EP2462784B1 - Method of starting a discharge lamp and circuit for operation of such a lamp - Google Patents

Description

Technical area

The invention relates to a method for starting up a discharge lamp according to the preamble of claim 1. It also relates to a circuit arrangement for operating a discharge lamp according to the preamble of claim 3.

State of the art

The invention relates to a circuit arrangement for operating a discharge lamp according to the preamble of patent claim 3, as used in the applicant's own house, and by which the method according to the preamble of claim 1 is implemented:

The circuit arrangement has a resonant circuit, with a capacitive element connected in parallel with the discharge lamp and an inductive element in series in front of the lamp and the capacitive element and behind a circuit point between two switches. The switches, typically designed as MOSFETs, are used to apply power to the resonant circuit. By suitable means causes the two switches close and open again in alternating sequence, wherein the switching frequency is predetermined. Typically, the means for effecting comprise an application specific integrated circuit (ASIC), from which potential outputs are connected to the control inputs of MOSFETs.

The resonant circuit is there to provide for the provision of an ignition voltage across the electrodes of the lamp, ie parallel to the capacitive element of the resonant circuit. For this purpose, it is supplied with a square-wave voltage via a half-bridge circuit in order to be set in oscillation in or near resonance. In order to set the ignition voltage in a defined manner, regulation takes place to a predetermined current intensity of the alternating current under variance of the frequency of the square-wave voltage. For this purpose, means are provided in the circuit arrangement for measuring the current intensity of a current flowing through one of the switches, and suitable means for determining the switching frequency define these during ignition as a function of the measured current intensity. From patent

DE 198 05 733 A1 a similar circuit arrangement is known.

Prior to the ignition of the discharge lamp, the electrodes, which are typically helical, are to be preheated. Preheating is accomplished by providing ohmic heat loss by sending a current through the electrodes. This is done in the circuit also by driving the switch and thereby acting on the resonant circuit with alternating current. However, the frequency is different than when the lamp is lit.

In previously used in the applicant's home circuit arrangements, the frequency of the alternating current during preheating was predetermined, and indeed to values above the resonant frequency of the resonant circuit.

The electrical parameters of electronic components may vary from item to item, even though a nominal value is desired per se. If, as before, the frequency during preheating is determined in advance, then The set preheating depends sensitive on the parameters of the electronic components, in particular of the capacitive element and the inductive element of the resonant circuit. It is then possible that a circuit arrangement is rejected as not sufficiently functioning in the production, even if all components work on their own and only parameter deviations are given in the components.

Control of the preheat current is known from some circuit arrangements.

Presentation of the invention

The object of the present invention is to provide a method according to the preamble of claim 1, by which a discharge lamp is reliably put into operation, even if deviations in their electrical parameters are given in the electronic components used in this case. It is another object of the present invention to provide a circuit arrangement for operating a discharge lamp according to the preamble of patent claim 3, which functions as reliable as the Schaltungsan-order from the applicant's house in its previous embodiment, but at the same time a reliable Preheating possible.

This object is achieved in a method having the features of the preamble of claim 1 by the features of the characterizing part of patent claim 1, and in a circuit arrangement having the features according to the preamble of claim 3 by the features of the characterizing part of claim 3.

Particularly advantageous embodiments can be found in the dependent claims.

According to the invention, the pre-heating is controlled to a predetermined current, in principle the same way as in the ignition, namely by the means for controlling the frequency are already activated before the ignition. However, since it is desired to control to a different current level, the measuring device is caused to obtain measured values for the current intensity and to transmit the means for controlling the frequency, which correspond to a current intensity that deviates from the current intensity measured during the ignition in a predetermined manner. Thus, in a first situation, the regulation is carried out on the basis of measured values for a first current strength and in a second situation the regulation on measured values for a second current intensity, in each case for the same actual current intensity. Following on from the methods of the prior art, the first situation is preferably that of the ignition, in which the actual current intensity is predetermined by the measured values. During preheating, the control can then take place on the basis of measured values which deviate from the actual current intensity in a predetermined manner. Typically, the peak value of the current is measured. When this reaches a predetermined limit, the switching frequency of the half-bridge is increased.

Thus, the measurement of the current intensity is deliberately falsified, especially during preheating. In the simplest case, simply an offset is impressed. Then the effect Control circuit that sets a different current to this offset current than it would otherwise be the case or when igniting the case.

Such an offset is approximately provided by applying a potential to the preheat at a node which is not applied during ignition.

It is possible in this way to use the already known circuit arrangement, which has the control circuit which is used when the lamp is ignited, and the same control circuit can then also be used to control the preheating current. As a result, a synergy effect is achieved, it must be provided for the regulation of Vorheizstroms not specifically a separate control loop. A control ASIC on the market which has no property for controlling the preheating current can regulate the preheating current with the circuit according to the invention.

In the circuit arrangement according to the preamble of claim 3 control means are provided according to the invention for influencing the measured values obtained by the means for measuring, so that when passing through a commissioning program at an appropriate time such influencing of the measured values can take place, namely in particular during preheating.

Preferably, the control means comprises a source for providing a fixed potential (typically defined to ground) at a circuit point of the circuitry. This can be z. B. an output for driving a transformer preheating with mosfet switch be. Alternatively, another output signal can be used which has a different potential during preheating than in the other operating states. This is z. For example, the output RTPH on the Infineon control Asic ICV1FL02G. By manipulating voltages dropping across resistors, and thus across these flowing currents, the measured current is also manipulated, with otherwise the same current flowing through one of the switches. Thus, a particular current may flow through the one of the switches, and a first value for the current may be measured when the fixed potential is not provided, and when the fixed current potential is provided, a second value for the current may be measured. This is precisely the goal to be able to use that electronics, which adjusts to a predetermined current. Then, by manipulating the current sense values, the same loop can be used in both preheat and ignite.

In a simple way, the means for measuring the current intensity comprise a voltage divider with two resistance elements. It is then sufficient to couple a circuit point between the two resistance elements via a further resistance element with the source in order to set the falling over the two resistive elements voltages in a different relationship. The further resistance element preferably has a resistance which is at least 5 times and preferably at least 10 times as great as the maximum resistance of the two resistance elements. The reason for this is that not excessively large additional currents should be generated, but only the potential to be changed should. The greater the resistance of the further resistance element, the more the effect of a simple offset in the measurement of the current intensity is achieved.

In the preferred embodiment, the circuitry, as is well known in the art, includes an application specific circuit having two potential outputs for driving the switches and a potential input associated with the means for measuring and, for example, the node between the two resistive elements is coupled. In the context of the invention, a third potential output is provided or used, which serves to provide the source.

Since some application-specific circuits are not necessarily the ideal voltage source, in a preferred embodiment, the third potential output is coupled to ground via a zener diode, to which a capacitive element is preferably additionally connected in parallel. It then flows from the potential output current via the zener diode, and the voltage dropping at this voltage is then regarded as stable, so that a stable voltage source is provided, that is, the potential at the circuit point of the circuit arrangement is particularly well defined.

Short description of the drawing (s)

Fig. 1

den Schaltplan einer Schaltungsanordnung für eine Entladungslampe gemäß dem Stand der Technik,

Fig. 2

einen Schaltplan für eine Entladungslampe, wie er gemäß einer ersten Ausführungsform der Erfindung realisiert ist,

Fig. 3

einen Schaltplan für eine Entladungslampe, wie er gemäß einer zweiten Ausführungsform der Erfindung realisiert ist, und

Fig. 4

zwei Graphen zur Veranschaulichung der Vorteile der Erfindung gegenüber dem Stand der Technik.

In the following, the invention will be explained in more detail with reference to two embodiments. It shows:

Fig. 1

the circuit diagram of a circuit arrangement for a discharge lamp according to the prior art,

Fig. 2

a circuit diagram for a discharge lamp, as realized according to a first embodiment of the invention,

Fig. 3

a circuit diagram for a discharge lamp, as realized according to a second embodiment of the invention, and

Fig. 4

two graphs illustrating the advantages of the invention over the prior art.

Preferred embodiment of the invention

To a discharge lamp LP, for example, a low-pressure discharge lamp, a capacitive element C _{1 is} connected in parallel. The two electrodes El ₁ and El _{2 of} the lamp LP are coupled to the two sides of a capacitor C ₁ . In series with the lamp LP and thus also of the capacitive element C ₁ , an inductive element L is connected. The electrode El ₂ is coupled to a potential V via a capacitive element C ₂ , via a capacitive element C ₃ to ground. Two switches Q ₁ and Q ₂ , which are designed as MOSFETs, can couple the series connection of inductive element and discharge lamp or capacitive element C ₁ to the potential V (switch Q ₁ ) or to ground (switch Q ₂ ). The control inputs of the switches are coupled via resistor elements R ₁ or R ₂ to potential outputs A1, A2 of an application-specific circuit 100. Means provided in the circuit precisely control the switches Q ₁ and Q ₂ alternately, so that alternately charging and discharging the capacitor C ₁ from the potential V via the switch Q ₁ or to the ground via the Switch Q ₂ takes place. Since the elements L and C _{1 form} a resonant circuit, the current intensity of the current flowing through the electrodes El ₁ and El _{2 of} the lamp LP can be sensitively adjusted. This is done by varying the frequency by suitable means in the integrated circuit 100.

The resonant circuit with the elements L and C ₁ is used in particular during the ignition of the discharge lamp LP. The resonant circuit is brought close or in resonance, so that extremely high voltages between the electrodes El ₁ and El _{2 are} applied, so that it comes to the ignition of the discharge lamp.

In this phase of ignition, it is important that predetermined voltages drop. For this purpose, the current is regulated. The switch Q ₂ connects the inductive element L via a resistor element R ₃ to ground. Parallel to the resistance element R ₃ , a voltage divider with the resistance elements R ₄ and R _{5 is} provided, and the node between these two resistance elements R ₄ and R ₅ is connected to a potential input E1 of the application-specific circuit. The potential input allows the measurement of the voltage drop across the resistor R ₅ and thus the current of the current flowing through the switch Q ₂ current. Depending on the voltage thus measured, the frequency of the opening and closing of the switches Q ₁ and Q ₂ is then determined in the application-specific circuit 100. The value measured at the potential input for the potential or the voltage dropping to ground therefore determines the output potential at the potential outputs A1 and A2 and their frequency.

Before ignition, the electrodes El ₁ and El _{2 must be} preheated. In the prior art, the control that is used when the discharge lamp LP is ignited is not yet used. Instead, in the application-specific circuit 100, a specific frequency for the current intensity is provided, with which the outputs A1 and A2 are applied during preheating. It turns then a certain alternating current, which is used as a preheating current.

The disadvantage here is that scatters and fluctuations in the parameters of the capacitive element C ₁ and the inductive element L are not taken into account. If, for example, the actual capacity C ₁ deviates greatly from the setpoint value, the preheating current is severely distorted: Fig. 4 shows on the basis of the curve 10 that, for example, when varying the capacitive element C ₁ between 4 and 5.5 nF, the preheating can vary between about 600 and 425 mA. This variation is too high for practical applications.

In the invention, a further potential output A3 is provided, which is coupled via a resistance element R ₆ to the circuit point between the resistance elements R ₄ and R ₅ , ultimately with the potential input E1. If the resistance element R _{3 has} a resistance of 1 Ω, the resistance elements R ₄ and R ₅ each have resistances of 1 kΩ, so R _{6 is} to be selected, for example, with a resistance of 10 kΩ. If one now applies a potential of 12 V to ground at the potential output A3, when a voltage of 2 V typically drops across the resistance elements R ₄ and R ₅ , then an offset results at the potential at the node between the resistance elements R ₄ and R ₅ . The control threshold for the current is reduced by this offset. The application-specific circuit 100 'is equal to the application-specific circuit 100, the potential output A3 is additionally used. If the potential of 12 V is applied during preheating at the potential output A3, but the potentials detected above the potential input E1 are still measured inside the application-specific circuit 100 'and the regulation takes place as a function of these measured values, the offset in the measured values control to a different current than would be the case if the potential at the potential output A3 is not applied.

By suitable choice of the potential at the potential output A3 and the resistor element R ₆ suitable for the resistor elements R ₄ and R ₅ , the preheating current can thus be in a defined ratio to the ignition current. During preheating, the potential is now applied to the potential output A3, then it is regulated to a specific preheating current. During ignition, no potential is applied so that the circuit point between the resistance elements R ₄ and R ₅ remains unaffected. Then, a control of the ignition current in a conventional manner.

At the curve 12 in Fig. 4 It can be seen that by controlling the preheating current, even with larger fluctuations in the value of the capacitance of the capacitive element C ₁ almost always the same preheating current flows. This is exactly the desired effect. The components of the control loop typically have a lower tolerance than the components L and C ₁ .

Deviating from the embodiment according to Fig. 2 can according to Fig. 3 be provided that an application-specific circuit 100 'is used, which is not necessarily suitable as a voltage source. Then, the potential output A3 via a resistor element R ₇ and a parallel circuit of a Zener diode and a capacitive element C ₄ are coupled to ground, simultaneously via the resistor element R ₈ with the node between the resistive elements R ₄ and R ₅ . When a potential is applied to the potential output A3, then a current flows through the Zener diode Z, and the voltage dropping across it is sufficiently stable to provide a type of voltage source, ie a fixed potential.

The invention uses in the embodiments according to Fig. 2 and Fig. 3 the intelligence of the application-specific circuit, as known from the prior art. The intelligence is used in the prior art to control to a certain current at the ignition of the lamp LP. By the extension of the application-specific circuit 100 to the application-specific circuit 100 'and the interconnection according to Fig. 2 or Fig. 3 The same intelligence can also be used to regulate to a certain amount of current during preheating.

Claims (4)

1. Circuit arrangement for operating a discharge lamp (LP) comprising a capacitive element (C₁), which is connected in parallel with the discharge lamp, and an inductive element (L) in series upstream of the discharge lamp (LP) and the capacitive element (C₁), with the result that a resonant circuit is formed, and comprising two switches (Q₁, Q₂) for applying current to the resonant circuit, comprising means (100') for effecting the closing of the two switches in mutually alternating sequence with a switching frequency, comprising means (R₃, R₄, R₅; 100') for measuring the current intensity of a current flowing via one of the switches (Q₂) and comprising means (100') for fixing the switching frequency depending on the measured current intensity, characterized in that the circuit arrangement has control means (A3) for influencing the measured values obtained by the measuring means, wherein these control means comprise a source (A3) for providing a fixed potential to a circuit point in the circuit arrangement, wherein the circuit arrangement comprises an application-specific circuit, which has two potential outputs (A1, A2) for the actuation of the switches, one potential input (E1) of the measuring means (100') and a third potential output (A3) for providing the source (A3).
2. Circuit arrangement according to Claim 1, in which the measuring means have a voltage divider comprising two resistor elements (R₄, R₅), and wherein a circuit point between the two resistor elements (R₄, R₅) is coupled to the source (A3) via a further resistor element (R₆; R₇, R₈).
3. Circuit arrangement according to Claim 2, in which the further resistor element (R₆) has a resistance which is at least five times as great as the greatest resistance of the two resistor elements (R₄, R₅).
4. Circuit arrangement according to Claim 1, in which the third potential output (A3) is coupled to a ground via a resistor (R₇), via a Zener diode (Z) and preferably additionally a capacitive element (C₄), which is connected in parallel with the Zener diode (Z).

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