Electronic mains connection device for a gas-discharge lamp

Description

[0001] The present invention relates to an electronic mains connection device for a gas-discharge lamp, acting as a stabilizing current limiting element and comprising an inverter circuit which from rectified mains current or some other direct current converts the service current for a lamp to such a high frequency that the impedance of a discharge lamp is like normal resistance.

[0002] Thus, the invention relates to an inverter circuit embodied by means of semi-conductors and applied in a mains connection device of gas-discharge lamps for feeding current to the lamp.

[0003] In this context, the term gas-discharge lamps refers to lamps generally used for lighting and whose internal impedance in normal alternating current service of 50 or 60 Hz is characteristically negative resistance and which thus require a gas-discharge stabilizing current limiting element. Such lamps comprise fluorescence lamps, low-pressure and high-pressure sodium lamps, mercury vapour lamps and halogen lamps.

[0004] Prior known are a plurality of various electronic circuit solutions effected by means of semi-conductors and passive components suitable as the connection means for a gas-discharge lamp. These solutions are based on converting direct current one way or another to alternating current having substantially 50 Hz higher frequency. At this higher frequency a lamp is fed with the electric energy required by its gas-discharge. The advantages gained include improved light efficiency due to increased service frequency, reduction of the mechanical size of necessary electromagnetic components and thereby reduction of the connection device's own power loss as well as reduction of the weight of a connection device. An obvious advantage is also that it is generally easy to combine the control of a lamp's illumination level with an electronically effected connection device solution. In most circuit solutions for an electronic connection device, it is easy to develop sufficient voltage for the ignition of a discharge lamp without a separate igniter. Furthermore, an electronic connection device does not produce sound disturbances providing that service frequency is selected from above the hearing range. It is possible to eliminate a disturbing flicker from the light emitted by the lamp. An electronic connection device can also be effected, so that the curve of a current taken up by the apparatus from the alternating mains is nearly sine-shaped and its power factor is cos cp=1, whereby separate components for the compensation of the mains current are not required.

[0005] The prior art embodiments of an electronic connection device generally include some lamp current limiting impedance; a choke, a capacitor, a resistor or a combination thereof connected in series with a lamp and a source of supply voltage (DE-A-2 550 550).

[0006] Physically known is that the impedance of a discharge lamp turns from negative resistance to what is like normal resistance with the lamp operated at an alternating voltage whose frequency is within the range of 1 kHz ... 150 kHz. Partially based on this phenomenon, it is known to employ a so-called blocking-oscillator circuit in one form or another (e.g. US-A-3 629 648, 3906302 and 4168453).

[0007] In such a circuit, a lamp is directly coupled in series with a switching element (e.g a transistor) to a DC supply voltage. An inductance is parallel- coupled with the lamp. When the switching element is closed currents flow through the lamp and the inductance, these currents having the same direction. When the switching element is opened and inverted voltage is developed across the lamp by the magnetic energy in the inductance, this energy discharging through the lamp.

[0008] It is noted that US―A―3999100 gives an example of an inverter circuit for a metal halide lamp which does not include a limiting impedance. The switching frequency is however the mains frequency and current limiting is achieved by a feed-back circuit which senses the lamp current and regulates the voltage across the inverter switches accordingly.

[0009] The present invention is also based on a circuit solution capable of operating discharge lamps at the above-mentioned relatively high frequencies on which a discharge lamp behaves as normal resistance. However, a circuit solution according to the invention differs from the prior art solutions in that it does not require any inductive or capacitive member for the stabilization of a lamp's gas-discharge.

[0010] It has been found experimentally that a discharge lamp can be operated by connecting it by means of inverter switches directly to a source of supply voltage by reversing the polarity of a lamp on each half-cycle. The switching frequency must then be so high that a discharge lamp behaves as a resistance.

[0011] However, the above-described mode of operation is not stable but there is a tendency in the lamp towards "a breakaway phenomenon" which is substantially slower than the length of a cycle of service frequency and, as a consequence of which, the current tends to increase with the voltage remaining constant. To overcome this phenomenon according to the invention, such a current breakaway phenomenon is prevented by measuring the rate of a current running through the lamp and by employing a feed-back control circuit for maintaining this current rate at a desired value. In the feed-back circuit it is possible to employ a measuring device with a filtering time constant, which e.g. at a service frequency of 40 kHz can be circa 0,2 ms.

[0012] The characterizing features of the present invention are set forth in the accompanying claims.

[0013] The following advantages are gained by the solution of the invention:

1. No need for winding components or capacitors dimensioned for the main current.

2. No need for capacitors whose operating temperature has a fixed range, the connection device being applicable for use at a higher operating temperature as disposed e.g. directly in connection with a lamp.

3. The connection device is low in costs since the above-mentioned expensive components are left out.

4. The above components are also the most bulky in the prior art connection devices and thus the present connection device can be made more compact without said components and be used in smaller spaces.

5. The main circuit of the connection device can be entirely effected by means of semi-conductors.

[0014] In the following, some embodiments of the invention are described in more detail with reference made to the accompanying drawings, in which

Fig. 1 illustrates the principle diagram of a mains connection device of the invention.

Fig. 2 shows another embodiment of the invention as a principle diagram.

Fig. 3 and 4 show subsequent modifications of the invention the same way as Fig. 1.

Fig. 5 shows a circuit diagram for a mains connection device according to one embodiment of the invention with only those components shown which are most essential for the operation of the device.

[0015] Referring to Fig. 1, a gas-discharge lamp 1 is connected to a source of DC voltage by way of four electronic switches 3-6 in a manner that these switches make up an inverter circuit by means of which the polarity of supply voltage at the terminals of lamp 1 is reversed at a high frequency which is within the range of circa 1 kHz ... 150 kHz. This reversal of polarity is effected in a manner that, with switches 3 and 4 closed, switches 5 and 6 are open and when the latter switches are closed, the former switches are opened. In addition, between closing and opening of the switches there can be an interval of adjustable length when all switches are open. This can be used for the regulation of the lamp's illumination level. As pointed out above, the circuit solution of a connection device of the invention is not provided with any current limiting impedance element but, instead, the current is limited by means of the lamp's 1 own resistance-like impedance at said high inverting frequency. However, this would not be possible without an additional arrangement of the invention since the current of lamp 1 would tend to break away on an interval substantially longer than the inverting cycle. In order to eliminate this breakaway phenomenon, the invention provides a feed-back control, wherein a current transformer 7 or some other current measuring means, such as a resistor, is used to sense the current of lamp 1 and, on the basis of this current rate, a control unit 8 controls the open times and/or operating frequency of the inverter circuit switches 3-6 in a manner that the current of lamp 1 remains constant.

[0016] The circuit illustrated in Fig. 2 is otherwise similar to that of Fig. 1 except that a lamp 1 is connected to an inverter circuit and to a source of DC voltage by means of an auto-transformer 9 which increases the supply voltage of lamp 1 with respect to the voltage of the voltage supply. This transformer 9 can be further used for glowing the cathodes of lamp 1 to improve the ignitability of the lamp. In addition, the transformer 9 can serve to create an ignition voltage peak sufficient for the ignition of lamp 1.

[0017] The embodiment of Fig. 3 differs from that of Fig. 1 in that switches 6 and 4 are replaced by capacitors 10 in order to simplify the circuit. This is a suitable approach in the applications in which the temperature limitation set by the capacitors is of no significance.

[0018] In the embodiment of Fig. 4, switches 3 and 6 of the circuit solution shown in Fig. 1 are replaced by an auto-transformer 11, one of the terminals of the voltage supply being connected to its central tap. The magnetic inductance of this transformer 11 can be conventionally employed for creating an ignition voltage peak for lamp 1. A resistor 16 is used for measuring a current passing through the lamp in the other direction which measuring method, as for the operation of the device,. replaces the measuring effected in other embodiments by means of a current transformer.

[0019] Fig. 5 illustrates a further developed embodiment corresponding to Fig. 3, comprising parallel to a lamp 1 an ignition voltage peak creating inductance 13 and parallel to that an overvoltage protector 14. A current transformer 7 senses a current passing through lamp 1, said current rate being passed through a rectifying circuit 15 to a control unit 8. On the basis of this current rate, a control unit 8 issues control pulses for the control electrodes of transistors serving as switches 3 and 5, the duration and/or operating frequency of said control pulses changing as necessary for maintaining the current passing through lamp 1 constant. In order to set this current to be maintained constant at various values for the regulation of illumination emitted by lamp 1, said contol unit 8 is provided with a regulator 12 capable of having effect on the opening times of switch transistors 3 and 5 or on their inverting frequency.

Claims

1. Electronic mains connection device for a gas-discharge lamp (1), said device acting as a stabilizing current limiting element and comprising an inverter circuit (3-6) which from rectified mains voltage or some other DC voltage supply converts the service current for a lamp to such a high frequency that the impedance of the discharge lamp (1) is like normal resistance, characterized in that the limitation of a current is arranged to be effected by means of the lamp's own resistance-like impedance on both half- cycles, whereby the limitation of a current is effected during a period substantially longer than a cycle of inverter operation by means of a lamp current feedback control circuit (7, 8) which controls the opening times and/or operating frequency of switches (3-6) of said inverter circuit.

2. A mains connection device as set forth in claim 1, characterized in that a lamp (1) is connected to an inverter circuit by way of an auto-transformer (9) in a manner that the voltage of said lamp is higher than that of the voltage supply (Fig. 2).

3. A mains connection device as set forth in claim 1 or 2, characterized in that two of the switches of the inverter circuit between one terminal of the lamp and the terminals of the voltage supply are replaced by capacitors (10) (Figs. 3 and 5).

4. A mains connection device as set forth in claim 1, characterized in that two of the switches of the inverter circuit between one terminal of the lamp and the terminals of the voltage supply are replaced by an auto-transformer (11), one of the terminals of said voltage supply being connected to its central tap (Fig. 4).

5. A mains connection device as set forth in any of the preceding claims, characterized in that the feed-back circuit has a measuring device for the lamp current having a filtering time constant.

6. A mains connection device as set forth in claim 1, characterized in that for the ignition of said discharge lamp (1) a separate ignition element, (9; 13) is coupled parallel to the lamp.

7. A mains connection device as set forth in any of the preceding claims, wherein the switches consist of transistors, characterized in that a unit (8) for the regulation of the transistors' (3, 5) control voltage is accompanied by a device (12) for setting the current of lamp (1) for the regulation of illumination.

Revendications

1. Appareil électronique pour connecter une lampe à décharge (1) au réseau, cet appareil agissant en tant qu'élément stabilisateur limiteur de courant et comprenant un circuit inverseur (3-6) qui, à partir d'une tension du réseau redressée, ou d'une autre source de tension continue, convertit le courant pour le fonctionnement d'une lampe en lui conférant une haute fréquence telle que l'impédance de la lampe à décharge (1) soit analogue à une résistance normale, caractérisé en ce que la limitation de courant est aménagée pour être effectuée au moyen de l'impédance propre de la lampe, analogue à une résistance, sur les deux alternances, la limitation de courant étant effectuée pendant une période sensiblement plus longue qu'un cycle de fonctionnement de l'inverseur, au moyen d'un circuit (7, 8) de commande de courant de lampe, du type à rétroaction, qui commande les temps d'ouverture et/ou la fréquence de fonctionnement des interrupteurs (3-6) dudit circuit inverseur.

2. Appareil pour connexion au réseau selon la revendication 1, caractérisé en ce qu'une lampe (1) est connectée à un circuit inverseur par un autotransformateur (9), de manière que la tension de cette lampe soit supérieure à celle de la source de tension (Fig. 2).

3. Appareil pour connexion au réseau, selon la revendication 1 ou 2, caractérisé en ce que deux des interrupteurs du circuit inverseur situés entre une borne de la lampe et les bornes de la source de tension sont remplacés par des condensateurs (10) (Figs. 3 et 5).

4. Appareil pour connexion au réseau, selon la revendication 1, caractérisé en ce que deux des interrupteurs du circuit inverseur situés entre une borne de la lampe et les bornes de la source de tension sont remplacés par un autotransformateur (11) à la prise centrale duquel est connectée l'une des bornes de ladite source de tension (Fig. 4).

5. Appareil pour connexion au réseau, selon l'une quelconque des revendications précédentes, caractérisé en ce que le circuit à rétroaction comporte un dispositif de mesure du courant de lampe, ayant une constante de temps de filtrage.

6. Appareil pour connexion au réseau, selon la revendication 1, caractérisé en ce que, pour l'allumage de ladite lampe à décharge (1), un élément d'allumage séparé (9, 13) est couplé à la lampe, en parallèle.

7. Appareil pour connexion au réseau selon l'une quelconque des revendications précédentes, dans lequel les interrupteurs sont constitués par des transistors, caractérisé en ce qu'une unité (8) pour réguler la tension de commande des transistors (3, 5) est accompagnée par un dispositif (12) pour régler le courant de la lampe (1), aux fins de réglage de l'illumination.

Ansprüche

1. Elektronische Vorrichtung zum Anschließen einer Gasentladungslampe (1) an das Stromnetz, wobei die Vorrichtung als stabilisierendes Strombegrenzungselement wirkt und einen Wechselrichterkreis (3-6) aufweist, der aus einer gleichgerichteten Netzspannung oder einer anderen Gleichspannungsversorgung den Betriebsstrom für eine Lampe auf eine so hohe Frequenz umwandelt, daß die Impedanz der Entladungslampe (1) dem normalen Widerstand gleich ist, dadurch gekennzeichnet, daß die Anordnung für die Begrenzung eines Stroms so getroffen ist, daß sie mittels der der Lampe eigenen widerstandsartigen Impedanz auf beiden Halbperioden durchführbar ist, wobei die Begrenzung eines Stroms während einer Zeitspanne, die erheblich länger ist als eine Periode des Wechselrichterbetriebs, mittels eines Lampenstrom-Rückkopplungssteuerkreises (7, 8) erfolgt, der die Öffnungszeiten und/oder die Arbeitsfrequenz von Schaltern (3-6) des Wechselrichterkreises steuert.

2. Netzanschlußvorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß eine Lampe (1) mit einem Wechselrichterkreis über einen Koppeltransformator (9) in der Weise verbunden ist, daß die Spannung der Lampe höher ist als die der Spannungsversorgung (Fig. 2).

3. Netzanschlußvorrichtung nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß zwei der Schalter des Wechselrichterkreises zwischen einer Klemme der Lampe und den Klemmen der Spannungsversorgung durch Kondensatoren (10) ersetzt sind (Fig. 3 und 5).

4. Netzanschlußvorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß zwei der Schalter des Wechselrichterkreises zwischen einer Klemme der Lampe und den Klemmen der Spannungsversorgung durch einen Koppeltransformator (11) ersetzt sind, wobei eine Klemme der Spannungsversorgung an dessen Mittelanzapfung angeschlossen ist (Fig. 4).

5. Netzanschlußvorrichtung nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, daß der Rückkopplungskreis eine eine Filter-Zeit-konstante besitzende Meßvorrichtung für den Lampenstrom aufweist.

6. Netzanschlußvorrichtung nach Anspruch 1, dadurch gekennzeichnet, daß für das Zünden der Entladungslampe (1) eine getrenntes Zündelement (9; 13) zur Lampe parallelgeschaltet ist.

7. Netzanschlußvorrichtung nach einem der vorangehenden Ansprüche, bei welcher die Schalter aus Transistoren bestehen, dadurch gekennzeichnet, daß einer Einheit (8) zum Regeln der Steuerspannung der Transistoren (3, 5) eine Vorrichtung (12) zum Einstellen des Stroms der Lampe (1) für die Regelung der Beleuchtungsstärke zugeordnet ist.

Drawing