EP0800335A2 - Circuit for operating electric lamps - Google Patents

Circuit for operating electric lamps Download PDF

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Publication number
EP0800335A2
EP0800335A2 EP97104699A EP97104699A EP0800335A2 EP 0800335 A2 EP0800335 A2 EP 0800335A2 EP 97104699 A EP97104699 A EP 97104699A EP 97104699 A EP97104699 A EP 97104699A EP 0800335 A2 EP0800335 A2 EP 0800335A2
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EP
European Patent Office
Prior art keywords
circuit
transistor
control
parallel
auxiliary
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97104699A
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German (de)
French (fr)
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EP0800335A3 (en
EP0800335B1 (en
Inventor
Bernd Rudolph
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Osram GmbH
Original Assignee
Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
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Publication of EP0800335A3 publication Critical patent/EP0800335A3/en
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Publication of EP0800335B1 publication Critical patent/EP0800335B1/en
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14—Circuit arrangements
    • H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
    • H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
    • H05B41/282—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices
    • H05B41/2825—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a bridge converter in the final stage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S315/00—Electric lamp and discharge devices: systems
    • Y10S315/05—Starting and operating circuit for fluorescent lamp
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S315/00—Electric lamp and discharge devices: systems
    • Y10S315/07—Starting and control circuits for gas discharge lamp using transistors

Definitions

  • the invention relates to a circuit arrangement for operating electric lamps according to the preamble of patent claim 1.
  • Such a circuit arrangement is disclosed, for example, in European patent EP 0 093 469.
  • This document describes an inverter, in particular a self-oscillating half-bridge inverter with two alternating switching inverter transistors, in the control circuit of which a time switching device is arranged.
  • These time switches essentially consist of an auxiliary transistor and an RC element, the ohmic resistance of which is bridged by a Zener diode, and the capacitor of which is connected in parallel to the base-emitter path of the auxiliary transistor. Due to the Zener diodes, the time switching devices have voltage-dependent time constants which enable the frequency and the duty cycle of the half-bridge inverter to be controlled and the defined heating and ignition conditions for the low-pressure discharge lamps to be set.
  • the circuit arrangement according to the invention is intended, on the one hand, to ensure satisfactory preheating of the lamp electrodes during operation of the above-mentioned fluorescent lamps and, on the other hand, to avoid an excessive rise in the pen current.
  • the circuit arrangement according to the invention has a self-oscillating half-bridge inverter, to the output of which a load circuit designed as a resonance circuit is connected, in which at least one electric lamp is arranged.
  • the two inverter transistors have a control circuit, in each of which an auxiliary transistor is connected.
  • these auxiliary transistors are connected to the control circuits of the inverter transistors in such a way that the emitter or source resistance of these inverter transistors is formed by a parallel circuit consisting of at least one ohmic resistor and the control path of the corresponding auxiliary transistor arranged in parallel therewith.
  • the control inputs of the two auxiliary transistors are connected according to the invention to the output of a common control circuit.
  • the parallel circuits according to the invention which form the emitter resistances of the half-bridge inverter transistors, advantageously each have at least one further ohmic resistor which is connected in series with the control path of the corresponding auxiliary transistor and is arranged in parallel with the at least one ohmic resistor of the relevant parallel circuit.
  • the dimensioning of these ohmic resistors is advantageously chosen such that for each of the parallel circuits according to the invention, which form the emitter resistor of a half-bridge inverter transistor, the total resistance of the ohmic resistors arranged parallel to the control path of the auxiliary transistor is approximately one order of magnitude greater than the total resistance of the ohmic resistors connected in series with the auxiliary transistor is.
  • a capacitor is advantageously arranged parallel to the control paths of the auxiliary transistors, to which in turn at least one discharge resistor is connected in parallel.
  • the output of the control circuit is connected to the control inputs of the auxiliary transistors via at least one charging resistor.
  • the resistance values of these charging resistors are smaller than the resistance values of the discharge resistors, so that the time constant for the discharge process of the capacitors connected in parallel with the auxiliary transistors is considerably greater than the time constant for the charging process of these capacitors.
  • at least one auxiliary transistor is advantageously connected to the output of the control circuit via at least one diode.
  • the half-bridge inverter transistors are advantageously bipolar transistors, while the auxiliary transistors are advantageously field-effect transistors.
  • the preferred exemplary embodiment of the circuit arrangement according to the invention also has a voltage divider which is connected to a resonant circuit component via a tap in the load circuit and monitors the voltage drop across this component.
  • the control input of one of the auxiliary transistors is connected to this voltage divider, advantageously via a threshold value element.
  • This voltage divider allows the electrical conductivity of the drain-source path of the aforementioned auxiliary transistor to be varied continuously as a function of the voltage drop at the resonant circuit component connected to the voltage divider.
  • the effective emitter resistance of the corresponding half-bridge inverter transistor also changes continuously.
  • the above-mentioned voltage divider thus additionally offers the possibility of regulating the voltage drop at the resonant circuit component in a continuous manner.
  • the figure shows the circuit arrangement according to the preferred embodiment.
  • This circuit arrangement is used to operate a T5 fluorescent lamp LP, which has an electrical power consumption (nominal power) of approximately 35 W.
  • Appropriate dimensioning of the Electrical components of the preferred embodiment of the circuit arrangement according to the invention are given in the table.
  • This circuit arrangement has a self-oscillating half-bridge inverter equipped with two npn bipolar transistors Q1, Q2.
  • the half-bridge inverter is supplied with a DC voltage, which is obtained in the usual way by rectification from the grid voltage.
  • a load circuit designed as a resonance circuit is connected to the output M of the half-bridge inverter. It contains the primary winding RKa of a toroidal transformer, a resonance inductor L1, the electrode filament E1 of the lamp LP, a resonance capacitor C1 and the electrode filament E2 of the fluorescent lamp LP.
  • the discharge path of the low-pressure discharge lamp LP is connected in parallel to the resonance capacitor C1.
  • the resonance capacitor C1 is also connected via the electrode coil E2 to the center tap V1 between the two coupling capacitors C2, C3, which in turn are arranged parallel to the half-bridge inverter Q1, Q2.
  • the half-bridge inverter is controlled with the aid of the toroidal core transformer, the primary winding RKa of which is part of the load circuit and the secondary windings RKb, RKc are each arranged in a control circuit of the half-bridge inverter transistors Q1, Q2.
  • the circuit arrangement has a starting device which essentially consists of the starting capacitor C5, the diac DC, the diode D3 and the ohmic resistors R2, R12, R13, R14.
  • the two bipolar transistors Q1, Q2 of the half-bridge inverter are each equipped with a free-wheeling diode D1, D2, which are connected in parallel to the collector-emitter path of the corresponding transistor Q1, Q2.
  • An ohmic resistor R1 and a capacitor C4 are arranged in parallel with the freewheeling diode D1. So far, the circuit arrangement corresponds to a self-oscillating, half-bridge inverter, such as that on pages 62-63 of the book Switching power supplies "by W. Hirschmann / A. Hauenstein, publisher Siemens AG.
  • the control circuits of the two bipolar transistors Q1, Q2 each contain a basic series resistor R3 or R4, which is connected via an inductor L2 or L3 to the secondary winding RKb or RKc of the toroidal core transformer arranged in this control circuit.
  • the emitter resistance of the bipolar transistor Q1 is formed by a parallel circuit consisting of the ohmic resistors R5, R6 and the auxiliary transistor T1. This parallel connection is designed such that the low-resistance resistor R6 is arranged in series with the drain-source path of the auxiliary transistor T1 and the higher-resistance resistor R5 is connected in parallel with this series circuit consisting of the resistor R6 and the drain-source path of the auxiliary transistor T1 .
  • the emitter resistance of the bipolar transistor Q2 is formed by a parallel circuit consisting of the ohmic resistors R7, R8 and the auxiliary transistor T2.
  • This parallel connection is also designed such that the low-resistance resistor R8 is arranged in series with the drain-source path of the auxiliary transistor T2 and the higher-resistance resistor R7 is connected in parallel with this series circuit consisting of the resistor R8 and the drain-source path of the auxiliary transistor T2 is.
  • the control circuits of the two half-bridge inverter transistors Q1, Q2 also each have a base-emitter parallel resistor R9 or R10, which is connected in parallel to the base-emitter path of the corresponding bipolar transistor Q1, Q2 and improves the switching behavior of these two bipolar transistors Q1, Q2.
  • the two auxiliary transistors T1, T2 are field effect transistors which are controlled with the aid of the control circuit IC.
  • the purpose of the output of the control circuit IC is connected on the one hand via the ohmic resistor R11 and the diode D5 to the gate connection of the field effect transistor T1 and on the other hand via the ohmic resistor R21 to the gate connection of the field effect transistor T2.
  • a capacitor C6 or C7 and an ohmic resistor R15 or R16 are connected in parallel to the gate of the field effect transistor T1 or T2.
  • a Zener diode Z1, Z2 serving as overvoltage protection is arranged in parallel to the gate of each auxiliary transistor T1, T2.
  • the circuit arrangement also has a voltage divider, which essentially consists of the resistors R17, R18 and R19.
  • This voltage divider is connected via capacitor C8 and branch point V2 to a connection of resonance capacitor C1 and to a connection of lamp electrode E1, so that the voltage divider is connected in parallel with the resonance capacitor C1 in terms of alternating current.
  • the center tap V3 between the resistors R18, R19 of the voltage divider is connected via a diode D6 and a Zener diode DZ to the gate terminal of the field effect transistor T2.
  • the Zener diode DZ and the diode D6 are polarized in opposite directions.
  • the starting capacitor C5 charges via the resistors R12, R13 to the breakdown voltage of the DC DC, which then generates trigger pulses for the base of the bipolar transistor Q2 and thereby causes the half-bridge inverter to oscillate.
  • the start capacitor C5 is discharged via the resistor R2 and the diode D3 to such an extent that the diac DC does not generate any further trigger pulses.
  • the two inverter transistors Q1, Q2 switch alternately, so that the center tap M of the half bridge is alternately connected to the positive or negative pole of the DC voltage supply.
  • the taps M and V1 generates a medium-frequency alternating current in the load circuit designed as a series resonance circuit, the frequency of which corresponds to the clock frequency of the half-bridge inverter.
  • the clock frequency of the half-bridge inverter is usually more than 20 kHz.
  • the electronic components of the circuit arrangement according to the invention are also dimensioned such that the clock frequency of the self-oscillating half-bridge inverter is above the resonance frequency of the series resonance circuit L1, C1.
  • the auxiliary transistors T1, T2 are initially in the blocked state, so that only the higher-impedance resistors R5 and R7 are effective as the emitter resistor for the bipolar transistors Q1, Q2.
  • the control circuit IC switches its output voltage from approximately 0 V to approximately 10 V to 12 V, so that the control voltage for switching the field effect transistor T2 through the resistor R21 is built up on the capacitor C7.
  • the discharge resistor R15 has a considerably larger resistance value than the charging resistor R11, the time constant of the capacitor C6 for the discharge process is considerably greater than for the charging process, so that the control voltage for the auxiliary transistor T1 required for switching through is still present at the capacitor C6 when the duty cycle of the bipolar transistor Q2 has already ended.
  • the capacitor C6 is recharged via the resistor R11 and the diode D5.
  • the effective emitter resistance for the bipolar transistors Q1 is given by the total or equivalent resistance of the resistors R5 and R6 which are now connected in parallel, if the resistance of the drain-source path of the auxiliary transistor T1 is disregarded.
  • the effective emitter resistance of the bipolar transistor Q2 which essentially results from the equivalent resistance of the parallel resistors R7 and R8 when the auxiliary transistor T2 is switched on. Due to the now significantly lower effective emitter resistance of the bipolar transistors Q1, Q2 and the resulting reduced negative feedback of the half-bridge inverter, the clock frequency of the half-bridge inverter drops. The detuning between the clock frequency of the half-bridge inverter and the resonance frequency of the resonance circuit L1, C1 drops so far that the ignition voltage required to ignite the lamp LP is generated at the resonance capacitor C1 by the method of resonance increase.
  • the then electrically conductive discharge path of the lamp LP constitutes a shunt to the resonance capacitor C1, so that only the operating voltage of the lamp LP drops via the resonance capacitor C1.
  • the resonance circuit components C1, L1 are dimensioned in the preferred embodiment such that only a relatively small pin current flows through the electrodes E1, E2.
  • the resonance circuit of the preferred embodiment therefore has a comparatively large resonance inductance L1 and a relatively high quality. Due to the high quality of the resonance circuit, a high voltage drop can build up on the resonance circuit components C1, L1.
  • the voltage divider R17, R18, R19 together with the Zener diode DZ and the diode D6 now offers an additional possibility to limit or regulate the voltage drop in the resonance circuit C1, L1.
  • the voltage drop across the resonance capacitor C1 or the lamp LP is detected by this voltage divider and divided down according to the resistance values of the ohmic resistors R17, R18, R19.
  • the Zener diode DZ remains and thus also the current path, which starts from the gate of the field effect transistor T2 via the Zener diode DZ and the resistor R19 leads to the negative pole of the DC voltage source, de-energized and the field effect transistor T2 maintains its full control signal.
  • the amplitude of the resonance capacitor voltage reaches this critical value, the voltage drop between the gate of the field effect transistor T2 and the branch point increases when the negative half-wave of the resonance capacitor voltage passes through V3 so far that the Zener diode DZ becomes conductive.
  • the gate of the field effect transistor T2 only receives a reduced control signal since part of the control signal coming from the control circuit IC flows through the now conductive zener diode DZ and the voltage divider resistor R19 to the negative pole of the DC voltage source.
  • the rectifier diode D6 is polarized so that the Zener diode DZ is only sensitive to the negative half-wave of the resonant capacitor voltage.
  • a reduced control signal for the gate of the field effect transistor T2 reduces the conductivity of the drain-source path of the field effect transistor T2 and thus increases the effective emitter resistance of the bipolar transistor Q2.
  • the effective emitter resistance of the bipolar transistor Q2 is calculated from the no longer negligible resistance of the drain-source path of the auxiliary transistor T2 and the resistance values of the ohmic resistors R7 and R8. This increase in the effective emitter resistance of the transistor Q2 causes a shortened on-time of the bipolar transistor Q2 and increases the clock frequency of the half-bridge inverter accordingly, whereby the open circuit voltage at the resonance capacitor is reduced.
  • the invention is not limited to the exemplary embodiment explained in more detail above.
  • the circuit arrangement according to the invention can also be used for dimming the lamp LP.
  • the control circuit IC is to be designed in such a way that it not only switches between two voltage stages 0 V and 12 V for driving the auxiliary transistors T1, T2, as described in the exemplary embodiment above, but also provides a continuously variable output voltage after the lamp has been ignited .

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  • Circuit Arrangements For Discharge Lamps (AREA)

Abstract

The circuit has a converter with two alternately switching converter transistors (Q1,Q2), first and second auxiliary transistors (T1,T2) in the control circuits for the first and second converter transistors respectively and a resonant load circuit connected to the converter output (M) and contg. at least one lamp (LP). The emitter or source resistance of the first and second converter transistor is a parallel circuit contg. at least one Ohmic resistor (R5,R7) and the control path of the first and second auxiliary transistor (T1,T2) respectively. The control inputs of both auxiliary transistors are connected to the output of a common control circuit (IC).

Description

Die Erfindung betrifft eine Schaltungsanordnung zum Betrieb elektrischer Lampen gemäß dem Oberbegriff des Patentanspruches 1.The invention relates to a circuit arrangement for operating electric lamps according to the preamble of patent claim 1.

Eine derartige Schaltungsanordnung ist beispielsweise in der europäischen Patentschrift EP 0 093 469 offenbart. Diese Schrift beschreibt einen Wechselrichter, insbesondere einen selbstschwingenden Halbbrückenwechselrichter mit zwei alternierend schaltenden Wechselrichtertransistoren, in deren Steuerkreis jeweils eine Zeitschaltvorrichtung angeordnet ist. Diese Zeitschaltvorrichtungen bestehen im wesentlichen jeweils aus einem Hilfstransistor und einem RC-Glied, dessen ohmscher Widerstand durch eine Zenerdiode überbrückt wird, und dessen Kondensator parallel zur Basis-Emitter-Strecke des Hilfstransistors geschaltet ist. Aufgrund der Zenerdioden besitzen die Zeitschaltvorrichtungen spannungsabhängige Zeitkonstanten, die eine Steuerung der Frequenz und des Tastverhältnisses des Halbbrückenwechselrichters sowie das Einstellen definierter Heiz- und Zündbedingungen für die Niederdruckentladungslampen ermöglichen. Nachteilig wirkt sich hier allerdings die große Toleranzabhängigkeit der Elektrodenvorheiz-, Zünd- und Betriebsparameter von den verwendeten elektronischen Bauteilen aus. Während der Elektrodenvorheizphase wird eine unsymmetrische Steuerung des Halbbrückenwechselrichters angewendet. Aufgrund dessen liefert eine Schaltungsanordnung gemäß der EP 0 093 469 bei gleicher Dimensionierung der Lastkreisbauteile und bei gleicher Spannung an den Lampen während der Elektrodenvorheizphase einen geringeren Heizstrom als eine vergleichbare Schaltungsanordnung mit symmetrischer Ansteuerung des Halbbrückenwechselrichters. Dieser Nachteil der Schaltungsanordnung gemäß der in der vorgenannten Patentschrift beschriebenen Schaltungsanordnung tritt besonders bei den sogenannten T2- und T5-Leuchtstofflampen, die vergleichsweise empfindlichen Elektroden besitzen, hervor. Um mit der Schaltungsanordnung entsprechend der EP 0 093 469 auch für die vorgenannten Lampentypen eine ausreichende Vorheizung der Elektrodenwendeln zu gewährleisten, müßte ein Resonanzkondensator mit einer vergleichsweise großen Kapazität verwendet werden. Diese Maßnahme würde aber zu einer höheren Belastung der gesamten Bauteile der Schaltungsanordnung während des Brennbetriebes der Lampen führen. Insbesondere würde dann der sogenannte Stiftstrom, das ist der durch die Lampenelektrodenwendeln fließende Dauerheizstrom, der sich additiv aus dem Strom durch den parallel zur Lampe angeordneten Resonanzkondensator und aus dem über die Entladungsstrecke der Lampe fließenden Strom zusammensetzt, derart zunehmen, daß mit frühzeitigen Lampenausfällen, bedingt durch eine zu starke thermische Belastung der Elektrodenwendeln, gerechnet werden müßte.Such a circuit arrangement is disclosed, for example, in European patent EP 0 093 469. This document describes an inverter, in particular a self-oscillating half-bridge inverter with two alternating switching inverter transistors, in the control circuit of which a time switching device is arranged. These time switches essentially consist of an auxiliary transistor and an RC element, the ohmic resistance of which is bridged by a Zener diode, and the capacitor of which is connected in parallel to the base-emitter path of the auxiliary transistor. Due to the Zener diodes, the time switching devices have voltage-dependent time constants which enable the frequency and the duty cycle of the half-bridge inverter to be controlled and the defined heating and ignition conditions for the low-pressure discharge lamps to be set. However, the large tolerance dependence of the electrode preheating, ignition and operating parameters on the electronic components used has a disadvantageous effect here. Asymmetrical control of the half-bridge inverter is used during the electrode preheating phase. Because of this, a circuit arrangement according to EP 0 093 469 delivers a lower heating current than a comparable one with the same dimensioning of the load circuit components and with the same voltage on the lamps during the electrode preheating phase Circuit arrangement with symmetrical control of the half-bridge inverter. This disadvantage of the circuit arrangement according to the circuit arrangement described in the aforementioned patent document is particularly evident in the so-called T2 and T5 fluorescent lamps, which have comparatively sensitive electrodes. In order to ensure sufficient preheating of the electrode filaments for the aforementioned lamp types with the circuit arrangement according to EP 0 093 469, a resonance capacitor with a comparatively large capacitance would have to be used. However, this measure would lead to a higher load on the entire components of the circuit arrangement during the burning operation of the lamps. In particular, the so-called pin current, i.e. the continuous heating current flowing through the lamp electrode filaments, which is additively composed of the current through the resonance capacitor arranged in parallel with the lamp and the current flowing over the discharge path of the lamp, would increase to such an extent that premature lamp failures would result due to excessive thermal stress on the electrode coils, would have to be expected.

Es ist die Aufgabe der Erfindung, eine einen selbstschwingenden Halbbrückenwechselrichter aufweisende Schaltungsanordnung zum Betrieb elektrischer Lampen mit einer verbesserten, auf die verschiedenen Betriebsphasen der Lampen abgestimmten Ansteuerung der Wechselrichtertransistoren bereitzustellen. Insbesondere soll die erfindungsgemäße Schaltungsanordnung beim Betrieb der obengenannten Leuchtstofflampen einerseits eine zufriedenstellende Vorheizung der Lampenelektroden gewährleisten und andererseits einen zu starken Anstieg des Stiftstromes vermeiden.It is the object of the invention to provide a circuit arrangement having a self-oscillating half-bridge inverter for operating electrical lamps with an improved control of the inverter transistors which is matched to the different operating phases of the lamps. In particular, the circuit arrangement according to the invention is intended, on the one hand, to ensure satisfactory preheating of the lamp electrodes during operation of the above-mentioned fluorescent lamps and, on the other hand, to avoid an excessive rise in the pen current.

Diese Aufgabe wird erfindungsgemäß durch die kennzeichnenden Merkmale des Patentanspruchs 1 gelöst. Besonders vorteilhafte Ausführungen der Erfindung sind in den Unteransprüchen beschrieben.This object is achieved by the characterizing features of claim 1. Particularly advantageous embodiments of the invention are described in the subclaims.

Die erfindungsgemäße Schaltungsanordnung weist einen selbstschwingenden Halbbrückenwechselrichter auf, an dessen Ausgang ein als Resonanzkreis ausgebildeter Lastkreis angeschlossen ist, in dem mindestens eine elektrische Lampe angeordnet ist. Die beiden Wechselrichtertransistoren besitzen einen Steuerkreis, in den jeweils ein Hilfstransistor geschaltet ist. Erfindungsgemäß sind diese Hilfstransistoren derart in die Steuerkreise der Wechselrichtertransistoren geschaltet, daß der Emitter- bzw. Sourcewiderstand dieser Wechselrichtertransistoren von einer Parallelschaltung gebildet wird, die aus mindestens einem ohmschen Widerstand und der parallel dazu angeordneten Steuerstrecke des entsprechenden Hilfstransistors besteht. Außerdem sind die Steuereingänge der beiden Hilfstransistoren erfindungsgemäß an den Ausgang einer gemeinsamen Steuerschaltung angeschlossen. Diese Maßnahmen erlauben es, den effektiven Emitterwiderstand bzw. Sourcewiderstand der Halbbrückenwechselrichtertransistoren und damit die Rückkoppelung für die Halbbrückenwechselrichtertransistoren in Abhängigkeit von den verschiedenen Betriebsphasen - das sind bei Niederdrukkentladungslampen: Vorheizung der Lampenelektroden, Zündung der Lampe, Brennbetrieb der Lampe - umzuschalten. Dieses Umschalten der Rückkoppelung für die Halbbrückenwechselrichtertransistoren verändert das Tastverhältnis und/ oder die Taktfrequenz des Halbbrückenwechselrichters. Die dadurch erzielbare Frequenzverstimmung zwischen der Resonanzfrequenz des Lastkreises und der Taktfrequenz des Halbbrückenwechselrichters ermöglicht für jede der drei vorgenannten Betriebsphase eine optimale Anpassung der elektrischen Parameter im Lastkreis. Die Rückkoppelung der Halbbrückenwechselrichtertransistoren läßt sich durch eine geeignete Dimensionierung der ohmschen Widerstände der erfindungsgemäßen Parallelschaltungen, die die Emitterwiderstände bzw. Sourcewiderstände der Halbbrückenwechselrichtertransistoren bilden, in weiten Grenzen beeinflußen.The circuit arrangement according to the invention has a self-oscillating half-bridge inverter, to the output of which a load circuit designed as a resonance circuit is connected, in which at least one electric lamp is arranged. The two inverter transistors have a control circuit, in each of which an auxiliary transistor is connected. According to the invention, these auxiliary transistors are connected to the control circuits of the inverter transistors in such a way that the emitter or source resistance of these inverter transistors is formed by a parallel circuit consisting of at least one ohmic resistor and the control path of the corresponding auxiliary transistor arranged in parallel therewith. In addition, the control inputs of the two auxiliary transistors are connected according to the invention to the output of a common control circuit. These measures make it possible to switch the effective emitter resistance or source resistance of the half-bridge inverter transistors and thus the feedback for the half-bridge inverter transistors depending on the different operating phases - in the case of low-pressure discharge lamps, these are: preheating the lamp electrodes, igniting the lamp, operating the lamp. This switching of the feedback for the half-bridge inverter transistors changes the pulse duty factor and / or the clock frequency of the half-bridge inverter. The frequency detuning that can be achieved in this way between the resonance frequency of the load circuit and the clock frequency of the half-bridge inverter enables the electrical parameters in the load circuit to be optimally adapted for each of the three aforementioned operating phases. The feedback of the half-bridge inverter transistors can be achieved by suitable dimensioning of the ohmic resistors of the invention Parallel circuits, which form the emitter resistances or source resistances of the half-bridge inverter transistors, influence within wide limits.

Vorteilhafterweise besitzen die erfindungsgemäßen Parallelschaltungen, die die Emitterwiderstände der Halbbrückenwechselrichtertransistoren bilden, jeweils wenigstens einen weiteren ohmschen Widerstand, der in Serie zu der Steuerstrecke des entsprechenden Hilfstransistors geschaltet und parallel zu dem mindestens einen ohmschen Widerstand der betreffenden Parallelschaltung angeordnet ist. Die Dimensionierung dieser ohmschen Widerstände ist vorteilhafterweise derart gewählt, daß für jede der erfindungsgemäßen, den Emitterwiderstand eines Halbbrückenwechselrichtertransistors bildenden Parallelschaltungen der Gesamtwiderstand der parallel zur Steuerstrecke des Hilfstransistors angeordneten ohmschen Widerstände um ungefähr eine Größenordnung größer als der Gesamtwiderstand der in Serie zu dem Hilfstransistor geschalteten ohmschen Widerstände ist. Diese Maßnahmen gewährleisten, daß die Rückkoppelung des Halbbrückenwechselrichters in weiten Grenzen variiert werden kann.The parallel circuits according to the invention, which form the emitter resistances of the half-bridge inverter transistors, advantageously each have at least one further ohmic resistor which is connected in series with the control path of the corresponding auxiliary transistor and is arranged in parallel with the at least one ohmic resistor of the relevant parallel circuit. The dimensioning of these ohmic resistors is advantageously chosen such that for each of the parallel circuits according to the invention, which form the emitter resistor of a half-bridge inverter transistor, the total resistance of the ohmic resistors arranged parallel to the control path of the auxiliary transistor is approximately one order of magnitude greater than the total resistance of the ohmic resistors connected in series with the auxiliary transistor is. These measures ensure that the feedback of the half-bridge inverter can be varied within wide limits.

Vorteilhafterweise ist parallel zu den Steuerstrecken der Hilfstransistoren jeweils ein Kondensator angeordnet, zu denen wiederum jeweils mindestens ein Entladewiderstand parallel geschaltet ist. Außerdem ist der Ausgang der Steuerschaltung jeweils über mindestens einen Ladewiderstand mit den Steuereingängen der Hilfstransistoren verbunden. Die Widerstandswerte dieser Ladewiderstände sind kleiner als die Widerstandswerte der Entladewiderstände, so daß die Zeitkonstante für den Entladevorgang der parallel zu den Hilfstransistoren geschalteten Kondensatoren erheblich größer als die Zeitkonstante für den Ladevorgang dieser Kondensatoren ist. Ferner erfolgt vorteilhafterweise bei mindestens einem Hilfstransistor die Verbindung zum Ausgang der Steuerschaltung über mindestens eine Diode. Diese Maßnahmen gewährleisten eine zuverlässige Ansteuerung der Hilfstransistoren aus einer gemeinsamen Steuerschaltung.A capacitor is advantageously arranged parallel to the control paths of the auxiliary transistors, to which in turn at least one discharge resistor is connected in parallel. In addition, the output of the control circuit is connected to the control inputs of the auxiliary transistors via at least one charging resistor. The resistance values of these charging resistors are smaller than the resistance values of the discharge resistors, so that the time constant for the discharge process of the capacitors connected in parallel with the auxiliary transistors is considerably greater than the time constant for the charging process of these capacitors. Furthermore, at least one auxiliary transistor is advantageously connected to the output of the control circuit via at least one diode. These measures ensure reliable control of the auxiliary transistors from a common control circuit.

Die Halbbrückenwechselrichtertransistoren sind vorteilhafterweise Bipolartransistoren, während die Hilfstransistoren vorteilhafterweise Feldeffekttransistoren sind.The half-bridge inverter transistors are advantageously bipolar transistors, while the auxiliary transistors are advantageously field-effect transistors.

Das bevorzugte Ausführungsbeispiel der erfindungsgemäßen Schaltungsanordnung weist außerdem einen Spannungsteiler auf, der über einen Abgriff im Lastkreis mit einem Resonanzkreisbauteil verbunden ist und den Spannungsabfall an diesem Bauteil überwacht. Der Steuereingang einer der Hilfstransistoren ist, vorteilhafterweise über ein Schwellwertelement, an diesen Spannungsteiler angeschlossen. Dieser Spannungsteiler erlaubt es, die elektrische Leitfähigkeit der Drain-Source-Strecke des vorgenannten Hilfstransistors in Abhängigkeit des Spannungsabfalls an dem mit dem Spannungsteiler verbundenen Resonanzkreisbauteil stetig zu variieren. Dadurch verändert sich auch der wirksame Emitterwiderstand des entsprechenden Halbbrückenwechselrichtertransistors stetig. Der obengenannte Spannungsteiler bietet also zusätzlich die Möglichkeit, den Spannungsabfall an dem Resonanzkreisbauteil in kontinuierlicher Weise zu regulieren.The preferred exemplary embodiment of the circuit arrangement according to the invention also has a voltage divider which is connected to a resonant circuit component via a tap in the load circuit and monitors the voltage drop across this component. The control input of one of the auxiliary transistors is connected to this voltage divider, advantageously via a threshold value element. This voltage divider allows the electrical conductivity of the drain-source path of the aforementioned auxiliary transistor to be varied continuously as a function of the voltage drop at the resonant circuit component connected to the voltage divider. As a result, the effective emitter resistance of the corresponding half-bridge inverter transistor also changes continuously. The above-mentioned voltage divider thus additionally offers the possibility of regulating the voltage drop at the resonant circuit component in a continuous manner.

Nachstehend wird die Erfindung anhand eines bevorzugten Ausführungsbeispiels näher erläutert.The invention is explained in more detail below on the basis of a preferred exemplary embodiment.

Die Figur zeigt die Schaltungsanordnung gemäß des bevorzugten Ausführungsbeispiels. Diese Schaltungsanordnung dient zum Betrieb einer T5-Leuchtstofflampe LP, die eine elektrische Leistungsaufnahme (Nennleistung) von ungefähr 35 W besitzt. Eine geeignete Dimensionierung der elektrischen Bauteile des bevorzugten Ausführungsbeispiels der erfindungsgemäßen Schaltungsanordnung ist in der Tabelle angegeben.The figure shows the circuit arrangement according to the preferred embodiment. This circuit arrangement is used to operate a T5 fluorescent lamp LP, which has an electrical power consumption (nominal power) of approximately 35 W. Appropriate dimensioning of the Electrical components of the preferred embodiment of the circuit arrangement according to the invention are given in the table.

Diese Schaltungsanordnung weist einen mit zwei npn-Bipolartransistoren Q1, Q2 bestückten selbstschwingenden Halbbrückenwechselrichter auf. Der Halbbrückenwechselrichter wird mit einer Gleichspannung versorgt, die auf übliche Weise durch Gleichrichtung aus der Netzspannung gewonnen wird. An den Ausgang M des Halbbrückenwechselrichters ist ein als Resonanzkreis ausgebildeter Lastkreis angeschlossen. Er enthält die Primärwicklung RKa eines Ringkerntransformators, eine Resonanzinduktivität L1, die Elektrodenwendel E1 der Lampe LP, einen Resonanzkondensator C1 und die Elektrodenwendel E2 der Leuchtstofflampe LP. Die Entladungsstrecke der Niederdruckentladungslampe LP ist parallel zum Resonanzkondensator C1 geschaltet ist. Der Resonanzkondensator C1 ist ferner über die Elektrodenwendel E2 an den Mittenabgriff V1 zwischen den beiden Koppelungskondensatoren C2, C3 angeschlossen, die ihrerseits parallel zum Halbbrückenwechselrichter Q1, Q2 angeordnet sind.This circuit arrangement has a self-oscillating half-bridge inverter equipped with two npn bipolar transistors Q1, Q2. The half-bridge inverter is supplied with a DC voltage, which is obtained in the usual way by rectification from the grid voltage. A load circuit designed as a resonance circuit is connected to the output M of the half-bridge inverter. It contains the primary winding RKa of a toroidal transformer, a resonance inductor L1, the electrode filament E1 of the lamp LP, a resonance capacitor C1 and the electrode filament E2 of the fluorescent lamp LP. The discharge path of the low-pressure discharge lamp LP is connected in parallel to the resonance capacitor C1. The resonance capacitor C1 is also connected via the electrode coil E2 to the center tap V1 between the two coupling capacitors C2, C3, which in turn are arranged parallel to the half-bridge inverter Q1, Q2.

Die Ansteuerung des Halbbrückenwechselrichters erfolgt mit Hilfe des Ringkerntransformators, dessen Primärwicklung RKa Bestandteil des Lastkreises ist, und dessen Sekundärwicklungen RKb, RKc jeweils in einem Steuerkreis der Halbbrückenwechselrichtertransistoren Q1, Q2 angeordnet sind. Um das Anschwingen des Halbbrückenwechselrichters zu gewährleisten, besitzt die Schaltungsanordnung eine Startvorrichtung, die im wesentlichen aus dem Startkondensator C5, dem Diac DC, der Diode D3 und den ohmschen Widerständen R2, R12, R13, R14 besteht. Die beiden Bipolartransistoren Q1, Q2 des Halbbrückenwechselrichters sind jeweils mit einer Freilaufdiode D1, D2 ausgestattet, die parallel zur Kollektor-Emitter-Strecke des entsprechenden Transistors Q1, Q2 geschaltet sind. Parallel zur Freilaufdiode D1 sind ein ohmscher Widerstand R1 und ein Kondensator C4 angordnet. Soweit entspricht die Schaltungsanordnung einem selbstschwingenden, Halbbrückenwechselrichter wie er beispielsweise auf den Seiten 62-63 des Buches

Figure imgb0001
Schaltnetzteile" von W. Hirschmann/ A. Hauenstein, Herausgeber Siemens AG offenbart ist.The half-bridge inverter is controlled with the aid of the toroidal core transformer, the primary winding RKa of which is part of the load circuit and the secondary windings RKb, RKc are each arranged in a control circuit of the half-bridge inverter transistors Q1, Q2. In order to ensure that the half-bridge inverter starts to oscillate, the circuit arrangement has a starting device which essentially consists of the starting capacitor C5, the diac DC, the diode D3 and the ohmic resistors R2, R12, R13, R14. The two bipolar transistors Q1, Q2 of the half-bridge inverter are each equipped with a free-wheeling diode D1, D2, which are connected in parallel to the collector-emitter path of the corresponding transistor Q1, Q2. An ohmic resistor R1 and a capacitor C4 are arranged in parallel with the freewheeling diode D1. So far, the circuit arrangement corresponds to a self-oscillating, half-bridge inverter, such as that on pages 62-63 of the book
Figure imgb0001
Switching power supplies "by W. Hirschmann / A. Hauenstein, publisher Siemens AG.

Die Steuerkreise der beiden Bipolartransistoren Q1, Q2 enthalten jeweils einen Basisvorwiderstand R3 bzw. R4, der über eine Induktivität L2 bzw. L3 mit der in diesem Steuerkreis angeordneten Sekundärwicklung RKb bzw. RKc des Ringkerntransformators verbunden ist. Der Emitterwiderstand des Bipolartransistors Q1 wird von einer aus den ohmschen Widerständen R5, R6 und dem Hilfstransistor T1 bestehenden Parallelschaltung gebildet. Diese Parallelschaltung ist derart ausgeführt, daß der niederohmigere Widerstand R6 in Serie zur Drain-Source-Strecke des Hilfstransistors T1 angeordnet ist und der hochohmigere Widerstand R5 parallel zu dieser aus dem Widerstand R6 und der Drain-Source-Strecke des Hilfstransistors T1 bestehenden Serienschaltung geschaltet ist. Analog dazu wird der Emitterwiderstand des Bipolartransistors Q2 von einer aus den ohmschen Widerständen R7, R8 und dem Hilfstransistor T2 bestehenden Parallelschaltung gebildet. Diese Parallelschaltung ist ebenfalls derart ausgeführt, daß der niederohmigere Widerstand R8 in Serie zur Drain-Source-Strecke des Hilfstransistors T2 angeordnet ist und der hochohmigere Widerstand R7 parallel zu dieser aus dem Widerstand R8 und der Drain-Source-Strecke des Hilfstransistors T2 bestehenden Serienschaltung geschaltet ist. Die Steuerkreise der beiden Halbbrückenwechselrichtertransistoren Q1, Q2 weisen außerdem jeweils einen Basis-Emitter-Parallelwiderstand R9 bzw. R10 auf, der parallel zur Basis-Emitter-Strecke des entsprechenden Bipolartransistors Q1, Q2 geschaltet ist und das Schaltverhalten dieser beiden Bipolartransistoren Q1, Q2 verbessert.The control circuits of the two bipolar transistors Q1, Q2 each contain a basic series resistor R3 or R4, which is connected via an inductor L2 or L3 to the secondary winding RKb or RKc of the toroidal core transformer arranged in this control circuit. The emitter resistance of the bipolar transistor Q1 is formed by a parallel circuit consisting of the ohmic resistors R5, R6 and the auxiliary transistor T1. This parallel connection is designed such that the low-resistance resistor R6 is arranged in series with the drain-source path of the auxiliary transistor T1 and the higher-resistance resistor R5 is connected in parallel with this series circuit consisting of the resistor R6 and the drain-source path of the auxiliary transistor T1 . Analogously, the emitter resistance of the bipolar transistor Q2 is formed by a parallel circuit consisting of the ohmic resistors R7, R8 and the auxiliary transistor T2. This parallel connection is also designed such that the low-resistance resistor R8 is arranged in series with the drain-source path of the auxiliary transistor T2 and the higher-resistance resistor R7 is connected in parallel with this series circuit consisting of the resistor R8 and the drain-source path of the auxiliary transistor T2 is. The control circuits of the two half-bridge inverter transistors Q1, Q2 also each have a base-emitter parallel resistor R9 or R10, which is connected in parallel to the base-emitter path of the corresponding bipolar transistor Q1, Q2 and improves the switching behavior of these two bipolar transistors Q1, Q2.

Bei den beiden Hilfstransistoren T1, T2 handelt es sich um Feldeffekttransistoren, die mit Hilfe der Steuerschaltung IC angesteuert werden. Zu diesem Zweck ist der Ausgang der Steuerschaltung IC einerseits über den ohmschen Widerstand R11 und die Diode D5 mit dem Gate-Anschluß des Feldeffekttransistors T1 und andererseits über den ohmschen Widerstand R21 mit dem Gate-Anschluß des Feldeffekttransistors T2 verbunden. Parallel zum Gate des Feldeffekttransistors T1 bzw. T2 sind jeweils ein Kondensator C6 bzw. C7 und ein ohmscher Widerstand R15 bzw. R16 geschaltet. Außerdem ist parallel zum Gate jedes Hilfstransistors T1, T2 jeweils eine als Überspannungsschutz dienende Zenerdiode Z1, Z2 angeordnet.The two auxiliary transistors T1, T2 are field effect transistors which are controlled with the aid of the control circuit IC. To this The purpose of the output of the control circuit IC is connected on the one hand via the ohmic resistor R11 and the diode D5 to the gate connection of the field effect transistor T1 and on the other hand via the ohmic resistor R21 to the gate connection of the field effect transistor T2. A capacitor C6 or C7 and an ohmic resistor R15 or R16 are connected in parallel to the gate of the field effect transistor T1 or T2. In addition, a Zener diode Z1, Z2 serving as overvoltage protection is arranged in parallel to the gate of each auxiliary transistor T1, T2.

Die Schaltungsanordnung besitzt ferner einen Spannungsteiler, der im wesentlichen aus den Widerständen R17, R18 und R19 besteht. Dieser Spannungsteiler ist über den Kondensator C8 und den Verzweigungspunkt V2 mit einem Anschluß des Resonanzkondensators C1 und mit einem Anschluß der Lampenelektrode E1 verbunden, so daß der Spannungsteiler wechselstrommäßig parallel zum Resonanzkondensator C1 geschaltet ist. Der Mittenabgriff V3 zwischen den Widerständen R18, R19 des Spannungsteilers ist über eine Diode D6 und eine Zenerdiode DZ mit dem Gate-Anschluß des Feldeffekttransistors T2 verbunden. Die Zenerdiode DZ und die Diode D6 sind gegensinnig gepolt.The circuit arrangement also has a voltage divider, which essentially consists of the resistors R17, R18 and R19. This voltage divider is connected via capacitor C8 and branch point V2 to a connection of resonance capacitor C1 and to a connection of lamp electrode E1, so that the voltage divider is connected in parallel with the resonance capacitor C1 in terms of alternating current. The center tap V3 between the resistors R18, R19 of the voltage divider is connected via a diode D6 and a Zener diode DZ to the gate terminal of the field effect transistor T2. The Zener diode DZ and the diode D6 are polarized in opposite directions.

Nach dem Einschalten der Schaltungsanordnung lädt sich der Startkondensator C5 über die Widerstände R12, R13 auf die Durchbruchsspannung des Diacs DC auf, der dann Triggerimpulse für die Basis des Bipolartransistors Q2 erzeugt und dadurch das Anschwingen des Halbbrückenwechselrichters veranlaßt. Nach dem Durchschalten des Transistors Q2 wird der Startkondensator C5 über den Widerstand R2 und die Diode D3 soweit entladen, daß der Diac DC keine weiteren Triggerimpulse generiert. Die beiden Wechselrichtertransistoren Q1, Q2 schalten alternierend, so daß der Mittenabgriff M der Halbbrücke abwechselnd mit dem Plus- oder Minuspol der Gleichspannungsversorgung verbunden ist. Dadurch wird zwischen den Abgriffen M und V1 im als Serienresonanzkreis ausgebildeten Lastkreis ein mittelfrequenter Wechselstrom erzeugt, dessen Frequenz mit der Taktfrequenz des Halbbrückenwechselrichters übereinstimmt. Die Taktfrequenz des Halbbrückenwechselrichters beträgt üblicherweise mehr als 20 kHz. Die elektronischen Bauteile der erfindungsgemäßen Schaltungsanordnung sind außerdem so dimensioniert, daß die Taktfrequenz des selbstschwingenden Halbbrückenwechselrichter oberhalb der Resonanzfrequenz des Serienresonanzkreises L1, C1 liegt. Die Hilfstransistoren T1, T2 befinden sich zunächst im gesperrten Zustand, so daß als Emitterwiderstand für die Bipolartransistoren Q1, Q2 nur die hochohmigeren Widerstände R5 bzw. R7 wirksam sind. Diese vergleichsweise großen Emitterwiderstände R5, R7 verursachen eine relativ starke Gegenkoppelung des Halbbrückenwechselrichters. Dadurch erreicht der Ringkerntransformator bereits innerhalb einer vergleichsweise kurzen Zeitspanne seine Sättigungsmagnetisierung, so daß die Taktfrequenz des Halbbrückenwechselrichters entsprechend hoch ist. Die Taktfrequenz des Halbbrückenwechselrichters liegt damit zunächst so weit oberhalb der Resonanzfrequenz des Resonanzkreises L1, C1, daß der sich am Resonanzkondensator C1 aufbauende Spannungsabfall nicht ausreicht, um die Leuchtstofflampe LP zu zünden. Während dieser unmittelbar nach dem Anschwingen des Halbbrückenwechselrichters stattfindenden Elektrodenvorheizphase fließt durch die Elektrodenwendeln E1, E2 der Lampe LP und über den Resonanzkondensator C1 ein mittelfrequenter Heizstrom, der die Elektrodenwendeln E1, E2 erhitzt. Nach Ablauf der durch die Steuerschaltung IC vorbestimmten Vorheizdauer schaltet die Steuerschaltung IC ihre Ausgangsspannung von ca. 0 V auf ungefähr 10 V bis 12 V um, so daß die Steuerspannung zum Durchschalten des Feldeffekttransistors T2 über den Widerstand R21 am Kondensator C7 aufgebaut wird.After switching on the circuit arrangement, the starting capacitor C5 charges via the resistors R12, R13 to the breakdown voltage of the DC DC, which then generates trigger pulses for the base of the bipolar transistor Q2 and thereby causes the half-bridge inverter to oscillate. After the transistor Q2 has been switched on, the start capacitor C5 is discharged via the resistor R2 and the diode D3 to such an extent that the diac DC does not generate any further trigger pulses. The two inverter transistors Q1, Q2 switch alternately, so that the center tap M of the half bridge is alternately connected to the positive or negative pole of the DC voltage supply. As a result, between the taps M and V1 generates a medium-frequency alternating current in the load circuit designed as a series resonance circuit, the frequency of which corresponds to the clock frequency of the half-bridge inverter. The clock frequency of the half-bridge inverter is usually more than 20 kHz. The electronic components of the circuit arrangement according to the invention are also dimensioned such that the clock frequency of the self-oscillating half-bridge inverter is above the resonance frequency of the series resonance circuit L1, C1. The auxiliary transistors T1, T2 are initially in the blocked state, so that only the higher-impedance resistors R5 and R7 are effective as the emitter resistor for the bipolar transistors Q1, Q2. These comparatively large emitter resistances R5, R7 cause a relatively strong negative feedback of the half-bridge inverter. As a result, the toroidal transformer already reaches its saturation magnetization within a comparatively short period of time, so that the clock frequency of the half-bridge inverter is correspondingly high. The clock frequency of the half-bridge inverter is initially so far above the resonance frequency of the resonance circuit L1, C1 that the voltage drop building up at the resonance capacitor C1 is not sufficient to ignite the fluorescent lamp LP. During this electrode preheating phase, which takes place immediately after the half-bridge inverter starts to oscillate, a medium-frequency heating current flows through the electrode filaments E1, E2 of the lamp LP and via the resonance capacitor C1 and heats the electrode filaments E1, E2. After the preheating period predetermined by the control circuit IC, the control circuit IC switches its output voltage from approximately 0 V to approximately 10 V to 12 V, so that the control voltage for switching the field effect transistor T2 through the resistor R21 is built up on the capacitor C7.

Während der Transistor Q2 eingeschaltet ist, das heißt, während der Mittenabgriff M des Halbbrückenwechselrichters auf Massepotential liegt, baut sich analog dazu über den Widerstand R11 und über die Diode D5 am Kondensator C6 die Steuerspannung zum Durchschalten des Feldeffekttransistors T1 auf. Während der Bipolartransistor Q2 eingeschaltet ist wird der Kondensator C6 von der Steuerschaltung IC über den Ladewiderstand R11 und über die Diode D5 auf die zum Durchschalten des Hilfstransistors T1 erforderliche Steuerspannung aufgeladen. Da der Entladewiderstand R15 einen erheblich größeren Widerstandswert als der Ladewiderstand R11 besitzt, ist die Zeitkonstante des Kondensators C6 für den Entladevorgang wesentlich größer als für den Ladevorgang, so daß am Kondensator C6 auch dann noch die zum Durchschalten erforderliche Steuerspannung für den Hilfstransistor T1 anliegt, wenn die Einschaltdauer des Bipolartransistors Q2 bereits beendet ist. In jeder Einschaltphase des Bipolartransistors Q2 wird der Kondensator C6 über den Widerstand R11 und die Diode D5 nachgeladen.While the transistor Q2 is switched on, that is, while the center tap M of the half-bridge inverter is at ground potential, is building analogously, the control voltage for switching the field effect transistor T1 on via the resistor R11 and the diode D5 on the capacitor C6. While the bipolar transistor Q2 is switched on, the capacitor C6 is charged by the control circuit IC via the charging resistor R11 and via the diode D5 to the control voltage required for switching on the auxiliary transistor T1. Since the discharge resistor R15 has a considerably larger resistance value than the charging resistor R11, the time constant of the capacitor C6 for the discharge process is considerably greater than for the charging process, so that the control voltage for the auxiliary transistor T1 required for switching through is still present at the capacitor C6 when the duty cycle of the bipolar transistor Q2 has already ended. In each switch-on phase of the bipolar transistor Q2, the capacitor C6 is recharged via the resistor R11 and the diode D5.

Bei durchgeschaltetem Feldeffekttransistoren T1 ist der wirksame Emitterwiderstand für den Bipolartransistoren Q1 durch den Gesamt- oder Ersatzwiderstand der nun parallel geschalteten Widerstände R5 und R6 gegeben, wenn man von dem Widerstand der Drain-Source-Strecke des Hilfstransistors T1 absieht. Dasselbe gilt in ähnlicher Weise für den wirksamen Emitterwiderstand des Bipolartransistors Q2, der sich bei durchgeschaltetem Hilfstransistor T2 im wesentlichen aus dem Ersatzwiderstand der Parallelwiderstände R7 und R8 ergibt. Aufgrund des nun erheblich niedrigeren effektiven Emitterwiderstandes der Bipolartransistoren Q1, Q2 und der daraus resultierenden verminderten Gegenkoppelung des Halbbrückenwechselrichters sinkt die Taktfrequenz des Halbbrückenwechselrichters. Die Verstimmung zwischen der Taktfrequenz des Halbbrückenwechselrichters und der Resonanzfrequenz des Resonanzkreises L1, C1 sinkt dabei soweit, daß am Resonanzkondensator C1 durch die Methode der Resonanzüberhöhung die zur Zündung der Lampe LP erforderliche Zündspannung erzeugt wird.When the field effect transistors T1 are switched on, the effective emitter resistance for the bipolar transistors Q1 is given by the total or equivalent resistance of the resistors R5 and R6 which are now connected in parallel, if the resistance of the drain-source path of the auxiliary transistor T1 is disregarded. The same applies in a similar way to the effective emitter resistance of the bipolar transistor Q2, which essentially results from the equivalent resistance of the parallel resistors R7 and R8 when the auxiliary transistor T2 is switched on. Due to the now significantly lower effective emitter resistance of the bipolar transistors Q1, Q2 and the resulting reduced negative feedback of the half-bridge inverter, the clock frequency of the half-bridge inverter drops. The detuning between the clock frequency of the half-bridge inverter and the resonance frequency of the resonance circuit L1, C1 drops so far that the ignition voltage required to ignite the lamp LP is generated at the resonance capacitor C1 by the method of resonance increase.

Nach dem Durchzünden der Lampe LP stellt die dann elektrisch leitfähige Entladungsstrecke der Lampe LP einen Nebenschluß zum Resonanzkondensator C1 dar, so daß über den Resonanzkondenator C1 nur noch die Betriebsspannung der Lampe LP abfällt.After the lamp LP has been ignited, the then electrically conductive discharge path of the lamp LP constitutes a shunt to the resonance capacitor C1, so that only the operating voltage of the lamp LP drops via the resonance capacitor C1.

Wegen der empfindlichen Elektroden E1, E2 der Lampe LP sind die Resonanzkreisbauteile C1, L1 im bevorzugten Ausführungsbeispiel so dimensioniert, daß nur ein relativ geringer Stiftstrom durch die Elektroden E1, E2 fließt. Der Resonanzkreis des bevorzugten Ausführungsbeispiels besitzt daher eine eine vergleichsweise große Resonanzinduktivität L1 und eine relativ hohe Güte. Aufgrund der hohen Güte des Resonanzkreises kann sich an den Resonanzkreisbauteilen C1, L1 ein hoher Spannungsabfall aufbauen. Der Spannungsteiler R17, R18, R19 bietet nun zusammen mit der Zenerdiode DZ und der Diode D6 eine zusätzliche Möglichkeit, den Spannungsabfall im Resonanzkreis C1, L1 zu begrenzen bzw. zu regulieren.Because of the sensitive electrodes E1, E2 of the lamp LP, the resonance circuit components C1, L1 are dimensioned in the preferred embodiment such that only a relatively small pin current flows through the electrodes E1, E2. The resonance circuit of the preferred embodiment therefore has a comparatively large resonance inductance L1 and a relatively high quality. Due to the high quality of the resonance circuit, a high voltage drop can build up on the resonance circuit components C1, L1. The voltage divider R17, R18, R19 together with the Zener diode DZ and the diode D6 now offers an additional possibility to limit or regulate the voltage drop in the resonance circuit C1, L1.

Am Abgriff V2 im Serienresonanzkreis wird von diesem Spannungsteiler der Spannungsabfall am Resonanzkondensator C1 bzw. an der Lampe LP detektiert und entsprechend der Widerstandswerte der ohmschen Widerstände R17, R18, R19 heruntergeteilt. Solange die Amplitude der Resonanzkondensatorspannung einen kritischen Wert, der durch eine geeignete Dimensionierung der Spannungsteilerwiderstände auf einen gewünschten Wert eingestellt werden kann, unterschreitet bleibt die Zenerdiode DZ und damit auch der Strompfad, der ausgehend vom Gate des Feldeffekttransistors T2 über die Zenerdiode DZ und den Widerstand R19 zum Minuspol der Gleichspannungsquelle führt, stromlos und der Feldeffekttransistor T2 behält sein volles Steuersignal. Erreicht die Amplitude der Resonanzkondensatorspannung diesen kritischen Wert, so steigt beim Durchlaufen der negativen Halbwelle der Resonanzkondensatorspannung der Spannungsabfall zwischen dem Gate des Feldeffekttransistors T2 und dem Verzweigungspunkt V3 so weit an, daß die Zenerdiode DZ leitfähig wird. Das hat zur Folge, daß das Gate des Feldeffekttransistors T2 nur noch ein reduziertes Steuersignal erhält, da ein Teil des von der Steuerschaltung IC kommenden Steuersignals über die nun leitfähige Zenerdiode DZ und den Spannungsteilerwiderstand R19 zum Minuspol der Gleichspannungsquelle abfließt. Die Gleichrichterdiode D6 ist so gepolt, daß die Zenerdiode DZ nur auf die negative Halbwelle der Resonanzkondensatorspannung sensitiv reagiert. Ein reduziertes Steuersignal für das Gate des Feldeffekttransistors T2 verringert die Leitfähigkeit der Drain-Source-Strecke des Feldeffekttransistors T2 und erhöht so den wirksamen Emitterwiderstand des Bipolartransistors Q2. Der effektive Emitterwiderstand des Bipolartransistors Q2 berechnet sich in diesem Fall aus dem nicht mehr zu vernachlässigenden Widerstand der Drain-Source-Strecke des Hilfstransistors T2 und den Widerstandswerten der ohmschen Widerstände R7 und R8. Diese Erhöhung des effektiven Emitterwiderstandes des Transistors Q2 bewirkt eine verkürzte Einschaltdauer des Bipolartransistors Q2 und vergrößert die Taktfrequenz des Halbbrückenwechselrichters entsprechend, wodurch die Leerlaufspannung am Resonanzkondensator reduziert wird.At the tap V2 in the series resonance circuit, the voltage drop across the resonance capacitor C1 or the lamp LP is detected by this voltage divider and divided down according to the resistance values of the ohmic resistors R17, R18, R19. As long as the amplitude of the resonance capacitor voltage falls below a critical value, which can be set to a desired value by suitable dimensioning of the voltage divider resistors, the Zener diode DZ remains and thus also the current path, which starts from the gate of the field effect transistor T2 via the Zener diode DZ and the resistor R19 leads to the negative pole of the DC voltage source, de-energized and the field effect transistor T2 maintains its full control signal. If the amplitude of the resonance capacitor voltage reaches this critical value, the voltage drop between the gate of the field effect transistor T2 and the branch point increases when the negative half-wave of the resonance capacitor voltage passes through V3 so far that the Zener diode DZ becomes conductive. The result of this is that the gate of the field effect transistor T2 only receives a reduced control signal since part of the control signal coming from the control circuit IC flows through the now conductive zener diode DZ and the voltage divider resistor R19 to the negative pole of the DC voltage source. The rectifier diode D6 is polarized so that the Zener diode DZ is only sensitive to the negative half-wave of the resonant capacitor voltage. A reduced control signal for the gate of the field effect transistor T2 reduces the conductivity of the drain-source path of the field effect transistor T2 and thus increases the effective emitter resistance of the bipolar transistor Q2. In this case, the effective emitter resistance of the bipolar transistor Q2 is calculated from the no longer negligible resistance of the drain-source path of the auxiliary transistor T2 and the resistance values of the ohmic resistors R7 and R8. This increase in the effective emitter resistance of the transistor Q2 causes a shortened on-time of the bipolar transistor Q2 and increases the clock frequency of the half-bridge inverter accordingly, whereby the open circuit voltage at the resonance capacitor is reduced.

Die Erfindung beschränkt sich nicht auf das oben näher erläuterte Ausführungsbeispiel. Beispielsweise kann die erfindungsgemäße Schaltungsanordnung auch zum Dimmen der Lampe LP genutzt werden. Zu diesem Zweck ist die Steuerschaltung IC derart auszubilden, daß sie zur Ansteuerung der Hilfstransistoren T1, T2 nicht nur zwischen zwei Spannungstufen 0 V und 12 V umschaltet, wie beim Ausführungsbeispiel oben beschrieben wurde, sondern außerdem nach dem Zünden der Lampe eine kontinuierlich veränderbare Ausgangsspannung bereitstellt. Tabelle Dimensionierung der elektrischen Bauteile der Schaltungsanordnung gemäß des bevorzugten Ausführungsbeispiels R1 3,3 MΩ R2, R11 22 kΩ R3, R4 8,2 Ω R5 18 Ω R6, R8 1 Ω R7 15 Ω R9, R10 47 Ω R12, R13 560 kΩ R14 1 MΩ R15 220 kΩ R16 470 kΩ R17, R18 330 kΩ R19 56 kΩ R21 47 kΩ C1 3,3 nF C2, C3 200 nF C4 1,5 nF C5, C6, C7 100 nF C8 100 pF L1 4 mH L2, L3 10 µH D1, D2, D3, D5 1N4946GP D6 1N414B Z1, Z2 Zenerdiode, 12 V DZ Zenerdiode, 39 V DC Diac Q1, Q2 BUF 620 T1, T2 STK14N05 IC Timer, IC 40106 RKa, RKb, RKc Ringkern R8/4/3,8 The invention is not limited to the exemplary embodiment explained in more detail above. For example, the circuit arrangement according to the invention can also be used for dimming the lamp LP. For this purpose, the control circuit IC is to be designed in such a way that it not only switches between two voltage stages 0 V and 12 V for driving the auxiliary transistors T1, T2, as described in the exemplary embodiment above, but also provides a continuously variable output voltage after the lamp has been ignited . table Dimensioning of the electrical components of the circuit arrangement according to the preferred embodiment R1 3.3 MΩ R2, R11 22 kΩ R3, R4 8.2 Ω R5 18 Ω R6, R8 1 Ω R7 15 Ω R9, R10 47 Ω R12, R13 560 kΩ R14 1 MΩ R15 220 kΩ R16 470 kΩ R17, R18 330 kΩ R19 56 kΩ R21 47 kΩ C1 3.3 nF C2, C3 200 nF C4 1.5 nF C5, C6, C7 100 nF C8 100 pF L1 4 mH L2, L3 10 µH D1, D2, D3, D5 1N4946GP D6 1N414B Z1, Z2 Zener diode, 12 V DZ Zener diode, 39 V DC Diac Q1, Q2 BUF 620 T1, T2 STK14N05 IC Timer, IC 40106 RKa, RKb, RKc Toroidal core R8 / 4 / 3.8

Claims (10)

Schaltungsanordnung zum Betrieb elektrischer Lampen, wobei die Schaltungsanordnung folgende Merkmale aufweist: - einen selbstschwingenden Halbbrückenwechselrichter mit zwei alternierend schaltenden Wechselrichtertransistoren (Q1, Q2), - einen ersten Hilfstransistor (T1), der in den Steuerkreis des ersten Halbbrückenwechselrichtertransistors (Q1) geschaltet ist, - einen zweiten Hilfstransistor (T2), der in den Steuerkreis des zweiten Halbbrückenwechselrichtertransistors (Q2) geschaltet ist, - einen an den Ausgang (M) des Wechselrichters angeschlossenen, als Resonanzkreis ausgebildeten Lastkreis, in den mindestens eine elektrische Lampe (LP) geschaltet ist,
dadurch gekennzeichnet, daß - der Emitter- bzw. Sourcewiderstand des ersten Halbbrückenwechselrichtertransistors (Q1) von einer Parallelschaltung (R5, T1) gebildet wird, die aus mindestens einem ohmschen Widerstand (R5) und der parallel dazu angeordneten Steuerstrecke des ersten Hilfstransistors (T1) besteht, - der Emitter- bzw. Sourcewiderstand des zweiten Halbbrückenwechselrichtertransistors (Q2) von einer Parallelschaltung (R7, T2) gebildet wird, die aus mindestens einem ohmschen Widerstand (R7) und der parallel dazu angeordneten Steuerstrecke des zweiten Hilfstransistors (T2) besteht, - die Steuereingänge beider Hilfstransistoren (T1, T2) an den Ausgang einer gemeinsamen Steuerschaltung (IC) angeschlossen sind. Circuit arrangement for operating electric lamps, the circuit arrangement having the following features: a self-oscillating half-bridge inverter with two alternating switching inverter transistors (Q1, Q2), a first auxiliary transistor (T1) which is connected to the control circuit of the first half-bridge inverter transistor (Q1), a second auxiliary transistor (T2) which is connected to the control circuit of the second half-bridge inverter transistor (Q2), a load circuit which is connected to the output (M) of the inverter and is designed as a resonance circuit and into which at least one electric lamp (LP) is connected,
characterized in that - The emitter or source resistance of the first half-bridge inverter transistor (Q1) is formed by a parallel circuit (R5, T1) consisting of at least one ohmic resistor (R5) and the control path of the first auxiliary transistor (T1) arranged in parallel therewith, - The emitter or source resistance of the second half-bridge inverter transistor (Q2) is formed by a parallel circuit (R7, T2) consisting of at least one ohmic resistor (R7) and the control path of the second auxiliary transistor (T2) arranged in parallel therewith, - The control inputs of both auxiliary transistors (T1, T2) are connected to the output of a common control circuit (IC). Schaltungsanordnung nach Anspruch 1, dadurch gekennzeichnet, daß parallel zu den Steuerstrecken der Hilfstransistoren (T1, T2) jeweils ein Kondensator (C6, C7) angeordnet ist.Circuit arrangement according to Claim 1, characterized in that in each case one capacitor (C6, C7) is arranged parallel to the control paths of the auxiliary transistors (T1, T2). Schaltungsanordnung nach Anspruch 2, dadurch gekennzeichnet, daß parallel zu den Kondensatoren (C6, C7) jeweils mindestens ein Entladewiderstand (R15, R16) geschaltet ist.Circuit arrangement according to Claim 2, characterized in that at least one discharge resistor (R15, R16) is connected in parallel with the capacitors (C6, C7). Schaltungsanordnung nach Anspruch 1, dadurch gekennzeichnet, daß bei mindestens einem Hilfstransistor (T1) die Verbindung zum Ausgang der Steuerschaltung (IC) über mindestens eine Diode (D5) erfolgt.Circuit arrangement according to Claim 1, characterized in that in the case of at least one auxiliary transistor (T1) the connection to the output of the control circuit (IC) is made via at least one diode (D5). Schaltungsanordnung nach den Ansprüchen 1 und 3, dadurch gekennzeichnet, daß der Ausgang der Steuerschaltung (IC) jeweils über mindestens einen Ladewiderstand (R11, R21) mit den Steuereingängen der Hilfstransistoren (T1, T2) verbunden ist, wobei die Widerstandswerte dieser Ladewiderstände (R11, R21) kleiner als die Widerstandswerte der Entladewiderstände (R15, R16) sind.Circuit arrangement according to Claims 1 and 3, characterized in that the output of the control circuit (IC) is in each case connected to the control inputs of the auxiliary transistors (T1, T2) via at least one charging resistor (R11, R21), the resistance values of these charging resistors (R11, R21) are smaller than the resistance values of the discharge resistors (R15, R16). Schaltungsanordnung nach Anspruch 1, dadurch gekennzeichnet, daß die Hilfstransistoren (T1, T2) Feldeffekttransistoren sind.Circuit arrangement according to claim 1, characterized in that the auxiliary transistors (T1, T2) are field effect transistors. Schaltungsanordnung nach Anspruch 1, dadurch gekennzeichnet, daß beide Parallelschaltungen (R5, T1; R7; T2) jeweils wenigstens einen weiteren ohmschen Widerstand (R6; R8) aufweisen, der in Serie zur Steuerstrecke des entsprechenden Hilfstransistors (T1; T2) und parallel zu dem mindestens einen Widerstand (R5; R7) der betreffenden Parallelschaltung (R5, T1; R7; T2) geschaltet ist.Circuit arrangement according to Claim 1, characterized in that the two parallel circuits (R5, T1; R7; T2) each have at least one further ohmic resistor (R6; R8) which is connected in series to the control path of the corresponding auxiliary transistor (T1; T2) and in parallel with the at least one resistor (R5; R7) of the relevant parallel circuit (R5, T1; R7; T2) is connected. Schaltungsanordnung nach Anspruch 1, dadurch gekennzeichnet, daß der Steuereingang mindestens eines Hilfstransistors (T2) an einen Spannungsteiler (R17, R18, R19) angeschlossen ist, der über einen Verzweigungspunkt (V2) im Lastkreis mit einem Resonanzkreisbauteil (C1) verbunden ist.Circuit arrangement according to Claim 1, characterized in that the control input of at least one auxiliary transistor (T2) is connected to a voltage divider (R17, R18, R19) which is connected to a resonant circuit component (C1) via a branch point (V2) in the load circuit. Schaltungsanordnung nach Anspruch 8, dadurch gekennzeichnet, daß der Steuereingang des mindestens einen Hilfstransistors (T2) über ein Schwellwertelement (DZ) an den Spannungsteiler (R17, R18, R19) angeschlossen ist.Circuit arrangement according to Claim 8, characterized in that the control input of the at least one auxiliary transistor (T2) is connected to the voltage divider (R17, R18, R19) via a threshold value element (DZ). Schaltungsanordnung nach Anspruch 1, dadurch gekennzeichnet, daß die Steuerschaltung (IC) während des Brennbetriebes der Lampe (LP) eine kontinuierlich veränderbare Ausgangsspannung erzeugt.Circuit arrangement according to claim 1, characterized in that the control circuit (IC) generates a continuously variable output voltage during the burning operation of the lamp (LP).
EP97104699A 1996-04-03 1997-03-19 Circuit for operating electric lamps Expired - Lifetime EP0800335B1 (en)

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DE19613149A1 (en) 1997-10-09
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