EP2247167A2 - Method for determining a type of a gas discharge lamp and electronic preswitching device for operating at least two different types of gas discharge lamp - Google Patents

Abstract

The method involves preheating a coil (W1,W2) of the gas discharge lamp (La) for a predetermined preheating time. A characteristic physical parameter for the type of gas discharge lamp is determined at the end of the preheating time and the measured value of the parameter is provided. The lamp type is determined on the basis of the provided measured value. The preheating time is extended for a predetermined period of time. An independent claim is also included for an electronic ballast with a preheating device for operating different types of gas-discharge lamps.

Description

Technical area

The present invention relates to a method for determining a type of gas discharge lamp by means of an electronic ballast for operating different types of gas discharge lamps, wherein the different types of gas discharge lamps differ in at least one operating parameter, the method comprising the steps of: preheating at least one coil of the Gas discharge lamp for a predetermined preheat time, measuring a physical quantity characteristic of the type of the gas discharge lamp at the end of the preheat time and providing the measured value of that magnitude, and determining the lamp type from the provided measurement value. The invention also relates to a corresponding electronic ballast for operating at least two different types of gas discharge lamps.

State of the art

Electronic ballasts are known, which are suitable for the operation of different types of gas discharge lamps, in particular for the operation of different types of low-pressure discharge lamps. Such devices are referred to as multi-lamp devices or as intelligent electronic ballasts. In a multi-lamp device, operating parameters are stored for the types of lamps that can be operated with this device. In particular, different types of lamps differ in the lamp current required for their operation. The device selects the operating parameters to be used depending on the type of the connected lamp. For this it must first recognize the lamp type.

A part of the currently known devices detects the lamp type by evaluating the cold resistance of a filament of the lamp at each start. In the case of gas discharge lamps in which the lamp filaments are preheated, the heat resistance of a lamp filament can also be evaluated at the end of the preheating phase. However, it can lead to error detection. If the lamp type is changed, then the Vorheizparametersatz still used by the previous lamp is used for the newly connected lamp, so that it is not preheated optimally. This can lead to the determined value for the heat resistance of the coil being within a range that can not be clearly assigned to a lamp type. This can lead to error detection. However, if a lamp is operated with incorrect parameter values, it may not ignite properly or the lamp life will be shortened.

Presentation of the invention

The object of the present invention is therefore to develop an aforementioned method and an aforementioned electronic ballast in such a way error detection of the lamp type can be avoided.

This object is achieved by a method having the features of patent claim 1 and by an electronic ballast having the features of patent claim 10.

The present invention is based on the finding that this object can be achieved if the duration of preheating is prolonged. For this purpose, if the lamp type can not be determined unambiguously in the first step, the preheating time is extended by a predetermined period of time and a renewed determination of the lamp type is carried out at the end of the extended preheating time. It has been found that then there is an unambiguous assignability of the determined value for the heat resistance of the lamp filament to a lamp type, if the preheating time is chosen to be sufficiently long. However, the manufacturers of electronic ballasts for gas discharge lamps strive to keep the preheating time as short as possible in order to avoid that between the switching on and the ignition of the lamp a noticeable pause for the user. This conflict of interest is solved in accordance with the present invention by first selecting a preheating time, which is preferably less than or equal to one second for preheating the set lamp type, and extending the preheating time only in those cases where unambiguous identification is not possible ,

According to a preferred embodiment of the invention, the method further comprises the step of storing the determined lamp type. The method also particularly preferably comprises the steps to be carried out at the start of the method of reading the stored lamp type and determining the predetermined preheating time as a function of the read-out type of lamp based on a stored in the electronic ballast between types of gas discharge lamps to be operated with the electronic ballast and associated operating parameters , For the first commissioning, a lamp type is stored at the factory, which is used to determine the operating parameters to be used for the first preheating. Storing the determined lamp type is only required if this differs from the already stored lamp type.

According to an alternative preferred embodiment of the invention, instead of storing the determined lamp type, associated with the determined lamp type operating parameters based on a stored in the electronic ballast between types of to be operated with the electronic ballast gas discharge lamps and associated operating parameters and determined operating parameters for use for the next preheating provided.

Preferably, the physical quantity characteristic of the type of gas discharge lamp is the value of a value related to the electrical resistance of the preheated coil.

Furthermore, the duration of the extended preheating time is preferably selected such that the measured value provided is located in a nearly stationary area. The heat resistance of the coil increases with the preheat time and asymptotically approaches a limit. In particular, the curve behavior in the steeply increasing range depends on the age of the coil, while the influence of the age of the coil in the stationary region of the curve is negligible. Thus, in the stationary region of the curve, it is possible to conclude particularly reliably from the electrical resistance of the coil to the type of coil and thus to the type of the lamp.

According to a preferred embodiment of the invention, the lamp type is determined on the basis of the provided measured value by comparing the provided measured value with a table of values, then checking whether the provided measured value falls within a range of the table of values unambiguously attributable to a lamp type, and finally at unique assignability of the provided measured value to a lamp type of this lamp type is selected as the determined lamp type. Preferably, different value tables are used for different operating parameters used in the preheating of the at least one helix. This also helps to increase the reliability of the lamp detection.

The preferred embodiments mentioned in connection with the method according to the invention, together with their advantages, can also be realized in the case of an electronic ballast according to the invention.

Further advantageous embodiments will become apparent from the dependent claims.

Short description of the drawing (s)

Fig. 1

in schematischer Darstellung ein Ausführungsbei- spiel eines erfindungsgemäßen elektronischen Vor- schaltgeräts;

Fig. 2

in schematischer Darstellung Wertetabellen für verschiedene Vorheizparameter;

Fig. 3

den Warmwiderstand R_w einer Wendel und eine damit zusammenhängende gemessene Spannung U_mess in Abhän- gigkeit von der Vorheizzeit; und

Fig. 4

ein Ablaufdiagramm eines erfindungsgemäßen Verfah- rens zum Ermitteln eines Lampentyps.

In the following, an embodiment of an electronic ballast according to the invention and a method according to the invention will now be described in more detail with reference to the accompanying drawings. Show it:

Fig. 1

a schematic representation of an exemplary embodiment of an electronic ballast according to the invention;

Fig. 2

schematic representation of value tables for various preheating parameters;

Fig. 3

the heat resistance R _{w of} a coil and a related measured voltage U _mess as a function of the preheating time; and

Fig. 4

a flow diagram of a method according to the invention for determining a lamp type.

Preferred embodiment of the invention

Fig. 1 shows a schematic representation of an embodiment of an electronic ballast according to the invention. This comprises an input with a first input terminal E1 and a second input terminal E2, between which a mains voltage U _{N is} applied. The input E1 and E2 are followed by a rectifier GL, which is designed to rectify the mains voltage U _N. After rectifier GL, a power-factor correction circuit PFC is provided, which up-regulates the rectified voltage to a constant value and ensures a sinusoidal current drain from the grid. Between the output terminals of the power-factor correction circuit PFC, a half-bridge circuit is coupled to a first half-bridge switch S1 and a second half-bridge switch S2. To the output of the half-bridge circuit, that is between the switches S1 and S2, a connected to the electronic ballast to be operated gas discharge lamp La load circuit is connected. This comprises a series resonant circuit which is composed of a choke coil L _D and a resonant capacitor C _R coupled between a first output terminal A1 and ground. Between the first output terminal A1 and a second output terminal A2 of the electronic ballast, a gas discharge lamp La to be operated with the electronic ballast is coupled. This in Fig. 1 embodiment shown represents an electronic ballast for operating a gas discharge lamp. However, the principle of the present invention is also applicable to ballasts with which more than one lamp can be operated simultaneously. The second output terminal A2 is also coupled via a coupling capacitor C _K1 to ground. Between the high potential terminal of the switch S1 and the second output terminal A2 may optionally be provided a second coupling capacitor C _K2 , which is indicated in the figure by dashed lines.

In particular, the present invention relates to a preheating device of the electronic ballast, which serves to preheat at least one and preferably both coils W1 and W2 of the gas discharge lamp La. By preheating the lamp filaments before igniting the lamp a gentler lamp start and thus a longer life of the lamp is achieved. The preheater has for this purpose a heating transformer with a primary winding TP and two secondary windings TS1 and TS2. The primary winding TR is connected via a switch S3 and a trapezoidal capacitor C _T to the output of the half-bridge between the two switches S1 and S2. The first secondary winding TS1 is coupled to the first lamp filament W1, while the second secondary winding TS2 is coupled to the second lamp winding W2. The other end of the primary winding TP is for detecting a current flowing through the primary winding TP _TP current I which is proportional to the current flowing through the secondary windings and through the lamp filaments streams connected to a measuring circuit 20th The measuring circuit 20 includes a shunt resistor and provides at its output derived from this voltage U _mess . This voltage U _mess is supplied to an input ME1 of a microcontroller 10. The microcontroller 10 also has outputs MA1, MA2 and MA3, via which it controls the switches S1 and S2 of the half-bridge and the switch S3, via which the heating device is coupled to the half-bridge. Fig. 1 also shows a memory 12 of the microcontroller 10 for storing data required for the operation of the gas discharge lamp La. According to the preferred embodiment, the memory 12 is part of the microcontroller 10. Instead of a memory but could also be provided more memory, which could be arranged outside the microcontroller. If the intention is to operate several lamps of the same type simultaneously with the electronic ballast, the heating transformer comprises four instead of two secondary windings in the case of a device designed for the operation of two lamps. In the case of devices designed to operate more than two lamps, a heating transformer with one primary winding and one secondary winding for each coil to be heated is provided in each case for two lamps, the primary windings of the heating transformers being connected in parallel.

• Fig. 2 zeigt beispielhaft zwei solche Wertetabellen. Für die linke Wertetabelle wurden alle drei Lampentypen mit den Vorheizparametern für den Typ 1 beheizt und am Ende der Vorheizzeit wurde die auf der senkrechten Achse aufgetragene Spannung U_mess gemessen. Für jeden Lampentyp ergibt sich dabei ein Wertebereich, in dem die gemessene Spannung U_mess eindeutig einem Lampentyp zugeordnet werden kann. Dazwischen befinden sich die schraffierten Bereiche, in denen keine eindeutige Zuordnung möglich ist. Für die rechte Wertetabelle wurden alle drei Lampentypen mit den Vorheizparametern für den Typ 2 beheizt. Es zeigt sich gegenüber der linken Tabelle eine leichte Verschiebung der Wertebereiche nach oben. Jedoch kann es selbst bei Verwendung von an die Vorheizparameter angepassten Wertetabellen vorkommen, dass ein Messwert der Spannung U_mess in den schraffierten Bereich fällt, in dem keine eindeutige Zuordnung zu einem Lampentyp möglich ist. Dies ist darauf zurückzuführen, dass sich das Aufheizverhalten und der Wendelwiderstand auch mit dem Alter einer Lampe ändern oder die eingelegte Lampe beziehungsweise deren Wendel außerhalb der erlaubten Fertigungstoleranzen liegt.
• Fig. 3 zeigt die Abhängigkeit des Warmwiderstands R_w sowie der gemessenen Spannung U_mess von der Vorheizzeit. Wie der Figur zu entnehmen ist, steigt der Warmwiderstand R_w zuerst steil und dann immer flacher an und nähert sich schließlich einem Grenzwert. Da die Vorheizzeit möglichst kurz sein soll, liegt die einem Lampentyp zugeordnete Vorheizzeit M1, die vorzugsweise etwa 0,9 s beträgt, im ansteigenden Bereich der Kurve R_w. Mit zunehmendem Alter der Wendel wird der Anstieg der Kurve steiler, was in der Figur durch gestrichelte Linien angedeutet ist. Die Kurve für die gemessene Spannung U_mess verhält sich entsprechend und fällt mit zunehmendem Alter steiler ab. Dies bedingt eine Abweichung des zur Zeit M1 gemessenen Wertes von dem Sollwert für eine neue Lampe und kann zu Fehlerkennungen des Lampentyps führen. Bei dem erfindungsgemäßen Verfahren wird daher, wenn bei der ersten Messung der Wert der gemessenen Spannung U_mess in einen schraffierten Bereich der Wertetabelle fällt, die Vorheizzeit auf den Wert M2 verlängert und am Ende der verlängerten Vorheizzeit M2 eine erneute Messung der Spannung U_mess durchgeführt. Die verlängerte Vorheizzeit M2 wird dabei so gewählt, dass die Kurven R_w und U_mess sich dort ihrem stationären Bereich nähern, in dem sich das Alter der Wendel nicht mehr so stark bemerkbar macht. Dies ermöglicht eine zuverlässige Lampenerkennung. Die verlängerte Vorheizzeit M2, die für alle mit dem elektronischen Vorschaltgerät zu betreibenden Lampentypen gleich gewählt werden kann, ist zwar über 1 s. Dies ist jedoch tolerierbar, da sie nur in den Fällen zur Anwendung kommt, in denen nach der Vorheizzeit M1 eine eindeutige Lampenerkennung noch nicht möglich war.
• Fig. 4 zeigt ein Ablaufdiagramm eines bevorzugten Ausführungsbeispiels des erfindungsgemäßen Verfahrens. Im Schritt S10 wird das elektronische Vorschaltgerät durch einen Benutzer eingeschaltet. Nach dem Einschalten erfolgt in einem Schritt S12 das Auslesen des abgespeicherten Lampentyps durch den Mikrocontroller 10. Für die erste Inbetriebnahme des elektronischen Vorschaltgeräts ist werkseitig ein Lampentyp abgespeichert. Im nächsten Schritt S14 werden die Betriebsparameter in Abhängigkeit des Lampentyps anhand der gespeicherten Zuordnung der Betriebsparameter zu einem Lampentyp festgestellt. Insbesondere fungiert der Lampentyp als Zeiger, der auf einen Satz von Betriebsparametern zeigt. Anschließend werden in dem Schritt S16 die Wendeln W1 und W2 der Lampe La vorgeheizt, indem der Mikrocontroller 10 ein Schließen des Schalters S3 veranlasst. Während des Vorheizens wird in einem Schritt S18 geprüft, ob die für den Lampentyp vorgesehene Vorheizzeit M1 abgelaufen ist. Sobald dies der Fall ist, wird in einem Schritt S20 die an dem Eingang ME1 des Mikrocontrollers 10 anliegende Spannung U_mess erfasst. In einem Schritt S22 wird die erfasste Spannung U_mess mit der für die Vorheizparameter des Lampentyps geltenden Wertetabelle verglichen und geprüft, ob der Wert der Spannung U_mess einem Lampentyp eindeutig zuordenbar ist. Ist dies der Fall, so wird der ermittelte Lampentyp in einem Schritt S24a abgespeichert und das Verfahren ist beendet. Ist am Ende der Vorheizzeit M1 noch keine eindeutige Zuordnung der erfassten Spannung U_mess zu einem Lampentyp möglich, so wird in einem Schritt S24b die Vorheizphase fortgesetzt. Während der Fortsetzung der Vorheizphase wird in einem Schritt S26b geprüft, ob die verlängerte Vorheizzeit M2 erreicht ist. Ist dies der Fall, so wird in einem Schritt S28b wiederum die an dem Eingang ME1 des Mikrocontrollers 10 anliegende Spannung U_mess erfasst und in einem Schritt S30b der zugehörige Lampentyp anhand der für die verwendeten Vorheizparameter geltenden Wertetabelle ermittelt. In einem Schritt S32b wird der ermittelte Lampentyp abgespeichert, womit das Verfahren beendet ist. Statt den ermittelten Lampentyp in den Schritten S24a und S32b immer abzuspeichern, kann auch zuvor geprüft werden, ob der ermittelte Lampentyp mit dem bereits abgespeicherten Lampentyp übereinstimmt. Ein erneutes Abspeichern des Lampentyps ist dann nur erforderlich, wenn dies nicht der Fall ist.

In the following, the operation of the electronic ballast will be described as far as the detection of the type of the connected gas discharge lamp La is concerned. The electronic ballast according to the invention is a multi-lamp device which is designed to operate different types of gas discharge lamps, the gas discharge lamps differing by at least one operating parameter. In particular, the gas discharge lamps are low-pressure discharge lamps, which differ in the lamp current required for their operation. With the electronic ballast according to the preferred embodiment of the invention, in particular, three types of lamps can be distinguished. These different lamp types have different coils, which differ in their electrical resistance from each other. In order to be able to operate different lamps with one device, an association between the individual lamp types and the operating parameters required for their operation is stored in the memory 12. The operating parameters include the lamp current, which flows after the ignition of the lamp through the latter and the preheating time during which the lamp filaments W1 and W2 are preheated before the ignition of the lamp by the switch S3 is closed and a current flow through the heating transformer through the coils W1 and W2 is induced. The optimal preheating time for a lamp also depends on the type of lamp, and the aim is to keep it as short as possible. Currently, a preheating time of maximum 1 s is tolerated. Since the filaments of the different lamp types differ in their electrical resistance, a value related to the electrical resistance of the filaments is measured. In particular, one measures the voltage U _mess derived from the shunt resistor of the measuring circuit 20 connected in series with the primary winding TP of the heating transformer at the end of the preheating time. In order to determine the lamp type, it is based on expected values for the heat resistance of a coil, which was heated with the correct operating parameters. However, if a lamp of a different type than before is connected after a lamp replacement, the new lamp will not be heated with the optimum parameters for it. Therefore, according to the preferred embodiment of the invention for determining the lamp type from the measured voltage U _mess for different preheating different value tables are used which indicate an association between the lamp type and the voltage U measured at the end of the preheating phase U _mess as a function of the preheating parameters used. These value tables are also stored in the memory 12 or in a separate memory.

• Fig. 2 shows by way of example two such value tables. For the left value table, all three lamp types were heated with the preheating parameters for type 1 and at the end of the preheating time, the voltage U _meas applied to the vertical axis was measured. For each lamp type, this results in a range of values in which the measured voltage U _mess can be clearly assigned to a lamp type. In between are the hatched areas in which no clear assignment is possible. For the right value table, all three lamp types were heated with the preheat parameters for type 2. There is a slight shift of the value ranges upwards compared to the left table. However, even when using value tables adapted to the preheating parameters, it may happen that a measured value of the voltage U _mess falls within the shaded area, in which no clear assignment to a lamp type is possible. This is due to the fact that the heating behavior and the filament resistance also change with the age of a lamp or the inserted lamp or its filament lies outside the permitted manufacturing tolerances.
• Fig. 3 shows the dependence of the heat resistance R _w and the measured voltage U _mess of the preheating time. As can be seen from the figure, the warm resistance R _w first increases steeply and then flatter and finally approaches a limit value. Since the preheating time should be as short as possible, the preheating time M1 associated with one lamp type, which is preferably approximately 0.9 s, lies in the rising region of the curve R _w . With increasing age of the helix the rise of the curve becomes steeper, which in the Figure is indicated by dashed lines. The curve for the measured voltage U _mess behaves accordingly and decreases steeper with increasing age. This causes a deviation of the value measured at the time M1 from the setpoint value for a new lamp and can lead to false identifications of the lamp type. In the method according to the invention, therefore, if in the first measurement the value of the measured voltage U _mess falls within a shaded area of the value table, the preheating time is extended to the value M2 and a renewed measurement of the voltage U _{mess is} carried out at the end of the extended preheating time M2. The extended preheating time M2 is chosen so that the curves R _w and U _mess approach there to their stationary area, in which the age of the coil is no longer so strongly noticeable. This allows reliable lamp detection. The prolonged preheating time M2, which can be selected to be the same for all lamp types to be operated with the electronic ballast, is more than 1 s. However, this is tolerable, since it is used only in those cases in which after the preheating M1 an unambiguous lamp detection was not yet possible.
• Fig. 4 shows a flowchart of a preferred embodiment of the method according to the invention. In step S10, the electronic ballast is turned on by a user. After switching on, the readout of the stored lamp type by the microcontroller 10 takes place in a step S12. For the first startup of the electronic ballast, a lamp type is stored at the factory. In the next step S14, the operating parameters become dependent the lamp type determined based on the stored assignment of the operating parameters to a lamp type. In particular, the lamp type acts as a pointer pointing to a set of operating parameters. Subsequently, in step S16, the filaments W1 and W2 of the lamp La are preheated by causing the microcontroller 10 to close the switch S3. During preheating, it is checked in a step S18 whether the preheating time M1 provided for the lamp type has expired. As soon as this is the case, the voltage U _mess applied to the input ME1 of the microcontroller 10 is detected in a step S20. In a step S22, the detected voltage U _{mess is} compared with the table of values applicable to the preheating parameters of the lamp type and it is checked whether the value of the voltage U _mess can be unambiguously assigned to a lamp type. If this is the case, the determined lamp type is stored in a step S24a and the method is ended. If at the end of the preheating time M1 no clear assignment of the detected voltage U _mess to a lamp type is possible, the preheating phase is continued in a step S 24b. During the continuation of the preheat phase, it is checked in a step S26b whether the extended preheat time M2 has been reached. If this is the case, the voltage U _mess applied to the input ME1 of the microcontroller 10 is again detected in a step S28b, and in a step S30b the associated lamp type is determined on the basis of the value table valid for the preheating parameters used. In a step S32b, the determined lamp type is stored, thus completing the process. Instead of always storing the determined lamp type in steps S24a and S32b, it is also possible to check beforehand whether the determined lamp type matches the already stored lamp type matches. A renewed storage of the lamp type is only required if this is not the case.

Claims (13)

Method for determining a type of gas discharge lamp (La) by means of an electronic ballast for operating different types of gas discharge lamps, wherein the different types of gas discharge lamps differ in at least one operating parameter, the method comprising the steps of: a) preheating at least one coil (W1, W2) of the gas discharge lamp (La) for a predetermined preheating time (M1); b) measuring a physical quantity characteristic of the type of gas discharge lamp (La) at the end of the preheating time and providing the measured value (U _mess ) of this magnitude; and c) determining the lamp type based on the provided measurement value (U _mess );
characterized in that
the preheating extended by a predetermined period of time and the steps b) and c) are repeated, if the lamp type in step c) can not be determined uniquely. Method according to claim 1,
characterized by the following further step: d) storing the determined lamp type. Method according to claim 2,
characterized by the following steps to be carried out before step a): e1) reading the stored lamp type; and e2) determining the predetermined preheating time (M1) in
Dependence of the lamp type read on the basis of a stored in the electronic ballast association between types to be operated with the electronic ballast gas discharge lamps and associated operating parameters. Method according to claim 1,
characterized by the following further steps: f1) determining operating parameters associated with the determined lamp type on the basis of an association stored in the electronic ballast between types of gas discharge lamps to be operated with the electronic ballast and associated operating parameters; and f2) providing the operating parameters determined in step (f1) for use in the next preheat. Method according to one of the preceding claims, characterized in that
the predetermined preheat time (M1) is less than or equal to one second. Method according to one of the preceding claims, characterized in that
in step b) the value of a value related to the electrical resistance of the preheated coil (W1, W2) is measured. Method according to one of the preceding claims,
characterized in that
the duration of the extended pre-heating time (M2) is selected such that the measured value (U _mess ) provided is in a virtually stationary range. Method according to one of the preceding claims,
characterized in that
Step c) contains the following substeps: c1) Compare the provided measurement value (U _mess )
with a value table; c2) Check whether the provided measured value (U _mess ) in
falls within a range of the look-up table that is unique to a lamp type; and c3) with clear assignment of the provided measurement value (U _mess ) to a lamp type selecting this lamp type as the determined lamp type. Method according to claim 8,
characterized in that
depending on the operating parameters used in preheating the at least one helix (W1, W2) different value tables are used. Electronic ballast for operating at least two different types of gas discharge lamps, which are characterized by at least one different operating parameters with - A pre-heater for preheating at least one coil (W1, W2) of at least one to be operated with the ballast gas discharge lamp (La); - At least one memory device (12) for storing an assignment of operating parameters to the at least two different lamp types, wherein one of the operating parameters to be used in preheating the at least one coil (W1, W2) preheat time (M1) and to store one of the next Preheat phase underlying lamp type or associated operating parameters; - A measuring device (20) for measuring a characteristic of the lamp type of the ballast to be operated at least one gas discharge lamp (La) physical quantity and for providing a measured value (U _mess ) of the physical quantity; and a control unit (10) which is designed to switch on the preheating device for a preheating time (M1) assigned to the at least one storage device (12), the current type of lamp by means of the preheating time provided by the measuring device (20) Determine measured value (U _mess ) and store the determined lamp type or associated with this operating parameter in the at least one memory device (12);
characterized in that
the control unit (10) is further adapted to extend the duration of the preheating time by a predetermined period of time if the lamp type is provided by the measured value (U _mess ) is not clearly determinable, and
the control unit (10) is furthermore designed to determine the lamp type once more based on the measured value (U _mess ) provided at the end of the extended preheat time (M2). Electronic ballast according to claim 10,
characterized in that
in the at least one memory device (12) or in an additional memory, an association between measured values (U _mess ) provided by the measuring device and the at least two different lamp types is stored as a function of the operating parameters used in the preheating phase, wherein there is one core area for each lamp type of measured values (U _mess ), which can be clearly assigned to the lamp type. Electronic ballast according to claim 10 or 11,
characterized in that
the preheating device comprises at least one heating transformer having a primary inductance (TP) and in each case a secondary inductance (TS1, TS2) for each filament (W1, W2) to be heated; and
the measuring device (20) is designed to determine the current (I _TP ) flowing in the preheating phase through the at least one primary inductance (TP). Electronic ballast according to claim 12,
characterized in that
the measuring device (20) comprises a shunt resistor which is connected to the at least one primary inductance (TP) of the heating transformer is connected in series; and
the measuring device (20) is designed to provide a voltage derived from the shunt resistor (U _mess ).

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