FR2674722A1 - METHOD FOR STARTING AN ELECTRICAL LOAD LIKE A DISCHARGE LAMP, DEVICE FOR ELECTRICALLY SUPPLYING A LOAD LIKE A DISCHARGE LAMP AND DISCHARGE LAMP LIGHTING SYSTEM, IN PARTICULAR FOR A VEHICLE. - Google Patents

Abstract

The invention applies in particular to the automotive industry. It consists of a method of igniting an electric charge such as a discharge lamp, intended to supply it with sufficient supply energy at a high voltage and for a very short period of time, repeatedly or not. The invention is characterized in that the method comprises the steps of: a) accumulating the energy called up by the electric charge and supplied by the converter in a storage device placed in series with the electric charge, b) releasing in the charges the stored energy for a sufficient time to ensure proper starting, the circuit comprising the converter, the energy storage device and the energy consuming load self-adjusting to the starting condition.

Description

The present invention relates to a method for priming a load

  Like a discharge lamp It also relates to a power supply device embodying the method of the invention, and a lamp system to

  discharge, in particular for vehicles.

  The invention finds application in particular in the field of electric discharge lamps installed in

  headlamps for motor vehicles.

  In the prior art, it is known to couple a discharge lamp to a battery or a source of relatively continuous voltage via a converter and a step-up transformer which converts a low DC voltage into a high voltage.

  alternating and / or pulsed voltage.

  On the other hand, the discharge lamps used in particular in the vehicle headlights, must be powered according to different current characteristics voltage depending on the moments In particular, it is necessary to achieve a priming and then maintaining the conditions

ignition during steady state.

  Indeed, the lamp is filled with a gas susceptible under current voltage conditions determined to ionize and generate a plasma that

  produces photons in the band of visible light.

  It is this phenomenon that is used to provoke with

  little electric power an important illumination.

  But to make the gas capable of ionizing, it is necessary to place its thermodynamic state under conditions which will be called hereinafter conditions of initiation In this transformation, the lamp is related to its

  electrical supply circuit to a Zener diode.

  Therefore, at the beginning of the operation of the lamp, during a first ignition, it performs a cold boot for example by producing a succession of very high voltage pulses (of the order of 12 kilo volts) These pulses are lamp terminals for a very short period of time, usually

the order of 1 microsecond.

  When the thermodynamic state of the gas in the lamp is suitable, the lamp verifies a starting condition: for example when the current flowing through the lamp i L is greater than the threshold i S allowing the appearance of the illumination phenomenon. turns on and the converter is placed by a control circuit which tests the starting condition (or its realization) in

maintenance phase.

  The phase or mode of maintenance is, for the converter, a mode in which a low-voltage alternating voltage (of the order of 80 volts, for

example), is generated.

  However, the operation of the lamp can be interrupted for a brief moment This is the case, especially when the lamp is installed in a vehicle and the driver makes several calls lighthouse, or when he

  change of lighting mode ("code", "full light", etc.).

  In this case, the lamp contains a still hot gas but the current that passes through it could completely disappear,

  in any case, go back below the boot threshold is.

  It is then necessary to place the converter in a mode of

  so-called hot priming operation.

  Such a priming requires that in a first step a succession of very high voltage pulses be generated as for all priming, then that a high voltage (of the order of 450 volts), intermediate between the very high voltage and low voltage supra This intermediate high voltage must be maintained for a time that depends on the lamp, and

  lasts generally of the order of 1 millisecond.

  The invention particularly relates to hot starting which follows a lamp extinction after a

steady state.

  The lamp, during the priming regime, sees a voltage law decreasing at its terminals This voltage remains higher than the nominal operating voltage

  of the lamp in its stable steady state.

  however, in the embodiments of the prior art, the converter is dimensioned at these high voltages which are provided only during the cold or hot priming phases, and therefore during a very small fraction of the total operating time of the device.

  including the lamp and its power supply circuit.

  In addition, the converters of the prior art would require three independent sections to produce

  the three aforementioned necessary voltages.

  To overcome these drawbacks of the prior art, there is provided a method of igniting an electric charge such as a discharge lamp which uses a converter producing at least three voltage waveforms without adding a component relative to a converter producing only the very high voltage and low voltage waveforms To perform the hot start for a very short time interval, the method of the invention comprises repeatedly or not, the steps of: a ) accumulating power demanded by the electrical load and provided by the converter in a storage device placed in series with the electrical load, and (b) releasing the stored energy for a period of time sufficient to ensure proper priming, the circuit comprising the converter, the energy storage device and the energy-consuming load self-adapting to the boot condition. The invention also relates to a device for supplying an electric charge such as a discharge lamp for implementing the method according to the invention. The device comprises a device generating a voltage waveform, such as a converter, which transmits electrical energy to a storage device such as a capacitor connected to the load. The invention also relates to a discharge lamp lighting system, in particular for a vehicle, powered by

a device according to the invention.

  Other features and advantages of the present invention will be better understood using the

  description and appended figures which are:

  Figure 1: a block diagram of a device implementing the method of the invention; FIGS. 2a, 2b, 2c: diagrams of the voltage and current across the various components according to the invention during an execution of the hot start method according to the invention; FIGS. 3a, 3b, 3c, 3d: the shapes of the currents and voltages at the end of the execution of the process

priming according to the invention.

  FIG. 1 shows a schematic diagram of a device implementing the method of the invention. In general, the method uses a source of energy adapted to supply the electric charge as a discharge lamp according to the

  different modes of operation thereof.

  However, the energy source will be described only as regards the steady state operation, during the hot start mode For other modes, the skilled person knows how to achieve such a power source. According to the invention, the initiation process consists in producing, by means of the electrical source, a quantity of energy sufficient to reach a certain

boot condition.

  In a preferred embodiment, the energy is produced by a voltage source. In addition, it is preferred to carry out a succession of square shaped pulses or voltage pulses that are accumulated in

a storage device.

  In the preferred embodiment, the

  Energy storage device is a capacitor.

  But other embodiments of the device implementing the method are possible for example using a current source, or else other forms

than a square voltage.

  In addition, the power supply device comprises a converter supplied with DC voltage, for example

  provided by the on-board battery in a vehicle.

  The energy from the converter is stored in the storage device until reaching a threshold corresponding to a condition of ignition of the electrical charge In the case where the electric charge is a discharge lamp, the energy is transmitted under To achieve proper charging of the capacitor, it is necessary that the voltage pulses, or any waveform from the

  converter, of positive average value.

  In a preferred embodiment, the form

  voltage wave is unidirectional.

  However, it is clear that the voltage can be rectified if the waveform is alternative, before being communicated across the capacitor In this case, it is necessary that the power device 1 comprises a rectifier connected to the path d feeding so

  to supply the capacitor with a rectified voltage.

  This rectifier may be arranged at the primary or secondary (preferably secondary) of the transformer if the converter comprises a transformer. In the case where the energy is in the form of a voltage, the starting condition is reached when the voltage across the capacitor reaches a given value, which depends on the internal condition of the discharge lamp being ignited. As a typical example of commercial discharge lamps, this value is an intermediate high voltage of about 450 volts. When the storage device has reached this value, the energy is discharged from the storage device

in the electric charge.

  On the other hand, the converter may comprise at least one step-up transformer. As a result, the storage device may be arranged at the primary or at the secondary of the transformer. In a preferred embodiment, the capacitor is placed at the secondary of the transformer. providing at least one low voltage (for the device holding mode). In a preferred embodiment, the capacitor is placed in series with the lamp so as to

  not having to withstand a high voltage at its terminals.

  this characteristic of the invention makes it possible to use less expensive capacitors such as capacitors

electrochemical type.

  On the other hand, it is clear that it is possible to use special components capable of providing very high voltages during switching, for example.

  obtained using a synthetic self.

  In FIG. 1, the reference 1 denotes a supply device implementing the priming method of the invention, and capable of generating: a) mono-directional voltage pulses of very high peak value, b) an AC voltage higher than the

  arc voltage (or nominal voltage) of the lamp 3.

  Reference 2 denotes a capacitor

  accumulator placed in series with the discharge lamp 3.

  The current flowing in the circuit of FIG. 1 denotes the voltage at the terminals of the device 1 and the voltage at the terminals of the discharge lamp. It is noted that one of the advantages of the invention is to avoid using a very high voltage capacitor, since this capacitor 2 is arranged in series and not in parallel as is known in the state of the art.

art.

  FIGS. 2 a, 2 b, 2 c show a timing diagram of execution of the method of the invention. In FIG. 2 a, there is shown a succession of square pulses which are repeated in number N during a discharge period of the discharge lamp This recurrent voltage is defined by a peak value Vmax, a recurrence period T, and a given duty cycle t / T which is a function of the characteristics of the entire

  supply circuit of the discharge lamp.

  FIG. 2b shows the shape of the currents flowing through the circuit of FIG. 1. The values of these currents are still insufficient to cause a discharge process that can be used to create an illumination. 1 supply device is square, the current is constituted by a recurrence of triangles having about the same frequency characteristics as the voltage recurrence of Figure 2 a The maximum current is relatively low compared to the intensities usually dissipated or

  charged in a discharge lamp.

  In FIG. 2c, the voltage v L is represented at the terminals of the discharge lamp 3. Because of the accumulation of the charges dQ = Cdv, it is noted that the voltage rises during each period T up to to reach a sufficiently high value by the number N of recursion pulses When the voltage VL has reached the value VLS of the warm start threshold, the

  recurrence of supply voltage v is stopped.

  The condition of stopping the production by the converter of the recurrence of pulses, or, in general, of the generation of charge energy, is provided by a detection means arranged in the power supply device. invention, and not shown in the drawing, which detects that the selected ignition condition is verified We then observe the following phenomenon in Figures 3 to 3 d Note that these values are reached naturally, the system comprising the lamp and the feed device of the invention self-adapting to the point of view of

boot.

  In FIG. 3a, the last recurrence v of the voltage slots is shown at the instant t 0 the last voltage slot v produced by the supply device 1 begins at this moment, the voltage across the capacitance increases approximately linearly as a function of the time constant of the general circuit constituted by the lamp supply device and the capacitor When at time t1, the voltage slot v drops to zero, the capacitor is discharged due to the natural change of state of the lamp which goes from an almost infinite impedance before ignition, to a value of a few hundred ohms immediately after the last ignition pulse This discharge of the capacitor is done according to a time constant of discharge corresponding to the general time constant of the series circuit constituted by the supply device

  1, the capacitor 2, and the discharge lamp 3.

  In FIG. 3c, the evolution of the voltage across the discharge lamp 3 is represented. At the time of the appearance of the last voltage slot, the voltage at the terminals of the lamp goes from a value -vm to value + vm corresponding to the highest voltage obtained at the terminals of capacitor 2 Then at time t1, when the voltage of supply device 1 is interrupted, the voltage at the terminals of the lamp is suddenly reversed to reach to the value -vm and slowly decreases to zero, since we have the equation

VL = v vc.

  Similarly, the current flowing through the circuit is shown in FIG. 3d. Between times t 0 and tl, the current changes from zero to a value imax corresponding to the maximum voltage delivered in the circuit. Then, after the instant t 1 the current goes down to a strongly negative value which corresponds to a hot start current The current i then goes back to a zero value During this ascent, it is possible to switch the feed device 1 to

  maintenance of the ignition of the discharge lamp.

  Thus, it has been possible to prime the discharge lamp without using high voltage components as was the case in the prior art. As a result, the power supply device 1 may comprise a converter which is not oversized and which guarantees priming

  hot or cold priming of the discharge lamp.

  The power supply device of the invention is mounted in a lamp lighting system

for discharge.

Claims (7)

  1) A method of igniting an electric charge such as a discharge lamp for effecting hot initiation during a very short time interval, comprising repeatedly or not, the steps of: a) accumulating called energy by the electric charge and provided by the converter in a storage device placed in series with the electric charge, b) releasing the stored energy into the charge for a sufficient time, to ensure proper initiation, the circuit comprising the converter, the energy storage device and the energy-consuming load self-adapting to the boot condition. 2) Method according to claim 1, characterized in that the energy is supplied in the form of a voltage   whose waveform is alternative.   3) Method according to claim 1, characterized in that the energy is supplied in the form of a voltage   whose waveform is impulse.   4) Method according to claim 2 or 3, characterized in that the voltage is mono-directional,   at least at the terminals of the storage device.   Method according to claim 3 or 4, characterized in that the pulses are produced by the converter under a frequency and a duty cycle predetermined.   6) Method according to claim 3, characterized in that the sequence of pulses is interrupted by the   detection that the boot condition is verified.   7) Device for supplying an electric charge such as a discharge lamp (3), characterized in that, to implement the method according to one it   any of claims 1 to 6, it comprises a   device (1) generating a voltage waveform (v), such as a converter, which transmits electrical energy to a storage device such as a capacitor (2) connected to the load (3). 8) Device according to claim 7, characterized in that the capacitor (2) is arranged in series between the electric charge (3) and the converter (1) -   9) Device according to claim 7, characterized in that it also comprises a means for detecting a boot condition whose output interrupts the production of the charging energy of the   capacitor, when the boot condition is checked.   10) Discharge lamp lighting system, in particular for a vehicle, characterized in that it comprises at least one feed device according to one of the   Claims 7 to 9 for priming at least a discharge lamp.