EP1583403B1 - Ballast for at least one lamp - Google Patents

Abstract

A starter for a lamp (La) comprises at least two series switches (S1,S2) having a control circuit , power connection (Uo) and resonance lighting circuit between the switches and lamp comprising a series inductance (L1) and resonance capacitor (C1) ac parallel to the lamp connections (10,12). A retarding inductance (LB1) is in series with the lamp.

Description

Technical area

The present invention relates to a ballast for at least one lamp, in particular a ballast according to the preamble of claim 1.

The problem underlying the invention is the sake of clarity for the sake of the example of a high-pressure discharge lamp shown, for example, in the WO 02/30162 A2 , of the WO 03/024161 A1 or the US 2002/0041165 A1 are described. Of course, the invention can also be used in other types of lamps, in particular other circuit topologies with resonance ignition. To operate a high-pressure discharge lamp, a sinusoidal AC operating voltage is required, the operating frequency depending on the geometry of the lamp burner in the range between 45 kHz to 55 kHz usually wobbled in a sawtooth 100 Hz cycle or gesweept. The Sweepbetrieb generally prevents the excitation of acoustic resonances and thus contributes to the stabilization of the plasma arc. The output stage of an electronic ballast for the above-mentioned operating frequency range is usually realized with an LC resonant circuit. To reduce the amount of components and thus space and cost-saving realization of the ballast, the LC output circuit in addition to its impedance and filtering behavior can be designed so that by resonant excitation, the generation of Lampeenzündspannung, typically depending on the lamp at 3.5 kV to 5 kV is possible. The possibility of resonant generation of the ignition voltage is a special constraint on the design and dimensioning of the LC circuit, since in this case both the inductance used and the capacity used a sufficiently high energy carrying capacity must have, so that the necessary Zündspannungshöhe can be achieved. In the case of the inductance, therefore, an air gap is usually to be provided.

High-pressure discharge lamps now have the property that immediately after the ignition breakdown the nominal operating mode with nominal lamp impedance does not set, but the still cold lamp reacts with a gas amplification breakthrough and often completely immediately after the ignition breakdown for a short time, typically 0.5 μs to 100 μs becomes conductive, d. H. the burning voltage can be less than 5V. With respect to the resonant output circuit charged to ignition voltage, this represents a sudden short circuit over which the effective capacitances charged to ignition voltage (including lamp line) are correspondingly discharged quickly and abruptly. Depending on the size of the effective capacitance and the remaining line inductances, these brief short-circuit currents can rise to several 100 A.

This unsteady start-up behavior of a high-pressure lamp after Zünddurchbruch represents for the components involved, in particular for the capacitors in the resonant circuit as well as due to stray currents for the rest of the electronic ballast, a stress situation that often lead to failures and thus the destruction of the ballast can.

State of the art

From the prior art, no measure is known to prevent this stress situation. The US 2001/0020830 A1 shows in her Fig. 5 a similar topology as a preferred embodiment of a ballast according to the invention, however, the known circuit arrangement relates to a different problem and does not solve the above-presented object of the present invention:

The US 2001/0020830 A1 basically relates to circuit arrangements for high-pressure discharge lamps and in particular the implementation of ignition circuits in rectangular ECGs.

A rectangular operation basically means nothing other than an alternating DC operation, ie the lamp is principally operated with direct current, but for reasons of unilateral electrode wear, the current direction is changed now and then. The latter occurs at a low frequency in the range of approximately 100 Hz. The adaptation of the intermediate circuit voltage of the electronic ballast to the usually lower lamp voltage is carried out using a buck converter circuit. In this case, a throttle was operated on a capacitor for smoothing. In the FIGS. 1 and 4 of the US 2001/0020830 A1 In each case, the inductor L2 is operated on the capacitor C2, while in Fig. 5 This reference the reactor L1 is operated on the capacitor C1. Since the lamps usually tolerate little ripple, the smoothing capacitor usually has to be made large, for example 100 nF. Since, as stated, large smoothing capacitor to be selected is arranged parallel to the lamp, there is the problem that the ignition is difficult or completely prevented, as well as the large smoothing capacitor must be charged by the ignition voltage.

The US 2001/0020830 A1 now deals with topologies in which different firing arrangements have been inserted within the range smoothing capacitor and lamp:

In Fig. 1 of the US 2001/0020830 A1 For example, a resonant circuit comprising the inductor L1 and the capacitor C1 is switchably inserted. The smoothing capacitor C2 does not see the ignition voltage here. After the Zünddurchbruch the lamp, the inductor L1 is arranged as a useless part in the lamp current path and should not need too much power at a suitable dimensioning.

The solution according to the Fig. 5 of the US 2001/0020830 A1 concerns another approach: Here, the Tiefsetzarrangement, comprising the inductance L2 and the capacitor C1, itself aufresoniert to ignite, but due to the large smoothing capacitor initially much current, but little voltage in the resonant circuit arises. This large resonant circuit current is now taken up by a transformer comprising the inductance L2 of the resonant circuit and an inductance L3 as an I / U converter, transformed into a correspondingly high voltage and fed to the lamp. L2 acts as primary side and L3 as secondary side. Accordingly, typical numbers of turns are, for example, one turn for L2 and 10 to 100 turns for L3. By this procedure, the lamp now sees the high resonance current as a high resonance voltage and thereby ignites. Because of her for the task of US 2001/0020830 A1 When dimensioned dimensioning is associated with a low current-carrying capacity, the inductances can not act as brake inductances in the sense of the present invention.

Presentation of the invention

The object of the present invention is to develop a generic ballast in such a way that it allows an improved, especially safer lamp start. In this case, in particular, the stress to which the components are exposed, reduced and thus a longer life of such a ballast can be achieved.

This object is achieved by a ballast with the features of claim 1.

The invention is based on the finding that the current can be kept below a predefinable, still acceptable threshold immediately after Zünddurchbruch when a brake inductance is arranged in series with the lamp.

For the purposes of the present application, the term alternating current is understood to mean the circuit structure that results in the AC equivalent circuit diagram. For example, the resonance capacitance is arranged parallel to the first and second terminal for the lamp when it is directly connected to ground or indirectly, for example via a power supply, is coupled to the ground or combinations of these two variants.

A preferred embodiment is characterized in that the resonance inductance and the first brake inductance are wound on a common core. This concept is based on the recognition that a separate brake inductance, which is not wound on the core of the resonance inductance, also has to be made large, so that it can carry the same energy as the resonance inductance. In particular, it would also have to have a core with an air gap. The measure of this preferred embodiment can thus save a core. This results in a reduction of the costs as well as the size.

It is preferred here that the winding sense of the resonance inductance and this brake inductance on the core is in the same direction.

However, the use of only one Bremsinduktivität that is wound on the same core in the same direction as the resonance inductance, but that of the resonance inductance, which also represents the filter inductance in the nominal mode, shares of the rectangular voltage signal at the connection point of the two switches are transmitted to the first brake inductance and thereby harmonics in the spectrum of the lamp driving current are included. This is due to the lamp on a signal that has rectangular components and sensitive lamps leads to the disadvantages known to the person skilled in the art, for example poor luminous values, increasing the risk of extinction, etc.

This problem can be addressed by providing a second brake inductor arranged serially to the resonant capacitance. Preferably, the first and second Bremsinduktivität are the same size.

When the resonant inductance, the first and second brake inductances are wound on the same core, in particular in the same direction, the effects of the two brake inductances compensate each other in the nominal mode, and the resonant arrangement including its filtering effect is identical to the arrangement with only a single resonant choke.

On the other hand, after the ignition breakdown, the effects of the first and second brake inductances do not completely cancel each other out. By loose coupling namely creates a residual stray inductance, which also has the full power and energy carrying capacity and thus can limit the amount of discharge current through the lamp sufficiently well after Zünddurchbruch.

It is preferred that the leakage inductance resulting from the coupling of the first and the second brake inductance is at least 10 μH, preferably at least 40 μH.

The values of the brake inductances themselves are preferably at least 60 μH, more preferably at least 120 μH.

In general, it can be stated that the first brake inductance or the first and the second brake inductance, depending on how sensitive the lamp is to be operated, the current through the lamp after the Zünddurchbruch the lamp to a maximum of 50 A, preferably to a maximum of 30 A. , limit.

As is obvious to a person skilled in the art, it is irrelevant for the realization of the invention whether an LC resonant circuit for the nominal operation of the lamp and an LC resonant ignition circuit are formed separately or realized by one and the same LC circuit.

Further advantageous embodiments will become apparent from the dependent claims.

Brief description of the drawings

Figur 1

ein erstes Ausführungsbeispiel eines erfindungsgemäßen Vorschaltgeräts mit einer Bremsinduktivität;

Figur 2

ein zweites Ausführungsbeispiel eines erfindungsgemäßen Vorschaltgeräts mit einer Bremsinduktivität;

Figur 3

ein drittes Ausführungsbeispiel eines erfindungsgemäßen Vorschaltgeräts mit zwei Bremsinduktivitäten; und

Figur 4

ein viertes Ausführungsbeispiel eines erfindungsgemäßen Vorschaltgeräts mit zwei Bremsinduktivitäten.

Figur 5

ein fünftes Ausführungsbeispiel eines erfindungsgemäßen Vorschaltgeräts mit zwei Bremsinduktivitäten.

In the following, embodiments of the invention will now be described in detail with reference to the accompanying drawings. Show it:

FIG. 1

a first embodiment of a ballast according to the invention with a brake inductance;

FIG. 2

A second embodiment of a ballast according to the invention with a Bremsinduktivität;

FIG. 3

A third embodiment of a ballast according to the invention with two Bremsinduktivitäten; and

FIG. 4

A fourth embodiment of a ballast according to the invention with two Bremsinduktivitäten.

FIG. 5

A fifth embodiment of a ballast according to the invention with two Bremsinduktivitäten.

Preferred embodiment of the invention

FIG. 1 shows a first embodiment of a ballast according to the invention. There are two switches S ₁ and S ₂ , which are mutually opened and closed. Corresponding drive circuits are well known to the person skilled in the art. They are supplied by a supply voltage U ₀ , which is also connected to two coupling capacitors C _K1 and C _K2 . A lamp La is connected to a resonance ignition circuit having a resonance inductance L ₁ and a resonance capacitance C ₁ . To control the discharge current of the effective capacitances directly after the ignition breakdown, a brake inductance L _{B1 is} provided, which is arranged in series with the lamp La, specifically between the lamp La and the resonant inductance L ₁ . For optimum control of the discharge current, the Brake inductance L _{B1 have the} same energy carrying capacity as the resonance inductance L ₁ used to generate the resonance voltage. As shown, the resonance inductance L ₁ and the brake inductance L _{B1 are} coupled in the same direction.

While FIG. 1 shows a ballast according to the invention with a half-bridge arrangement is in FIG. 2 an embodiment shown with a full bridge arrangement in which the coupling capacitors C _K1 and C _{K2 are} replaced by switches S ₃ and S ₄ .

At the in FIG. 3 illustrated embodiment of a ballast according to the invention, a second brake inductance L _{B2 is} provided, which is arranged in series with the resonance capacity. It is wound on the same core as the resonance inductance L ₁ and the first brake inductance L _B1 , in particular also in the same direction.

Preferably, the air gap is arranged below the second brake inductance to produce a leakage inductance of sufficient magnitude.

The effective brake inductance is accordingly the stray inductance L _stray resulting from the coupling of the first brake inductance L _B1 with the second brake inductance L _B2 . L _litter is at least 10 μH, preferably at least 40 μH. The maximum current I _max results when all the effective capacitances are combined into an effective capacitance C and U is the voltage across such an effective capacitance $$I_{\mathrm{Max}}=\sqrt{\frac{\frac{1}{2}{\mathit{<figure-callout\; id="2"\; label="CU"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">CU</figure-callout>}}^2}{\frac{1}{2}{L}_{\mathit{litter}}}}$$

The brake inductance (s) is / are to be interpreted such that the current through the lamp after ignition breakdown is limited to a maximum of 50 A, preferably to a maximum of 30 A.

FIG. 4 shows that in FIG. 3 illustrated ballast according to the invention in full bridge arrangement, the coupling capacitors C _K1 and C _{K2 are} replaced by switches S ₃ and S ₄ again.

In the embodiments of the Figures 1-4 For example, the brake inductance LB1, which is connected in series with the lamp, is always connected between the lamp La and the resonance inductor L1. Ie. the brake inductance LB1, which is connected in series with the lamp, is connected to the terminal of the lamp La, which is coupled to the resonance ignition circuit. This connection has a high voltage against a ground potential before ignition. If the lamp La is connected to the ballast via a longer cable, between the said terminal of the lamp La and the ground potential, a parasitic capacitance is formed which may have a value of several hundred picofarads. In the embodiments of the Figures 1-4 For example, during the gas amplification breakdown of the lamp La, the energy stored in the parasitic capacitance may unrestrainedly discharge via a protective earth or ground terminal. This discharge may cause the ballast to malfunction or be destroyed. In particular, because discharge currents flow via ground lines and thus reference potentials of the ballast are moved.

Remedy against high discharge currents from parasitic capacitances provides an embodiment of a ballast according to the invention FIG. 5 , This embodiment corresponds essentially to the embodiment FIG. 3 , The difference to FIG. 3 is that now the lamp La is connected between the brake inductance LB1 and the resonance inductor L1. The brake inductance LB1 is thus connected to the lamp terminal designated by 12. This alternative arrangement of the brake inductance LB 1 causes discharge currents of parasitic capacitances to flow through the brake inductance LB1 and thus the value of these discharge currents is also reduced. Also, discharge currents of parasitic capacitances can in the embodiment according to FIG. 5 the ballast does not disturb or destroy.

The above statements on winding direction and couplings also apply to this brake inductance LB 1.

In the embodiment according to FIG. 5 is an alternative arrangement of the brake inductance LB1 compared to the embodiment according to FIG. 3 shown. Accordingly, the embodiments of the FIGS. 1, 2 and 4 be carried out with the alternative arrangement of the brake inductance LB1. This is advantageous when parasitic capacitances to earth potential have large values. If a symmetrical wiring of the lamp La is desired, the Bremsinduktivität LB 1 can also be divided and arranged on both sides of the lamp La.

Claims (12)

1. Ballast for at least one lamp (La) having

   - at least two switches (S₁, S₂), two switches in each case being arranged in series;

   - a control circuit for alternately opening and closing at least two switches arranged in series;

   - a connection for applying a supply voltage (U₀) to in each case two switches (S₁, S₂) arranged in series;

   - a resonant starting circuit, the resonant starting circuit being coupled on the input side to the junction point between two switches (S₁, S₂) arranged in series and on the output side to a first connection (10) for the lamp (La), the resonant starting circuit having a resonant inductance (L₁) which is arranged in series with the junction point between the two switches (S₁, S₂) and the first connection (10) for the lamp (La), and a resonant capacitance (C₁) which is arranged for alternating current purposes in parallel with the first and second connections (10, 12) for the lamp (La),

   characterized
   in that at least a first braking inductance (L_B1) is provided which, for alternating current purposes, is firstly arranged in series with the lamp (La) and secondly in parallel with the resonant capacitance (C₁) the resonant inductance (L₁) and the first braking inductance (L_B1) being wound onto a common core.
2. Ballast according to Claim 1,
   characterized
   in that the core is part of the resonant inductance (L₁).
3. Ballast according to either of Claims 1 and 2,
   characterized
   in that the winding sense of the resonant inductance (L₁) and the first braking inductance (L_B1) on the core is the same.
4. Ballast according to one of the preceding claims,
   characterized
   in that a second braking inductance (L_B2) is provided which is arranged in series with the resonant capacitance (C₁).
5. Ballast according to Claim 4,
   characterized
   in that the first and the second braking inductances (L_B1, L_B2) are equal in value.
6. Ballast according to either of Claims 4 and 5,
   characterized
   in that the resonant inductance (L₁) and the first and the second braking inductances (L_B1, L_B2) are wound onto the same core.
7. Ballast according to one of Claims 4 to 6,
   characterized
   in that the winding sense of the resonant inductance (L₁) and the first and the second braking inductances (L_B1, L_B2) is the same.
8. Ballast according to one of Claims 4 to 7,
   characterized
   in that the coupling of the first and the second braking inductances (L_B1, L_B2) produces a stray inductance (L_stray) which is at least 10 µH, preferably at least 40 µH.
9. Ballast according to one of the preceding claims,
   characterized
   in that each braking inductance (L_B1, L_B2) is at least 60 µH, preferably at least 120 µH.
10. Ballast according to one of the preceding claims,
    characterized
    in that the first braking inductance (L_B1) or the first and the second braking inductances (L_B1, L_B2) are designed to limit the current (I_max) through the lamp (La) after the initial breakdown in the lamp (La) to a maximum of 50 A, preferably to a maximum of 30 A.
11. Ballast according to one of the preceding claims,
    characterized
    in that the first braking inductance (L_B1) is connected between the lamp (La) and the resonant inductance (L₁).
12. Ballast according to one of Claims 1 to 10,
    characterized
    in that the lamp (La) is connected between the first braking inductance (L_B1) and the resonant inductance (L₁).

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