EP1330946B1 - Circuit arrangement for operating several gas discharge lamps - Google Patents

Abstract

A circuitry arrangement for operating n gas discharge lamps, n being a whole number greater than 1, includes a single inverter, fed with d.c. voltage, for generating an a.c. voltage alterable in its frequency, delivered to a load circuit arranged at the inverter's output. The load circuit includes a series resonant circuit of an inductance and capacitance, n gas discharge lamps connected to a common node point between the inductance and capacitance, which lamps are connected in parallel to one another, and (n-1) balancing transformers for balancing currents in two gas discharge lamps. The load circuit further has for each gas discharge lamp at least one d.c. current supply line, connected between an output side terminal of a corresponding balancing transformer winding and gas discharge lamp and via which there is delivered to each gas discharge lamp a d.c. current, so as to avoid an unintended extinguishing of a lamp.

Description

The present invention relates to a circuit arrangement for operating at least two gas discharge lamps according to the preamble of claim 1.

Through the use of so-called two- or multi-lamp ballasts can in To a certain extent, a reduction of the circuit complexity can be achieved. Of the Advantage over the use of ballasts, each only one drive only gas discharge lamp, is that a large part of the Components of the ballast, such as the rectifier, the Harmonic filter, the control circuit and the inverter for operating multiple Lamps can be used simultaneously.

The inverter and the load circuit of a known two-lamp ballast, which is disclosed in EP 0 490 329 A1, are shown schematically in FIG. 4 and will be briefly explained below. The inverter is formed by two controllable switches S1 and S2, which are arranged in a half-bridge arrangement, at the input of which a DC supply voltage V _BUS is present. From a control circuit 1, the two switches S1 and S2 are driven so that they alternately open and shoot, so that at the midpoint of the half-bridge results in a high-frequency AC voltage U _ac . This alternating voltage is supplied to the load circuit, which initially has on the input side a series resonant circuit consisting of an inductance L _a and a capacitor C _r . At the common node between the inductance L _a and the capacitance C _r , the two gas discharge lamps LA1 and LA2 are each connected in parallel via a coupling capacitor C _k1 or C _k2 .

In addition, the two gas discharge lamps LA1 and LA2 is preceded by a balancing transformer L _bal whose windings are traversed by the two lamp currents. This occurs in opposite directions, so that in the case of deviations of the current amplitudes, a magnetization is produced which induces a voltage in the windings, which in turn acts in a symmetrizing manner. By the balancing transformer L _bal thus component tolerances and lamp tolerances and different temperature conditions, which would result in that the two lamps LA1 and LA2 burn with different brightness, can be compensated to a certain extent.

However, the balancing effect of the transformer L _bal is limited and does not ensure complete alignment of the lamp currents. For example, the lamps are connected in parallel at low currents, which result at low dimming levels, since the voltage drop across the balancing transformer can only be a fraction of the burning voltage of the lamps. This is particularly evident at lower temperatures, where the burning voltage reaches a maximum with small lamp currents.

This case is shown in FIG. In this case, the two lamps are to be operated at a brightness which corresponds to a certain nominal current I _SOLL . Due to tolerances, however, both lamps are not identical, but have slightly shifted characteristic curves U _arc1 and U _arc2 , as shown in FIG. For example, the second lamp generally requires a slightly higher _burning voltage U _arc2 than the first lamp for a given current. Therefore, in order to be able to operate both lamps with the nominal current I _SOLL , two different _burning voltages U _SOLL1 and U _SOLL2 would be required. However, since the ballast with the inverter only provides a voltage _value U _SOLL1 , which is determined in the example shown by the lamp with the lower burning voltage, ie by the first lamp with the characteristic U _arc1 , this voltage U _{SOLL1 is} also at the second Lamp on. As a result, the second lamp does not assume the desired current value I _SOLL , but possibly forms a second operating point with a different current value I _arc2 and thus of course also with a different brightness. However, there is also the danger that the second lamp with the higher operating voltage may not be able to form a fixed operating point and, as a result, it will disappear.

Therefore, in order to avoid the extinction of one of the two lamps LA1 or LA2 at low brightness values, the control of the inverter always takes place in the case of the ballast shown in FIG. 4 after that lamp LA1 or LA2, which currently has the lower lamp current. For this purpose, the ballast on two detection circuits 2 ₁ and 2 ₂ , each detecting the current flowing through a lamp LA1 and LA2 current by determining the drop across a measuring resistor R _SENS1 or R _SENS2 voltage. The actual values V _IST1 and V _IST2 generated by the two detection _circuits 2 ₁ and 2 ₂ are then fed to a comparison circuit 3, which selects the correspondingly lower value and forwards the final actual value V _IST to the control circuit 1 for controlling the inverter.

Thus, a separate detection circuit is necessary for each lamp to be reliable to be able to ensure that neither of the two lamps goes out. Of the However, circuit complexity is thereby increased again. About that In addition, it should be noted that due to the switching capacities of the lamps or through the wiring always a capacitive current flows through the lamps. However, a perfect regulation is only guaranteed if the actual effective component of the lamp current is determined. These are elaborate and expensive circuits necessary. Finally, in multi-flame systems, at where more than two lamps are connected to a single inverter, a complex selection circuit for selecting the lowest actual value needed.

From DE 42 43 955 A1 is a ballast for at least one parallel operated Gas discharge lamp pair known, showing the features of claim 1.

From US 5 729 095 A a high frequency ballast is known.

From US 5 173 643 A is a ballast for lamps in a series circuit known.

It is therefore an object of the present invention to provide a simplified Circuit arrangement for operating at least two gas discharge lamps indicate that the extinguishing of one of the lamps is reliably avoided.

The object is achieved by a circuit arrangement with the features of claim 1 solved. There are n (n is integer and greater 1) gas discharge lamps with a operated with a single inverter, which is fed with a DC voltage and generates a variable in their frequency AC voltage, the one on the Output of the inverter arranged load circuit is supplied. The load circuit contains one consisting of an inductance and a capacitance Series resonant circuit and the n to the common node between the Inductance and the capacity of connected gas discharge lamps. Further contains the load circuit (n-1) balancing transformers for balancing the currents of two gas discharge lamps each.

To prevent one of the lamps from extinguishing, the load circuit points to each Gas discharge lamp on a DC power supply line, respectively between the output side terminal of the winding of the balancing transformer and the gas discharge lamp attacks and over each gas discharge lamp DC is supplied. Thus receives each gas discharge lamp in addition to the above Resonance circuit and the inverter supplied AC voltage in addition a independent power source, which supplies the lamp with a direct current. This additional direct current preferably corresponds approximately to half of the nominal 1% current at 25 ° C - 35 ° C. He causes, even in the event that due to the predetermined AC voltage can not form a stable operating point, none of Lights go out. In addition, the additional direct current also prevents this Occurrence of so-called running layers.

Further developments of the invention are the subject of the dependent claims. So have the DC power lines preferably one in series with the lamp switched resistor on and are at their input side terminal to a common supply voltage connected. This supply voltage can for example, by means of a connected to the output of the inverter Diode are obtained, preferably between the diode and the DC power supply lines arranged a grounded capacitor is.

The measures according to the invention can extinguish the lamps reliably prevented. However, it may be due to more asymmetrical Wiring and lamp capacities come to large brightness differences, since the balancing transformers attempt the relatively large currents and consequently in a lamp with less wiring capacity an additional active current is generated. To avoid this and a better one Symmetrization of the lamp currents can, according to another Development of the invention, the two windings of a balancing transformer each by a series connection of a capacitor and a resistor be connected to each other. This has the consequence that the balancing effect of Transformers is reduced for small lamp currents, without causing the DC sources are affected. The reduction of the balancing effect works only on the AC components of the lamp voltage, so only on that part, which at low levels of dimming is predominantly asymmetrical Wiring capacity is affected.

The circuit according to the invention is characterized in that it in a simple manner be extended from a two-lamp system to a multi-flame system can. In addition, it is no longer necessary for each lamp its own Provide detection circuit for measuring the lamp current. Rather, it is sufficient to use only a single detection circuit, which the Sum of the active powers of the arranged in the load circuit gas discharge lamps detected and generates a corresponding actual value. Based on a comparison between this actual value and a predetermined setpoint can then Inverters are controlled. The capture of the sum of the active services can For example, in a half-bridge inverter in a simple way take place that arranged over a arranged at the base of the half-bridge measuring resistor declining voltage is determined.

The invention proposed DC power supply lines with the in Series to the lamps switched resistors, which input side to a common supply voltage can also be connected multi-lamp systems are used in which no Balanced transformers are provided. A corresponding circuit arrangement is the subject of claim 9.

Fig. 1

ein Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung für ein zweiflammiges Lampensystem;

Fig. 2

eine Darstellung der Wirkung der erfindungsgemäßen Gleichstrom-Versorgungsleitungen;

Fig. 3

ein Ausführungsbeispiel einer erfindungsgemäßen Schaltungsanordnung für ein dreiflammiges Lampensystem;

Fig. 4

eine bekannte Schaltungsanordnung eines zweiflammigen Lampensystems; und

Fig. 5

eine Darstellung der sich bei Lampen mit verschiedenen Kennlinien ergebenden Effekte.

In the following the invention will be explained in more detail with reference to the accompanying drawings. Show it:

Fig. 1

An embodiment of a circuit arrangement according to the invention for a two-lamp system;

Fig. 2

a representation of the effect of the DC power supply lines according to the invention;

Fig. 3

An embodiment of a circuit arrangement according to the invention for a three-lamp system;

Fig. 4

a known circuit arrangement of a two-lamp system; and

Fig. 5

a representation of the resulting in lamps with different characteristics effects.

The circuit arrangement shown in FIG. 1 is similar in its basic structure to the known circuit shown in FIG. Again, only one single inverter consisting of two controllable switches S1 and S2 is provided for operating the two gas discharge lamps LA1 and LA2. The arranged in a half-bridge arrangement switches S1 and S2 are supplied with a DC voltage V _BUS and generate by alternately opening and closing a high-frequency AC voltage U _ac , which is supplied to the load circuit. The load circuit contains the series resonant circuit consisting of the inductance L _a and the capacitance C _r , at the center of which the two lamps LA 1 and LA 2 are connected via two coupling capacitors C _k1 and C _k2 . Again, the lamps LA1 and LA2 are preceded by a balancing transformer L _bal .

The DC power supply lines according to the invention are each connected to a point between the lamp LA1 or LA2 and the output side of the corresponding winding of the balancing transformer L _bal . They each contain a resistor R _dc1 or R _dc2 connected in series to the corresponding lamp LA1 or LA2 and are connected on the input side to a common DC voltage source. The resistance _values for the two resistors R _dc1 and R _dc2 are identical. The DC voltage source is formed in the example shown by a connected to the output of the inverter diode D1 and a grounded capacitor C _dc as a low-pass filter, which form of the high-frequency AC voltage U _ac a smoothed DC voltage U _dc .

The first lamp LA1 supplied direct current I _dc1 is then calculated as follows: I dc 1 = U dc R dc 1 + R arc 1 where R _{arc1 is} the resistance of the gas discharge lamp LA1. The direct current supplied to the second lamp LA2 results analogously. The two resistors R _dc1 and R _dc2 are designed so that the additional direct current in about half of the nominal 1% current at 25 ° C corresponds to 35 ° C.

The recovery of the DC voltage U _dc from the AC voltage U _{ac of} the inverter has the further advantage that after switching off the inverter and the lamps LA1 and LA2 supplied DC power is deactivated, so that both lamps LA1, LA2 are turned off safely. However, it would also be possible to use a separate DC voltage source from the inverter. The direct current supplied to the lamps LA1, LA2 also prevents the occurrence of so-called running layers.

However, the balancing effect of the transformer L _bal only works up to a certain dimming level. At brightness values below this dimming level, the lamp current is so low that capacitive currents that are greater than the lamp currents themselves can arise. These capacitive currents can arise, for example, due to the fact that the supply lines of the lamps are laid asymmetrically, as a result of which additional wiring capacities C _par and thus capacitive currents I _par occur, as shown schematically in the second lamp LA2. If these capacitive currents I _{par are} greater than the lamp currents, the balancing transformer L _bal reacts in such a way that the asymmetry is increased. The lamp LA1, which does not have the additional wiring capacity, is then supplied with an additional active current I _arc1 , which can be estimated in the following way: I arc 1 ≈ I arc 2 2 + I par 2

To counter this, the balancing effect of the transformer L _{bal is} to be reduced for low lamp currents, without this affecting the DC sources. This is achieved in that the two output-side terminals of the windings of the balancing transformer L _bal by a frequency-dependent impedance, which consists in the present example of the series connection of a resistor R _bal and a capacitor C _bal , are interconnected. This connection allows a certain balance of small asymmetries. However, the reduction of the balancing effect has an effect only on the AC component of the lamp voltage, ie only on that part which is responsible for the capacitive currents at small dimming levels.

The effect of the circuit according to the invention is shown schematically in FIG. The graph shown here shows the voltage applied to the lamps LA1 and LA2 and time-varying lamp voltage U _arc1 and U _arc2 . Although the same AC voltage U _ac1 or U _{ac2 is still} supplied to both lamps, since they are now DC-decoupled, they can assume a different DC voltage _component U _dc1 or U _dc2 . As a result, each lamp can exactly take on the voltage that it would have to form for the given brightness value or lamp current. This provides the ability to drive both lamps through a single inverter and still operate both at the desired brightness.

Moreover, since the risk of accidental wiping of one of the two lamps LA1 and LA2 is no longer given, it is no longer necessary. as in the case of the circuit arrangement shown in FIG. 4, to provide a separate detection circuit for each lamp. Instead, as shown in FIG. 1, only a single detection circuit 2 may be used, for example in the form of a low-pass filter, which detects the voltage drop across a measuring resistor R _SENS arranged at the base of the half-bridge circuit and accordingly generates an actual value V _IST . This actual value now corresponds to the sum of the active powers of both gas discharge lamps LA1 and LA2. The actual value produced by the detection circuit 2 V _IS is supplied to the control circuit 1, according to a comparison of the actual value V _is the two switches controls with a desired brightness corresponding the target value V _TARGET S1 and S2 of the inverter.

Another advantage of the circuit arrangement according to the invention is also that it can be extended without difficulty to more than two lamps. This is illustrated in Figure 3, which illustrates the extension of the system to three gas discharge lamps LA1, LA2 and LA3. The extension consists merely in that now several _balancers L _bal12 and L _bal23 are used, which respectively symmetrize the currents of two lamps LA1 and LA2 or LA2 and LA3. Again, to cause the output-side terminals of the balancing transformers _bal12 L and L _bal23 over the previously described series combination of a resistor R or R _{bal12 bal23} and a capacitance C _bal12 or C _bal23 connected to a decoupling of the DC components. An extension of the system to n gas discharge lamps is then only that (n-1) balancing transformers are used, which each symmetrize the currents of two lamps.

Especially when expanding to more than two gas discharge lamps, the Advantage of the circuit arrangement according to the invention, since still the use a single detection circuit 2 is sufficient, whereby a significant Simplification of the circuit is achieved.

Claims (9)

1. Circuitry arrangement for the operation of n gas discharge lamps (LA1, LA2, LA3), n being a whole number greater than 1, with a single inverter (S1, S2), fed with d.c. voltage (V_BUS), for the generation of an a.c. voltage (U_ac) alterable in its frequency, which is delivered to a load circuit arranged at the output of the inverter (S1, S2), the load circuit having the following:

   a series resonant circuit of an inductance (L_a) and a capacitance (C_r), and

   n gas discharge lamps (LA1, LA2, LA3) connected to the common node point between the inductance (L_a) and the capacitance (C_r), which lamps are connected in parallel to one another,

   characterized in that,
   the load circuit further has for each gas discharge lamp (LA1, LA2, LA3) a d.c. current supply line via which there is delivered to each gas discharge lamp (LA1, LA2, LA3) a d.c. current, and
   in that the circuitry arrangement has a detection circuit which detects the sum of the effective powers of the gas discharge lamps (LA1, LA2, LA3) arranged in the load circuit and generates a corresponding actual value (V_IST),
   and a control circuit which controls the inverter on the basis of a comparison between a desired value (V_SOLL) and the actual value (V_IST) generated by means of the detection circuit.
2. Circuitry arrangement according to claim 1,
   characterized in that,
   the circuitry arrangement has (n-1) balancing transformers (L_bal, L_bal12, L_bal23) for the balancing of the current in each case of two gas discharge lamps (LA1, LA2, LA3),
3. Circuitry arrangement according to claim 1 or 2,
   characterized in that,
   each of the d.c. supply lines is in each case connected between the output side terminal of the corresponding winding of the balancing transformer (L_bal, L_bal12, L_bal23) and the corresponding gas discharge lamp (LA1, LA2, LA3)
4. Circuitry arrangement according to any of claims 1 to 3,
   characterized in that,
   the d.c. supply lines have each a resistance (R_dc1, R_dc2, R_dc3) connected in series and in that at their input side terminal there is applied a common supply voltage (U_dc), the resistance values of these resistances (R_dc1, R_dc2, R_dc3) being the same.
5. Circuitry arrangement according to any of claims 1 to 4,
   characterized in that,
   the common supply voltage (U_dc) is formed by means of a diode (D1) connected to the output of the inverter.
6. Circuitry arrangement according to any of claims 1 to 5,
   characterized in that,
   a low pass filter (C_dc) is arranged between the diode (D1) and the d.c. current lines.
7. Circuitry arrangement according to any of claims 1 to 6,
   characterized in that,
   the output terminals of the windings of a balancing transformer (L_bal, L_bal12, L_bal23) are connected with one another in each case by means of a series circuit of a capacitor (C_bal, C_bal12, C_bal23) and a resistance (R_bal, R_bal12, R_bal23).
8. Circuitry arrangement according to any of claims 1 to 7,
   characterized in that,
   the inverter is formed by means of two switches (S1, S2) arranged in a half-bridge arrangement.
9. Circuitry arrangement according to any of claims 1 to 8,
   characterized in that,
   the detection circuit detects the voltage dropped via a resistance (R_SENS) arranged at the base point of the half-bridge.

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