EP2067385A1

EP2067385A1 - Circuit arrangement and method for starting a discharge lamp

Info

Publication number: EP2067385A1
Application number: EP06793799A
Authority: EP
Inventors: Siegfried Mayer; Olaf Busse; Arwed Storm
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2006-09-25
Filing date: 2006-09-25
Publication date: 2009-06-10
Also published as: CN101529991B; AU2006348908B2; AU2006348908A1; US8093836B2; WO2008037290A1; US20100045201A1; CN101529991A

Abstract

The present invention relates to a circuit arrangement for starting a discharge lamp (20) with a driving apparatus, at whose output a drive signal with a predeterminable frequency can be provided; an inverter (14), which is coupled to the output of the drive apparatus and at whose output a square-wave signal with a predeterminable duty factor can be provided; a load circuit (16), which is coupled to the output of the inverter (14) and has at least one connection for the discharge lamp (20); a first control loop (Ri) with a first reference variable, a first manipulated variable and a first controlled variable, wherein the first control loop (Ri) has a first time constant; a second control loop (Ra) with a second reference variable, an auxiliary manipulated variable and a second controlled variable, wherein the second control loop (Ra) has a second time constant; wherein the auxiliary manipulated variable of the second control loop (Ra) represents the first reference variable of the first control loop (Ri), and the first time constant is smaller than the second time constant at least by a factor of 10, and wherein the first manipulated variable represents the duty factor of the output signal of the inverter (14). The invention furthermore relates to a method for starting a discharge lamp (20) using such a circuit arrangement.

Description

Circuit arrangement and method for igniting a discharge lamp

Technical area

The present invention relates to a circuit arrangement for igniting a discharge lamp with a drive device, at the output of which a drive signal having a predeterminable frequency can be provided, an inverter which is coupled to the output of the drive device and at the output of which a rectangular signal having a predeterminable duty cycle can be provided. a load circuit, which is coupled to the output of the inverter and has at least one connection for the discharge lamp, a first control loop having a first reference variable, a first control variable and a first controlled variable, wherein the first control loop has a first time constant, a second control loop with a second control variable, an auxiliary control variable and a second controlled variable, wherein the second control loop has a second time constant. It also relates to a method for igniting a discharge lamp on such a circuit arrangement.

State of the art

High and low pressure discharge lamps require high voltages for ignition, which are provided by electronic ballasts. As is well known, discharge lamps are used in a wide temperature range, for example, from -25 ° C to + 60 ° C. The problem here is that the inductance of the lamp inductor, which is usually arranged in the load circuit, is temperature-dependent. Thus, the maximum magnetic flux density and thus the inductance in the temperature range mentioned can vary by up to 20%. A particular problem is that the inductance decreases with an increase in temperature. Thus, the lamp choke goes earlier at higher temperatures in saturation. With the mentioned reduction of the inductance by 20%, the resonance Frequency of the load circuit, the resonance is exploited to the ignition, by about 10%. Therefore, if one approaches the resonance frequency of high frequencies, the resonance and thus the formation of high currents is achieved much earlier than at lower temperatures. This involves the risk of destruction of the switches of the inverter, which are in particular often realized as a MOSFET.

This problem was counteracted in the prior art by the fact that the saturation limit of the lamp inductor was chosen to be very high, so that even at high ambient temperatures, saturation could be reliably ruled out. This leads to the following undesirable disadvantages: On the one hand, a throttle which is generously dimensioned with regard to the saturation behavior requires a lot of space, since with constant winding losses in normal operation a larger throttle design must be used. This also increases the case size of the electronic ballast. Both measures significantly increase the cost of the electronic ballast.

On the other hand increases the power loss of the throttle or the electronic ballast in normal operation with the same throttle design, but higher saturation limit of the throttle. This results in the requirement of a larger housing design for the electronic ballast, so that it comes with respect to the thermal stress to no shortening of the life.

Presentation of the invention

The present invention is therefore based on the object, the above-mentioned circuit arrangement or the aforementioned method ren educate such that it can be realized with a lamp inductor, which is dimensioned significantly smaller than in the prior art. This object is achieved by a circuit arrangement having the features of claim 1 and by a method having the features of claim 11.

The present invention is firstly based on the recognition that in principle why the actual value U _ιs t of the lamp voltage U _L monitored and should be increased in small steps up to the intended maximum voltage. However, the present invention is based particularly on the insight that due to the saturation of the lamp inductor at high temperatures, a non-Lineahtät between the actual value U _ιst the voltage U _L of the lamp and the actual value l _ιst of the current I ₀ occurs through the choke. Due to this non-linearity, the monitoring of the voltage alone is not sufficient, but both variables must be monitored separately, since it is no longer possible to close from one to the other. However, since the current I _{0 increases} very rapidly when the inductance saturates, the slow determination of the lamp voltage U _L as a result of the measurement and control time constants is not fast enough to switch off the inverter switches. The latter is in one embodiment of the invention between 200 and 400 microseconds. If the switch-on time t _on of the square-wave signal driving the switch of the inverter is 3 to 10 μs, this also shows that the regulation of the lamp voltage U _L with the specified time constant is too slow. Assuming that the control should be so fast that can be switched off quickly enough with an exponential increase in the current I _D after saturation of the lamp inductor, one arrives at the idea according to the invention, the actual value l of the inductor _current I ₀ to regulate or monitor. The latter is possible in the exemplary embodiment with a time constant of 100 to 200 ns. Regulation of the actual _{value of} the inductor _current I ₀ alone does not take into account that at the same time the lamp voltage U _{L should be increased} stepwise up to a maximum value which lies in the range of the intended ignition voltage Uz. On the one hand, it is therefore _{necessary to} increase the actual value U t of the lamp voltage U _L ZU in order to reach the ignition voltage U _z at _any time, and at the same time to regulate the actual value l of the inductor _current I ₀ , in order to ensure that in the case of saturation. - A -

If the lamp choke does not generate undesirably high current values which could destroy the switches of the inverter.

The present invention solves this problem in a particularly skilful manner in that the two control circuits, ie the inherently slow control circuit for controlling the lamp voltage and the fast control circuit for controlling the inductor current I _D , are linked together. In particular, they are linked such that the auxiliary control variable of the second control loop represents the first command variable of the first control loop. If the second reference variable corresponds to the nominal value of the voltage across the discharge lamp, the second controlled variable corresponds to the actual value of the voltage across the discharge lamp, the first reference variable to the nominal value of the current through the inductor and the first controlled variable to the actual value of the current through the inductor, in other words the actual value of the lamp voltage is gradually increased (slower control circuit) and the resulting increase in the actual value l t of the inductor _current (fast control loop) is monitored.

As has been shown in realized embodiments, with this arrangement, a reliable control up to eight to ten times the saturation current of the lamp inductor is possible.

The present invention therefore makes it possible to generate a particularly constant ignition voltage independent of temperature influences. Another advantage is that stable voltages can be generated with this control regardless of the slope of the load circuit. In addition, the components, in particular the lamp choke, the MOSFETs of the inverter and the capacitors used in the circuit arrangement, during the ignition far less heavily loaded by the invention than in the prior art, whereby the life of the components increases. Furthermore, the lamp inductor can be dimensioned for low-loss loss. This means that a smaller throttling design can be used, which in turn leads to more space Cost saving contributes. The monitoring of the actual _{value of} the lamp voltage in accordance with the present invention also makes it possible to realize the capacitors in a smaller dimension and a smaller design, as a result of which high voltages can be avoided.

As an alternative to the presented embodiment, in which the second reference variable has met the desired value of the voltage across the discharge lamp and the second controlled variable the actual value of the voltage across the discharge lamp, it is of course readily possible, as a second reference variable, the desired value of the current through the inductor and to use the actual value of the current through the choke as second controlled variable.

The second reference variable preferably corresponds to the time average within a predefinable time period. In a preferred embodiment, this period is between 200 μs and 1 ms.

While the frequency is varied in the circuit arrangements known from the prior art in order to achieve the ignition voltage, the frequency preferably remains fixed in the circuit arrangement according to the invention. Thus, a frequency can be fixed, measures for varying the frequency can be omitted.

The first time constant is preferably 10 to 1000 ns, preferably 100 to 200 ns. The second time constant is preferably 10 to 1000 μs, preferably 200 to 400 μs. If one compares the on-time t _on of the inverter-driving signal, which is on the order of between 1 and 50 μs, preferably between 3 and 10 μs, it can be seen that the current regulation is much faster, the voltage regulation much slower. The frequency of the switch driving the inverter driving signal is preferably in between 30 kHz and 100 kHz. The first control loop is thus so fast that, when there is an exponential increase in the current I _D through the choke, after the saturation of the lamp inductor begins can be shut down quickly enough, even before the switches of the inverter critical current ranges occur.

As already mentioned, the first control loop and the second control loop each have a disturbance variable which primarily represents the ambient temperature.

Preferably, a circuit arrangement according to the invention further comprises an ignition detection device, which is designed to detect an ignition of the discharge lamp and after the detection of the ignition to switch the first and the second control loop from the ignition operation to the continuous operation.

Further preferred embodiments emerge from the subclaims.

The preferred embodiments described in the foregoing with reference to the circuit arrangement according to the invention and their advantages apply correspondingly, as far as applicable, to the method according to the invention.

Brief description of the drawing (s)

In the following, an embodiment of a circuit arrangement according to the invention will now be described in more detail with reference to the accompanying drawings. Show it:

1 is a schematic representation of the coupling of a first and a second control loop in a first embodiment of a circuit arrangement according to the invention;

2 is a schematic representation of the coupling of a first and a second control loop in a second embodiment of a circuit arrangement according to the invention; and 3 shows the signal flow graphs associated with the embodiment of FIG.

Preferred embodiment of the invention

Fig. 1 shows a schematic representation of the coupling of a first, inner R ₁ and a second, outer control loop R ₃ according to a first embodiment of a circuit arrangement according to the invention. Accordingly, the reference variable of the outer control loop R _{3 is} the desired value U _SO ιι the lamp voltage U _{L of} a discharge lamp, not shown. The feedback signal is formed by the actual value U _ιst the lamp voltage U _L, which simultaneously represents the controlled variable of the outer loop. The differ- ence .DELTA.U from the desired value U _S oiι and the actual value U _ιs t of the lamp voltage U _L represents the control error, which is fed to a block 10, which contains for averaging a I element (integrator), and a table or a conversion formula with which from the integral on the difference .DELTA.U a setpoint I soii of the inductor current I _D can be set. This serves as the control variable of the inner control loop. There, first the difference .DELTA.l to the actual value l _is the throttle _current I _{0 is} formed, which is fed to a block 12 to there via a formula or a lookup table a change .DELTA.t _on the turn-on and thus the duty cycle of the inverter 14, preferably as Half-bridge circuit is formed with two MOSFET transistors, signal to be supplied. The inverter 14 feeds the load circuit 16 and thereby generates the actual value l of the throttle _current I _D - the actual value l t is used via a feedback 18 as a feedback _{variable of} the inner control loop R ₁ . On the lamp 20, in particular the loading circuit that includes a resonance capacitor, the lamp voltage U _L is determined from the actual value _ιs l t of the inductor current I _D of the actual value U t _ιs formed. This serves as a feedback variable of the outer control loop R _a .

The time constant of the inner control loop R ₁ is between 10 and 1000 ns, preferably between 100 and 200 ns. The time constant of the external ren control circuit R ₃ is between 10 and 1000 microseconds, preferably between 200 and 400 microseconds.

Fig. 2 shows a schematic representation of a second embodiment of the invention with the coupling of a first control loop R ₁ and a second control loop R ₃ , wherein the introduced with reference to FIG. 1 reference numerals for the same and similar elements continue to apply and therefore will not be described again , In contrast to FIG. 1, however, in the present case the actual value l of the inductor _current I _{0 is} used as the controlled variable of the outer control circuit R ₃ . Correspondingly, the reference variable of the outer control loop is the desired value I _{SO of} the inductor current ID-. This variable is preferably determined at the resonant capacitor of the ignition circuit, which is part of the load circuit.

Fig. 3 shows the signal flow graphs associated with the embodiment of Fig. 1. After the start in step 100, the desired value Usoii is set to the starting value U _SO ιistart in step 1 10. In step 120 it is checked whether U _SO ιι is smaller than a maximum value U _ma χ the voltage U _L to the lamp. This is to ensure avoidance of damage to the circuit arrangement that the area in which the lamp usually ignites, will not leave. If U _S oiι via U _ma χ, this leads to the termination of the ignition process in step 130. If, however, U _SO ιι under LLax, in step 140 the difference .DELTA.U is formed from the current actual value U _ιs t of the lamp voltage U _L and the predetermined desired value U _SO ιι- This difference .DELTA.U is supplied to the block 10 and provides in step 150 the current Setpoint l _SO ιι for the inductor current I ₀ . In step 160 it is now checked whether the current value for l _so n is smaller than a maximum current value l _max . If this is not the case, in step 170, the ignition process is aborted. If l _so n is smaller l _max , the difference .DELTA.l from the setpoint 1 is _so n and the actual value l is _{formed of} the throttle _current I _D in step 175. In block 12, the value Δt _on , that is to say the time duration by which the switch-on duration of the switches of the inverter is to be increased, is determined in step 180 on the difference .DELTA.l. The current time t _on becomes then calculated in step 190. Subsequently, it is checked in step 200 whether the lamp has ignited. If this is the case, continuous operation is activated in step 210. If the check in step 200 shows that the lamp has not yet ignited, U _S oiι is increased by a predefinable increment ΔUsoii in step 220 and fed back to the input of step 120 as the current Usoii. From the control with the changed on-time t _on , a new actual value l of the inductor _current I _{D is} formed in step 230 via the load circuit, which is fed back in step 170. Via the high pressure discharge lamp 20 of the inductor current is from the actual value, an actual value I ₀ l _ιst U _ιst the lamp voltage U _L at the step 240 is formed.

In the exemplary embodiment illustrated in FIG. 3, the achievement or exceeding of a maximum value U _ma χ of the lamp voltage U _L and the reaching or exceeding of a maximum value l _ma χ of the inductor current I _{D were} specified as termination criteria. Additionally or alternatively, it could be provided that before a termination in step 130, the lamp is operated for a predefinable period of time at a maximum value U _ma χ the lamp voltage U _L and the abort is made only after exceeding a predeterminable period.

Claims

claims

1 . Circuit arrangement for igniting a discharge lamp (20)

- A drive device, at whose output a drive signal with a predetermined frequency can be provided;

- An inverter (14) which is coupled to the output of the Ansteuervorrich- device and at the output of a square wave signal with a predetermined duty cycle can be provided;

- A load circuit (16) which is coupled to the output of the inverter (14) and at least one terminal for the discharge lamp (20), wherein the load circuit comprises a lamp inductor connected in series between the output of the inverter (14) and the at least a terminal for the discharge lamp (20) is coupled;

- A first control loop (R ₁ ) having a first command variable, a first manipulated variable and a first controlled variable, wherein the first control loop (R ₁ ) has a first time constant; - A second control loop (R ₃ ) with a second command variable, one

Auxiliary control variable and a second controlled variable, wherein the second control loop (Ra) has a second time constant; and characterized in that the auxiliary control variable of the second control loop (R ₃ ) represents the first control variable of the first control loop (R ₁ ), wherein the first time constant is smaller by at least a factor of 10 than the second time constant, and wherein the first control variable the Duty cycle of the output signal of

Inverter (14) represents.

2. A circuit arrangement according to claim 1, characterized in that the first reference variable to the setpoint (l _SO ιι) of the current (ID) through the lamp inductor and the first controlled variable corresponds to the actual value (l _ιst ) of the current (ID) through the lamp inductor.

3. Circuit arrangement according to one of claims 1 or 2, characterized in that the second command variable the setpoint (l _SO ιι) of the current (ID) through the lamp inductor and the second controlled variable the actual value (l _ιs t) of the current (I ₀ ) through the lamp choke corresponds.

4. Circuit arrangement according to one of claims 1 or 2, characterized in that the second reference variable the setpoint (U _S oiι) of the voltage across the discharge lamp (20) and the second controlled variable the actual value (U _ιst ) of the voltage at the discharge lamp (20 ) corresponds.

5. Circuit arrangement according to one of claims 3 or 4, characterized in that the second reference variable corresponds to the time average within a predeterminable period.

6. Circuit arrangement according to one of the preceding claims, characterized in that the frequency is fixed.

7. Circuit arrangement according to one of the preceding claims, characterized in that the first time constant is 10 to 1000 ns, preferably 100 to 200 ns.

8. Circuit arrangement according to one of the preceding claims, characterized in that the second time constant is 10 to 1000 microseconds, preferably 200 to 400 microseconds

9. Circuit arrangement according to one of the preceding claims, characterized in that the first control circuit (R ₁ ) has a first disturbance and the second control circuit (Ra) has a second disturbance, which in each case represents the ambient temperature.

10. Circuit arrangement according to one of the preceding claims, characterized in that it further comprises an ignition detection device which is designed to detect an ignition of the discharge lamp (20) and after the detection of the ignition of the first (R ₁ ) and the second control circuit (R _3rd ) to switch from ignition operation to continuous operation.

1 1. A method for igniting a discharge lamp (20) on a circuit arrangement with a drive device which provides at its output a drive signal with a predeterminable frequency, an inverter (14) which is coupled to the output of the drive device and at its output a square wave signal with a specifiable

Duty cycle, a load circuit (16) which is coupled to the output of the inverter (14) and at least one terminal for the discharge lamp (20), wherein the load circuit (1 6) comprises a lamp inductor connected in series between the output of the inverter - Ters (14) and the at least one terminal for the discharge lamp

(20) is coupled to a first control loop (R ₁ ) having a first reference variable, a first control variable and a first controlled variable, the first control loop (R ₁ ) having a first time constant, a second control loop (Ra) having a second reference variable, an auxiliary control variable and a second controlled variable, wherein the second control circuit (R ₃ ) has a second

Has time constant; characterized by the following steps:

- Coupling of the first (R ₁ ) and the second control loop (R ₃ ) such that the auxiliary control variable of the second control loop (R ₃ ) represents the first Fuhr- rungsgröße of the first control loop (R ₁ ); - Setting the first time constant at least by a factor of 10 smaller than the second time constant;

- Using the duty cycle of the output signal of the inverter (14) as a first manipulated variable.