EP0746185A1 - Monitoring circuit for a two lamp system - Google Patents

Abstract

The circuit monitors the function of at least two fluorescent lamps (LL1,LL2), using a detection network (R1,..R7, C1,D1) connected to the lamp current circuits and coupled to a control circuit (5) for a switch (V3,RE,S1) allowing the lamps to be connected in parallel upon detection of lamp failure. The control circuit has a storage capacitor coupled to the detection network as the input element, its charge corresponding to the voltage across the monitored lamp current circuits, with two alternatively-activated switch stages (VI,R8,..R10,C3 ; V2,D3,D4, R11,...R14, C4), with different response thresholds used to provide the switching signals for the controlled switch.

Description

The invention relates to a circuit arrangement according to the preamble of claim 1.

Luminaires often do not only have a single fluorescent lamp, so it is not uncommon to supply at least two lamp circuits together with a single electronic ballast. Such an application is described for example in EP-B1-0 146 683. The known circuit arrangement has a monitoring device for monitoring the lamp circuits for an error state in which high ignition voltage is impermissibly longer than a predetermined period of time. This can occur if one of the fluorescent lamps no longer ignites properly or leaks at the end of its service life. If this fault condition is determined, the monitoring device switches off an inverter of the electronic ballast and thus prevents the ignition voltage from being present again. Of course, this also switches off each of the connected, operable fluorescent lamps.

Obviously, the circuit arrangement known from EP-B1-0 146 683 has the disadvantage that the electronic ballast switches off, although, for. B. only a single fluorescent lamp is defective and properly working fluorescent lamps would still be operational. This disadvantage is remedied by a circuit arrangement known from EP-A-0 558 772 for operating a plurality of fluorescent lamps with one ballast. In addition to the monitoring device mentioned, it has a switching device which is arranged between the lamp chokes and the fluorescent lamps and by means of which the lamp circuits can be connected together to only one of the lamp chokes depending on a fault condition, in which one of the fluorescent lamps Ignition voltage is present for longer than a specified period of time. This period is shorter than the response delay of the monitoring device.

If one considers the lamp circuits as series resonance circuits, then this switching measure forms one from two series resonance circuits, it being irrelevant which of the two fluorescent lamps is deactivated. If the fluorescent lamp working correctly has ignited, the lamp current flows in this single resonant circuit without an inadmissibly high ignition voltage occurring. The result of this is that the monitoring device which responds with a delay switches off the inverter, although operable fluorescent lamps are still connected.

The known switching device is designed to be resettable, so that it deactivates itself when the defective fluorescent lamp is removed and falls back into its rest position. For this purpose, the criterion is used that the holding current of the switching device is halved when the defective fluorescent lamp, which up to that point still carries current through the lamp filaments, is removed. The switching device detects this change and falls back into the rest position. After changing the lamp, the normal operating state is thus automatically restored, in which both fluorescent lamps burn without the electronic ballast having to be switched off.

The known circuit arrangement is quite advantageous because, in the case of a multi-lamp electronic ballast, it enables the unimpeded operation of functional lamp circuits even when faults occur in one of the connected lamp circuits. However, the design of the known circuit arrangement has the disadvantage that its functional principle is implemented with the aid of a predetermined time grid, the boundary conditions of which are critical. It is obvious to a person skilled in the art that the response delay the monitoring device operating in the start / stop mode should not be chosen too large, because if the high ignition voltage is present too long if all lamp circuits fail. On the other hand, however, the switching device to be activated beforehand should not switch over prematurely to lamp operation on only one lamp inductor, but should have switched over again before the inverter of the electronic ballast is completely switched off. Although the time sequence of the individual circuit measures given in the known circuit arrangement is obvious, complex electrical adjustment measures are required so that possible circuit states may possibly be clearly excluded in such a narrow, critical time frame due to operating tolerances of the lamps on the one hand and component tolerances of the electronic ballast on the other hand .

The present invention is therefore based on the object, based on the considerations on which the known solution is based, of creating a further embodiment of a circuit arrangement of the type mentioned at the outset, with which the advantages of the known solution are achieved without having to accept the disadvantages thereof.

In a circuit arrangement of the type mentioned, this object is achieved according to the invention by the features described in the characterizing part of patent claim 1.

The solution according to the invention is based on the idea that the starting behavior of a functional fluorescent lamp takes place in a certain time pattern and that a sequential sequence of circuit measures in one of the possible and initially described fault cases of an inconvenient or incapable fluorescent lamp is useful to ensure at least the continued operation of functional fluorescent lamps , but it is not necessary it is also imperative to force the error monitoring into an appropriate time grid.

On the one hand, the solution according to the invention ensures a defined sequential sequence in the detection of the circuit states in the event of a lamp fault, but, in contrast to previously known solutions, does not base the control of the corresponding circuit states on a predetermined time grid. Rather, the individual monitoring steps are derived solely from the course or the instantaneous state of the ignition voltage, which is simulated as the charge state of a storage capacitor. The control circuit and the monitoring circuit are equipped with different voltage-dependent threshold values for the capacitor charge, so that they respond in succession to a high ignition voltage that is present for too long. The solution according to the invention is therefore reliable, but is still simpler in terms of circuitry and less expensive to manufacture than the known solution.

Developments of the invention are characterized in the subclaims.

• Figur 1 ein Blockschaltbild eines elektronischen Vorschaltgerätes zum parallelen Betreiben von zwei Leuchtstofflampen mit Überwachungseinrichtungen zum Umschalten der Betriebsweise bei einem Ausfall einer oder beider Leuchtstofflampen und
• Figur 2 ein Prinzipschaltbild der Überwachungseinrichtung nach Figur 1 zum Detektieren eines Lampenausfalles und davon abhängiger Umschaltung der Lampenstromkreise gemäß Figur 1 auf Einlampenbetrieb.

An embodiment of the invention is described below with reference to the drawing. It shows:

• Figure 1 is a block diagram of an electronic ballast for parallel operation of two fluorescent lamps with monitoring devices for switching the mode of operation in the event of a failure of one or both fluorescent lamps and
• FIG. 2 shows a basic circuit diagram of the monitoring device according to FIG. 1 for detecting a lamp failure and switching the lamp circuits according to FIG. 1 dependent on it to single-lamp operation.

A block diagram of an electronic ballast known per se for parallel operation of at least two fluorescent lamps LL1 and LL2 is shown in FIG. Therefore, FIG. 1 shows only schematically components of the electronic ballast, such as a line rectifier 1 with radio protection, to which line voltage un is supplied on the input side and which supplies a rectified line voltage u = to a step-up converter 2. Its output voltage uzw is offered to an inverter 3, which outputs a high-frequency, pulse-shaped output voltage uhb. The actual lamp circuits are connected to the output of this inverter 3. They contain two lamp chokes DR1 and DR2, which in the normal operating mode shown in FIG. 1 are each connected to one of the filaments of the two fluorescent lamps LL1 and LL2. Ignition capacitors CZ1 and CZ2 are connected in parallel to the discharge paths of the fluorescent lamps LL1 and LL2, respectively. As usual, a half-bridge capacitor CHB is provided in the reflux branch of the two lamp circuits.

A monitoring circuit 4 is also assigned to the lamp circuits, which detects a faulty operating state in which the high ignition voltage at at least one of the fluorescent lamps LL1 or LL2 is present for too long and then switches off the inverter 3. However, the only monitoring criterion is that the high ignition voltage is present for too long, so that the monitoring circuit 4 always switches off the inverter 3 even if only one of the fluorescent lamps LL1 or LL2 is working incorrectly with the filaments intact, ie. H. cannot be ignited.

Single lamp operation is not yet possible. To make this possible, a controlled switch S1 with a changeover contact s is additionally provided in the lamp circuits. This switch S1 is assigned a control circuit 5, which is integrated in the lamp circuits and detects the operating function of the fluorescent lamps LL1 and LL2.

The control circuit 5 detects an operating state in which the lamp ignition voltage on one of the fluorescent lamps LL1 or LL2 is present longer than specified, in any case before the monitoring circuit 4 responds. If this faulty operating state is determined, the control circuit 5 switches the switch S1. The changeover contact s disconnects one of the lamp circuits and places this lamp circuit in parallel with the other at the output of only one of the two lamp chokes, e.g. B. DR1. Thus, a single one is formed from two series resonance circuits, in which the two ignition capacitors CZ1 and CZ2 lie parallel to one another.

Due to this switching measure, it is irrelevant for the further operating function which of the two fluorescent lamps LL1 or LL2 is defective. It is therefore possible to operate only one fluorescent lamp, regardless of the reason for which the second fluorescent lamp was deactivated. This measure also allows the deactivated fluorescent lamp to be replaced during operation of the second and thus to remedy the fault without the electronic ballast having to be switched off.

The control circuit 5 is designed so that it resets itself after the fault has been remedied, i. H. as soon as the defective fluorescent lamp LL1 or LL2 is removed. By resetting the control circuit 5, the switch S1 is also switched back to the circuit state shown in FIG. 1, which restores the normal operating state and can also start the newly installed fluorescent lamp.

However, if a faulty operating state should have occurred in both monitored lamp circuits, the high ignition voltage cannot be eliminated even by switching to operation with only one fluorescent lamp.

Then the monitoring device 4 also responds and switches off the inverter 3.

FIG. 2 shows a circuit arrangement with its functionally essential elements as an example of the configuration of the control circuit 5. In order to establish the connection between the block diagram of FIG. 1 and the circuit arrangement of FIG. 2, the connection points of the control circuit 5 to the lamp circuits are denoted by a to d. The connections a and b are the connection points to the lamp chokes DR1 and DR2, the connections c and d designate the connection points to the filaments of the fluorescent lamps LL1 and LL2.

The connections c and d of the control circuit 5 assigned to the lamp filaments are brought together in a coupling point via series resistors R1 and R2. Analogously, the lamp chokes DR1 and DR2 are connected in parallel via a varistor R3 and R4 to a further coupling point. Both coupling points are connected via two further resistors R5 and R6 to a rectifier network connected to ground, consisting of the parallel connection of a first diode D1 with a smoothing capacitor C1 and a further resistor R7.

For clarification, the monitoring circuit 4, which is also known per se, is indicated in FIG. It is connected via a first connection e to the coupling point of the two series resistors R1 and R2, with a further connection f to an electrolytic capacitor C2, which is arranged via a further diode D2 between the connection point of the two further resistors R5 and R6 and ground reference potential. The monitoring circuit 4, as indicated schematically, has a double function. It supplies a regulated potential via the connection e as a starting condition for the lamp circuits. Via the connection f, on the other hand, a potential is tapped at the electrolytic capacitor C2, that at the lamp circuits applied voltage is proportional. If the high ignition voltage of both lamp circuits remains, although the control circuit 5 to be described has been activated because none of the fluorescent lamps LL1 or LL2 ignites in good time, the monitoring circuit 4 detects a faulty operating state of both lamp circuits and switches off the inverter 3.

Before a complete shutdown of the inverter 3 is carried out, it should be determined via the control circuit 5 whether this faulty operating state occurs in only one of the monitored lamp circuits or in both, ie. H. the inverter 3 should be prevented from being switched off as long as at least one of the monitored fluorescent lamps LL1 or LL2 is working properly. For this purpose, the potential at the electrolytic capacitor C2 is additionally evaluated.

For this purpose, a first transistor V1 is provided, which is at ground reference potential on the emitter side and is connected to the electrolytic capacitor C2 via a collector resistor R8. The base control of this first transistor V1 forms a voltage divider formed from a further resistor R9 and the parallel connection from a further resistor R10 and a further capacitor C3 and arranged between the electrolytic capacitor C2 and ground reference potential, the center tap of which is connected to the transistor base. This first transistor V1, with its collector resistor R8 and its switching path, is therefore parallel to the electrolytic resistor C2 and forms a switchable impedance.

Furthermore, a second transistor V2 is provided, the E-center of which, like that of the first transistor V1, is at the ground reference potential and the collector of which is connected to the base of the first transistor V1. The base of this second transistor V2 is on the one hand via another Capacitor C4 coupled to the ground reference potential, on the other hand connected to the electrolytic capacitor C2 via a series connection of a first Z diode D3 with a further resistor R11. Furthermore, the collector of the first transistor is connected via a further resistor R12 to a series circuit which is on the other hand at ground reference potential and consists of a second Zener diode D4 and two further resistors R13 and R14, the connection point between the latter being connected to the base of the second transistor V2 .

A parallel circuit consisting of a clamp diode D5, a further resistor R15 and a further capacitor C5, which forms the gate-source network for a field-effect transistor V3, is arranged between the connection point of the second Z-diode D4 with the further resistor R12 and ground reference potential . Its source electrode is connected to ground and its drain electrode is connected to the winding of a switching relay RE. Another Z diode D8 for voltage limitation is connected in parallel with this winding. For the power supply, the relay winding is connected to the output of the inverter 3 via a diode / capacitor network. As a voltage generator, this network converts the output voltage uhb of the inverter 3 into a smoothed DC voltage and supplies the operating voltage for the switching relay RE.

Finally, an embodiment of the switch S1 is indicated in FIG. 2, which in this case has two changeover contacts s1, s2. Connection contacts k1, k2 and k3 correspond to the connection contacts specified in the embodiment according to FIG. 1, so that the switching function described results here due to the series connection. The series connection of two relay contacts takes into account the conditions due to a high ignition voltage. Another connection contact k4 of the second switching element is connected to a clamp network consisting of two further diodes and connected to the output of the step-up converter 2. To this When the switch S1 is switched over, the potential between the contact connections k2 and k1, that is to say between the second lamp inductor DR2 and the second fluorescent lamp LL2, is limited to an admissible value and any residual energy still contained in the second lamp inductor is derived.

The function of the exemplary embodiment of the control circuit 5 shown in FIG. 2 and described above is explained in more detail below. If the electronic ballast is started to ignite both fluorescent lamps LL1 and LL2, a high ignition voltage builds up on them, which after the ignition process is reduced to the much lower operating voltage. If both fluorescent lamps ignite normally, this process takes place in a predetermined period of time 4. Neither the control circuit 5 nor the monitoring circuit 4 are activated. The switch S1 thus remains in the switching position shown in FIG. 1 in normal operation.

In the case of a fluorescent lamp LL1 or LL2 that does not ignite, the high ignition voltage in the lamp circuit in question is maintained longer than would be the case with a normal ignition process. The development of this functional state during the ignition phase, but also in the event of a lamp failure during the burning operation, is detected by the resistors R1 to R7, the first capacitor C1 and the two diodes D1, D2 as a charge growing on the electrolytic capacitor C2. The collector resistor R8 and the base control of the first transistor V1 with the resistors R9, R10 and the third capacitor C3 designed as a filter capacitor are dimensioned such that this first transistor V1 is very quickly turned on due to the potential building up on the electrolytic capacitor C2. The connection point between the collector resistor R8 of the first transistor V1 and the further resistor R12 is thus essentially pulled down to ground reference potential. This means that both the second transistor V2 the control circuit 5 and its field-effect transistor V3 are kept securely blocked. The controlled switch S1 thus remains in the position shown in FIGS. 1 and 2.

Normally, both fluorescent lamps LL1 and LL2 ignite in good time, so that the voltage on the fluorescent lamps goes back from the high value of the ignition voltage to normal, lower operating voltage. The switchable impedance lying parallel to the electrolytic capacitor C2 via the collector resistor R8 of the first transistor V2 and its switching path is dimensioned in such a way that the potential at the electrolytic capacitor C2 is kept at a defined, low potential in the normal operating mode of the lamp circuits, which is sufficient for the first transistor Keep V1 conductive. In the event of a fault, however, the potential at the electrolytic capacitor C2 continues to increase until the breakdown voltage of the first Z diode D3 is exceeded. The voltage at the base of the second transistor V2 is raised via the voltage divider R11, R14, so that the latter is controlled in a conductive manner and switches off the first transistor V1. This increases the potential at the collector of the first transistor V1, i. H. at the connection point of its collector resistor R8 with the further resistor R12. This potential shift increases the gate-source voltage at the field effect transistor V3, so that it opens and the relay RE draws current and the controlled switch S1 closes. The changeover contacts s1, s2 of the controlled switch S1 are thus actuated and the electronic ballast is switched to 1-lamp operation.

In the event of a failure of both lamp circuits, a high ignition voltage remains, so the potential at the electrolytic capacitor C2 continues to increase despite this switching measure. This ultimately leads to the monitoring circuit 4 being activated, the response threshold of which is clearly above the breakdown voltage of the first Z diode D3 of the control circuit 5. In this case the Inverter 3 of the electronic ballast reset by the monitoring circuit 4.

Usually, however, not both lamp circuits fail at the same time, so that in the event of a fault, it is sufficient to switch the controlled switch S1 using the control circuit 5 and thus to operate the electronic ballast in the 1-lamp operating mode. In this operating state, the potential at the electrolytic capacitor C2 drops, but it is still sufficient to keep the control circuit 5 activated. This is ensured via the second Zener diode D4 and the voltage divider R13, R14 connected to it in that this second Zener diode D4 has a significantly lower breakdown voltage than the second Zener diode D3.

If the deactivated fluorescent lamp is now removed from the lamp circuit, the potential at the electrolytic capacitor C2 drops further. The breakdown voltage of the second Zener diode D4 is also fallen below, so that it blocks and consequently the second transistor V2 is also deactivated. The first transistor V1 thus opens and in turn blocks the field effect transistor V3. The relay RE is de-energized and the controlled switch S1 falls back into its position shown in FIGS. 1 and 2. The replaced fluorescent lamp can thus be started normally without the electronic ballast having to be reset even briefly.

For the sake of simplicity, the described embodiment referred to the operation of two fluorescent lamps, which is the normal case. Now, however, a user could also want to operate a 2-lamp luminaire with only one lamp. The circuit arrangement described offers him this possibility without manipulation of the ballast. On the other hand, the expert is familiar with, such as. B. also emerges from the introduction mentioned EP-A-0 558 772 to operate more than two fluorescent lamps with a ballast.

This publication shows in detail which circuit measures would have to be taken for this. Therefore, there is no longer any need for a detailed description of this.

Claims (5)

Circuit arrangement for operating at least one, preferably two, fluorescent lamps (LL1, LL2) using an electronic ballast (1, 2, 3), at the outputs of which the fluorescent lamps on the one hand each have a lamp inductor (DR1, DR2) and on the other hand have a common half-bridge capacitor (CHB ) are connected and a switching device (S1, 5) arranged between the lamp chokes and the fluorescent lamps, by means of which the lamp circuits can be connected in parallel depending on an error condition in which the ignition voltage is applied to one of the fluorescent lamps for longer than a predetermined period of time and a control circuit for this purpose (5), which comprises a detection network connected to the lamp circuits (R1 to R7, C1, D1) for detecting the fault state and a switch (V3, RE, S1) connected to the control circuit and reversed by it in the fault state, characterized in that the control circuit as an input element has a storage capacitor (C2) connected to the detection network, the charge state of which corresponds to the profile of the voltage across the monitored lamp circuits, and furthermore this capacitor has two switching stages (V1, R8 to R10, C3 or V2, D3, D4, R11) that can be activated alternatively to one another to R14, C4), each with a lower or, in comparison, a higher voltage-dependent response threshold for generating a blocking or changeover signal for the controlled switch. Circuit arrangement according to Claim 1, characterized in that the storage capacitor is designed as a voltage-proof electrolytic capacitor (C2). Circuit arrangement according to one of claims 1 or 2, characterized in that the first switching stage (V1, R8 to R10, C3) of the control circuit (5) a first Transistor (V1) comprises a collector resistor (R8), which is connected together with the switching path of this transistor to the storage capacitor (C2) in parallel against ground reference potential and that the connection point between this collector resistor and the collector of the transistor via a coupling resistor (R12) with the Output of the control circuit is connected. Circuit arrangement according to Claim 3, characterized in that the second switching stage (V2, D3, D4, R11 to R14, C4) of the control circuit (5) has a second transistor (V2), across the switching path of which the base of the first transistor (V1) is on Ground reference potential is set and its base network is connected to the storage capacitor (C2) with a predetermined breakdown voltage via a first Z diode (D3) and that a second Z diode (D4) is arranged between the output of the control circuit and the base of this second transistor, whose breakdown voltage is lower than that of the first Zener diode (D3). Circuit arrangement according to one of Claims 1 to 4, characterized in that, in addition to the control circuit (5), a monitoring circuit (4) likewise connected to the storage capacitor (C2) for stopping an inverter (3) of the electronic ballast in one by activating the controlled switch (S1) unrecoverable error state is provided with a voltage-dependent activation threshold that is clearly higher than the response threshold of the control circuit or the breakdown voltage of its first Zener diode (D3).

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