CN101253817A - Ballasts for discharge lamps with adaptive preheating - Google Patents

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

Ballasts for discharge lamps with adaptive preheating

technical field

The invention relates to an electronic ballast for a discharge lamp, and more particularly to an electronic ballast for a discharge lamp with preheatable electrodes.

current technology

Electronic ballasts for operating discharge lamps are known, as are electronic ballasts designed for operating discharge lamps with preheatable electrodes. In principle, an electronic ballast generates a supply power for a connected discharge lamp from a given power source (for example a mains supply), in particular a high-frequency AC voltage supply, wherein this supply power has the power required for operating the discharge lamp. characteristic.

Usually, the electrodes of a discharge lamp are preheated before the discharge is ignited. In this way, the emission capability of the electrodes can be improved and their lifetime extended. The preheating process typically lasts from 0.4 s to slightly more than 2 s and is carried out according to a preheating program determined in the sequence control unit.

Contents of the invention

The problem underlying the invention is to provide 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 the ballast has a measuring device designed to repeatedly measure the an electrode temperature-dependent variable of at least one electrode of the connected discharge lamp; and a control device designed to ignite the discharge in response to the measurement when the electrode temperature-dependent variable varies non-monotonically.

Preferred developments of the invention are given in the dependent claims.

The invention is based on the realization that the desired short preheating time can be achieved by using as high a preheating current or preheating voltage as possible, but when the voltage at the electrodes of the connected discharge lamp exceeds a critical value during the preheating process , there will be a lateral discharge (Querentladung).

Lateral discharges are undesirable, especially because the temperature of the electrodes decreases due to lateral discharges. At lower temperatures, the electrodes emit poorly, and ignition of the discharge at too low a temperature increases the wear of the electrodes.

Lateral discharges can be recognized by this temperature drop of the electrodes during the preheating process. The temperature drop at the electrode can be determined by means of a non-monotonic change of the electrode temperature-dependent variable during the preheating time. For example, when an electrode is discharged laterally, its resistance and hence the voltage drop across it also decreases. The current through the electrodes increases due to the lower resistance. The degree to which this behavior is pronounced also depends on whether the heating power supply is more of a voltage source or more of a current source. In practice, the characteristics of the heating power supply lie between these two 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. In order to measure the electrode temperature, any electrode temperature-dependent characteristic can be measured. Suitable variables are specified within the scope of the dependent claims.

Furthermore, the electronic ballast according to the invention has a control device which responds to the measurements of the measuring device. If there is a non-monotonic variation of the electrode temperature-dependent variable, the control device initiates an ignition discharge.

The more measurements are taken during the warm-up process, the better the temperature changes of the electrodes can be tracked and thus the more reliably the control device can intervene. However, multiple measurements imply a certain overhead and the electronics must be designed accordingly. In principle, it is also possible to implement lateral discharge detection with very few measuring points. However, such a detection with fewer measuring points is also less reliable.

In one embodiment of the invention, the electrode temperature-dependent variable considered for the detection of transverse discharges is the voltage at the electrodes. If a transverse discharge occurs, the voltage at the electrodes involved drops to a certain extent.

On the other hand, it is also preferred that the electrode resistance is measured as a variable related to the electrode temperature. The electrode resistance during the preheating time is obtained 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 meaningful to observe the voltage on one of the electrodes for lateral discharge detection. If the electronic ballast is the significant voltage source, a transverse discharge detection via the quotient of the hot and cold resistances determined by the (additional) current measurement is suitable.

It is possible that the electrode temperature reaches a sufficient value earlier than expected. In order to minimize the preheating time, ignition should then be brought about, for example, by a control circuit.

The quotient of the current electrode resistance and cold resistance is suitable as the variable to be measured. The cold resistance of an electrode is understood here to mean the resistance of the electrode at an electrode temperature corresponding to room temperature (20° C.). The quotient of the current electrode resistance (ie thermal resistance) and cold resistance, like the electrode resistance itself, is approximately proportional to the electrode temperature. Since it is divided by the cold resistance, a normalized variable is used in this connection. This is interesting because the cold resistance will be quite different from lamp to lamp, but gives no indication of the temperature change during warm-up. For example, the control device can be designed to determine the quotient of the thermal resistance measured by the measuring device and the cold resistance also measured by the measuring device.

Preferably, the discharge is ignited as soon as the current quotient of the electrode resistance and the cold resistance reaches between 4 and 7 within the warm-up time. More preferably, the discharge is ignited starting from the lower limit 4.5 and irrespective of this up to the upper limit 6 .

The intervention of the control circuit during the preheating process is not only meaningful in the above case in the form of a pre-ignition discharge, but also in the form of an adaptation of the operating parameters of the electronic ballast in response to the measurement, because the simple Inadequate execution of the predetermined preheating sequence can lead to unsatisfactory results of the preheating process, even if the discharge is introduced earlier according to the embodiment of the invention as described above.

Even if electronic ballasts are designed and used to operate discharge lamps of the same type in each case, the preheating process takes place differently for each individual discharge lamp. The preheating process differs from lamp to lamp as a result of manufacturing tolerances, in particular of the preheatable electrodes, or as a result of differences in the ambient temperature.

The control device compares the measured value of the measuring device with the standard value of the variable related to the electrode temperature. When there is a deviation between the measured value and the standard value, the control device matches the subsequent progress of the preheating process by changing the operating parameters of the electronic ballast, so that the expected deviation between the subsequent measurement and the corresponding standard value get smaller. The process is therefore a closed loop control.

Examples of operating parameters of electronic rectifiers suitable for matching electrode temperature changes during preheating are the following: preheating current flowing through electrodes, preheating voltage on electrodes, frequency of high frequency AC voltage supply generated by electronic ballasts , the duty factor of the AC voltage supply and the size of the DC voltage supply.

In order to make standard values of variables related to the electrode temperature available for comparison by the control device, these standard values can be stored in memory devices within the electronic ballast or fixedly wired in the form of an electronic circuit, for example with The circuit form of threshold value elements (comparators) to which the measured value is supplied and whose threshold value is used to determine whether there are deviations from the standard value is fixedly wired. Such a circuit can also realize a control device at the same time.

The preferred embodiment of the electronic ballast also allows greater flexibility when using different types of lamps, since the course of the preheating process is adapted to standard values by the control device. Although different types of lamps may have different electrodes, an efficient preheating process can still be achieved by the control circuit.

The adaptation of the preheating process to the standard preheating process described above does not make the detection of lateral discharges superfluous. Lateral discharges can also occur in the case of multiple matching of operating parameters. It is also possible, in particular if only a few measurements are taken within the expected warm-up time, that the electrode temperature has a sufficient value earlier.

In order to track changes in a variable related to electrode temperature during warm-up, this variable is measured at least every 100 ms. With typical warm-up times, it is then possible to carry out several measurements during the warm-up process.

The lamp type identification can be advantageously used if the electronic ballast should be able to operate not only with one type of lamp, but also with several different types of lamps. Preferably, the lamp type is determined by measuring the cold resistance of the electrodes of the connected discharge lamp. In a preferred embodiment of the invention, the memory device is designed to store a set of suitable preheating parameters for different lamp types, such as preheating duration, standard values for heating current and heating voltage, and heating voltage and the maximum heating current. If the electronic ballast recognizes the connected lamp type by means of the cooling resistor, the control unit controls the preheating process based on standard values corresponding to the lamp type.

In the case of work on a power supply network, there may be occasions when the power supply network fails. Electronic ballasts can be equipped with timing elements to determine if the network interruption is shorter than a predetermined time. If this is the case, the cold resistance is not measured after a network interruption, otherwise the cold resistance is measured.

The above and the following descriptions of individual features relate to the type of device and also to the method according to the invention, without this being mentioned in detail or explicitly.

In principle, therefore, the present invention also relates to a method for operating a discharge lamp equipped with electrodes that can be preheated, the method having the following steps: connecting the discharge lamp; Repeated measurements of an electrode temperature-dependent variable of at least one of the electrodes are performed; in case the electrode temperature-dependent variable varies non-monotonically, a discharge is ignited by the control means responsive to the measurement. The invention also relates to the refinements explained above and below implicitly for this method.

Description of drawings

The invention will be further elucidated below with the aid of examples. The individual features disclosed here are also essential to the invention in other combinations.

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

FIG. 2 shows the time profile of the variables related to the electrode temperature.

FIG. 3 shows the time profile of the electrode temperature-dependent variables and the associated heating current adapted during the preheating process.

FIG. 4 shows a variant of FIG. 2 .

FIG. 5 shows another variant of FIG. 2 .

FIG. 6 shows yet another variant of FIG. 2 .

Detailed ways

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

The electronic ballasts are fed by grid supply lines N1 and N2. The generator G generates the supply power for the connected low-pressure discharge lamp LA from the supplied mains supply N1 , N2 . The generator G comprises: a rectifier for rectifying the AC voltage supply; a power factor correction circuit for extracting a possibly sinusoidal current from the mains supply; an intermediate circuit capacitor; and a half-bridge converter. In this case, the DC voltage required to feed the half-bridge converter is present at the intermediate circuit capacitor. The half-bridge converter generates a high-frequency alternating voltage between output A1 and reference potential GND or between output A1 and another potential of the intermediate circuit voltage.

A series circuit comprising a lamp inductor L, a coupling capacitor CC, a lamp terminal KL1A, a low-pressure discharge lamp LA, a lamp terminal KL2A and a resistor R1 is connected between the first output A1 and the reference potential GND. In parallel to the series circuit comprising lamp terminal KL1A, low-pressure discharge lamp LA and lamp terminal KL2A is connected a series circuit comprising lamp terminal KL1B, resonant capacitor CR and lamp terminal KL2B. There is an electrode E1 between the lamp terminals KL1A and KL1B, and an electrode E2 between the lamp terminals KL2A and KL2B.

There is a connection node K1 between the lamp terminals KL2A and R1. A control device C and a measuring device M are connected between the second output A2 of the generator and the connection node K1. The control device C and the measuring device M are part of a microcontroller and are therefore shown with a common box. Both the control device C and the measuring device M have a reference to a reference potential GND. The control device C can adjust an operating parameter (here heating current) of the generator G via the control line SL. The measuring device is connected in series with reference potential GND via node K1. Furthermore, the measuring device M is connected in series with the resonant capacitor CR via the lamp terminal KL2B. Between resonant capacitor CR and measuring device M there is a connection node K2. The lamp terminal KL2B is connected to this connection node.

The voltage drop across resistor R1 is proportional to the current through electrode E2 between lamp terminals KL2A and KL2B. The voltage across resistor R1 can be detected by 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 profile of the variables that are dependent on the temperature of the electrodes of the low-pressure discharge lamp LA during the preheating process. During the warm-up time, the measuring device M measures (here 10 times) the resistance RW of the electrode E2 between the lamp terminals KL2A and KL2B. The preheating process starts at time t0 and ends at time t1. As the temperature increases, the resistance RW of the electrodes also increases and reaches its then maximum value at the end of the preheating time t1 (here after 0.5 s). Before the preheating process results in significant heating, the electrode resistance has the value RK, its cold resistance. The quotient of RW and RK as a function of time is shown here as a variable related to electrode temperature. The quotient here reaches a value of 5 at the end t1 of the preheating time, which corresponds to an electrode temperature of approximately 800° C.

FIG. 3 a shows the temporal profile of the quotient of the hot and cold resistances, and FIG. 3 b shows the associated heating current IE2 (heating current through the electrode 2 ), which is matched during the preheating process. In the control device C, five standard values for the quotients of the hot and cold resistances and the heating current that occur during the course of the preheating process are respectively stored for the different lamp types. Before the preheating process begins, the measuring device M determines the cold resistance of the electrode E2. The lamp type is detected by means of the cold resistance RK of the electrode E2, and a standard value corresponding to the detected lamp type is selected as a comparison measure for the control device C of the preheating process. The crosses in FIGS. 3a and 3b each correspond to a standard value stored in the control device. The solid line in Fig. 3a corresponds to the actual distribution of the quotient of the hot and cold resistances, while the solid line in Fig. 3b corresponds to the actual distribution of the heating current during the warm-up time. It can be seen in FIG. 3a that the quotient of the hot and cold resistances firstly does not increase fast enough to correspond to the standard value. The control intervenes appropriately and increases the heating current so that the quotient of the hot and cold resistances has a greater slope. In this case, the heating current change is selected proportionally to the difference between the quotient of the hot and cold resistances and the associated standard value.

Figure 4 shows the quotient of RW and RK as a function of time during preheating for two different preheating processes. During the first preheating process (dotted line), a typical distribution as shown in Fig. 2 is seen. The preheating process ends 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. And when the quotient reaches a value of 5, the electrodes are hot enough and the discharge is ignited.

If a transverse discharge occurs at the electrode E2 during the preheating process, the temperature of the electrode, which was raised at first, is lowered again. This is shown in FIG. 5 and is also indicated by the reduction in the quotient of the current electrode resistance RW and cold resistance RK. In this case, the measuring device M carries out ten measurements of the electrode resistance RW in the interval between t0 and t1. If within this interval the electrode resistance decreases after its first increase, this is a sign of a lateral discharge; the discharge is ignited.

Figure 6 also shows a similar distribution. If a lateral discharge occurs on one of the electrodes, the voltage on this electrode drops sharply. The voltage UKL2 on the electrode E2 is measured by the measuring device M. If, during the preheating process, the voltage UKL2 decreases after its first increase, an ignition discharge is also brought about by the control device C here.

Claims (10)

1. But one kind be used to drive the electrode that has preheating (E1, the electric ballast of discharge lamp E2) (LA) is characterized in that, this electric ballast has:

   -measurement mechanism (M), its be designed to the discharge lamp (LA) that duplicate measurements in warm connects at least one electrode (E1, variable E2), relevant with electrode temperature (RW, UKL2); And

   -control device (C), it is designed to, and (RW UKL2) gives me a little in response to measurement during non-monotone variation and sets off at the variable relevant with electrode temperature.
2. 2. electric ballast according to claim 1, wherein relevant with electrode temperature variable (RW) are electrode (E1, one of E2) voltage (UKL2) on.
3. 3. electric ballast according to claim 1, (RW UKL2) is electrode (E1, E2) one of resistance (RW) to wherein relevant with electrode temperature variable.
4. 4. each described electric ballast in requiring according to aforesaid right, wherein control device (C) is designed to determine electrode (E1, E2) merchant (RW/RK) of the cold resistance (RK) of one of current thermal resistance (RW) and beginning.
5. 5. electric ballast according to claim 4, it is designed to, when thermal resistance and cold resistance (RW, merchant RK) (RW/RK) surpass last in limited time, light discharge.
6. 6. electric ballast according to claim 5, wherein the upper limit is more than or equal to 4, and is less than or equal to 7.
7. 7. each described electric ballast in requiring according to aforesaid right, wherein control device (C) is designed to, and in response to measurement, comes the matched electrodes temperature by the running parameter of regulating electric ballast in warm.
8. 8. each described electric ballast in requiring according to aforesaid right, wherein measurement mechanism (M) is designed to, the variable that every at least 100ms measurement is once relevant with electrode temperature (RW, UKL2).
9. 9. in requiring according to aforesaid right each, electric ballast according to claim 7 at least, has storage device (C), and wherein in storage device (C), store the variable (RW relevant respectively with electrode temperature at different lamp type, UKL2) standard value, and wherein measurement mechanism is designed to:

   -after connecting electric ballast and electrode (E1, before warm E2) begins, detecting electrode (E1, E2) one of cold resistance (RK),

   -by electrode (E1, E2) one of cold resistance (RK) detects lamp type, and

   -select the standard value corresponding, as the comparison yardstick of control device (C) for warm with detected lamp type.
10. 10. each described electric ballast in requiring according to aforesaid right is used to drive low-pressure discharge lamp (LA).

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