WO2007025983A1

WO2007025983A1 - Ballast for a discharge lamp with adaptive preheating

Info

Publication number: WO2007025983A1
Application number: PCT/EP2006/065811
Authority: WO
Inventors: Olaf Busse; Markus Heckmann; Reinhard Lecheler; Alfons Lechner; Siegfried Mayer; Thomas Pollischansky; Bernd Rudolph; Bernhard Schemmel; Kay Schmidtmann; Harald Schmitt; Thomas Siegmund; Arwed Storm; Horst Werni
Original assignee: Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH
Priority date: 2005-08-31
Filing date: 2006-08-30
Publication date: 2007-03-08
Also published as: EP1920643A1; EP1920643B1; DE502006004609D1; DE202005013753U1; JP2009506510A; CN101253817A

Abstract

The present invention relates to an electronic ballast for discharge lamps which have preheatable electrodes. The electronic ballast has a measuring apparatus (M), which is designed to repeatedly measure a variable (RW, UKL2), which has been correlated with the electrode temperature, of at least one of the electrodes (E1, E2) of a connected discharge lamp (LA) during the preheating operation. Furthermore, the electronic ballast has a control apparatus (C), which is designed to ignite the discharge in response to the measurement in the event of a non-monotonic profile of the variable (RW, UKL2), which has been correlated with the electrode temperature. Furthermore, during the preheating operation one embodiment of the invention can intervene in an appropriate manner in this preheating operation by means of the control apparatus (C).

Description

Ballast for a discharge lamp with adaptive preheating

Technical area

The present invention relates to an electronic ballast for discharge lamps, specifically for such discharge lamps having preheatable electrodes.

State of the art

Electronic ballasts for the operation of discharge lamps, even those which are designed to operate discharge lamps with preheatable electrodes, are known per se. In principle, an electronic ballast from a given supply, for example a mains supply, generates a supply power for a connected discharge lamp, which has the characteristics necessary for the operation of the discharge lamp, in particular a high-frequency AC voltage supply.

Often, the electrodes of a discharge lamp are preheated prior to the ignition of the discharge. In this way, the emissivity of the electrodes can be improved and their service life extended. A preheat process typically lasts between 0.4 s and just over 2 s and occurs after a preheat program set in a scheduler.

Presentation of the invention

The invention is based on the problem of specifying an improved ballast for discharge lamps with preheatable electrodes.

The invention relates to an electronic ballast for operating a discharge lamp with preheatable electrodes, characterized in that it comprises a measuring device which is designed to repeatedly measure, during the preheating process, a size correlated to the electrode temperature of at least one of the electrodes of a connected discharge lamp and a control device which is designed to respond to the value correlated to the electrode temperature with a non-monotonous profile on the measurement to ignite the discharge.

Preferred embodiments of the invention are specified in the dependent claims.

The invention is based on the finding that a desired short preheating time can be achieved with the use of the largest possible preheating currents or preheating voltages, but when the voltage across an electrode of a connected discharge lamp during the preheating process exceeds a critical value, but a transverse discharge occurs can.

Transverse discharges are not desirable, i.a. because with a transverse discharge the electrode temperature decreases again. At lower temperatures the electrode is less emissive and igniting the discharge at too low a temperature increases the wear of the electrode.

Transverse discharges can be detected at such a temperature decrease of an electrode during the preheating process. A decrease in temperature across an electrode can be detected by a nonmonotonic history of a value correlated to electrode temperature within the preheat time. For example, with a transverse discharge across the electrode, your resistance and the voltage drop across it also decrease. However, the current through the electrode increases due to the lower resistance. How strongly these behaviors are pronounced also depends on whether the heating power supply has more of a voltage source characteristic or a current source characteristic. Really, the properties of the heating power supply will be between these extremes. The electronic ballast according to the invention has a measuring device which is designed to measure the temperature of one or both electrodes of a connected discharge lamp during the preheating process. To measure the electrode temperature, any property correlated to this can be measured. Suitable quantities are dealt with within the scope of the dependent claims.

Furthermore, the electronic ballast according to the invention has a control device which responds to the measurement of the measuring device. If there is a nonmonotonic course of a variable correlated to the electrode temperature, the control device initiates the ignition of the discharge.

The more measurements are made during the preheating process, the better the course of the electrode temperature can be reconstructed and the more reliable the control device can intervene. But many measurements mean a certain effort; The electronics must be designed accordingly. In principle, a transverse discharge detection with very few measuring points is also conceivable. However, this is also less reliable with few measuring points.

In one embodiment of the invention, the quantity correlated to the electrode temperature, which is used for cross-discharge detection, is the voltage across one of the electrodes. If a transverse discharge occurs, the voltage over the affected electrode breaks down to a certain extent.

On the other hand, it may also be preferable to measure the electrode resistance as a quantity correlated to the electrode temperature. The electrode resistance during the preheating time results from the preheating voltage and the preheating current, so it is easy to determine.

If the electronic ballast has a pronounced current source characteristic, it is more appropriate to observe the voltage across one of the electrodes for cross-discharge detection. Is the electronic ballast if a pronounced voltage source is advisable, then a transverse discharge detection via the quotient of the hot and cold resistance, which is determined by an (additional) current measurement, is recommended.

It is possible that the electrode temperature will reach a sufficient level sooner than expected. In order to minimize the preheating time, ignition should then be initiated, for example via the control circuit.

The size to be measured is the quotient of the current electrode resistance and the cold resistance. The cold resistance of an electrode is understood here to mean the resistance of an electrode when its temperature corresponds to the room temperature (20 ° C.). The quotient of actual electrode resistance, ie the heat resistance, and the cold resistance, as well as the electrode resistance itself, are approximately proportional to the temperature of the electrodes. Since it is divided by the cold resistance, but a normalized in this regard size is used. This is interesting because the cold resistance can vary from lamp to lamp, but does not say anything about the temperature during the preheating process. For example, the control device can be designed to carry out the determination of the quotient of the heat resistance measured by the measuring device and the cold resistance likewise measured by the measuring device.

Preferably, as soon as the quotient of actual electrode resistance and cold resistance reaches a value between 4 and 7 during the preheating time, the discharge is ignited. More preferably, when the discharge is fired from a lower limit of 4.5 and, independently, to an upper limit of 6.

Intervention of the control circuit in the preheating process is useful not only in the cases described above in the form of premature ignition of the discharge, but also in the form of an adaptation of the operating parameters of the electronic ballast in response to the measurement. device, because a simple execution of a given Vorheizablaufes can lead to an unsatisfactory result of preheating, even if, as in the embodiments of the invention described above, the discharge is initiated early.

Even if an electronic ballast is designed and used to operate discharge lamps of the same type in each case, the preheating process may be different for each individual discharge lamp. A different from lamp to lamp course of preheating can be due to manufacturing tolerances, especially the preheatable electrodes, or in ambient temperature differences.

The control device compares the measured values of the measuring device with standard values of the value correlated to the electrode temperature. If there is a deviation between the measured and standard values, the control device adjusts the following course of the preheating process by changing an operating parameter of the electronic ballast so that the expected deviation between a following measurement and a corresponding standard value becomes smaller. This process is therefore a regulation.

Examples of operating parameters of the electronic ballast, which are suitable for adjusting the course of the electrode temperature during the preheating process are: the Vorheizstrom through the electrodes, the Vorheizspannung to the electrodes, the frequency of the electronic ballast generated high-frequency AC power supply, the duty cycle just this AC power supply and the height of the DC power supply.

In order for the standard values of the value correlated to the electrode temperature to be available for comparison by the control device, these can be stored in a memory device within the electronic ballast, or else hard-wired in the form of an electronic circuit, for example a circuit, which has threshold values. (comparators) to which the measured values are fed and whose threshold values decide whether there is a deviation from the standard values. Such a circuit could simultaneously implement the control device as well.

Due to the adaptation of the course of the preheating process to standard values by the control device, the preferred embodiment of the electronic ballast can also have increased flexibility when using different lamp types. Although different types of lamps may have different electrodes, the control circuit can be used to effect an efficient preheating process.

The above-described adaptation of the preheating process to a standard preheating operation does not make the detection of transverse discharges superfluous. Even with multiple adjustment of the operating parameters transverse discharges can occur. It is also possible that the electrode temperature assumes a sufficient value early, especially if only a few measurements are carried out during the expected preheating time.

In order to follow the course of the value correlated to the electrode temperature during the preheating process, it is measured at least every 100 ms. In the usual preheating so several measurements during the preheating process are possible.

If the electronic ballast can be operated not only with one but with several different lamp types, it is advantageous to use a lamp type identification. Preferably, the lamp type is determined by measuring the cold resistance of an electrode of a connected discharge lamp. In a preferred embodiment of the invention, the memory device is designed for each lamp type a set of matching preheat parameters For example, the preheating time, default values for the heating current and the heating voltage and maximum values for heating voltage and heating current. If the electronic ballast has recognized the connected lamp type on the basis of the cold resistance, then the control device controls the preheating process in accordance with the standard values corresponding to the lamp type.

When operating on the supply network, it may happen that in the meantime this supply fails. The electronic ballast may be equipped with a timer to determine if the mains interruption was shorter than a predetermined duration. If this is the case, then no measurement of the cold resistance is carried out after the power interruption, otherwise already.

The above and the following description of the individual features relate to the device category and also to a method according to the invention, although this is not explicitly mentioned in detail.

The invention thus also relates in principle to a method for operating a discharge lamp equipped with preheatable electrodes, comprising the steps of: connecting the discharge lamp, repeatedly measuring a value correlated to the electrode temperature of at least one of the electrodes of a connected discharge lamp during preheating with a measuring device, igniting the discharge a non-monotonic course of the value correlated to electrode temperature by a control device which responds to the measurement, and also relates to the embodiments implicitly and subsequently also explained for this method. Brief description of the drawings

In the following, the invention will be explained in more detail with reference to exemplary embodiments. The individual features disclosed may also be essential to the invention in other combinations.

FIG. 1 shows a circuit diagram of an electronic ballast according to the invention.

FIG. 2 shows a time course of a variable correlated to the electrode temperature.

FIG. 3 shows a time profile of a variable correlated to the electrode temperature and an associated heating current, which is adapted during the preheating process.

FIG. 4 shows a variation of FIG. 2.

FIG. 5 shows a further variation of FIG. 2.

FIG. 6 also shows a variation of FIG. 2.

Preferred embodiment of the invention

The electronic ballast is fed from the mains supply lines N1 and N2. A generator G generates from the given mains supply N1, N2 a supply power for a connected low-pressure discharge lamp LA. The generator G includes a rectifier for rectifying the AC voltage supply, a power factor correction circuit for a possible sinusoidal current drain from the mains supply, a DC link capacitor and a Halbbrückenin- verter, wherein over the DC link capacitor for supplying the Halbbrückeninverters necessary DC voltage is applied. The half-bridge inverter generates a high-frequency alternating voltage between the output A1 and the reference potential GND or the other potential of the intermediate circuit voltage.

Between the first output A1 and the reference potential GND, a series circuit of a lamp inductor L, a coupling capacitor CC, a lamp terminal KU A, the low-pressure discharge lamp LA, a lamp terminal KL2A and a resistor R1 is connected. Parallel to the series connection of the lamp terminal KL1 A, the low-pressure discharge lamp LA and the lamp terminal KL2A a series circuit of a lamp terminal KL1 B, a resonant capacitor CR and a lamp terminal KL2B is connected. Between the lamp terminals KL1 A and KL1 B is the electrode E1 and between the lamp terminals KL2A and KL2B is the electrode E2.

Between the lamp terminal KL2A and the resistor R1 is a connection node K1. Between a second output at the generator A2 and the connection node K1, a control device C and a measuring device M is connected. The control device C and the measuring device M are part of a microcontroller, and are therefore drawn with a common enclosure. Both the control device C and the measuring device M have a reference to the reference potential GND. The control device C can set operating parameters of the generator G via a control line SL, here the heating current. The measuring device is connected via the node K1 in series with the reference potential GND. Furthermore, the measuring device M is connected in series with the resonance capacitor CR via the lamp terminal KL2B. Between the resonant capacitor CR and the measuring device M is a connection node K2. At this connection node, the lamp terminal KL2B is connected.

The voltage dropped across the resistor R1 is proportional to that through the electrode E2 between the lamp terminals KL2A and KL2B flowing electricity. The voltage across the resistor R1 can be detected by the measuring device M. The voltage between the lamp terminals KL2A and KL2B can also be detected by the measuring device M.

FIG. 2 shows a typical course of a variable correlated to the electrode temperature of the low-pressure discharge lamp LA during the preheating process. The measuring device M measures, here 10 times, the resistance RW of the electrode E2 between the lamp terminals KL2A and KL2B during the preheating time. The preheating process starts at time tθ and ends at time t1. With increasing temperature, the resistance RW of the electrode also increases and reaches its highest value until the end of t1 of the preheating time, here after 0.5 s. Before the preheating has led to a significant heating, the electrode resistance has the value RK, its cold resistance. As a value correlated to the electrode temperature, the quotient of RW and RK is shown as a function of time, which reaches the value 5 at the end t1 of the preheating time, which corresponds to an electrode temperature of almost 800 ° C.

Figure 3a shows a time course of the quotient of hot and cold resistance and Figure 3b shows the associated heating current IE2, the heating current through electrode 2, which is adjusted during the preheating process. In the control device C, five standard values for the quotient of hot and cold resistance and the heating current appearing in the course of the preheating process are stored for different lamp types. Before starting the preheating process, the measuring device M determines the cold resistance of the electrode E2. Based on the cold resistance RK of the electrode E2, the lamp type is detected and the standard values corresponding to the detected lamp type are selected as a comparison scale for the control device C for the preheating process. The crosses in FIGS. 3a and 3b respectively correspond to the standard values stored in the control device. The solid line in Figure 3a corresponds to the actual course of the Quotient of hot and cold resistance and the solid line in Figure 3b corresponds to the actual course of the heating current during the preheating time. In Figure 3a it can be seen that the quotient of hot and cold resistance initially does not increase fast enough to correspond to the standard values. The controller adapts and increases the heating current so that the quotient of hot and cold resistance has a greater slope. The heating current change is here proportional to the difference between the measured quotient of the hot and cold resistance and the associated standard value.

FIG. 4 shows the quotient of RW and RK as a function of time during the preheating process for two different preheating operations. In the first preheating process (dot-dashed line), you can see a typical course, as in Figure 2. The preheating is completed at time t1. In the second preheating process (solid line), the quotient reaches the value 5 before the expected end t1 of the preheating time. However, when the quotient reaches 5, the electrode is hot enough and the discharge is ignited.

If a transverse discharge occurs at the electrode E2 during the preheating process, the initially increased temperature of the electrode drops again. This is shown in FIG. 5 and is also expressed in that the quotient of the current electrode resistance RW and the cold resistance RK decreases. The measuring device M here makes ten measurements of the electrode resistance RW in the interval between t0 and t1. If the electrode resistance falls within this interval after it has risen first, this is an indication of a transverse discharge; the discharge is ignited.

The situation is similar with FIG. 6. If a transverse discharge occurs over one of the electrodes, the voltage across this electrode breaks down. The voltage UKL2 across the electrode E2 is measured by the measuring device M. If the voltage UKL2 drops during the preheat process after it has risen initially, then the ignition of the discharge is also caused here via the control device C.

Claims

claims

1 . Electronic ballast for operating a discharge lamp (LA) with preheatable electrodes (E1, E2), characterized in that it comprises

a measuring device (M), which is designed during the preheating process a correlated to the electrode temperature size

(RW, UKL2) at least one of the electrodes (E1, E2) of a connected discharge lamp (LA) to be repeatedly measured

and a control device (C) which is designed to ignite the discharge in a non-monotonic progression of the value (RW, UKL2) correlated to the electrode temperature in response to the measurement.

An electronic ballast according to claim 1, wherein the quantity (RW) correlated with the electrode temperature is the voltage (UKL2) across one of the electrodes (E1, E2).

3. Electronic ballast according to claim 1, wherein the to the

Electrode temperature correlated size (RW, UKL2) is the resistance (RW) of one of the electrodes (E1, E2).

4. Electronic ballast according to one of the preceding claims, wherein the control circuit (C) is adapted to the quotient (RW / RK) from the current heat resistance (RW) and the initial cold resistance (RK) of one of the electrodes (E1, E2) to investigate.

5. An electronic ballast according to claim 4, which is adapted to ignite the discharge when the quotient (RW / RK) of hot and cold resistance (RW, RK) exceeds an upper limit.

6. Electronic ballast according to claim 5, wherein the upper limit is greater than or equal to 4 and less than or equal to 7.

7. Electronic ballast according to one of the preceding claims, wherein the control device (C) is adapted during the preheating process in response to the measurement to adjust the electrode temperature by adjusting an operating parameter of the electronic ballast.

8. Electronic ballast according to one of the preceding claims, wherein the measuring device (M) is adapted to the electrode temperature correlated size (RW, UKL2) at least all

100 ms to measure.

9. Electronic ballast according to one of the preceding claims, at least according to claim 7, which has a storage device (C) and in which in the storage device (C) for different lamp types each default values of the electrode temperature correlated variable (RW, UKL2) are stored and wherein the measuring device is designed to

after the electronic ballast has been switched on and before the start of the preheating process of the electrodes (E1, E2), the cold resistance (RK) of one of the electrodes (E1, E2) is detected,

- Based on the cold resistance (RK) of one of the electrodes (E1, E2) to detect the lamp type and

to select the standard values corresponding to the detected lamp type, as a comparative standard for the control device (C) for the preheating process.

10. Electronic ballast according to one of the preceding claims for operating a low-pressure discharge lamp (LA).