WO2006111269A1

WO2006111269A1 - Operating devices with lamp regulation by analysis of the lamp temperature

Info

Publication number: WO2006111269A1
Application number: PCT/EP2006/003060
Authority: WO
Inventors: Nebojsa Jelaca; Markus Mayrhofer
Original assignee: Tridonicatco Gmbh & Co. Kg
Priority date: 2005-04-22
Filing date: 2006-04-04
Publication date: 2006-10-26
Also published as: EP1872635A1; EP1872635B1; CN101164390A; CN101164390B; DE102005018763A1

Abstract

The following steps are carried out for the regulation of the operation of a fluorescent lamp powered by an AC voltage: controlled superimposition of a DC voltage on the fluorescent lamp, recording the lamp voltage for the fluorescent lamp and analysis of the lamp voltage as input parameter for the regulation of the lamp power. The DC component and optionally other parameters of the lamp voltage are analyzed.

Description

Control gear with lamp control with evaluation of the lamp temperature

The present invention relates to the operation of AC powered fluorescent lamps, such as gas discharge lamps. More specifically, the invention relates to controls for such lamps, which take into account the directly or indirectly determined lamp temperature in the lamp control. Typically, such regulations are used in control gear 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 increased lamp ambient temperature dependency at low dimming levels is caused, inter alia, by the fact that the lamp voltage at high ambient temperatures and small lamp currents (as they occur with dimmed lamp power) increases sharply and may assume unacceptably 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 a possibly spatially and thermally separately provided 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 prior art, it is already known in principle to provide information about such critical states (low temperatures, low dimming values) to a control device for the lamp power. EP 838 132 A1 teaches in this context that the voltage applied to the lamp should be used as an indicator of the lamp temperature. When the lamp voltage rises sharply, a critical state is concluded and the lamp is switched off, if necessary. However, the use of the total lamp voltage as an indicator of such critical conditions of lamp operation is problematic in that the lamp voltage is not clear for detecting this condition. Rather, the non-linearity of a fluorescent lamp can also lead to high lamp voltages in non-critical states that do not require further intervention require the control device. For the rest, the EP sees

838 132 Al analog control in which the lamp voltage reproducing voltage signal is simply added to a control signal, so as to modify the lamp power according to a detected state.

The invention has accordingly set itself the task of providing an improved technique for detecting the ambient lamp temperature.

The central idea of the invention is to apply a targeted DC voltage to the lamp voltage. The above-mentioned critical states can then be detected by detecting and evaluating the lamp voltage. The targeted admission of the DC component thus enables a more accurate compared to the prior art detection of the lamp temperature.

The above object solved by the features of the independent claims. The dependent claims further form the central idea of the invention in a particularly advantageous manner.

According to a first aspect of the present invention, there is provided a method of determining the temperature of an AC lamp powered fluorescent lamp. In this case, the AC voltage is deliberately superimposed on a DC voltage. The lamp voltage of the fluorescent lamp is detected, evaluated as a parameter for the temperature of the fluorescent lamp and used as the input variable of the lamp control.

At least as part of the evaluation of the lamp voltage, the DC voltage component of the lamp voltage can be evaluated. Additional parameters of the lamp voltage can optionally also be taken into account during the evaluation. The lamp voltage can be evaluated, for example, based on an asymmetry of the periodically extending lamp voltage.

The evaluation of the lamp voltage can be determined, for example, based on the distances of successive zero crossings of the lamp voltage.

The impedance can be evaluated digitally, in particular if the total lamp power control is digital.

The evaluation of the lamp voltage can be determined, for example, by digital counting of the distances between successive half-waves (zero crossings) of the lamp voltage.

If a critical state is detected by means of the indirect detection of the lamp temperature by means of evaluation of the lamp voltage, the power of the lamp can be specifically controlled to a power lying above this predetermined dimming value (set value), especially at low dimming values.

This increase in the lamp power over a predetermined dimming value or setpoint can thus be carried out in particular at low lamp powers, in which u.a. There is a risk of the lamp extinguishing at low ambient temperatures.

Such a method can be used in an electronic ballast.

Accordingly, the present invention also relates to an electronic ballast for Fluorescent lamps that use a digital circuit for

Implementation of such a method.

Finally, the present invention also relates to a circuit for determining the temperature of a fluorescent lamp operated with alternating voltage. In this case, means, i. one provided the DC voltage source for the targeted superposition of a DC voltage to the fluorescent lamp. Finally, a detection circuit for the voltage of the fluorescent lamp is provided, the output signal of which can be supplied to an evaluation circuit, which evaluates the detected lamp voltage as a parameter for the temperature of the fluorescent lamp and considered, for example, in the course of a digital lamp control.

The means for the targeted superposition of a DC voltage to the fluorescent lamp may have a DC voltage path, which is provided parallel to the AC operating voltage for the lamp.

The present invention also relates to an electronic ballast having such a circuit.

Finally, the invention also relates to a luminaire which has such an electronic ballast.

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.

1a shows a schematic representation of relevant components of an electronic ballast, 1b and 1c are simplified circuit diagrams for explaining the background of the present invention;

FIGS. 2 and 3 are illustrative of the indirect digital detection of the impedance of the lamp, which may then be used as a lamp temperature parameter;

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, and

Fig. 6 shows the application of the invention to multi-lamp lights.

4 shows that the lamp voltage V _D i _S at low temperatures (see example -15 ° C.) in the region of low dimming values (represented by the lamp _current I _DΪS ) can rise very sharply and possibly exceed admissible limit values. In the reference example of a lamp temperature of 35 ⁰ C, this effect occurs less strongly or not at all. At the same time, however, it can be seen from FIG. 4 that the lamp voltage V _D i _{S is} altogether no clear parameter for the temperature of the lamp. As can be seen a slightly higher lamp currents may range in the lamp voltage V _D _S i at higher temperatures (Example 35 ⁰ C) even that at low temperatures (for example -15 ⁰ C) exceed. The illustrated dependence 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) both a dependence on the discharge current

V _ö i _s as well as from the ambient temperature T has. At a certain operating point in which the lamp current

I _DIS ^Vorrι ballast is kept substantially constant, thus there is a dependence of the lamp impedance Z _D i _S of the ambient temperature T.

As schematically illustrated in FIG. 1 b, the present invention now proposes to selectively store a DC voltage V _DC from a high-impedance source for the high-frequency operating voltage for the lamp U _HF , such that the voltage applied to the lamp is then different with respect to different criteria, such as the DC component, it can be evaluated under which conditions the lamp is currently operated:

The source voltage V _{DC of} the DC source is divided according to the resistance ratio of the internal resistance of the DC source Zi to the impedance of the lamp Zi at the current operating point, wherein the lamp resistance Z ₁ depends inter alia on the ambient temperature of the lamp T. This can also be done via the resistance ratio

the dependence of the measured DC component 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 lies outside a defined range, and in particular if it lies above a defined threshold value, the electronic ballast can take appropriate countermeasures to meet. It makes sense, the DC share of

Lamp voltage V _DC , _Z L detected over a certain time range and then averaged to account for temporal compensation operations in the lamp.

Now, if this average value of the DC component of the lamp voltage V _DC , _Z L increases beyond an allowable threshold, the ballast, for example. Automatically increase the lamp power, and indeed until the DC component of the lamp voltage V _DC , _ZL back to allowable Values, ie has fallen below the predetermined threshold. By "automatically increasing the lamp power through the electronic ballast" is to be understood that the electronic ballast also increases the lamp power beyond possibly supplied externally set values (dimming commands, etc.) and thus the stability of the lamp control a higher priority than the strict compliance specified outside values (dimming commands, etc.) is granted.

In addition to the DC component of the lamp voltage, further parameters of the lamp voltage can also be evaluated in order to detect critical states.

This increase in the lamp power can be limited 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 in time, for example because the ambient temperature of the lamp has increased again, the electronic ballast decreases the lamp power back again until either the default again

Threshold for the DC component of the lamp voltage V _DC , _{ZL is} reached, or now the predetermined target value (dimming command, etc.) for the lamp power has been reached correctly.

In Fig. Ia, an electronic ballast according to the invention is shown schematically, for example.

An inverter with two switches Sl, S2 converts a provided DC voltage (DC link voltage, bus voltage) into a high-frequency operating voltage for a resonant load circuit. The alternating voltage is tapped at the midpoint of the two switches Sl, S2. The resonant load circuit has an inductance L _R , a capacitor C _R and a coupling capacitor C _κ . A lamp, which is indicated schematically by means of its internal resistance R _D i _s , is operated as generally known, with this high-frequency AC voltage.

The control of the switches Sl, S2 and in particular the switching frequency of the alternating switching of the two switches Sl, S2 is carried out by a lamp control, which can be performed digitally according to the invention.

As already explained at the beginning, the described alternating operating voltage for the lamp is deliberately superposed on a DC voltage component V _DC . For this purpose, a diode D and a resistor R _{DC are} provided parallel to the inductance L _R and the coupling capacitor C _κ , which represent a DC voltage path parallel to the resonant circuit for the AC voltage. This represents only an example of how targeted a DC voltage component V _{DC can be added} to the lamp operating voltage. Parallel to the lamp is a voltage divider with two

Resistors Rl, R2 provided. A signal that the

Lamp voltage V _ZL reproduces, is at the midpoint of the

Voltage divider Rl, R2 tapped and the lamp control circuit supplied.

As shown schematically in Fig. 1, of course, the lamp control circuit further operating parameters such as the lamp current, etc., and externally predetermined setpoints (Dimmbefehle, etc.) are supplied.

A development of the present invention is shown in Figure 6 and relates to the application to multi-lamp electronic ballasts, in which therefore several individual lamps are operated in parallel. In these multi-lamp luminaires often the problem arises that the balancing of the lamp performance is often not guaranteed, especially at low dimming and low temperatures. This manifests itself noticeably for a user in that the lamp powers and thus the generated light output of the two lamps operated by the same electronic ballast noticeably differ. Of course, this also means that, for the reasons stated above, the lamp voltages of the two lamps operated by the same electronic ballast can have greatly different values.

In the case of a lamp with a plurality of lamps, according to the present invention it can be provided that in each case the DC component of the lamp _voltages V _DC , _ZL1 or V _DC , _{ZL2 is} evaluated. Then the difference between the two DC components of the lamp _voltages V _DC , _ZLI or V _DC , _{ZL2 is} determined by means of a comparator and used as a further input variable for the lamp control. Thus, according to this aspect, if the difference of the DC parts of the lamp voltages of the is too large for several lamps, so here is the

Lamp power may be increased beyond a specified setpoint. This increase in the application of the invention to multi-flame control gear now not (only) the goal to avoid extinction of one of the two lamps, but primarily, at low ambient temperatures of the two lamps beyond a certain threshold asymmetry of the light output of the two lamps reduce.

As already mentioned several times, according to the present invention, the lamp power control can be carried out digitally.

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

2 shows a circuit implementation of this _exemplary embodiment with an up / down counter 107 which _receives a signal U _ZER0 as the actual input signal and, _furthermore, as control signals a high-frequency reference clock signal CLK and a reset or reset signal.

The advantage here is the digital detection of the feedback signal by evaluation, for example, the zero crossings of the lamp voltage.

The signal U _ZERO assumes during each positive half wave of the voltage applied to the terminal V _L lamp voltage to a positive and otherwise a negative voltage level and thus detects the zero crossing of the lamp voltage. The counter 107 is designed in particular as a 9-bit counter and is initialized when the reset signal is applied to a middle counter reading, for example to the output counter value N ₀ = 255. The counter 107 is started at zero crossing of the lamp voltage and counts during the following half wave of

Lamp voltage either up or down. Thus, the zero crossings are digitally counted.

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 No within certain tolerance limits, so as not to prematurely infer the presence of a rectifying effect. The output signal of the comparator 103 is supplied via a clocked by a latch signal D flip-flop 108 of the Meßphasensteuerung 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 successively every 255th Period of the lamp voltage, a DC component is reported.

Claims

Claims :

A method of controlling the operation of an AC powered fluorescent lamp, comprising the following steps:

- Targeted superposition of a DC voltage to the fluorescent lamp, - Recording the lamp voltage of the fluorescent lamp, and

- Evaluation of the lamp voltage as an input variable of the regulation of the lamp power.

2. The method of claim 1, wherein the evaluation of the lamp voltage comprises at least the detection of the DC voltage component.

3. The method of claim 1 or 2, wherein the lamp voltage is evaluated based on an asymmetry of the periodically extending lamp voltage.

4. The method according to any one of claims 2 or 3, wherein the zero crossings of the lamp voltage are detected.

5. The method of claim 3 or 4, wherein the lamp voltage is evaluated by digital counting the distances of successive zero crossings of the lamp voltage.

6. The method according to any one of the preceding claims, characterized in that the lamp voltage is evaluated digitally.

7. The method according to any one of the preceding claims, wherein depending on the evaluation of the lamp voltage, the power of the lamp is increased to a value which is above an externally predetermined desired value.

8. The method of claim 7, wherein the increase in lamp power occurs only at low lamp power.

9. The method according to any one of the preceding claims, wherein the control of the lamp power is digital.

10. A method of sensing the temperature of an AC powered fluorescent lamp, comprising the steps of:

- targeted superposition of a DC voltage to the fluorescent lamp,

- Recording the lamp voltage of the fluorescent lamp, and

- Evaluation of at least the DC voltage component and possibly further parameters of the lamp voltage as a parameter for the temperature of the fluorescent lamp.

11. Use of a method according to one of the preceding claims in an electronic ballast.

12. Electronic ballast for fluorescent lamps, comprising a digital circuit for implementing a method according to one of claims 1 to 9.

13. A circuit for determining the temperature of a fluorescent lamp operated with AC voltage, comprising: - Means for targeted superposition of a

DC voltage to the fluorescent lamp,

a lamp voltage detecting circuit, and a lamp power regulating circuit which supplies the lamp voltage as an input.

14. A circuit according to claim 13, wherein the means for the targeted superposition of a DC voltage to the fluorescent lamp have a DC voltage path which is provided in parallel to AC operating voltage for the lamp.

15. The circuit of claim 13 or 14, wherein the control circuit is adapted to detect an asymmetry of the periodically extending lamp voltage.

16. A circuit according to any one of claims 13 to 15, wherein the control circuit comprises means for determining the distances of the zero crossings of the lamp voltage.

17. A circuit according to any one of claims 13 to 16, wherein the evaluation circuit is executed digitally.

18. The circuit of claim 17, wherein the evaluation circuit comprises a digital counter for detecting the distances of successive zero crossings of the lamp voltage.

19. A circuit according to any one of claims 13 to 18, wherein the control circuit depends on the evaluation of the lamp voltage, the power of the lamp to a Increase value above an externally supplied to the circuit setpoint.

20. Electronic ballast, comprising a circuit according to one of claims 13 to 19. '

21. A ballast according to claim 20, further comprising a digital control circuit for the lamp power.

22, luminaire, comprising a ballast according to one of claims 20 or 21.

23. A method of controlling the operation of a plurality of parallel operated and AC powered fluorescent lamps, comprising the following steps:

- targeted superposition of a DC voltage to each of the fluorescent lamps,

- Recording the lamp voltage of each fluorescent lamp, and

- Evaluation of the respective lamp voltages as input variables of the regulation of the lamp power.

24. The method of claim 23, wherein the difference of the lamp voltages is detected.

25. The method of claim 24, wherein the difference of the DC voltage components of the lamp voltages is detected.

26. The method of claim 25, wherein the lamp powers are increased when the difference of the DC voltage components of Lamp voltages exceeds a threshold.

27. Operating device for controlling a plurality of parallel operated and operated with alternating voltage fluorescent lamps, comprising:

a circuit for selectively superimposing a DC voltage on each of the fluorescent lamps,

a circuit for detecting the lamp voltage of each fluorescent lamp, and a lamp control circuit which takes into account the respective lamp voltages as input quantities for the regulation of the lamp powers.

28. Operating device according to claim 27, wherein the lamp control circuit detects the difference of the lamp voltages.

29. Operating device according to claim 28, wherein the lamp control circuit detects the difference of the DC voltage components of the lamp voltages.

30. Operating device according to claim 29, wherein the lamp control circuit increases the lamp powers when the difference of

DC voltage components of the lamp voltages exceeds a threshold.