EP2257134B1 - Switching assembly for operating a series connection of at least two low pressure gas discharge lamps and method for same - Google Patents

Description

description

Circuit arrangement for operating a series circuit of at least two low-pressure gas discharge lamps and corresponding method

Technical area

The invention relates to a circuit arrangement for operating a series connection of at least one first and one second low-pressure gas discharge lamp, having an input with a first and a second input terminal for applying an AC supply voltage, an output having at least a first terminal arrangement, the first and a second terminal pair for connecting the first low-pressure gas discharge lamp, and a second connection arrangement, which has a first and a second terminal pair for connecting the second low-pressure gas discharge lamp, wherein a first terminal of the second terminal pair of the first terminal arrangement with a first terminal of the first terminal pair of the second terminal arrangement is coupled, a resonant circuit having a coupled between the first input terminal and a first terminal of the first terminal pair of the first terminal arrangement resonant choke and a resonance capacitor r, which is coupled between the first terminal pair of the first terminal arrangement and the second terminal pair of the second terminal arrangement. The invention also relates to a method of operating a series circuit of at least a first and a second low-pressure gas discharge lamp on such a circuit arrangement.

State of the art

Circuit arrangements for operating a series circuit of a plurality of low-pressure gas discharge lamps are already known from the prior art. Such circuitry includes a resonant circuit including a resonant choke and a resonant capacitor; the resonance capacitor is connected in parallel with the series connection of the gas discharge lamps. Furthermore i.a. at least one so-called sequence start capacitor, which is connected in the series connection of two lamps in parallel with one of the two lamps. This allows the reduction of the effectively required ignition voltage for the series connection of the lamps, since up to the ignition of the non-capacitively bridged lamp almost all over the series connection voltage applied to this lamp and this is ignited in front of the other lamp. This ensures sequential ignition of the lamps (sequence), and the necessary Gesamtzündspannung for this configuration results approximately from the ignition voltage plus the burning voltage of a lamp. The disadvantage here is the fact that even during the preheating of the lamps, the total voltage across the lamps practically applied to a lamp. This value must not exceed a maximum value, otherwise the lamps will ignite before sufficient heating of the electrodes and the switching resistance of the lamps will be very negatively affected.

In the present case, the interest is in particular the preheating of electrodes of the gas discharge lamps. It is state of the art to use additional heating coils on the resonance choke for this purpose. By such an approach However, on the one hand, not inconsiderable continuous heating powers occur in the electrodes, which adversely affects the efficiency of the entire system including the circuit arrangement and the gas discharge lamps. On the other hand, several heating coils - three additional heating coils are usually used in a series connection of two gas discharge lamps - consuming to wrap, lead and isolate. In particular, the isolation of many additional heating coils is costly. If special throttle valves are used, which provide separate chambers for insulating the heating windings, significantly less winding space is available for the main winding of the resonance choke, and it is necessary to use thinner and thus higher-resistance wire. This generally has considerable thermal problems with this component.

It is also known to use additional heating circuits for the preheating of electrodes of the gas discharge lamps. This is based on the disclosure of the document DE 44 25 859 A1 directed. The circuit arrangement described in this document comprises a heating circuit with the aid of which the electrodes of two gas discharge lamps can be preheated. Such a heating circuit has, for a series connection of two lamps, a separate heating transformer, a bridge rectifier, two transistors (one of which is a voltage-proof power supply), a plurality of diodes, as well as a plurality of ohmic resistors. With such a heating circuit, it is possible to ensure sufficient preheating of the electrodes of the gas discharge lamps. However, it is a special challenge to reliably pre-heat the electrodes to achieve at least two series-connected gas discharge lamps without having to use a variety of additional components.

In Scripture US 4 145 638 (Kaneda ) discloses an apparatus for operating 2 discharge lamps. The lamps are operated at mains frequency and ignited sequentially with conventional starters.

In Scripture EP 0 395 159 (De Bijl ) discloses an apparatus for operating 2 discharge lamps. The lamps are serially operated in a full bridge. In case of failure of a bridge branch of the remaining bridge branch operates a lamp on.

Presentation of the invention

It is therefore an object of the invention to provide a solution as the electrodes of at least two low-pressure gas discharge lamps can be reliably preheated with the least possible technical effort and operated with low Dauerheizverlusten.

This object is achieved by a circuit arrangement with the features according to claim 1, as well as by a method with the features of claim 5. Advantageous embodiments of the invention are the subject of the dependent claims.

In a circuit arrangement of the type mentioned is therefore provided that it further comprises a capacitive voltage divider. This voltage divider has a parallel to the first terminal assembly coupled first capacitor and a parallel to the second connection arrangement coupled second capacitor.

Accordingly, the effect according to the invention is achieved by a capacitive voltage divider, by means of which an electrical voltage applied between the first connection pair of the first connection arrangement and the second connection pair of the second connection arrangement is divided. In this way, it is possible, the voltage applied to the resonant capacitor and thus over the lamps during preheating total electrical voltage over a for a single Gas discharge lamp allowable value and thus to increase the preheating current in this branch, without increasing the resonance capacitor whose capacity determines the Dauerheizverluste. Thus, the ratio of the current intensity of the current flowing through the "outer" electrodes - those electrodes which are coupled to the first terminal pair of the first terminal arrangement and the second terminal pair of the second terminal arrangement - during preheating to the current intensity of this current during operation ( that is after ignition of the gas discharge lamps). In other words, in this way the ratio of the current of the Dauerheizstroms to the current of the preheating, or the ratio of the Dauerheizleistung to preheating reduced. This reduction is attributable to the fact that the current intensity of the current flowing via the "outer" electrodes of the gas discharge lamps or via the resonance capacitor is determined directly by the amplitude of the voltage applied to the resonance capacitor.

On the one hand, it is possible with the circuit arrangement according to the invention to reliably preheat the outer electrodes of the gas discharge lamps; On the other hand, the circuit arrangement according to the invention results in significantly reduced losses in continuous operation. This succeeds in the circuit arrangement according to the invention without the use of a large number of expensive active and passive components, as described in the subject matter according to document DE 44 25 859 A1 be used. The circuit arrangement according to the invention solves the above object with only a capacitive voltage divider, which makes them more cost-effective and component reduced as the known circuit arrangements can be made.

The capacitance values of both the first and second capacitors are preferably smaller than the capacitance value of the resonance capacitor. In this way, a reliable ignition of the gas discharge lamps can be made possible. For example, the capacitance values of the first and second capacitors may be 5% to 25% of the capacitance value of the resonant capacitor. On the other hand, the first and the second capacitor should be chosen so large that the parasitic capacitances of the first and the second terminal arrangement do not affect the voltage distribution across the lamps. In one embodiment, it is provided that for an operating frequency of the AC supply voltage in a value range between about 40 kHz and about 50 kHz, the first and the second capacitor each have a capacitance value from a value range of 10 pF to 5 nF, preferably from a value range of 100 pF to 2.5 nF. Then, the above requirements regarding the voltages at the gas discharge lamps are satisfied. In one embodiment, the capacitance value of the first capacitor may be 1 nF and the capacitance value of the second capacitor 560 pF and the capacitance value of the resonant capacitor 10 may be nF.

The capacitance value of the first capacitor preferably differs from the capacitance value of the second capacitor. Thus, it is achieved that the gas discharge lamps are ignited sequentially, that is, one after the other. Because of the different capacitance values of the two capacitors, namely, the first breaks Voltage to a first of the gas discharge lamps, which has an immediate increase in the voltage across the other gas discharge lamp and thereby the ignition of this gas discharge lamp result. The ratio of the capacitance values of the two capacitors is preferably in a value range of 0.5 to 0.8. For example, this ratio may be 2/3.

It has proven to be particularly advantageous if an additional winding is wound on the resonance choke, which is coupled to a second terminal of the second terminal pair of the first terminal arrangement and to a second terminal of the first terminal pair of the second terminal arrangement. Then, the "inner" electrodes of the gas discharge lamps, which are connected to the second terminal pair of the first terminal arrangement and the first terminal pair of the second terminal arrangement, are preheated. In this case too, the ratio of the continuous heating current to the preheating current is reduced to a comparable extent as in the outer electrodes, because the voltage at the resonance choke during preheating and ignition is, to a first approximation, proportional to the voltage at the resonance capacitor. Consequently, the number of turns of the secondary heating coil and thus the Dauerheizverluste can be reduced. Compared to the known circuit arrangements in which three or more additional windings are wound on the resonance choke, the present circuit arrangement comes with only a single additional winding at the resonance choke (provided that two gas discharge lamps are operated). The resonance choke as a component can thus in comparison to the prior art be made much easier and cheaper; the additional winding can be isolated from the main winding of the resonance choke without much effort. Furthermore, more winding space is available for the main winding of the resonance choke, so that the thermal problems occurring in the prior art are effectively counteracted.

In order to further reduce the continuous heating losses or the pin currents of the gas discharge lamps, a dummy element, in particular a choke, can be coupled between the terminals of the first terminal pair of the first terminal arrangement and / or between the terminals of the second terminal pair of the second terminal arrangement.

An inventive method is designed to operate a series circuit of at least a first and a second low-pressure gas discharge lamp to a circuit arrangement of the type mentioned. In the method, it is provided that an electrical voltage applied between the first connection pair of the first connection arrangement and the second connection pair of the second connection arrangement is divided by means of a capacitive voltage divider, which has a first capacitor coupled in parallel with the first connection arrangement and coupled in parallel with the second circuit arrangement having second capacitor.

The preferred embodiments presented with reference to the circuit arrangement according to the invention and their advantages apply correspondingly to the method according to the invention.

Short description of the drawing

The invention will now be explained in more detail by means of a preferred embodiment and with reference to the drawing, wherein the single figure illustrates in diagrammatic representation a circuit arrangement according to an embodiment of the invention.

Preferred embodiment of the invention

A circuit arrangement 1 shown in the figure comprises an input 2 with a first input terminal 3 and a second input terminal 4. The second input terminal 4 represents a reference potential of a control unit, not shown in the figure. With this reference potential is also not shown in the figure and coupled by the control unit controllable inverter, which provides a supply AC voltage U _v . This alternating supply voltage U _v is applied between the first and the second input terminal 3, 4. The AC supply voltage U _v generated by the inverter from a DC link DC voltage, which is not shown in the figure DC bus capacitor is applied. The DC link DC voltage is applied between a DC link 5 and the reference potential 4 of the control unit.

The circuit arrangement 1 also comprises an output with a first and a second connection arrangement, respectively for connecting a low-pressure gas discharge lamp 6, 7. The first connection arrangement comprises a first terminal pair 8 with a first and a second terminal 8a, 8b and a second terminal pair 9 with a first and a second terminal 9a, 9b. Accordingly, the second connection arrangement comprises a first connection pair 10 with a first connection 10a and a second connection 10b and a second connection pair 11 with a first connection 11a and a second connection 11b.

The first terminal 9a of the second terminal pair 9 of the first terminal arrangement is directly connected to the first terminal 10a of the first terminal pair 10 of the second terminal arrangement. Thus, there is a series connection of the two gas discharge lamps 6, 7.

The first input terminal 3 of the input 2 is coupled via a resonance choke 12 to the first terminal 8a of the first terminal pair 8 of the first terminal arrangement. The resonant choke 12 together with a resonant capacitor 13 forms a resonant circuit of the circuit arrangement 1. The resonant capacitor 13 is between the second terminal 8b of the first terminal pair 8 of the first terminal arrangement and the second terminal 11b of the second terminal pair 11 of the second Connection arrangement switched. The inductance value of the resonance choke 12 in the exemplary embodiment is 1.3 mH and the capacitance value of the resonance capacitor 13 is 7.5 nF.

In addition to the resonance choke 12, an additional winding 14 is wound on the same component, via which the inner electrodes of the gas discharge lamps 6, 7 can be preheated. The internal electrodes of the gas discharge lamps 6, 7 are understood to mean those electrodes which are connected to the second terminal pair 9 of the first terminal arrangement and to the first terminal pair 10 of the second terminal arrangement. The additional winding 14 is coupled via a capacitor 15 to the second terminal 9b of the second terminal pair 9 of the first terminal arrangement. On the other hand, the auxiliary winding 14 is connected to the second terminal 10b of the first terminal pair 10 of the second terminal arrangement.

Those electrodes of the gas discharge lamps 6, 7 which are coupled to the first terminal pair 8 of the first terminal arrangement and the second terminal pair 11 of the second terminal arrangement are referred to below as outer electrodes. In order to ensure reliable preheating of the outer electrodes of the gas discharge lamps 6, 7, a capacitive voltage divider 16 is connected in parallel with the resonance capacitor 13. The capacitive voltage divider 16 comprises a first capacitor 16a and a second capacitor 16b. In this case, the first capacitor 16a is between the first terminal 8a of the first terminal pair 8 and the first terminal 9a of the second terminal pair 9 of the first terminal arrangement connected. In other words, the first capacitor 16a is connected in parallel to the first terminal arrangement. The second capacitor 16b is connected between the first terminal 10a of the first terminal pair 10 and the first terminal 11a of the second terminal pair 11 of the second terminal arrangement. Thus, the second capacitor 16b is connected in parallel to the second terminal arrangement. Generally, the capacitive voltage divider 16 must be coupled to the outer terminals 8, 11. The connection point arranged between the capacitors 16a, 16b must be connected to exactly one of the connections 9 (9a or 9b) or 10 (10a or 10b). The capacitance values of the first and second capacitors 16a, 16b in the exemplary embodiment are 1 nF and 560 pF, respectively.

The circuit arrangement 1 also has a first and a second coupling capacitor 17, 18. The first terminal 11a of the second terminal pair 11 of the second terminal arrangement is connected via the first coupling capacitor 17 to the DC link 5, that is electrically decoupled from the DC link 5 by means of the first coupling capacitor 17. On the other hand, the first terminal 11a of the second terminal pair 11 of the second terminal arrangement is connected via the second coupling capacitor 18 to the reference potential 4 of the control unit. The two coupling capacitors 17, 18 ensure that no direct currents can flow via the gas discharge lamps 6, 7. Such DC currents could lead to an apparent inhomogeneity of the gas discharge lamps 6, 7 radiated light lead (cataphoresis). In addition, the advantage is achieved by the symmetrical arrangement of the coupling capacitors 17, 18, that the current load of the DC link capacitor is the lowest.

In addition, a throttle 19 is connected between the first and the second connection 8a, 8b of the first connection pair 8 of the first connection arrangement. Accordingly, a throttle 20 is connected between the first and the second connection 11a, 11b of the second connection pair 11 of the second connection arrangement. The throttles 19, 20 have the task of minimizing the Dauerheizverluste or the pin currents of the gas discharge lamps 6, 7.

• Zunächst wird die Zwischenkreisgleichspannung bereitgestellt, nämlich zum Beispiel durch Schließen eines Netzschalters durch eine Bedienperson. Liegt die Zwischenkreisgleichspannung an dem Zwischenkreiskondensator an, so ist auch die Steuereinheit in Betrieb, sie kann die Versorgungswechselspannung U_V unter entsprechender Ansteuerung des Wechselrichters erzeugen. Vor der Inbetriebnahme der Gasentladungslampen 6, 7 wird zunächst eine Vorheizphase eingeleitet, in welcher die Elektroden - nämlich sowohl die äußeren als auch die inneren Elektroden - der Gasentladungslampen 6, 7 aufgeheizt werden. Die Elektroden werden dabei auf eine solche Temperatur aufgeheizt, die für einen schonenden Start der Gasentladungslampen 6, 7 sorgt.

The mode of operation of the circuit arrangement 1 will be explained in more detail below:

• First, the DC link voltage is provided, for example, by closing a power switch by an operator. If the intermediate circuit DC voltage is applied to the DC link capacitor, the control unit is also in operation; it can generate the AC supply voltage U _V with appropriate control of the inverter. Before the gas discharge lamps 6, 7 are put into operation, a preheating phase is first of all initiated, in which the electrodes - namely both the outer and the inner electrodes - of the gas discharge lamps 6, 7 are heated. The electrodes are heated to a temperature which ensures a gentle start of the gas discharge lamps 6, 7.

The control unit initiates the preheat phase by setting the frequency of the AC supply voltage U _V to a preheat frequency. During the preheating phase, the alternating supply voltage U _V is thus set such that the gas discharge lamps 6, 7 are not yet ignited. The presence of the capacitive voltage divider 16 makes it possible to set the voltage applied to the resonance capacitor 13 during the preheating phase to a value which is higher than the ignition voltage of a single gas discharge lamp 6, 7. In this way, the outer electrodes of the gas discharge lamps 6, 7 with relatively high currents - the current strength of the current flowing through the resonant capacitor 13 current is determined by the amplitude of the voltage - acted upon and thereby reliably preheated. At the same time, the ratio of the current intensity of the continuous heating current flowing in operation via the outer electrodes to the current intensity of the preheating current flowing through the resonance capacitor 13 during the preheating phase is reduced by the use of the capacitive voltage divider 16. So also reduces the ratio of the continuous heating power to the preheating. In other words, the current strength of the Dauerheizstroms can be reduced and thereby lower Dauerheizverluste be achieved. These losses can be further reduced by means of the throttles 19, 20.

After completion of the preheating phase, the frequency of the AC supply voltage U _V is lowered so that the gas discharge lamps 6, 7 ignite. Due to the different capacitance values of the capacitors 16a, 16b, the ignition of the gas discharge lamps 6, 7 takes place sequentially. This means that the gas discharge lamps 6, 7 are ignited one after the other.

Overall, therefore, a circuit arrangement 1 is provided which enables reliable preheating of electrodes of a series connection of at least two gas discharge lamps 6, 7. In this case, the circuit arrangement 1 comes without additional cost-intensive and technically complex preheating circuits; It can be produced inexpensively and reduced component. Reliable preheating of the electrodes is ensured by a capacitive voltage divider 16 including first and second capacitors 16a, 16b. It is unnecessary to use a plurality of additional windings on the resonance choke 12, it is sufficient only an additional winding 14, which can be wound without much effort and with a few turns.

Claims (5)

1. Circuit arrangement (1) for operating a series circuit of at least one first and one second low-pressure gas-discharge lamp (6, 7), having

   - an input (2) with a first and a second input connection (3, 4) for application of a supply AC voltage (U_v),

   - an output (8, 9, 10, 11) with at least one first connection arrangement (8, 9), which has a first and a second connection pair (8, 9) for connection of the first low-pressure gas-discharge lamp (6), and a second connection arrangement (10, 11), which has a first and a second connection pair (10, 11) for connection of the second low-pressure gas-discharge lamp (7), wherein a first connection (9a) of the second connection pair (9) of the first connection arrangement (8, 9) is coupled to a first connection (10a) of the first connection pair (10) of the second connection arrangement (10, 11),

   - a resonant circuit having a resonant inductor (12), which is coupled between the first input connection (3) and a first connection (8a) of the first connection pair (8) of the first connection arrangement (8, 9), and having a resonant capacitor (13),

   characterized in that
   the resonant capacitor (13) is connected between the second connection (8b) of the first connection pair (8) of the first connection arrangement and the second connection (11b) of the second connection pair (11) of the second connection arrangement,
   the circuit arrangement (1) also has a capacitive voltage divider (16), which has a first capacitor (16a), which is coupled in parallel with the first connection arrangement (8, 9), and a second capacitor (16b), which is coupled in parallel with the second connection arrangement (10, 11), wherein the first capacitor (16a) is connected between the first connection (8a) of the first connection pair (8) and the first connection (9a) of the second connection pair (9) of the first connection arrangement,
   and wherein the second capacitor (16b) is connected between the first connection (10a) of the first connection pair (10) and the first connection (11a) of the second connection pair (11) of the second connection arrangement.
2. Circuit arrangement (1) according to Claim 1, characterized in that, for an operating frequency of the supply AC voltage (U_v) in a value range between about 40 kHz and about 50 kHz, the first and the second capacitor (16a, 16b) each has a capacitance value from a value range from 10 pF to 5 nF, preferably from a value range from 100 pF to 2.5 nF.
3. Circuit arrangement (1) according to Claim 1 or 2, characterized in that an additional winding (14) is wound on the resonant inductor (12) and is coupled to a second connection (9b) of the second connection pair (9) of the first connection arrangement (8, 9), and to a second connection (10b) of the first connection pair (10) of the second connection arrangement (10, 11).
4. Circuit arrangement (1) according to one of the preceding claims, characterized in that a reactive element (19, 20), in particular an inductor (19, 20), is coupled between the connections (8a, 8b) of the first connection pair (8) of the first connection arrangement (8, 9) and/or between the connections (11a, 11b) of the second connection pair (11) of the second connection arrangement (10, 11).
5. Method for operating a series circuit of at least one first and one second low-pressure gas-discharge lamp (6, 7) on a circuit arrangement (1) having an input (2) with a first and a second input connection (3, 4) for application of a supply AC voltage (U_v), having an output (8, 9, 10, 11) with at least one first connection arrangement (8, 9), which has a first and a second connection pair (8, 9) for connection of the first low-pressure gas-discharge lamp (6), and a second connection arrangement (10, 11), which has a first and a second connection pair (10, 11) for connection of the second low-pressure gas-discharge lamp (7), wherein a first connection (9a) of the second connection pair (9) of the first connection arrangement (8, 9) is coupled to a first connection (10a) of the first connection pair (10) of the second connection arrangement (10, 11), and having a resonant circuit having a resonant inductor (12), which is coupled between the first input connection (3) and a first connection (8a) of the first connection pair (8) of the first connection arrangement (8, 9), and having a resonant capacitor (13),
   characterized in that
   the resonant capacitor (13) is connected between the second connection (8b) of the first connection pair (8) of the first connection arrangement and the second connection (11b) of the second connection pair (11) of the second connection arrangement,
   an electrical voltage which is applied between the first connection pair (8) of the first connection arrangement (8, 9) and the second connection pair (11) of the second connection arrangement (10, 11) is divided by means of a capacitive voltage divider (16), which has a first capacitor (16a), which is coupled in parallel with the first connection arrangement (8, 9), and a second capacitor (16b), which is coupled in parallel with the second connection arrangement (10, 11), wherein the first capacitor (16a) is connected between the first connection (8a) of the first connection pair (8) and the first connection (9a) of the second connection pair (9) of the first connection arrangement,
   and wherein the second capacitor (16b) is connected between the first connection (10a) of the first connection pair (10) and the first connection (11a) of the second connection pair (11) of the second connection arrangement.

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