EP1233657B1 - Protective circuit for a fluorescent lamp - Google Patents

Protective circuit for a fluorescent lamp Download PDF

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Publication number
EP1233657B1
EP1233657B1 EP02001285A EP02001285A EP1233657B1 EP 1233657 B1 EP1233657 B1 EP 1233657B1 EP 02001285 A EP02001285 A EP 02001285A EP 02001285 A EP02001285 A EP 02001285A EP 1233657 B1 EP1233657 B1 EP 1233657B1
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EP
European Patent Office
Prior art keywords
resistor
voltage
point
component
protective circuit
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EP02001285A
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German (de)
French (fr)
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EP1233657A2 (en
EP1233657A3 (en
Inventor
Harald Schmitt
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Osram GmbH
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Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
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Publication of EP1233657A3 publication Critical patent/EP1233657A3/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
    • H05B41/295—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 and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
    • H05B41/298—Arrangements for protecting lamps or circuits against abnormal operating conditions
    • H05B41/2981—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions
    • H05B41/2985—Arrangements for protecting lamps or circuits against abnormal operating conditions for protecting the circuit against abnormal operating conditions against abnormal lamp operating conditions

Definitions

  • the present invention relates to a protection circuit for a fluorescent lamp having a first and a second lamp filament, comprising a DC voltage source with a positive and a negative pole, a half-bridge arrangement having a first and a second switch, wherein the half-bridge arrangement is powered by the DC voltage source and the first and second the second switch being interconnected to form a first reference point, the first reference point being connected to the negative pole via a first resistor, a coupling capacitor arranged in serial connection between the half-bridge arrangement and the first or second coil, the coil side Terminal of the decoupling capacitor forms a second reference point, which is connected via a second resistor to the negative terminal, a comparator having a first and a second input and an output, wherein the first input to the first Re reference point and the second input is connected to the second reference point, wherein the output is connected via a detection capacitor to the negative terminal, and an evaluation circuit with which the voltage drop across the detection capacitor voltage is evaluated to exceed a predetermined voltage level to cause deactivation of the half-bridge arrangement
  • Such a protection circuit is for example off EP-A-886 460 or WO-A-00/11916 is known and incorporated, for example by the assignee of the present invention in ballasts for fluorescent lamps.
  • the protection circuit is at the end of life of the fluorescent lamp, ie if the lamp is not defective, evaluate a criterion that in good time before overheating in the helix area (risk of melting the socket) leads to a shutdown of the half-bridge arrangement (also known as end-of -Life-shutdown). In this case, use is made of the fact that the filaments of a fluorescent lamp are covered with emitters in order to reduce the work function of the electrons.
  • the two reference points lie on average at a potential which corresponds to half the voltage provided by the DC voltage source.
  • the second of the two reference points is at a different potential and thus the reference points at different potential.
  • the potential difference is used to charge a detection capacitor, wherein the evaluation circuit is advantageously realized so that a voltage level is adjustable, beyond which a deactivation of the half-bridge arrangement is effected.
  • the term "relamping" is known. This is understood in a lighting system comprising several lamps to allow the insertion of a new lamp, without that the supply voltage and thus the other lamps must be turned off. Rather, it should be ensured that the voltage applied across the entire process of replacement mains voltage causes the newly inserted lamp immediately burns again. Also for this circuit structures are for example off US-A-5770925 known.
  • the disadvantage of the prior art approach is that the additional implementation of the relamping function of such ballasts, which is a mass product, significantly more expensive and therefore often be omitted.
  • ballasts in which an end-of-life detection and relamping are realized
  • ballasts in which only the end-of-life detection is realized.
  • all lamps must be turned off to effect a reset of the end-of-life detection. Only after switching off all lamps a new lamp can be used instead of the decrepit lamp. Afterwards all lamps can be switched on again. Especially in large factory buildings such interruptions are undesirable.
  • the object of the present invention is therefore to make available a cost-effective realization of the end-of-life detection and the relamping function.
  • the generic protection circuit further comprises a third resistor which bridges the decoupling capacitor and a fourth resistor which connects the first reference point to the positive pole of the DC voltage source, wherein the first, the second, the third and the fourth resistor are selected so that the first and the second reference point without inserted fluorescent lamp are at the same potential.
  • the invention is based on the idea of designing the end-of-life detection circuit or realizing the relamping function in such a way that as many components as possible are shared.
  • a cost-effective realization of the additional relamping function can thus be realized almost without additional expenditure, which results in a very desirable price reduction.
  • the idea consists in supplying the comparator, which detects an asymmetry, with identical fluorescent potential at its two inputs identical potentials, which cause a resetting of the shutdown of the half-bridge arrangement.
  • the two reference points are on average at half the potential of the DC voltage provided by the DC voltage source. This is usually the so-called intermediate circuit voltage and is usually provided on a DC link capacitor.
  • the ratio of the first resistance to the fourth resistance is the same big as the ratio of second resistance to third resistance.
  • the two reference points are even with the fluorescent lamp removed at a potential corresponding to half of the DC voltage source provided DC voltage.
  • the first resistor comprises a first and a second series resistor connected in series and the second resistor comprises a third and a fourth series resistor connected in series, wherein the first reference point with the connection point of the first partial resistor and the fourth resistor and the second reference point with the Connection point of the third resistor and the third partial resistance is connected and the first input of the comparator is connected to the connection point between the first and second partial resistance and the second input of the comparator is connected to the connection point between the third and the fourth partial resistance.
  • resistors of the voltage dividers need to be designed as high-voltage resistors.
  • the comparator and evaluation must be low voltage suitable. Rather, it is sufficient if a high-voltage resistor is provided per voltage divider, which results in a further cost reduction.
  • the ratio of the sum of the first and second partial resistances to the fourth resistance becomes equal to the ratio of the sum of the third and fourth partial resistance to the third resistor.
  • the two reference points are again at a fluorescent lamp removed at a potential which corresponds to half of the DC voltage source provided DC voltage.
  • the comparator comprises a first and a second switching element, each comprising a working, a control and a reference electrode
  • the fourth partial resistor comprises a fifth and a sixth series resistor connected in series
  • the connection point between the first and the second partial resistance is connected to the reference electrode of the first and to the control electrode of the second switching element
  • the connection point between the third partial resistance and the fifth partial resistance is connected to the control electrode of the first switching element
  • the connection point between the fifth and the sixth resistor is connected to the reference electrode of the second switching element
  • the working electrode of the first switching element and the working electrode of the second switching element to each other and via a series circuit of a fifth resistor and the Detek tion capacitor are connected to ground.
  • the ratio of the partial resistances three, five and six, the potential difference leading to the onset of charging of the detection capacitor can be adjusted.
  • the comparator is realized in a very simple and inexpensive form.
  • the ratio of the fourth resistance to the sum of the first and the second partial resistance is equal to the ratio of the third resistance to the sum of the third, fifth and sixth partial resistance.
  • the reference points are in turn drawn at fluorescent lamp at a potential corresponding to half of the DC voltage source provided DC voltage.
  • the evaluation circuit may comprise a holding member with a triggering potential and be designed so that as soon as the triggering potential assumes a predetermined potential, in particular already by a single pulse, the holding member is activated to deactivate the half-bridge circuit until a reset operation by removing the fluorescent lamp is triggered. This measure ensures a safe deactivation of the half-bridge arrangement and thus for a particularly high reliability of the protection circuit according to the invention.
  • a first threshold component in particular a Zener diode, can be arranged, with which the threshold can be set, above which a deactivation of the half-bridge circuit is triggered. This measure enables the activation of the holding member at a predeterminable voltage on the detection capacitor.
  • the Zündnapssbegrenzungsscrien can in this case have a measuring element for measuring a proportional to the ignition current size, so that the value of this size is suitable for activating the holding member.
  • This embodiment makes use of the fact that the ignition current is approximately proportional to the ignition voltage and therefore can be used as a measure of the ignition voltage. Since the ignition current is easier to measure than the ignition voltage, this results in a simple construction of the circuit arrangement.
  • a second threshold device in particular a Zener diode arranged with the threshold is adjustable, beyond which a deactivation of the half-bridge circuit is triggered.
  • This variant allows a particularly simple adaptation of the potentials of the ignition voltage limiting circuit to the potentials of the holding member.
  • the measuring element may in particular be a resistor which is arranged serially to one of the half-bridge switches.
  • This embodiment is the Recognizing that the ignition current is also provided by the half-bridge arrangement and therefore the current flowing through the half-bridge arrangement is proportional to the ignition current.
  • a resistor is arranged serially to one of the half-bridge switch as the measuring element, it is particularly easy to determine a variable proportional to the ignition current.
  • Common practice is the switching of a storage capacitor between plus and minus pole.
  • operating circuits for fluorescent lamps in which the voltage at said storage capacitor increases with increasing amplitude of the ignition voltage.
  • One type of operating circuit that has this characteristic are so-called pump circuits.
  • pump circuits it is possible to monitor the ignition voltage by monitoring the voltage across said storage capacitor.
  • the tripping potential point of the holding member is connected via a Zündnapssbegrenzungsscrien with the voltage of the storage capacitor.
  • the ignition voltage limiting circuit consists of a resistor which adapts the voltage on the storage capacitor to the tripping potential required for tripping.
  • the embodiments according to the invention preferably also include suitable screening circuits in order to provide direct voltages for evaluation at the reference and potential points.
  • the half-bridge arrangement converts the DC voltage provided by the DC voltage source into an AC voltage which is reflected in the subsequent protection circuit.
  • To evaluate the signals at the reference points are essentially DC voltages interesting, so that by suitable Siebscrienen For example, using capacitors, ensures that they are provided for further processing.
  • a capacitor C1 provides a voltage Uz, which serves to supply the subsequent circuit arrangement.
  • a half-bridge arrangement comprises a first switch S1 and a second switch S2. The controls of the switches S1 and S2 are well known to those skilled in the art and therefore not shown in FIG. 1 for reasons of clarity.
  • the half-bridge arrangement feeds via a decoupling capacitor C2 a fluorescent lamp L A with a first filament W1 and a second filament W2.
  • the fluorescent lamp L A is connected to an ignition circuit Zs, which is designed to cause an ignition of the lamp L A
  • the center of the half-bridge arrangement forms a first reference point A, which is connected via a lamp inductor L D with the lamp L A.
  • the winding-side terminal of the decoupling capacitor C2 forms a second reference point B.
  • the potentials of both reference points A, B are fed to a comparator V G whose output is connected to a detection capacitor C3.
  • the across the capacitor C3 C3 voltage U is fed to an evaluation circuit AS, which causes a deactivation of the half-bridge arrangement upon exceeding a predetermined voltage level.
  • the potentials of the reference points A and B due to the absence of emitter on one of the two helical electrodes W1, W2 and the thus increasing increase the work function of one of the two helical electrodes W1, W2, even if the increase in work function only is minimal.
  • the potential difference between the two reference points leads to the charging of the capacitor C3 and thus to the build-up of the voltage U C3 . If this exceeds a certain value, the half-bridge arrangement is switched off by the evaluation circuit As and thus an overheating in the coil area prevented.
  • the reference points A and B are on average at half the voltage U Z.
  • the decoupling capacitor C2 could also be arranged elsewhere, for example between the lamp inductor L D and the filament electrode W2.
  • consumption of the emitter on the helical electrode W1 prior to consumption of the emitter on the helical electrode W2 would increase the voltage at the helix electrode W1, resulting in a rise in the voltage across the capacitor C2.
  • the potential B would increase in relation to the potential A.
  • the potential at the reference point A would drop from the potential at the reference point B.
  • a relamping function is realized by resetting the voltage across the capacitor C3 by applying identical potential to the two inputs of the comparator.
  • the first reference point A via a resistor R1
  • the second reference point B via a resistor R2 to the negative pole of the voltage U Z is connected.
  • the positive pole of the voltage U Z is on the one hand via a resistor R3, which bridges the capacitor C2, connected to the reference point B, on the other hand via a resistor R4 to the reference point A.
  • suitable dimensioning of the two voltage divider R4, R1 and R3, R2 can be achieved be that the potentials at the reference points A, B are identical when removed lamp L A and thus lead to a reset of the end-of-life detection.
  • a dimensioning of the ratio of the resistance R1 to the resistance R4 and from the resistance R2 to the resistance R3 equal to 1, that half the voltage of U Z at the two reference points A, B is established.
  • the resistors R1 and R2 are divided into two partial resistors R11, R12 and R21, R22.
  • By suitable dimensioning of the partial resistors it can be ensured that the majority of the voltages applied to the reference points A, B drop off at the partial resistors R11 and R21. Accordingly, the comparator V G is subjected only to low voltages and can therefore be realized with less voltage-resistant components.
  • FIGS. 3a / b an overall circuit for operating a fluorescent lamp is shown, which can be connected to a power supply via the terminals K1 and K2.
  • a fuse SI is arranged, followed by a filter circuit comprising a capacitor C4 and an inductor L3 before the mains signal is rectified in a power rectifier N GR .
  • the rectified output signal of the mains rectifier N GR is buffered in the capacitor C1 and serves to supply the subsequent circuit arrangement.
  • Resistor R22 of FIG. 2 is divided into two partial resistors R221 and R222.
  • the capacitor C3 is a resistor R5 connected in parallel, which allows a discharge of the capacitor C3.
  • the resistor R12 is connected in parallel with a capacitor C5, while the series connection of the resistors R221 and R222 is connected in parallel with a capacitor C6. These measures ensure that DC signals are present at the bases of two switching elements T1, T2 contained in the comparator.
  • the control electrode of the switching element T1 is connected to the connection point D between the resistor R21 and the resistor R221. Connected to the junction point C of the resistors R11 and R12 is the reference electrode of the switching element T1 and the control electrode of the switching element T2.
  • the reference electrode of the switching element T2 is connected to the connection point E between the resistors R221 and R222.
  • both switching elements T1, T2 are connected via a resistor R6 to the connection point F, to which the capacitor C3 is connected. Since the voltage is constant at the reference point A, a voltage of 15 V can be set by suitable selection of the resistors R11 and R12, for example at the connection point C. By suitable dimensioning of the resistors R21, R221 and R222 can be set in normal operation, ie the potential at point A is equal to the potential at point B, a voltage which is at point D 18 V and at point E 12 V. In this state, the two switching elements T1, T2 are disabled.
  • the switching element T1 begins to conduct when the voltage at point D becomes smaller than the voltage at point C. As long as the voltage at point E is less than the voltage at point C remains the switching element T2 locked. By conducting the switching element T1, the capacitor C3 is again charged via the resistor R6. With the height of the voltage difference between the potential points C and D or C and E, the switching threshold and thus the degree of asymmetry at which the shutdown occurs, can be additionally set.
  • the voltage at the point F which corresponds to the state of charge of the capacitor C3, is transmitted via a diode D1 and a Zener diode Z1 to a tripping potential point G in a holding member HG.
  • the holding member HG is supplied via the charge stored in a capacitor C7 of a starting circuit ST.
  • the switching element T4 turns on.
  • the switching element T3 turns on and thus supplies the holding current for a retaining element that is self-holding in this way.
  • the resistor R8 in combination with the capacitor C8 and the resistor R9 in combination with the capacitor C9 provide for the elimination of interference, thereby preventing accidental activation of the holding member. Characterized in that the switching element T4 conducts, the potential at point I drops to 0 V.
  • the two switches S1 and S2 of the half-bridge circuit have respective drive circuits A S1 , A S2 .
  • Each drive circuit A S1 , A S2 comprises an inductance L1, L2, which is coupled to the lamp inductor L D. As soon as the potential at point I falls to 0 V, the diode D2 begins to conduct, thus grounding the signal fed via the inductance L2 into the drive circuit A S2 , so that the switch S2 is no longer activated. This also leads to a shutdown of the switch S1.
  • a ZündHarndsbegrenzungsscrien Z SB With the point G of the holding member H G is further connected a Zünddozenssbegrenzungsscrien Z SB . It comprises a measuring resistor R10, which is arranged in series with the switch S2. The potential at the point J, that is, the voltage dropping across the resistor R10 is proportional to the ignition current and thus proportional to the ignition voltage.
  • the Zündtemposbegrenzungsweakened Z SB has the task, for example, to prevent destruction of the ignition circuit Z S in air pullers ..
  • the ignition circuit Z S comprises two capacitors C10 and C11 and PTC1 PTC.
  • the resistor R14 serves to cause a time delay of the response of the Zünddozenssbegrenzungscnies. Via the diodes D3 and Z2, the level can be set at which a Zünddozenssbegrenzung by acting on the point G of the holding member H G and thus a shutdown of the half-bridge arrangement is performed.
  • the voltage across resistor R10 is filtered by resistor R9 and capacitor C9.
  • the level of the critical ignition voltage can also be influenced by the value of the resistor R10.
  • the diode D3 protects the holding member H G also against negative voltage spikes.

Abstract

a protective circuit for a fluorescent lamp includes a third resistor (R3) that bridges a decoupling capacitor (C2), and a fourth resistor (R4) that connects a first reference point (A) to a positive pole of a DC voltage source (UZ), the resistors being selected such that the reference points are at the same potential without the fluorescent lamp inserted.

Description

Die vorliegende Erfindung betrifft eine Schutzschaltung für eine Leuchtstofflampe mit einer ersten und einer zweiten Lampenwendel, umfassend eine Gleichspannungsquelle mit einem Plus- und einem Minuspol, eine Halbbrückenanordnung mit einem ersten und einem zweiten Schalter, wobei die Halbbrückenanordnung von der Gleichspannungsquelle gespeist wird und der erste und der zweite Schalter unter Bildung eines ersten Referenzpunktes miteinander verbunden sind, wobei der erste Referenzpunkt über einen ersten Widerstand mit dem Minuspol verbunden ist, einem Auskoppelkondensator, der in einer seriellen Verbindung zwischen der Halbbrückenanordnung und der ersten oder der zweiten Wendel angeordnet ist, wobei der wendelseitige Anschluß des Auskoppelkondensators einen zweiten Referenzpunkt bildet, der über einen zweiten Widerstand mit dem Minuspol verbunden ist, einen Vergleicher, der einen ersten und einen zweiten Eingang und einen Ausgang aufweist, wobei der erste Eingang mit dem ersten Referenzpunkt und der zweite Eingang mit dem zweiten Referenzpunkt verbunden ist, wobei der Ausgang über einen Detektionskondensator mit dem Minuspol verbunden ist, und eine Auswerteschaltung, mit der die am Detektionskondensator abfallende Spannung auswertbar ist, um bei Überschreiten eines vorbestimmten Spannungspegels eine Deaktivierung der Halbbrückenanordnung zu bewirken.The present invention relates to a protection circuit for a fluorescent lamp having a first and a second lamp filament, comprising a DC voltage source with a positive and a negative pole, a half-bridge arrangement having a first and a second switch, wherein the half-bridge arrangement is powered by the DC voltage source and the first and second the second switch being interconnected to form a first reference point, the first reference point being connected to the negative pole via a first resistor, a coupling capacitor arranged in serial connection between the half-bridge arrangement and the first or second coil, the coil side Terminal of the decoupling capacitor forms a second reference point, which is connected via a second resistor to the negative terminal, a comparator having a first and a second input and an output, wherein the first input to the first Re reference point and the second input is connected to the second reference point, wherein the output is connected via a detection capacitor to the negative terminal, and an evaluation circuit with which the voltage drop across the detection capacitor voltage is evaluated to exceed a predetermined voltage level to cause deactivation of the half-bridge arrangement.

Stand der TechnikState of the art

Eine derartige Schutzschaltung ist zum Beispiel aus EP-A-886460 oder WO-A-00/11916 bekannt und wird beispielsweise von der Anmelderin der vorliegenden Erfindung in Vorschaltgeräte für Leuchtstofflampen eingebaut. Die Schutzschaltung besteht darin, am Lebensdauerende der Leuchtstofflampe, d.h. wenn die Lampe noch nicht defekt ist, ein Kriterium auszuwerten, das rechtzeitig vor einer Überhitzung im Wendelbereich (Gefahr eines Schmelzens der Fassung) zu einer Abschaltung der Halbbrückenanordnung führt (auch bekannt als End-of-Life-Abschaltung). Hierbei macht man sich zunutze, daß die Wendeln einer Leuchtstofflampe mit Emitter bedeckt sind, um die Austrittsarbeit der Elektronen zu reduzieren. In der Schlußphase macht sich ein Fehlen des Emitters auf einer der beiden Lampenwendeln der Leuchtstofflampe dadurch bemerkbar, daß sich die Austrittsarbeit wieder langsam erhöht und sich damit die am Auskoppelkondensator abfallende Spannung ändert. Im Normalbetrieb, d.h. wenn beide Wendeln noch über Emitter verfügen, liegen die beiden Referenzpunkte im Mittel auf einem Potential, das der halben Spannung entspricht, die von der Gleichspannungsquelle zur Verfügung gestellt wird. Am Lebensdauerende liegt der zweite der beiden Referenzpunkte auf einem anderen Potential und damit die Referenzpunkte auf unterschiedlichem Potential. Die Potentialdifferenz wird genutzt, um einen Detektionskondensator aufzuladen, wobei die Auswerteschaltung vorteilhafterweise so realisiert wird, daß ein Spannungspegel einstellbar ist, bei dessen Überschreiten eine Deaktivierung der Halbbrückenanordnung bewirkt wird.Such a protection circuit is for example off EP-A-886 460 or WO-A-00/11916 is known and incorporated, for example by the assignee of the present invention in ballasts for fluorescent lamps. The protection circuit is at the end of life of the fluorescent lamp, ie if the lamp is not defective, evaluate a criterion that in good time before overheating in the helix area (risk of melting the socket) leads to a shutdown of the half-bridge arrangement (also known as end-of -Life-shutdown). In this case, use is made of the fact that the filaments of a fluorescent lamp are covered with emitters in order to reduce the work function of the electrons. In the final phase, a lack of the emitter on one of the two lamp filaments of the fluorescent lamp is noticeable in that the work function increases again slowly and thus changes the voltage dropping at the coupling-out capacitor. In normal operation, ie when both coils still have emitters, the two reference points lie on average at a potential which corresponds to half the voltage provided by the DC voltage source. At the end of the service life, the second of the two reference points is at a different potential and thus the reference points at different potential. The potential difference is used to charge a detection capacitor, wherein the evaluation circuit is advantageously realized so that a voltage level is adjustable, beyond which a deactivation of the half-bridge arrangement is effected.

Im Zusammenhang mit dem Austausch einer defekten Lampe ist der Begriff "Relamping" bekannt. Darunter versteht man bei einer Beleuchtungsanlage, die mehrere Lampen umfaßt, das Einsetzen einer neuen Lampe zu ermöglichen, ohne daß die die Versorgungsspannung und damit die anderen Lampen ausgeschaltet werden müssen. Vielmehr soll sichergestellt werden, daß die über den ganzen Vorgang des Austausches anliegende Netzspannung dazu führt, daß die neu eingesetzte Lampe sofort wieder brennt. Auch hierfür sind Schaltungsstrukturen zum Beispiel aus US-A-5770925 bekannt. Der Nachteil bei der Vorgehensweise aus dem Stand der Technik besteht darin, daß die zusätzliche Realisierung der Relamping-Funktion derartige Vorschaltgeräte, bei denen es sich um ein Massenprodukt handelt, deutlich verteuern und daher häufig weggelassen werden. Im Ergebnis gibt es demnach teurere Vorschaltgeräte, bei denen eine End-of-Life-Detektion sowie das Relamping realisiert sind, und es gibt eine zweite Kategorie von Vorschaltgeräten, bei denen nur die End-of-Life-Detektion realisiert ist. Bei den letztgenannten müssen beispielsweise beim Auswechseln einer Leuchtstofflampe in einer Fabrikhalle sämtliche Lampen ausgeschaltet werden, um damit eine Rücksetzung der End-of-Life-Detektion zu bewirken. Erst nach dem Ausschalten aller Lampen kann eine neue Lampe anstelle der altersschwachen Lampe eingesetzt werden. Anschließend können alle Lampen wieder angeschaltet werden. Insbesondere in großen Fabrikhallen sind derartige Unterbrechungen unerwünscht.In connection with the replacement of a defective lamp, the term "relamping" is known. This is understood in a lighting system comprising several lamps to allow the insertion of a new lamp, without that the supply voltage and thus the other lamps must be turned off. Rather, it should be ensured that the voltage applied across the entire process of replacement mains voltage causes the newly inserted lamp immediately burns again. Also for this circuit structures are for example off US-A-5770925 known. The disadvantage of the prior art approach is that the additional implementation of the relamping function of such ballasts, which is a mass product, significantly more expensive and therefore often be omitted. As a result, there are therefore more expensive ballasts, in which an end-of-life detection and relamping are realized, and there is a second category of ballasts, in which only the end-of-life detection is realized. In the case of the latter, for example, when replacing a fluorescent lamp in a factory floor, all lamps must be turned off to effect a reset of the end-of-life detection. Only after switching off all lamps a new lamp can be used instead of the decrepit lamp. Afterwards all lamps can be switched on again. Especially in large factory buildings such interruptions are undesirable.

Darstellung der ErfindungPresentation of the invention

Die Aufgabe der vorliegenden Erfindung besteht deshalb darin, eine kostengünstige Realisierung der End-of-Life-Detektion sowie der Relamping-Funktion verfügbar zu machen.The object of the present invention is therefore to make available a cost-effective realization of the end-of-life detection and the relamping function.

Erfindungsgemäß wird diese Aufgabe dadurch gelöst, daß die gattungsgemäße Schutzschaltung weiterhin einen dritten Widerstand aufweist, der den Auskoppelkondensator überbrückt und einen vierten Widerstand, der den ersten Referenzpunkt mit dem Pluspol der Gleichspannungsquelle verbindet, wobei der erste, der zweite, der dritte und der vierte Widerstand so gewählt sind, das der erste und der zweite Referenzpunkt ohne eingesetzte Leuchtstofflampe auf demselben Potential liegen.According to the invention this object is achieved in that the generic protection circuit further comprises a third resistor which bridges the decoupling capacitor and a fourth resistor which connects the first reference point to the positive pole of the DC voltage source, wherein the first, the second, the third and the fourth resistor are selected so that the first and the second reference point without inserted fluorescent lamp are at the same potential.

Der Erfindung liegt die Idee zugrunde, die End-of-Life-Detektionsschaltung so auszulegen bzw. die Relamping-Funktion so zu realisieren, daß möglichst viele Bauelemente gemeinsam genutzt werden. Bei einem Massenprodukt wie der vorliegenden Schutzschaltung läßt sich hierdurch nahezu ohne Zusatzaufwand eine kostengünstige Realisierung der Relamping-Zusatzfunktion realisieren, was in einer sehr erwünschten Preisreduktion resultiert.The invention is based on the idea of designing the end-of-life detection circuit or realizing the relamping function in such a way that as many components as possible are shared. In the case of a mass product such as the present protection circuit, a cost-effective realization of the additional relamping function can thus be realized almost without additional expenditure, which results in a very desirable price reduction.

Vorliegend besteht die Idee darin, dem Vergleicher, der eine Asymmetrie detektiert, bei entnommener Leuchtstofflampe an seinen zwei Eingängen identische Potentiale zuzuführen, die ein Rücksetzen der Abschaltung der Halbbrückenanordnung bewirken.In the present case, the idea consists in supplying the comparator, which detects an asymmetry, with identical fluorescent potential at its two inputs identical potentials, which cause a resetting of the shutdown of the half-bridge arrangement.

Wie bereits oben erwähnt, liegen die beiden Referenzpunkte im Mittel auf dem halben Potential der von der Gleichspannungsquelle zur Verfügung gestellten Gleichspannung. Diese ist gewöhnlich die sogenannte Zwischenkreisspannung und wird üblicherweise an einem Zwischenkreiskondensator bereitgestellt. Bei einer besonders bevorzugten Realisierung der Erfindung ist das Verhältnis aus erstem Widerstand zum vierten Widerstand gleich groß wie das Verhältnis aus zweitem Widerstand zum dritten Widerstand. Insbesondere für den Fall, daß das Verhältnis 1 gewählt wird, liegen die beiden Referenzpunkte auch bei entnommener Leuchtstofflampe auf einem Potential, das der halben von der Gleichspannungsquelle zur Verfügung gestellten Gleichspannung entspricht.As already mentioned above, the two reference points are on average at half the potential of the DC voltage provided by the DC voltage source. This is usually the so-called intermediate circuit voltage and is usually provided on a DC link capacitor. In a particularly preferred implementation of the invention, the ratio of the first resistance to the fourth resistance is the same big as the ratio of second resistance to third resistance. In particular, in the event that the ratio 1 is selected, the two reference points are even with the fluorescent lamp removed at a potential corresponding to half of the DC voltage source provided DC voltage.

Weiterhin ist bevorzugt, durch geeignet dimensionierte Spannungsteiler den Vergleicher nur mit einer niedrigen Spannung zu beaufschlagen. Dies resultiert in einer weiteren Kostenreduktion. Hierfür umfaßt der erste Widerstand einen ersten und einen zweiten zueinander in Serie geschalteten Teilwiderstand und der zweite Widerstand einen dritten und einen vierten zueinander in Serie geschalteten Teilwiderstand, wobei der erste Referenzpunkt mit dem Verbindungspunkt des ersten Teilwiderstands und des vierten Widerstands und der zweite Referenzpunkt mit dem Verbindungspunkt des dritten Widerstands und des dritten Teilwiderstands verbunden ist und der erste Eingang des Vergleichers mit dem Verbindungspunkt zwischen erstem und zweitem Teilwiderstand verbunden ist und der zweite Eingang des Vergleichers mit dem Verbindungspunkt zwischen dem dritten und dem vierten Teilwiderstand verbunden ist. Bei dieser Ausführungsform müssen nicht alle Widerstände der Spannungsteiler als Hochspannungswiderstände ausgeführt sein. Ebenso müssen die Vergleicher- und Auswerteschaltung nur niederspannungsgeeignet sein. Vielmehr genügt es, wenn pro Spannungsteiler ein Hochspannungswiderstand vorgesehen wird, was in einer weiteren Kostenreduktion resultiert.Furthermore, it is preferable to apply the comparator only with a low voltage by suitably dimensioned voltage dividers. This results in a further cost reduction. For this purpose, the first resistor comprises a first and a second series resistor connected in series and the second resistor comprises a third and a fourth series resistor connected in series, wherein the first reference point with the connection point of the first partial resistor and the fourth resistor and the second reference point with the Connection point of the third resistor and the third partial resistance is connected and the first input of the comparator is connected to the connection point between the first and second partial resistance and the second input of the comparator is connected to the connection point between the third and the fourth partial resistance. In this embodiment, not all resistors of the voltage dividers need to be designed as high-voltage resistors. Likewise, the comparator and evaluation must be low voltage suitable. Rather, it is sufficient if a high-voltage resistor is provided per voltage divider, which results in a further cost reduction.

Bevorzugt wird das Verhältnis aus der Summe des ersten und zweiten Teilwiderstands zum vierten Widerstand gleich dem Verhältnis aus der Summe des dritten und vierten Teilwiderstands zum dritten Widerstand gewählt. Für den Fall, daß die Verhältnisse wieder zu eins gewählt werden, liegen die beiden Referenzpunkte bei entnommener Leuchtstofflampe wiederum auf einem Potential, das der halben von der Gleichspannungsquelle zur Verfügung gestellten Gleichspannung entspricht.Preferably, the ratio of the sum of the first and second partial resistances to the fourth resistance becomes equal to the ratio of the sum of the third and fourth partial resistance to the third resistor. In the event that the ratios are again selected to one, the two reference points are again at a fluorescent lamp removed at a potential which corresponds to half of the DC voltage source provided DC voltage.

Eine besonders zweckmäßige Realisierung des Vergleichers sieht vor, daß der Vergleicher ein erstes und ein zweites Schaltelement umfaßt, die jeweils eine Arbeits-, eine Steuer- und eine Bezugselektrode umfassen, wobei der vierte Teilwiderstand einen fünften und einen sechsten zueinander in Serie geschalteten Teilwiderstand umfaßt, wobei der Verbindungspunkt zwischen dem ersten und dem zweiten Teilwiderstand mit der Bezugselektrode des ersten und mit der Steuerelektrode des zweiten Schaltelements verbunden ist, der Verbindungspunkt zwischen dem dritten Teilwiderstand und dem fünften Teilwiderstand mit der Steuerelektrode des ersten Schaltelements - verbunden ist, der Verbindungspunkt zwischen dem fünften und dem sechsten Widerstand mit der Bezugselektrode des zweiten Schaltelements verbunden ist, die Arbeitselektrode des ersten Schaltelements und die Arbeitselektrode des zweiten Schaltelements miteinander und über eine Serienschaltung aus einem fünften Widerstand und dem Detektionskondensator mit Masse verbunden sind. Zudem kann durch das Verhältnis der Teilwiderstände drei, fünf und sechs die Potentialdifferenz, die zum Einsetzen des Ladens des Detektionskondensators führt, eingestellt werden. Bei dieser Ausführungsform ist der Vergleicher in sehr einfacher und kostengünstiger Form realisiert.A particularly expedient realization of the comparator provides that the comparator comprises a first and a second switching element, each comprising a working, a control and a reference electrode, wherein the fourth partial resistor comprises a fifth and a sixth series resistor connected in series, wherein the connection point between the first and the second partial resistance is connected to the reference electrode of the first and to the control electrode of the second switching element, the connection point between the third partial resistance and the fifth partial resistance is connected to the control electrode of the first switching element, the connection point between the fifth and the sixth resistor is connected to the reference electrode of the second switching element, the working electrode of the first switching element and the working electrode of the second switching element to each other and via a series circuit of a fifth resistor and the Detek tion capacitor are connected to ground. In addition, by the ratio of the partial resistances three, five and six, the potential difference leading to the onset of charging of the detection capacitor can be adjusted. In this embodiment, the comparator is realized in a very simple and inexpensive form.

Bevorzugt ist das Verhältnis aus dem vierten Widerstand zu der Summe aus dem ersten und dem zweiten Teilwiderstand gleich dem Verhältnis aus dem dritten Widerstand zur Summe aus dem dritten, fünften und sechsten Teilwiderstand. Insbesondere für den Fall, daß das Verhältnis gleich 1 ist, liegen die Referenzpunkte bei gezogener Leuchtstofflampe wiederum auf einem Potential, das der halben von der Gleichspannungsquelle zur Verfügung gestellten Gleichspannung entspricht.Preferably, the ratio of the fourth resistance to the sum of the first and the second partial resistance is equal to the ratio of the third resistance to the sum of the third, fifth and sixth partial resistance. In particular, in the event that the ratio is equal to 1, the reference points are in turn drawn at fluorescent lamp at a potential corresponding to half of the DC voltage source provided DC voltage.

Die Auswerteschaltung kann ein Halteglied mit einem Auslösepotential umfassen und derart ausgelegt sein, daß, sobald der Auslösepotentialpunkt ein vorbestimmtes Potential annimmt, insbesondere bereits durch einen einmaligen Impuls, das Halteglied aktivierbar ist, um die Halbbrückenschaltung solange zu deaktivieren, bis durch Entfernen der Leuchtstofflampe ein Rücksetzvorgang ausgelöst wird. Diese Maßnahme sorgt für eine sichere Deaktivierung der Halbbrückenanordnung und damit für eine besonders hohe Zuverlässigkeit der erfindungsgemäßen Schutzschaltung.The evaluation circuit may comprise a holding member with a triggering potential and be designed so that as soon as the triggering potential assumes a predetermined potential, in particular already by a single pulse, the holding member is activated to deactivate the half-bridge circuit until a reset operation by removing the fluorescent lamp is triggered. This measure ensures a safe deactivation of the half-bridge arrangement and thus for a particularly high reliability of the protection circuit according to the invention.

Zwischen dem Vergleicher und dem Auslösepotentialpunkt des Halteglieds kann ein erstes Schwellwertbauelement, insbesondere eine Zenerdiode, angeordnet sein, mit dem die Schwelle einstellbar ist, bei deren Überschreiten eine Deaktivierung der Halbbrückenschaltung ausgelöst wird. Diese Maßnahme ermöglicht die Aktivierung des Halteglieds bei einer vorgebbaren Spannung am Detektionskondensator.Between the comparator and the triggering potential point of the holding member, a first threshold component, in particular a Zener diode, can be arranged, with which the threshold can be set, above which a deactivation of the half-bridge circuit is triggered. This measure enables the activation of the holding member at a predeterminable voltage on the detection capacitor.

Besonders vorteilhaft ist es, die Kombination aus End-of-Life-Detektion und Relamping-Funktion weiterhin mit einer Zündspannungsbegrenzungsschaltung zu kombinieren, hierzu wird mit dem Auslösepotentialpunkt des Halteglieds eine Zündspannungsbegrenzungsschaltung derart verbunden, daß bei Detektion einer Überschreitung einer vorbestimmten Zündspannung dasselbe Halteglied aktivierbar ist. Dadurch muß das Halteglied nur einmal ausgebildet werden, was in einer weiteren deutlichen Kostenreduktion resultiert.It is particularly advantageous to combine the combination of end-of-life detection and relamping function with an ignition voltage limiting circuit, this is done with the tripping potential point of the holding member a Zündspannungsbegrenzungsschaltung connected such that upon detection of exceeding a predetermined ignition voltage, the same holding member is activated. As a result, the holding member must be formed only once, resulting in a further significant cost reduction.

Die Zündspannungsbegrenzungsschaltung kann hierbei ein Meßglied zur Messung einer zum Zündstrom proportionalen Größe aufweisen, so daß der Wert dieser Größe zum Aktivieren des Halteglieds verwendbar ist. Diese Ausführungsform nutzt aus, daß der Zündstrom annähernd proportional zur Zündspannung ist und daher als Maß für die Zündspannung verwendet werden kann. Da der Zündstrom einfacher zu messen ist als die Zündspannung, ergibt sich hierdurch ein einfacher Aufbau der Schaltungsanordnung.The Zündspannungsbegrenzungsschaltung can in this case have a measuring element for measuring a proportional to the ignition current size, so that the value of this size is suitable for activating the holding member. This embodiment makes use of the fact that the ignition current is approximately proportional to the ignition voltage and therefore can be used as a measure of the ignition voltage. Since the ignition current is easier to measure than the ignition voltage, this results in a simple construction of the circuit arrangement.

Bevorzugt ist zwischen einem Potentialpunkt der Zündspannungsbegrenzungschaltung, dessen Potential zum Zündstrom proportional ist, und dem Auslösepotentialpunkt des Halteglieds ein zweites Schwellwertbauelement, insbesondere eine Zenerdiode angeordnet, mit der die Schwelle einstellbar ist, bei deren Überschreiten eine Deaktivierung der Halbbrückenschaltung ausgelöst wird. Diese Variante ermöglicht eine besonders einfache Anpassung der Potentiale der Zündspannungsbegrenzungsschaltung an die Potentiale des Halteglieds.Preferably, between a potential point of the Zündspannungsbegrenzungschaltung whose potential is proportional to the ignition current, and the trigger potential point of the holding member, a second threshold device, in particular a Zener diode arranged with the threshold is adjustable, beyond which a deactivation of the half-bridge circuit is triggered. This variant allows a particularly simple adaptation of the potentials of the ignition voltage limiting circuit to the potentials of the holding member.

Das Meßglied kann insbesondere ein Widerstand sein, der seriell zu einem der Halbbrückenschalter angeordnet ist. Dieser Ausführungsform liegt die Erkenntnis zugrunde, daß der Zündstrom auch durch die Halbbrückenanordnung zur Verfügung gestellt wird und daher der die Halbbrückenanordnung durchfließende Strom zum Zündstrom proportional ist. Indem als Meßglied ein Widerstand seriell zu einem der Halbbrückenschalter angeordnet wird, läßt sich besonders einfach eine zum Zündstrom proportionale Größe ermitteln.The measuring element may in particular be a resistor which is arranged serially to one of the half-bridge switches. This embodiment is the Recognizing that the ignition current is also provided by the half-bridge arrangement and therefore the current flowing through the half-bridge arrangement is proportional to the ignition current. By a resistor is arranged serially to one of the half-bridge switch as the measuring element, it is particularly easy to determine a variable proportional to the ignition current.

Allgemein üblich ist das Schalten eines Speicherkondensators zwischen Plusund Minuspol. Es existieren Betriebsschaltungen für Leuchtstofflampen, bei denen die Spannung am besagten Speicherkondensator mit steigender Amplitude der Zündspannung ansteigt. Eine Art von Betriebsschaltung, die diese Eigenschaft aufweisen sind sog. Pumpschaltungen. Bei diesen Schaltungen ist es möglich, die Zündspannung zu überwachen, indem man die Spannung an besagtem Speicherkondensator überwacht. Dazu wird der Auslösepotenzialpunkt des Halteglieds über eine Zündspannungsbegrenzungsschaltung mit der Spannung des Speicherkondensators verbunden. Im einfachsten Fall besteht die Zündspannungsbegrenzungsschaltung aus einem Widerstand, der die Spannung am Speicherkondensator an die für eine Auslösung nötige Auslösespannung am Auslösepotenzialpunkt anpasst.Common practice is the switching of a storage capacitor between plus and minus pole. There are operating circuits for fluorescent lamps, in which the voltage at said storage capacitor increases with increasing amplitude of the ignition voltage. One type of operating circuit that has this characteristic are so-called pump circuits. In these circuits, it is possible to monitor the ignition voltage by monitoring the voltage across said storage capacitor. For this purpose, the tripping potential point of the holding member is connected via a Zündspannungsbegrenzungsschaltung with the voltage of the storage capacitor. In the simplest case, the ignition voltage limiting circuit consists of a resistor which adapts the voltage on the storage capacitor to the tripping potential required for tripping.

Bevorzugt umfassen die erfindungsgemäßen Ausführungsformen weiterhin geeignete Siebschaltungen, um an den Referenz- und Potentialpunkten Gleichspannungen zur Auswertung bereitzustellen. Wie für den Fachmann offensichtlich, wird durch die Halbbrückenanordnung die von der Gleichspannungsquelle zur Verfügung gestellte Gleichspannung in eine Wechselspannung umgewandelt, die sich in der nachfolgenden Schutzschaltung widerspiegelt. Zur Auswertung der Signale an den Referenzpunkten sind im wesentlichen Gleichspannungen interessant, so daß durch geeignete Siebschaltungen beispielsweise unter Verwendung von Kondensatoren, sichergestellt wird, daß diese zur Weiterverarbeitung bereitgestellt werden.The embodiments according to the invention preferably also include suitable screening circuits in order to provide direct voltages for evaluation at the reference and potential points. As is apparent to those skilled in the art, the half-bridge arrangement converts the DC voltage provided by the DC voltage source into an AC voltage which is reflected in the subsequent protection circuit. To evaluate the signals at the reference points are essentially DC voltages interesting, so that by suitable Siebschaltungen For example, using capacitors, ensures that they are provided for further processing.

Weitere vorteilhafte Ausführungsformen sind den Unteransprüchen zu entnehmen.Further advantageous embodiments can be found in the dependent claims.

Beschreibung der Zeichnungen:Description of the drawings:

Im Folgenden werden Ausführungsbeispiele der Erfindung unter Hinweis auf die beigefügten Zeichnungen näher beschrieben. Es stellen dar:

Fig. 1
eine erste Ausführungsform einer erfindungsgemäßen Schutzschaltung;
Fig. 2
eine zweite Ausführungsform einer erfindungsgemäßen Schutzschaltung; und
Fig. 3a/b
eine dritte Ausführungsform einer erfindungsgemäßen Schutzschaltung. Diese dritte Ausführungsform ist aus Platzgründen auf die Fig. 3a und Fig. 3b aufgeteilt. Die Schaltungsteile der Fig. 3a und 3b sind an den korrespondierenden Anschlussstellen J1-J5 als verbunden zu verstehen. Ein Bezug auf diese Figuren erfolgt mit der Bezeichnung Fig. 3a/b.
In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. They show:
Fig. 1
a first embodiment of a protection circuit according to the invention;
Fig. 2
a second embodiment of a protection circuit according to the invention; and
Fig. 3a / b
A third embodiment of a protection circuit according to the invention. This third embodiment is divided for reasons of space on the Fig. 3a and Fig. 3b. The circuit parts of Fig. 3a and 3b are to be understood as connected at the corresponding connection points J1-J5. A reference to these figures is made with the name Fig. 3a / b.

Im Folgenden werden für gleiche und gleichwirkende Elemente der verschiedenen Ausführungsbeispiele durchweg gleiche Bezugszeichen verwendet.In the following, the same reference numerals are used throughout for identical and equivalent elements of the various embodiments.

Hauptteil der Beschreibung:Main part of the description:

Bei der in Fig. 1 dargestellten Schutzschaltung stellt ein Kondensator C1 eine Spannung Uz bereit, die zur Versorgung der nachfolgenden Schaltungsanordnung dient. Eine Halbbrückenanordnung umfaßt einen ersten Schalter S1 und einen zweiten Schalter S2. Die Ansteuerungen der Schalter S1 und S2 sind dem Fachmann hinlänglich bekannt und deshalb aus Übersichtlichkeitsgründen in Fig. 1 nicht dargestellt. Die Halbbrückenanordnung speist über einen Auskoppelkondensator C2 eine Leuchtstofflampe LA mit einer ersten Wendel W1 und einer zweiten Wendel W2. Die Leuchtstofflampe LA ist mit einer Zündschaltung Zs verbunden, die ausgelegt ist, eine Zündung der Lampe LA zu bewirkenIn the protection circuit shown in Fig. 1, a capacitor C1 provides a voltage Uz, which serves to supply the subsequent circuit arrangement. A half-bridge arrangement comprises a first switch S1 and a second switch S2. The controls of the switches S1 and S2 are well known to those skilled in the art and therefore not shown in FIG. 1 for reasons of clarity. The half-bridge arrangement feeds via a decoupling capacitor C2 a fluorescent lamp L A with a first filament W1 and a second filament W2. The fluorescent lamp L A is connected to an ignition circuit Zs, which is designed to cause an ignition of the lamp L A

Der Mittelpunkt der Halbbrückenanordnung bildet einen ersten Referenzpunkt A, der über eine Lampendrossel LD mit der Lampe LA verbunden ist. Der wendelseitige Anschluß des Auskoppelkondensators C2 bildet einen zweiten Referenzpunkt B. Die Potentiale beider Referenzpunkte A, B werden einem Vergleicher VG zugeführt, dessen Ausgang mit einem Detektionskondensator C3 verbunden ist. Die am Kondensator C3 abfallende Spannung UC3 wird einer Auswerteschaltung As zugeführt, die bei Überschreiten eines vorbestimmten Spannungspegels eine Deaktivierung der Halbbrückenanordnung herbeiführt. Am Lebensdauerende der Lampe LA verschieben sich die Potentiale der Referenzpunkte A und B infolge des Fehlens von Emitter auf einer der beiden Wendelelektroden W1, W2 und der damit einsetzenden Erhöhung der Austrittsarbeit einer der beiden Wendelelektroden W1, W2, selbst wenn die Erhöhung der Austrittsarbeit nur minimal ist. Die Potentialdifferenz zwischen den beiden Referenzpunkten führt zum Laden des Kondensators C3 und damit zum Aufbau der Spannung UC3. Sofern diese einen bestimmten Wert überschreitet, wird durch die Auswerteschaltung As die Halbbrückenanordnung abgeschaltet und damit eine Überhitzung im Wendelbereich verhindert. Im Normalbetrieb liegen die Referenzpunkte A und B im Mittel auf der halben Spannung UZ. Der Auskoppelkondensator C2 könnte auch an anderer Stelle angeordnet sein, beispielsweise zwischen der Lampendrossel LD und der Wendelelektrode W2. In der vorliegenden Anordnung würde bei einem Verbrauch des Emitters auf der Wendelelektrode W1 vor einem Verbrauch des Emitters auf der Wendelelektrode W2 die Spannung an der Wendelelektrode W1 ansteigen, was zu einem Steigen der am Kondensator C2 abfallenden Spannung führen würde. Dadurch würde das Potential B gegenüber dem Potential A ansteigen. Bei einem Verbrauch des Emitters auf der Wendelelektrode W2 vor einem Verbrauch des Emitters auf der Wendelelektrode W1 würde das Potential am Referenzpunkt A gegenüber dem Potential am Referenzpunkt B abfallen.The center of the half-bridge arrangement forms a first reference point A, which is connected via a lamp inductor L D with the lamp L A. The winding-side terminal of the decoupling capacitor C2 forms a second reference point B. The potentials of both reference points A, B are fed to a comparator V G whose output is connected to a detection capacitor C3. The across the capacitor C3 C3 voltage U is fed to an evaluation circuit AS, which causes a deactivation of the half-bridge arrangement upon exceeding a predetermined voltage level. At the end of the life of the lamp L A , the potentials of the reference points A and B due to the absence of emitter on one of the two helical electrodes W1, W2 and the thus increasing increase the work function of one of the two helical electrodes W1, W2, even if the increase in work function only is minimal. The potential difference between the two reference points leads to the charging of the capacitor C3 and thus to the build-up of the voltage U C3 . If this exceeds a certain value, the half-bridge arrangement is switched off by the evaluation circuit As and thus an overheating in the coil area prevented. In normal operation, the reference points A and B are on average at half the voltage U Z. The decoupling capacitor C2 could also be arranged elsewhere, for example between the lamp inductor L D and the filament electrode W2. In the present arrangement, consumption of the emitter on the helical electrode W1 prior to consumption of the emitter on the helical electrode W2 would increase the voltage at the helix electrode W1, resulting in a rise in the voltage across the capacitor C2. As a result, the potential B would increase in relation to the potential A. When consumption of the emitter on the helical electrode W2 prior to consumption of the emitter on the helical electrode W1, the potential at the reference point A would drop from the potential at the reference point B.

Eine Relamping-Funktion wird dadurch realisiert, daß die Spannung am Kondensator C3 zurückgesetzt wird, indem die beiden Eingänge des Vergleichers mit identischem Potential beaufschlagt werden. Hierzu ist der erste Referenzpunkt A über einen Widerstand R1, der zweite Referenzpunkt B über einen Widerstand R2 mit dem Minuspol der Spannung UZ verbunden. Der Pluspol der Spannung UZ ist einerseits über einen Widerstand R3, der den Kondensator C2 überbrückt, mit dem Referenzpunkt B verbunden, andererseits über einen Widerstand R4 mit dem Referenzpunkt A. Durch geeignete Dimensionierung der beiden Spannungsteiler R4, R1 sowie R3, R2 kann erreicht werden, daß die Potentiale an den Referenzpunkten A, B bei entnommener Lampe LA identisch sind und damit zu einem Zurücksetzen der End-of-Life-Detektion führen. Insbesondere ergibt sich bei einer Dimensionierung des Verhältnisses aus dem Widerstand R1 zum Widerstand R4 sowie aus dem Widerstand R2 zum Widerstand R3 gleich 1, daß sich die halbe Spannung von UZ an den beiden Referenzpunkten A, B einstellt.A relamping function is realized by resetting the voltage across the capacitor C3 by applying identical potential to the two inputs of the comparator. For this purpose, the first reference point A via a resistor R1, the second reference point B via a resistor R2 to the negative pole of the voltage U Z is connected. The positive pole of the voltage U Z is on the one hand via a resistor R3, which bridges the capacitor C2, connected to the reference point B, on the other hand via a resistor R4 to the reference point A. By suitable dimensioning of the two voltage divider R4, R1 and R3, R2 can be achieved be that the potentials at the reference points A, B are identical when removed lamp L A and thus lead to a reset of the end-of-life detection. In particular, given a dimensioning of the ratio of the resistance R1 to the resistance R4 and from the resistance R2 to the resistance R3 equal to 1, that half the voltage of U Z at the two reference points A, B is established.

Bei der in Fig. 2 dargestellten Ausführungsform sind die Widerstände R1 und R2 in zwei Teilwiderstände R11, R12 bzw. R21, R22 aufgeteilt. Durch geeignete Dimensionierung der Teilwiderstände kann sichergestellt werden, daß der Großteil der Spannungen, die an den Referenzpunkten A, B anliegen, an den Teilwiderständen R11 bzw. R21 abfallen. Demnach wird der Vergleicher VG nur mit Niederspannungen beaufschlagt und kann daher mit weniger spannungsfesten Bauelementen realisiert werden.In the embodiment shown in FIG. 2, the resistors R1 and R2 are divided into two partial resistors R11, R12 and R21, R22. By suitable dimensioning of the partial resistors it can be ensured that the majority of the voltages applied to the reference points A, B drop off at the partial resistors R11 and R21. Accordingly, the comparator V G is subjected only to low voltages and can therefore be realized with less voltage-resistant components.

Bei der in den Fig. 3a/b dargestellten Ausführungsform ist eine Gesamtschaltung zum Betrieb einer Leuchtstofflampe dargestellt, die über die Klemmen K1 und K2 an ein Stromnetz angeschlossen werden kann. Nach der Klemme K1 ist eine Sicherung SI angeordnet, darauf folgt ein Siebkreis umfassend einen Kondensator C4 und eine Induktivität L3 bevor das Netzsignal in einem Netzgleichrichter NGR gleichgerichtet wird. Das gleichgerichtete Ausgangssignal des Netzgleichrichters NGR wird in dem Kondensator C1 zwischengespeichert und dient zur Versorgung der nachfolgenden Schaltungsanordnung. Der Widerstand R22 von Fig. 2 ist aufgeteilt in zwei Teilwiderstände R221 und R222. Dem Kondensator C3 ist ein Widerstand R5 parallel geschaltet, der eine Entladung des Kondensators C3 ermöglicht. Dem Widerstand R12 ist ein Kondensator C5 parallel geschaltet, während der Serienschaltung aus den Widerständen R221 und R222 ein Kondensator C6 parallel geschaltet ist. Durch diese Maßnahmen ist sichergestellt, daß an den Basen zweier im Vergleicher enthaltener Schaltelemente T1, T2 Gleichspannungssignale anliegen. Die Steuerelektrode des Schaltelements T1 ist mit dem Verbindungspunkt D zwischen dem Widerstand R21 und dem Widerstand R221 verbunden. Mit dem Verbindungspunkt C der Widerstände R11 und R12 ist zum einen die Bezugselektrode des Schaltelements T1, zum anderen die Steuerelektrode des Schaltelements T2 verbunden. Die Bezugselektrode des Schaltelements T2 ist mit dem Verbindungspunkt E zwischen den Widerständen R221 und R222 verbunden. Die Arbeitselektroden beider Schaltelemente T1, T2 sind über einen Widerstand R6 mit dem Verbindungspunkt F verbunden, an dem der Kondensator C3 angeschlossen ist. Da am Referenzpunkt A die Spannung konstant ist, läßt sich durch geeignete Wahl der Widerstände R11 und R12 beispielsweise am Verbindungspunkt C eine Spannung von 15 V einstellen. Durch geeignete Dimensionierung der Widerstände R21, R221 und R222 läßt sich bei Normalbetrieb, d.h. das Potential am Punkt A ist gleich dem Potential am Punkt B, eine Spannung einstellen, die am Punkt D 18 V und am Punkt E 12 V beträgt. In diesem Zustand sind die beiden Schaltelemente T1, T2 gesperrt.In the embodiment shown in FIGS. 3a / b, an overall circuit for operating a fluorescent lamp is shown, which can be connected to a power supply via the terminals K1 and K2. After the terminal K1 a fuse SI is arranged, followed by a filter circuit comprising a capacitor C4 and an inductor L3 before the mains signal is rectified in a power rectifier N GR . The rectified output signal of the mains rectifier N GR is buffered in the capacitor C1 and serves to supply the subsequent circuit arrangement. Resistor R22 of FIG. 2 is divided into two partial resistors R221 and R222. The capacitor C3 is a resistor R5 connected in parallel, which allows a discharge of the capacitor C3. The resistor R12 is connected in parallel with a capacitor C5, while the series connection of the resistors R221 and R222 is connected in parallel with a capacitor C6. These measures ensure that DC signals are present at the bases of two switching elements T1, T2 contained in the comparator. The control electrode of the switching element T1 is connected to the connection point D between the resistor R21 and the resistor R221. Connected to the junction point C of the resistors R11 and R12 is the reference electrode of the switching element T1 and the control electrode of the switching element T2. The reference electrode of the switching element T2 is connected to the connection point E between the resistors R221 and R222. The working electrodes of both switching elements T1, T2 are connected via a resistor R6 to the connection point F, to which the capacitor C3 is connected. Since the voltage is constant at the reference point A, a voltage of 15 V can be set by suitable selection of the resistors R11 and R12, for example at the connection point C. By suitable dimensioning of the resistors R21, R221 and R222 can be set in normal operation, ie the potential at point A is equal to the potential at point B, a voltage which is at point D 18 V and at point E 12 V. In this state, the two switching elements T1, T2 are disabled.

Wenn nun die Spannung am Referenzpunkt B steigt, steigen die Spannungen an den Punkten D und E. Wenn die Spannung am Punkt D größer als die Spannung am Punkt C wird, bleibt das Schaltelement T1 nach wie vor gesperrt. Wenn jedoch die Spannung am Punkt E größer als die Spannung am Punkt C wird, beginnt das Schaltelement T2 zu leiten, wodurch der Kondensator C3 über dem Widerstand R6 geladen wird.Now, when the voltage at the reference point B increases, the voltages rise at the points D and E. When the voltage at the point D becomes greater than the voltage at the point C, the switching element T1 remains locked. However, when the voltage at point E becomes greater than the voltage at point C, switching element T2 begins to conduct, charging capacitor C3 across resistor R6.

Für den Fall, daß die Spannung am Punkt B sinkt, beginnt das Schaltelement T1 zu leiten, wenn die Spannung am Punkt D kleiner wird als die Spannung am Punkt C. Solange die Spannung am Punkt E kleiner ist als die Spannung am Punkt C, bleibt das Schaltelement T2 gesperrt. Durch das Leiten des Schaltelements T1 wird der Kondensator C3 wiederum über den Widerstand R6 geladen. Mit der Höhe der Spannungsdifferenz zwischen den Potentialpunkten C und D bzw. C und E lässt sich die Schaltschwelle und damit der Grad der Asymmetrie, bei welchem die Abschaltung erfolgt, zusätzlich einstellen. Die Spannung am Punkt F, die mit dem Ladezustand des Kondensators C3 korrespondiert, wird über eine Diode D1 und eine Zenerdiode Z1 an einen Auslösepotentialpunkt G in einem Halteglied HG übertragen. Das Halteglied HG wird versorgt über die in einem Kondensator C7 einer Startschaltung ST gespeicherte Ladung. Sobald die Spannung am Punkt G steigt, schaltet das Schaltelement T4 durch. Sobald das Schaltelement T4 durchgeschaltet hat, schaltet das Schaltelement T3 durch und liefert so den Haltestrom für ein auf diese Weise selbsthaltendes Halteglied. Der Widerstand R8 in Kombination mit dem Kondensator C8 sowie der Widerstand R9 in Kombination mit dem Kondensator C9 sorgen für die Beseitigung von Störungen, wodurch ein versehentliches Aktivieren des Halteglieds verhindert wird. Dadurch, daß das Schaltelement T4 leitet, sinkt das Potential am Punkt I auf 0 V. Die beiden Schalter S1 und S2 der Halbbrückenschaltung verfügen über jeweilige Ansteuerschaltungen AS1, AS2. Jede Ansteuerschaltung AS1, AS2 umfaßt eine Induktivität L1, L2, die mit der Lampendrossel LD gekoppelt ist. Sobald das Potential an Punkt I auf 0 V fällt, beginnt die Diode D2 zu leiten und erdet damit das über die Induktivität L2 in die Ansteuerschaltung AS2 eingespeiste Signal, so daß der Schalter S2 nicht mehr angesteuert wird. Dies führt auch zu einem Abschalten des Schalters S1.In the event that the voltage at point B decreases, the switching element T1 begins to conduct when the voltage at point D becomes smaller than the voltage at point C. As long as the voltage at point E is less than the voltage at point C remains the switching element T2 locked. By conducting the switching element T1, the capacitor C3 is again charged via the resistor R6. With the height of the voltage difference between the potential points C and D or C and E, the switching threshold and thus the degree of asymmetry at which the shutdown occurs, can be additionally set. The voltage at the point F, which corresponds to the state of charge of the capacitor C3, is transmitted via a diode D1 and a Zener diode Z1 to a tripping potential point G in a holding member HG. The holding member HG is supplied via the charge stored in a capacitor C7 of a starting circuit ST. As soon as the voltage rises at the point G, the switching element T4 turns on. As soon as the switching element T4 has switched through, the switching element T3 turns on and thus supplies the holding current for a retaining element that is self-holding in this way. The resistor R8 in combination with the capacitor C8 and the resistor R9 in combination with the capacitor C9 provide for the elimination of interference, thereby preventing accidental activation of the holding member. Characterized in that the switching element T4 conducts, the potential at point I drops to 0 V. The two switches S1 and S2 of the half-bridge circuit have respective drive circuits A S1 , A S2 . Each drive circuit A S1 , A S2 comprises an inductance L1, L2, which is coupled to the lamp inductor L D. As soon as the potential at point I falls to 0 V, the diode D2 begins to conduct, thus grounding the signal fed via the inductance L2 into the drive circuit A S2 , so that the switch S2 is no longer activated. This also leads to a shutdown of the switch S1.

Mit dem Punkt G des Halteglieds HG ist weiterhin eine Zündspannungsbegrenzungsschaltung ZSB verbunden. Sie umfaßt einen Meßwiderstand R10, der seriell zum Schalter S2 angeordnet ist. Das Potential am Punkt J, d.h. die am Widerstand R10 abfallende Spannung ist proportional zum Zündstrom und damit proportional zur Zündspannung. Die Zündspannungsbegrenzungsspannung ZSB hat die Aufgabe, beispielsweise bei Luftziehern eine Zerstörung der Zündschaltung ZS zu verhindern.. Die Zündschaltung ZS umfaßt zwei Kondensatoren C10 und C11 sowie einen Kaltleiter PTC1.With the point G of the holding member H G is further connected a Zündspannungsbegrenzungsschaltung Z SB . It comprises a measuring resistor R10, which is arranged in series with the switch S2. The potential at the point J, that is, the voltage dropping across the resistor R10 is proportional to the ignition current and thus proportional to the ignition voltage. The Zündspannungsbegrenzungsspannung Z SB has the task, for example, to prevent destruction of the ignition circuit Z S in air pullers .. The ignition circuit Z S comprises two capacitors C10 and C11 and PTC1 PTC.

Der Widerstand R14 dient dazu, eine zeitliche Verzögerung des Ansprechverhaltens der Zündspannungsbegrenzungschaltung zu bewirken. Über die Dioden D3 und Z2 kann der Pegel eingestellt werden, bei dem eine Zündspannungsbegrenzung durch Beaufschlagung des Punkts G des Halteglieds HG und damit eine Abschaltung der Halbbrückenanordnung ausgeführt wird. Die Spannung am Widerstand R10 wird gesiebt durch den Widerstand R9 und den Kondensator C9. Selbstverständlich kann der Pegel der kritischen Zündspannung auch durch den Wert des Widerstands R10 beeinflußt. Die Diode D3 schützt das Halteglied HG überdies vor negativen Spannungsspitzen. Durch die Zündspannungsbegrenzungsschaltung ZSB lassen sich die Bauelemente der Zündschaltung ZS und die Lampendrossel LD kleiner dimensionieren.The resistor R14 serves to cause a time delay of the response of the Zündspannungsbegrenzungschaltung. Via the diodes D3 and Z2, the level can be set at which a Zündspannungsbegrenzung by acting on the point G of the holding member H G and thus a shutdown of the half-bridge arrangement is performed. The voltage across resistor R10 is filtered by resistor R9 and capacitor C9. Of course, the level of the critical ignition voltage can also be influenced by the value of the resistor R10. The diode D3 protects the holding member H G also against negative voltage spikes. By the Zündspannungsbegrenzungsschaltung Z SB , the components of the ignition circuit Z S and the lamp inductor L D can be made smaller.

Claims (13)

  1. Protective circuit for a fluorescent lamp (LA) with a first and a second lamp filament (W1, W2), comprising:
    a DC voltage source (UZ) with a positive and a negative pole;
    a half-bridge arrangement with a first and a second switch (S1, S2), the half-bridge arrangement being fed by the DC voltage source (UZ), and the first and the second switch (S1, S2) being interconnected to form a first reference point (A), the first reference point (A) being connected to the negative pole via a first resistor (R1);
    a decoupling capacitor (C2) that is arranged in a serial connection between the half-bridge arrangement and the first or the second lamp filament (W1; W2), the connection of the decoupling capacitor (C2) on the filament side forming a second reference point (B) that is connected to the negative pole via a second resistor (R2);
    a comparator (VG) that has a first and a second input and an output, the first input being connected to the first reference point (A), and the second input being connected to the second reference point (B), the output being connected to the negative pole via a detection capacitor (C3);
    an evaluation circuit (AS) with the aid of which the voltage (UC3) dropping across the detection capacitor (C3) can be evaluated in order to deactivate the half-bridge arrangement upon overshooting of a predetermined voltage level;
    characterized in that
    it further comprises a third resistor (R3) that bridges the decoupling capacitor (C2), and a fourth resistor (R4) that connects the first reference point (A) to the positive pole of the DC voltage source (UZ), the first, the second, the third and the fourth resistor (R1, R2, R3, R4) being selected such that the first and the second reference point (A, B) are at the same potential without the fluorescent lamp (LA) inserted.
  2. Protective circuit according to Claim 1,
    characterized in that
    the ratio of the first resistor (R1) to the fourth resistor (R4) is of the same magnitude as the ratio of the second resistor (R2) to the third resistor (R3), in particular is equal to 1.
  3. Protective circuit according to Claim 1 or 2,
    characterized in that
    the first resistor (R1) comprises a first and a second component resistor (R11, R12) connected together in series, and the second resistor comprises a third and a fourth component resistor (R21, R22) connected together in series, the first reference point (A) being connected to the tie point of the first component resistor (R11) and the fourth resistor (R4), and the second reference point (B) being connected to the tie point of the third resistor (R3) and the third component resistor (R21), and
    the first input of the comparator (VG) being connected to the tie point between the first and second component resistor (R11, R12), and the second input of the comparator (VG) being connected to the tie point between the third and the fourth component resistor (R21, R22).
  4. Protective circuit according to Claim 3,
    characterized in that
    the ratio of the sum of the first and second component resistor (R11, R12) to the fourth resistor (R4) is equal to the ratio of the sum of the third and fourth component resistor (R21, R22) to the third resistor (R3), in particular is equal to 1.
  5. Protective circuit according to one of the preceding claims,
    characterized in that
    the comparator (VG) comprises a first and a second switching element (T1, T2), which in each case comprise a working, a control and a reference electrode,
    the fourth component resistor (R22) comprising a fifth and a sixth component resistor (R221, R222) connected together in series,
    the tie point between the first and the second component resistor (R11, R12) being connected to the reference electrode of the first (T1) and to the control electrode of the second switching element (T2), the tie point between the third component resistor (R21) and the fifth component resistor (R221) being connected to the control electrode of the first switching element (T1), the tie point between the fifth and the sixth resistor (R221, R222) being connected to the reference electrode of the second switching element (T2), and the working electrode of the first switching element (T1) and the working electrode of the second switching element (T2) being interconnected and being connected to frame via a series circuit composed of a fifth resistor (R6) and the detection capacitor (C3).
  6. Protective circuit according to Claim 5,
    characterized in that
    the ratio of the fourth resistor (R4) to the sum of the first and the second component resistor (R11, R12) is equal to the ratio of the third resistor (R3) to the sum of the third, fifth and sixth component resistor (R21, R221, R222), in particular is equal to 1.
  7. Protective circuit according to one of the preceding claims,
    characterized in that
    the evaluation circuit (AS) comprises a holding element (HG) with a trigger potential point (G) and is designed in such a way that as soon as the trigger potential point (G) has assumed a predetermined potential, in particular owing simply to a single pulse, the holding element (HG) can be activated in order to deactivate the half-bridge circuit until a resetting operation is triggered by removal of the fluorescent lamp (LA).
  8. Protective circuit according to Claim 7,
    characterized in that
    arranged between the comparator (VG) and the trigger potential point (G) of the holding element (HG) is a first threshold component (Z1), in particular a Zener diode, with the aid of which it is possible to set the threshold upon the overshooting of which deactivation of the half-bridge circuit is triggered.
  9. Protective circuit according to one of Claims 7 or 8,
    characterized in that
    a starting-voltage-limiting circuit (ZSB) is connected to the trigger potential point (G) in such a way that the holding element (HG) can be activated upon detection of an overshooting of a predetermined starting voltage.
  10. Protective circuit according to Claim 9,
    characterized in that
    the starting-voltage-limiting circuit (ZSB) has a measuring element (R10) for measuring a variable proportional to the starting current, such that the value of this variable can be used to activate the holding element (HG).
  11. Protective circuit according to Claim 10,
    characterized in that
    arranged between a potential point (J) of the starting-voltage-limiting circuit (ZSB) whose potential is proportional to the starting current, and the trigger potential point of the holding element (HG) is a second threshold component (Z2), in particular a Zener diode, with the aid of which it is possible to set the threshold upon the overshooting of which a deactivation of the half-bridge circuit is triggered.
  12. Protective circuit according to one of Claims 10 or 11,
    characterized in that
    the measuring element (R10) is a resistor which is arranged in series with one of the half-bridge switches (S1; S2).
  13. Protective circuit according to one of the preceding claims,
    characterized in that
    it also comprises suitable filter circuits (C6, C5, C8, R8, C9, R9, R14) in order to provide DC voltages for evaluation at the reference and potential points (A, B, G, J).
EP02001285A 2001-02-20 2002-01-17 Protective circuit for a fluorescent lamp Expired - Lifetime EP1233657B1 (en)

Applications Claiming Priority (2)

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DE10108138A DE10108138A1 (en) 2001-02-20 2001-02-20 Protection circuit for a fluorescent lamp
DE10108138 2001-02-20

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EP1233657A3 EP1233657A3 (en) 2006-05-24
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EP (1) EP1233657B1 (en)
CN (1) CN100477880C (en)
AT (1) ATE368367T1 (en)
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US20020114114A1 (en) 2002-08-22
US6650514B2 (en) 2003-11-18
TW540255B (en) 2003-07-01
CN100477880C (en) 2009-04-08
EP1233657A2 (en) 2002-08-21
CN1374824A (en) 2002-10-16
EP1233657A3 (en) 2006-05-24
DE10108138A1 (en) 2002-08-29
CA2373571A1 (en) 2002-08-20
ATE368367T1 (en) 2007-08-15

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