CN102948263B - Circuit arrangement for operating discharge lamp - Google Patents

Abstract

The invention relates to a circuit arrangement for operating a discharge lamp (FL). The lamps (W _h , W _c ) of the luminaire are heated using a transmitter (TR1). To identify the luminaire, the transmitter's filament is bridged with a resistor (R5).

Description

Circuit arrangement for operating discharge lamps

technical field

The invention relates to a circuit arrangement for operating a discharge lamp comprising: a first port and a second port for connection to a mains DC voltage; an inverter with a bridge circuit comprising at least a first electronic switch and a second electronic switch, wherein a first bridge midpoint is provided between the first electronic switch and the second electronic switch, wherein the series circuit formed by the first electronic switch and the second electronic switch is connected to the Between a first port and a second port of a voltage; a control device for controlling at least a first electronic switch and a second electronic switch; a first port and a second port for connection with a hot filament of a discharge lamp; having a first port and a second port inductor, wherein the first port of the inductor is connected to the first bridge midpoint, wherein the second port of the inductor is connected to the first port for the hot filament of the discharge lamp; having a first port and a first capacitor at the second port, wherein the first port is connected to the first port for the hot filament, wherein the second port is connected to the reference potential; Two ports; a second capacitor having a first port and a second port, wherein the first port is connected to the cold filament, wherein the second port is connected to a reference potential; a first voltage divider connected between the cold filament and the reference potential device, wherein the first voltage divider includes a first ohmic resistor and a second ohmic resistor, wherein the tap of the voltage divider is connected to the first input terminal of the control device; a pre- heating means, wherein the first secondary winding is connected between the first port and the second port for the cold filament of the discharge lamp; a third capacitor connected in series with the first secondary winding of the preheating means; and composed of at least one A series circuit formed by a third ohmic resistor and a fourth ohmic resistor, wherein the series circuit is connected between the first port and the second port for the DC voltage of the power supply, wherein between the third ohmic resistor and the fourth ohmic resistor The junction between them is connected to the cold filament of the discharge lamp.

Background technique

The difficulty on which the invention is based is that electronic ballasts for discharge lamps essentially generate a high ignition voltage when they are ignited. In order to avoid hazards to the operator of the discharge lamp or to the surrounding environment, several electronic ballasts are used to check whether the lamp is connected to the output of the electronic ballast before an ignition attempt is carried out. To do this, electronic ballasts typically detect the presence of a cold filament or cold end of the lamp. The following configurations relate to expensive electronic ballasts with variable-voltage filament heating. In this case, either a separate heating transformer is used for preheating, or an additional winding is provided on the lamp inductor.

In order to explain in detail the difficulty on which the invention is based, a partial circuit of the disclosed circuit arrangement which is relevant to the invention is shown schematically in FIG. 1 .

The variant shown in FIGS. 1a to 1d shows a discharge lamp F1 with a hot filament _Wh and a cold filament _Wc . Within the framework of the invention, the term "hot filament" designates a filament that is connected to the center point of the first bridge, and the term "cold filament" designates a filament that is connected to a reference potential. The ports for the hot filaments of the electronic ballast are denoted A1 and A2, and the ports for the cold filaments are denoted A3 and A4. The secondary winding of a heating transformer (not shown) for heating the filament W _c is denoted SEK1 .

In the variant according to FIGS. 1a and 1b, the cold filament _Wc of the discharge lamp F1 is connected to a reference potential—currently ground. A simple measurement path enables the control device μC to determine whether the filament W _c is present. To this end, port A3 for the cold filament is connected to an auxiliary voltage source UH via a voltage divider comprising ohmic resistors R3 and R4. The taps of the voltage divider are connected to the input of the control unit μC. To prevent current from flowing from the auxiliary voltage source UH through the secondary winding SEK1 to the reference potential, it is necessary to disconnect the filament _Wc from the secondary winding SEK1. This can be achieved by a separate element in series with the secondary winding SEK1. In the variant according to FIG. 1 a the separating element is a capacitor C _S , and in the variant according to FIG. 1 b the separating element is a diode D1 .

Both variants suffer from the disadvantage that by connecting the filament W _c directly to the reference potential, incorrect wiring can lead to damage of the electronic ballast or of the discharge lamp. Furthermore, the variant according to Fig. 1b has another disadvantage, since the diodes only allow the passage of the half-wave of the heating current, and this results in: firstly, a higher voltage must be present on the filament _Wc , which increases the transverse discharge Dangerous; secondly, in single-lamp installations, ie in electronic ballasts for operating individual discharge lamps, symmetrical transformer heating is no longer provided. Especially for electronic ballasts with lamp identification, the latter does not offer any advantages. However, the symmetry can be established by an additional second diode connected in series with the hot filament W _h . However, these diodes must be sufficiently voltage-resistant and fast enough to be able to withstand the short-term exposure to the ignition voltage in the event of a lamp failure.

In the variant shown in Figures 1c and 1d, the filament _Wc is not directly connected to the reference potential. Instead, a connecting capacitor C _K1 is connected between the discharge lamp F1 and the reference potential. Compared to the variants shown in FIGS. 1 a and 1 b , this results in greater stability against wiring errors. However, there is no longer a direct connection of the filament W _c to the reference potential at this time. To establish the measuring path, port A4 for the cold filament _Wc is connected via an ohmic resistor R8 to the mains DC voltage, usually the intermediate circuit voltage U _ZW . Resistor R8 is designed to be high-ohmic for the protection of control unit μC. However, the voltage at the connecting capacitor C _K1 depends on the instantaneous operating state and can range from 0 V to a maximum value of the intermediate circuit voltage U _ZW , for example 400 V.

A disadvantage of the variants shown in FIGS. 1c and 1d is thus that the dielectric strength of the separate components, capacitor _CS in FIG. 1c and diode D1 in FIG. 1d , must be higher.

For electronic ballasts designed to operate different types of discharge lamps connected to their output ports, i.e. for identifying the type of discharge lamp, for example applied, connected to its filament resistor For converters, the capacitor C _S must have a very high capacitance, so that its influence can be ignored when performing type identification. Especially when the compressive strength has to be high, this leads to devices having an extremely large construction. In order to be able to ignore the voltage drop across the capacitor _CS during the preheating of the filament _Wc , a large capacitance is likewise necessary. A second capacitor can alternatively be inserted in the heating circuit of the hot filament to re-establish the symmetry.

A further state of the art in relation to an operating circuit for a low-pressure discharge lamp with a device for early detection of the EOL by measuring the DC voltage between the electrodes of the low-pressure discharge lamp is known from EP 1 343 359 A2. In this case, electrode interrogation can be performed by detecting the individual connections via the individual electrodes to the individual reference potentials.

Contents of the invention

It is therefore the object of the invention to improve the circuit arrangement mentioned at the outset in such a way that, on the one hand, only the smallest possible installation space is required for the components necessary for a reliable detection of whether the discharge lamp is connected to the electronic ballast; On the other hand, the circuit arrangement can be used in electronic ballasts with a filament recognition device without impairing the filament recognition at the same time.

The invention is realized by a circuit arrangement for operating a discharge lamp, which comprises:

- a first port and a second port for connection to a mains DC voltage;

- an inverter with a bridge circuit comprising at least one first electronic switch and a second electronic switch, wherein a first bridge is formed between the first electronic switch and the second electronic switch point, wherein a series circuit consisting of said first electronic switch and said second electronic switch is connected between said first port and a second port for said supply DC voltage;

- control means for controlling at least said first electronic switch and said second electronic switch;

- a first port and a second port for connection to a hot filament of said discharge lamp;

- an inductor having a first port and a second port, wherein the first port of the inductor is connected to the first bridge midpoint, wherein the second port of the inductor is connected to the said first port connection of a hot filament of a discharge lamp;

- a first capacitor having a first port and a second port, wherein said first port is connected to said first port for said hot filament, wherein said second port is connected to said reference potential;

- a first port and a second port for connection to a cold filament of said discharge lamp;

- a second capacitor having a first port and a second port, wherein the first port is connected to the cold filament, wherein the second port is connected to the reference potential;

- a first voltage divider connected between the cold filament and the reference potential, wherein the first voltage divider comprises a first ohmic resistor and a second ohmic resistor, wherein the taps of the voltage divider connected to the first input terminal of the control device;

- Preheating device with a primary winding and at least one first secondary winding, wherein said first secondary winding is connected between said first port and a second port for said cold filament of said discharge lamp between;

- a third capacitor in series with said first secondary winding of said preheating means; and

- a series circuit consisting of at least one third ohmic resistor and a fourth ohmic resistor, wherein said series circuit is connected between a first port and a second port for said supply DC voltage, wherein at said first the junction between the three ohm resistor and the fourth ohm resistor is connected to the cold filament of the discharge lamp;

It is characterized in that the circuit arrangement further comprises:

- A fifth ohmic resistor connected in parallel to the series circuit formed by the first secondary winding and the third capacitor.

The invention is based on the recognition that, in order to be able to detect the filament, the capacitor arranged in series with the secondary winding SEK1 must also have a relatively high capacitance. However, it can be realized in a compact construction if the maximum voltage applied to the capacitor is limited. All that is required for this is a small ohmic resistor, which is connected in parallel to the series circuit formed by the first secondary winding and capacitor C _S . In this case, the ohmic resistor can be designed as an SMD component. The installation space required for the additional ohmic resistor is only a fraction of the space that would be occupied by a capacitor _CS , which has high capacitance and is designed to withstand high voltages. In addition, the high capacitance of the capacitor also enables identification of the filament. Due to the small size of the capacitor, the expected value of the small installation space for the structural elements necessary to detect the presence of the discharge lamp can be minimized. Preheating of the filament(s) is also not affected by the invention.

A preferred embodiment has the advantage that the circuit arrangement additionally comprises a second voltage divider with a sixth ohmic resistor and a seventh ohmic resistor, wherein the second voltage divider is connected between the first and the second voltage divider for the supply DC voltage. Between the ports, wherein the tap of the second voltage divider is connected to the input of the control device. The magnitude of the current mains DC voltage can thus be determined by means of this voltage divider. This approach takes into account the fact that - e.g. the voltage on the capacitor is limited until a 63 volt capacitor can be used - the voltage offset at the input of the microprocessor is only at the initial measurement signal, i.e. without using the fifth ohm The case of the resistor is in the range of 5 to 10% of the voltage on the input of the microprocessor. However, since the circuit components for power factor correction (PFC=Power Factor Correction) are usually not yet active at the point in time when the signal at the first input of the control device is detected, the intermediate circuit voltage, ie the mains DC voltage Can be set to a value between 150V and 400V. Because power factor correction is usually only activated after the filament W _c is found. Under these conditions, it can be very difficult to evaluate a voltage excursion of 5 to 10% - when the withstand voltage of capacitor C _S is chosen to be very high - and - as is preferable, when the withstand voltage of capacitor C _S When the intensity is selected as low as possible - completely impossible. According to this preferred embodiment, the current value of the DC voltage of the mains is therefore determined at the point in time when the signal at the first input of the control device is detected.

The control device is preferably further designed such that the difference between the voltage at the second input and the voltage at the first input is formed. Complicated division can be avoided by forming this difference. Alternatively, however, it is also possible to evaluate the proportional relationship between the voltage at the second input and the voltage at the first input, but this requires a more powerful control device.

The control device is preferably further designed such that the difference corresponds to the voltage at the first input or the voltage at the second input. This standardization likewise achieves the effect that the requirements for the computing functions of the control device can be reduced.

In order to simplify the evaluation process, and in particular to avoid a distinction between different cases, the first voltage divider and the second voltage divider are preferably dimensioned such that the difference is always a positive number.

In general, the control device is preferably designed such that the calculation of the mentioned difference is carried out before the activation of the preheating device is switched on. Particularly preferably, the control device is designed in such a way that the formation of the difference takes place after a predetermined 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 continuous operation, no additional waiting time results, since after switching on the electronic ballast, the control device still needs a certain time for normal operation. This procedure takes into account the fact that, due to the high ohmic resistances of the circuit arrangement, in particular the third and fourth ohmic resistors, and the high capacitance of the capacitor _CS , after about 100 ms, the first A reliable signal is only present at the input.

According to a preferred embodiment, the control device is designed in such a way that the normalized difference value is compared with a predefinable threshold value, and if the normalized difference value is greater than the predefinable threshold value, no preheating signal is output. This measure has the advantage that the predeterminable threshold value can be varied in order to take into account component tolerances, for example within the framework of a correction of the circuit arrangement.

The first capacitor preferably has a dielectric strength of between one-tenth and one-fifth of the maximum DC voltage of the supply to be connected between the first and second ports. Practice has shown that this range is the best compromise between the size of the installation space and the compressive strength.

The preheating device preferably comprises a second secondary winding, wherein the second secondary winding is connected between the first and the second port for the hot filament of the discharge lamp. This enables a symmetrical preheating of the two filaments of the discharge lamp.

As already mentioned, the preheating device is realized by a separate heating conveyor. Alternatively, the inductor is the primary winding of the preheater. The circuit arrangement according to the invention can thus be realized with a particularly favorable cost advantage while requiring only a minimum of installation space.

Further preferred embodiments are described in the dependent claims.

Description of drawings

Embodiments of the present invention will now be described in detail below with reference to the accompanying drawings. The figure shows:

1a) to 1d) schematically show a fragment of a schematic diagram in a known circuit arrangement according to the prior art, and

FIG. 2 schematically shows an embodiment of a circuit arrangement according to the invention.

Detailed ways

The reference numerals used in FIGS. 1 a to 1 d also apply further to the exemplary embodiment of the circuit arrangement according to the invention shown schematically in FIG. 2 , as far as identical or identically acting elements are concerned. Therefore the components will not be described again.

The embodiment of the circuit arrangement according to the invention shown in FIG. 2 has a first input port E1 and a second input port E2 for connection to a mains direct voltage, in particular a so-called The intermediate circuit voltage U _ZW . Firstly, an electrolytic capacitor C1 is connected between the input ports E1 and E2 to ensure the stability of U _ZW . A voltage divider comprising ohmic resistors R1 and R2 is connected in parallel with capacitor C1. The tap of the voltage divider R1, R2, namely the voltage UR2, is connected to the input E2 of the control unit μC. Furthermore, an inverter is connected between the inputs E1 and E2, which inverter is implemented in the invention as a half-bridge circuit. Wherein, the half-bridge circuit includes a first electronic switch S1 and a second electronic switch S2 , which are connected in series between the input terminals E1 and E2 while forming the midpoint BM of the first half-bridge.

The control unit μC is designed—in a manner known per se—to control the switches S1 , S2 of the inverter. The inductor L1 is connected on the one hand to the midpoint BM of the first half-bridge and on the other hand to the output terminal A1. In order to realize the preheating device for the filaments _Wh and _Wc , the second capacitor C2, the heating transformer TR1 is connected between the first half-bridge midpoint BM and the reference potential, which is currently the second output E2 of the circuit arrangement. The series circuit formed by the primary winding PR and the switch SH, wherein the switch SH is likewise controlled by the control device μC. The heating transformer TR1 has a first secondary winding SEK1 and a second secondary winding SEK2. The first secondary winding SEK1 is connected in series with the capacitor _CS , wherein the series circuit is connected in parallel with the cold filament _Wc . The second secondary winding SEK2 is connected in parallel with the hot filament W _h .

As already mentioned, the ports A1, A2 are provided for the hot filament _Wh of the discharge lamp F1 and the ports A3, A4 are provided for the cold filament _Wc of the discharge lamp F1. The ignition capacitor _CZ is connected in parallel with the discharge lamp F1, specifically between the terminal A1 and the reference potential. The ignition capacitor is designed to realize, together with the inductor L1, a resonant circuit which can ignite the discharge lamp F1.

Port A4 is connected to taps of a voltage divider consisting of high ohmic ohmic resistors R7 and R8. The third and fourth ohmic resistors are therefore designed to be high-ohmic, so that the resulting losses can be neglected. The cold filament W _c can be supplied with voltage on this path in order to provide the control unit μC with the measurement signal U _mess at its input E1 via a tap of a further voltage divider comprising ohmic resistors R3 and R4 . Connect capacitor C _k1 in parallel with voltage divider R3, R4. According to the invention, an ohmic resistor R5 is connected in parallel to the series circuit formed by the first secondary winding SEK1 and the capacitor _CS . The ohmic resistor is preferably designed as an SMD component and dimensioned in such a way that the dielectric strength of the capacitor C _S must be designed to be only one-fifth to one-tenth of the intermediate circuit current U _ZW .

When the intermediate circuit current is about 400V, the capacitance _CS is preferably set to 63V. The ohmic resistance R5 is preferably between 50 and 100 kΩ, in a particularly preferred embodiment 82 kΩ. The control unit μC is designed such that the signals U _R2 and U _mess are detected and evaluated as early as 100 ms after the intermediate circuit current U _ZW has been applied to the inputs E1 , E2 of the circuit arrangement.

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

The control unit μC is designed in such a way that the difference between the voltage _UR2 and _Umess is generated and adapted to the voltage _UR2 . The difference is further designed in such a way that the normalized difference is compared with a predeterminable threshold value, and if the normalized difference value is greater than the predeterminable threshold value, then switching off to avoid preheating of the discharge lamp F1 Switch SH. To take into account component tolerances, predefinable threshold values stored in the control unit μC can be changed during the calibration of the circuit arrangement.

Claims (18)

1. A circuit arrangement for operating a discharge lamp comprising: - a first port (E1) and a second port (E2) for connection to a mains DC voltage (U _ZW ); - an inverter with a bridge circuit comprising at least one first electronic switch (S1) and a second electronic switch (S2), wherein between said first electronic switch (S1) and said second electronic switch A first bridge midpoint (BM) is formed between switches (S2), wherein a series circuit consisting of said first electronic switch (S1) and said second electronic switch (S2) is connected in between said first port (E1) and second port (E2) of a DC voltage (U _ZW ); - control means (μC) for controlling at least said first electronic switch (S1) and said second electronic switch (S2); - a first port (A1) and a second port (A2) for connection to the hot filament ( _Wh ) of said discharge lamp (FL); - an inductor (L1) having a first port and a second port, wherein said first port of said inductor (L1) is connected to said first bridge midpoint (BM), wherein said inductor The second port of (L1) is connected to said first port (A1) for the hot filament ( _Wh ) of said discharge lamp (FL); - a first capacitor (C _z ) having a first port and a second port, wherein said first port is connected to said first port (A1 ) for said hot filament (W _h ), wherein said The second port is connected to the reference potential; - a first port (A3) and a second port (A4) for connection to the cold filament ( _Wc ) of said discharge lamp (FL); - a second capacitor (C _k1 ) having a first port and a second port, wherein said first port is connected to said cold filament (W _c ), wherein said second port is connected to said reference potential; - a first voltage divider (R3, R4) connected between said cold filament (W _c ) and said reference potential, wherein said first voltage divider (R3, R4) comprises a first ohmic resistor ( R3) and a second ohmic resistor (R4), wherein the taps of said voltage divider (R3, R4) are connected to the first input of said control means (μC); - a preheating device with a primary winding and at least one first secondary winding (SEK1), wherein said first secondary winding (SEK1) is connected to said cold filament (W) for said discharge lamp (FL) _c ) between said first port (A3) and a second port (A4); - a third capacitor (C _S ) in series with said first secondary winding (SEK1 ) of said preheating means; and - a series circuit consisting of at least one third ohmic resistor (R7) and a fourth ohmic resistor (R8), wherein said series circuit is connected at a first port (E1) for said mains DC voltage (U _ZW ) and the second terminal (E2), wherein the junction between the third ohmic resistor (R7) and the fourth ohmic resistor (R8) is connected to the cold filament (W _c ) connection; It is characterized in that the circuit arrangement further comprises: - a fifth ohmic resistor (R5) connected in parallel to the series circuit formed by said first secondary winding (SEK1) and said third capacitor (C _S ), The circuit arrangement further comprises a second voltage divider (R1, R2) with a sixth ohmic resistor (R1) and a seventh ohmic resistor (R2), wherein the second voltage divider (R1, R2) is connected to Between said first port (E1) and said second port (E2) for said mains DC voltage (U _ZW ), wherein the taps of said second voltage divider (R1, R2) are connected to The second input of the control means (μC) is connected. 2. The circuit arrangement as claimed in claim 1, characterized in that the control device (μC) is designed such that a voltage between the voltage on the second input and the voltage on the first input is formed difference. 3. The circuit arrangement according to claim 2, characterized in that the control device (μC) is further designed such that the difference corresponds to the voltage at the first input or at the second Standard for the voltage on the two inputs. 4. The circuit arrangement as claimed in claim 1, characterized in that the first voltage divider and the second voltage divider are dimensioned such that the difference is always positive. 5. The circuit arrangement as claimed in claim 2 or 3, characterized in that the control means ([mu]C) are further designed in such a way that the formation of the difference takes place before starting to activate the preheating means. 6. The circuit arrangement as claimed in claim 4, characterized in that the control means ([mu]C) are further designed in such a way that the formation of the difference takes place before starting to activate the preheating means. 7. The circuit arrangement according to claim 5, characterized in that the control device (μC) is designed such that a predeterminable period of time, in particular 50 to 200 ms, after switching on the circuit arrangement , preferably 100 ms to form the difference. 8. The circuit arrangement as claimed in claim 6, characterized in that the control device (μC) is designed such that the formation of the difference takes place within a predeterminable time period after switching on the circuit arrangement. 9. The circuit arrangement as claimed in claim 2 or 3, characterized in that the control device (μC) is designed in such a way that the normalized difference value is compared with a predeterminable threshold value, if the normalized difference value If it is greater than the preset threshold, the output of the preheating signal will not be performed. 10. The circuit arrangement as claimed in claim 8, characterized in that the control means (μC) are designed in such a way that the normalized difference value is compared with a predefinable threshold value, and if the normalized difference value is greater than a possible If the preset threshold value is set, the output of the preheating signal will not be performed. 11. The circuit arrangement as claimed in claim 9, characterized in that the predeterminable threshold value is variable, in particular the predeterminable threshold value can be varied by calibrating the circuit arrangement. 12. The circuit arrangement as claimed in claim 10, characterized in that the predeterminable threshold value is variable, in particular the predeterminable threshold value can be varied by calibrating the circuit arrangement. 13. The circuit arrangement according to any one of claims 1-3, characterized in that the first capacitor (C _S ) has a compressive strength between the ones to be connected at the first between one-tenth and one-fifth of the maximum power supply DC voltage (U _ZW ) between the first port (E1) and the second port (E2). 14. The circuit arrangement according to claim 12, characterized in that the first capacitor (C _S ) has a dielectric strength which is between the one to be connected at the first port (E1) and the between one-tenth and one-fifth of the maximum DC voltage (U _ZW ) of the power supply between the second ports (E2). 15. The circuit arrangement according to any one of claims 1-3, characterized in that the preheating means comprise a second secondary winding (SEK2), wherein the second secondary winding (SEK2) Connected between said first port (A1 ) and said second port (A2) for a hot filament ( _Wh ) of said discharge lamp (FL). 16. The circuit arrangement according to claim 14, characterized in that the preheating means comprise a second secondary winding (SEK2), wherein the second secondary winding (SEK2) is connected to the between said first port (A1 ) and said second port (A2) of the hot filament (W _h ) of the lamp (FL). 17. The circuit arrangement according to any one of claims 1-3, characterized in that the inductor (L1) is a primary winding of the preheating device. 18. The circuit arrangement as claimed in claim 16, characterized in that the inductor (L1) is a primary winding of the preheating device.