FR2940741A1 - Impulsional electrical power circuit i.e. pulse ballast, for supplying power to planar discharge lamp of lighting system in e.g. shop, has current source connected to common point of primary and third self-inductors of branch of lamp - Google Patents

Abstract

The circuit has a first self-inductor assembly formed of a primary self-inductor (L1) and a secondary self-inductor (L2) arranged in series with each other. A second self-inductor assembly is formed of a third self-inductor (L3) and a fourth self-inductor (L4). First and second switching arms respectively include switches (X1, X2) arranged in parallel with diodes (D1, D2). The second switching arm is connected to a branch point of a discharge lamp (EL). A current source (I1) is connected to a common point of the primary and third self-inductors of a branch of the lamp. Independent claims are also included for the following: (1) a lighting system comprising a lamp whose terminal is connected with a branch of the lamp (2) a method for utilizing a lighting system.

Description

TECHNICAL FIELD OF THE INVENTION The invention relates to a pulsed ballast which can be used as a high-voltage pulsed supply of dielectric barrier discharge lamps.

io 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 an alternating high voltage. 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 (so-called 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 a light radiation having a desired spectral distribution, for example a visible light radiation in the visible spectrum. for the 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 für 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 itself, 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 suitable for powering a flat coplanar discharge lamp. It is simple in design but requires a high voltage power source.

It is an object of the present invention to provide a pulsed discharge lamp ballast of a different design that does not require a high voltage power supply. Objects of the invention

According to the invention, this problem is solved by an electrical circuit which associates a current source, two switching branches and an induction branch, these three branches being connected to a lamp branch.

More specifically, a first object of the invention is an electrical pulse circuit for supplying a discharge lamp, comprising a direct current source and first and second so-called switching branches 15 connected to a so-called lamp branch, and disposed of as follows: (a) the lamp branch comprises first and second terminals connectable to a discharge lamp; a first pair of self-inductors consisting of a first and second self-inductance placed in series, the second self-inductance being connected to the first terminal of said lamp branch; a second pair of self-inductance composed of a third and fourth self-inductance; the third self-inductance being connected to the second terminal of said lamp branch; (B) the first and second switching branches each comprise a switch in parallel with a diode, said first switching branch being connected to a point of the lamp branch which lies between the first and second self-inductance, said second switching branch being connected to a point of the lamp branch which lies between the third and the fourth self-inductance; (c) the current source is connected to the common point of said first and third self-inductances of said lamp branch. The advantage of the circuit according to the invention is that the current source can use a relatively low voltage supply; so it can be a pretty cheap component. For example, it is possible to use a power supply limited to 120 V or even to 100 V. One can even use to form a current source a rectifier connected directly to the mains (220 V for example). The second and fourth self-inductors allow them to benefit from the transformation ratio to obtain a voltage across the higher lamp.

In this circuit, the switches of said first and second switching branches may each be constituted by a plurality of switches placed in series and synchronized with each other, and / or the diodes may each be constituted by a plurality of diodes set in motion. series. In this circuit, the first and third self-inductors may comprise a coil with a magnetic planar core.

A second object of the invention is a lighting system comprising a circuit as described above and a discharge lamp (UV or visible, especially planar) whose two terminals are connected to the terminals of the lamp branch. In this lighting system, each first and second pair of self-inductors and the lamp form a resonant circuit of frequency equal to 25 1 / (2Tr'JLC), where C is the lamp capacity and L is the inductance first and second pair of self-inductances, said capacitance C being advantageously between 0.5 nF and 5 nF.

In an advantageous embodiment, the lamp is flat and has a planar-type electrode configuration, and its capacitance C is between 1.5 nF and 3.5 nF.

A third object of the invention is the use of a circuit as described above for powering a discharge lamp or a backlight system of a display screen.

A fourth subject of the invention is a method of using a lighting system as described above in which the switches are alternately actuated so that one is closed when the other is open. . The switches may be controlled by a programmable circuit, which controls the width of the voltage pulse generated across the lamp, its frequency, and possibly the modulation of this frequency.

figures

Figures 1 to 6 refer to the invention. 1s Figure 1 shows an embodiment of a circuit according to the invention. Figures 2 to 4 relate to a test performed at a current insufficient to turn on the lamp. Figure 2 shows the control pulse of the switches in one embodiment of the invention. This control voltage Uc corresponds to the grid voltage applied to the MOSFETs. The scales are: time unit 10 ps, voltage unit: 10 V. Figure 3 shows the current lm flowing in the switches, and the voltage Uxi developed. The scales are: 5 ps time unit, 5 A current unit (bottom), 500 V voltage unit (top). Fig. 4 shows the voltage Uxi applied to the switch and the current IEL of the lamp. The scales are: 500 ns time unit, 1 A current unit (bottom), 500 V voltage unit (top). Figures 5 and 6 relate to a test performed at a current sufficient to turn on the lamp. Figure 5 shows the voltage U'xi and current xi at the switches. The scales are: 5 ps time unit, 5 A current unit (bottom), 500 V voltage unit (top).

FIG. 6 shows the voltage U'x1 at the switch and the current EL passing through the lamp for a single pulse. The scales are: 500 ns time unit, 5 A current unit (bottom), 500 V voltage unit (top).

Example

The following example illustrates in Figure 1 an embodiment of the invention, but does not limit it.

In this example according to the invention, the circuit comprises a direct current source and two switching branches, each of these branches being connected to a lamp branch.

The lamp branch includes first and second terminals connectable to a discharge lamp (EL), as well as first and second pairs of self-inductors (the self-inductance being commonly referred to as a self). The first pair of self-inductors is composed of a first (L1) and second (L2) self-inductance placed in series, the second self-inductance (L2) being connected to the first terminal of said lamp branch. The second self-inductance pair is composed of a third (L3) and fourth (L4) self-inductance in series. The fourth self-inductance (L4) is connected to the second terminal of said lamp branch. Each of the first (L1) and third (L3) self-inductances is in series with the current source (I1) which is outside the lamp branch, and which is connected to the common point of the first ( L1) and third (L3) self-inductance.

The first and second switching branches each comprise a switch (X1, X2) in parallel with a diode (D1, D2). The term diode 30 here comprises any non-linear unidirectional electronic device, which allows current to pass only in one direction. The switches (X1, X2) and the diodes (D1, D2) are in series with the lamp branch, and in particular with the second (L2) and the fourth (L4) self-inductances (L2, L4), and with the lamp (EL) if a lamp (EL) is connected to said first and second terminals.

The first switching branch is connected to a point of the lamp branch which lies between the first (L1) and the second (L2) self-inductance. The second switching branch is connected to a point of the lamp branch which lies between the third (L3) and the fourth (L4) self-inductance.

The operating principle of the circuit according to the invention is as follows: Thanks to the first (L1 + L2) and second (L3 + L4) pairs of self-inductors, the circuit is able to generate a voltage across the lamp which is greater than that of the voltage of the switches (X1, X2). The pulse energy generated by the actuation of the switches X1 and X2 is stored alternately in the first (L1) and third (L3) self-inductance when one of the switches X2 or X1 leads. This pulse energy is alternately discharged into the lamp (EL) by the first (L1, L2) or the second (L3, L4) pair of self-inductances when the switch X1 or X2 is off. Then, we close the switch X1 or X2, and the first (L1) or third (L3) self-inductance recharge again. In this example, the first (L1) and third (L3) auto-inductors are of the same type and inductance. Similarly, the second (L2) and fourth (L4) self-inductances are of the same type and the same inductance.

In the circuit according to the invention, it is important that at least one of the two switches (X1, X2) is closed (i.e. passes a current), otherwise it can create a surge

The lamp (EL) behaves like a capacitor. The two pairs of auto-inductors (L1 + L2, L3 + L4) form with the lamp (EL) a resonant circuit whose frequency is equal to 1 / (2TPJLC) where C is the capacity of the lamp and L l inductance of the pair of self-inductances (L1 + L2, L3 + L4). Therefore, the inductance of the pair of self-inductors (L1 + L2, L3 + L4) must be matched to the lamp capacity (EL). In this example, the first (L1) and third (L3) self-inductance is a coil with a magnetic planar core.

In this example, the circuit is sized so that the edge rise time is less than 1 ps. The capacity of the lamp (EL) being fixed, it is the inductance of the self-inductance which is decisive, and which must be chosen appropriately. In this example, for a lamp (EL) with a capacity of 1 nF, a value of pH can be chosen for L1 + L2, which leads to a rise time of about 500 ns. To achieve the same rise time with a lamp with a capacity of 3 nF, a capacity of 3 pH is chosen.

In a variant (not shown), the switches (X1, X2) each consist of one of a plurality of switches placed in series and synchronized with each other, and / or the diodes (D1, D2) each consist of a plurality e diodes put in series. In another variant (not shown), the switches (X1, X2) are controlled by a programmable circuit, in particular to control the width of the generated pulse, its frequency, and the possible modulation of this frequency.

The circuit can be used in a ballast to supply a discharge lamp, in particular a flat discharge lamp (EL). For this, the plane lamp (EL) is connected to the first and second terminals of the lamp branch, the current source (I1) and the switches (X1, X2) are alternately operated so that one is closed when the other is open, and care is taken to avoid voltage peaks which may occur when none of the two switches (X1, X2) are closed. The switches (X1, X2) are controlled so that switching in the switching branches is effected at a substantially zero current.

The ballast according to the invention can also be used to power a backlighting device (such as a cold cathode discharge lamp) in a liquid crystal display screen.

In the example, a circuit according to the invention was realized with a current source (150 V, 10 A) and two pairs of four MOSFET coupled switches in series. The instantaneous voltage (dV / dt) across the lamp was about 1500 V in 500 ns. At a frequency of 40 kHz, the power supply at 60 V was 134 W for a luminous flux of 205 lux (surface ~ o of the flat lamp: about 0.09 m2). At a frequency of 25 kHz, the power supply at 42 V was 134 W for a luminous flux of 150 lux.

Figures 2 to 6 show the results of measurements made on this circuit.

FIGS. 2 to 4 relate to a test with a supply voltage of 52 V and a supply current of 1.4 A; the lamp was off. Figure 2 shows the control pulses of the switches (Ucx1, Ucx2), which are of the order of 18 V. The repetition frequency was of the order of 40 kHz, the width of the voltage pulse of the order of 1.77 ps. FIG. 3 shows the current I x1 flowing in the switches (width of the current pulse of the order of 11.8 ps), and the developed voltage U x 1 (frequency of the order of 40 kHz). Figure 4 shows the voltage at the switch Uxi and the lamp current IEL.

Figures 5 and 6 relate to a test with a supply voltage of 59.2 V and a supply current of 2.2 A; the lamp was on, and the luminous flux was 205 Lux. Figure 5 shows the current xi flowing in each switch and the voltage U'x1 at each switch. The control pulses 30 were of the order of 30 V. The repetition frequency was of the order of 40 kHz. Figure 6 shows the current EL circulating in the lamp and the voltage U'xi developed in the switches.

Claims (9)

REVENDICATIONS1. Impulse electrical circuit for supplying a discharge lamp, characterized in that it comprises a direct current source (11) and first and second so-called switching branches connected to a so-called lamp branch, and arranged in the following manner: a) the lamp branch comprises - first and second terminals connectable to a discharge lamp (EL); a first pair of self-inductors consisting of a first (L1) and second self-inductance (L2) placed in series, the second self-inductance (L2) being connected to the first terminal of said lamp branch; a second pair of self-inductors composed of a third (L3) and fourth self-inductance (L4); the third self-inductance (L3) being connected to the second terminal of said lamp branch; (b) the first and second switching branches each comprise a switch (X1, X2) in parallel with a diode (D1, D2), said first switching branch being connected to a point of the lamp branch which lies between the first (L1) and second (L2) self-inductance, said second switching branch being connected to a point of the lamp branch which lies between the third (L3) and the fourth (L4) self-inductance; (c) the current source (11) is connected to the common point of said first (L1) and third (L3) self-inductances of said lamp branch. 2. Circuit according to claim 1, characterized in that the switches (X1, X2) of said first and second switching branches are each constituted by a plurality of switches placed in series and synchronized with each other, and / or characterized by the diodes (D1, D2) each consist of a plurality of diodes placed in series. 3. Circuit according to any one of claims 1 to 2, characterized in that the first (L1) and third (L3) self-inductance comprise a coil with a magnetic core plane. 4. Lighting system comprising a circuit according to any one of claims 1 to 3 and a discharge lamp (EL) whose two terminals are connected to the terminals of the lamp branch. 10 An illumination system according to claim 4, wherein each first (L2, L1) and second (L4, L3) pair of self-inductors and the lamp (EL) form a resonant circuit of frequency equal to 1 / ( 2TrILC), where C is the lamp capacity (EL) and L the inductance of the first and second pair of self-inductors (L1 + L2; L3 + L4), the capacitance C being between 0.5 nF and 5 nF. 6. Lighting system according to claim 5, characterized in that said lamp (EL) is flat and has a plane-plane type electrode configuration, and in that the capacitor C is between 1.5 nF and 3.5 nF. 7. Use of a circuit according to any one of claims 1 to 3 for supplying a discharge lamp (EL) or a backlight system of a display screen. 8. A method of using a lighting system according to any one of claims 4 to 6 wherein is actuated alternately switches (X1, X2) so that one is closed when the other is open. 9. Method according to claim 8, characterized in that the switches (X1, X2) are controlled by a programmable circuit, which controls the width of the voltage pulse generated at the terminals of the lamp (EL), its frequency, and possibly the modulation of this frequency.