EP0490330A1 - Control circuit for gasdischarge lamps - Google Patents

Abstract

The invention relates in general to an electronic ballast (EVG) for fluorescent lamps. In particular, it relates to circuit arrangements inside the electronic ballast for separately measuring lamp current and heater coil current of lamp. Such an electronic ballast comprises an AC voltage generator (30, WR), whose frequency can be controlled, a series resonant circuit (L2, C17), which is connected to the output of the AC voltage generator (30) and to whose capacitor (C17) the gas discharge lamp is connected in parallel, and a current measuring element (R32) responding to the lamp current (IL1), at least one heating circuit of the heater coils of the gas discharge lamp being connected independently of the series resonant circuit (L2, C17) to the AC voltage generator (30), and a further current measuring element (R10) connected to said heating circuit serving to measure the heating current (JW). <IMAGE>

Description

The invention relates generally to an electronic ballast (EVG) for fluorescent lamps. In particular, it relates to circuit arrangements within the electronic ballast for the separate detection of lamp current and filament current of a lamp.

Electronic ballasts of modern design serve to control fluorescent lamps and regularly have the features specified in the preamble of claim 1.

The applicant's European patent application EP-A-0338 109 discloses an electronic ballast which has an AC voltage generator with a controllable frequency, a series resonant circuit whose capacitance is parallel to the lamp and a current measuring element for measuring the lamp current. However, not only the lamp current flowing over the electrodes of the lamp is measured, but also the heating current flowing over the filaments of the lamp. A differentiated statement about the level of the lamp current or the level of the heating coil current cannot be made.

When the circuit is implemented, the AC voltage generator is switched off in the event of a filament breakage, since parasitic capacitances to ground can result in voltage increases at the open end of the filament. The AC voltage generator must therefore be switched off for safety reasons. After switching off, the heating coil current no longer flows. An automatic restart with a newly inserted lamp cannot take place since the ballast receives no information about the insertion of the new lamp.

The invention has for its object to provide an electronic ballast that allows a separate detection of heating current and lamp current and does not turn off the AC generator even in the event of a filament breakage, so that the heating current can still be measured and an automatic restart is possible.

The object of the invention is achieved with the characterizing features of claim 1.

Advantageous embodiments of the invention are achieved with the dependent claims.

• Fig. 1 ein Blockschaltbild eines erfindungsgemäßen EVG,
• Fig. 2 ein Blockschaltbild eines erfindungsgemäßen Systemgedankens, bei dem mehrere dezentrale EVGs mit einem zentralen Steuergerät über eine Busleitung 12 verbunden sind,
• Fig. 3 ein Blockschaltbild eines Ausführungsbeispiels der erfindungsgemäßen Steuer- und Regeleinrichtung als integrierte Schaltung 17,
• Fig. 4 ein Prinzipschaltbild eines Eingangskreises 20 mit zwei Meßwerterfassungen,
• Fig. 5 ein Ausführungsbeispiel der transformatorgekoppelten Wendelbeheizung einer Leuchtstofflampe mit drei Meßfühlern,
• Fig. 6 ein Ausführungsbeispiel eines erfindungsgemäßen Ausgangskreises 40 mit Symmetrierelement TR1 für zwei Leuchtstofflampen,
• Fig. 7 ein Prinzipschaltbild des Wechselspannungsgenerators mit ihn ansteuernder Treiberschaltung 31,
• Fig. 8a-c jeweils ein Blockschaltbild der Sende- und Empfangseinrichtung 10 mit verschieden ausgestalteten Koppelschaltungen zur Busleitung 12,
• Fig. 9 ein Helligkeits-Zeitdiagramm zur Erläuterung des Abschalt- und des Notbeleuchtungsbetriebes,
• Fig. 10 ein Helligkeits-Zeitdiagramm zur Erläuterung der Softstart- bzw. Softstop-Funktion bei einer Systemkonfiguration gem. Fig. 2.

Based on the drawing, exemplary embodiments of the invention are explained in more detail below. Show it

• 1 is a block diagram of an electronic ballast according to the invention,
• 2 shows a block diagram of a system concept according to the invention, in which several decentralized electronic ballasts are connected to a central control device via a bus line 12,
• 3 shows a block diagram of an exemplary embodiment of the control and regulating device according to the invention as an integrated circuit 17,
• 4 shows a basic circuit diagram of an input circuit 20 with two measured value recordings,
• 5 shows an exemplary embodiment of the transformer-coupled filament heating of a fluorescent lamp with three sensors,
• 6 shows an exemplary embodiment of an output circuit 40 according to the invention with a balancing element TR1 for two fluorescent lamps,
• 7 shows a basic circuit diagram of the AC voltage generator with driver circuit 31 driving it,
• 8a-c each show a block diagram of the transmitting and receiving device 10 with differently configured coupling circuits for the bus line 12,
• 9 is a brightness-time diagram to explain the shutdown and emergency lighting operation,
• 10 is a brightness-time diagram to explain the soft start or soft stop function in a system configuration according to FIG. Fig. 2.

1 shows a block diagram of an exemplary embodiment of an electronic ballast according to the invention. The mains voltage U _N is - if necessary via a switch S1 - the

Input circuit 20 (rectifier circuit) supplied. This generates the intermediate circuit voltage U _O , U _dc , which the AC voltage generator 30

(Inverter) is fed. The AC voltage generator 30 outputs its high-frequency output voltage U _HF to an output load circuit 40 which contains one or more fluorescent lamps LA1, LA2. A plurality of system measured values (process variables) can be taken from both the AC voltage generator 30 and the load circuit 40. Together the measured values fed to a control and regulating circuit 17, which in turn generates the digital control signals for the inverter 30. These are potential-shifted via a driver circuit 31 and fed to the output MOS-FETs of the inverter. The control and regulating device 17 is also assigned a transmitting and receiving device 10, which is connected via a bus line 12 to other electronic ballasts and / or to a central control device 50.

The latter is shown in Fig. 2 . There, a plurality of electronic ballasts 60-1, 60-2, 60-3, ..., 60-i are connected to a common bus line 12. All ECGs are connected via this bus line to the central control device 50, to which a display unit 51 is assigned. Via bus line 12, it is now possible to control one or more of the aforementioned electronic ballasts and to transmit commands to them, such as switching off, switching on, igniting or the like. Brightness values can also be preset and, in return, error information can be queried from the individual devices. The control unit 50 is thus informed of the overall system status at all times, which means that a high degree of operational reliability can be guaranteed and accelerated maintenance of the decentralized ECGs or for their fluorescent lamps is possible.

The functional blocks 20, 30, 40, 10, 17 shown in FIG. 1 will now be explained in more detail with reference to the following figures.

3 shows the control and regulating device 17 as an integrated circuit. The plurality of measured values m which correspond to the process signals of FIG. 1 are fed to it. It emits two digital control signals for the output stage transistors of the inverter 30, which are amplified and potential-shifted via a driver circuit 31.

In addition to the m measured values, the control and regulating device 17 is also supplied with n target values. These influence the predeterminable control behavior. Furthermore, a transmitting and receiving device 10 is provided as part of the control and regulating circuit 17 or separately, which is connected directly or by means of a coupling circuit to the bus line 12. It forms the serial interface, which enables the control and regulating device to transmit error and operating status information to the central control device 50.

The aforementioned n setpoints can also be supplied to this transmitting and receiving device 10, which they send to the control and control device after appropriate preparation Control circuit 17 passes on. Setpoints can be, for example, the emergency lighting level (NOT), the minimum brightness level (MIN) and the maximum brightness level (MAX), within the latter of which the specifiable brightness level (DIMM) can move during operation.

Serial digital data words, the length of which are 8 bits, are used as command and data words and as error information words. Other value lengths are possible. An address is assigned to each decentralized ECG, which makes it possible to address individual ECGs via the address of the transmitting and receiving device 10 and to query information from them or to issue commands to them. The bidirectional mode of operation of the bus line 12 enables a large number of decentralized electronic ballasts to be connected to a central control unit (50) without problems and with little effort.

FIG. 4 shows a basic circuit diagram of an input circuit as can be used for supplying the alternating voltage generator 30 from a supply network with the voltage U _N. The input circuit consists of capacitive input filters and possibly a harmonic choke. The Y-circuit capacitors are used for radio interference suppression. A surge arrester or a VDR is connected in parallel. This is followed by a full-wave rectifier, which can be omitted if the device is operated with direct voltage. Downstream of the rectifier is an intermediate circuit capacitor C4, which charges up to approx. 300 V with a residual ripple of approx. 10% at 220 V mains voltage.

Due to a crest factor to be kept low, the intermediate circuit voltage U _{O should} be smoothed well.

Parallel to the intermediate circuit capacitor C4 is a voltage divider R18, R28, from which a measurement signal proportional to the intermediate circuit voltage can be tapped. A signal which is proportional to the supply voltage is detected at a low-pass filter R21, C25 and, like the intermediate-circuit voltage-dependent measurement signal, is fed to the control and regulating device 17. Both measurement signals are used to monitor the supply voltage and thus the operational safety of the ECG.

5 shows an exemplary embodiment of a load circuit 40 according to the invention with a heat exchanger L5 for preheating the filaments of the fluorescent lamp LA1. In Fig. 5 only one of a pair of lamp circles is shown. The embodiment of the invention has a pair of these branches, ie two Fluorescent lamps LA1, LA2 at an AC voltage output, which outputs the high-frequency AC voltage U _HF between the series-connected power switching transistors V21 and V28. The AC voltage generator is supplied with an intermediate circuit voltage U _dc from the input circuit 20 shown in FIG. 4. Since the fluorescent lamps have a negative internal resistance during operation, they must be supplied with high voltage peaks during the ignition process (ZÜND) and with appropriate heating energy when heating the filaments. Starting from the output connection of the inverter 30, a series resonance circuit L2, C15 leads via a balancing element TR1, which will be explained later, to the discharge path H2, H4 of the fluorescent lamp. Furthermore, a measuring resistor R32 is connected in series with the fluorescent tube, at which a voltage proportional to the lamp current I _L1 is tapped and fed to the control and regulating circuit 17. An ignition capacitor C17 is connected to ground (ZERO) between coil L2 and capacitor C15. With the aid of this arrangement, the dimmer characteristic of the discharge lamp can be made more uniform, since with increasing frequency the resistance of the capacitor C15 decreases and the resistance of the discharge lamp increases. In addition, this capacitor is connected to ground even when the filament breaks, so that no voltage increases occur at the open lamp holder, since the resistance of the ignition capacitor C17 is sufficiently small at the maximum frequency of the AC voltage generator. Parallel to the ignition capacitor C17 is also the primary winding of the heat exchanger L5 and in series with this a Zener diode V15 and a measuring resistor R10. A voltage proportional to the heating coil current I _W1 is tapped from the latter and fed to the control and regulating circuit 17 as a further system measurement variable. Since the inverter 30 impresses an output voltage and the heat exchanger is essentially parallel to the fluorescent lamp LA1, a voltage is impressed on its secondary windings via the heat exchanger. The two secondary windings each supply one of the two heating coils H1, H2 and H3, H4 potential-free. The sum of the heating coil currents I _{W1 / 2 is} measured at the primary-side measuring resistor R10. With the separate supply of the heating coils, both argon and krypton lamps can be operated without any problems since the different properties of the two lamps are essentially compensated for by the use of the L5 heat exchanger.

The Zener diode V15, which is still connected in series, generates a direct current component in the primary winding of L5, which is not transmitted, however, but is missing in the lamp current I _L1 and thus the discharge of the lamp with an additional one DC component in the order of magnitude of approx. 1% of the actual discharge current is supplied. This prevents the effect of the "running layers" that occur when the lamps are dimmed. The "running layers" consist in particular of light / dark zones which occur during dimming and run along the tube at a predetermined speed. A superimposition of low direct current accelerates this running effect in such a way that it no longer has a disturbing effect.

For heating, the inverter 30 is operated at a high frequency f _max , so that an AC voltage occurs at C17 which is not suitable for igniting the lamp LA1. In this operating state, the filaments of the lamp are heated via L5, the lamp absorbing a high and then a lower heating current due to the thermistor effect of the filaments. After a preheating time of approx. 750 ms, the ignition (IGNITION) of the lamp is initiated.

When the fluorescent lamp is ignited, the frequency f of the inverter 30 is reduced so that it comes closer to the resonance frequency f of the output series resonance circuit L2, C15. This creates a voltage surge at C17, which is of the order of approximately 750 V (peak). This will ignite a functional lamp.

As soon as the lamp LA1 or LA2 has ignited, the series resonance circuit L2, C15 or L3, C16 is strongly damped. On the one hand, this causes a shift in the resonance frequencies f _O and, on the other hand, an immediate drop in the AC voltage applied to the respective lamp. The decrease is detected by the control and regulating circuit 17 via the voltage divider R27, R25 connected in parallel to the lamp. This then initiates the actual operating phase (DIMM) of the lamps.

For effective lamp operation, the frequency f of the inverter 30 is regulated so that the lamp output corresponds to the predetermined target value, ie the desired brightness level. The higher the frequency in the operating state, the lower the lamp brightness. The operating frequency of the alternating voltage generator 30 can also be shifted to values which are in the order of magnitude of the heating frequency or above. At a maximum power (MAX), an output frequency can also be set which is below the ignition frequency but still above the resonance frequency of the series resonance circuit L2, C15.

The operating state of the lamp circuit 14 can vary greatly depending on the lamp used, for example argon or krypton lamps, or depending on the lamp power selected.

The combination of the capacitor C24 and the diodes V30, V31 results in a frequency-dependent damping of the output circuit when the voltage rises. It is particularly important when there are high frequencies and high impedances, e.g. if there is no lamp or if the filament is already warm. The wiring of this type helps to limit the voltage rise when the lamp is not ignited or missing when it is undesirable. C24 is selected so that the damping remains small enough at the time of ignition.

Fig. 6 shows the output circuit of Fig. 5 for the two-lamp - two fluorescent lamps on an inverter - operation. The symmetry transformer TR1 is also shown here in full. Each winding is traversed by one of the two lamp currents. This happens in opposite directions, so that in the event of a deviation in the current amplitude, a resulting magnetization occurs, which induces a voltage in the inductive element which has a symmetrical effect. Such a transformer is advantageous if the two lamps would burn differently bright in the dimmed state due to component tolerances and lamp tolerances as well as different temperature conditions. The symmetry element TR1 avoids this in the case of two-lamp luminaires. If several pairs of lamps are operated at an AC voltage output, such a balancing element TR1 must be provided for each pair.

From Fig. 6 it can also be seen that an individual series resonance circuit is connected upstream of each fluorescent lamp and that an individual ignition capacitor C17, C18 is connected in parallel. This enables a relatively independent ignition phase and synchronization in dimming mode. In parallel with the ignition capacitors C17, C18 there is a voltage divider R25-R28, which feed a signal proportional to the output AC voltage to the control and regulating device 17. In the same way, it is also possible to connect the voltage dividers directly parallel to the fluorescent lamp, ie behind the balancing element TR1. In series with the lamps, this was already explained for a lamp circuit with reference to FIG. 5, there is one current measuring shunt R31, R32 each. A signal proportional to the lamp current is obtained from them, which signal can be multiplied in the control and regulating circuit 17 by the aforementioned lamp voltage signal. This ensures that at any time of the actual lamp power _is P or E brightness proportional signal is available, which can be preset to a precise brightness control as the feedback.

7 shows the inverter 30 in more detail with its output power transistors V28, V21. Between them, the high-frequency AC voltage U _{HF is} output to the load circuit 40 explained above. The two power transistors are controlled via a control circuit 31, which receives its control signals from the control and regulating circuit 17. Possibly. unbalanced turn-off / turn-on delays come into consideration for the respective transistors, so that a common conduction of both transistors V21, V28 can be avoided in principle. The upper transistor is supplied via a bootstrap circuit (not shown), the lower transistor and the system controller 10, 17, 31 receive their drive voltage via a series resistor and a smoothing capacitor C5 from the intermediate circuit voltage U _O. In addition to the aforementioned power supply from the intermediate circuit, there is also a low-loss AC voltage coupling from the oscillating inverter 30 via a coupling capacitor C21, the diodes V12, V7 and the inductance L7 into the storage capacitance C5.

The current that can be supplied to the smoothing capacitor C5 through the series resistor or a current source I _q is sufficient to supply the IC31 and the control and regulating circuit 17 in the switched-off mode (SLEEP).

When the inverter is in operation, the supply, coupled out via a capacitor C21, rectified via the named components V12, V7, L7 and smoothly coupled in via C5, is sufficient. This supply voltage generation is almost loss-free since only reactive elements are used to limit the current. A voltage signal U _Kap proportional to the branch current I _max is obtained by means of the anti-parallel diodes V14, V15 connected in the lower inverter half-branch of the transistor V21 and the resistor R34 connected in parallel. Like the other process signals, this is fed to the control and regulating circuit 17. From this, he can determine the current direction of the current flowing through the inverter at the moment before V21 is opened. If this current is negative, the load circuit 40 of the inverter 30 is in an impermissible capacitive range. It represents a danger for the controlling inverter. In addition to the pure amplitude detection, one can also Phase position considerations are used, in which the load current I _{L1 is set} in relation to the inverter branch current I _max and from this the relative phase of both currents is used to detect the operating state.

Detection of an impermissible capacitive operating behavior is answered by the control circuit 17 by increasing the operating frequency f of the inverter 30, with which the load circuit 40 is again operated inductively. The above-mentioned capacitive mode of operation mainly occurs with a low supply voltage. With the branch current detection, destruction of components can be safely avoided.

8 shows the transmitting and receiving device 10 and the coupling filter connected upstream of it, with which the bus coupling to the control line 12 takes place. In this example, the digital interface 10 is given the setpoints for minimum, maximum and emergency lighting brightness (U _NOT , U _MIN , U _MAX ). Furthermore, a digital input DAT is provided, via which both the control signals arrive from a central control device to the decentralized ECG and the error signals are transmitted from the decentralized ECG to the central control device. The serial interface enables remote control of the electronic ballast by means of a digital command signal or command word. An 8 bit data word is provided as such a digital signal. It is differentiated by the two capacitors C22, C23, then potential-shifted by half the supply voltage of the control circuit 17 or of the transmit and receive circuit 10 and then fed to the digital input DAT of the interface 10 via a damping capacitor C12. This means that both the 50 Hz mains frequency can be suppressed and the input currents of each interface can be kept low. 8b shows a further embodiment of the bus coupling. Here, the two bus lines 12 are inductively coupled to the data input of the digital interface. If ECGs are operated with the coupling filter shown in Fig. 8a on different phases of the three-phase network, compensating currents can flow that interfere with the data transmission. Although these compensating currents can also flow in the circuit according to FIG. 8b, they cancel each other out because there is no ground connection on the primary side. An advantageous further development of this circuit is shown in FIG. 8c. The circuit is protected against polarity reversal by using a secondary winding with center tap. Optical coupling can also be used, but this has an increased power consumption.

255 (corresponding to 8 bit) brightness values are provided as control signals. The control signal "OFF", represented by the binary word "zero" is also possible. With the aforementioned signal OFF, the entire ECG switches to an energy-saving shutdown mode (SLEEP) immediately or after a short period of time. In it, the measuring current consumption of the entire ballast is minimal. The inverter 30 and the control circuit 31 are shut down and, after a slight further time delay, if necessary, the essential assemblies of the control and regulating circuit 17. Only the receiving circuit of the transmitting and receiving device 10 and the monitoring circuit for the detection of an emergency operation (EMERGENCY) remain activated. The total circuit power thus drops below 1 W. However, if a new control signal arrives in such a state, the control and regulating circuit 17 immediately carries out the switch-on sequence which, with preheating and ignition process (IGNITION), transfers to steady-state operation and is used for one immediate setting of the desired brightness value (DIMM) is ensured.

In addition to controlling the brightness and the emergency lighting mode and the switch-off mode (SLEEP mode), the control and regulating circuit 17 is also responsible for extracting the information from all of the aforementioned process variables which are important for monitoring and controlling the electronic ballast.

These are voltage monitoring, emergency operation maintenance and monitoring of the fluorescent lamps with regard to filament breakage or gas defects. The various operating states of the fluorescent tube, such as ignition, preheating and stationary operation, can also be distinguished by the measured variables. The measured process variables and those used for checking are summarized below:
Supply voltage U _ac , U _N ,
_Undervoltage / overvoltage U _Nmin , U _Nmax ,
Battery voltage U _B ,
_{DC link voltage} U _O , U _dc ,
Lamp current / operating current I _L1 , I _L2 ,
Lamp voltage U _L1 , U _L2 ,
Output voltage U _HF ,
Output current I _HF ,
Spiral current I _W1 , I _W2 ,
AC generator branch current I _chap .

Overvoltage and undervoltage in the intermediate circuit and in the supply circuit are detected using the variables listed. The control and regulating circuit 17 switches off all functions when the voltage becomes too high, and can only function again when the voltage has been switched off and on again.

The occurrence of undervoltage - which leads to dangerous capacitive operation of the inverter - is answered by the fact that the control circuit 31 is blocked. As long as the mains supply does not have the necessary voltage to guarantee the heating process of the coils and to avoid capacitive operation, the control and regulating device 17 does not ignite. The ignition process is only triggered after a predetermined threshold value has been exceeded. This happens automatically.

An emergency mode switchover to a predeterminable emergency lighting brightness takes place, for example, when a DC voltage U _{N is} detected by the control circuit 17 via the usual AC supply input of the switch-on circuit 20 and via the sensors R21, C25 (FIG. 4). For this purpose, a counter logic is used, which initiates emergency operation if the specified threshold value is not exceeded or undershot. This can happen after a specified dead time that bridges individual, possibly missing, half-waves.

If the normally feeding AC voltage U _ac , U _N fails in a lighting system, an emergency voltage supply U _B , which is obtained from batteries or a generator, is placed on the mains voltage line. The ECGs recognize this automatically.

In emergency mode, the brightness of the fluorescent lamps is no longer specified by the digitally specified brightness value DIMM, but by a trim value that can be specified locally on the device and can be specified via the input U _NOT . If the ECG is in switch-off mode (SLEEP) when this emergency operation occurs, ie the lamp and inverter are switched off, it will first carry out the normal ignition process (IGNIT) in order to subsequently switch to the emergency operating brightness.

When the end of the emergency operating state is recognized, the electronic ballast returns to the previous state; this can be the OFF state if the electronic ballast was previously there. However, this can also be the original brightness value (DIMM), if this was available before requesting emergency operation.

The detection of the filament current detects whether either a lamp is not inserted or one of the two filaments is broken. In one of these error cases, the inverter 30 is operated at its maximum frequency f _max , which on the one hand results in the heating current still flowing when the defective lamp has been replaced and on the other hand reduces the voltage on the defective lamp to the smallest possible extent . This is important to comply with the safety regulations according to VDE. The inductive part of the series resonance circuit in the output becomes so high at the above-mentioned high frequency f _max with respect to the capacitive resistance of the ignition capacitor C17 that the voltage at the output is limited to harmless values and there is no danger for the maintenance personnel.

If a functional lamp is inserted, the ignition process (IGNITION) is initiated without waiting for the preheating time to elapse.

The internal sequence control in the control and regulating circuit 17 also limits the number of start attempts to two and sets (sends) whenever there is an error, e.g. B. the lamp is missing if a filament break or a gas defect is present, an error signal via the transmitting and receiving device 10 on the bidirectional bus 12. This also applies in emergency mode, since emergency mode cannot be maintained if the lamp is defective.

Wiring errors that lead to a short circuit in the discharge path of the lamp can then be detected on the basis of the process signals if the lamp voltages are monitored for a predetermined minimum value. If the value falls below this specified value, as in the case of the mains overvoltage monitoring, the entire ECG is switched off.

Also the unwillingness to ignite the lamp, e.g. B. by gas defect, is recognized by the control and regulating circuit 17. If the lamp cannot be ignited within a predetermined ignition timing, i. H. if the voltage across the ignition capacitor C17 does not drop within this period, the said lock is activated.

In addition to a complete shutdown and an error message, you can also wait for a repeat time after which you have to try again to start and start again is undertaken. If no ignition success is achieved here either, the control and regulating circuit 17 reacts as in the case of a broken heating coil and sets the frequency of the inverter 30 to the maximum value f _max .

When the lamp is replaced, which the control and regulating circuit 17 recognizes by an increase in the lamp voltage or by a change in the heating coil current, an attempt is made to fire again after a new lamp is inserted.

The following is explained for the brightness control of the fluorescent lamps. A real brightness control is used, since this guarantees the same lamp outputs regardless of the lamp type - with essentially the same lamp efficiency. The measured values determining the actual value, lamp current and lamp voltage, are multiplied and compared in analog or digital form with the setpoints predetermined by remote control via the transmitting and receiving device 10. The comparison result controls the frequency f of the alternating voltage generator 30 directly or via a controller. If a more precise gradation of brightness is desired, a logarithmic setpoint adjustment can take place. Exponential actual value weighting can be carried out in the same way. In addition to the independence of the lamp type, compensation is also achieved for lamp age, the existing operating temperature and also the possibly fluctuating mains voltage U _N.

With the process signal-controlled operating state monitoring, it is also possible to ignite the lamps to small brightness values, whereby the normally occurring light pulse can be avoided. The latter is due to the energy stored in the output circuit by the ignition process, which is then suddenly discharged into the lamp after ignition. For suppression or elimination, a quick ignition detection - by changing the lamp lamp voltage U _L1 , U _L2 - is provided, and a rapid reduction in the lamp current after ignition is carried out. The latter by instantly shifting the inverter output frequency towards higher frequencies. As a result, the glow area between the ignition and the stationary gas discharge is artificially extended. This would result in a reduction in lamp life under normal circumstances. This is according to the embodiment avoided, however, since the extension of the glow phase is used only for the critical low brightness values. For large brightness values, the current is kept at a higher level, which shortens the glow phase becomes. This can be set via digital control words and the transmitting and receiving device 10 via software.

FIG. 9 shows a brightness-time diagram in which the brightness of the lamp controlled by the electronic ballast according to FIG. 1 is varied as a function of time. First, maximum brightness is provided, followed by a switch-off cycle specified via the bus line 12 and the digital interface 10. The brightness is acc. a predetermined slope reduced to zero, then the inverter 30, its driver circuit 31 and essential parts of the control IC 17 turn off to save electricity. A subsequent emergency lighting state leads - despite the system being switched off - to controlled ignition and a build-up of the brightness of the lamp to the preset emergency lighting brightness (EMERGENCY). This can be changed via the setpoint specification U _NOT for each decentralized ECG. Likewise, the maximum and minimum brightness value (MIN, MAX) shown in FIG. 9 can be set or adjusted via a corresponding setpoint value.

A program-controlled "soft start" is shown schematically in FIG. 10 as a brightness-time diagram. The ECG 60 is initially in the switched-off state (OFF). The "Softstart" command now leads either to an automatic, slope-controlled increase in lamp brightness - after it has been ignited - or to a program-controlled incremental increase in lamp brightness levels. In the latter case, the central control unit 50 sends incrementally increasing brightness values in certain time segments. The decentralized ECGs follow the requirements almost without delay. This enables a rate of change-controlled (regulated) rise and fall of the decentralized light sources.

Claims (7)

Electronic ballast for a gas discharge lamp with
an AC voltage generator (30, WR) whose frequency is controllable;
a series resonance circuit (L2, C17) connected to the output of the AC voltage generator (30), to whose capacitor (C17) the gas discharge lamp is connected in parallel; and
a current measuring element responsive to the lamp current (I _L1 ), characterized by
at least one heating circuit for the heating filaments of the gas discharge lamp, which is connected to the AC voltage generator (30) independently of the series resonance circuit (L2, C17), and
a further current measuring element connected to the heating circuit for measuring the heating current. Electronic ballast according to claim 1,
marked by
a heat exchanger (L5) with a primary winding connected to the AC voltage generator (30) and with two secondary windings, one secondary winding being arranged in each heating circuit; and by means of a resistor (10) in series with the primary winding, from which a measurement variable proportional to the heating current (I _W ) can be tapped. Electronic ballast according to claim 2,
characterized by
that the heat exchanger (L5) is arranged alternately in parallel with the capacitor (C17) of the series resonant circuit (L2, C17). Electronic ballast according to claim 3,
characterized by
that the coil (L2) of the series resonant circuit between the AC voltage generator (30) and the primary winding of the heat exchanger (L5) is arranged in series. Electronic ballast according to claim 1,
characterized,
that the lamp current (I _L1 ) is led to ground via a resistor (R32), a measurement variable proportional to the lamp current (I _L1 ) being able to be tapped at the resistor (R32). Electronic ballast according to claim 1,
marked by
a voltage measuring element arranged parallel to the gas discharge lamp and comprising two resistors (R27, R25) connected in series, a measurement variable proportional to the lamp voltage (U _L1 ) being able to be tapped between the two resistors. Electronic ballast according to one of claims 2 to 6,
marked by
a control and regulating device (17) to which the respective measured variables (I _W , I _L1 , U _L1 ) and predeterminable threshold values can be supplied, the control and regulating device (17) shifting the frequency of the AC voltage generator to the frequency maximum when a lamp defect is detected.

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