the two series-connected power semiconductor switches S₁, S₂ accordingly. The output AC voltage u _{W is} delivered to the load circuit 10 between the two switches. Equivalent to the half-bridge circuit principle shown here, an inverter with a full bridge can be used, in which case the load circuit must be connected between the two center taps of the parallel inverter output branches. The coupling capacitor C _{L of} the load circuit can be omitted.

As a further measured variable, the DC intermediate circuit current, which can be supplied to the inverter (the output branch of the inverter), is now measured by means of the current measuring point 25, which is preferably designed as a current measuring shunt. The current measuring point 25 can be connected with the same effect in front of the DC link smoothing capacitor C₀ shown, since this does not absorb direct current for stationary operation. Furthermore, the alternating current i _W flowing in the load circuit 10 measured by means of the current measuring point 26, which is preferably also designed as a current measuring shunt and has a common reference point with the current measuring point 25. A common reference point can be both the positive and the negative supply voltage connection. This depends on the connection of the load circuit 10 to the inverter 20.

The voltage measuring point 28, which is also shown and which detects the voltage of the load or the inverter output voltage u _W , can be used for a monitoring circuit or for detecting lamp types or types (via the burning or ignition voltage).

The load current i _W detected by means of the current measuring point 26 can also be conducted via an alternating current / effective value generator 31 before it is fed to the functional element 22 or an A / D converter. A maximum current sensor can be used equivalent to the RMS generator. With sinusoidal current, you can derive the effective value by dividing the voltage over the maximum value. Other AC / DC converters can also be used. The direct current I _dc detected via the current measuring point 25 can be smoothed or converted in an analogous manner.

The converter 31 shown in FIG. 3 forms an implementation example; it can also be arranged after the summing point 24 or after the function element 22 without modifying the transfer function of the system according to FIG.

The 4a, 4b and 4c show possible Umsteuerkennlinien or redistribution dependencies, such as 22 and 23 are used in the combination unit 24 or the function blocks 22,23. A dependency on the command variable p is shown. Two weighting factors g are plotted in the ordinate direction, which, when multiplied by the respective input variable I _W or I _{dc, give} the weighted portion of the synthetic measurement variable I _q . A dependency on is equivalent to the dependency on the reference variable p of any power or current proportional system size. This can be both a target size and an actual size.

4 a shows a linear, continuous redistribution for the example of the functional element 23, in this case there is a constant change between the two current quantities I _dc and I _Weff between the power zero and the nominal power P _N. As the one size increases, the other size decreases until the synthetic combination current I _q at nominal power only consists of the direct current value I _dc , while at zero power it only consists of I _Weff .

4b shows a similar behavior of the function elements 22, 23 , but here the redistribution is limited to a predetermined range p _S1 ≦ p ≦ p _S2 . Within this range there is a continuously linear redistribution between the two current quantities mentioned. Outside the _specified power range, the AC current _value I _Weff is contained in the low _load range, ie for low values of p, dominantly or solely in the combination _variable I _q . The lamp power is therefore (almost) entirely determined and regulated by I _Weff in the strongly dimmed range. As a result, excellent synchronization of lamps which are fed from different electronic ballasts 1 is achieved for the same lamp types (also in the low-load range). In the power range above the first range mentioned, namely for p> p _S2 , the lamp power is dominated by the direct current variable I _dc or formed solely. I _dc determines the measured value I _q for the lamp power in the full load range, so a lamp type-independent power setting is possible on this basis alone. There is a simple adjustment, the suitability of the electronic ballast for different lamp types (Argon, Krypton ...) or different nominal powers (40W, 60W ...) are guaranteed.

4c shows a further variant of the redistribution between the two current quantities I _dc and I _Weff . Here is a hysteresis-related switchover is shown, the respective basic values at which a switchover takes place are denoted by p _S1 and p _S2 . For values above p _S1 , the direct current _variable I _{dc dominates} in the synthetic current variable I _q . If the power value _drops further, the proportion of I _dc in I _{q is} suddenly reduced to an insignificant value, whereas, in contrast, the value of I _{Weff is increased with} equal _priority . In practice, it is advisable to slightly attenuate the sudden changeover so that there is a constant redistribution at switching points p _S1 and p _S2 within the scope of the hysteresis. With a correspondingly increasing power value, the system does not _switch back at p _S1 , but rather according to the hysteresis p _S2 -p _S1 at the second threshold value p _S2 (this prevents vibrations). As mentioned, the switching points or threshold values can also depend on or be formed from other power or current-promoting system variables, for example from I _S1 , I _S2 (values in the range of the direct current I _dc ).

The respective weighting factors g shown in FIGS. 4a to 4c can be specified digitally or analogously. 5 shows the linear equation implemented according to FIG. 4 a for determining the synthetic current value I _q . The value 1-p corresponds to one of the weighting factors g; that weighting factor shown in dashed lines in FIG.

The power parameter P _mess output by the multiplier unit 30 or the voltage-controlled amplifier OTA essentially _indicates the power P consumed _on the gas discharge lamp, regardless of the actual operating state of the inverter. It eliminates the difficulties that a strongly fluctuating power output to the gas discharge lamp (s) has different effects in relation to the relatively constant inverter losses. If the inverter losses are essentially constant over the entire power range, even if there is a recognizable frequency dependency, a variation of the power consumed by the gas discharge lamp by 100% (0% ... 100% of P _N ) is made possible. In this case, especially when the lamp power is low, the inverter losses fall the spread of the losses of various devices, clearly weighting the overall current account. This can be compensated for by the redistribution in the current variable I _q or power variable P _q . If the efficiency of the gas discharge lamps used is essentially known, the power P absorbed by the tube can be set _to in direct relation to its regulating light output line P _from . This is slightly dependent on the gas filling of the gas discharge lamp, such as argon, krypton or neon. A measurement / calculation of the power P _mess absorbed by the tube ensures the required uniformity of the brightness control process and its wide range with acceptable accuracy.

Finally, it should be mentioned that the DC input current I _{dc of} the inverter 20 can pulsate strongly due to the switching operations of its power semiconductors S 1, S 2. When the load circuit 10 is switched on in the intermediate circuit supply voltage circuit, i _dc , I _dc corresponds to the load current i _W. When the load circuit 10 is switched to "free running", in which it is decoupled from the intermediate circuit supply voltage, the intermediate circuit input current I _dc , i _dc drops to zero. A corresponding smoothing measure, for example by means of a low-pass filter, enables the provision of a processable constant quantity. The time constant of this smoothing can be selected depending on the desired response time of the brightness control to change commands or changes in brightness.

The exemplary embodiments shown have been explained using one or more gas discharge lamps GE. It goes without saying that other load circuits 10, in particular lighting elements, can also be operated in the same way with the same advantage. This also applies, for example, to low-voltage halogen lights / lamps (12V, 24V) which can be controlled by inverters via transformers and which, according to the invention, can be dimmed uniformly in a previously unattained range.

Claims (15)

1. Method of controlling the brightness (dimming) of gas discharge lamps (GE) in dependence upon a control parameter, or a desired-value parameter/value (p, P_Soll), in which
      an output a.c voltage (u_W, U_lampe), or an output a.c. current (i_w, I_lampe), derived from an intermediate circuit d.c. voltage (U₀, U_dc), variable in pulse duty factor (d) and/or frequency (f), is delivered to one or more gas discharge lamps (GE),
      an intermediate circuit d.c. current (I_dc) derived from the d.c. voltage (U₀, U_dc) and transformed into the variable output a.c. voltage/current (u_w, i_w) is measured and delivered as first measured parameter (I_dc) and
      the output a.c. current (i_w, I_lampe) delivered to the gas discharge lamp (GE) is measured, is transformed into a d.c. parameter (i_Wmax, I_Weff) corresponding to the a.c. current (i_w) and is delivered as second measured parameter (I_Weff),
      characterised in that,
      the two measured parameters (I_dc, I_Weff) are combined with one another (22, 23, 24) to form a synthetic measured parameter (I_q, i_q) in such a manner that the combination of the two measured parameters (I_Weff, I_dc) is dependent upon the control parameter (P, P_Soll), whereby with increasing control parameter (p) the contribution of the first measured parameter (I_dc) to the synthetic measured parameter (I_q, iq) increases to the extent that the contribution of the second measured parameter (I_weff) to the synthetic measured parameter (I_q, iq) at the same time decreases.
2. Method of controlling the brightness according to claim 1,
   characterised in that,
   the two measured parameters (I_Weff, I_dc) are combined linearly.
3. Method of controlling the brightness according to any preceding claim,
   characterised in that,
   the control parameter (p, P_Soll) can be provided in analog or digital form and a combination, or the linear combination (I_q), is formed by means of digital or analog multiplication (22, 23) of the respective measured parameters (I_dc, I_Weff) with oppositely-going weighting factors (g) corresponding to the control parameter (p, P_Soll) and by subsequent addition (24) of the weighted products.
4. Method of controlling the brightness according to any preceding claim,
   characterised in that,
   the intermediate circuit supply voltage (U_dc), or a battery voltage (U₀) forming this supply voltage, is measured and delivered as third measured parameter (U_dc),
   and in that,
   the third measured parameter (U_dc) is multiplied with the synthetic measured parameter (I_q, iq) and the product of the multiplication is delivered as actual-value power parameter (P_mess), corresponding to the lighting power (P_ab) emitted by, or to the power(s) (P_auf) consumed by, the gas discharge lamp or lamps (GE).
5. Method according to claim 4,
   characterised in that,
   for the multiplication and for delivery of the actual-value power parameter (P_mess) there is employed a digital/analog converter (DAU, 30) or a voltage or current controlled amplifier (OTA, 30) the reference input or amplification control input of which is supplied with the third measurement parameter (U_dc) and the digital or analog input of which is supplied with the synthetic measured parameter (I_q).
6. Method according to claim 4 or 5,
   characterised in that,
   the frequency (f) and/or the pulse duty factor (d) of the output a.c. voltage (u_w) delivered from an inverter (20), that is part of the electronic ballast (EVG, 1), is so varied by a controller or amplifier (40) in dependence upon the difference between control parameter (p, P_Soll) and the actual-value power parameter (P_ab, P_mess) that the desired lighting power (P_ab, P_mess) is provided by the gas discharge lamp(s).
7. Method according to claim 1 or 2,
   characterised in that,
   with desired-value parameter (p, P_Soll) increasing from zero, the synthetic measured parameter (I_q, i_q) has a substantially linearly continuously increasing proportion of the first measured parameter (I_dc), and corresponds completely or virtually completely to the first measured parameter (I_dc) at or from rated power (P_N) or rated current (I_N) of the gas discharge lamp(s) (GE).
8. Method according to claim 1 or 2,
   characterised in that,
   as combination there is taken a substantially linear continuous redistribution of the proportions of the first and second measured parameters (I_q, i_q) between a first predeterminable threshold value (P_S1, I_S1) and a second predeterminable threshold value (P_S2, I_S2), in particular in dependence upon the control parameter (p, P_Soll).
9. Method according to claim 4,
   characterised in that,
   the conversion of the measured output a.c. current (i_w, I_lampe) into a d.c. parameter corresponding to the a.c. parameter, in particular an effective or maximum value (i_Wmax, I_Weff), is effected by circuitry or program means after the multiplication (30) with the third measured parameter (U_dc).
10. Electronic ballast (1, EVG) for controlling the brightness (dimming) of a gas discharge lamp (GE), in particular gas discharge lamps of different types, such as argon or krypton lamps, or of different rated powers (P_N),
       having an inverter (20) which delivers an output a.c voltage (u_w) of variable frequency (f) and/or variable pulse duty factor (d) to a load circuit (10) containing the gas discharge lamp (GE),
       having a first and a second current measuring element (25, 26) for detecting a lamp current (I_Weff, I_Lampe) and a d.c. current taken by the inverter (20) or an intermediate circuit smoothing capacitor (C₀) and
       having a first voltage measuring element (27) for detecting an intermediate circuit d.c. voltage (U₀) of the inverter (20),
    characterised in that,
       the measured current parameters (I_Weff, I_dc) of the current measuring elements (25, 26) are brought together or combined into a synthetic measured current parameter (I_q) and
       the synthetic measured parameter (I_q) multiplied with the measured parameter of the d.c. voltage (U_dc, U₀) forms in substance an actual-value power parameter (P_mess) representing the lamp power consumed or emitted (P_ab, P_auf) for a power control circuit (40, 20, p, P_Soll, GE, 10).
11. Electric ballast according to claim 10,
    characterised in that,
    the power control circuit (40, GE, 10, p, P_Soll) has a controller (40) to which the difference between predeterminable desired-value power parameter (P_Soll, p) and actual-value power parameter (P_mess) can be supplied and which delivers to the inverter (20) at least one setting parameter (f_soll, d_soll) by means of which the frequency (f) and/or the pulse duty factor (d) of the inverter output a.c. voltage (u_w) can be varied.
12. Electric ballast according to claim 10 or claim 11,
    characterised in that,
    the current measuring elements (25, 26) are resistance shunts which deliver their respective measured parameters (i_w, I_dc) symmetrically with respect to the same reference point, preferably the positive intermediate circuit supply terminal (U₀) of the inverter (20).
13. Electronic ballast according to claim 10,
    characterised in that,
    the combination of first and second measured current parameters (I_dc, I_Weff) is dependent upon the desired-value parameter (p, P_Soll) of the power control circuit (20, 40, 10, GE) in such a manner that
    at higher power (P_Soll, P_mess) the first measured current parameter (I_dc) forms the main part of synthetic measured parameter (I_q), whilst at lower power (P_Soll, P_mess) the main part is formed by the second measured current value (I_Weff).
14. Method according to claim 1,
    characterised in that,
    the dependency of the proportions of first or second measured current parameters (I_dc, I_Weff) in the formation of the synthetic measured current parameter (I_q) is controlled by a power parameter (P_mess; U_dc*I_dc; U_W*I_Weff) or measured parameter (I_dc, I_Weff) which in the steady-state case is equivalent to the control parameter/desired-value power parameter (P_Soll, p).
15. Method according to claim 1 or 2,
    characterised in that,
    the combination of the measured current parameters (I_dc, I_Weff) in the synthetic measured parameter (I_q) is effected by hysteretic switching between the two measured current parameters (I_dc, I_Weff), the threshold value (p_S1, P_S2, I_S1, I_S2) predetermining the switching point being formed by a system parameter dependent upon lamp power, such as power desired-value parameter (p, P_Soll), first measured current parameter (I_dc) or lamp power actual-value parameter (P_mess).

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