EP0178735B1 - Circuit arrangement for the ignition and operation of gas discharge lamps - Google Patents

Description

beträgt.The invention relates to a circuit arrangement for igniting and operating gas discharge lamps with a choke coil arranged between the lamp and the AC supply source and having an inductance L and an ignition device connected to the lamp, at least part of the choke coil being a capacitor with a capacitance C, at least temporarily in parallel is switched, its reactance

is.

In a circuit arrangement of this type known from DE-OS 31 45 234, the choke coil, a capacitor is only connected in parallel after the lamp has been ignited. This capacitor only serves to compensate for the power factor and to regulate the lamp current to the nominal value after the ignition phase has ended.

When operating gas discharge lamps, problems often occur during the ignition process. This ignition process consists of three stages, namely a first ionization of the discharge path, called breakdown, a subsequent low-current glow discharge between the lamp electrodes and the subsequent transition of the glow discharge into the actual high-current arc discharge. A common cause of ignition difficulties is an unstable transition from glow to arc discharge. For lamps with e.g. Amalgam filling, such as high-pressure sodium lamps filled with Na / Hg amalgam, occurs in the case of an unfavorable amalgam distribution in the discharge vessel, the discharge approach on the amalgam instead of on the electrodes. This makes the glow / arc transition difficult and the lamp remains in the glow phase, i.e. the ignition failed. Similar problems arise when relighting lamps that are still hot. Here the effect often occurs that the transition from the glow to the arc discharge is brief, i.e. during a small part of an AC half-wave, and then the change back into a glow discharge takes place.

Safe ignition of cold gas discharge lamps and easy re-ignition of lamps that are still hot can be achieved with the help of so-called superimposed igniters (DE-OS 31 08 547 and 31 08 548 and US Pat. No. 3,944,876). These known ignition circuits generate ignition pulses between 2 and 5 or 7 and 15 kV. The use of these circuits as external igniters for discharge lamps, e.g. As an incandescent lamp replacement with an E-27 base, it is not possible because the permissible voltage values prescribed for the E-27 base are exceeded. In this application, it is therefore necessary to accommodate the ignition circuits in the lamp base. However, this is made more difficult by the fact that the capacitors required are relatively large and thus make a compact lamp structure difficult. In addition, in the circuits according to the aforementioned DE-OS, even when accommodated in the lamp base under certain operating conditions, voltages can still occur between the base contacts which exceed the permissible values for the E-27 base. Furthermore, when using the known ignition circuits on high-pressure sodium lamps with increased sodium pressure to improve the color properties, it is found that it is not possible to restart the hot lamps immediately, especially at low mains voltage (198 V), but rather a certain period of time elapses when many of these lamps are used Areas of application, in particular, for example in the household sector, is not acceptable.

Furthermore, it is known from DE-PS 622 171 and US-PS 38 90 537 to apply a significantly increased starting current to the lamp to improve the starting and starting properties - in particular to avoid a glow phase that is too long. This increased current flow takes place at least during about a network half-wave, but mostly for a much longer time. In the case of a choke coil, such an increased current can take place through a parallel path to the choke, the AC impedance of which is comparable or less than that of the choke coil. If this parallel path is set up with a correspondingly large capacitor, the glow / arc transition is improved, but re-ignition problems occur at the subsequent zero crossings, which lead to the lamp being extinguished. This emerges from a lecture given by Mr. van Vliet on "Ignition of gas discharge lamps" at the "Third International Symposium on the Science and Technology of Light Sources" in Toulouse from April 18 to 21, 1983, where the circuit arrangement mentioned at the outset was shown, in which the inductor is bridged by a resistor or a large capacitor.

The invention is therefore based on the object of providing a circuit arrangement for igniting and operating gas discharge lamps with a choke coil bridged by a capacitor, in which no re-ignition problems occur in the zero-current crossing and which nevertheless enables reliable ignition of the lamp both in the cold and in the hot state .

This object is achieved in a circuit arrangement of the type mentioned in the introduction in that the capacitor in order to achieve an ignition current which is higher than the normal lamp operating current serves, is connected in series with an ohmic resistor with a value R, the time constant R. C is between 10 ps and 1 ms, and / or can be switched off after the lamp has been ignited.

Surprisingly, it has been shown that, in order to improve the starting properties, it is not necessary - as in the known prior art - to let an increased current flow through the lamp, at least during the part of the half-wave following the ignition. Rather, it is sufficient if a significantly increased current flows for only a fraction of the half-wave during the ignition process.

Even if the AC impedance of the capacitor is considerably greater than the impedance of the choke coil, a high but short charging current pulse can still flow through the capacitor and thus through the lamp during the ignition process, which is sufficient to safely ignite the lamp. In contrast, only a small current flows through the capacitor during normal operation. In this way, the lamp is also started with an increased luminous flux, and this starting phase is also shortened.

The capacitor only works when the lamp is ignited. The time constant R. C is chosen so that the pulse-like charging times of the capacitor do not become too short. Charging times that are too short would impair the ignition behavior of the lamp. Since short charging times require very high peak currents, they could also stimulate the lamp to emit infrared radiation, which could lead to malfunctions in remote control systems working with infrared radiation.

The capacitor can be switched off after the lamp has been ignited. However, if there is a certain size ohmic resistor in series with the capacitor, the capacitor may remain in the circuit after the lamp is fired. This series resistor is normally so low that only a very small current flows through the parallel circuit consisting of this resistor and the capacitor to the choke coil, so that the capacitor behaves as switched off to the outside.

So that the capacitor is discharged when the lamp is not ignited, which is advantageous for subsequent ignition, according to another advantageous embodiment according to the invention, the capacitor has a further ohmic resistor with a value R _{addition in} parallel that its discharge time constant R _add . C is between 0.05 and 20 ms. The resistance value R _add is again greater than the impedance of the choke coil.

In order to avoid possible overloading and in order to save energy, the passive component (s) lying in the parallel current path to the inductor can be switched off after the lamp has been ignited. There is preferably a switch in the parallel current path to the inductor which is opened after the lamp has been ignited. This switch can be a bimetallic switch or part of a switching relay located in the main lamp circuit. However, these switches are not particularly fast; in addition, their contacts wear out over time due to the high lamp ignition current. It is therefore more advantageous to use fast and maintenance-free semiconductor switching elements as switches, e.g. Transistors, triacs or thyristors.

• Fig. 1 eine Schaltungsanordnung zum Zünden und Betrieb einer Gasentladungslampe mit einer Drosselspule die von einem Kondensator in Reihe mit einem Widerstand überbrückt ist,
• Fig. 2 den Drosselteil einer Schaltungsanordnung zum Zünden und Betrieb von Gasentladungslampen, wobei die Drosselspule von einem Kondensator in Reihe mit einem Bimetallschalter überbrückt ist,
• Fig. 3 einen der Schaltungsanordnung nach Fig. 1 ähnlichen Drosselteil mit einem zusätzlichen Schaltrelais,
• Fig. 4 einen Drosselteil, bei dem die parallel zur Drosselspule liegenden passiven Bauelemente mit Hilfe eines Halbleiterschaltelements abschaltbar sind,
• Fig. 5 einen Drosselteil ähnlich dem nach Fig. 4, bei dem die Drosselspule in zwei Teilspulen unterteilt ist.

Some embodiments according to the invention are described in more detail with reference to the drawing. Show it:

• 1 is a circuit arrangement for igniting and operating a gas discharge lamp with a choke coil which is bridged by a capacitor in series with a resistor,
• 2 shows the choke part of a circuit arrangement for igniting and operating gas discharge lamps, the choke coil being bridged by a capacitor in series with a bimetal switch,
• 3 a throttle part similar to the circuit arrangement according to FIG. 1 with an additional switching relay,
• 4 shows a choke part in which the passive components lying parallel to the choke coil can be switched off with the aid of a semiconductor switching element,
• Fig. 5 shows a choke part similar to that of FIG. 4, in which the choke coil is divided into two sub-coils.

A and B are input terminals for connection to an AC network of e.g. Designated 220 V, 50 Hz. A gas discharge lamp 2 is connected to these input terminals via a choke coil 1. The circuit part behind the connecting terminals C and D is the actual ignition device 3 for the lamp 2, which can advantageously be integrated in the lamp base. This ignition device 3 contains a high-voltage transformer 4, the secondary winding of which is connected between the choke coil 1 and the lamp 2. A surge capacitor 5 is connected in series with a charging resistor 6 to one side of the primary winding of the high-voltage transformer 4. The other side of the primary winding is connected to a symmetrically switching four-layer diode 7 (Sidac) (cf. US Pat. No. 3,866,088), the other side of which is connected to the connection point between surge capacitor 5 and charging resistor 6. In parallel with this circuit is a high-frequency yoke capacitor 8. The described ignition device 3 works as a superposition igniter and can be accommodated in the base of the lamp 2. The ignition pulses generated by the ignition device 3 trigger the initial ionization of the gas mixture in the lamp 2 that initiates the ignition process.

The ignition pulses are generated as follows: The surge capacitor 5 is charged via the charging resistor 6. As soon as it reaches a voltage that is above the breakdown voltage of the Sidac 7, it switches to its low-resistance state, so that the surge capacitor 5 discharges through the primary winding of the high-voltage transformer 4. As a result, a high-voltage pulse is generated in the secondary winding of the transformer 4, which pulse reaches the lamp 2 via the HF return capacitor 8. After the discharge of the surge capacitor 5, the Sidac 7 becomes non-conductive again. The charging resistor 6 and the breakdown voltage of the Sidacs 7 are selected so that approximately one to five firing pulses occur in the vicinity of the maximum of the AC mains voltage. As soon as the lamp 2 is safely ignited, the voltage between the terminals C and D collapses to the lamp voltage, so that the breakdown voltage of the Sidacs 7 is no longer reached and further ignition pulses are omitted. In practice, the RF return capacitor 8 can be kept very small and often even omitted, since the path consisting of the surge capacitor 5 and the charging resistor 6 can also serve as an RF return.

Somit kann im Normalbetrieb der Lampe 2 nur ein kleiner Strom in dem mit dem Kondensator 9 gebildeten Parallelstrompfad fließen. Beim Zünden der Lampe fließt jedoch kurzzeitig ein hoher Ladestrom durch den Kondensator 9 und damit durch die Lampe 2. Dieser kurze Ladestrom reicht zum Zünden der Lampe 2 aus. Der mit dem Kondensator 9 in Reihe geschaltete Widerstand 10 dient zur Begrenzung des Ladestroms, um nachteilige Wirkungen eines zu hohen Ladestroms auf die Lampe 2 bzw. andere Schaltungsteile zu verhindern. Hierfür ist der Wert R des ohmschen Widerstandes 10 so gewählt, daß die Zeitkonstante R . C zwischen 10 µs und 1 ms beträgt, so daß die impulsartigen Ladezeiten des Kondensators 9 ausreichend lang sind.The inductance of the choke coil 1 is selected so that the normal lamp current flows in normal operation, ie after the lamp 2 has been warmed up. If an initial ionization occurs in the lamp 2 due to the high-voltage pulse generated by the ignition device 3, current can flow through the choke coil 1 to the lamp 2. However, since this current is limited to approximately the nominal lamp current by the inductance L of the choke coil 1 and, in addition, the rate of current rise is limited by the choke, in many cases this alone is not sufficient to reliably ignite the lamp 2. Therefore, a current path is provided in parallel to the choke coil 1 with a capacitor 9 in series with an ohmic resistor 10. The capacitance C of the capacitor 9 is designed so that its reactance for the frequency of the AC network is a few hundred ohms to a few kilohms (depending on the coil size ) is and is therefore large against the impedance of the inductor 1

Thus, during normal operation of the lamp 2, only a small current can flow in the parallel current path formed with the capacitor 9. When the lamp is ignited, however, a high charging current flows briefly through the capacitor 9 and thus through the lamp 2. This short charging current is sufficient to ignite the lamp 2. The resistor 10 connected in series with the capacitor 9 serves to limit the charging current in order to prevent adverse effects of an excessively high charging current on the lamp 2 or other circuit parts. For this purpose, the value R of the ohmic resistor 10 is chosen so that the time constant R. C is between 10 microseconds and 1 ms, so that the pulse-like charging times of the capacitor 9 are sufficiently long.

In the circuit arrangement according to FIG. 2 there is only one capacitor 9 in the parallel current path to the inductor 1, which capacitor can be switched off with the aid of a bimetal switch 11. In the cold state, the contacts 12 and 13 of the bimetallic switch 11 are closed, so that the capacitor 9 is connected in parallel with the inductor 1 and its charging current generates an ignition pulse for the lamp 2, as has been described with reference to FIG. 1. After the lamp 2 has been ignited, the bimetal strips of the bimetal switch 11 heat up due to the current flowing through them, as a result of which the contacts 12 and 13 open. As a result, the parallel current path is interrupted, so that the lamp 2 is supplied with its normal current exclusively via the inductor 1.

Bimetal switches take a certain amount of time to close after the lamp has been extinguished. During this time, the parallel current path to the inductor is not yet closed again, so that reliable re-ignition of the lamp, which is still hot, is not always guaranteed. This disadvantage can be avoided if a switching relay 14 according to FIG. 3 is used instead of a bimetal switch. The relay coil 15 is in series with the choke coil 1 in the main circuit of the lamp 2. The actual relay switch 16 is in the parallel current path to the choke coil 1 in series with the capacitor 9 and the ohmic resistor 10. The lamp is ignited here, as shown in FIG. 1 has been described. After the lamp has been ignited, such a high lamp current flows through the relay coil 15 that it is excited and the relay switch 16 opens.

4 shows a circuit arrangement with an even faster switching element. In this case, the capacitor 9, the ohmic resistor 10 and a triac 17 lie in the parallel current path to the inductor 1. The control electrode of the triac 17 is connected via a trigger diode 18 and a protective resistor 19 to a capacitor 20, which in turn is charged via a resistor 21. If the voltage across the capacitor 20 exceeds the breakdown voltage of the trigger diode 18 of approximately 30 V, the trigger diode becomes conductive and thus the triac 17 is also switched to its conductive state. By appropriate selection of the resistor 21 it can be achieved that the switching time of the triac 17 lies before the response time of the ignition device 3 and thus an increased current can flow through the lamp 2 during the ignition process. As soon as the lamp is safely ignited, only the lamp voltage which is considerably lower than the mains AC voltage is present across the series connection of the resistor 21 and the capacitor 20. Therefore, the capacitor 20 can no longer charge up to the breakdown voltage of the trigger diode 18, so that the triac 17 remains blocked.

Thus, the capacitor discharges at extinguished lamp 2 9, 4 in the circuit arrangement of FIG. Connected in parallel with capacitor 9 a further ohmic resistor 22, whose value R _zus such is chosen that the discharge time constant R _add . C is between 0.05 and 20 msec. This facilitates subsequent ignition of the lamp, since otherwise the charging current may be too low.

5, in contrast to that of FIG. 4, the choke coil is divided into two parts 1a and 1b, the parallel current path with the parallel connection of the capacitor 9 and the further ohmic resistor 22 in series with the triac 17 only Choke coil part 1a is parallel. The choke coil part 1b is always in the main circuit of the lamp 2.

Typical data of the components used in the exemplary embodiments are, for example:

The high voltage transformer 4 had no core and had a transmission ratio of 1:60. Of course, transformers with a core and versions as an autotransformer can also be used.

Even with a mains voltage of only 200 V, a reliable cold start of 70W high pressure sodium lamps could be achieved with these components, in particular with the circuit arrangements according to FIGS. 1, 4 and 5. It was also possible to re-ignite the lamp, which was still hot, after about 3 seconds. If, on the other hand, components and ignition voltages of the same size arrangement were used in the known circuits according to DE-OS 31 08 547 or 31 08 548, a period of time of more than 15 seconds passed before re-ignition. Such a period of time is not acceptable in many applications.

Finally, it should be noted that the igniter used does not necessarily have to be a superimposed igniter, but other types also come, e.g. Antenna detonator (see DE-OS 31 09 539), in question.

Claims (7)

1. A circuit arrangement for igniting and operating gas discharge lamps having a choke coil arranged between the lamp and the a.c. supply source with an inductance L and an ignition device connected to the lamp, a capacitor having a capacitance C being connected in parallel with at least a part of the choke coil at least temporarily and having a reactive impedance of

characterized in that the capacitor (9) is used for achieving an ignition current which is increased as compared with the normal lamp operating current, is connected in series with an ohmic resistor (10) having a value R, the time constant R.C thereof lying between 10 us and 1 ms, and/or can be switched off after ignition of the lamp (2).

2. A circuit arrangement as claimed in Claim 1, characterized in that a further ohmic resistor (22) is connected in parallel to the capacitor (9), this resistor having a value R_zus such that its discharge time constant R_zus.C lies between 0.05 and 20 ms.

3. A circuit arrangement as claimed in Claim 1 or 2, characterized in that all passive elements (9, 10, 22) arranged in the current path parallel to the choke coil (1) can be switched off after ignition of the lamp (2).

4. A circuit arrangement as claimed in any one of the preceding Claims, characterized in that the current path parallel to the choke coil (1) includes a switch (11; 14; 17), which is opened after ignition of the lamp (2).

5. A circuit arrangement as claimed in Claim 4, characterized in that the switch is a bimetal switch (14).

6. A circuit arrangement as claimed in Claim 4, characterized in that the switch (16) forms part of a switching relay (15) arranged in the main current circuit of the lamp.

7. A circuit arrangement as claimed in Claim 4, characterized in that the switch is a semiconductor switching element (17).

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