EP1326486A1 - Operating circuit for discharge lamps with pre-heating electrodes - Google Patents

Abstract

The circuit has an alternating current voltage generator (G) to produce a voltage at the start of search operation to move through a frequency range that includes a resonant frequency of a circuit. The circuit records the response of the resonant circuit (C14, T11) by measuring an electrical variable corresponding to the resonant frequency. A lamp (LP) is preheated at this frequency by preheating transformers.

Description

Technical field

The invention relates to an operating circuit for a Discharge lamp with preheatable electrodes.

State of the art

It is known for discharge lamps in which electrodes are preheated should be, for the preheating operation of the operating circuit Exploit resonant circuit resonance. For example, the electrodes to be preheated to a frequency generator Operating circuit be connected and on the other hand via a Capacitor and optional additional components of a preheater be connected. The preheating device thus contains an oscillating circuit, during which vibrations current flows through the electrodes. If the operating device generates an oscillation in the resonant circuit, the electrodes are accordingly preheated. The preheating mode can can be ended, for example, by heating a PTC thermistor.

In an unpublished earlier German patent application with the File number 101 02 837.7 ("Operating device for gas discharge lamps with The applicant has already switched off the filament heating ") Operating device proposed, in which the preheating via a Preheating transformer takes place and at a resonance frequency of one Vibration circuit is preheated, in which the transformer with its Primary winding is switched.

Presentation of the invention

The present invention is based on the technical problem, a Operating circuit for discharge lamps with preheatable electrodes specify which has an improved preheater.

According to the invention, the operating circuit is designed for this is to generate an alternating voltage at the start of operation, the one Resonance frequency of the resonant circuit containing frequency range drive through and the response of the resonant circuit by measuring an electrotechnical quantity so that the resonance frequency identified and the lamp preheated with this resonance frequency can.

Advantageous embodiments are in the dependent claims played.

The invention proceeds from that cited in the unpublished Patent application already contained basic idea, a resonant circuit and use its resonance for preheating. It continues from an operating circuit in which the operating frequency of the Operating circuit can be changed and adjusted. The invention suggests a frequency range after the start of operation Search resonance frequency of the resonant circuit, which is selected so that it can be safely assumed that the resonance frequency in it Find. The resonance frequency can, for example, by Determining the amplitude of a voltage value or a current value be identified. The frequency range does not have to be complete drive through, rather the drive through can be stopped, if the resonance frequency has already been found. For example one could look for increasing voltage or current values and a drop in the values suggest that the maximum was run through and define this maximum as a resonance peak.

The resonant frequency of the resonant circuit can thus be identified and used for the subsequent preheating process. In this A particularly efficient preheating can be ensured in this way which, on the other hand, is influenced by component tolerances or temperature fluctuations, which can change inductances, for example, excluded are.

Another advantageous possibility consists of the amount of detected amplitude in the resonance peak conclusions on the type of a used discharge lamp to pull. Because if that Operating circuit is designed so that not only the operating frequency, but other operating parameters are adjustable, so it can be used for different lamp types can be used. Is particularly comfortable this procedure if the operating circuit turns on automatically sets the lamp type used. The lamp type can of course by an additional coding of the lamp can be detected. Simpler and However, it is more convenient to have the existing technical properties of the Use lamp for detection. In particular, the ohmic. Resistance of the lamp electrodes in different lamp types differently. As a result, there are various damping effects Resonance that is captured and used to draw conclusions about the lamp type can be. The operating circuit can then be the appropriate one Set operating parameters.

In principle, the detection of the lamp type can also be useful if basically only one lamp type is provided. It can then be prevented be that a mechanically fitting, but electrotechnical unsuitable lamp type is used and operated. In this case the operating circuit could detect the wrong type of lamp Refuse to switch on.

The use of a preheating transformer is preferred Preheater, as already quoted in the unpublished Pre-registration is presented. The related disclosure content, especially with regard to the various connection options and design variants for the resonant circuit is hereby expressly stated in Referred. In any case, two secondary windings of the Preheating transformer each with one of the electrodes Discharge lamp can be connected in order to be able to preheat it. Further the preheating transformer must be connected to the resonant circuit, it is preferred that the resonant circuit is on the primary side, that is Primary winding is connected to the resonant circuit. This allows the corresponding vibrations in the resonant circuit by a Start the frequency generator of the operating circuit without on the Need to translate the voltage level of the secondary side.

An inexpensive way to measure the response of the Resonant circuit to identify the resonance frequency and possibly also to determine the strength of the resonance with regard on the lamp type recognition is the measurement of the maximum amplitude of the Voltage on the primary winding of the preheating transformer. This will this voltage is preferably rectified, as in the exemplary embodiment shown.

The frequency generator of the operating circuit is preferably in the form of a realized digital control that generates digital frequencies. It can Passing through the frequency range according to the invention take place step by step. In this respect, it is not the actual resonance frequency, but the corresponding incremental next frequency recorded. Basically it plays no matter for the technical function of the invention, whether the Resonance frequency is exactly hit. For the purpose of preheating only the excessive resonance can be used. Because of the Attenuation of the resonance due to the ohmic resistances of the electrodes the response is generally not very narrow anyway, so the Resonance frequency should only be roughly hit.

A favorable order of magnitude for the resonance frequency is the double operating frequency of the operating circuit in continuous operation of the Discharge lamp. Typical orders of magnitude can be, for example 80 - 100 kHz for the resonance frequency and about 40 - 50 kHz for the Continuous operating frequency.

Description of the drawings

Figur 1

zeigt ein schematisiertes Schaltdiagramm einer erfindungsgemäßen Betriebsschaltung.

Figur 2

zeigt einen beispielhaften Ablauf der Funktionsweise der Betriebsschaltung.

Figur 3

zeigt zwei Messkurven zur Illustration des in Figur 2 dargestellten Ablaufs.

An exemplary embodiment of the invention is explained below in order to illustrate it in more detail. Individual features disclosed here can also be essential to the invention in other combinations. In addition, it should be pointed out that the invention can also have the character of a method and that the above and the following disclosure should also be interpreted with regard to method features.

Figure 1

shows a schematic circuit diagram of an operating circuit according to the invention.

Figure 2

shows an exemplary sequence of the operation of the operating circuit.

Figure 3

shows two measurement curves to illustrate the process shown in Figure 2.

In Figure 1 is an electronic ballast as the invention Operating circuit shown. With LP is a low pressure discharge lamp referred to, the preheatable spiral electrodes are shown. G denotes an AC voltage generator, which is a digital controller with digital frequency definition and facilities for the in Figure 2 and the associated description explains the process. On one Output A becomes a high frequency AC voltage with respect to a Reference ground potential M specified. It can be, for example Half-bridge oscillator with two controlled by a digital control Act switching transistors.

In a conventional manner, there is between the output A and ground Lamp LP switched, wherein between the supply voltage side (in Figure 1 upper) electrode and the output A from a series circuit a coupling capacitor C11 for blocking DC components and a lamp choke L11. The lamp choke is used to adjust the Discharge lamp to the generator G. A between the supply-side electrode, the discharge lamp LP and Ground ignition capacitor C12 is used to generate a Ignition voltage and can also be used for adaptation. The ignition capacitor is parallel to the discharge lamp LP, namely strictly speaking, to one connection of each electrode.

There is also a so-called trapezoidal capacitor C13 between the output A. and mass is provided to relieve the switching of the mentioned Switching transistors are used. So far, that is described in FIG. 1 Operating circuit shown constructed conventionally and the specialist familiar from other publications, so details here are not must be explained in more detail.

Between the supply voltage side of the trapezoidal capacitor C13 and ground is a parallel resonance capacitor C14 and parallel to it a primary winding T11 of a preheating transformer. The Parallel resonance capacitor C14 and the primary winding T11 form one Resonant circuit with a resonance frequency determined by these quantities. When calculating the resonance frequency, that on the primary winding is T11 effective primary inductance. The heating transformer can have a so-called loose coupling in order for the Primary inductance to achieve sufficiently high values. The resonance frequency is designed to be about twice the continuous operating frequency equivalent. The choice of double continuous operating frequency has the advantage that with the continuous operating frequency no vibration excitation of the Resonant circuit. Since almost square wave voltages are used and these have essentially odd harmonics is one Frequency choice close to twice the operating frequency cheap. A range of +/- 20% of twice the operating frequency is preferred.

The preheating transformer has two secondary windings T12 and T13, said loose coupling between the secondary windings and the primary winding T11 shown in Figure 1 with the dashed lines is. The secondary windings T12 and T13 are each with the electrodes the discharge lamp LP connected, so in the secondary windings induced currents flow through the electrodes. Therefore the Resonant circuit from the parallel resonance capacitor C14 and Primary winding T11 together with the secondary windings T12 and T13 as a preheater.

By doubling compared to the continuous operating frequency The resonant frequency is the resonant circuit in continuous operation in the Low resistance compared to the trapezoidal capacitor C13 and therefore does not interfere the functions of the operating circuit in continuous operation. In continuous operation so there are only very small voltages on the primary winding T11, so the resulting additional heating currents in the spiral electrodes are negligible.

In preheating mode, however, the frequency generator G is supposed to be the resonant circuit with a frequency in the immediate vicinity of its resonance frequency energize so that large currents flow through the primary winding T11 and corresponding preheating currents in the secondary windings T12 and T13 induced.

Regarding the functioning and the circuit structure of the Operating circuit from Figure 1 is otherwise in addition to the already cited unpublished advance notification.

The invention now provides that the digital control of the Frequency generator G a certain frequency range at the start of operation passes through the resonance frequency of the resonant circuit C14, T11, around the To search for resonance frequency to a certain extent. This is exemplified in FIG shown. The resonance frequency is around 90 kHz supposed. At the beginning, the frequency of the half-bridge oscillator in the Frequency generator set to 95 kHz by the digital control.

The digital control measures the voltage at the primary winding T11 or on the parallel resonance capacitor C14 (UC14) and searches during the in Figure 2 depicted the maximum value of this voltage to the Identify resonance frequency. This maximum value is shown in FIG Umax abbreviated. It is stored in a memory of the digital control and is initially at 0.

After a very brief operation at a half-bridge frequency of 95 kHz, the voltage UC14 is measured and judged whether it is greater than Umax is. Since Umax is still at 0, this question is answered in the affirmative. So that can according to the arrow pointing to the right, the measured value for UC14 can be stored as a new value for Umax. Accordingly, the predefined half-bridge frequency (fHB) of 95 kHz as the resonance frequency fres stored in another memory.

Thereupon, the half-bridge frequency becomes around 1 kHz, for example reduced, is now 94 kHz. The next question is whether the Half-bridge frequency is greater than 85 kHz, is therefore affirmed, so that the process of measuring the voltage UC14 runs back.

It can be seen that this loop is carried out until the Half-bridge frequency has reached 85 kHz. Since the Umax storing memory was only overwritten if the new one If the measured value was greater than the previous measured value, the largest measured value lies in the umax memory. The same applies to the associated Resonance frequency, which is namely the half-bridge frequency at which this Umax value was measured.

After running at 85 kHz, the question in the middle of Figure 2 no, so that Umax can now be evaluated. In which present example, maximum voltage values below 35 V, between 35 V and 40 V and over 40 V different and each a 24 W lamp, assigned to an 18 W lamp or a 13 W lamp. This assignment is possible because the lamps have lower power filament electrodes have thinner wires and therefore because of the higher ohmic Resistors cause the least attenuation of the resonance. As a result, the primary winding voltages UC14 are at low-watt lamps.

In the following, the digital control can be used for preheating determined correct resonance frequency of the resonant circuit C14, T11 perform, the resonance frequency regardless of fluctuations due to temperature changes or component fluctuations between different individual operating circuits apply. Incidentally, can the digital control for preheating, such as the preheating time, and also for the subsequent continuous operation that for the corresponding one Set the appropriate parameter for the lamp type.

FIG. 3 shows an exemplary course of a representation of the Primary winding voltage UC14 on an oscillograph. At the bottom The actual voltage UC14 is plotted with the range changing frequency oscillates while in the upper range the rectified and smoothed voltage is shown, which is actually the Measurement by the digital controller is based. From the left edge of the Figure up to the dashed vertical line is the one based on Figure 2 explained frequency sweep from 95 kHz to 85 kHz performed. It's closed recognize that the voltage UC14 in between a maximum has accepted. At the end of the run, the digital control closes the corresponding frequency value so that the preheating operation is on the right from the dashed vertical line with the resonance frequency can be carried out.

Claims (8)

Operating circuit for a discharge lamp (LP) with preheatable electrodes,
which operating circuit has a device (C14, T11, T12, T13, G) for preheating the electrodes, which has a resonant circuit (C14, T11) which vibrates during preheating,
characterized in that the operating circuit is designed to generate an alternating voltage at the start of operation, passing through a frequency range containing the resonance frequency of the resonant circuit (C14, T11) and thereby responding to the resonant circuit (C14, T11) by measuring an electrotechnical variable (UC14 ) to be detected so that the resonance frequency can be identified and the lamp (LP) can be preheated with this resonance frequency. Operating circuit according to claim 1, wherein a resonance amplitude (Umax) of the resonant circuit (C14, T11) is determined by the type an inserted discharge lamp (LP). Operating circuit according to claim 2, for the operation of a A plurality of lamp types is designed and is also designed to assigned operation with the recognized lamp type Operating parameters. Operating circuit according to one of the preceding claims, in which the preheater (C14, T11, T12, T13, G) one Preheater transformer (T11, T12, T13) contains two Has secondary windings (T12, T13), each with a Electrode of the discharge lamp (LP) are connected. Operating circuit according to Claim 4, in which the primary winding (T11) of the preheating transformer (T11, T12, T13) in the resonant circuit of the Preheater (C14, T11, T12, T13, G) is switched. Operating circuit according to claim 4 or 5, wherein the response of the resonant circuit (C14, T11) over the maximum amplitude (Umax) the voltage (UC14) on the primary winding (T11) of the Preheating transformers (T11, T12, T13) can be detected. Operating circuit according to one of the preceding claims, the one digital control (G) and in which the passage of the Frequency range is gradual. Operating circuit according to one of the preceding claims, in which the resonance frequency is about twice as large as one Continuous operating frequency.

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