EP0706307A2 - Circuit for controlling the light intensity and the operating mode of discharge lamps - Google Patents

Abstract

Output circuit arrangement for an electronic ballast, with at least one pair of series resonance circuits (L3, C18; L2, C17), which connect the output of an AC voltage generator (30) with a pair of gas discharge lamps (LA1, LA2), at least one pair of ignition capacitors (C17, C18), of which one of a pair is connected in parallel to one of a pair of GE lamps (LA1, LA2), and with at least one inductive balancing element (TR1), which is dependent on the lamp currents (IL1, IL2) one pair of GE lamps (LA1, LA2) can be magnetized in opposite directions. <IMAGE>

Description

The invention relates generally to an electronic ballast (EVG) for fluorescent lamps. In particular, it relates to output circuit arrangements within the electronic ballast.

Modern electronic ballasts are used to control fluorescent lamps. The fluorescent lamps are operated more gently on the one hand and on the other hand the efficiency of such lamp types can be increased. An electronic ballast regularly has the following features.

A supply voltage, which can be a direct or alternating voltage, is fed to a rectifier and an intermediate circuit capacitor via a mains input filter. If the device is operated exclusively with DC voltage, the latter rectifier can be omitted. A high intermediate circuit voltage U₀ is formed on the intermediate circuit capacitor, which is of the order of magnitude of approximately 300 V with a conventional mains voltage supply of 220 V. An AC voltage generator is connected to the DC link, which is formed by a half-bridge or full-bridge inverter. It outputs a frequency-variable output voltage to an output load circuit which, unless a half-bridge circuit with an artificial voltage means tap is provided, has a series resonance circuit. The discharge path of the gas discharge lamp or fluorescent lamp to be controlled is in series with the series resonant circuit.

The output frequency of the inverter is approximately 10 kHz - 50 kHz.

At the frequencies mentioned, the efficiency of the connected fluorescent lamps is increased compared to operation on the 50 Hz supply network. An increased luminous efficiency is achieved with the same electrical power consumption. Furthermore, due to the high frequency, the inductance of the series resonant circuit on the output side of the inverter can be kept small. Finally, the variable frequency control enables brightness control of the fluorescent lamp, which is difficult to regulate (dimmable) in the normal network. Finally, there is that An ignition of the fluorescent lamp can also be prepared and initiated via the frequency control.
To protect the fluorescent lamps, the aforementioned ignition process also includes a so-called warm start, in which the heating filaments of the fluorescent lamp are preheated before the lamp is subjected to a high ignition voltage due to resonance phenomena, which leads to ignition and thus to the operation of the gas discharge lamp. The variation of the frequency that controls the ignition allows an almost infinitely variable brightness control within wide limits even during operation of the gas discharge lamp by frequency shift. Such a continuous and continuous control of the brightness requires special measures due to the negative internal resistance of the fluorescent lamp in operation.

An essential aspect for the development of a modern electronic ballast is therefore a control option that is as versatile as possible, in particular a brightness control. This with regard to the operating behavior and the brightness control of the fluorescent lamps connected to a respective electronic ballast.

In addition to versatile control and regulation, it is another concern of modern ECGs to ensure comfortable handling and operation of many decentralized light sources. This is particularly the case with regard to large-scale projects in which extensive lighting systems with a large number of light sources have to be installed.

The invention has for its object to provide an improved output circuit arrangement for an electronic ballast.

Taking into account the aforementioned technical problems, improved control of a plurality of gas discharge lamps connected to the electronic ballast should be possible in particular with the aid of the output circuit arrangement.

The object is achieved by an output circuit arrangement according to claim 1.

The output circuit arrangement according to the invention for an electronic ballast comprises at least a pair of series resonance circuits, which connect the output of the alternating voltage generator of the electronic ballast to a pair of gas discharge lamps, and at least one pair of ignition capacitors, one of which in each case one pair in parallel to one each A pair of GE lamps is connected, and at least one inductive balancing element, which can be magnetized in opposite directions by the lamp currents of a pair of GE lamps. Thus, according to the invention, a differently bright glow of the gas discharge lamps controlled by an electronic ballast can be avoided and for each gas discharge lamp a relatively independent ignition phase and synchronism in dimming operation are guaranteed.

In order to be able to handle the control functions and the brightness control particularly precisely and comfortably, a control and regulating device can be provided which takes over all essential control, regulating and monitoring functions for a decentralized ECG. It is assigned a transmitting and receiving device that serves as an external interface. Control commands and brightness commands can be supplied here, which are executed by the control and regulating device, depending on the currently valid process variables (measured variables) of the respective decentralized ECG.

A pair of fluorescent lamps are advantageously operated on an AC voltage generator in a respective decentralized ECG. This corresponds to a so-called two-lamp electronic ballast.

In addition to the convenient brightness control, the control and regulation device allows an increased lifespan of the fluorescent lamps and the granting of safety interests. Using the aforementioned control and regulating device, the operating behavior and the respective operating state of the fluorescent lamps supplied by an electronic ballast can be precisely controlled and monitored. In this way, warm start, ignition, dimming and switch-off processes (IGNITION, DIMM, OFF, ON) are strung together with high precision and gentle on the lamp. Inadmissible operating conditions are avoided, and sufficient heating of the heating coils is ensured before each ignition. In addition to brightness-controlled dimming (DIMM), the entire ECG can also be shut down if no brightness is required for a long period of time (SLEEP). In this state, the ECG consumes only a minimal amount of power. Avoidable losses are actually avoided.

In addition to regular dimming, in which the brightness of the fluorescent lamps can be varied as required (DIMM) between a minimum value (MIN) and a maximum value (MAX), emergency operation (EMERGENCY) is also possible, in which the lamp assumes an emergency lighting light level. This can be specified locally on the respective device. It is automatically activated under certain hazard conditions.

The transmitting and receiving device is advantageously connected to a central control device via a bidirectional bus line. This allows remote control of a large number of decentralized ECGs from a central location. In addition to remote control, the control unit also provides operating status information. Errors that occur in the lighting system are recognized and displayed on the basis of error messages sent by the decentralized ECGs via the bidirectional bus line have been sent to the central control unit. This simplifies and speeds up maintenance work. A variety of monitoring functions are already provided locally, such as overvoltage and undervoltage monitoring. It noticeably increases the lifespan of the fluorescent lamps.

The brightness control of the decentralized ECGs, which is controlled via the bus line, takes place via serial digital control words that represent control commands or brightness data information. Organization in functional groups is particularly advantageous, in which a plurality of electronic ballasts, which are arranged, for example, in a room, can be controlled simultaneously and with a single command.

The coupling of the transmitting and receiving devices to the bus line is advantageously effected by a differentiator. It provides a strong attenuation of the 50 Hz network frequencies and works with very low input currents. The attenuation of the network frequencies goes so far that reverse polarity protection is also provided; the application of 220 V to the bus line remains without damage.

If the fluorescent lamps are switched to dimmed operation after an ignition process, there may be short-term light pulses. They have their cause in the energy of the ignition process stored in the output circuit, which then expresses itself undesirably as a light pulse in dimmed operation. This can be remedied by extending the glow phase - which actually shortens the lifespan - between ignition and stationary operation. However, an actual shortening of the service life is avoided by the fact that the glow area is only extended at low brightness values. The greater the brightness, the shorter the glow phase and the faster the transition from ignition to normal operation.

If, according to the invention, the control and regulating device is supplied with a plurality m of measured variables from the electronic ballast, a large number of operating states and possibly dangerous states can be identified and avoided therefrom. Furthermore, real power control is possible, which works regardless of the lamp type (for example, argon lamps or krypton lamps). The lamp brightness control is advantageously achieved by frequency modulation or by a combination of frequency modulation and duty cycle change.

Monitoring also includes checking the heating coil currents of the fluorescent lamps. They allow a precise determination of whether certain lamps are defective or possibly not installed at all.

The "running layers" that occur during strong dimming operation are advantageously avoided if a low DC component is superimposed on the high-frequency lamp alternating current.

If a pair of fluorescent lamps are used per ECG, which are fed by a common AC voltage generator, the inductive balancing element according to the invention effects symmetrical operation of both fluorescent lamps. The lamp-specific heat exchangers, which are connected with their primary winding to the AC output circuit, enable voltage-controlled coil heating. The control and regulating device can draw conclusions about the nature of the heating coil at any time via primary current detection and thus identify already damaged fluorescent lamps or fluorescent lamps that will soon fail.

• 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.

Further advantageous aspects and embodiments of the output circuit according to the invention are set out in more detail in the subclaims. 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 supplied to the input circuit 20 (rectifier circuit), possibly via a switch S1. This generates the intermediate circuit voltage U₀, U _dc , which is fed to the AC voltage generator 30 (inverter). 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 are 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, as a result of which 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 multitude of measured values m which correspond to the process signals of FIG. 1 are fed to it. It gives 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 pass on to the control and regulating circuit 17 after appropriate preparation. 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 device (50) without problems and with little effort.

FIG. 4 shows a basic circuit diagram of an input circuit as can be used to supply the AC 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. An intermediate circuit capacitor C4 is connected downstream of the rectifier, 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 U₀ 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.

FIG. 5 shows an exemplary embodiment of a load circuit 40 according to the invention with a heat exchanger L5 for preheating the turning device in the fluorescent lamp LA1. In Fig. 5 only one of a pair of lamp circles is shown. The exemplary 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 Wendein. 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. Parallel to the ignition capacitor C17 there 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. The sum of the heating coil currents I _W1 is thus measured at the primary-side measuring resistor R10.

The Zener diode V15, which is still connected in series, generates a DC component in the primary winding of L5, which is not transmitted, however, but is missing in the lamp current I _L1 and thus supplies the discharge of the lamp with an additional DC component in the order of approximately 1% of the actual discharge current . 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 alternating voltage occurs at C17 which is not suitable for igniting the lamp LA1. In this operating state, the filaments in 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 f₀ 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. An output frequency can also be set at a maximum power (MAX) 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 frequency-dependent damping of the output circuit when the voltage rises. It is particularly important when high frequencies and high impedances occur, e.g. in the case of a missing lamp or when preheating when the filament is already warm The wiring of this type helps to limit the excess voltage when the lamp is not lit or is missing if 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 takes place in opposite directions, so that when there is 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 resonant circuit is connected upstream of each fluorescent lamp and 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 in 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 is. In this way it is ensured 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 alternating 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. asymmetrical switch-off / switch-on delays for the respective transistors come into consideration, 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 control 10, 17, 31 receive their drive voltage via a series resistor and a smoothing capacitor C5 from the intermediate circuit voltage U₀. 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, a phase angle analysis can also be 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 the transmit and receive circuit 10 and then supplied 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 equalizing currents can also flow in the circuit according to FIG. 8b, they cancel each other out because there is no primary ground connection. 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 him the Measuring current consumption of the entire ballast minimal. The inverter 30 and the control circuit 31 are shut down and, if necessary, after a slight further time delay, 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 U₀, 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 a 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 Wendein 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 voltage input of the switch-on circuit 20 and via the sensors R21, C25 (FIG. 4). A counter logic is used for this purpose, which initiates emergency operation if there is no exceeding or falling below a predetermined threshold value. This can happen after a predetermined 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 set the emergency operating brightness afterwards.

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 a 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 to comply with the safety regulation important according to VDE. The inductive part of the series resonant 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 non-hazardous 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, which lead to a short circuit in the discharge path of the lamp, can be detected on the basis of the process signals when the lamp voltages are monitored for a predetermined minimum value. If the value falls below this specified value, as in the case of 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 target time, i. H. if the voltage across the ignition capacitor C17 does not fall within this time period, the lock mentioned intervenes.

In addition to a complete shutdown and an error message, a repeat time can also be waited for after which a new attempt to start and start is made. 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 has been 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, as well as a quick reduction of the lamp current after ignition. The latter by instantly shifting the inverter output frequency towards higher frequencies. As a result, the glow zone 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. This can be set via digital control words and the transmitting and receiving device 10 by 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 binary 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 condition leads - despite switched off system - for a controlled ignition and a build-up of the brightness of the lamp to the preset emergency lighting brightness (NOT). This can be changed for each decentralized ECG via the setpoint specification U _NOT . 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 device 50 sends brightness values that increase incrementally 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 (8)

Output circuit arrangement for an electronic ballast (EVG),
marked by
at least one pair of series resonance circuits (L3, C18; L2, C17), which connect the output of the AC voltage generator (30, WR) of the electronic ballast (EVG) with a pair of gas discharge lamps (LA1, LA2, GE lamp), at least one Pair of ignition capacitors (C17, C18), one of a pair of which is connected in parallel to one of a pair of GE lamps (LA1, LA2), and
at least one inductive balancing element (TR1) which can be magnetized in opposite directions by the lamp currents (I _L1 , I _L2 ) each of a pair of GE lamps (LA1, LA2). Output circuit arrangement according to claim 1,
characterized,
that the ignition capacitor (C17, C18) acts between the coil (L2, L3) and a capacitor (C16, C15) of the series resonant circuit. Output circuit arrangement according to claim 1 or 2,
characterized,
that the balancing element (TR1) is a two-winding transformer, the two windings of which have the same number of turns. Output circuit arrangement according to claim 1 or 2,
characterized,
that at least one pair of current measuring elements (R31, R32), preferably a pair of low-resistance shunts, is provided, one current measuring element (R31 R32) each being connected in series with one gas discharge lamp,
that at least one pair of voltage measuring elements (R25-R28), preferably a pair of voltage dividers, is provided, wherein one voltage measuring element (R25, R27, R26, R28) is connected in parallel to one gas discharge lamp and that all the measured variables taken from the measuring elements (U _L1 , U _L2 , I _L1 , I _L2 ) of the control and / or regulating device. Output circuit arrangement according to claim 1,
characterized,
that the heating filaments of a gas discharge lamp each from a heating transformer (L5, L4) with a primary and a secondary winding for each heating filament of the gas discharge lamp can be heated in a voltage-controlled manner, each heating transformer (L4, L5) being connected on the primary side in parallel to the gas discharge lamp whose heating filaments he heats. Output circuit arrangement according to claim 5,
characterized,
that each heat exchanger (L4, L5) has a current measuring element (R10, R11) connected in series on the primary side, the respective output signal (I _L1 , I _L2 ) of the control and / or regulating device (17) for detecting the heating coil properties and for deriving one Error signals can be fed from this. Output circuit arrangement according to claim 1 or 5,
characterized,
that a slight direct current component can be superimposed on the lamp current (I _L1 , I _L2 ), which component is present continuously or depending on the brightness of the gas discharge lamp and is preferably about 1% of the lamp current. Output circuit arrangement according to claim 7,
characterized,
that a Zener diode (V16, V17), which is connected in series to the heat exchanger (s) (L4, Lf), causes the DC component in the lamp current.

Images