EP1322142A1 - Electronic ballast with monitoring circuit for lamp rectifying effect - Google Patents

Abstract

A rectifying circuit (RC) (2) connects to an alternating voltage source (Uo). A smoothing circuit (3) links to the RC's output and generates an intermediate circuit voltage (Uz) for feeding a current inverter (CI) (4). A load circuit (5) has connectors for a gas discharge lamp (LA) and connects to the CI's output. A monitoring circuit (10) recognizes a rectifying effect in the LA.

Description

The present invention relates to an electronic ballast for operation at least one gas discharge lamp, which has a monitoring circuit, with the help of which a rectification effect occurring in the gas discharge lamp is recognized can be.

As with other lamps, gas discharge lamps occur due to Signs of wear of the heating coils at the end of the life of the Gas discharge lamp the effect on the lamp electrodes over time wear unevenly or the removal of the emission layers on the Lamp electrodes is different. As a result of this different wear there are differences in the emissivity of the two lamp electrodes.

This difference in emissivity means that one Lamp electrode to the other a higher current flows than in the opposite direction, so that the time course of the lamp current during one of the two half-waves has an excess. Due to the different ablation of the two Lamp electrodes thus create asymmetries that are not only stronger Cause light flickering at the end of the life of the gas discharge lamp, but in In extreme cases, only operate during a half-wave. The In this case, gas discharge lamp acts like a rectifier, which is why this effect is also referred to as the so-called "rectification effect".

Another consequence of the rectifying effect explained above is that the more worn electrode when starting the gas discharge lamp stronger heated because the work function of this electrode is higher. This effect can In particular with thin fluorescent tubes, there is a danger to the environment lead, because of the small diameter of the lamps inevitably also increased warming occurs. This warming can even go as far as parts of the lamp glass bulb melt.

In order to recognize the rectification effect that occurs in a gas discharge lamp Known from WO 99/34647 A1, which on a gas discharge lamp to be monitored applied lamp voltage or a variable dependent thereon and over integrate one or more half-waves. If the integration result of one If the specified target value differs, this is called the presence of a rectification effect interpreted. This solution enables the rectification effect in both directions recognizable, regardless of which of the two lamp filaments is stronger is worn out.

The solution known from WO 99/34647 A1 thus enables a reliable one Detection of the rectification effect, although this requires an additional component in the form of an integrator is necessary. When designing new electronic Ballasts, however, require additional components to be avoided as far as possible. The present invention is therefore an object an alternative way of recognizing a rectifying effect specify which can be implemented as simply as possible.

The task is performed by an electronic ballast, which has the characteristics of the Has claim 1 solved. According to the invention, the monitoring circuit contains a filter, by means of which the lamp voltage by a rectifying effect resulting DC voltage component is determined. There is also an evaluation circuit provided, by means of which it is determined whether the DC voltage component within or is outside a permissible range, with a location outside the permissible range is an indication of the presence of a rectification effect.

The filter is preferably connected to the load circuit by a filter Voltage divider formed, over which the lamp voltage drops, with a lower Resistor of the voltage divider is bridged by a capacitor. This The task of the capacitor is the AC component of the voltage to be measured largely suppress, so that at the connection point of the voltage divider forming resistors on which the measuring voltage for the evaluation circuit is removed, a DC voltage arises from a low AC voltage is superimposed. Through this circuit according to the invention thus the conditions on the lamp in which the AC component is much higher as the possible DC component, largely reversed, so that subsequently a simple evaluation is made possible. This circuit is characterized by its simple structure, which allows for extensive integration of the entire circuit allows.

Developments of the invention are the subject of the dependent claims. So can Facilitation of the evaluation of the tapped measurement voltage can be provided Measuring voltage previously in a positive range by a predetermined value to raise. This can be done, for example, by a power source connected to one of the Voltage divider connected to the measuring line connecting the evaluation circuit becomes. Alternatively, there is the option of connecting a resistor to the measuring line connect, its further connection with a positive supply potential is connected.

The evaluation of the measurement voltage supplied to the evaluation circuit can be based on easily done with the help of comparators that determine whether the Measurement voltage exceeds an upper or lower limit. Preferably however, the measurement voltage with the help of an analog / digital converter into one At least 2 bit existing digital value implemented and then digitally evaluates. This variant enables greater accuracy and reliability the determination of the rectification effect and also contributes to the integration of the Circuit at.

The design of the evaluation circuit in digital form is particularly of then Advantage if the electronic ballasts have a control circuit that also works predominantly or completely digitally. Another beneficial one A development of the invention therefore consists in the fact that a control circuit the at least one operating parameter is provided by a switching regulator formed smoothing circuit for generating an intermediate circuit voltage detected and a controllable switch of the switching regulator depending on the value of the controls detected operating parameters, the detected operating parameters with the help an analog / digital converter into a digital value consisting of at least 2 bits is implemented and the control circuit based on this digital value in a digital Control part calculates switching information for operating the switch. This Switching information is then transmitted to a driver circuit, which this in implement a corresponding control signal to control the switch.

In this advantageous development, the regulation of DC link voltage digital and implemented with an accuracy of more than 2 bit, which on the one hand achieves very high stability for the control and on the other others will get a circuit that takes up little space. In Further development of this idea can be provided, furthermore at least one To record operating parameters of the load circuit, this also in at least one Implement 2 bit existing digital value and switching information to operate the To calculate the inverter.

As described above, is the monitoring circuit for detecting the Rectification effect is also at least partially digital, so with one also digital design of the control circuits for the DC link voltage and the Inverters a high level of integration of the entire circuit can be achieved.

In particular, it can be provided instead of a multiplicity of analog / digital converters to provide a single one that is used to implement all recorded operating parameters or Measured values in time multiplex for the respective control loops or the Monitoring circuit works. The analogue / digital converter (s) preferably set the recorded values into digital values with an accuracy of 12 bit.

Fig. 1

ein erstes Ausführungsbeispiel eines erfindungsgemäßen elektronischen Vorschaltgeräts mit einer Überwachungsschaltung zum Erkennen eines Gleichrichteffekts;

Fig. 2 und 3

Diagramme zur Verdeutlichung der Auswertung des Messsignals zum Erkennen des Gleichrichteffekts; und

Fig. 4

eine Variante des erfindungsgemäßen Vorschaltgerätes.

The invention will be explained in more detail below with reference to the accompanying drawings. Show it:

Fig. 1

a first embodiment of an electronic ballast according to the invention with a monitoring circuit for detecting a rectification effect;

2 and 3

Diagrams to illustrate the evaluation of the measurement signal to identify the rectification effect; and

Fig. 4

a variant of the ballast according to the invention.

The electronic ballast shown in FIG. 1 is connected on the input side to the mains supply voltage U ₀ via a high-frequency filter 1. At the output of the high-frequency filter 1 there is a rectifier circuit 2 in the form of a full-bridge rectifier, which converts the mains supply voltage U ₀ into a rectified input voltage for the smoothing circuit 3. The smoothing circuit 3 is used for harmonic filtering and smoothing the rectified supply voltage and comprises a smoothing capacitor C1 and a step-up converter having an inductor L1, a controllable switch in the form of a MOS field-effect transistor S1 and a diode D1. Instead of the step-up converter used here, other switching regulator types can also be used.

A corresponding switching of the MOS field-effect transistor S1 generates an intermediate circuit voltage U _Z which is present across the storage capacitor C2 connected to the smoothing circuit 3 and which is fed to the inverter 4. The inverter 4 is formed by two further MOS field effect transistors S2 and S3, which are arranged in a half-bridge arrangement. An alternating high-frequency activation of the two field effect transistors S2, S3 generates an AC voltage at their center tap, which is fed to the load circuit 5 with the gas discharge lamp LA connected to it. This gas discharge lamp LA can in particular be a fluorescent tube.

The control of the three MOS field-effect transistors S1 to S3 of the smoothing circuit 3 and the inverter 4 is carried out by a control circuit 6, which generates corresponding switching information and transmits it to a driver circuit 7. The driver circuit 7 converts the switching information generated by the control circuit 6 into corresponding control signals for the gates of the three MOS field-effect transistors S1 to S3. This switching information is generated taking into account several operating parameters, which are tapped at different points in the smoothing circuit 3 and the load circuit 5 and fed to the control circuit 6. To regulate the intermediate circuit voltage U _Z , on the one hand the intermediate circuit voltage U _z itself and the current flowing through the inductance L1 or a voltage value corresponding to this current I _L are measured. The operating parameter recorded for the control of the inverter 4 is taken from the load circuit 5 and corresponds, for example, to the lamp voltage or the lamp current.

Both control loops formed in the manner described above are digital. For this purpose, the control circuit 6 has three analog / digital converters ADC 1 to ADC 3 on the input side, which convert the analog operating parameters taken from the smoothing circuit 3 or the load circuit 5 into digital values with an accuracy of at least 2 bit, preferably of 12 bit. The three digital values are then fed to an arithmetic block 8 which, taking these current operating parameters into account, calculates control signals for the three switching elements S1 to S2 and transmits them to the driver circuit 7. On the one hand, this digital version enables a very precise regulation of the intermediate circuit voltage U _z and the power for the lamp LA and, on the other hand, offers the possibility of largely integrating the control circuit 6 and thus making it very compact. In the present example, the control unit 6 is designed as a so-called application-specific integrated circuit (ASIC). The various components of the control circuit 6 are synchronized via a central clock generator 9, which transmits corresponding clock signals to the various units.

In the following, the monitoring circuit according to the invention for Detection of a rectification effect in the lamp LA are explained. This is a Evaluation circuit 10 is provided, which is also integrated in the control circuit 6. To recognize the rectification effect, the lamp LA is one of three resistors R1 to R3 and a capacitor C3 formed voltage divider 11 connected in parallel which a measurement signal is tapped and fed to the evaluation circuit 10. The lower branch of the voltage divider 11 contains a parallel connection from the Resistor R3 and capacitor C3, between this parallel circuit and a further resistor R2 is arranged at the tap point for the measurement signal. there the measuring signal is in turn by a fourth analog / digital converter ADC4 in a digital value consisting of at least 2 bits - preferably 12 bits implemented and then processed by the evaluation circuit 10 in a digital manner or evaluated.

The function of this voltage divider 11 can be seen in FIGS. 2a and 2b, which on the one hand show the time profile of the lamp voltage U _LA (FIG. 2a) and on the other hand the input signal U tapped at the connection point between the two resistors R1 and R2 and fed to the control circuit 6 _i (Fig. 2b). The task of the capacitor C3 is to largely suppress the AC component of the lamp voltage U _LA . From the voltage signal U _LA shown in Fig. 2a, which essentially consists of an AC signal with a very low DC voltage component - shown by the dash-dotted line - is accordingly a DC voltage signal is formed and fed to the control circuit 6, which is supplied by one only low AC voltage is superimposed. The voltage divider 11 thus has the function of a filter which largely reverses the conditions present on the lamp LA.

In order to simplify the processing of the input signal U _i by the analog / digital converter ADC4, this is assigned an off-set voltage ΔU and raised to a positive range. This is done by an internal current source I _q within the control circuit 6, which can be connected via a controllable switch S _q to the measuring line 12 connecting the voltage divider 11 to the evaluation circuit 10. This switching element S _q is activated by the evaluation circuit 10. The signal which results in this way and is actually to be evaluated by the evaluation circuit 10 is shown in FIG. 2c.

In the ideal case, in which there is no DC component at all at the lamp LA, the measurement signal U _i shifted by the value ΔU should fluctuate periodically by this value ΔU. In the example shown in FIGS. 2a to 2c, however, the output signal, ie the voltage U _LA applied to the lamp _{LA, is} already afflicted with a certain direct current, so that the measurement signal U; is slightly above the reference value ΔU. The evaluation circuit 10 now determines whether this deviation from the reference signal ΔU exceeds a predetermined maximum limit upwards or downwards, which is shown in FIG. 2c by the two dotted lines. In the example shown here, however, the DC component is so small that the upper or lower limit is never exceeded at any time, so that no rectifying effect is determined.

In the example shown in FIGS. 3a to 3c, however, the DC voltage component of the lamp voltage U _{LA applied} to the lamp LA is significantly higher, so that the measurement voltage U _i shifted by the offset voltage ΔU exceeds the upper limit value several times. This is recognized by the evaluation circuit 10 and interpreted as the presence of a rectification effect. The evaluation circuit 10 consequently transmits a corresponding signal to the arithmetic block 8 of the control circuit 6, which in response to this signal either completely switches off the electronic ballast or at least reduces the power supplied to the lamp LA in order to avoid excessive heating.

For dimensioning the capacitor C3 provided in the voltage divider 11 applies that this must not be too large, otherwise the evaluation will be too sluggish would. Furthermore, a large capacitor would be relatively expensive and would Increase circuitry costs. On the other hand, the capacitor not to be too small, otherwise the suppression of the AC voltage component is not done sufficiently and accordingly the accuracy of the Evaluation would be reduced.

4 shows a further variant of the ballast according to the invention. The The measurement signal tapped at the voltage divider 11 is not raised here by an internal current source within the control circuit 6, but by a resistor R4 connected to the measuring line 12, the other terminal is connected to a positive supply voltage potential V +. Like that in Fig. 1 illustrated embodiment, this variant is characterized by its simple structure and their high reliability.

The advantage of the monitoring circuit according to the invention for recognizing the rectification effect is that the circuit is very simple and does not require any complicated additional components. The digital processing of the measurement signal U _i also ensures a high degree of reliability in the detection of a rectification effect, it being possible for a rectification effect to be detected in both directions of the lamp LA. In the example shown, instead of the four analog / digital converters ADC1 to ADC4, only a single analog / digital converter can be used, which works in time-division multiplexing for processing the various operating parameters or measured values. Another variant is to use two comparators instead of the fourth analog / digital converter ADC4 to determine whether the measurement signal is outside or within the permissible range.

Claims (19)

Electronic ballast for at least one gas discharge lamp (LA), preferably for a fluorescent tube, with a rectifier circuit (2) that can be connected to an AC voltage source (U ₀ ), a smoothing circuit (3) connected to the output of the rectifier circuit (2) for generating an intermediate circuit voltage (U _z ) and an inverter (4) fed with the intermediate circuit voltage (U _Z ), to the output of which a connection for the lamp (LA) containing load circuit (5) is connected,
and with a monitoring circuit for detecting a rectification effect occurring in the gas discharge lamp (LA),
characterized in that the monitoring circuit contains a filter (11), by means of which the DC voltage component resulting from a rectification effect is determined from the lamp voltage,
and that the monitoring circuit also contains an evaluation circuit (10), by means of which it is determined whether the DC voltage component lies within or outside a permissible range, a position outside the permissible range being an indication of the presence of a rectification effect. Electronic ballast according to claim 1,
characterized in that the filter is formed by a voltage divider (11) connected to the load circuit (5), a resistor (R3) of the voltage divider (11) arranged below the tap point of the voltage divider (11) being bridged by a capacitor (C3) , Electronic ballast according to claim 2,
characterized in that a further resistor (R2) is arranged between the parallel circuit formed from the resistor (R3) and the capacitor (C3) and the tap point. Electronic ballast according to claim 2 or 3,
characterized in that the measurement voltage tapped at the voltage divider (11) is raised by a predetermined value into a positive range before the evaluation by the evaluation circuit (10). Electronic ballast according to claim 4,
characterized in that a current source (I _q ) is provided for raising the measuring voltage and can be connected to the measuring line (12) connecting the voltage divider (11) to the evaluation circuit (10). Electronic ballast according to claim 5,
characterized in that the current source (I _q ) is connected via a switching element (S _q ) controlled by the evaluation circuit (10). Electronic ballast according to claim 4,
characterized in that a resistor (R4) connected to the measuring line (12) connecting the voltage divider (11) to the evaluation circuit (10) is provided for raising the measuring voltage , said resistor being connected with its further connection to a supply voltage potential (V +). Electronic ballast according to one of the preceding claims,
characterized in that the measuring voltage supplied to the evaluation circuit (10) is compared with the aid of comparators with an upper and lower limit value. Electronic ballast according to one of claims 1 to 7,
characterized in that the measurement voltage supplied to the evaluation circuit (10) is converted into a digital value consisting of at least 2 bits with the aid of an analog / digital converter (ADC4) and the evaluation circuit (10) evaluates this digital value. Electronic ballast according to one of the preceding claims,
characterized in that the smoothing circuit (3) is formed by a switching regulator and the ballast further has a control circuit (6) which detects at least one operating parameter (U _i , I _L , U _Z ) of the smoothing circuit (3) and a controllable switch ( S1) of the switching regulator depending on the value of the detected operating parameter (U _i , I _L , U _Z ),
The control circuit (6) has at least one analog / digital converter (ADC1, ADC2) for converting the detected operating parameter (U _i , I _L , U _Z ) into a digital value consisting of at least 2 bits,
and wherein the control circuit (6) calculates a switching information for operating the controllable switch (S1) of the switching regulator on the basis of this digital value in a digital control circuit (8) and transmits it to a driver circuit (7) which converts this switching information into a corresponding control signal for driving the Implemented switch (S1). Electronic ballast according to claim 10,
characterized in that the control circuit (6) detects the intermediate circuit voltage (U _Z ). Electronic ballast according to claim 10 or 11,
characterized in that the control circuit (6) also detects at least one operating parameter of the load circuit (5),
The control circuit (6) has a further analog / digital converter (ADC3) for converting this operating parameter into a digital value consisting of at least 2 bits, on the basis of this digital value in a digital control circuit (8), switching information for operating the inverter (4) calculated and transmitted to the driver circuit (7), which converts this switching information into a corresponding control signal for controlling the inverter (4). Electronic ballast according to claim 12,
characterized in that the control circuit (6) detects the lamp current. Electronic ballast according to one of claims 10 to 13,
characterized in that the evaluation circuit (10) is part of the control circuit (6). Electronic ballast according to one of claims 10 to 14,
characterized in that the control circuit (6) has a single time-division multiplexing analog / digital converter for converting all the acquired operating parameters or measured values. Electronic ballast according to one of claims 10 to 15,
characterized in that the analogue / digital converter (ADC1-ADC4) convert the recorded operating parameter or measured values into digital values with an accuracy of 12 bits. Electronic ballast according to one of claims 10 to 16,
characterized in that the control circuit (6) is designed as an application-specific integrated circuit. Electronic ballast according to one of the preceding claims,
characterized in that the evaluation circuit (10) switches off the electronic ballast when a rectifying effect is detected. Electronic ballast according to one of claims 1 to 17,
characterized in that the evaluation circuit (10) reduces the power supplied to the lamp (LA) when a rectification effect is detected.

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