EP2138014A1

EP2138014A1 - Circuit arrangement for igniting and operating a discharge lamp

Info

Publication number: EP2138014A1
Application number: EP07728439A
Authority: EP
Inventors: Joachim MÜHLSCHLEGEL
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2007-04-24
Filing date: 2007-04-24
Publication date: 2009-12-30
Also published as: CN101658072A; CN101658072B; WO2008128577A1; US20100060180A1; TW200917901A

Abstract

The invention relates to a circuit arrangement for igniting and operating a gas discharge lamp. Said circuit arrangement comprises a half-bridge circuit acting as a step-down inverter, a lamp inductance (L1) and a resonance capacitor (19), which form a resonant circuit (17), and an ignition transformer (18) the secondary winding (L3) of which is connected on the end to a lamp electrode and on the other end to the junction (22) between the lamp inductance (L1) and the resonance capacitor (19). The primary winding (L2) of the ignition transformer is connected on the one end to the junction (22) between the lamp inductance (L1) and the resonance capacitor (19) and on the other end to the junction (20) of two series-connected diodes (D1, D2), said diodes being connected to the power supply (3) and to ground (1).

Description

description

[1] Circuit arrangement for the ignition and operation of a discharge lamp.

Technical area

[2] The invention relates to circuit arrangements and electronic operating devices for the ignition and operation of discharge lamps. Electronic control gear for gas discharge lamps has been on the rise for years, offering significant advantages over conventional ballasts, such as higher light quality, better light output and automatic shutdown of the gas discharge lamps at the end of their life. So far, circuits with a so-called full bridge have been used for high-pressure gas discharge lamps, which operate the lamp with a kind of alternating direct current. This is necessary because most high pressure gas discharge lamps can not operate with higher frequency AC currents due to resonances in the burner vessel. For the ignition usually a pulse igniter is used, for which another switch is needed to trigger the ignition pulse. Since this type of inverter is very complicated and expensive, it has recently gone over to operate the lamps with a symmetrical half-bridge.

State of the art

[3] To ignite the lamp with such a circuit can also be used a pulse ignitor. In EP 1 585 372 A1 a half-bridge circuit with such a pulse ignition device is disclosed. The circuit of the ignitor is not specified in this document, they but usually consists of at least one switch, a firing capacitor and an ignition transformer. This additional switch and the corresponding control of the same cause not to be underestimated costs. For a short time, however, attempts have been made to use a resonance ignition for the ignition of the gas discharge lamp. For example, US Pat. No. 7,170,235 B2 proposes combining an inverter in half or full bridge circuit with a resonance ignition of the gas discharge lamp. The resonance is in this case generated with its own high frequency controlled switch, which also causes high costs with the associated drive circuit.

task

[4] The object of the present invention is therefore to provide a circuit arrangement with a half-bridge, which has a resonance ignition without the use of a high-frequency-controlled switch or without a controlled switch.

Presentation of the invention

[5] This object is solved by the features of patent claim 1 and method claim 11. Particularly advantageous embodiments of the invention are described in the dependent claims.

The circuit arrangement according to the invention consists of a half-bridge whose center 24 is connected to a lamp inductor Ll, which forms a series resonant circuit 17 together with a resonant capacitor 19. This series resonant circuit 17 is connected via the primary winding L2 of a Zundtransformators 18 an excessive voltage for the ignition and the acquisition of the gas discharge lamp 5 ready. This high-frequency resonance voltage is also applied to the primary winding L2 of the ignition transformer 18 and causes a current through the primary winding L2, which is derived via two series-connected diodes Dl and D2, and is transformed into a high voltage in the secondary winding L3. Alternatively, instead of the second diode D2, a low-cost, slow-acting switch can be used, which is switched on during the ignition phase and remains switched off after the ignition of the gas discharge lamp. By this measure, the resonance voltage of the series resonant circuit is superimposed on a high ignition voltage, which can ignite the gas discharge lamp 5 safely. A more expensive because fast switch with complex high-frequency control can thus be saved.

[7] A favorable dimensioning for 7OW gas discharge lamps can look like this:

Short description of the drawing [8] FIG. 1 Circuit diagram of the circuit arrangement according to the invention according to the first embodiment.

[9] FIG. 2 Circuit diagram of the circuit arrangement according to the invention with a DC voltage suppression capacitor C2 according to the second embodiment.

[10] FIG. 3 Representation of relevant signals during resonance excitation according to the first embodiment.

[11] FIG. 4 Effect of the DC suppression capacitor C2 of the second embodiment in rated operation.

[12] Fig. 5 Representation of relevant signals at resonance excitation according to the second embodiment.

Preferred embodiment of the invention

[13] In the following, two embodiments of the present invention will be described.

First embodiment

[14] The circuit arrangement of the first embodiment consists of a symmetrical half-bridge, which contains two serially arranged switches Sl and S2 with the associated coupling capacitors C3 and C4. The open ends of the series circuits are connected, on the one hand, to the voltage supply 3 and, on the other hand, to the circuit ground 1. Between the power supply 3 and the circuit ground 1 is the intermediate circuit voltage U _z . Between the connection points 24 of the two switches and 26 of the two capacitors, a series circuit of a lamp inductor Ll, the secondary winding L3 of a Zundtransformators 18 and the gas discharge lamp 5 is connected. At the connection point 22 of the lamp inductor Ll and the secondary winding of the ignition transformer L3, a resonance capacitor 19 is connected, which is composed of at least one of the capacitances Cl and / or CIl and / or C5. The resonant capacitor 19 together with the lamp inductor Ll the series resonant circuit 17. The primary winding is also connected to one side to the connection point 22. The other side is connected to the connection point of two series-connected diodes, which in turn are connected at the ends to the power supply 3 and to the circuit ground 1. The cathodes of the diodes each point in the direction of the power supply 3.

[15] If the half-bridge is now operated at a suitable frequency during the ignition phase, the resonant circuit from the resonance capacitor 19 enters into resonance with Ll, and a peak voltage arises which clearly exceeds the positive and the negative DC link - voltage oscillates. The peak value of the resonance voltage can be 300V - 1500V higher than the DC link voltage. Since the primary winding with one side is also connected to the resonance capacitor 19, during the resonance excitation, a high superimposition voltage is formed on the secondary side of the ignition transformer, which is added to the resonance voltage and this resulting voltage then forms the gas discharge lamp connected to the circuit arrangement can ignite. The ignition voltage can reach a maximum amplitude of 1000V - 3000V.

[16] The process will be described below with reference to FIG. 3. Waveform 30 represents the voltage at half-bridge center 24 versus circuit ground 1. It can clearly be seen to toggle between about 0 and 400V. The signal curve 34 represents the voltage at the resonance capacitor 19. By the resonant excitation, the rectangular waveform is transformed into a sine wave and a voltage with an amplitude of approximately 900 V is generated. The waveform 36 shows the voltage across the lamp, which is composed of the voltage 34 at the resonant capacitor 19 and a superimposed over the Zund transformer part. A voltage with an amplitude of approx. 2000V is generated. The resonance voltage applied across the resonant capacitor 19 is applied to the diode center 20 via the primary winding L2 of the ignition transformer 18. Since the resonance voltage is substantially higher than the intermediate circuit voltage U _z , alternately the first diode D 1 or the second diode D 2 becomes conductive, depending on whether the positive or the negative half-wave of the resonance voltage is present. As a result, the voltage at point 20 is clamped to the voltage at voltage supply point 3 or to ground 1. This creates a waveform that is very similar to a square wave. In resonance mode, therefore, a considerable current flows through the primary winding L2 of the ignition transformer 18, from which the ignition transformer 18 generates the aforementioned superposition voltage. [17] When the lamp has ignited, the bridge will be operated with a low frequency square wave voltage in the range of approximately 60Hz - 500Hz. In order to realize the voltage-lowering property of the arrangement, a high-frequency control is superimposed on this low-frequency operation, so that the switch closed at low-frequency is clocked in terms of high-frequency. The frequency of the control is selected so that the bridge switches switch quasi-resonant, so that only small switching losses occur. Quasi-resonant in this context means that the inductor current is at the boundary between lagging and non-lagging operation. The high-frequency square-wave voltage of the bridge is smoothed by the resonant circuit 17, which acts as an LC filter in this frequency range, and is supplied to the lamp as a square-wave voltage with a high-frequency voltage ripple.

The winding ratio of the ignition transformer and the voltage ripple on the resonant capacitor 19 are selected so that in normal operation (high-burned lamp) through the primary winding L2 of the ignition transformer 18 no or only a very small current flows, since the diodes Dl and D2 are predominantly in locking state. Due to the negligible current through the primary winding L2 affects almost the entire Leerlaufinduk- activity of the secondary winding L3 as a filter inductance. The inductance of the secondary winding L3 when the primary winding L2 is open can be regarded as an open-circuit inductance. By Umschwingvorgänge during commutation short current pulses may arise, which are derived via the diodes Dl and / or D2. The current pulses can be detected on the one hand by voltage pulses at point 22 or other on the one hand by coupled voltage pulses to the primary winding via the ignition transformer 18 arise. The coupled voltage pulses occur due to the lamp commutation, and are transmitted from the secondary side of the ignition transformer to the primary side.

^ 19] The two diodes Dl and D2 thus act as switching elements that generate during the ignition phase an AC flow through the primary winding L2 and thus a high ignition voltage, and are open during normal operation and prevent current flow through the primary winding, so that the ignition transformer in this phase acts as a choke with high inductance.

^ 20] A favorable dimensioning for 7OW gas discharge lamps can look like this:

Second embodiment

[21] The second embodiment is very similar to the first embodiment. Therefore, only the differences from the first embodiment will be set forth.

[22] As an alternative to this dimensioning, a DC block can be connected between the primary winding L2 and the diode center 20. Capacitor C2 are switched, which prevents the current flow in the primary winding during normal operation. Of course, the DC block capacitor C2 can also be arranged at a suitable other point of the path from point 22 to point 1 or to point 3. The DC block capacitor gives you more freedom in dimensioning for the winding ratio and the voltage ripple on Cl. This can be understood with reference to FIG. 4. Signal 31 shows the intermediate circuit voltage, which is applied at point 3. Signal 35 shows the voltage at the center of the diode against the ground point 1. The voltage is within the intermediate circuit voltage, since at higher voltages the diodes would become conductive and thus clamp the voltage to the intermediate circuit voltage as in resonance mode. Signal 37 shows the voltage at the primary winding L2 against the ground point 1. Since only direct current can flow via the diodes D1 and D2, C2 prevents the current flow in the event that the voltage ripple at the diode end 20 of the primary winding L2 in normal operation temporarily above the intermediate circuit voltage. In this case, C2 is charged after the commutation of the low-frequency lamp current to a voltage corresponding to the difference between the peak value at the primary winding and the intermediate circuit voltage. Signal 33 represents the current through the primary winding L2. It is not difficult to see that almost no current flows through the primary winding L2, even though the voltage ripple on the capacitor 19 is higher than the intermediate circuit voltage. Due to the fact that no current flow through the primary winding takes place, in normal operation the ignition transformer can fully act as a smoothing choke, and the gas discharge Protect lamp 5 from the high voltage ripple on capacitor 19.

[23] During resonant excitation in the generation of the ignition voltage, C2 almost does not hinder the flow of current. Fig. 5 shows the current in the primary winding L2 (signal 43) and the voltage across the lamp during the Zundvor- gang. In this case, a high-frequency alternating current alternately flows through Dl and D2, so that C2 is constantly reloaded. The signal 53 represents this current. This high-frequency alternating current in the primary winding in this case flows through C2. Signal 52 represents the voltage across resonant capacitor 19, and signal 54 represents the firing voltage across the lamp. The comparison with FIG. 3 reveals that the generation of the ignition voltage by the DC block capacitor C2 is not impaired.

Third embodiment

[24] The third embodiment is similar to the second embodiment. Therefore, only the differences from the second embodiment will be described.

In the third embodiment, the second diode D2 is replaced by a controlled switch which, together with the DC negative-pressure capacitor (C2), allows current to flow through the primary winding L2 of the ignition transformer 18 during ignition. For this purpose, the switch is closed during the Zundbetriebs, whereas it is open during normal operation of the gas discharge lamp. Thus flows during normal operation of the gas discharge lamp 5 no appreciable current. When opening the switch after the ignition takes over the diode Dl the still flowing through the primary winding L2 of Zundtransfor- mators 18 stream.

Fourth embodiment

[26] The fourth embodiment is similar to the third embodiment. Therefore, only the differences from the second embodiment will be described.

[27] The fourth embodiment is further simplified compared to the third embodiment. The first diode Dl is saved in this embodiment, so that when opening the switch, the interruption of the current flow through the primary winding L2 of the ignition transformer 18 causes an excessive voltage across the primary winding L2 of the ignition transformer 18. In this case, the switch must be designed for this increased load or have a corresponding circuit for suppressing the excessive voltage.

Claims

claims

1. Circuit arrangement for igniting and operating a gas discharge lamp with a half-bridge arrangement which operates as a low-setting inverter in quasi-resonant operation, a lamp inductor (L1) and a resonant capacitor (19) which form a resonant circuit (17) and an ignition transformer ( 18) whose secondary winding (L3) on the one hand connected to a lamp electrode and on the other hand to the connection point (22) between the lamp inductor (Ll) and resonant capacitor (19) is connected, characterized in that the primary winding (L2) of the ignition transformer (18) is connected at its first end to the connection point (22) between lamp inductor (Ll) and resonance capacitor (19) and connected at its second end to the connection point (20) of two series-connected diodes (Dl, D2), wherein the first diode (Dl ) to the power supply (3), and the second diode (D2) is connected to circuit ground (1).

2. A circuit arrangement according to claim 1, characterized in that in the path between the connection point (22), between the lamp inductor (Ll) and resonant capacitor (19), and the circuit ground (1) or the supply voltage (3) a Gleichspannungsunterdrü- ckungskondensator (C2 ) is switched.

3. Circuit arrangement according to claim 2, characterized in that between the primary winding (L2) of the ignition transformer and the connection point (20) of serially connected diodes (Dl, D2) a DC voltage suppression capacitor (C2) is connected.

4. Circuit arrangement according to one of the preceding claims, characterized in that the ratio of the inductances (L3 / L2) of the ignition transformer (18) is in the range between 0.5 and 10.

5. Circuit arrangement according to one of the preceding claims, characterized in that the ratio of the inductances (L3 / L2) of the ignition transformer (18) is in the range between 0.7 and 5.

6. Circuit arrangement according to one of the preceding claims, characterized in that during the ignition operation on the resonant capacitor (19) produces a resonance voltage whose amplitude is between 300V and 1700V.

7. Circuit arrangement according to one of the preceding claims, characterized in that the voltage ripple at the connection point (22) between the lamp inductor (Ll) and resonant capacitor (19) during operation with a low-frequency square current is greater than 10 OV from maximum to maximum.

8. Circuit arrangement according to one of the preceding claims, characterized in that the second diode (D2) is designed as a controlled switch.

9. Circuit arrangement according to one of the preceding claims, characterized in that the controlled switch is closed during the ignition process, and is open during operation with the low frequency rectangular current.

10. Circuit arrangement according to claim 7, characterized in that the first diode (Dl) is omitted.

11. A method for igniting and operating a gas discharge lamp (5) with a capacitor (19), a series circuit of an inductance (Ll), a transformer (18) and the gas discharge lamp (5), wherein during the ignition, the inductance (Ll) as Resonance inductance acts, the transformer acts as an ignition transformer and the capacitor (19) acts as a resonant capacitor, whereas during operation of the gas discharge lamp, the inductance (Ll) acts as a lamp choke, the transformer (18) as Filterdros- sei and the capacitor (19) as a filter capacitor, wherein the inductance (Ll) and the capacitor (19) form a resonant circuit (17) during ignition, characterized in that the resonant circuit (17) generates a first voltage during ignition, which generates a current through the primary winding (L2 ) of the ignition transformer results and then a second voltage at the secondary winding (L3) of the transformer (18) is formed, and the first and the second voltage add up to an ignition voltage such that the ignition voltage across the lamp is increased by a factor of 1.5-10 from the first voltage, during operation, the current through the primary winding (L2) of the transformer (18) is small that the secondary winding (L3) of the ignition transformer mators (18) with a large part of their Leerlaufinduk- tivity acts as a filter choke.

12. A method for ignition and operation of a gas discharge lamp (5) according to claim 11, marked thereby, that the ignition voltage is increased by a factor of 1.5-3 relative to the first voltage.

13. Method for igniting and operating a gas discharge lamp (5) according to claim 11 or 12, characterized in that the resonant circuit is no longer appreciably excited during the lamp operation, and the current through the primary winding (L2) of the transformer (18) thereby becomes negligibly small.

14. A method for the ignition and operation of a gas discharge lamp (5) according to claim 11 to 13, character- ized in that at least one switching element is in series with the primary winding, which during the ignition current flow through the primary winding

(L2) of the transformer (18), and which during operation prevents the flow of current through the primary winding (L2) of the transformer (18).