EP2282614B1 - Switchg system and method for igniting a discharge lamp - Google Patents

Description

Technical area

The invention relates to a circuit arrangement for igniting a discharge lamp, comprising a primary circuit, which consists of the series connection of an inductor, a firing capacitor and a first switch, wherein the switch is designed as a threshold and the inductance consists of the primary winding of the ignition transformer, and the primary circuit is formed is to generate a firing pulse for the discharge lamp at the secondary winding of an ignition transformer.

State of the art

The invention relates to a circuit arrangement for igniting a discharge lamp according to the preamble of the main claim.

A circuit arrangement according to the preamble of claim 1 is for example off DE 19 544 838 known.

Fig. 1 shows a circuit arrangement for igniting a discharge lamp according to a further prior art, in the primary circuit, a high circulating current is generated by a primary winding L1 of an ignition transformer TR, which is transformed into a high secondary ignition voltage U3. This ignition voltage U3 is applied to the gas discharge lamp. The primary circuit consists of a series connection of the primary winding L1 of the ignition transformer TR, a firing capacitor C1 and a first switch in the form of a spark gap SG. In the usual state of the art operation, in which the ignition capacitor C1 slowly is charged until the voltage applied to it U1 is large enough to break the spark gap, the voltage at the spark gap SG is substantially equal to the voltage at the ignition capacitor C1, since the inductance of the primary winding of the ignition transformer TR is permeable to DC voltage. The ignition capacitor C1 is in this case charged via a voltage source U11, R11 until its voltage has reached the breakdown voltage of the spark gap, and this breakthrough. In this case, the voltage U2 at the spark gap SG drops to very low values in a very short time, which results in a very high current through the primary winding L1 and the spark gap SG. The charge of the ignition capacitor C1 discharges to a large extent. Due to the high primary-side current, a firing pulse is generated on the secondary side of the ignition transformer TR, which is applied to the gas discharge lamp. The current and thus the height of the ignition pulse is dependent on the charging voltage U1 at the time of breakthrough of the spark gap SG. The primary circuit is thus subjected to a voltage U1, which provides for the charging of the ignition capacitor C1 and for switching on the spark gap SG. However, spark gaps have the disadvantage that the breakdown voltage is heavily toleranced, and the ignition energy present in the primary circuit due to the charging of the ignition capacitor C1 likewise fluctuates greatly. This makes the ignition of the gas discharge lamp a statistical process, which is very undesirable.

In another prior art, instead of the spark gap, a controllable semiconductor switch, e.g. a thyristor or a MOS-FET used. But semiconductor switches have the disadvantage of a high internal resistance compared to the spark gap, which has a significantly lower primary current result, and thus a significantly smaller ignition pulse.

task

It is an object of the invention to provide a circuit arrangement for igniting a discharge lamp, comprising a primary circuit, which consists of the series circuit of an inductance, a firing capacitor and a first switch, wherein the switch is designed as a threshold value and the inductance consists of the primary winding of the ignition transformer, and the primary circuit is designed to generate at the secondary winding of an ignition transformer an ignition pulse for the discharge lamp, by means of which the ignition energy can be deterministically predetermined.

Presentation of the invention

The solution of the object with respect to the circuit arrangement is carried out according to the invention with a circuit arrangement for igniting a discharge lamp, with a primary circuit consisting of the series circuit of an inductor, a firing capacitor and a first switch, wherein the switch is designed as a threshold and the inductance of the primary winding of the Ignition transformer is made, and the primary circuit is formed on the secondary winding of an ignition transformer, a firing pulse for the discharge lamp wherein the primary circuit has two decoupled voltages, a first voltage that is substantially correlated with the energy of the firing pulse, and a second voltage that controls the switching timing of the switch, wherein the first voltage is less than the threshold of the first switch , By this measure, the ignition timing of the discharge lamp can be decoupled from the ignition energy, and the ignition energy can be set to a predetermined value. Because the first switch is designed as a threshold value switch, it is switched on when the second voltage corresponds to its threshold value.

According to the invention, the voltages are decoupled by an inductance or a diode with an inductance. The decoupling by an inductance is particularly suitable when using a fast-response first switch, whereas the decoupling by a diode has a broader field of application.

The design as a threshold switch opens a variety of possible physical switches, the first switch may be eg a spark gap, or be a Sidac or a component with a similar threshold characteristic. A spark gap as a threshold value switch offers the advantage of a very low internal resistance and an associated high ignition efficiency. In this case, the threshold value switch preferably has a parallel capacitance, via which a voltage across the threshold value switch can be established by charge transport to the capacitance. It is preferred to charge the parallel capacity a controllable voltage source or a controllable current source or a DC-DC converter or a charge pump used. Particularly preferably, a DC-DC converter is used to charge the parallel capacitor, which is designed as a throttle up converter with a second switch.

The choke up converter is preferably designed such that a Zener diode is arranged in series with the second switch. By this measure, the reverse voltage of the transistor can turn out smaller, and the reactor converter can be made cheaper.

Further advantageous developments and refinements of the circuit arrangement for igniting a discharge lamp according to the invention emerge from further dependent claims and from the following description.

Short description of the drawing (s)

• Fig. 1 eine Schaltungsanordnung zum Zünden einer Entladungslampe nach einem weiteren Stand der Technik,
• Fig. 2 eine erfindungsgemäße Schaltungsanordnung zum Zünden einer Entladungslampe in einer ersten Ausführungsform mit einer Diode als Entkopplungselement,
• Fig. 3 eine erfindungsgemäße Schaltungsanordnung zum Zünden einer Entladungslampe in einer zweiten Ausführungsform mit einer Diode als Entkopplungselement, die Teil eines Drosselaufwärtswandlers ist, der die Primärwicklung des Zündtransformators als Drossel verwendet,
• Fig. 4 eine erfindungsgemäße Schaltungsanordnung zum Zünden einer Entladungslampe in einer dritten Ausführungsform mit einer Diode als Entkopplungselement und einem Drosselaufwärtswandler,
• Fig. 5 eine erfindungsgemäße Schaltungsanordnung zum Zünden einer Entladungslampe in einer vierten Ausführungsform mit der Primärwicklung des Zündtransformators als Entkopplungselement und einer Schaltstrecke zur Erhöhung der zweiten Spannung,
• Fig. 6 einige relevante Signale, die die Arbeitsweise der erfindungsgemäßen Schaltungsanordnung bei einer Ladespannung des Zündkondensators von 500V verdeutlichen,
• Fig. 7 einige relevante Signale, die die Arbeitsweise der erfindungsgemäßen Schaltungsanordnung bei einer Ladespannung des Zündkondensators von 700V verdeutlichen,

Further advantages, features and details of the invention will become apparent from the following description of exemplary embodiments and with reference to the drawings, in which the same or functionally identical elements are provided with identical reference numerals. Showing:

• Fig. 1 a circuit arrangement for igniting a discharge lamp according to a further prior art,
• Fig. 2 a circuit arrangement according to the invention for igniting a discharge lamp in a first embodiment with a diode as a decoupling element,
• Fig. 3 a circuit arrangement according to the invention for igniting a discharge lamp in a second embodiment with a diode as a decoupling element which is part of a choke up converter, which uses the primary winding of the ignition transformer as a choke,
• Fig. 4 a circuit arrangement according to the invention for igniting a discharge lamp in a third embodiment with a diode as a decoupling element and a choke up converter,
• Fig. 5 a circuit arrangement according to the invention for igniting a discharge lamp in a fourth embodiment with the primary winding of the ignition transformer as a decoupling element and a switching path for increasing the second voltage,
• Fig. 6 some relevant signals that illustrate the operation of the circuit arrangement according to the invention at a charging voltage of the ignition capacitor of 500V,
• Fig. 7 some relevant signals that illustrate the operation of the circuit arrangement according to the invention at a charging voltage of the ignition capacitor of 700V,

Preferred embodiment of the invention

Fig. 2 shows a circuit arrangement according to the invention for igniting a discharge lamp in a first embodiment with a diode D1 as a decoupling element and a spark gap SG as the first switch. Through the diode D1, it is possible to apply a higher voltage U2 to the spark gap SG than to the ignition capacitor C1. For this purpose, the cathode of the diode is connected to the spark gap SG. According to the invention, the ignition capacitor C1 is always charged to a predetermined first voltage U1 in order to ensure a constant ignition energy. To the spark gap SG, a second voltage U2 is applied, which is high enough to break the spark gap SG, So turn it on. This can be done, for example, by an external voltage source, not shown here. Through the diode D1, the two voltages are decoupled from each other and can be set independently. The prerequisite for this, of course, is that the minimum breakdown voltage of the spark gap is above the first voltage U1. The first voltage U1 at the ignition capacitor C1 is set to a value that allows a predetermined desired Zündpulsenergie. This voltage can either be fixed, or be set variably depending on the operating state. In general, there is a relationship between the ignition pulse energy and the maximum voltage of the ignition pulse, so that an ignition pulse with higher Zündpulsenergie with otherwise the same primary circuit parameters always has a higher maximum voltage of the ignition pulse result. In order to protect the insulation of the entire system, so the ignition pulse can be generated so that it can always ignite the lamp depending on the current operating state safely, but at the same time is not unnecessarily high, so as not to burden the isolation of the system over charge.

Basically, a sufficiently high voltage can be applied to the spark gap in two ways: As already described above, a voltage source can be applied to the spark gap that is sufficiently high to allow it to break through. However, it is also possible to apply a charge to the capacitor C2 connected in parallel to the spark gap, by which the second voltage U2 is then generated at the capacitor and thus also at the spark gap. The capacity C2 may consist of the parasitic capacitance of the spark gap and connected components such as the diode D1. However, the capacitance can also be composed of this capacitance and the capacitance of a real capacitor connected in parallel with the spark gap. This depends on the real conditions and the design of the circuit arrangement according to the invention. Preferably, the capacitance C2 is chosen to be significantly smaller than the capacitance of the ignition capacitor C1, preferably C2 <0.3 * C1. This ensures that the influence of the capacitance C2 on the ignition energy remains negligibly small.

Fig. 3 shows a circuit arrangement according to the invention for igniting a discharge lamp in a second embodiment with a diode D1 as a decoupling element, which is part of a choke up converter 3, which uses the primary winding of the ignition transformer as a choke. With this circuit arrangement, no voltage source is required to provide the second voltage U2. The choke up converter 3 operates as a charge pump on the capacitance C2, and generates with few cycles a voltage across the capacitance C2, which is sufficient to ignite the spark gap. Because the second voltage U2 is generated by means of fewer cycles, the ignition time of the gas discharge lamp 5 connected to the ignition voltage U3 can be set very precisely. The Zener diode ZD1 serves to reduce the voltage at the second switch S1, which is designed as a transistor. As with the few cycles to the breakthrough of the spark gap, the efficiency of the choke up converter 3 is irrelevant, the Zener diode ZD1 can be installed in series with the second switch, or switching transistor S1. As a result, the switching transistor S1 must be designed for less blocking voltage. The losses in the zener diode ZD1 play no role here. Since switching transistors are less expensive with less blocking voltage, this trick helps to keep the cost of the circuit arrangement according to the invention low. The zener voltage of the zener diode ZD1 must be selected smaller than the stationary value of the first voltage U1, ie the voltage U1, to which the ignition capacitor C1 is ultimately charged. This is necessary because otherwise no current would flow through it when the switch / transistor S1 is turned on. In numbers, the should

Zener voltage U _zerier the zener diode ZD1 be 0.2 to 0.95 times the voltage U1 at the ignition capacitor C1: U _zener = (0.2..0.95) * U1. The choke boost converter 3 uses the primary winding of an ignition transformer TR as a reactor. This requires precise tuning of all components to allow the ignition transformer and the choke up converter to perform their functions optimally. In some cases, however, the function as a primary winding for the ignition transformer TR and the function as a choke for the choke up converter 3 can not be combined for the winding L1, since the inductance values of the winding L1 required for both applications can not be combined. In this case, a third embodiment of the circuit arrangement according to the invention is used.

Fig. 4 shows a circuit arrangement according to the invention for igniting a discharge lamp in a third embodiment with a diode as a decoupling element and a choke up converter. The throttle step-up converter here comprises an additional inductor L3, an additional diode D2 and the series connection of a zener diode ZD1 and a switch S1 known from the second embodiment. The input of the inductance converter is connected here to the charging voltage of the ignition capacitor C1. However, it may be useful in certain applications to use a different internal voltage source to supply the choke converter 3. Although this embodiment requires more components than the second embodiment, it also can be safely ignited with more complex boundary conditions and more difficult to start gas discharge lamps. This embodiment has the most degrees of freedom in design, thus can be solved by the appropriate adjustment of the component values virtually any even so complex ignition task. The throttle step-up converter operates again on the capacitor C2, which may be designed as a parasitic capacitance or as a parallel connection of a parasitic capacitance and a real capacitor. By briefly switching on and off the switch or switching transistor S1, the charge stored in the inductor L3 is transferred to the capacitor, which leads to a significant increase in voltage across the capacitor C2. This corresponds to the operation of the second embodiment, except that here the inductor L3 and the capacitance C2 can be better coordinated. The switch respectively Switching transistor S1 can be turned on and off several times in succession. In special cases, however, it is also possible that the necessary second voltage U2 is generated with a single switching on and off again of the switch or switching transistor S1.

The following table shows the component values of a preferred embodiment of the third embodiment: C1 68nF C2 0..5nF L1 1,3uH L2 700uH LD Unavailable U1 200V..700V D1 Diode with 600V blocking voltage D2 Diode with 600V blocking voltage ZD1 Zener diode with 400V Z voltage L3 470uH SG Spark gap with 800V ± 20% breakdown voltage

The voltage U1 can vary depending on the desired ignition energy of 200V to 700V. The ignition energy may depend on the lamp state of the gas discharge lamp 5, for example, it may turn out higher when the lamp is hot. For example, at a voltage U1 of 500V, the ignition energy is 0.5 * 70nF * (500v) 2 = 8.75mJ corresponding to a firing pulse level of 17kV. For example, at a voltage U1 of 700V, the ignition energy is 0.5 * 70nF * (700v) 2 = 17.15mJ corresponding to a firing pulse level of 22kV. The switch-on time of the switch / switching transistor S1 is varied in accordance with the voltage U1 so that the time duration during which the switch / switching transistor is closed, decreases at higher voltage U1 to reduce the voltage and current load of the switch / switching transistor S1. The switch-on duration of the switch / switching transistor S1 is therefore 2.5 V at a first voltage U1 of 500 V, and at a first voltage U1 of 700 V it is 0.2 μs.

Fig. 5 shows a circuit arrangement according to the invention for igniting a discharge lamp in a fourth embodiment with the primary winding of the ignition transformer as a decoupling element and a switching path for increasing the second voltage. This represents a somewhat simplified embodiment of the second embodiment. Here, the primary winding of the ignition transformer TR is used as a decoupling element, with the result that all necessary operations for the ignition must run very fast, since the primary winding of the ignition transformer TR as an inductive component for DC voltage and AC voltage of low frequency is permeable. Ideally, the voltage across the capacitor U2 is generated here with only one switching operation of the second switch S1. By briefly switching on S2, a resonant overvoltage occurs at the threshold value switch S1. As a result, the voltage U2 is substantially higher than the voltage U1 for a short time. The resonant voltage overshoot is only for a short time at the threshold value. This leads to the fact that the threshold value switch or the spark gap SG must switch very fast to this To exploit effect. If the spark gap SG switches too slowly, the voltages U1 and U2 have already equalized again, and the ignition mimic does not work. To improve the response of the threshold switch, it is advantageous to extend the duration of the resonant voltage overshoot. This can be achieved by increasing the effective primary inductance and by increasing the capacitance C2. For this purpose, an additional inductance can be connected in series with the primary winding (L1) and / or an additional capacitance can be connected in parallel with the threshold value switch. The additional inductance can be designed so that it goes into saturation after switching on SG when discharging C1. This has the advantage that when the SG is breached, only little voltage drops at the additional inductance and thus the ignition pulse height is reduced only slightly.

The following table shows the component values of a preferred embodiment of the fourth embodiment: C1 68nF C2 0,5..5nF L1 1,3uH LD 1..5uH L2 700uH U1 500..600V ZD1 Zener diode with 400V Z voltage SG Spark gap with 800V + 70% Durchburchsspannung

Of course, this switching mimic with a very fast threshold value switch or a fast spark gap SG can also be applied to a circuit arrangement known per se, such as that of FIG Fig. 1 apply. If a voltage is applied to the spark gap SG here by an external voltage source, not shown here, and the spark gap SG switches quickly, the voltage U1 applied to the ignition capacitor C1 can be decoupled from the voltage U2 initiating the threshold value switch or the spark gap SG by means of L1 without the need for additional components. This is the simplest embodiment for an inventive ignition method and only requires a fast switching first threshold switch and a voltage source capable of applying the voltage to the threshold switch at a high voltage change rate.

The Fig. 6 & 7 show some relevant signals that illustrate the operation of the circuit arrangement according to the invention at a charging voltage of the ignition capacitor of 500V or 700V. Plotted are here over a time axis of 2μs / DIV, the voltages U1, U2, U3 and the voltage across the second switch or switching transistor S1. The basis for these signals is a circuit arrangement according to the invention in the third embodiment. At time t ₁ , the second switch S1 and the transistor of the inductance converter respectively, which can be seen well at the voltage US1, to zero collapses. At time t ₂ , the second switch S1 or the transistor of the inductance converter switches off again, whereupon an oscillation sets in, which is also reflected in the spark gap voltage U2. This voltage increases abruptly at the switch-off time by a certain value. In this example, the design is chosen such that the voltage for the breakdown of the FA is already reached during a switching operation. In principle, however, this can only be the case after several switching operations. It can clearly be seen that the voltage U1 at the ignition capacitor is independent of the voltage U2 at the spark gap. At time t ₃ , the spark gap breaks through, and the voltage U1 discharges into a circulating current in the primary circuit, which generates a high ignition voltage curve of the ignition voltage U3 on the secondary side of the ignition transformer TR. If you compare the two Fig. 6 and 7 , the relationship between the voltage U1 at the ignition capacitor C1 and the ignition voltage U3 can be well recognized. In Fig. 6 the ignition capacitor C1 is charged to a voltage of 500V, and the resulting maximum ignition voltage is about 17 kV. In the Fig. 7 the ignition capacitor is charged to a voltage of 700V, and the maximum ignition voltage is about 22kV. Good to see is also the above-mentioned relationship between the turn-on of the second switch S1 and the voltage U1 on the ignition capacitor C1. Is the ignition capacitor C1 charged to 500V ( Fig. 6 ), the second switch S1 is turned on for about 2.5μs. This corresponds to the time span between the times t ₁ and t ₂ . Is the ignition capacitor C1 charged to 700V ( Fig. 7 ), the second switch S1 is only turned on for about 200ns.

Fig. 8 shows a circuit arrangement according to the invention for igniting a discharge lamp in a fifth embodiment with a diode D1 as a decoupling element and a spark gap SG as the first switch, which is similar to the first embodiment. In this embodiment, it is shown by way of example that the inductance in the ignition circuit does not only have to consist of the primary inductance L1 of the ignition transformer, but in series therewith also a choke LD can be connected, which together form the inductance L. Of course, this circuit variant can also be used in all other embodiments. By this measure it is possible to be able to better adapt the inductance value of L to the requirements of the circuit. This may be advantageous, above all, in the second embodiment and the fourth embodiment, since precise tuning of the components, in particular of the inductance value of the boost converter, regularly leads to an increase in converter efficiency. This makes it possible, in unfavorable cases with a single low-cost component to significantly increase the converter efficiency and thus the performance of the entire circuit arrangement.

Claims (8)

1. Circuit arrangement for starting a discharge lamp, with a primary circuit, which comprises a series circuit comprising an inductance (L), a starting capacitor (C1) and a first switch (SG), the switch being in the form of a threshold value switch, and the inductance comprising the primary winding (L1) of the starting transformer (TR), and the primary circuit being designed to generate a starting pulse for the discharge lamp at the secondary winding (L2) of a starting transformer (TR), wherein the primary circuit has two decoupled voltages, a first voltage (U1), which is correlated substantially with the energy of the starting pulse, and a second voltage (U2), which controls the operating time of the switch (SG), the first voltage (U1) being lower than the threshold value of the first switch (SG), characterized in that the inductance (L) or the inductance (L) in series with a diode (D1) is arranged between the first voltage (U1) and the second voltage (U2), the cathode of the diode (D1) being connected to the first switch (SG).
2. Circuit arrangement according to Claim 1, characterized in that the inductance (L) comprises a series circuit comprising the primary winding (L1) of the starting transformer (TR) with an additional inductor (LD).
3. Circuit arrangement according to Claim 2, characterized in that the additional inductor (LD) becomes saturated during discharge of the starting capacitor (C1) at the starting instant.
4. Circuit arrangement according to one of the preceding claims, characterized in that the first switch (SG) is a spark gap or a SIDAC or a component with an operative equivalent threshold value characteristic.
5. Circuit arrangement according to one of the preceding claims, characterized in that a capacitance (C2) is connected in parallel with the threshold value switch (SG).
6. Circuit arrangement according to one of the preceding claims, characterized in that it has a controllable voltage source or a controllable current source or a DC/DC voltage converter or charge pump for charging the parallel capacitance (C2).
7. Circuit arrangement according to Claim 6, characterized in that the DC/DC voltage converter is an inductor-type step-up converter (3) with a second switch (S1).
8. Circuit arrangement according to Claim 7, characterized in that a zener diode (ZD1) is arranged in series with the second switch (S1), the anode of the zener diode (ZD1) being connected to the switch.

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