EP0707438B1 - Ballast for at least one discharge lamp - Google Patents

Abstract

The circuit has inverter switches (S1,S2) coupled in series, and operated in an alternating mode using signals from a control circuit (1). The switches connect with the load circuit that has series resonance stage having a coil (L1) and capacitor (C3). The circuit connects to the lighting tube via a coupling capacitor (C1). The other electrode of the lamp is connected to a heating transformer (T) that has a pair of primaries (T1,T3) and a pair of secondaries (T2,T4). A switch (S3) in the supply line controls the generation of the heating current.

Description

The invention relates to a ballast for at least one gas discharge lamp according to the preamble of claim 1, and a method for operating a Gas discharge lamp with such a ballast.

Nowadays, high-quality ballasts are usually used for Gas discharge lamps preheated the lamp electrodes before the ignition voltage between them. It has been shown that the measure Lamp life is significantly extended.

Such as. described in EP 0 594 880 A1, the gas discharge lamp in the Usually operated on a series resonant circuit, the resonant circuit capacitor in generally lies parallel to the discharge path of the gas discharge lamp. The electrodes the lamp are designed as heating coils through which the current of the resonant circuit flows when the lamp is not lit. In preheating mode, the frequency is compared to Resonance frequency of the resonance circuit changed so that the above Resonance capacitor and thus no voltage above the gas discharge lamp Ignition of the gas discharge lamp causes. In this way an im flows substantially more constant current through the helixes Lamp electrodes so that they are preheated. After the preheating phase the frequency is set close to the resonance frequency of the resonance circuit, whereby the voltage across the resonance capacitor increases so that the Gas discharge lamp ignites.

With high-quality ballasts it is common nowadays to also use dimming to be provided for the gas discharge lamp. It has now been shown that with strong Dimming uses a premature aging of the gas discharge lamp. For this reason it is necessary to provide an arrangement in which the electrodes of the Gas discharge lamp can also be heated in ignited operation. In particular it is advantageous to set the heating of the electrodes depending on the degree of dimming, i.e. the more the lamp is dimmed - the darker it is - the stronger it needs to be be heated.

For this, EP 0 589 081 A1 a suitable circuit arrangement described. This points in Resonance circuit on the primary winding of a heating transformer, the Secondary windings are connected in parallel to the connections of the heating coils. In this way it is possible to use the heating coils even in ignited mode To supply energy. Furthermore, is parallel to the primary winding Heating transformer provided a controllable switch, which, if necessary, the Bridges the primary winding and thus simultaneously heats the heating coils prevents.

However, this arrangement has the disadvantage that the provision of Primary winding of the heating transformer in the series resonance circuit, at least as long as heating the coils is required, i.e. the primary winding parallel switch is open, damped the resonant circuit. this leads to a detuning of the resonance circuit, so that a reliable ignition and thus a reliable operation is no longer fully guaranteed.

A further circuit arrangement is known from WO 93 12631 A, which a Describes electronic ballast according to the preamble of claim 1. A lamp is connected to a coil and a series resonant circuit Capacitor ignited. The series resonance circuit is between a center tap two alternating switches of an inverter are connected. With a The lamp filament is coupled to a switch which can be controlled via a relay and which is in closed condition shorts the lamp electrodes. For preheating the The lamp contact is closed the relay contact, so that over the coil of the Series resonance circuit as well as the electrode coils and the switch high-frequency heating current flows, which heats the electrodes of the lamp. in the Preheating is the capacitor of the series resonant circuit through the shorted lamp electrodes bridged the lamp and the Series resonance circuit is strongly damped. As the electrode coils heat up, it grows their ohmic resistance, so that accordingly the voltage drop to the Electrodes and at the switch rises. When exceeding a certain one Threshold, the switch is opened using the relay, causing the heating circuit interrupted and a current flow through the electrode coils is prevented. Since the Capacity of the resonant circuit is no longer bridged by the heating circuit damping the series resonant circuit, and the lamp can be ignited. There even with this arrangement, the series resonance circuit is temporarily dampened also the problems described above.

The present invention is therefore based on the object of providing a ballast for at least one gas discharge lamp and a method for operating a To create gas discharge lamp with such a ballast, so that always a reliable, the lamp-sparing operation is guaranteed.

This object is achieved by a ballast with the features of claim 1 or a method with the features of claim 14 or 15 solved.

With the circuit arrangement according to the invention it is ensured that the Series resonance circuit unaffected and can work undamped. Furthermore it is by means of the method according to the invention, depending on the Inverters determine the degree of dimming of the gas discharge lamp which is necessary in each case Set heating voltage. In addition, it is different when using Lamps on the same ballast possible, for the selected one To provide the lamp with the necessary heating power without losing the To influence the operating conditions of the lamp.

Further advantageous embodiments of the invention are in the subclaims specified.

So it is especially for the energy balance of the ballast according to the invention advantageous that the further switch is switched so that the lamp only with Heating current is supplied if these are heated due to their operating state got to. This means that only as much energy as is absolutely necessary for heating the Lamp consumed.

The claims 24 relate advantageously to embodiments of the invention Ballast.

According to subclaims 5-8, configurations are provided which ensure that the control of the additional switch taking into account the control of the Inverter is kept as simple as possible and at the same time remains variable to the to be able to set the necessary heating power as precisely as possible.

According to subclaims 9-13, configurations of the heating circuit are specified which use the advantageous use of a heating transformer and also one Ensure the circuit structure is as simple and safe as possible.

According to subclaim 16, the gas discharge lamp is operated within the permissible operating range for the heating output guaranteed.

The invention is described below with reference to exemplary embodiments explained in more detail on the drawings.

Fig. 1 ein Ausführungsbeispiel eines elektronischen Vorschaltgerätes,

Fig. 2 Steuersignale der Schalter S1 und S3 gemäß Fig. 1,

Fig. 3 eine Variante des in Fig. 1 vorgesehenen Heiztransformators,

Fig. 4 ein Beispiel eines einstellbaren Heizstromes in Abhängigkeit vom Dimmgrad,

Fig. 5 eine Darstellung des effektiven Heizstroms in Abhängigkeit von der Pulsanzahl und

Fig. 6 eine Darstellung der effektiven Heizspannung bzw. Heizleistung in Abhängigkeit von der Pulsanzahl.

Show it:

1 shows an embodiment of an electronic ballast,

2 control signals of the switches S1 and S3 of FIG. 1,

3 shows a variant of the heating transformer provided in FIG. 1,

4 shows an example of an adjustable heating current as a function of the degree of dimming,

Fig. 5 shows the effective heating current as a function of the number of pulses and

6 shows the effective heating voltage or heating power as a function of the number of pulses.

In Figure 1, the essential parts of an embodiment are Ballast shown for a gas discharge lamp. This first has one Inverter consisting of the controllable switches S1 and S2, which by means of an inverter control circuit 1 can be driven in push-pull. Thus in Switch one switch on and the other off. The two Inverter switches S1 and S2 are connected in series between a positive one Supply voltage and ground switched. At the common junction of the two Inverter switch S1, S2 the load circuit is connected. This consists of one Series resonance circuit, which consists of a resonance circuit coil L1 and a Resonant circuit capacitor C3 is composed. The resonant circuit capacitor is C3 with its one terminal connected to ground. At the connection node between the resonance circuit capacitor C3 and the resonance circuit coil L1 is one Connection of a coupling capacitor C2 connected. The other connection of the Coupling capacitor C2 is with one of two cathodes, a gas discharge lamp LA connected. The two cathodes of the gas discharge lamp LA each have two Connections, between each of which a heating coil for heating the respective cathode is provided. The not connected to the coupling capacitor C2 Electrode of the gas discharge lamp LA has a connection K3 to ground connected.

A heating transformer T is also provided, which has two windings on the primary side T1 and T3 and two secondary windings T2 and T4. The one primary winding T1 is with its one connection to the connection node of the two inverter switches S1 and S2 connected and with their second Connection connected to the second primary winding T3. This is again connected to a connection of a further controllable switch S3. The second Connection of the further controllable switch S3 is in turn with a resistor R1 connected, which on the other hand is connected to ground. This results in a Series connection from the two primary-side windings of the heating transformer, the further controllable switch S3 and resistor R1, which are parallel to Inverter switch S2 are switched.

The further controllable switch S3 is in turn assigned to it by one Switching control 2 operated.

The two secondary windings T2 and T4 of the heating transformer T are over Series connections with respective diodes D3 and D4 each with one of the two Electrodes of the gas discharge lamp LA connected. Thus the winding T2 is over the Diode D3 with the heating coil connections K3 and K4 of one electrode and Winding T4 via the diode D4 with the heating coil connections K1 and K2 second electrode connected.

Finally, at the connection node between the further switch S3 and the Secondary winding T3 connected to a diode D1 with its anode, the cathode is connected to the positive supply voltage. After all, is parallel to Inverter switch S2 a diode D2 switched, the anode connection to ground connected is. This diode can be omitted when using FET transistors, if the transistors used have already integrated a diode circuit.

Below is an advantageous operation of the previously described Circuit arrangement described with reference to Figures 1 and 2.

In FIG. 2, control signals for the inverter switch S1 are shown in curve I, which periodically switch between levels L and H. The period length is PO, the signal being at level H for the duration tO. Now let's assume that the inverter switch S1 is closed as long as it is at level H is controlled. At the same time, the second inverter switch S2 switches, as before already explained, alternating with switch S1.

For the sake of completeness it should be mentioned that in the connected Series resonance circuit a vibration of the period of the control signals to the Inverter switches forms, when the period PO is close the resonance frequency of the series resonance circuit, the gas discharge lamp LA ignites.

By increasing the switching frequency of the inverter above the resonance frequency the resonance circuit is dimmed, i.e. the stronger the period PO deviates from the resonance frequency of the series resonance circuit, the stronger the Lamp dimmed, i.e. the darker it is. Such an operation alone would have, like previously mentioned, with the result that the lamp would age to an increased extent.

It is therefore provided that the control circuit 2 of the further controlled switch S3 to couple a coupling 3 to the inverter control circuit 1. this happens 3 in the form that the further controllable switch S3 is only switched on is when the inverter switch S1 is also switched on. is. This corresponds to the Synchronization of the control signals according to curve I and the control signals for the Switch S3 according to curves II to VIII.

Curves I and II are identical, so that switches S1 and S3 are in common mode switch and are switched on or off at the same time. It follows that then when the switch S1 is turned on, a primary-side current at the same time through the windings T1 and T3 of the heating transformer T over the closed further controllable switch S3 and the resistor R1 from the positive Supply voltage connection flows to ground. Since it is according to curve II in FIG. 3 an interrupted current, i.e. no direct current, is acting according to the Laws of magnetic induction on the secondary side of the Heating transformer, i.e. into the windings T2 and T4, with the same cycle one Voltage induced, which results in a current as described, the result flows through the connected heating windings and thus to heat the Electrodes of the gas discharge lamp LA leads. As soon as the further controllable switch S3 is opened, the current flow through the windings T1 and T3 is interrupted, so that due to the known physical laws an abrupt Voltage increase at the connection node between switch S3 and the winding T3 results. This rise in voltage is reduced to the value of the diode D1 positive supply voltage limited. In the switching phases in which the switch S3 is open, it results from the discharge in the heating transformer stored energy a demagnetization. Diodes D3 and D4 are also used Demagnetization of the heating transformer T necessary.

As previously mentioned, changing the clock frequency of the In the end, the inverter can be dimmed the gas discharge lamp LA. To the However, it is not to reduce the lifespan of a gas discharge lamp unnecessarily necessary, depending on the degree of dimming, the heating power of the Adapt electrode heating. This can be done according to curves II to VII in FIG. 2 in that not every time the inverter switch S1 is switched on further controlled switch S3 is also turned on. Rather, longer ones Clock periods P1 to P5 can be provided, for example, the period lengths P1 to P5 are an integer multiple of the cycle period of the inverter switch S1.

In other words, when the lamp is not dimmed or weakly dimmed no, or only a low heating power necessary, so that for example for the a further switching switch S3 a switching period P5 according to curve VII is provided could be. There is also the possibility that in undimmed operation the Heat development of the electrodes is so great that no additional heating of the Electrodes is necessary. In this case, the further controllable switch S3 remains opened so that no energy is consumed for additional heating, which the arrangement works with the greatest possible efficiency. It is therefore a Applying heating power is only necessary when dimming your own Heat generation is not sufficient.

Along with a stronger dimming of the gas discharge lamp LA must Providing a higher heating output, i.e. a more frequently recurring heating current, the clock period at the further switch S3 are reduced until they reach the highest Dimming level reaches a maximum heating output. This corresponds to curve II, at which, as already mentioned above, the switches S3 and S1 operate in common mode.

Another alternative and additionally applicable option is the heating output to set, is to switch the switching time in which the switch S3 is turned on change. While in curves II to VII the switch S3 is just as long is switched on like switch S1, and only the time during which switch S3 is switched off, is varied, switch S3 is significantly shorter according to curve VIII switched on. At the same time, this reduces the achievable heating current through the Heating coil.

4, curves 1 and 3 are the maximum and Minimum heating current in recommended by the manufacturer of a gas discharge lamp Dependence on the degree of dimming is shown. With curve 2 is the one with the previous one circuit and control method achievable heating current shown. From figure 4 it is thus clear that a heating current for the gas discharge lamp is easily adjustable, which is just above the minimum required heating current.

FIG. 5 shows a representation which shows the adjustable heating current as a function on the number of switch-on pulses omitted with respect to switch S1, i.e. which represents a correspondingly extended period. If the number of omitted switch-on pulses is 0 - as in II of Figure 2 - is a maximum Heating current achievable. This value can be reduced almost continuously.

Furthermore, a maximum heating voltage results according to FIG. 6, with this Voltage, as is also shown in FIG. 6, a maximum heating power can be achieved is. According to the continuously changeable heating current and Heating voltage is therefore, as shown, a continuous change in Adjustable heating output.

This shows that with simple means essentially independent of the operation of the Gas discharge lamp the heating power is adjustable. This causes the previously explained circuit not only for adjusting the dimming level but for the Adjustment of the heating power when using different lamps on their Requirements can be used in both preheating and dimming.

According to Figure 3, a circuit variant of the heating transformer T is shown. Here are not two windings connected in series on the primary side but one over a core wound winding T1 'is provided which is the secondary windings Operate T2 and T4.

The circuit arrangements described above are initially one pure control, in which the dependency between the switching frequency PO of the Inverter and the switching frequency of the further controllable switch S3 is specified. Nevertheless, regulation is of course also conceivable. In one in such a case, the lamp current is measured in a manner known per se and the Control circuits 1 and 2 supplied (not shown). In addition, one can Heating current proportional voltage across resistor R1 can be measured and the value of the heating current via a heating current detector 4 as the signal Inverter control circuits are supplied. In this way the heating current directly adjustable depending on the lamp current by means of control.

This arrangement also has the advantage that it can also be detected when a There is a broken coil, i.e. the lamp is defective and if the lamp is out of Arrangement was removed. By this detection via the heating current detector 4 and forwarding the information to the inverter control circuit 1 can immediately reduced the lamp voltage by changing the inverter frequency become. Likewise, a reinstallation of the lamp LA is detected, so that the Inverter can be operated so that the lamp LA automatically after insertion ignites.

Claims (16)

1. Ballast for at least one gas discharge lamp

   having an inverter which has two switches (S1, S2) in series, connected to a d.c. voltage source and switched with complementary timings,

   having a load circuit connected to the inverter, which load circuit includes a series resonant circuit (L1, C1) and the lamp (LA), and

   having a heating circuit (T, S3, R1) for the current supply of the lamp coils of the gas discharge lamp (LA), likewise connected to the inverter, which heating circuit is connected in parallel to one of the two switches of the inverter and includes a further controllable switch (S3) for control of the heating current,

   characterized in that,
      the heating circuit has a heating transformer (T) which on the primary side is connected in parallel to the one switch (S1, S2) of the inverter and on the secondary side is connected with the lamp coils of the gas discharge lamp (LA).
2. Ballast according to claim 1,
      characterized in that,
      the further controllable switch (S3) is so connected that the lamp (LA) is supplied with heating current only when the inverter switch (S2), with which the load circuit is connected in parallel, is open.
3. Ballast according to claim 1 or 2, the load circuit being in parallel to a switch of the inverter,
      characterized in that,
      the heating circuit (T, S3, R1) is connected in parallel to that switch of the inverter with which the load circuit (L1, C1, LA) is also in parallel.
4. Ballast according to claim 1 or 2,
      characterized in that,
      the heating circuit (T, S3, R1) is connected in parallel to that switch (S1) which is connected in series with the switch (S2) of the inverter with which the load circuit (L1, C1, LA) is in parallel.
5. Ballast according to any of claims 1 to 4,
      characterized in that,
      the switching period of the further controllable switch (S3) is variable by a whole number multiple of the timing period of the inverter.
6. Ballast according to any of claims 1 to 5,
      characterized in that,
      the length of time over which the further controllable switch (S3) supplies the heating device with heating current is shorter than the length of time for which the inverter switch (S2) with which the load circuit lies in parallel is open.
7. Ballast according to claim 6,
      characterized in that,
      the length of time for which the further controllable switch (S3) supplies the heating circuit with current is settable.
8. Ballast according to claim 7,
      characterized in that,
      the setting of the time range and/or the switching periods is effected in dependence upon the current in the load circuit (L1, C1, LA).
9. Ballast according to any of claims 1 to 8,
      characterized in that,
      the heating transformer (T) has an individual secondary-side winding (T2, T4) for each lamp coil and has on the primary side a common winding (T1') or windings (T1, T3) which are connected with one another in series and correspond to the secondary-side windings (T2, T4).
10. Ballast according to any of claims 1 to 9,
       characterized in that,
       the further controllable switch (S3) is connected in series with the primary side of the heating transformer (T).
11. Ballast according to any of claims 1 to 10,
       characterized in that,
       an impedance, preferably an ohmic resistance, lies in series with the further controllable switch (S3), whereby the voltage drop across this impedance is employed as detection signal for a heating current flowing and thus for a heating coil breakage or the absence of or a gas defect of the lamp (LA).
12. Ballast according to claim 11,
       characterized in that,
       the voltage drop across this impedance is employed as detection signal for the re-emplacement of a lamp.
13. Ballast according to any of claims 1 to 12,
       characterized in that,
       there is provided a circuitry arrangement for the demagnetisation of the heating transformer (T), which demagnetises the heating transformer (T) when this supplies no heating current to the lamp coil.
14. Method of operating a ballast according to any preceding claim,
       characterized in that,
       with the further controllable switch, after ignition of the lamp, the heating is turned off until a requirement therefor arises.
15. Method of operating a gas discharge lamp having a ballast according to any of claims 1 to 13,
       in which upon preheating of the lamp electrodes, the switches (S1, S2) of the inverter are operated with maximum timing frequency and
       with which for igniting the gas discharge lamp (LA) the timing frequency is reduced down to the vicinity of the resonance frequency of the series resonant circuit (L1, C3)
       characterized in that,
       upon preheating the further controllable switch (S3) is operated with a timing frequency which makes possible heating with maximum permitted heating power.
16. Method according to claim 15,
       characterized in that,
       after ignition of the gas discharge lamp (LA) the timing frequency of the further controllable switch (S3) is set in dependence upon a dimming condition of the gas discharge lamp (LA), so that the heating power lies between the maximum heating power permitted for the gas discharge lamp (LA) and the minimum necessary heating power.

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