EP2087777A1

EP2087777A1 - Circuit arrangement for firing a discharge lamp

Info

Publication number: EP2087777A1
Application number: EP06819374A
Authority: EP
Inventors: Christian Breuer; Martin BRÜCKEL; Andreas Huber; Ralf Hying; Bernhard Reiter
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2006-11-09
Filing date: 2006-11-09
Publication date: 2009-08-12
Also published as: JP2010509718A; KR20090079982A; US8143795B2; WO2008055547A1; CN101523996A; TW200833173A; US20100045196A1

Abstract

The present invention relates to a circuit arrangement for firing a discharge lamp, having a first and a second input connection for connecting an input voltage; an inverter, having an input and an output, wherein the input is coupled to the first and the second input connections; a first and a second output connection for connecting the discharge lamp (La); a resonance impedance coupled between the output of the inverter and the first output connection; a resonance circuit comprising the resonance impedance; and a control device (10) for controlling the frequency of the signal provided at the inverter output; the circuit arrangement further comprises a current measuring device arranged for the measuring of a current (I-ist(f )) correlating with the current in the resonance circuit, wherein the control device (10) is configured such that it controls the frequency at the output of the inverter as a function of the measured current (Ilst(f)). The invention further relates to a method for firing a discharge lamp on such a circuit arrangement.

Description

description

Circuit arrangement for igniting a discharge lamp

Technical area

The present invention relates to a circuit ^arrangement for igniting a discharge lamp having a first and a second input terminal for connecting an input voltage, an inverter having an input and an output, wherein the input is coupled to the first and the second input terminal, a first and a second output terminal for connecting a discharge lamp, a resonant inductor coupled between the output of the inverter and the ers ^¬ th output terminal, a resonant circuit comprising the resonant inductor, and a Regelvorrich ^¬ processing for controlling the frequency of the provided at the inverter output signal. It also relates to a method for igniting a discharge lamp on such a circuit arrangement.

State of the art

The present invention relates generally to the Proble ^¬ matics the generation of a sufficiently high for igniting a discharge lamp voltage by means of exciting a resonant circuit in the region of its resonant frequency. In the prior art, in particular the output ^¬ voltage of the resonance circuit is in this case measured or over the entire swept result of tolerances possible range of resonant frequencies, ie, alternately first from smaller to larger frequencies and then from larger to smaller frequencies, etc .. In the Vorgehens- way, in this case the output voltage of the Resonanzkrei ^¬ ses is measured, in particular using a voltage divider, in order to select the appropriate excitation frequency for the resonant circuit. Assuming that the ignition voltage is in the range of several kV, the elements of the voltage divider must be designed for this high voltage. Moreover, the measurement of off ^¬ output voltage requires a considerable amount of additional required components, which is reflected in undesirably high cost ten. Since the voltage at the output of Reso ^¬ nanzkreises is present as a result of the inverter as a removable clamping ^¬ voltage, in its measurement to eliminate the alternating component of a filter must be provided, which filter results in an additional expenditure of components and assembly. In the second variant, that is, the sweeping, though fewer components are required, however, the sweep of the toleranzbe ^¬ adhered entire range of possible resonant frequencies leads to a low average output voltage and thus to a deterioration of the ignition conditions.

Presentation of the invention

Therefore, the object of the present invention is to develop the above-mentioned circuit arrangement or the aforementioned method such that a control to the resonant frequency of the resonant circuit for the ignition of a discharge lamp is made possible at a lower cost.

This object is achieved by a circuit arrangement having the features of patent claim 1 and by a method having the features of patent claim 8. The present invention is based on the realization that a more cost effective control is enabled on the Resonanzfre ^acid sequence of the resonant circuit when the current flowing in the resonant circuit current is measured instead of measuring the output voltage of the resonant circuit. Since ^¬ by providing a designed for high voltages the voltage divider on the one hand be omitted. The current measurement is namely by a low-impedance shunt resistor, which is serially coupled into the circuit. The voltage at the shunt resistor is usually less than 1 V. On the other hand, ^another circumstance comes into play: Such a shunt resistor for current measurement is in electronic ballasts for operating a discharge lamp, ie for controlling various operating parameters during continuous operation of the discharge lamp , anyway provided and according to the present invention can now also be used in the control in connection with the ignition of the discharge lamp.

In addition, it should be noted that in the context of the present invention, in addition to an excitation with full resonance frequency, an excitation with an odd fraction of the resonant frequency can take place, whereby the requirements with regard to the switching speed of the electronic switch of the inverter can be reduced.

In a preferred embodiment, the circuit arrangement further comprises a voltage converter, which is coupled between the first and the second input terminal and the input of the inverter, wherein the current measuring device is designed as a shunt and in Voltage converter is arranged, and wherein the voltage ^{¬ converter is} connected to a reference potential such that the current through the shunt is correlated with the current in the resonant circuit. Compared with an arrangement of the shunt resistor in the resonant circuit provides this pre ^¬ hens, the advantage that there can be dispensed with a costly potenti ^¬ alfreie measurement.

Preferably, the control device comprises a first SpeI ^¬ chervorrichtung for storing a correlated with a maximum of the current in the resonant circuit value, an Ver ^¬ equal means for comparing a resultant at the instantaneous frequency of the signal at the output of the inverter with the current in the resonant circuit korre ^¬ profiled Value with the maximum stored in the first memory device, and a writing device, which is designed for the case that at the momen ^¬ tanen frequency of the signal at the output of the inverter resulting, correlated with the current in the resonant circuit value is greater than that previously entered maximum, to enter this value in the first storage device.

This measure has the advantage that regardless of tolerances or changes due to temperature dependencies and the like as a control variable always optimally current value for the current (or a correlated size) in the resonant circuit of the circuit arrangement for the present circuit arrangement taking into account the existing environmental conditions the control is used to the resonance frequency.

In a preferred embodiment, the control device further comprises a control device for controlling the frequency of the signal at the output of the inverter, a second memory device, in which a difference value is entered, wherein the comparison device is further designed, the difference between the stored in the first memory device maximum and at the current frequency of the signal at the output to form the inverter resultant value, and to compare it against the registered in the second storage device difference value, wherein the tax regulations direction is further adapted to change the frequency of the Sig ^¬ Nals at the output of the inverter as long as in a rich ^¬ tung to lower ie or increase until the difference is greater or greater than the entered difference value, and then again in the reverse direction to change, ie increase or decrease until the difference is again greater than or equal to the registered difference value.

In one known from the prior art, used in the control of the output voltage of the resonant circuit procedure was swept to a range of +/- 5 to +/- 10% to the actual resonant frequency to meet the tolerance-prone resonance frequency. Tolerances of the resonant frequency arise as a function of changing environmental conditions and as a result of component tolerances. In the present invention, although the range of the resonant frequency is also overshadowed - over the definition of the difference value entered in the second memory device, due to the notated maximum effects of tolerances and different temperatures on the maximum output voltage and the resonance frequency are irrelevant, so that the frequency range around the resonant frequency can be made much narrower than in the prior art. This results in a significant increase in the average output voltage of the resonant circuit compared to the known from the prior art approach. This allows a considerable improvement in the ignition tendency of the connected discharge lamp.

The last-mentioned preferred embodiment moreover provides a suitable means for eliminating the influence of noise in the detection of a signal correlated with the current of the resonant circuit. For example, this noise may be on the order of 1 to 5% of the useful signal. Another prior art related to the voltage measurement control algorithm known continuous frequency increase or continuous Fre ^¬ quenzerniedrigung would then reverse already when it measures a lower value after passing through a maximum. These superiors hens as would the influence of the noise does not take into ^¬ into account and reaching the actual maximum would prevent resulting in a lower voltage-time area than the present invention ^¬ would give again and again. By Mitnotieren the current maximum current (or a value correlated therewith) and dimensioning of the difference value so that the contribution of the noise is securely covered, can be the Fre ^¬ frequency range, is swept within which, minimize and maximize the voltage-time area. The latter results in an optimization of the ignition tendency of the a discharge lamp connected to a circuit arrangement according to the invention.

In a preferred embodiment of a circuit arrangement according to the invention, the difference value is at most 50% of the maximum, preferably between 5 and 30% of the maximum. In this case, the difference value, after the maximum changes during the ignition as mentioned above, can also be determined based on an average of the maximum obtained from experience.

The frequency at the output of the inverter before ^¬ Trains t in jumps of more than 1 kHz, preferably changed a maximum of 50 Hz. The time constant of the control device is at most 5 ms preferably, more preferably Hoechsmann ^¬ least 2 ms.

The preferred embodiments and their advantages described with reference to the circuit ^arrangement according to the invention also apply, as far as applicable, to the method according to the invention.

A particularly preferred embodiment of the method according to the invention comprises the following steps: a) measuring the instantaneous current value resulting at the instantaneous frequency; b) determining a difference between a stored current value corresponding to a current maximum of the current value and the current current value; bl) if the control is in progress from higher frequencies to lower frequencies: bll) if the difference is less than a stored difference value: Ernied ^¬ ring of the instantaneous frequency by a predetermined frequency value; bl2) if the difference is greater than or equal to a stored difference value: increase the mo- mentanen frequency by a predetermined frequency value; b2) if the control is running from smaller frequencies to larger frequencies: b21) if the difference is smaller than a stored difference value: increasing the current frequency by a predefinable frequency value; b22) if the difference is greater than or equal to a stored difference value: decreasing the instantaneous frequency by a predefinable frequency value; c) comparing the instantaneous current value with the current value stored as current maximum: c1) if the instantaneous current value is greater than the stored current value: storing the instantaneous current value instead of the previously stored current value; c2) if the instantaneous current is ^¬ value smaller than the stored current value: Verwer- fen of the instantaneous current value; d) repeating steps a), b) and c) until the ignition of the discharge lamp.

Instead of the respective current values, for example, the drop across the shunt voltage may be obtained at vorlie ^¬ constricting invention readily correlated therewith clamping ^¬ voltage values measured are evaluated and stored.

Further advantageous embodiments will become apparent from the dependent claims.

Short description of the drawing (s)

An ^exemplary embodiment of a circuit ^arrangement according to the invention will now be described in more detail below with reference to the attached drawings. Show it : Figure 1 is a schematic representation of a circuit diagram of an embodiment of a circuit arrangement according to the invention.

Fig. 2 is a schematic illustration of the time course of the comparison voltage at the shunt resistor at the on ^¬ go, according to the prior art (dashed) and the procedure of the OF INVENTION ^¬ dung (solid line); and

3 shows a signal flow graph which illustrates the procedure in the method according to the invention.

Preferred embodiment of the invention

Fig. 1 shows a schematic representation of an embodiment of an inventive Schaltungsanord ^¬ tion. At its input lies the so-called intermediate circuit voltage U _zw , which usually represents a DC voltage of a few 100V. This is followed by a tensioning ^¬-DC Converters, which is herein exemplified as a buck actuator and a switch Sl, inductor Ll, diode Dl and a capacitor Cl environmentally sums. This is followed by an inverter, which in the present example is designed in a full-bridge arrangement and comprises the switches S2, S3, S4 and S5. The discharge lamp La ^¬ is coupled to the output of the inverter via a resonant circuit, said resonant circuit, the inductors L2, L3 and the capacitor C2. The circuit arrangement further comprises a control device 10, which is dropped across a voltage converter arranged in the shunt resistor R _S h voltage U _RS hr ^¬ leads. It has four outputs to, as with the Arrows marked to control the switches S2, S3, S4, S5. In the control device 10, a first memory device 12, a comparison device 14, a writing device 16, a second memory device 18 and a control device 20 are provided, which will be discussed in more detail in connection with FIG.

The current in the resonant circuit flows through the sequence of elements S2, L2, C2, L3, S5, RSh at the time the switches S2 and S5 are closed. At the time when the switches S3 and S4 are closed, the current flows through the sequence of elements S4, L3, C2, L2, S3, RSh.

Fig. 2 shows the time course of the voltage U _RSh , which is correlated with the current in the resonant _circuit . A broken line shows the course which would result if a frequency range were continuously swept over that is set in such a way that the maximum is reached, taking into account noise, tolerance-related fluctuations and due to temperature dependencies. At point Pl, a signal having the resonant frequency f _res of the resonant circuit is provided at the output of Wech ^¬ selrichters. From point Pl to the point P2, the frequency is lowered, for example, where ^¬ at the maximum lowering is achieved by a superiors percentage value, for example 10% at the point P2. At the point P2, the frequency of the signal at the output of the inverter is therefore 0.9 f _res • From the point P2 - after reaching the minimum frequency mentioned - the frequency is continuously increased, at the point P3 again the resonance frequency f _{res is} reached. A further increase finally leads to point P4, at which the resonance frequency frequency by a predetermined amount, for example 10%, steps on ^¬ was. At the point P4, therefore, the frequency is 1.1 fres • From the point P4, the frequency is again ernied ^¬ rigt, etc.

On the solid curve, which results in a circuit arrangement according to the invention, is returned to Dis ^¬ discussion of Fig. 3.

3 shows a schematic representation of a signal flow graph for the method according to the invention. Although the value of the current of the resonant circuit is measured and evaluated in the signal flow graph of FIG. 3, in the context of the present invention instead of the current values, other current values, in particular also voltage values, can be evaluated and evaluated are stored, which are correlated with the current in the resonant circuit.

First, the method according to the invention is started in step 100. In step 110, the current value I-ist (f) of the current in the resonant circuit is measured as a function of the current frequency. With reference to in FIGS. 1 and Fig. 2 illustrated embodiment ent ^¬ expresses this in determining the voltage U _RS h at the shunt resistor R _S h is determined by the control device 10. Subsequently ^¬ ßend in step 120 in the comparison means the difference formed between the data stored in the first storage device 12 maximum value I _max of the current in Reso ^¬ nanzkreis and the resultant at the instantaneous frequency of the signal at the output of the inverter value I _ls (f). In the embodiment of FIGS. 1 and 2, the maximum of the voltage U _{Rsh is} stored in the first memory device 12.

For the following measures it is decisive whether the control is moving from higher frequencies to smaller frequencies or vice versa. This is checked in step 130. If the control is being moved from higher frequencies to lower frequencies, in step 140, the difference I _D iff previously determined is compared against egg ^¬ nen in the second storage device 18 stored difference value .DELTA.l. If the comparison shows that I _D iff smaller .DELTA.l is, in step 150, the tax advantage ^¬ device 20 is caused to the frequency in order to lower a pre give ^¬ NEN frequency step .DELTA.f. However, if I _D iff is greater than Δl, then in step 160 control device 20 is caused to increase the frequency by Δf.

However, if it determined in step 130 that the Rege ^¬ lung straight runs from lower frequencies to higher frequencies, so, in turn, is checked in step 170 whether I is smaller _dlff .DELTA.l. If this is the case, the frequency is increased by Δf in step 180. If the over ^¬ test in step 170 a no, so the frequency is decreased by .DELTA.f in step 190th Of course, as would be apparent to those skilled in the art, steps 130 and 160 or 170 could be reversed in order to achieve the same result.

Subsequently, in step 200 to determine whether a new maximum value is to be stored in the first memory device 12, it is checked whether the difference I _D i _{ff is} less than zero. If so, in step 210, the at the instantaneous frequency resulting current value I _lst (f) as a new value I _max stored in the first memory device 12. I is _D iff greater than zero, there is not a new Maxi mum ^¬, whereby the current value I _ls (f) is discarded in step 220th Then, the method returns to step 110 to Mes ^¬ solution of value I _lst resulting in a different frequency (f). These steps are repeated ^¬ until the ignition of the discharge lamp. As will be apparent to those skilled in the art, steps 130-190 and 200-220 may also be performed in parallel.

Returning to FIG. 2, the continuous curve ^¬ train now shows the time course of the voltage U _RSh in a circuit _{arrangement according} to the invention. Here, the points P5, P6 and P7 indicate the reversal points when sweeping the frequency. In the present example of the technique dargestell ^¬ th dashed curve has been with reference to in Fig. 2 to the state of running that was lowered the frequency of Pl to P2. Then P5 indicates the point at which the frequency is already increased again in the procedure according to the present invention and is lowered again after passing through a local maximum of the voltage U _Rsh at the shunt resistor R _sh at point P6. From the point P7, therefore, the frequency is increased again.

Accordingly, at points P5, P6 and P7, the difference between the maximum value stored in the first memory device 12 and the current value reaches the value of the difference value stored in the second memory device 18 and thus triggers a reversal of the sweep process. As can be clearly seen under ^¬, assessments of the curve according to the present Invention the minima actually achieved from each other, since they are always the same, stored in the second memory device 18 value ΔU _RSh smaller than the previous maximum. It can also be clearly recognized that the curve according to the invention has a significantly greater voltage-time surface than the curve of the prior art.

Claims

claims

1. Circuit arrangement for igniting a discharge lamp with

- A first and a second input terminal for connecting an input voltage (U _zw ); an inverter having an input and an output, the input coupled to the first and second input terminals;

- A first and a second output terminal for connecting the discharge lamp (La); a resonant choke (L2) coupled between the output of the inverter and the first output terminal;

a resonant circuit comprising the resonant choke (L2); and - a control device (10) for controlling the frequency (f) of the signal provided at the inverter output; characterized in that the circuit arrangement further comprises a current measuring device (R _sh ) which is arranged to ^measure a current which is correlated with the current in the resonant circuit, wherein the regulating device (10) is designed to set the frequency (f) at the output of the inverter as a function of the measured current (I _actual ).

2. Circuit arrangement according to claim 1, characterized in that the circuit arrangement further comprises a voltage converter (Ll, Dl, Sl, Cl), which between is the first and coupled to the second input terminal and the input of the inverter, wherein the current measuring device as a shunt (RSH) is formed and arranged in the voltage converter, and wherein the voltage converter is ver ^¬ connected in such a way to a reference potential, that the current (through the shunt Rsh) is correlated with the current in the resonant circuit.

3. Circuit arrangement according to one of claims 1 or 2, characterized in that the control device (10) comprises:

- a first memory device (12) for storing a with a maximum (I _max) of the current in Re ^¬ sonanzkreis correlated value;

- A comparison device (14) for comparing a resulting at the instantaneous frequency of the signal at the output of the inverter, with the current in the resonant _circuit correlated value (I _lst (f)) with the in the first memory device (12) stored maximum (I _max ); and - a write device (16) which is designed, in the event that at the instantaneous frequency of the signal at the output of the inverter result ^¬ de correlated with the current in the resonant circuit value (I _ls (f)) is greater than the previously entered maximum (I _max ), this value (I _lst (f)) in the first Spei ^¬ chervorrichtung (12) enter.

4. Circuit arrangement according to claim 3, characterized in that the control device (10) further comprises: - A control device (20) for controlling the frequency of the signal at the output of the inverter;

- A second memory device (18), in which a difference value (.DELTA.l) is entered; - Wherein the comparison _device (14) is further designed, the difference (I _Dlff (f)) between the in the first memory device (12) stored maximum (I _max ) and at the momentary Fre ^¬ frequency of the signal at the output of the inverter to _{generate the resulting} value (I _lst (f)) and to compare this value with the _difference value ( _Δl ) entered in the second memory device (18),

- Wherein the control device (20) is further designed to change the frequency of the signal at the output of the inverter in one direction, ie, to decrease or increase until the difference (I _Dlff (f)) is greater or greater equal as the entered difference value (Δl), and then again in the reverse direction to change, ie to increase or decrease until the difference (I _Dlff (f)) again greater than or greater than equal to the registered difference value (Δl ).

5. Circuit arrangement according to one of the preceding claims, characterized in that the difference value (.DELTA.l) is at most 50% of the maximum (Imax), preferably between 5 and 30% of the maximum (I m _ax ).

6. Circuit arrangement according to one of the preceding claims, characterized in that the frequency at the output of the inverter in jumps of at most 1 kHz, preferably at most 50 Hz, is changed.

7. Circuit arrangement according to one of the preceding claims, characterized in that the time constant of the regulating device (10) is at most 5 ms, preferably at most 2 ms.

8. A method for lighting a discharge lamp (La) on a circuit arrangement, a first and a second input terminal for connecting an input voltage (U _zw ), an inverter having an input and an output, wherein the input to the first and the second Input terminal is coupled, a first and a second output terminal for connecting the discharge lamp (La), a resonant choke (L29, which is coupled between the output of the inverter ^¬ and the first output terminal, a resonant circuit comprising the resonant choke (L2) and a control device (10) for controlling the frequency of the signal provided at the inverter output, characterized by the following steps:

- Measuring a current (I _lst (f)), which is correlated with the current in the resonant _circuit ; and - rules (10) of the frequency (f) at the output of the inverter as a function of the measured current (I-

XSt (f)) •

9. The method according to claim 8, characterized by the following further steps: a) measuring the resulting at the current frequency instantaneous current value (I _lst (f)); b) determining a difference (I _D iff) (between a ge ^¬ stored current value I _m ax), which corresponds to a current maximum of the current value, and the momenta ^¬ NEN current value (I _ls (f)); bl) if the control is running from larger frequencies to smaller frequencies: bll) if the difference (I _Dlff ) is smaller than a stored difference value (Δl):

Decreasing the instantaneous frequency by a predefinable frequency value (Δf); bl2) if the difference (ΣDiff) is greater than or equal to a stored difference value (Δl):

Increasing the instantaneous frequency by a predefinable frequency value (Δf); b2) if the control is running from smaller frequencies to larger frequencies: b21) if the difference (I _Dlff ) is less than a stored difference value (Δl): increasing the current frequency by a predefinable frequency value (Δf); b22) if the difference (ΣDiff) is greater than or equal to a stored difference value (Δl):

Decreasing the instantaneous frequency by a predefinable frequency value (Δf); c) comparing (14) the instantaneous current value (I _actual (f)) with the current value (Imax) stored as the current maximum: _c1 ) if the instantaneous current value (I _actual (f)) is greater than the stored current value (I _max ) : SpeI ^¬ manuals of the instantaneous current value (I _ls (f)) position on ^¬ of the previously stored current value (I max / r c2) if the instantaneous current value (I _ls (f)) is smaller than the stored current value (I _m ax) : Ver ^¬ throw the current current value (I _lst (f)); d) repeating steps a), b) and c) until the zuen ^¬ extension of the discharge lamp (La).

10. A method according to any one of claims 8 or 9, characterized in that instead of the respective current values thus measured korre ^¬ profiled voltage values, evaluated and stores ge ^¬.