DE202005013753U1 - Electronic ballast for operating discharge lamp, has control device to ignite lamp discharging in non-repetitive process for parameter e.g. voltage, that is correlated to temperature of electrodes during measurement of parameter - Google Patents

Abstract

The ballast has a measuring device (M) to repeatedly measure a parameter e.g. voltage and heating resistance, that are correlated to the temperature of electrodes (E1, E2) of a discharge lamp (LA) during a preheating operation of the electrodes. A control device (C) ignites the discharging of the lamp in a non-repetitive process for the parameter that is correlated to the temperature during the measurement.

Description

technical area

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

State of technology

electronic ballasts for the Operation of discharge lamps, including those designed to do so are to operate discharge lamps with preheatable electrodes, are known per se. in principle creates an electronic ballast from a given supply, For example, a power supply, a supply for a connected Discharge lamp, which for the operation of the discharge lamp necessary. Has characteristics, in particular a high-frequency AC power supply.

Often be the electrodes of a discharge lamp before igniting the Discharge preheated. In this way, the emissivity can be improve the electrodes and extend their life. One Preheating typically takes between 0.4 s and a little more than 2 s and takes place according to a flow control Preheat.

presentation the invention

Of the Invention is based on the problem, an improved ballast for discharge lamps specify with preheatable electrodes.

The The invention relates to an electronic ballast for operation a discharge lamp with preheatable electrodes, characterized in that it has, a measuring device, which is designed, during the Preheating a correlated to the electrode temperature size at least one of the electrodes of a connected discharge lamp is repeated to measure and a control device which is designed to in a non-monotonic course correlated to the electrode temperature Size appealing on the measurement to ignite the discharge.

preferred Embodiments of the invention are specified in the dependent claims.

The Invention is based on the knowledge that a desired short Preheating with the use of the largest possible Vorheizströmen or Vorheizspannungen can be achieved, but if the voltage on an electrode of a connected discharge lamp during the preheating process exceeds a critical value, however, a transverse discharge can occur.

cross discharges are not wanted i.a. because with a transverse discharge the electrode temperature again decreases. At lower temperatures, the electrode is less emissive and an ignition of Discharging at too low a temperature increases the wear of the electrode.

cross discharges can at such a temperature decrease an electrode during the preheating be detected. A drop in temperature over one Electrode can be determined by a non-monotone gradient of a to the electrode temperature correlated size within the preheating time can be determined. About takes in a transverse discharge over the Elek trode also your resistance and the voltage drop across it from. However, the current through the electrode decreases due to the lower Resistance too. How strongly these behaviors are pronounced hangs too depending on whether the heating power supply rather a voltage source characteristic or a power source characteristic. Real become the properties the heating power supply between these extremes are.

The electronic according to the invention ballast has a measuring device which is designed to be during the Preheating the temperature of one or both electrodes of a connected Discharge lamp to measure. For measuring the electrode temperature Any arbitrary correlated property can be measured. Suitable sizes become under the dependent claims dealt with.

Further has the electronic according to the invention ballast a control device, which is based on the measurement of the measuring device responds. Is a non-monotonous course one to the electrode temperature correlated size, so the control device initiates the ignition of the discharge.

ever more measurements during performed the preheating the better the course of the electrode temperature can be understood and the more reliable the control device can intervene. Many measurements mean but a little effort; the electronics must be designed accordingly be. In principle, a transverse discharge detection is also very important conceivable few measuring points. However, this is with few measuring points also less reliable.

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. kick a transverse discharge, so the voltage across the affected electrode collapses to a certain extent.

on the other hand may also be preferred as correlated to the electrode temperature Size the electrode resistance to eat. The electrode resistance during the preheating time results itself from the Vorheizspannung and the Vorheizstrom, so is easy to determine.

Has the electronic ballast a pronounced current source characteristic, so it makes more sense for transverse discharge detection, the voltage across one of the electrodes observe. Is the electronic ballast a pronounced voltage source, a transverse discharge detection over the quotient of warm and cold resistance, which over an (additional) current measurement is determined.

It is possible, that the electrode temperature earlier as expected reaches a sufficient value. To the preheating time should then, for example, via the control circuit, the ignition be initiated.

When offers to measure size the quotient of the current electrode resistance and the Cold resistance on. Under the cold resistance of an electrode is here the resistance of an electrode understood when its temperature the room temperature (20 ° C) equivalent. The quotient of current electrode resistance, ie the warm resistance, and the cold resistance, as well as the electrode resistance itself, approximately proportional to the temperature of the electrodes. Because of the cold resistance is shared, but a normalized in this regard size is used. This is interesting, because the cold resistance quite well from lamp to Lamp may vary, but nothing about the temperature history during the Preheating process says. For example, the control device can do so be designed to determine the quotient from that of the measuring device measured resistance and also from the measuring device make measured cold resistance.

Preferably becomes as soon as the quotient of current electrode resistance and Cold resistance during the preheating time reaches a value between 4 and 7, the discharge ignited. More preferable is when the discharge starts from a lower limit of 4,5 and independent thereof is ignited to an upper limit of 6.

One Intervention of the control circuit in the course of preheating is not only in the cases described above in the form of premature ignition of Discharge makes sense, but also appealing to the measurement in Form of adaptation of the operating parameters of the electronic ballast, because a simple run a predetermined Vorheizablaufes to an unsatisfactory result lead the preheating can, even if, as in the embodiments described above invention, the discharge early is initiated.

Also if an electronic ballast for the operation of discharge lamps is designed and used each of the same type, the Preheating but different for each discharge lamp run. A different from lamp to lamp course of the Preheating can in manufacturing tolerances, in particular the preheatable electrodes, or in ambient temperature differences justified be.

The Control device compares the measured values of the measuring device with Default values of the value correlated to the electrode temperature. at a deviation between the measured and standard value fits the control device by change an operating parameter of the electronic ballast the following course of preheating, so that the expected Deviation between a following measurement and a corresponding one Default value becomes smaller. This process is therefore a regulation.

Examples for operating parameters the electronic ballast, which adapt to the course of the electrode temperature while preheating process are: the preheating current through the electrodes, the preheating voltage at the electrodes, the frequency of the electronic ballast generated high-frequency AC power supply, the duty cycle just this AC power supply and the amount of DC power supply.

In order to the default values of the size correlated to the electrode temperature for comparison are available through the control device, these can stored in a memory device within the electronic ballast be, or else hardwired in the form of an electronic Circuit, such as a circuit, which threshold elements (Comparators), to which the measured values are supplied and their thresholds above decide whether there is a deviation from the default values. Such a circuit could at the same time implement the control device.

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 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 making adjustment of the preheating process to a standard preheating operation as described above the detection of transverse discharges is not superfluous. Even with multiple customization the operating parameters can Transverse discharges occur. It is also possible that the electrode temperature is early assumes a sufficient value, especially if only a few measurements while the expected preheating be performed.

Around the course of the correlated to the electrode temperature during the To follow preheating, this is measured at least every 100 ms. In the usual Preheat times are thus several measurements during the preheating possible.

Should the electronic ballast not just with one, but with several different lamp types can be operated Thus, a lamp type detection can advantageously be used. Preferably the lamp type changes over a measurement of the cold resistance of an electrode connected Discharge lamp detected. In a preferred embodiment According to the invention, the memory device is designed for various Lamp types each store a set of matching preheat parameters, for example, the preheating time, default values for the heating current and the heating voltage as well as maximum values for Heating voltage and heating current. Has the electronic ballast based the cold resistance detected the connected lamp type, so controls the control device, the preheating according to the lamp type corresponding default values.

At the Operation on the supply network, it may happen that in the meantime this supply network fails. The electronic ballast can be equipped with a timer to determine if the Power interruption shorter was, as a given duration. If this is the case, then it will the grid interruption no measurement of the cold resistance performed, otherwise beautiful.

The above and the following description of the individual features refer to the device category and also to one of the Invention corresponding method, without this in detail still explicitly mentioned becomes.

The The invention thus relates in principle also a method for operating a preheatable electrodes Equipped discharge lamp, with the steps: Connecting the Discharge lamp, repeated measurement of a correlated to the electrode temperature Size at least one of the electrodes of a connected discharge lamp during the preheating process with a measuring device, igniting the discharge at a nonmonotonic course of the electrode temperature correlated size through a control device, which responds to the measurement, and relates also apply to the above and implicitly also for this Explained method Configurations.

Short description the drawings

in the Below, the invention will be explained in more detail with reference to embodiments. The individual features disclosed can also be used in other combinations be essential to the invention.

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

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

3 shows a time course of a correlated to the electrode temperature size and an associated heating current, which is adjusted during the preheating process.

4 shows a variation of 2 ,

5 shows a further variation of the 2 ,

6 shows a variation of the 2 ,

preferred execution the invention

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

The electronic ballast is fed from the mains supply lines N1 and N2. A generator G generates a supply power from the given mains supply N1, N2 for an attached Low pressure discharge lamp LA. The generator G contains a Rectifier for rectifying the AC power supply, a Power factor correction circuit for as sinusoidal current drain from the mains supply, a DC link capacitor and a half-bridge inverter, being over the DC link capacitor for supplying the Halbbrückeninverters necessary DC voltage is applied. The half-bridge inverter generates a high-frequency AC voltage between the output A1 and the reference potential GND or the other Potential of the DC link voltage.

Between the first output A1 and the reference potential GND is a series circuit from a lamp inductor L, a coupling capacitor CC, a lamp terminal KL1A, the low-pressure discharge lamp LA, a lamp terminal KL2A and a resistor R1 connected. Parallel to the series connection from the lamp terminal KL1A, the low-pressure discharge lamp LA and the lamp terminal KL2A is a series circuit of a Lamp terminal KL1B, a resonant capacitor CR and a lamp terminal KL2B switched. Between the lamp terminals KL1A and KL1B 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 on the generator A2 and the connection node K1 is a control device C and a measuring device M connected. The Control device C and 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 via a control line SL Set the operating parameters of generator G, here the heating current. The measuring device is over the node K1 connected in series to the reference potential GND. Further is the measuring device M over the lamp terminal KL2B in series with the resonance capacitor CR connected. Between the resonant capacitor CR and the measuring device M is a connection node K2. At this connection node is the lamp connection KL2B is connected.

The above the Resistor R1 decreasing voltage is proportional to that through the electrode E2 between the lamp terminals KL2A and KL2B flowing current. The tension over the resistor R1 can be detected by the measuring device M. The voltage between the lamp terminals KL2A and KL2B can vary from the measuring device M also be detected.

2 shows a typical course of a correlated to the electrode temperature of the low-pressure discharge lamp LA size 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 t0 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.

3a shows a time course of the quotient of hot and cold resistance and 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 detected lamp type corresponding to the standard values as a reference scale for the control device C for the preheating selected. The crosses in the 3a and 3b each correspond to the default values stored in the control device. The solid line in 3a corresponds to the actual course of the quotient of hot and cold resistance and the solid line in 3b corresponds to the actual course of the heating current during the preheating time. In 3a you can see that the ratio of hot and cold resistance initially does not increase fast enough to meet the default 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.

4 shows the quotient of RW and RK as a function of time during the preheat process for two different preheat operations. In the first preheating process (dot-dashed line) you can see a typical course, as in 2 , The preheating process 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 in 5 is shown and also expressed in that the quotient of the current electrode resistance RW and the cold resistance RK decreases. The measuring device M here takes ten measurements of the electrode resistance RW in the interval between t0 and t1. If the electrode resistor fails within this interval, after having risen first, this is an indication of a transverse discharge; the discharge is ignited.

It is similar with 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 preheating process, after it has risen first, the ignition of the discharge is also caused here via the control device C.

Claims (10)

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 to have a value (RW, UKL2) correlated to the electrode temperature during the preheating process 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, in a non-monotonous course of the electrode temperature correlated size (RW, UKL2) in response to the measurement to ignite the discharge. An electronic ballast according to claim 1, wherein the magnitude correlated to the electrode temperature (RW) the voltage (UKL2) above one of the electrodes (E1, E2). An electronic ballast according to claim 1, wherein the value correlated to the electrode temperature (RW, UKL2) is the resistance (RW) is one of the electrodes (E1, E2). 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 one Cold resistance (RK) of one of the electrodes (E1, E2) to determine. Electronic ballast according to claim 4, which is designed to ignite the discharge when the quotient (RW / RK) from hot and cold resistance (RW, RK) exceeds an upper limit. An electronic ballast according to claim 5, wherein the upper bound is larger or is 4 and less than or equal to 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 of the electrode temperature by adjusting an operating parameter of the electronic ballast. 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 every 100 ms. Electronic ballast according to one of the preceding Claims, at least according to claim 7, which comprises a storage device (C) and in which in the memory device (C) for various Lamp types each default values correlated to the electrode temperature Size (RW, UKL2) are stored and in which the measuring device is designed is - to the switching on of the electronic ballast and before the start of the preheating the Electrodes (E1, E2), the cold resistance (RK) of one of the electrodes (E1, E2), - based the cold resistance (RK) of one of the electrodes (E1, E2) the lamp type to detect and - the Standard values corresponding to the detected lamp type, as a comparative scale for the control device (C) for to select the preheating process. Electronic ballast according to one of the preceding claims for operating a low-pressure discharge lamp (LA).