DE102010029511B4 - Circuit arrangement for operating a discharge lamp - Google Patents

Abstract

Circuit arrangement for operating a discharge lamp, comprising: - a first (E1) and a second terminal (E2) for coupling to a DC supply voltage (UZW); - An inverter with a bridge circuit comprising at least a first (S1) and a second electronic switch (S2), wherein between the first (S1) and the second electronic switch (S2), a first bridge center (BM) is formed, wherein the Series circuit of the first (S1) and the second electronic switch (S2) is coupled between the first (E1) and the second terminal (E2) for the DC supply voltage (UZW); - A control device (μC) for driving at least the first (S1) and the second electronic switch (S2); A first (A1) and a second terminal (A2) for coupling to the hot filament (Wh) of the discharge lamp (FL); An inductance (L1) having a first and a second terminal, the first terminal of the inductance (L1) being coupled to the first bridge center (BM), the second terminal of the inductance (L1) being connected to the first terminal (A1) for the hot filament (Wh) of the discharge lamp (FL) is coupled; - a first capacitor (CZ) having a first and a second terminal, said first terminal being coupled to said first terminal (A1) for said hot filament (Wh), said second terminal being coupled to a reference potential; A first (A3) and a second terminal (A4) for coupling to the cold filament (Wc) of the discharge lamp (FL); A second capacitor (CK1) having first and second terminals, the first terminal coupled to the first (A3) terminal for coupling to the cold filament (Wc), the second terminal coupled to the reference potential; A first voltage divider (R3, R4) coupled between the first (A3) terminal for coupling to the cold filament (Wc) and the reference potential, the first voltage divider (R3, R4) having a first (R3) and a second ohmic resistor (R4), wherein the tap of the voltage divider (R3, R4) is coupled to a first input of the control device (μC); ...

Description

Technical area

From the WO 2009/158330 A2 a circuit arrangement is known, which monitors a signal prior to the start of the inverter, which represents the presence of fluorescent lamps with intact lamp filaments.

From the US 2003/0076055 A1 a circuit arrangement is known which polls the lamp filaments or the correct wiring of a fluorescent lamp by means of a measuring resistor before the lamp start.

The present invention relates to a circuit arrangement for operating a discharge lamp, comprising a first and a second terminal for coupling with a DC supply voltage, an inverter with a bridge circuit comprising at least a first and a second electronic switch, wherein between the first and the second electronic switch a first bridge center is formed, wherein the series circuit of the first and the second electronic switch between the first and the second terminal for the DC supply voltage is coupled, a control device for driving at least the first and the second electronic switch, a first and a second connection to Coupling with the hot filament of the discharge lamp, an inductor having a first and a second terminal, wherein the first terminal of the inductance is coupled to the first bridge center, wherein the second terminal d inductance is coupled to the first terminal for the hot filament of the discharge lamp, a first capacitor having a first and a second terminal, wherein the first terminal is coupled to the first terminal for the hot filament, wherein the second terminal is coupled to a reference potential , a first and a second terminal for coupling to the cold filament of the discharge lamp, a second capacitor having a first and a second terminal, wherein the first terminal is coupled to the cold filament, the second terminal being coupled to the reference potential, a first A voltage divider coupled between the cold filament and the reference potential, the first voltage divider comprising first and second ohmic resistors, the tap of the voltage divider coupled to a first input of the controller, a preheater having a primary winding and at least a first secondary arwicklung, wherein the first secondary winding is coupled between the first and the second terminal for the cold filament of the discharge lamp, a third capacitor which is serially coupled to the first secondary winding of the preheater, and a series connection of at least a third and a fourth ohmic resistance, this Series connection is coupled between the first terminal and the second terminal for the DC supply voltage, wherein the node between the third and the fourth ohmic resistor is coupled to the cold filament of the discharge lamp.

State of the art

The problem underlying the present invention is that electronic ballasts for discharge lamps always generate high ignition voltages to ignite them. In order to avoid danger to operators or to the surroundings of the discharge lamp, some electronic ballasts will check that a lamp is connected to the output of the electronic ballast prior to making an ignition attempt. For this purpose, the electronic ballast usually checks whether the cold coil or the cold end of the lamp is present. The following statements relate to high-quality electronic ballasts, which have a transformer coil heating. In this case, either a separate heating transformer is used for preheating or provided an additional winding on the lamp inductor.

For a more detailed explanation of the problem underlying the present invention is on 1 referenced, in which the sections of known circuit arrangements which are of interest in connection with the present invention are shown schematically.

The in the 1a to 1d Variants shown show a discharge lamp Fl with a hot coil W _h and a cold coil W _c . The term "hot coil" in the context of the present invention refers to the coil which is coupled to the first bridge center, and "cold coil" to the coil which is coupled to the reference potential. The connections of the electronic ballast for the hot filament are designated A1 and A2, those for the cold filament with A3 and A4. The secondary winding of a heating transformer, not shown, used to heat the coil W _c is designated SEK1.

In the variants according to 1a and 1b the cold filament W _{c of} the discharge lamp Fl is connected to a reference potential, in the present case ground. A simple measurement path allows a controller .mu.C determine if the filament W _c is present. For this purpose, the terminal A3 for the cold filament via a voltage divider, which includes the ohmic resistors R3 and R4, with an auxiliary voltage source U _H coupled. The tap of the voltage divider is coupled to an input of the control device .mu.C. In order to prevent current flowing from the auxiliary voltage source U _H via the secondary winding SEK1 to the reference potential, it is necessary to decouple the filament W _c and the secondary winding SEK1. This can be achieved by a decoupling element that is serially coupled to the secondary winding SEK1. In the variant gemaß 1a represents the decoupling element is a capacitor C _S , while according to the variant 1b the decoupling element represents a diode D1.

Both variants have the disadvantage that due to the direct connection of the coil W _c to the reference potential, incorrect wiring can lead to damage to the electronic ballast or the discharge lamp. In addition, the variant has been appropriate 1b Another disadvantage, therefore, because the diode let pass only a half-wave of the heating and thus firstly a higher voltage to the coil W _{c is} necessary, thereby increasing the risk of cross-discharge, and secondly in a single-lamp device, that is an electronic ballast for Operating a single discharge lamp, a balanced transformer heating is no longer given. The latter is disadvantageous especially for electronic ballasts with lamp detection. However, the symmetry can be produced via an additional second diode in series with the hot filament W _h . However, these diodes must be voltage-proof and fast enough so that they can withstand short-term loads with the ignition voltage in the event of defective lamps.

In the in the 1c and 1d illustrated variants, the helix W _{c is} not directly coupled to the reference potential. Instead, a coupling capacitor C _{K1 is connected} between the discharge lamp Fl and the reference potential. This results in comparison to the in the 1a and 1b variants shown a greater robustness against miswiring. However, no direct connection of the helix W _c to the reference potential is now available. For the preparation of a measurement path of the terminal A4 for the cold coil W is _c via a resistor R8 to the DC supply voltage, which usually represents the intermediate circuit voltage U _ZW coupled. For the protection of the control device .mu.C the resistance R8 is formed high impedance. However, the voltage at the coupling capacitor C _K1 is dependent on the current operating state and may be between 0 V and the maximum value of the intermediate _circuit voltage U _ZW , for example, 400 V.

The disadvantage of in the 1c and 1d Therefore, the variants shown in the necessary higher dielectric strength of the decoupling element, which in 1c the capacitor C _S and in the 1d represents the diode D1.

For electronic ballasts, which are designed to operate different types of discharge lamps at their output terminals, that electronic ballasts that detect the type of discharge lamp used, for example, the coil resistance, the capacitor C _S would have an undesirably large capacity, so its influence during the type recognition remains negligible. In particular, with the required high dielectric strength, this results in an undesirably large design. The large capacity goods are also necessary to neglect a voltage drop across the capacitor C _S during preheating of the coil W _c . Alternatively, a second capacitor can be switched into the heating circuit of the hot coil to restore the symmetry.

Another prior art is known from the EP 1 343 359 A2 , which relates to an operating circuit for a low-pressure discharge lamp with an EOL early detection via a measurement of the DC voltage between the electrodes of the low-pressure discharge lamp. In this case, an electrode interrogation can be carried out by checking a respective connection via the respective electrode to a respective reference potential.

Presentation of the invention

The object of the present invention is therefore to develop a circuit arrangement mentioned in such a way that on the one hand, the components that are required for a reliable test, whether a discharge lamp is coupled to the electronic ballast, take as little space as possible, on the other hand, use in an electronic ballast with spiral detection is possible without affecting the coil detection.

This object is achieved by a circuit arrangement having the features of patent claim 1.

The invention is based on the finding that in order to enable a helix detection, the capacitor, which is arranged in series with the secondary winding SEK1, must continue to have a high capacitance. However, it can then be realized with a small design, if the maximum voltage drop across this capacitor is limited. For this purpose, a small ohmic resistance, which is connected in parallel with the series connection of the first secondary winding and the capacitor C _S , is sufficient. In this case, the ohmic resistance as SMD Be executed component. The space required by the additional ohmic resistor corresponds to only a fraction of the installation space which would be occupied by a capacitor C _S , which has a high capacitance and is designed for a high voltage. Due to the high capacitance of the capacitor can continue to be made a helix detection. Due to the small size of the capacitor, the desire for a small space for the components needed to detect the presence of a discharge lamp is minimized. The preheating of the helix (s) is not affected by the invention.

A preferred embodiment is characterized in that the circuit arrangement further comprises a second voltage divider having a sixth and a seventh ohmic resistance, wherein the second voltage divider is coupled between the first and the second terminal for the DC supply voltage, wherein the tap of the second voltage part with a Input of the control device is coupled. By means of this voltage divider can therefore be determined the size of the instantaneous DC supply voltage. The approach takes into account the fact that - for example, in a limitation of the voltage across the capacitor C _S so far that a 63-volt capacitor can be used - the voltage swing at the input of the microprocessor only in the range of 5 to 10% of original measurement signal, that is, the voltage at the input of the microprocessor without the use of the fifth ohmic resistance amounts. However, since at the time the detection of the signal at the first input of the control device is made, power factor correction (PFC) circuit components are not yet operative, the intermediate circuit voltage, that is, the DC supply voltage, may be between 150V and 400V Accept V. The power factor correction is namely activated only after detection of the coil W _c . The evaluation of a voltage swing of 5 to 10% under these conditions only with great difficulty - if the dielectric strength of the capacitor C _{S is} chosen large - possible, or completely impossible - at a, as preferred, as small as possible selected dielectric strength of the capacitor C _S , According to this preferred embodiment, therefore, the instantaneous value of the DC supply voltage at the time of detection of the signal at the first input of the control device is determined.

Preferably, the control device is further configured to form the difference between the voltage at the second input and the voltage at the first input. By forming the difference, complex divisions can be avoided. Alternatively, however, the ratio of the voltage at the second input to the ratio of the voltage at the first input can also be evaluated, which, however, requires a more powerful control device.

The control device is preferably further configured to normalize the difference to the voltage at the first input or the voltage at the second input. By this standardization is also achieved that the demands on the computing power of the control device can be reduced.

In order to simplify the evaluation, in particular to avoid a case distinction, the first and the second voltage divider are preferably dimensioned so that the difference is always positive.

In general, the control device is preferably designed so that the formation of the difference mentioned before the start of activation of the preheater is made. Particularly preferably, the control device is designed to make the formation of the difference a predefinable period of time, in particular 50 to 200 ms, preferably 100 ms, after switching on the circuit arrangement. If, for example, the discharge lamp is removed during operation, there is no extra waiting time, because after switching on the electronic ballast, the control device anyway requires a certain time until it has started up. This procedure takes into account the fact that due to the high-resistance resistors of the circuit arrangement, in particular the third and the fourth ohmic resistance, and the large capacitance of the capacitor C _S only after about 100 ms sets a reliable signal at the first input of the control device.

According to a preferred embodiment, the control device is designed to compare the normalized difference with a predefinable threshold value and, if the normalized difference is greater than the predefinable threshold value, not to output a preheat signal. This measure has the advantage that the predefinable threshold value can be varied in order to take into account component tolerances, for example in the context of the calibration of the circuit arrangement.

The first capacitor preferably has a dielectric strength which amounts to between one tenth and one fifth of the maximum supply direct voltage to be coupled between the first and the second connection. In practice, it has been shown that this dimensioning represents an optimal compromise between space size and dielectric strength.

Preferably, the preheating device comprises a second secondary winding, wherein the second secondary winding is coupled between the first and the second connection for the hot filament of the discharge lamp. This allows a symmetrical preheating of both filaments of the discharge lamp.

As already mentioned, the preheating device can be realized by a separate heating transformer. Alternatively, the inductance may be the primary winding of the preheater. As a result, a circuit arrangement according to the invention can be realized particularly cost-effectively with minimal space requirement.

Further preferred embodiments emerge from the subclaims.

Short description of the drawing (s)

Hereinafter, an embodiment of the present invention will be described in more detail with reference to the accompanying drawings. Show it:

1a) to 1d) in a schematic representation of sections of known circuit arrangements according to the prior art, and

2 a schematic representation of an embodiment of a circuit arrangement according to the invention.

Preferred embodiment of the invention

With respect to in the 1a to 1d have the same reference numerals, insofar as they relate to identical and identically acting components, further for the in 2 schematically illustrated embodiment of a circuit arrangement according to the invention. The components are therefore not re-introduced.

This in 2 illustrated exemplary embodiment of a circuit arrangement according to the invention has a first E1 and a second input terminal E2 for coupling with a DC supply voltage, which in particular represents the so-called intermediate circuit voltage U _ZW . Between the input terminals E1 and E2, an electrolytic capacitor C1 is first coupled to stabilize the intermediate circuit voltage U _ZW . The capacitor C1 is connected in parallel with a voltage divider comprising the ohmic resistors R1 and R2. The tap of the voltage divider R1, R2, that is, the voltage U _R2 , is connected to an input E2 of a control device μC. Between the inputs E1 and E2, an inverter is further coupled, which is realized in the present case as a half-bridge circuit. In this case, the half-bridge circuit comprises a first S1 and a second electronic switch S2, which are serially coupled to form a first half-bridge center point BM between the inputs E1 and E2.

The control device .mu.C is designed to control the switches S1, S2 of the inverter - in a manner known per se. An inductance L1 is coupled on the one hand to the first half-bridge center BM and on the other hand to the output terminal A1. In order to realize a preheating device for the coils W _h and W _c , the series connection of a second capacitor C2, a primary winding PR of a heating transformer TR1 and a switch SH is connected between the first half-bridge center BM and the reference potential, which in the present case represents the second input E2 of the circuit arrangement , wherein the switch SH is also controlled by the controller μC. The heating transformer TR1 has a first SEK1 and a second secondary winding SEK2. The first secondary winding SEK1 is connected in series with a capacitor C _S , this series connection of the cold filament W _c being connected in parallel. The second secondary winding SEK2 is connected in parallel to the hot filament W _h .

As already mentioned, connections A1, A2 are provided for the hot filament W _{h of} the discharge lamp Fl and connections A3, A4 for the cold filament W _{c of} the discharge lamp F1. The discharge lamp Fl, more precisely between the terminal A1 and the reference potential, a firing capacitor C _Z is connected in parallel. This is designed to realize together with the inductance L1 a resonant circuit, which allows the ignition of the discharge lamp F1.

The terminal A4 is coupled to the tap of a voltage divider comprising high-resistance resistors R7 and R8. The third and the fourth ohmic resistance are therefore executed high impedance, that the resulting losses can be neglected. In this way it is possible to provide the cold filament W _{c with} a voltage supply in order to provide a measuring signal U _mess to the control device .mu.C at the input E1 via the tap of a further voltage divider comprising the ohmic resistors R3 and R4. The voltage divider R3, R4, a coupling capacitor C _K1 is connected in parallel. According to the invention, the series circuit comprising the first secondary winding SEK1 and the capacitor C _{S is} connected in parallel with an ohmic resistor R5. This is preferably designed as an SMD component and dimensioned so that the capacitor C _S must be designed for a dielectric strength, which is only one fifth to one tenth of the intermediate circuit voltage U _ZW .

At an intermediate circuit voltage of about 400 V, the capacitor C _{S is} preferably designed for 63 V. The ohmic resistance R5 is preferably between 50 and 100 kΩ, in a particularly preferred embodiment 82 kΩ. The control device μC is designed to measure and evaluate the signals U _R2 and U _{mess at the} earliest 100 ms after applying the intermediate circuit voltage U _ZW to the inputs E1, E2 of the circuit arrangement.

The capacitance of the capacitor C _S is preferably between 0.1 μF and 10 μF, in a particularly preferred embodiment, in particular 1 μF.

The control device μC is designed to form the difference between the voltages U _R2 and U _mess and to normalize this difference to the voltage U _R2 . It is further configured to compare this normalized difference against a predefinable threshold value and, if the standardized difference is greater than the predefinable threshold value, to switch the switch SH to prevent preheating of the discharge lamp F1. The predefinable threshold, which is stored in the control device .mu.C, can be varied during a calibration of the circuit arrangement in order to take into account component tolerances.

Claims (12)

Circuit arrangement for operating a discharge lamp, comprising: - a first (E1) and a second terminal (E2) for coupling to a DC supply voltage (U _ZW ); - An inverter with a bridge circuit comprising at least a first (S1) and a second electronic switch (S2), wherein between the first (S1) and the second electronic switch (S2), a first bridge center (BM) is formed, wherein the Series circuit of the first (S1) and the second electronic switch (S2) is coupled between the first (E1) and the second terminal (E2) for the DC supply voltage (U _ZW ); - A control device (μC) for driving at least the first (S1) and the second electronic switch (S2); - a first (A1) and a second terminal (A2) for coupling to the hot filament (W _h ) of the discharge lamp (FL); - An inductance (L1) having a first and a second terminal, wherein the first terminal of the inductance (L1) is coupled to the first bridge center (BM), wherein the second terminal of the inductance (L1) with the first terminal (A1) for the hot filament (W _h ) of the discharge lamp (FL) is coupled; A first capacitor (C _Z ) having first and second terminals, the first terminal coupled to the first hot filament terminal (A1) (W _h ), the second terminal being coupled to a reference potential; - a first (A3) and a second terminal (A4) for coupling to the cold filament (W _c ) of the discharge lamp (FL); A second capacitor (C _K1 ) having first and second terminals, the first terminal coupled to the first (A3) terminal for coupling to the cold filament (W _c ), the second terminal coupled to the reference potential; A first voltage divider (R3, R4) coupled between the first (A3) terminal for coupling to the cold filament ( _Wc ) and the reference potential, wherein the first voltage divider (R3, R4) comprises a first (R3) and a second ohmic resistor (R4), wherein the tap of the voltage divider (R3, R4) is coupled to a first input of the control device (μC); A preheater having a primary winding and at least a first secondary winding (SEK1), the first secondary winding (SEK1) being connected between the first (A3) and the second terminal (A4) for coupling to the cold filament (W _c ) of the discharge lamp (FL) is coupled; - A third capacitor (C _S ), which is serially coupled to the first secondary winding (SEK1) of the preheater; and - a series circuit of at least a third (R7) and a fourth ohmic resistance (R8), said series circuit between the first terminal (E1) and the second terminal (E2) for the DC supply voltage (U _ZW ) is coupled, the node between the third (R7) and the fourth ohmic resistance (R8) are coupled to the second terminal (A4) for coupling to the cold filament (W _c ) of the discharge lamp (FL); characterized in that the circuit arrangement further comprises: - a fifth ohmic resistor (R5) which is connected in parallel with the series connection of the first secondary winding (SEK1) and the third capacitor (C _S ). Circuit arrangement according to Claim 1, characterized in that the circuit arrangement furthermore comprises a second voltage divider (R1, R2) having a sixth (R1) and a seventh ohmic resistance (R2), the voltage divider (R1, R2) being connected between the first (E1). and the second terminal (E2) for the DC supply voltage (U _ZW ) is coupled, wherein the tap of the second voltage divider (R1, R2) is coupled to a second input of the control device (.mu.C). Circuit arrangement according to Claim 2, characterized in that the control device (μC) is designed to form the difference between the voltage at the second input and the voltage at the first input. Circuit arrangement according to claim 3, characterized in that the control device (μC) is further configured to normalize the difference to the voltage at the first input or the voltage at the second input. Circuit arrangement according to one of claims 2 to 4, characterized in that the first and the second voltage divider are dimensioned so that the difference is always positive. Circuit arrangement according to one of claims 3 to 5, characterized in that the control device (μC) is further adapted to make the formation of the difference before the start of the activation of the preheating. Circuit arrangement according to claim 6, characterized in that the control device (.mu.C) is designed to make the formation of the difference a predefinable period of time, in particular 50 to 200 ms, preferably 100 ms, after the switching on of the circuit arrangement. Circuit arrangement according to one of claims 3 to 7, characterized in that the control device (.mu.C) is designed to compare the normalized difference against a predeterminable threshold value and, if the normalized difference is greater than the predefinable threshold, no output of a preheat signal. Circuit arrangement according to one of the preceding claims, characterized in that the predefinable threshold value can be varied, in particular by a calibration of the circuit arrangement. Circuit arrangement according to one of the preceding claims, characterized in that the third capacitor (C _S ) has a withstand voltage between one tenth and one fifth of between the first (E1) and the second terminal (E2) to be coupled maximum DC supply voltage (U _ZW ) is. Circuit arrangement according to one of the preceding claims, characterized in that the preheating device comprises a second secondary winding (SEK2), wherein the second secondary winding (SEK2) between the first (A1) and the second connection (A2) for the hot filament (W _h ) of Discharge lamp (FL) is coupled. Circuit arrangement according to one of the preceding claims, characterized in that the inductance (L1) represents the primary winding of the preheater.

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