EP1901591B1 - Ignition of gas discharge lamps in variable ambient conditions - Google Patents

Abstract

The method involves overlaying a direct current in a fluorescent lamp and determining a direct current portion of a fluorescent lamp current. A lamp power output of the fluorescent lamp is controlled with the determined direct current portion as a control variable and a variable analog or digital direct current-reference variable. An operation of the fluorescent lamp is controlled before igniting the lamp based on the direct current portion as the control variable. An independent claim is also included for an operating device for controlling a fluorescent lamp.

Description

The present invention relates to the operation of AC powered lamps, in particular fluorescent lamps, e.g. Gas discharge lamps. The invention relates to the control of such lamps, taking into account the ambient conditions, such as the ambient temperature. Such regulations are used in operating devices such as electronic ballasts.

Accordingly, fluorescent lamps operated with dimmable electronic ballasts can be operated close to the nominal mode - and thus at nominal power - and on the other hand with dimmed, ie reduced lamp power. The operation with nominal power is relatively unproblematic compared to the operation with reduced, in particular greatly reduced lamp power. Accordingly, the permissible lamp ambient temperatures in dimming operation are specified much narrower compared to the normal power operation. Namely, at low dimming values, the ambient temperature of the lamp plays a greater role for a stable regulation of the dimmed fluorescent lamps, ie a regulation with constant light output and in particular a regulation, which reliably prevents unwanted extinction of the lamp.

The stronger lamp ambient temperature dependence at low dimming levels is i.a. caused by the fact that the lamp voltage at low ambient temperatures and small lamp currents (as they occur with dimmed lamp power) increases sharply and may take inadmissibly high values. For this phenomenon, of course, the temperature in the immediate vicinity of the lamp is crucial, which does not necessarily have to be the ambient temperature of an optionally spatially and thermally separated from the lamp electronic ballast. Thus, the temperature of the electronic ballast can not be used directly to assess the lamp ambient temperature.

Moreover, in certain application scenarios, it can not be ruled out that the permissible temperature range specified for low dimming values will be left out, for example when dimmable electronic ballasts are operated in outdoor applications and at low temperatures in the dimmed state.

From the not yet published patent application DE 102005018763 It is already known to selectively superimpose a DC voltage to a fluorescent lamp, for example, to a high-frequency AC voltage in order then to evaluate the DC voltage resulting from the lamp in a further step. This DC component will be the Fluorescent lamp thereby supplied that a DC voltage path is provided in parallel to the AC operating voltage for the fluorescent lamp. The detection of the DC voltage component of the fluorescent lamp voltage takes place in this prior art only when the lamp is ignited. Before the ignition of the lamp, however, another control circuit is provided for the operation of the fluorescent lamp. At the time of ignition of the lamp must therefore be switched to the detection and evaluation of the DC voltage component. However, this switching between two control loops may be problematic in that it may, for example, lead to a visible increase in lamp output, which may be visible to the human eye.

Furthermore, in this prior art, an ignition detection by detecting a strongly decreasing lamp voltage is necessary in order to switch to the DC voltage evaluation and the corresponding control circuit can.

The invention has accordingly set itself the task of providing an improved and simplified technique for controlling a fluorescent lamp, which can reliably prevent the lamp from extinguishing even under extreme conditions.

The invention now addresses this problem and proposes already during the ignition of the lamp perform the DC detection and evaluate control technology.

Furthermore, it is an aspect of the invention that a variable DC value can be specified as a setpoint value, wherein the setpoint value can depend on the current operating state of the lamp (for example ignition, combustion mode, etc.).

The object is solved by the characterizing features of the claims, wherein the combination of the claims is characterized as a particularly advantageous solution to the problem.

According to a first aspect of the present invention, a method for controlling the operation of at least one (typically high-frequency) AC voltage operated fluorescent lamp according to claim 1.

In particular, the regulation of the lamp power will be made before their ignition and then of course continue in the burning operation.

The DC control variable may depend on the operating state of the lamp - such as preheating, ignition, or operation - and thus be temporally changeable.

The lamp resistance can preferably be kept constant.

The DC voltage component can be determined on the basis of a measurement signal derived at a voltage divider.

The DC voltage component of the lamp voltage can be determined based on the distances between the zero crossings of the lamp voltage.

The regulation of the lamp operation can be digital.

An externally specified dimming value can be taken into account for regulating the lamp power.

The power of the lamp may be increased to a value higher than the externally set dimming value depending on the value of the DC voltage portion of the lamp voltage.

According to a further aspect of the present invention, an operating device for controlling at least one AC voltage-operated fluorescent lamp according to claim 11.

The DC voltage command variable can be specified as a digital value.

In particular, the lamp control circuit is designed to regulate the lamp power even before the ignition of the fluorescent lamp.

The DC voltage command variable may depend on the operating state of the lamp - such as preheating, ignition, or operation - or detected operating parameters and thus be temporally variable.

Means may be provided which keep the lamp resistance constant.

Preferably, a voltage divider is provided for determining the DC voltage component.

The DC voltage component of the lamp voltage can be determined based on the distances between the zero crossings of the lamp voltage.

Means can be used for the digital control of the lamp power.

The lamp control circuit may have an input for externally preset dimming values.

The control circuit may, depending on the value of the DC voltage component of the lamp voltage, increase the power of the lamp to a value which is above the externally preset dimming value.

According to a next aspect of the present invention, an electronic ballast according to claim 21.

According to another aspect of the present invention is a luminaire according to claim 22.

Fig. 1a

zeigt dabei eine schematische Darstellung relevanter Bauteile eines elektronischen Vorschaltgeräts gemäß der vorliegenden Erfindung,

Fig.1b und 1c

zeigen vereinfachte Schaltbilder zur Erläuterung des Hintergrunds der vorliegenden Erfindung,

Fig. 2 und 3

dienen zur Erläuterung der indirekten digitalen Erfassung der Impedanz der Lampe, die dann als Parameter für die Lampentemperatur verwendet werden kann,

Fig. 4

zeigt die Abhängigkeit der Lampenspannung vom Lampenspannung für verschiedene Lampentemperaturen,

Fig. 5

zeigt die Abhängigkeit der Impedanz vom Lampenstrom für verschiedene Lampentemperaturen,

Fig. 6

zeigt eine vereinfachte schematische Darstellung eines erfindungsgemäßen elektronischen Vorschaltgeräts, und

Fig. 7

zeigt den Verlauf von verschiedenen Lampenparametern abhängig vom Betriebszustand der Lampe.

Further features, advantages and features of the present invention will now be explained in more detail with reference to the figures of the accompanying drawings.

Fig. 1a

shows a schematic representation of relevant components of an electronic ballast according to the present invention,

Fig.1b and 1c

show simplified circuit diagrams for explaining the background of the present invention,

FIGS. 2 and 3

serve to explain the indirect digital detection of the impedance of the lamp, which can then be used as a parameter for the lamp temperature,

Fig. 4

shows the dependence of the lamp voltage on the lamp voltage for different lamp temperatures,

Fig. 5

shows the dependence of the impedance on the lamp current for different lamp temperatures,

Fig. 6

shows a simplified schematic representation of an electronic ballast according to the invention, and

Fig. 7

shows the course of different lamp parameters depending on the operating status of the lamp.

In 4 and 5 is shown that the lamp voltage V _Dis at low temperatures (see example, -15 ° C) in the low dimming range (represented by the lamp current I _Dis ) can rise very high and may exceed permitted limits. In the reference example of a lamp temperature of 35 ° C, this effect occurs less strongly or not at all. At the same time it is off Fig. 4 to see that the lamp voltage V _Dis is not a clear parameter for the temperature of the lamp as a whole. As can be seen, in the region of slightly higher lamp currents, the lamp voltage V _Dis at higher temperatures (example 35 ° C.) may even exceed that at low temperatures (example -15 ° C.).

The illustrated dependency of the lamp voltage is due to the fact that the lamp resistance (ie the impedance of the discharge path of the lamp at the respective operating point) has both a dependence on the discharge current V _Dis and on the ambient temperature T. In a certain operating point, in which the Lamp current I _{Dis of} the ballast is kept substantially constant, thus there is a dependence of the lamp impedance Z _Dis of the ambient temperature T.

As in Fig. 1b and 1c schematically illustrated, the present invention proposes to store the usually high-frequency operating voltage for the lamp U _HF targeted a DC voltage V _DC from a high-impedance source, so that then used the DC component of the voltage applied to the lamp voltage as an indicator for it under which conditions the lamp is currently being operated:

die Abhängigkeit des aus der Messung hergeleiteten DC-Anteils der Lampenspannung V_DC,ZL von der Umgebungstemperatur T der Lampe erfasst werden.The source voltage V _{DC of} the DC source is divided according to the resistance ratio of internal resistance of the DC source Z _i to the impedance of the lamp Z _l at the current operating point, wherein the lamp resistance Z _l et al depends on the ambient temperature of the lamp T. This can also be done via the resistance ratio $${\mathrm{Z}}_{\mathrm{L}}\mathrm{/}\left({\mathrm{Z}}_{\mathrm{i}}\mathrm{+}{\mathrm{Z}}_{\mathrm{L}}\right)$$

the dependence of the DC component derived from the measurement of the lamp voltage V _{DC, ZL} on the ambient temperature T of the lamp is detected.

If the DC component of the lamp voltage V _{DC, ZL is} outside a defined range, and in particular if it is above a defined threshold value, the electronic ballast can take appropriate countermeasures. It makes sense to detect the DC component of the lamp voltage V _{DC, ZL} over a certain time range and then to average it to take account of temporal compensatory processes in the lamp.

If now this average value of the DC component of the lamp voltage V _{DC, ZL increases} beyond a permissible threshold value, the ballast can automatically increase the lamp power, for example, until the DC component of the lamp voltage V _{DC, ZL} returns to permissible values , ie has fallen below the predetermined threshold. By 'automatic increase of the lamp power through the electronic ballast' is to be understood that the electronic ballast also increases the lamp power over possibly supplied from the outside setpoints (Dimmbefehle, etc.) and thus the stability of the lamp control has a higher priority than the strict compliance specified outside values (dimming commands, etc.) is granted.

This increase in lamp power can be restricted according to the invention to the range of low dimming values.

It is important in this case to set the time constant of the control correctly: As is known, thermal compensation processes take place in a fluorescent lamp, so that the time constant of the control circuit in the electronic ballast must be matched to these processes.

If, for example, the DC component of the lamp voltage V _{DC, ZL} decreases again in time, for example because the ambient temperature of the lamp has increased again, the electronic ballast decreases the lamp power again until either the DC power again predetermined threshold value for the DC component of the lamp voltage V _{DC, ZL is} reached, or now correctly the predetermined target value (Dimmbefehl, etc.) for the lamp power has been reached.

In Fig. 1a schematically an embodiment of the present invention is shown.

The ballast according to the invention has an inverter 1 with two series-connected, connected to a DC voltage source DC voltage and alternately clocked transistor switches S1 and S2. The switching can be done by a control unit 2, which can be realized as a digital circuit or integrated circuit (IC).

At the junction of the two switches S1 and S2, a load circuit is connected, which has a resonant load circuit 3 and a lamp 4. The resonant load circuit 3 consists of an inductance L _R , a capacitor C _R and a coupling capacitor C _K.

The lamp 4, which is schematically denoted by its internal resistance R _disl , is connected to the resonant load circuit 3 and is operated by the provided by the inverter 1 high-frequency AC voltage. The lamp 4 may in particular be a fluorescent lamp such as a gas discharge lamp.

Parallel to the coupling capacitor C _K and the inductance L _R , a diode D is optionally connected in series with a preferably high-resistance resistor R_DC. Of the Resistor R_DC can also be connected directly to the DC bus voltage.

Thus, a direct voltage component V _DC is selectively added to the alternating operating voltage of the lamp 4. This DC voltage can also be superimposed in an alternative manner to the AC voltage of the fluorescent lamp.

As in Fig. 1 As can be seen, a voltage divider with two resistors R1, R2 is connected in parallel to the lamp 4. At the circuit node between the two resistors R1, R2 of the voltage divider, a measurement signal U _{L is} tapped, which corresponds to the voltage of the lamp 4.

This measurement signal U _L is the control unit 2 and in particular a circuit 5 and a setpoint generator 6 is supplied. On the basis of this measurement signal U _L , the circuit 5 or the setpoint generator 6 can measure the alternating voltage drop across the lamp 4. Since, however, this AC voltage contains a DC voltage component, a value is also evaluated by the circuit 5 or by the setpoint generator 6, which value corresponds to the DC voltage component of the lamp voltage.

The measurement signal U _L generated by the voltage divider is supplied to one input of a setpoint value transmitter 6. This setpoint generator 6 supplies a setpoint value for the DC voltage component of the lamp voltage as a function of the lamp voltage, that is, on the measurement signal U _L and / or as a function of the operating state (for example, unlit / burning mode) of the lamp (variable setpoint value).

The actual value or the controlled variable U _{DC, is} and the setpoint or the command variable U _{DC, should} be a DC controller 7 is supplied, which supplies depending on the control difference between the setpoint and the actual value a manipulated variable for the regulation of the DC voltage component , This manipulated variable may relate, for example, to the clock frequency of the two switches S1, S2.

As schematically in Fig. 1 can also be the lamp control circuit further operating parameters such as the lamp current, etc., and externally specified values (Dimmbefehle, etc.) are supplied.

As already mentioned, according to the present invention, the lamp operation can be carried out digitally.

Thus, preferably also the DC voltage component of the lamp voltage is evaluated digitally. This will now be with reference to FIGS. 2 and 3 be explained.

Fig. 2 shows a circuit implementation of this embodiment with an up / down counter 107, which receives as a real input signal, a signal UZERO and further as control signals a high-frequency reference clock signal CLK and a reset or reset signal. The signal UZERO assumes a positive and otherwise a negative voltage level during each positive half wave of the voltage applied to the terminal VL and thus detects the zero crossing of the lamp voltage. The counter 107 is initialized in case of concern of the reset signal to an average count, eg to the output counter value N ₀ = 255. The counter 107 is started at zero crossing of the lamp voltage and counts during the subsequent half cycle of the lamp voltage either up or down. If the measuring signal, ie the lamp voltage, returns to the zero crossing after a half period, the counting direction of the counter 107 is reversed. After a full period of the lamp voltage, the current count N of the counter 103 is a comparator connected, which may be formed for example by the comparator 103 already described above. This comparator 103 compares the current counter reading N with the initialization value or the original counter reading of the counter 107. If there is no rectification effect, the counter reading N must have reached the output value N ₀ again after reaching the next zero crossing of the lamp voltage. On the other hand, if the count N deviates from the output value N ₀ , a DC voltage component is present in the lamp voltage. Advantageously, the comparator 103 compares the count N with the output value N ₀ within certain tolerance limits, so as not to prematurely infer the presence of a rectifying effect. The output signal of the comparator 103 is fed via a clocked by a latch signal D flip-flop 108 of the measuring phase control 900, which - as described above - evaluates this signal and in particular performs an event filtered score, ie only on the presence of a DC voltage component closes if one of the comparator 103, for example, 32 times in succession each 255. period of the lamp voltage a DC voltage component is reported.

The invention will now be described with reference to the in Fig. 6 illustrated block diagram further explained.

The system according to the invention for the reliable ignition of, for example, gas discharge lamps contains two essential components namely a control unit or a controller 11 and a controlled system 12, which comprises the above-mentioned inverter or half-bridge 1, a resonance load circuit 3 and the lamp 4.

The control unit 11 essentially controls two switches of the inverter 1 for providing a high-frequency alternating voltage for ignition or for operation of the gas discharge lamp 4.

The power P_lamp and / or the voltage V_lamp of the gas discharge lamp 4 are first detected by various known methods. The lamp voltage V_lamp is supplied to a unit 14 for evaluation of the DC voltage component of the lamp voltage. This evaluation can be performed by various methods, such as those discussed above FIGS. 2 and 3 described detection of the zero crossings of the lamp voltage.

The actual DC voltage component of the lamp voltage is compared with a nominal value DC target, and the difference V_DC_lamp of both values is supplied to a DC controller 18. In particular, one of the following regulators can be used for the DC regulator 18: Proportional controller (P controller), proportional-integral controller (PI controller), proportional-integral-derivative controller (PID controller), proportional-derivative controller (PD controller). In the described embodiment, the DC controller 18 is preferably a PI controller.

As described below, the output signal of the DC controller 18 is supplied as a setpoint to another control circuit, namely a lamp power control loop.

An analog-to-digital converter 13 converts the analogously detected lamp power P_lamp into a digital signal which is compared as an actual value with the manipulated variable of the DC controller 18 as a sol value. The result is supplied as a control difference to a power regulator 17 for regulating the lamp power.

As a manipulated variable, the power regulator 17 controls, for example, the frequency of the AC voltage of the lamp. Usually, the frequency of the inverter is accordingly controlled.

Thus, two control loops are provided, wherein the outer or first control loop has the DC controller 18 and predetermines the nominal value DC target for the DC component on the lamp 4 depending, for example, on the operating state or also on other parameters from the lamp circuit. In this first control circuit, an inner or second control loop with the power regulator 17 is provided, which then regulates the lamp operation to the (variably predetermined) DC component.

• Vorgabe eines ,dithering' oder sonstige regelmäßige oder zufällige Wechsel der DC-Sollwertvorgabe zur Verringerung beispielsweise von Quecksilbermigration,
• eine kontinuierliche Einstellung des Sollwerts im Gegensatz zu schaltbaren (stufenförmigen) Sollwertvorgaben,
• Lampenparameter, die beispielsweise auf einen Gleichrichtereffekt zurückschließen lassen, und
• der aktuelle Betriebszustand der Lampe (nicht in Betrieb, Vorheizung, Zündung, in Betrieb).

The following variables can influence the variable DC component (setpoint) by changing the DC setpoint DC target accordingly:

• Specification of a dithering or other regular or random change of the DC setpoint preselection to reduce, for example, mercury migration,
• a continuous setting of the setpoint in contrast to switchable (step-shaped) setpoint specifications,
• Lamp parameters, for example, can refer back to a rectifier effect, and
• the current operating status of the lamp (not in operation, preheating, ignition, in operation).

The rectifier effect may e.g. on older fluorescent lamps and lead to overload of the ballast. The fluorescent lamp then acts in a similar way to a rectifier, preferentially passing the lamp current in one direction while being less well transmitted in the opposite direction. Such a current shift between individual lamp branches can be detected by the evaluation of the impedance i. the DC voltage component of the lamp voltage can be detected. The power of the lamp 4 can thus be regulated accordingly.

Fig. 7 shows how the DC component can be made dependent on the operating state of the lamp 4.

After switching on the ballast (t = t1), the lamp voltage usually rises as long as there is no short circuit in the circuit. Once the lamp voltage reaches a certain setpoint preheat voltage, it is held constant for a time. During this preheat time, the DC component setpoint remains the same.

As soon as the preheating time is reached at t = t2, the control unit 11 lowers the frequency of the inverter 1. As a result, the voltage at the terminals of the lamp 4 increases. As long as this lamp voltage increases regularly, the DC component setpoint is reduced accordingly on a regular basis. This phase is up Fig. 7 between t2 and t3.

When an ignition of the lamp 4 takes place, the lamp voltage drops sharply at t = t3. This is detected by the system by detecting the lamp voltage, so that now the DC component setpoint can be maintained at a lower and constant level.

The activation of the control circuit thus ignites the lamp and keeps it safely in operation in the critical phase after ignition. The inner loop detects the lamp power and thus provides the opportunity to set a defined power. Furthermore, the inner loop is designed so that it can stabilize unstable operating points of the outer circle. This is necessary when operating at low temperatures and destabilized lamps (deposition of mercury).

The outer control loop keeps the DC voltage of the lamp constant, which corresponds to their resistance. The nominal value of the DC control loop is set to the 1% nominal power of a new lamp at nominal temperature. To ignite the lamp both control circuits are closed. The initial conditions here are a maximum frequency for the output of the power controller 17 and a minimum power for the output of the DC controller 18. The DC control loop will now reduce the existing control difference and ignite the lamp. After being ignited, the controls are used to set the DC setpoint.

In practice, it can be seen that an optimum 1% startup can be achieved using this method. Helpful here is that even before the breakthrough of the gas line, the partial ionization leads to a reduction of the lamp resistance and thus has a positive effect on the dynamics of the system. The invention described here guarantees the highest quality of a 1% start in all conditions.

One possible realization method of the lamp current detection is, as shown, the evaluation of the lamp voltage. The prerequisite for this, however, is a constant DC current that must be supplied to the lamp. The evaluation of the zeros, more precisely the ratio between T_pos, time during which the signal is positive, and T_neg, time during which the signal is negative, includes information about the lamp current, as well as the information of the lamp voltage.

wobei C und C1 jeweils eine Konstante ist,
und im Falle eines Gasdefekts auf die Lampenspannung: $$\mathit{N\_d}\mathit{c}=\frac{C2}{\mathit{\pi }}*\arcsin \left(\frac{-C}{\mathit{Vrms}*\sqrt{2}}\right),$$

wobei C und C2 jeweils eine Konstante ist.It is thus possible to control the lamp current during operation of the lamp and to regulate it to a lamp voltage in the gas defect or in the absence of a lamp. It is then a regulation of the ignition voltage load capacity independent. In operation, the current can thus be regulated: $$\mathit{N\_D}\mathit{c}=\frac{C1}{\mathit{\pi }}*\arcsin \left(\frac{-C}{\mathit{Irms}*\sqrt{2}}\right).$$

where C and C1 are each a constant,
and in the case of a gas defect on the lamp voltage: $$\mathit{N\_D}\mathit{c}=\frac{C2}{\mathit{\pi }}*\arcsin \left(\frac{-C}{\mathit{Vrms}*\sqrt{2}}\right).$$

where C and C2 are each a constant.

The always activated power control loop keeps the system stable. This means that even if the operating points are not always stable (for example, active - passive dipole, lamp - output circuit), the system is kept stable. Due to the high demands on the Ausregelgeschwindigkeit of the inner control loop ensures that the inner loop is not a bottleneck with respect to settling time.

Another advantage is the permanently switched on power control even before the ignition of the lamp, since the system already works completely and is initialized. There are no switching and initialization must be made. The ignition timing is no longer important in this system. It can vary greatly due to the lamp and the environment, which would be a disadvantage for an optimal start.

As already mentioned, the electrical properties of gas discharge lamps can vary widely under variable environmental conditions such as ambient temperature, aging state and burning time (mercury ionization). Such a change in the electrical properties of the gas discharge lamp means a change in the voltage / current characteristic of the lamp.

Since a certain minimum current of the lamp must be ensured in order to leave the gas path in the ionized state, and since this minimum current in turn depends on the state of the lamp, the inventive method or operating device avoids extinction of the gas discharge lamp, by falling below the ambient condition-dependent minimum lamp current prevented.

The method according to the invention makes use of the determination of the environment-dependent electrical parameters and thus of the minimum current, the lamp resistance being the electrical parameter permitting this inference. This lamp resistance can be determined by measurement using various known methods and forms the constant to be measured.

A control loop is provided according to the invention in order to keep the lamp resistance constant (constant DC current, measurement of the DC lamp voltage). The activation of the control circuit ignites the lamp and keeps it safely in operation in the critical phase after ignition. Thereby, a control of the lamp is achieved, which is applied in different operating conditions of the lamp (such as preheating, ignition, operation), wherein the DC component of the lamp voltage is evaluated. The control parameters adapt to the lamp condition, which is made possible by the combination of control loops. By such a scheme can be dispensed igniter detection, yet a clean start without light flash is achieved even at low dimming levels.

Claims (22)

1. A method for the regulation of the operation of at least one fluorescent lamp (4) operated with AC voltage, having the following steps:

   - targeted superposition (R_DC, D) of a DC voltage at the fluorescent lamp (4),

   - determination (5) of the DC voltage component of the fluorescent lamp voltage, and

   - regulation (7, 8) of the operation of the fluorescent lamp (4), at least before the ignition of the fluorescent lamp (4), on the basis of the determined DC voltage component as a regulation parameter.
2. A method according to claim 1, having the following steps before the ignition of the fluorescent lamp (4) :

   - targeted superposition (D, R_DC) of a DC voltage at the fluorescent lamp (4),

   - detection (5) of the DC voltage component of the fluorescent lamp voltage, and

   - evaluation (7) of the DC voltage component of the fluorescent lamp as an input parameter of the regulation (8) of the lamp power.
3. A method in accordance with any preceding claim,
   wherein the DC voltage reference parameter depends on the operating state of the lamp, such as for example pre-heating, ignition or operation.
4. A method in accordance with any preceding claim,
   wherein the lamp resistance is held constant.
5. A method in accordance with any preceding claim,
   wherein the DC voltage component is determined on the basis of a measurement signal derived at a voltage divider (R1, R2).
6. A method in accordance with any preceding claim,
   wherein the DC voltage component of the lamp voltage is determined on the basis of the spacings of the zero crossings of the lamp voltage.
7. A method in accordance with any preceding claim,
   wherein the regulation (7, 8) of the lamp power is effected digitally.
8. A method in accordance with any preceding claim,
   wherein the regulation of the DC lamp voltage is effected digitally.
9. A method in accordance with any preceding claim,
   wherein a dimming value predetermined externally is taken into account for the regulation of the lamp power.
10. A method according to claim 9,
    wherein, depending on the value of the DC voltage component of the lamp voltage, the power of the lamp is increased to a value which is above the externally predetermined dimming value.
11. An operating device for control of at least one fluorescent lamp (4) operated with AC voltage, having:

    - a circuit (R_DC, D) for targeted superposition of a DC voltage at the fluorescent lamps (4),

    - a circuit (R1, R2, 5) for the determination of the lamp voltage of the fluorescent lamp (4), and

    - a lamp regulation circuit (7, 8) for the regulation of the operation of the fluorescent lamp (4), at least before the ignition of the lamp (4), with the determined DC voltage component as a regulation parameter.
12. An operating device according to claim 11, having:

    - a circuit (RDC, D) for the targeted superposition of a DC voltage at the fluorescent lamps,

    - a circuit for the determination of the lamp voltage of the fluorescent lamp, and

    - a lamp regulation circuit for the regulation of the lamp power of the fluorescent lamp, to which the DC voltage component of the fluorescent lamp is delivered as an input parameter,

    wherein the lamp regulation circuit is constituted to regulate the lamp power already before the ignition of the fluorescent lamp.
13. An operating device according to any of claims 11 to 12, wherein the DC voltage reference parameter depends on the operating state of the lamp (4) - such as for example pre-heating, ignition or operation.
14. An operating device according to any of claims 11 to 13, wherein means of the lamp regulation circuit keep the lamp resistance constant.
15. An operating device according to any of claims 11 to 14, having a voltage divider (R1, R2) for the determination of the DC voltage component.
16. An operating device according to any of claims 12 to 15, wherein the DC voltage component of the lamp voltage is determined on the basis of the spacings of the zero crossings of the lamp voltage.
17. An operating device according to any of claims 12 to 16, having means (8) for the digital regulation of the lamp power.
18. An operating device according to any of claims 12 to 17, having means (8) for the digital regulation of the DC lamp voltage.
19. An operating device according to any of claims 12 to 18, wherein the lamp regulation circuit has an input for externally predetermined dimming values.
20. An operating device according to any of claims 12 to 19, wherein, depending on the value of the DC voltage component of the lamp voltage, the regulation circuit increases the power of the lamp (4) to a value which is above the externally predetermined dimming value.
21. Electronic ballast, having an operating device according to any of claims 11 to 20.
22. Luminaire, having a ballast according to claim 21.

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