EP1931181B1 - Ballast for a discharge lamp - Google Patents

Abstract

The ballast (BLST) has a direct current/direct current (DC/DC) voltage converter (Ccc) for supplying a rectified DC voltage (Vout) and including a transformer (TR1) that has main, secondary and auxiliary windings (n1-n3). The transformer supplies the rectified voltage. A voltage multiplier circuit (MU) of the converter supplies an ignition voltage (Vignit), where a voltage difference between the ignition and rectified voltages creates a starting voltage for a discharge lamp (LA).

Description

Field of the invention

The present invention relates to a lighting ballast for a discharge lamp and a fire device incorporating a lamp connected to such a ballast.

It finds a particular application in the field of motor vehicles.

State of the art

In order to improve both the light output and the energy efficiency of the light sources used in many fields, such as vehicle headlights or video projectors, the current technical evolution has led to the replacement of the filament lamps with high intensity gas discharge lamps. Unlike filament lamps, which were designed to be connected directly to a low-voltage source, such as a vehicle battery, or medium voltage, such as the 110 or 220V domestic sector, these new lamps require high voltages to create an electric arc to light them.

In the automotive field, for example, these high voltages are produced by a power supply module, which also provides power regulation, known as "ballast".

The most recent ballasts include in particular a DC / DC switching converter producing a high DC voltage of several hundred volts from the battery voltage for example, a DC / AC converter ensuring the supply of the lamp in steady state to from the high-voltage DC, and a high-voltage module supplying a generator producing the very high voltage necessary for lighting the lamp, the very high voltage being produced from the high DC voltage produced by the DC / DC converter.

According to a known state of the art, the DC / DC converter of such a ballast comprises a transformer comprising a main winding and two secondary windings with a transformation ratio equal to 8 with more than 20 turns in the two secondary windings and a rectifier voltage associated with each secondary winding, each rectifier comprising a diode and a capacitor. The main winding is connected to a switching unit connected to the power source. The repetitive interruption of the latter by the switching unit induces at the terminals of the two secondary windings of the transformer respectively two high voltages each rectified by the diode and filtered by the capacitor of the associated rectifier. The difference between these two high voltages makes it possible to obtain a voltage of 1000V. From this voltage of 1000V, an ignition voltage of about 25kV is obtained by the high voltage module connected between the DC / DC converter and the discharge lamp.

Such a solution has the following drawbacks. The transformer occupies a very large volume because of the important transformation ratio. In addition, because of this volume, the leakage elements are important which can create overvoltages in the switching unit and interfere with the control of the DC / DC converter. Moreover, the rectifying diodes must be dimensioned for a voltage of 1000V, which poses problems of realization and cost.

Document is also known US 6,124,681 , for example on the figure 3 of this document, a power factor correction circuit (Power Factor correction circuit) whose energy accumulated in a transformer is transferred by simple rectification diode two capacitors in series. Such a circuit constitutes a step-up converter, and not a voltage multiplier.

The document JP 2001 284 089 discloses a discharge lamp ballast comprising a converter, a voltage multiplier and a transformer comprising a main winding, a secondary winding and an auxiliary winding.

Object of the invention

The present invention aims to overcome these disadvantages of the state of the art.

• un convertisseur de tension continu/continu pour fournir une tension redressée continue,

caractérisé en ce que le convertisseur de tension continu/continu comporte :

• un transformateur comprenant un enroulement principal, un enroulement secondaire et un enroulement auxiliaire, le transformateur permettant de fournir la tension redressée continue, et
• un circuit multiplieur de tension pour fournir une tension d'amorçage, la différence de potentiel entre cette tension et la tension redressée continue permettant de créer une tension d'allumage pour la lampe à décharge.

Indeed, it relates according to a first object, a discharge lamp ballast comprising:

• a DC / DC voltage converter for providing a DC rectified voltage,

characterized in that the DC / DC voltage converter comprises:

• a transformer comprising a main winding, a secondary winding and an auxiliary winding, the transformer for providing the DC rectified voltage, and
• a voltage multiplier circuit for providing a starting voltage, the potential difference between this voltage and the DC rectified voltage for creating an ignition voltage for the discharge lamp.

As will be seen in detail below, the fact of combining a multiplier circuit with a transformer provided with a secondary winding and an auxiliary winding will make it possible to obtain a starting voltage from a continuous rectified voltage. and consequently will make it possible to reduce the number of turns in the secondary and auxiliary windings so as to obtain low transformation ratios and therefore a sizing of the transformer that does not lead to significant leakage elements. As a result, non-standard dimensioning of components such as diodes is avoided, while providing an input voltage of a high voltage module of the discharge lamp sufficiently high to provide the ignition voltage to said lamp.

• le circuit multiplieur de tension comporte deux condensateurs et deux diodes. Les deux condensateurs permettent de fournir la tension d'amorçage tandis que les deux diodes permettent le chargement des condensateurs pendant une phase d'allumage ;
• l'enroulement auxiliaire vient dans le prolongement de l'enroulement secondaire. Cela permet de générer la tension d'amorçage en utilisant la somme des tensions générées par l'enroulement secondaire et l'enroulement auxiliaire dont fait partie la tension redressée continue ;
• le ballast comporte en outre une résistance en sortie du circuit multiplieur de tension. Elle permet de retarder le chargement d'un condensateur fournissant la tension d'amorçage de sorte que la différence de potentiel entre cette tension et la tension redressée soit optimale pour l'allumage de la lampe ;
• le convertisseur continu/continu comprend un unique redresseur de tension. Il permet de fournir la tension redressée continue ;
• l'enroulement secondaire comporte un rapport de transformation avec l'enroulement principal de l'ordre de 5. Ainsi, le faible rapport de transformation permet de réduire le volume global du transformateur et donc les éléments de fuite ;
• l'enroulement auxiliaire comporte un rapport de transformation avec l'enroulement principal de l'ordre de 2. Ainsi, le faible rapport de transformation permet de réduire le volume global du transformateur et donc les éléments de fuite.

According to non-limiting embodiments, the ballast has the following additional features:

• the voltage multiplier circuit comprises two capacitors and two diodes. The two capacitors provide the ignition voltage while the two diodes allow charging capacitors during an ignition phase;
• the auxiliary winding comes in the extension of the secondary winding. This makes it possible to generate the ignition voltage using the sum of the voltages generated by the secondary winding and the auxiliary winding of which the DC rectified voltage is part;
• the ballast further comprises a resistance at the output of the voltage multiplier circuit. It makes it possible to delay the charging of a capacitor supplying the ignition voltage such that the potential difference between this voltage and the rectified voltage is optimal for lighting the lamp;
• the DC / DC converter comprises a single voltage rectifier. It provides the continuous rectified voltage;
• the secondary winding has a transformation ratio with the main winding of the order of 5. Thus, the low transformation ratio reduces the overall volume of the transformer and therefore the leakage elements;
• the auxiliary winding has a transformation ratio with the main winding of the order of 2. Thus, the low transformation ratio reduces the overall volume of the transformer and therefore the leakage elements.

The invention relates to a second object, a vehicle fire device comprising a discharge lamp to which is connected a ballast according to any one of the preceding characteristics, the ballast being able to provide a voltage to allow a lighting of the lamp for discharge.

Brief description of the figures

• la Fig. 1 représente schématiquement un dispositif de feu de véhicule comprenant une lampe à décharge et un ballast selon l'invention ;
• la Fig. 2 est un schéma d'un premier mode de réalisation non limitatif d'un ballast selon l'invention ;
• la Fig. 3 est un premier diagramme de tensions fournies par des composants du ballast selon la Fig. 2 ;
• la Fig. 4 représente schématiquement un convertisseur tension continu/continu du ballast de la Fig. 2 selon un premier mode de fonctionnement ;
• la Fig. 5 représente schématiquement un convertisseur tension continu/continu du ballast de la Fig. 2 selon un deuxième mode de fonctionnement ;
• la Fig. 6 représente une lampe à décharge reliée au ballast selon l'invention ;
• la Fig. 7 est un diagramme représentant l'évolution de la tension aux bornes de la lampe à décharge de la Fig. 6 ;
• la Fig. 8 représente une partie du diagramme de la Fig. 7 ; et
• la Fig. 9 est un schéma d'un deuxième mode de réalisation non limitatif d'un ballast selon l'invention.

Other features and advantages of the present invention will be better understood with the aid of the description and non-limiting drawings, among which:

• the Fig. 1 schematically represents a vehicle fire device comprising a discharge lamp and a ballast according to the invention;
• the Fig. 2 is a diagram of a first non-limiting embodiment of a ballast according to the invention;
• the Fig. 3 is a first diagram of voltages provided by ballast components according to the Fig. 2 ;
• the Fig. 4 schematically represents a DC / DC voltage converter of the ballast of the Fig. 2 according to a first mode of operation;
• the Fig. 5 schematically represents a DC / DC voltage converter of the ballast of the Fig. 2 in a second mode of operation;
• the Fig. 6 represents a discharge lamp connected to the ballast according to the invention;
• the Fig. 7 is a diagram showing the evolution of the voltage across the discharge lamp of the Fig. 6 ;
• the Fig. 8 represents a part of the diagram of the Fig. 7 ; and
• the Fig. 9 is a diagram of a second non-limiting embodiment of a ballast according to the invention.

Detailed description of non-limiting embodiments of the invention

To the Fig. 1 is shown a BLST ballast connected to a discharge lamp LA in the context of a non-limiting application of vehicle fire FX. The FX fire is for example, a traffic light (night lights, codes, taillights) or lighting called projector (lighthouse). In the description, the term "fire" will be used indifferently to designate such lighting or signaling devices.

The LA discharge lamp can be used for day and / or night lighting.

• une lampe à décharge LA enfermée dans un boîtier et disposée selon une configuration géométrique déterminée avec un réflecteur RL. La lampe à décharge est une lampe à arc, entre deux électrodes qui nécessite une impulsion de tension aux bornes de ses électrodes afin de créer un premier arc pour l'allumer. La lampe LA est, dans un exemple non limitatif, une lampe au xénon (avec Hg⁺ ou sans Hg- mercure) qui nécessite notamment une tension d'allumage Um de l'ordre de 25kV. Elle comprend une ampoule Bb et un module haute tension HV ;
• un ballast BLST relié au module haute tension HV de la lampe à décharge LA via un faisceau de fils, le ballast fournissant une tension Vdiff suffisante au module haute de tension HV de manière à ce que la lampe LA puisse s'allumer ; et
• un relais RS pour connecter le ballast BLST à une source d'alimentation Vbat.

Thus, such a fire FX mainly comprises:

• a discharge lamp LA encased in a housing and arranged in a geometric configuration determined with a reflector RL. The discharge lamp is an arc lamp between two electrodes that requires a voltage pulse across its electrodes to create a first arc to ignite it. The lamp LA is, in a non-limiting example, a xenon lamp (with Hg ⁺ or without Hg-mercury) which requires in particular an ignition voltage Um of the order of 25kV. It comprises a bulb Bb and a high voltage module HV;
• a BLST ballast connected to the HV high voltage module of the discharge lamp LA via a wire harness, the ballast supplying a sufficient voltage Vdiff to the high voltage module HV so that the lamp LA can light; and
• an RS relay for connecting the BLST ballast to a power source Vbat.

• un convertisseur de tension continu/continu Ccc pour fournir à la lampe à décharge LA :
  • une haute tension redressée continue Vout, et
  • une tension d'amorçage Vignit, les deux tensions Vout et Vignit étant générées à partir d'une source d'alimentation Vbat, ladite source étant dans l'exemple pris la tension batterie du véhicule Vbat ;
• un convertisseur continu/alternatif Cca pour fournir à la lampe à décharge LA une haute tension alternative à partir de la tension redressée continue Vout fournie par le convertisseur continu/continu Ccc ; et
• une unité de commande UC pour piloter le convertisseur continu/continu Ccc et le convertisseur continu/alternatif Cca.

A first embodiment of the BLST ballast is shown in FIG. Fig. 2 . It comprises :

• a DC / DC voltage converter Ccc for supplying the discharge lamp LA with:
  • a continuous high voltage rectified Vout, and
  • a starter voltage Vignit, the two voltages Vout and Vignit being generated from a power source Vbat, said source being in the example taken the battery voltage of the vehicle Vbat;
• a DC / AC converter for supplying the discharge lamp LA with an alternating high voltage from the voltage continuous rectified Vout supplied by the DC / DC converter; and
• a control unit UC for controlling the DC / DC converter Ccc and the DC / AC converter Cca.

Without limitation, all elements of the ballast BLST is positioned on the same PCB type PCB ("Printed Circuit Board").

The elements of the BLST ballast are described in detail below.

• DC / DC voltage converter.

The DC / DC converter Ccc makes it possible to adapt the power source, in this case the battery voltage Vbat, to the discharge lamp voltage by generating the continuous high voltage rectified Vout and the ignition voltage Vignit. As will be seen in detail below, from the potential difference between these two high voltages, the HV high voltage module of the discharge lamp LA will be able to generate a first ignition pulse Um, of the order of 25kV to turn on said lamp LA.

• un transformateur TR1 élévateur de tension;
• un organe de commutation GMOS ;
• un circuit redresseur RD ; et
• un circuit multiplieur MU.

According to a first non-limiting embodiment Fig. 2 , it comprises :

• a step-up transformer TR1;
• a GMOS switching member;
• a rectifier circuit RD; and
• a MU multiplier circuit.

In a non-limiting embodiment, the DC / DC converter Ccc may furthermore comprise a resistor R1 mounted at the output of the multiplier circuit MU to allow the charging of a capacitor of the high voltage module HV of the discharge lamp LA to be delayed as we will see in detail later.

The various components of the converter Ccc are described below.

• The transformer TR1 .

• un enroulement principal n1 relié en série à l'organe de commutation GMOS et à la source d'alimentation Vbat ;
• un enroulement secondaire n2 relié au circuit redresseur de tension RD ; et
• un enroulement auxiliaire n3 relié au circuit multiplieur MU et bobiné dans le prolongement de l'enroulement secondaire n2 (les deux enroulements n3 et n2 sont donc en série) ;

It comprises :

• a main winding n1 connected in series to the GMOS switching member and to the power source Vbat;
• a secondary winding n2 connected to the voltage rectifier circuit RD; and
• an auxiliary winding n3 connected to the multiplier circuit MU and wound in the extension of the secondary winding n2 (the two windings n3 and n2 are therefore in series);

As will be seen in detail below, having the secondary winding n2 in series with the auxiliary winding n3 will be able to generate the Vignit ignition voltage using the sum of the voltages generated by the secondary winding. n2 and the auxiliary winding n3 which includes the DC rectified voltage Vout. This reduces the number of turns in the auxiliary winding n3 in particular.

que ce soit lors d'une magnétisation du transformateur (lorsqu'un courant circule dans le transformateur), ou lors d'une démagnétisation, avec n2/n1, n3/n1 et n3/2 les rapports de transformations entre ces différents enroulements.The relationships that exist between the main voltage Vn1 across the main winding n1, the secondary voltage Vn2 across the secondary winding n2 and the auxiliary voltage Vn3 across the auxiliary winding n3 are as follows: $$\mathrm{Vn}2/\mathrm{Vn}1=\mathrm{not}2/\mathrm{not}1;\mathrm{Vn}3/\mathrm{Vn}1=\mathrm{not}3/\mathrm{not}1;\mathrm{Vn}3/\mathrm{Vn}2=\mathrm{not}3/\mathrm{not}2$$

either during a magnetization of the transformer (when a current flows in the transformer), or during a demagnetization, with n2 / n1, n3 / n1 and n3 / 2 the transformation ratios between these different windings.

In a non-limiting embodiment, the secondary winding n2 is defined in such a way that the transformation ratio n2 / n1 between this winding n2 and the main winding n1 is equal to 5.

In a non-limiting embodiment, the auxiliary winding n3 is defined in such a way that the transformation ratio n3 / n1 between this winding n3 and the main winding n1 is equal to 2.

In a nonlimiting example, the number of turns in the main winding n1 is equal to 4, the number of turns in the secondary winding n2 is equal to 20, and finally the number of turns in the auxiliary winding n3 is equal at 8.

et : $$\left(\mathrm{n}\mathrm{3}\mathrm{+}\mathrm{n}\mathrm{2}\right)\mathrm{/}\mathrm{n}\mathrm{2}\mathrm{=}\left(\mathrm{n}\mathrm{3}\mathrm{/}\mathrm{n}\mathrm{1}\mathrm{+}\mathrm{n}\mathrm{2}\mathrm{/}\mathrm{n}\mathrm{1}\right)\mathrm{/}\left(\mathrm{n}\mathrm{2}\mathrm{/}\mathrm{n}\mathrm{1}\right)\mathrm{=}\left(\mathrm{8}\mathrm{/}\mathrm{4}\mathrm{+}\mathrm{20}\mathrm{/}\mathrm{4}\right)\mathrm{/}\left(\mathrm{20}\mathrm{/}\mathrm{4}\right)\mathrm{=}\left(\mathrm{2}\mathrm{+}\mathrm{5}\right)\mathrm{/}\mathrm{5}\mathrm{=}\mathrm{7}\mathrm{/}\mathrm{5}$$

We obtain : $$\mathrm{not}\mathrm{2}\mathrm{/}\mathrm{not}\mathrm{1}\mathrm{=}\mathrm{20}\mathrm{/}\mathrm{4}\mathrm{=}\mathrm{5}\mathrm{and\; N}\mathrm{3}\mathrm{/}\mathrm{not}\mathrm{1}\mathrm{=}\mathrm{8}\mathrm{/}\mathrm{4}\mathrm{=}\mathrm{2}\mathrm{;}$$

and $$\left(\mathrm{not}\mathrm{3}\mathrm{+}\mathrm{not}\mathrm{2}\right)\mathrm{/}\mathrm{not}\mathrm{2}\mathrm{=}\left(\mathrm{not}\mathrm{3}\mathrm{/}\mathrm{not}\mathrm{1}\mathrm{+}\mathrm{not}\mathrm{2}\mathrm{/}\mathrm{not}\mathrm{1}\right)\mathrm{/}\left(\mathrm{not}\mathrm{2}\mathrm{/}\mathrm{not}\mathrm{1}\right)\mathrm{=}\left(\mathrm{8}\mathrm{/}\mathrm{4}\mathrm{+}\mathrm{20}\mathrm{/}\mathrm{4}\right)\mathrm{/}\left(\mathrm{20}\mathrm{/}\mathrm{4}\right)\mathrm{=}\left(\mathrm{2}\mathrm{+}\mathrm{5}\right)\mathrm{/}\mathrm{5}\mathrm{=}\mathrm{7}\mathrm{/}\mathrm{5}$$

As will be seen later, these low transformation ratios and the associated number of turns are sufficient to generate a Vignit ignition voltage necessary for the ignition of the discharge lamp LA.

Of course, another number of turns can be used as well as other transformation ratios to obtain the Vignit ignition voltage and the sufficient rectified voltage Vout allow for the ignition of the lamp LA.

• The GMOS switching organ

It is driven by switching pulses and its repetitive opening-closing makes it possible to induce the induced secondary voltage Vn2 across the secondary winding n2 and the induced auxiliary voltage Vn3 across the auxiliary winding n3. In a non-limiting embodiment, the switching member is a MOSFET transistor.

• The RD rectifier circuit

It makes it possible to supply the DC rectified voltage Vout from the induced secondary voltage Vn2, the circuit RD comprising for this purpose a rectifying diode Dout and a filtering capacitor Cout. In a non-limiting embodiment, the rectifying diode Dout is connected to the node P1 between the secondary windings n2 and auxiliary winding n3 by its cathode as illustrated in FIG. Fig. 2 .

• The MU multiplier circuit

It makes it possible to supply the Vignit ignition voltage. In a non-limiting embodiment, the multiplier MU is composed of two diodes D1, D2 and two capacitors C1, C2. The capacitors C1 and C2 provide the ignition voltage Vignit, while the diodes D1 and D2, during the ignition phase, on the one hand to charge the capacitors C1 and C2 associated and on the other hand their avoid being discharged in a sense as we will see later.

According to a second embodiment illustrated in Fig. 9 , the DC / DC converter Ccc has the same elements as in the first embodiment but with an inverted bias of the rectifying diode Dout and the diodes of the multiplier circuit D1, D2. Moreover, the rectifier circuit RD makes it possible to rectify the induced auxiliary voltage Vn3 instead of the induced secondary voltage Vn2. At this time, the rectified voltage Vout is positive and the ignition voltage Vignit is negative.

• DC / AC voltage converter

This converter makes it possible to make the rectified high voltage Vout alternative necessary for the operation of the steady-state discharge lamp LA, that is to say during normal operation of the lamp, from the continuous rectified voltage Vout supplied by the DC / DC converter.

In a manner known to those skilled in the art, the DC / AC converter Cca comprises four transistors (not shown) mounted in complete bridge, the simultaneous opening or closing of a pair of transistors being controlled alternately with that of the another pair to make the voltage rectified. In a non-limiting embodiment, these transistors are NPN transistors of the IGBT type "Insulated Gate Bipolar Transistor", well adapted to the high voltages involved, both during the ignition phase and during the steady state of the lamp LA.

• The UC control unit

In a manner known to those skilled in the art, the control unit UC makes it possible to control, by means of control signals in response to external control commands, the width of the switching pulses of the DC / DC converter Ccc, as well as the operation of the complete bridge of the AC / DC converter whether in the ignition phase or in steady state.

Indeed, as we will see later, the BLST ballast provides the voltage necessary to turn on the lamp during an ignition phase, but also provides the voltage required to operate the lamp when it is on.

Thus, the BLST ballast operates in the following manner.

The operation is described for the first embodiment illustrated in FIG. Fig. 2 . The same operating principle will apply for the embodiment illustrated in FIG. Fig. 9 .

As an example, a supply voltage Vbat equal to 10 V is used. In general, this battery voltage Vbat varies between 8V (for example during a start) and 12V with possible peaks at 19V (norm given by the manufacturer).

1) Ignition phase

During the ignition phase, the ballast BLST will provide on the one hand the continuous rectified voltage Vout and on the other hand the ignition voltage Vignit, the potential difference between these two voltages, to feed the high module HV lamp voltage LA to turn on said lamp.

These two voltages are provided from a loading of respective capacitors, each load being effected alternately thanks to the switching member GMOS.

Thus, as will be seen below, when the switching member GMOS is closed, it allows a loading of the second capacitor C2 of the multiplier circuit MU for supplying the ignition voltage Vignit, while when it is open , it allows to charging the filter capacitor Cout for providing the DC rectified voltage Vout, and charging the first capacitor C1 MU multiplier circuit to also provide the Vignit boot voltage.

It is recalled that the charging of a capacitor is progressive. Consequently, the switching member GMOS, which is controlled by cutting pulses, allows through its opening and closing repetitive gradually load the three capacitors alternately.

In a non-limiting example, the switching frequency of the GMOS switching element is 100 kHz during this ignition phase.

It will be recalled that the MOSFET transistor that composes the switching member GMOS comprises a gate voltage Vgs and a drain-source voltage Vds that vary as a function of the opening-closing of the MOSFET transistor also causing a variation of the main voltages Vn1, secondary induced. Vn2 and induced auxiliary Vn3 of transformer TR1. The evolution of these voltages Vn1, Vn2, Vn3 associated with the transformers TR1 makes it possible to charge the capacitors C1, C2, Cout supplying the continuous rectified voltage Vout and the ignition voltage Vignit.

The variation of the transformer voltages TR1 as a function of the two states (closed-open) of the MOSFET transistor is described below when the capacitors C1, C2, Cout are fully charged.

• Closed MOSFET transistor

As can be seen at Fig. 3 in the intervals t0-t1, t2-t3, etc., when the MOSFET is closed, the gate voltage Vgs is positive, and the drain-source voltage Vds is zero.

The main winding n1 is connected directly to the power source Vbat. The main voltage Vn1 is equal to the battery voltage Vbat, ie is equal to 10V in the example taken.

A main current Ip is then generated and passes through the main winding n1 of the transformer TR1. This results in a creation of a magnetic flux in the transformer TR1 creating an induced secondary current In2 and an induced auxiliary current In3, the latter respectively inducing an induced secondary voltage Vn2 across the secondary winding n2 and an induced auxiliary voltage Vn3 at the terminals of the auxiliary winding n3 as illustrated in FIG. Fig. 4 . The induced currents ln2 and ln3 go in the opposite direction of the clockwise.

Given the transformation ratios respectively equal to 5 and 2, the induced secondary voltage Vn2 is equal to 50 and the induced auxiliary voltage Vn3 is equal to 20 as illustrated in FIG. Fig. 3 .

Given the direction of induced currents ln2 and ln3 (meaning shown in dotted lines on the Fig. 4 ), the righting diode Dout is then blocked. It is represented in dashed line at Fig. 4 . It is the same for the first diode D1 MU multiplier circuit.

On the other hand, the second diode D2 of the multiplying circuit MU is conducting (there is approximately 0V at its terminals).

As the second diode D2 is conducting, the second capacitor C2 of the multiplier circuit MU is loaded via this second diode D2. The first diode D1 being blocked, the first capacitor C1 of the multiplier circuit MU discharges via the second diode D2 to the second capacitor C2.

The second capacitor C2 is thus charged with the induced secondary voltages Vn2, induced auxiliary Vn3 and the voltage Vc1 of the first capacitor C1.

avec la tension Vc1 = +560V = -Vout - Vn3 provenant de l'étape où le transistor MOSFET est ouvert comme décrit plus loin.The voltage Vc2 across the second capacitor C2 of the multiplier circuit MU is therefore equal to: $$\mathrm{Vc}2=\mathrm{Vn}2+\mathrm{Vn}3+\mathrm{Vc}1,\mathrm{is}=50+20+560\mathrm{V}=+630\mathrm{V}$$

with the voltage Vc1 = + 560V = -Vout - Vn3 from the step where the MOSFET transistor is open as described below.

Since the voltage Vc2 is equal to the ignition voltage Vignit, we obtain Vignit = + 630V.

Thus, the ignition voltage Vignit is well supplied by the charging of the second capacitor C2 of the multiplier circuit MU and is well generated from the rectified voltage Vout.

It will be noted that the transformation ratio of n3 / n1 = 2 makes it possible to obtain a Vignit ignition voltage greater than 600V in the worst case of ignition (Vout_min = 400V and Vbat_min = 8V).

• Vignit min
• = Vc1 + Vn2_on +Vn3_on
• = Vn2_off+Vn3_off+Vn2_on +Vn3_on
• = Vout_min +n3/n2*Vout_min +n2/n1*Vbat_min+n3/n1*Vbat_min
• = Vout_min *(n3+n2)/n2 + Vbat min * (n3+n2)/n1
• = 400*7/5+8*7 = 616V.

Indeed, in this case, the ignition voltage Vignit is equal to:

• Vignit min
• = Vc1 + Vn2_on + Vn3_on
• = Vn2_off + Vn3_off + Vn2_on + Vn3_on
• = Vout_min + n3 / n2 * Vout_min + n2 / n1 * Vbat_min + n3 / n1 * Vbat_min
• = Vout_min * (n3 + n2) / n2 + Vbat min * (n3 + n2) / n1
• = 400 * 7/5 + 8 * 7 = 616V.

With Vn3_off / Vn2_off = n3 / n2 and Vn1 = Vbat, and Vn2_off, Vn3_off the voltages across respective windings n2 and n3 when the MOSFET is open, and Vn2_on, Vn3_on the voltages when the MOSFET is closed.

• Open MOSFET transistor

As can be seen at Fig. 3 in the intervals t1-t2, t3-t4, etc., the MOSFET transistor is open.

The gate voltage Vgs is zero, the MOSFET transistor behaves like a diode passing from the source to the drain.

The drain-source voltage Vds is therefore positive as illustrated in FIG. Fig. 3 . The opening of the MOSFET transistor prevents the main current Ip from flowing.

The conservation of the magnetic flux in the transformer TR1 causes the appearance of the secondary currents In2 and auxiliary ln3 respectively in the secondary winding n2 and the auxiliary winding n3 as illustrated in FIG. Fig. 5 in a clockwise direction.

Given the direction of induced currents In2 and In3 (as illustrated in dashed lines on the Fig.5 ), the recovery diode Dout is busy, as well as the first diode D1 of the multiplier circuit MU, while the second diode D2 of the multiplier circuit MU is blocked (it is represented in dotted lines).

The Dout rectifying diode being conducting (one has about 0V at its terminals), the filtering capacitor Cout is charged by said diode Dout.

The GMOS switching element is controlled in such a way that the charge of the filter capacitor Cout is equal to -400V. For this purpose, there is a control device (not shown) which measures the charge of the filter capacitor Cout.

Therefore Vout = -400V at the end of the loading of the capacitor Cout. As in this case, the induced secondary voltage Vn2 is equal to the rectified voltage Vout, Vn2 = -400V as illustrated in FIG. Fig. 3 .

Given the transformation ratio n2 / n1 = 5, the main voltage Vn1 = -400/5 = -80V.

Given the transformation ratio n3 / n1 = 2, the induced auxiliary voltage Vn3 = -80 * 2 = -160V.

Moreover, the first diode D1 being conducting (one has about 0V at its terminals), the first capacitor C1 of the multiplier circuit MU is charged through this diode D1.

The first capacitor C1 is thus charged with the induced secondary voltages Vn2 and induced auxiliary Vn3.

So we get $$\mathrm{Vc}\mathrm{1}\mathrm{=}\mathrm{-}\mathrm{Vn}\mathrm{2}\mathrm{-}\mathrm{Vn}\mathrm{3}\mathrm{=}\mathrm{-}\mathrm{Vout}\mathrm{-}\mathrm{Vn}\mathrm{3}\mathrm{=}\mathrm{400}\mathrm{V}\mathrm{+}\mathrm{160}\mathrm{V}\mathrm{=}\mathrm{+}\mathrm{560}\mathrm{V}$$

It will be noted that the second capacitor C2 of the multiplier circuit MU can not at this time be discharged towards the first capacitor C1 because the second diode D2 is blocked. On the other hand, the second capacitor C2 discharges into the circuit (capacitor C3) of the lamp LA as will be seen below.

Note that the charging time of the second capacitor C2 is around tens of microseconds (1 / 100kHz) while the discharge time is around a few milliseconds (thanks to a resistance R1 as discussed below) .

Thus, when the MOSFET switching transistor is closed, the capacitor C2 becomes charged thereby providing the Vignit ignition voltage from the rectified voltage Vout, while when the MOSFET transistor is open, the filter capacitor Cout is charged thereby providing the rectified voltage Vout.

It will be noted that the diodes D1 and D2 of the multiplier circuit MU must be sized to hold a voltage of the order of 800V. Indeed, the maximum reverse voltage Vrmax of the diodes is equal to: $$\mathrm{Vrmax}\mathrm{=}\mathrm{Vout\_max}\mathrm{*}\left(\mathrm{not}\mathrm{3}\mathrm{+}\mathrm{not}\mathrm{2}\right)\mathrm{/}\mathrm{not}\mathrm{2}\mathrm{+}\mathrm{Vbat\_max}\mathrm{*}\left(\mathrm{not}\mathrm{3}\mathrm{+}\mathrm{not}\mathrm{2}\right)\mathrm{/}\mathrm{not}\mathrm{1}\mathrm{=}\mathrm{450}\mathrm{*}\mathrm{1}\mathrm{,}\mathrm{4}\mathrm{+}\mathrm{19}\mathrm{*}\mathrm{7}\mathrm{=}\mathrm{763}\mathrm{V}\mathrm{.}$$

Indeed, Vrmax is equal to Vignit. Indeed, when the first capacitor C1 is charged, the first diode D1 is conducting (therefore the voltage at its terminals is 0V), so the voltage of the second diode D2 corresponds to Vignit. Similarly, when the second capacitor C2 is charged, the second diode D1 is conducting (therefore the voltage at its terminals is 0V), so the voltage of the first diode D1 corresponds to Vignit.

Thus, a rectified voltage Vout of -400V and a Vignit ignition voltage of + 630V are obtained, the potential difference Vdiff = Vignit-Vout being equal to 1030V. This potential difference Vdiff makes it possible to provide the very high ignition voltage Um of 25kV necessary for lighting the discharge lamp LA in the following manner.

The voltage difference Vdiff is applied to the HV high voltage module as indicated in FIG. Fig. 6 .

• un condensateur C3,
• un transformateur TR2 comprenant un enroulement primaire et un enroulement secondaire et apte à fournir une tension très élevée Um, de l'ordre de 25kV, à partir de la différence de tension Vdiff fournie par le convertisseur continu/continu Ccc,
• un éclateur à gaz Gz connecté en série avec l'enroulement primaire du transformateur TR2, et
• l'ampoule Bb de la lampe à décharge LA.

This HV module includes:

• a capacitor C3,
• a transformer TR2 comprising a primary winding and a secondary winding and able to provide a very high voltage Um, of the order of 25kV, from the voltage difference Vdiff supplied by the DC / DC converter Ccc,
• a gas spark gap Gz connected in series with the primary winding of the transformer TR2, and
• the Bb bulb of the LA discharge lamp.

When the LA lamp is off, the gas spark gap Gz behaves like an open switch. When the voltage difference Vdiff is applied to the input of the high voltage module HV, the capacitor C3 is charged. When it reaches a predetermined threshold of charging, of the order of 800V in a non-limiting example, the spark gap Gz becomes abruptly conductive and creates a current pulse in the primary winding of the transformer TR2 which produces in the secondary the very high Um voltage of 25kV, thus creating a first electric arc necessary for lighting the lamp LA. At the same time, when the gas spark gap becomes on, the capacitor C3 discharges very quickly in the transformer TR2.

Thus, the discharge lamp LA turns on.

2) Permanent regime

When the lamp is on, in order to function properly, an AC voltage is applied to its terminals. This voltage is of the order of -85V steady state for a xenon lamp with mercury (Hg ⁺ ) and of the order of -42V for a mercury-free xenon lamp (Hg ^- ).

As previously described, the control unit UC acts to activate and deactivate the transistors of the DC / AC converter so that it supplies this AC voltage from the rectified voltage Vout necessary to continue operating the lamp LA. This AC voltage is obtained from the DC rectified voltage Vout supplied by the DC / DC converter Ccc.

It is recalled that the DC / DC converter Ccc provides the power necessary for the rectified voltage Vout is in this case equal to -85V. In a non-limiting example, the frequency switching speed of the GMOS switching element is 300kHz in steady state.

Thus, it will be noted that in the ignition phase, the MOSFET switching transistor remains open longer than steady state.

The Fig. 7 summarizes the evolution of the voltage Ula across the discharge lamp LA during the ignition phase and during the steady state.

It should be noted that the scale of the intervals t0-t1, t1-t2, t2-t3, t3-t4 is around milliseconds, while the scale of the interval t4-t5 and the sequence lies around seconds.

The interval t0-t1 represents the ignition phase, while the interval t3-t4 represents the steady-state operating phase.

The intervals t1-t2 and t2-t3 represent transition phases.

At time t0 = 0, all the capacitors Cout, C1, and C2 are at 0. The ignition voltage Vignit and the rectified voltage Vout are at 0.

In the interval t0-t1, the capacitors Cout, C1 and C2 are charged. The Vignit ignition voltage and the rectified voltage Vout increase.

At time t1, they reach respectively 630V and -400V, the difference being 1030V. The voltage Ula of the lamp LA is equal to the voltage difference Vignit - Vout.

We have reached the end of the ignition phase.

Between t1 and t2, the rectified voltage Vout begins to decrease (the capacitor Cout of the rectifier circuit discharges) while the ignition voltage Vignit drops to -400V because the capacitor C3 discharges suddenly, its voltage Vc3 becomes zero, the rectified voltage Vout remaining at -400V.

From time t3, the rectified voltage continues Vout is made alternative by means of the DC / AC converter Cca. The voltage Ula of the lamp LA is equal to the rectified voltage Vout.

At time t3, there is thus a first switching of the switching transistors of the DC / AC converter Cca. Then from time t4, the steady state of the discharge lamp LA is installed around -85V.

It will be noted that between the time t3 and the time t4, there is a waiting time between the first switching of the complete bridge of the DC / AC converter Cca and a second switching, of the order of a few tens of milliseconds, in order to prevent the discharge lamp from extinguishing. Indeed, the created electric arc must be maintained long enough to heat the first electrode of the lamp LA before reversing the direction of the arc (that is to say before reversing the current in the lamp which as a result will go through zero), to heat the second electrode of the lamp LA.

The evolution of the two Vignit and Vout straightening voltages is illustrated more precisely in the Fig. 8 .

The two curves Cvignit and Cvout representative respectively of the two voltages Vignit and Vout illustrate the progressive loading of capacitors C2 and Cout corresponding. As can be seen, the slope of the curve Cvignit representative of the ignition voltage Vignit is greater than that of the curve Cvout representative of the rectified voltage Vout because the filter capacitor Cout is dimensioned so as to be larger than the second capacitor C2. Indeed, the capacitor Cout generates the greatest power to the lamp LA and corresponds to a reserve of energy. Indeed, in steady state, it is the only one to supply energy to the lamp LA.

Because of this difference in slope, the Vignit ignition voltage can reach its maximum value + 630V at time t1 before the rectified voltage reaches its -400V. This could generate a voltage difference at time t1 less than 1030V, for example at about 800V, the rectified voltage Vout reaching only 200V for example. This voltage difference Vdiff can cause ignition of the lamp LA.

However, since the conduction threshold of the gas spark gap Gz is of the order of 800V, the voltage difference Vdiff is at the threshold limit of the gas spark gap; also the LA lamp may not light properly.

In order to remedy this drawback, the resistor R1 of the BLST ballast makes it possible to delay the charging of the capacitor C3 of the lamp LA with the ignition voltage Vignit as illustrated by the curve CRvignit. Thus, the two voltage Vignit and Vout will reach their maximum value at the same time so as to provide a potential difference sufficient to exceed the loading threshold of the gas spark gap thus allowing a reliable ignition of the lamp LA. Thus, the resistor R1 makes it possible to wait for the rectified voltage Vout to be stabilized at -400V in order to make it possible to obtain a voltage difference Vdiff greater than the conduction threshold of the gas spark gap Gz so as to obtain an arc of sufficient voltage. (25kV) required for reliable ignition of the LA lamp.

Moreover, this resistor R1 prevents current peaks in the second diode D2 and thus prevents the latter from being damaged.

Note that in the description, the vehicle fire application was taken as an example, but of course, the described ballast can be used in other applications such as, in non-limiting examples, interior lighting building ("Interior Lighting ") Or street lighting (" General Lighting ").

• Elle permet d'avoir des rapports de transformation (5 et 2) réduits ce qui réduit les éléments de fuite dues aux capacités et self parasites des spires d'un enroulement; il y a donc moins de risque de surtension sur le transistor de l'organe de commutation GMOS et donc moins de problème CEM (compatibilité électromagnétique).
• Du fait du faible rapport de transformation n3/n1, elle permet d'avoir des diodes D1, D2 dimensionnées pour des tensions de l'ordre de 700 à 800V maximum (pour tenir la tension d'amorçage de 630V) au lieu de 1000V pour la solution de l'état de la technique antérieur, ce qui permet d'utiliser des composants plus standard et donc de réduire le coût des composants.
• Elle permet d'obtenir des enroulements plus petits dans le transformateur TR1 et donc une longueur de fil plus petite; par conséquent le volume global du transformateur est réduit. Le fait d'avoir une longueur de fil réduite, permet de diminuer les pertes cuivres.
• Il existe moins de contrainte au niveau de l'isolement effectué entre l'enroulement secondaire et l'enroulement auxiliaire afin que ces derniers ne se touchent pas. En effet, un tel isolement doit pouvoir tenir 560V (-Vn2-Vn3 comme décrit précédemment) au lieu de 1000V dans l'état de la technique antérieur.
• Elle permet d'obtenir, grâce à la résistance R1, un allumage fiable de la lampe à décharge grâce à une différence de potentiel suffisante pour rendre passant l'éclateur à gaz.
• Le fait d'avoir réduit le volume du transformateur TR1 permet d'avoir une surface sur la carte électronique PCB réduite, et par conséquent une augmentation de la fiabilité, une réduction des coûts de test, un temps de process amélioré, et enfin un coût report sur PCB meilleur.
• La durée de vie du transformateur TR1 est augmentée puisque la tension maximum générée dans ledit transformateur est de 630V contre 1000V pour la solution de l'état de la technique antérieur. Par conséquent, le stress vu par les enroulements est réduit, c'est-à-dire que l'on obtient une meilleure tenue au claquage. Le transformateur est donc plus fiable.
• Enfin, elle permet de réduire le nombre de composants nécessaire à la fonction d'allumage uniquement, grâce au circuit multiplieur. Deux diodes D1, D2 et deux condensateurs C1, C2 suffisent pour générer la tension d'amorçage Vignit à partir des enroulements secondaire n2 et auxiliaire n3.

In conclusion, the invention has the following advantages.

• It allows to have transformation ratios (5 and 2) reduced which reduces the leakage elements due to the capacitances and self parasitic turns of a winding; there is therefore less risk of overvoltage on the transistor of the switching member GMOS and therefore less problem EMC (electromagnetic compatibility).
• Because of the low transformation ratio n3 / n1, it allows to have diodes D1, D2 sized for voltages of the order of 700 to 800V maximum (to maintain the starting voltage of 630V) instead 1000V for the solution of the state of the prior art, which allows the use of more standard components and thus reduce the cost of components.
• It makes it possible to obtain smaller windings in the transformer TR1 and thus a smaller length of wire; therefore, the overall volume of the transformer is reduced. The fact of having a reduced length of wire makes it possible to reduce the brass losses.
• There is less constraint in the isolation between the secondary winding and the auxiliary winding so that they do not touch each other. Indeed, such isolation must be able to hold 560V (-Vn2-Vn3 as previously described) instead of 1000V in the state of the prior art.
• It makes it possible, thanks to the resistor R1, to reliably ignite the discharge lamp by virtue of a potential difference that is sufficient to make the spark gap open.
• Having reduced the volume of the transformer TR1 allows for a reduced surface area on the PCB PCB, and therefore an increase in reliability, a reduction in test costs, an improved process time, and finally a cost report on PCB better.
• The lifetime of the transformer TR1 is increased since the maximum voltage generated in said transformer is 630V against 1000V for the solution of the state of the prior art. As a result, the stress seen by the windings is reduced, that is to say that a better resistance to breakdown is obtained. The transformer is therefore more reliable.
• Finally, it reduces the number of components required for the ignition function only, thanks to the multiplier circuit. Two diodes D1, D2 and two capacitors C1, C2 are sufficient to generate the ignition voltage Vignit from the secondary windings n2 and auxiliary windings n3.

Claims (6)

1. A ballast (BLST) for a discharge lamp (LA) comprising:

   a direct / direct voltage converter (Ccc) in order to provide a rectified direct voltage (Vout), and comprising:

   - a single voltage rectifier (RD);

   - a transformer (TR1) comprising a main winding (n1), a secondary winding (n2) and an auxiliary winding (n3), the transformer (TR1) making it possible to provide the rectified direct voltage (Vout); and

   - a voltage multiplier circuit (MU) in order to provide a starting voltage (Vignit), the difference in potential (Vdiff) between this voltage (Vignit) and the rectified direct voltage (Vout) making it possible to create a switching-on voltage (Um) for the discharge lamp (LA),

   characterised in that

   - the auxiliary winding (n3) is in series with the secondary winding (n2); and

   - the voltage multiplier circuit (MU) is combined with the secondary (n2) and auxiliary (n3) windings of the transformer (TR1).
2. Ballast (BLST) according to claim 1, characterised in that the voltage multiplier circuit (MU) comprises two capacitors (C1, C2) and two diodes (D1, D2).
3. Ballast (BLST) according to one of the preceding claims, characterised in that it additionally comprises a resistor (R1) at the output from the voltage multiplier circuit (MU).
4. Ballast (BLST) according to one of the preceding claims, characterised in that the secondary winding (n2) comprises a transformation ratio (n2/n1) of approximately 5 with the main winding (n1).
5. Ballast (BLST) according to one of the preceding claims, characterised in that the auxiliary winding (n3) comprises a transformation ratio (n3/n1) of approximately 2 with the main winding (n1).
6. Lighting device (FX) for a vehicle, comprising a discharge lamp (LA) to which there is connected a ballast (BLST) according to any one of the preceding claims, the ballast (BLST) being able to provide a voltage (Vdiff) in order to permit switching on of the discharge lamp (LA).

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