WO2010061131A2

WO2010061131A2 - Pulse ballast for planar lights

Info

Publication number: WO2010061131A2
Application number: PCT/FR2009/052291
Authority: WO
Inventors: Laurent Joulaud; Jimmy Roure; Olivier Maulat; Jingwei Zhang; Aude Montgermont
Original assignee: Saint-Gobain Glass France
Priority date: 2008-11-26
Filing date: 2009-11-25
Publication date: 2010-06-03
Also published as: FR2939006B1; WO2010061131A3; FR2939006A1

Abstract

The invention relates to an electrical circuit for supplying power to a pulsed discharge light, comprising two switching arms, a light arm, and two power supply arms, placed in the following manner: (a) the first and second switching arms each comprise a switch (X1, X2), a self-inductor (L1, L2), and a diode (D1, D2) so that, in each switching arm, (a) the switcher (X1, X2) is parallel to the diode (D1, D2) and in series with the self-inductor (L1, L2); (b) the lighting arm includes two terminals connectable to a discharge light (EL), one of said terminals also being connected to the common point of said first and second switching arms, the other also being connected to the two power supply arms; and (c) the power supply arms each include a voltage supply (V1, V2) that charges a capacitor (C1, C2), said voltage supplies (V1, V2) being placed in series with, and the common point thereof being connected to, the lighting arm.

Description

Ballast pulsed for flat lamps

Technical field of the invention

The invention relates to a pulsed ballast that can be used as a high-voltage pulse power supply for dielectric barrier flat discharge lamps. This ballast has two switching branches and two power supply branches.

State of the art

The ultraviolet flat discharge dielectric barrier lamps generally comprise two planar glass elements and kept substantially parallel to each other, thus delimiting an internal space filled with a gas capable of emitting ultraviolet radiation when excited by a high voltage alternating or pulse applied to at least one pair of electrodes. In a first configuration, each electrode is disposed on one side of a separate glass element (so-called "plane-plane" configuration). In a second configuration, the electrodes are arranged on the same face of a glass element ("coplanar" configuration). In a third configuration, a pair of electrodes is disposed in coplanar configuration on one side of a glass element, and one or more other electrodes are disposed on one face of the other glass element. In all these configurations, the surface on which the electrode is deposited may be the inner face or the outer face of the glass element. It is also possible to arrange the electrode in the glass element (for example, reinforced glass). This ultraviolet radiation can excite a suitable phosphor material disposed on one side of at least one of the two glass elements, which makes it possible to obtain light radiation having a desired spectral distribution, for example light radiation in the visible spectrum, which can be used for lighting of living rooms, offices or shops. Such lighting systems are known; they are described for example in patent applications WO 2008/023124, WO 2004/015739 (first configuration), WO 2007/042689 (second configuration) and WO 2007/023237 (third configuration).

In such a lamp, the discharge is excited by an alternating or pulsed voltage supplied by a power supply provided with a ballast, which must, on the one hand, be capable of supplying the high voltage necessary to ignite the discharge, and on the other hand, limit the current in steady state. It is known that the use of a sinusoidal alternating supply current applied to the electrodes of a discharge lamp does not lead to a good light output. The article "Half-Bridge and Full-Bridge Choke Converter Concepts for the Pulsed Operation of Large Dielectric Barrier Discharge Lamps" by K. Kyrberg et al., Published in IEEE Transactions on Power Electronics, Vol. 22, No. 3 (May 2007), pages 926-933) and US Patent Application US 2007/0018590 A1 (Patent-Treuhand-Gesellschaft fur elektrische Glühlampen GmbH) disclose ballasts for co-planar discharge ultraviolet flat lamps; these ballasts, which are improvements of so-called "Class E" ballasts, provide a high voltage of non-sinusoidal or even impulse shapes.

The ballasts described in the aforementioned application US 2007/0018590 are half-bridge type converters. In its simplest version, this converter comprises two branches each provided with a switch and a diode connected in series, said branches being connected to the circuit of the discharge lamp, said circuit comprising an inductor and the discharge lamp properly said, knowing that one of said branches is in parallel connection with said circuit of the lamp. The terminals of the series circuit having the two switch branches are connected to a voltage source.

This ballast is capable of providing a pulse voltage adapted to feeding a flat discharge lamp. Its advantage is to be of simple design. In some operating modes, however, it may have disadvantages. These disadvantages are of two different natures. On the one hand, when using these ballasts, it seems to be more difficult to connect the discharge lamp to the ground, which is however desirable for security reasons. Indeed, the two terminals of the discharge lamp are connected to switching points of the ballast; however, in a high voltage system, grounding a terminal connected to a switching point can generate electromagnetic disturbances. On the other hand, the supply voltage required to power a discharge lamp, which would be of the order of 1.5 kV in the stationary state, requires the use of relatively expensive high voltage sources.

The present invention aims to present a pulsed ballast for flat discharge lamps that does not have these disadvantages.

Objects of the invention

According to the invention, this problem is solved by an electrical circuit which employs two high voltage sources placed in series. More precisely, this electric circuit for supplying a pulsed discharge lamp is characterized in that it comprises two so-called switching branches, a so-called lamp branch, and two so-called supply branches, arranged in the following manner:

(a) the first and second switching branches each comprise a switch (X1, X2), an auto-inductor (L1, L2) and a diode (D1, D2), so that in each switching branch switch (X1, X2) is in parallel with the diode (D1, D2), and in series with the self-inductance (L1, L2);

(b) the lamp branch comprises two terminals which can be connected to a discharge lamp (EL), one of said terminals being also connected to the common point of said first and second switching branches, the other being also connected to the two branches feeding;

(c) the supply branches each comprise a voltage supply (V1, V2) charging a capacitor (C1, C2), said voltage supplies (V1, V2) being put in series, and their common point being connected to the lamp branch.

This circuit can be used to power a discharge lamp, typically in a lighting system that includes a discharge lamp (EL) whose two terminals are connected to the terminals of the lamp branch of said circuit. To use it, the switches (X1, X2) are alternately actuated so that one is closed when the other is open.

figures

Figures 1 to 4 refer to the invention.

Figure 1 shows an embodiment of a circuit according to the invention which comprises an optional capacitor (C3) but advantageous. FIG. 2 shows another embodiment of a circuit according to the invention, which comprises in each switching branch a noise suppression device (P1, P2).

FIG. 3 shows voltage / current versus time curves provided by a device according to the invention at the supply terminals of the lamp branch.

FIG. 4 shows an embodiment similar to that of FIG. 2, but in which some of the components have been replaced by a plurality of components of the same type placed in series.

detailed description

According to the invention, two power supply branches are used in series, each comprising a voltage source (V1, V2), and two so-called switching branches, each comprising a switch (X1, X2) connected in parallel. with a diode (D1, D2).

The term "diode" here includes any unidirectional nonlinear electronic device, which allows current to pass only in one direction.

Each switching branch comprises in series a self-inductance (L1, L2), commonly called a "self", which limits the current pulses when the switch (X1, X2) of said branch is actuated. The self-inductance (L1, L2) limits the current flowing through the lamp (EL), knowing that the lamp (EL) behaves like a capacitor. The self-inductance (L1, L2) forms with the lamp (EL) a resonant circuit whose frequency is equal to 1 / (2TTΛ / LC) where C is the capacitance of the lamp and L the inductance of the car -inductance (L1, L2). Consequently, the inductance of the self-inductance (L1, L2) must be adapted to the capacitance of the lamp (EL) and the control pulse width, preferably less than or equal to one microsecond to obtain a good luminous efficiency. The capacitance C is advantageously between 0.5 nF and 5 nF, and in particular between 1.5 nF and 3.5 nF for the plane-plane configuration. This capacitance depends in particular on the surface of the electrode. The high capacitance values imply suitable dimensioning of the components. The value of the self-inductance L is advantageously between 15 and 20 μH. By way of example, with C = 3 nF and L = 15 μH, a frequency of approximately 800 kHz is obtained, that is to say a period of the order of one microsecond (knowing that a frequency of 1 MHz corresponds to 1 μsec).

Advantageously, the self-inductance (L1, L2) is a coil with a magnetic plane core, preferably based on an amorphous metal. Advantageously, the self-inductances (L1, L2) are of the same type and of the same inductance.

In an advantageous embodiment, the switches (X1, X2) each consist of a plurality of switches placed in series and synchronized with each other, and / or the diodes (D1, D2) each consist of a plurality of diodes placed in series, and / or the voltage sources (V1, V2) are each constituted by a plurality of voltage sources placed in series, and / or the capacitors (C1, C2) each consist of a plurality of capacitors placed in series. Such an embodiment is illustrated in FIG. 4. In this figure, the switches X1 and X2 are each represented by four switches (respectively X11, X12, X13, X14 and X21, X22, X23, X24) placed in series and synchronized. , and the diodes D1 and D2 are each represented by four diodes (respectively D11, D12, D13, D14 and D21, D22, D23, D24) placed in series, and the voltage sources V1 and V2 are each represented by four sources of voltage (respectively V11, V12, V13, V14 and V21, V22, V23, V24) placed in series, and the capacitors C1 and C2 are each represented by four capacitors (respectively C11, C12, C13, C14 and C21, C22, C23 , C24) placed in series, and the diodes D3 and D4 are each represented by two diodes (respectively D31, D32 and D41, D42) placed in series. The switches (X1, X2) may be static electrical switches, typically based on semiconductors (for example of the MOSFET type). In one variant, one of the switches is static and the other magnetic, which simplifies the control system. Instead of each switch (X1, X2), it is possible to use a plurality of switches (such as MOSFETs) in series, the switching of which, for the static switches, is synchronized by means of optical couplers or, preferably, magnetic. Thus, one does not need to use high voltage switches, which are expensive. To switch, for example, a voltage of 3.2 kV using a group of four synchronized switches, MOSFET switches can be used, each of which switches only a voltage of 0.8 kV.

The two voltage sources (V1, V2) can each provide the same DC voltage, or a different DC voltage. Instead of a voltage source (V1, V2) a plurality of voltage sources connected in series can be used. Thus, there is no need to use high voltage sources that are expensive. For example, it is possible to use two voltage sources capable of delivering a voltage of between 350 and 800 V. In a particular embodiment, which can be combined with all the other embodiments of the present invention, the circuit according to the invention further comprises a capacitor (C3) between the lamp and the common point of the supply branches. This makes it possible to minimize the effective lamp voltage (EL). Advantageously, the effective voltage applied to the lamp does not exceed 1 kV. The capacitance of the capacitor C3 must be large compared to the capacitance of the lamp (EL), for example 50 to 100 times larger. For example, for a lamp capacitance (EL) of 3 nF, a capacitance C3 of between 100 nF to 200 nF can be used.

The diodes (D1, D2) are clipping diodes, for example power zener diodes. Their function is to protect the switches (X1, X2) against transient overvoltages during switching. Instead of a diode (D1, D2), a plurality of diodes placed in series can be used.

The capacitors (C1, C2) are advantageously integrated in the voltage sources (V1, V2). These are filter capacitors. Their capacitance is advantageously between about 1 and 100 μF, and preferably between 3 and 60 μF.

In a particular embodiment, which can be combined with all the other embodiments of the present invention, each switching branch further comprises a diode (D3, D4), connected in series with the power supply branch, which prevents current reversal; this limits or even suppresses post-switching oscillations. These diodes (D3, D4) are high voltage fast diodes. It is also possible to use for each switching branch a plurality of diodes placed in series, to reduce the voltage seen by each diode (D3, D4).

In a particularly advantageous embodiment of the circuit according to the invention, the switches (X1, X2) are controlled by a circuit programmable, in particular to control the width of the generated pulse, its frequency (advantageously between 10 and 100 kHz, and even more advantageously between 20 and 60 kHz (a value of 40 KHz is well suited), and the possible modulation of this This frequency modulation is advantageously in the form of pulse trains, for example, with pulses approximately 2 μsec wide, pulse trains comprising approximately 5 to 10 pulses are generated. these pulse trains being spaced apart by approximately 10 and 100 μs, which corresponds to a repetition frequency of approximately 10 to 100 kHz.

In another particular embodiment, which can be combined with all the other embodiments of the present invention, each switching branch includes a noise canceling device (P1, P2) in series with the self-inductance (L1 , L2), as shown in Figure 2. This noise suppression device (P1, P2) is preferably a saturable self-inductance, preferably amorphous magnetic core, typically cobalt or cobalt-based alloy. This device cuts the oscillations that result from switching, that is to say the overvoltage applied to the diodes.

The circuit according to the invention can be used in a ballast to power a discharge lamp. For this purpose, a plane lamp is connected to the terminals of the lamp branch, the voltage sources (V1, V2) are turned on and the switches (X1, X2) are alternately actuated so that one be closed when the other is open. Advantageously, the switches (X1, X2) are controlled so that switching in the switching branches is performed at substantially zero current. By way of example, such a lamp can work at a peak voltage of between 1, 4 and 4.0 kV in the stationary state, with a pulse frequency of approximately 10 and 100 kHz (advantageously between 20 and 40 kHz). , modulated by a frequency between 100 and 400 Hz (a value less than 100 Hz leads to a blinking perceptible by the human eye). It can typically have a nominal power of between 20 and 100 W. It can be designed to emit visible and / or ultraviolet light. Its electrodes can be coplanarly deposited on the same wall of a transparent glass plate (or UV-transparent material, such as quartz), or each electrode can be deposited on a different wall.

The circuit according to the invention can also be used to power a backlight system of a display screen, for example a liquid crystal display screen.

The circuit according to the invention has several advantages and characteristics. First of all, its efficiency is high: with a discharge lamp, up to 80% of the electrical energy can be converted into light energy. The ballast according to the invention allows the user to reduce the intensity of the lamp current ("dimming" effect), up to about 10% of the maximum power, or even less. To achieve this effect, the number of pulses per pulse train is reduced, and / or the time interval between two successive pulse trains is increased.

In addition, the output signal of the ballast according to the invention is symmetrical in voltage, centered around + X volts and - X volts (see for an example Figure 3), while the ballast according to the state of the art provides a signal shifted in voltage. This leads to more uniform wear of the lamp electrodes.

Moreover, for a given supply voltage, each voltage source (V1, V2) can work at a voltage which is only half of the voltage used by the ballasts according to the state of the art. Therefore, this voltage source can be of a simpler construction. On the other hand, two of these voltage sources are needed instead of one according to the state of the art.

Furthermore, in the ballast according to the invention, the absence of a transformer connected to the terminals of the lamp also makes it possible to simplify the design of the lamp. feeding, improves the durability of the diet and confers a better yield.

And finally, in the ballast according to the invention, one of the terminals of the discharge lamp is not connected to a switching point; thus, this terminal can be grounded without the risk of disturbing the circuit.

Example

We realized a circuit according to the invention. As voltage sources (V1, V2), current model transformers associated with filter capacitors having a capacitance of the order of 100 μF have been used.

As switches (X1, X2), type power transistors have been used.

Cool MOS ™ Power Transistor SPP20N60S5 provided by Infineon. As clipping diodes (D1, D2), Transil ™ diodes were used

1.5KE6V8A / 440A provided by STMicroelectronics.

As self-inductances (L1, L2), magnetic cores based on amorphous cobalt (VITROVAC ™ 6025 Z) with a coil of an inductance of 22 μH were used. As diodes (D3, D4), HiPerDynFRED ™ DSEP diodes 2x25-

12C provided by IXYS. For each branch, two independent diodes were put in series.

Measurements were made on two different flat lamps, one with an active area of 0.09 m2 (Table 1), the other with an active area of 0.2 m ²

(Table 2), for variable delays between two pulses (frequency: 20 kHz).

The column V _rms (AV) corresponds to the case where a capacitor (C3) has been additionally added between the lamp and the supply branches; this capacitor eliminates the DC component of the current. Table 1

Table 2

FIG. 3a shows, by way of example, the electrical signals measured on this ballast in "partial ignition" mode: the voltage pulses (of a width of about 35 μs, see the curve at the top) induce a current pulse ( see the curve at the bottom). It is noted that the voltage pulses are symmetrical around the zero point.

FIG. 3b shows, by way of example, the electrical signals measured on this ballast in "ignition" mode (scales enlarged with respect to those of FIG. 3a). The very steep tension front with a width of about 500 ns is recognized, which induces a current peak with a width at mid-height of about 400 ns. It is found that the circuit is capable of supplying a flat lamp under satisfactory lighting conditions, and with a high efficiency.

It can be seen that in a pulse zone between approximately 10 and approximately 40 μs, the brightness depends little on the width of the pulse.

It is found that the capacitor C3, which cuts the DC component of the current, leads to a decrease in the voltage for pulses which are not strictly symmetrical.

Claims

1. Electrical circuit for supplying a pulsed discharge lamp, characterized in that it comprises two so-called switching branches, a so-called lamp branch, and two so-called supply branches, arranged in the following manner:

(a) the first and second switching branches each comprise a switch (X1, X2), an auto-inductor (L1, L2) and a diode (D1, D2), so that in each switching branch switch (X1, X2) is in parallel with the diode (D1,

D2), and in series with the self-inductance (L1, L2);

2. Circuit according to claim 1, characterized in that the switches (X1, X2) are each constituted by a plurality of switches placed in series and synchronized with each other, and / or characterized in that the diodes (D1, D2) each consists of a plurality of diodes placed in series, and / or characterized in that the voltage sources (V1, V2) each consist of a plurality of voltage sources in series.

The circuit of claim 1 or 2, further comprising in each switching branch a diode (D3, D4) or a plurality of series-connected diodes positioned on the power supply side for limit or suppress post-switching oscillations.

4. Circuit according to any one of claims 1 to 3, characterized in that the lamp terminal which is not connected to the switching branches is connected to the ground.

5. Circuit according to any one of claims 1 to 4, characterized in that it further comprises between the lamp and the supply branches a capacitor (C3).

6. Circuit according to any one of claims 1 to 5, characterized in that it further comprises in each switching branch a noise suppression device (P1, P2) in series with the self-inductance (L1, L2).

7. Circuit according to any one of claims 1 to 6, characterized in that one of the switches (X1, X2) is a static switch and the other a magnetic switch.

8. Lighting system comprising a circuit according to any one of claims 1 to 7 and a discharge lamp (EL), the two terminals are connected to the terminals of the lamp branch.

9. Lighting system according to claim 8, wherein the self-inductance (L1, L2) and the lamp (EL) form a resonant circuit of frequency equal to 1 / (2τWLC), where C is the capacitance of the lamp (EL) and L the inductance of the self-inductance (L1, L2), said system being characterized in that the capacitance C is between 0.5 nF and 5 nF.

10. Lighting system according to claim 9, characterized in that said lamp (EL) has a planar type electrode configuration. plane, and in that the capacitance C is between 1.5 nF and 3.5 nF.

11. Use of a circuit according to any one of claims 1 to 7 for supplying a discharge lamp or a backlight system of a display screen.

12. A method of using a lighting system according to any one of claims 8 to 10, wherein is actuated alternately switches (X1, X2) so that one is closed when the other is open.

13. The method of claim 12, characterized in that the switching in the switching branches is performed at substantially zero current.

14. Method according to any one of claims 12 to 13, characterized in that the switches (X1, X2) are controlled by a programmable circuit, which controls the width of the pulse generated, its frequency, and optionally the modulation of this frequency.