WO2009109224A1

WO2009109224A1 - Circuit arrangement for starting and operating a gas discharge lamp

Info

Publication number: WO2009109224A1
Application number: PCT/EP2008/052651
Authority: WO
Inventors: Franz Maier
Original assignee: Osram Gesellschaft mit beschränkter Haftung
Priority date: 2008-03-05
Filing date: 2008-03-05
Publication date: 2009-09-11

Abstract

The invention relates to a circuit arrangement for starting and operating a gas discharge lamp, comprising a converter without control loop, the power output thereof depending on its input voltage, and the converter being controlled by means of an auxiliary voltage. Said auxiliary voltage (U_H) is produced depending on the input voltage (U_B) of the converter in such a manner that the input voltage dependency of the converter is substantially reduced. The invention further relates to a method for operating gas discharge lamps that have an output independent of the input voltage, an auxiliary voltage (U_H) depending on the input voltage (U_B) being produced and compensating the input voltage dependency of a used converter with respect to its power output.

Description

Confession

[1] Circuit arrangement for starting and operating a gas discharge lamp.

Technical area

The invention relates to a circuit arrangement for starting and operating a gas discharge lamp with a converter which has no control loop for power adjustment, and whose output depends on its input voltage.

State of the art

FIG. 1 shows a schematic block diagram of a circuit arrangement for starting and operating a gas discharge lamp according to the prior art. A control circuit 5 is provided with a switching input, so that the circuit arrangement can be activated by means of an activation switch 6. The control circuit controls a voltage-controlled oscillator 7 and a switching transistor 17. The voltage-controlled oscillator 7 outputs a signal which generates in a pulse shaping unit 9 in cooperation with the switch 17 for the deactivation or generation of the ignition assisting break phase, a pulse signal which then in the converter circuit 11 is input. This converts the low input DC voltage into a high pulse voltage to operate the lamp. The circuit parts are supplied by a static auxiliary power supply, which provides a steady DC voltage. The power output of the converter circuit 11 is heavily dependent on the input voltage here due to their topology.

task [4] It is an object of the invention to develop a circuit arrangement for starting and operating a gas discharge lamp with a converter without a control loop, the output power of which depends on its input voltage, so that the input voltage dependence of the converter is significantly reduced.

It is a further object of the invention to provide a method for operating a gas discharge lamp, when used in an operating device, the light intensity of the gas discharge lamp is largely independent of the input voltage of the operating device.

Presentation of the invention

[6] The object is achieved in that the converter is controlled by means of an auxiliary voltage, and the auxiliary voltage is generated in response to the input voltage of the converter, that the input voltage dependence of the converter is significantly reduced.

[7] The object is further achieved by a method for operating gas discharge lamps with power independent of the input voltage, wherein an auxiliary voltage dependent on the input voltage is generated, which significantly reduces the power dependence of a used circuit arrangement on its input voltage.

[8] The auxiliary voltage preferably has a linear dependence on the supply voltage. This offers the advantage of simple and inexpensive auxiliary voltage generation. [9] The gas discharge lamp is operated by a dielectrically impeded discharge. These lamps require a pulsed mode of operation with relatively high voltages, thus the circuit arrangement according to the invention is particularly suitable for these lamps.

[10] A start sequence is preferably used to start the lamp. A start sequence is a specified voltage and current train applied thereto for the purpose of starting the gas discharge lamp. The start sequence injects a lot of power into the lamp immediately after switching it on. This is followed by a pause, in which the power supply is turned off. Then a very small power is coupled into the lamp, which is gradually increased slowly up to the rated power. After the start sequence and successful start of the lamp, the auxiliary power supply is then changed so that the power to the lamp is substantially independent of the input voltage.

[11] The lamp is coupled to a transformer, which is provided in the output part of the converter. The converter is constructed so that it emits a pulse-shaped voltage, the duty cycle is pulse to break in nominal operation about 1 to 4. In the following, a mode of operation in which the lamp is operated at its nominal power in the steady state is regarded as rated operation.

Short description of the drawing (s)

[12] The invention will be explained in more detail below with reference to exemplary embodiments. Show it: - A -

[13] FIG. 1 A schematic block diagram of the circuit arrangement according to the invention.

[14] Fig. 2 A graph of a required dependence of the auxiliary voltage on the input voltage and a simplified real voltage dependence of the auxiliary voltage on the input voltage.

FIG. 3 A graph illustrating a dependence of the output power on the input voltage of a prior art converter and a converter according to the invention.

[16] FIG. 4 Circuit diagram of a preferred embodiment of the auxiliary voltage generation according to the invention.

[17] Fig. 5 A schematic block diagram of a

Circuit arrangement according to the prior art.

Preferred embodiment of the invention

FIG. 5 shows a schematic block diagram of a circuit arrangement according to the prior art. This is similar to the block diagram according to the invention in Fig. Ia, with the difference that instead of the constant auxiliary power supply 3, a static power supply 4 is used, which outputs a controlled independent of the input voltage regulated auxiliary voltage. This leads to the above-mentioned dependence of the lamp power of the input voltage U _B and thus to a dependent on the input voltage light output of a gas discharge lamp 50th [19] FIG. 1a shows a schematic block diagram of a preferred embodiment of the circuit arrangement according to the invention. The circuit is set by a switch 6 in operation. The switch causes an activation signal to the control circuit 5. The control circuit 5 then activates a voltage-controlled oscillator 7, the control voltage is generated by an auxiliary power supply 3. The auxiliary voltage supply 3 provides an auxiliary voltage U _H , which is dependent on the input voltage U _B. The voltage-controlled oscillator 7 outputs a signal having a duty factor of substantially 50%, with a frequency which is dependent on the magnitude of the control voltage, in this case the auxiliary voltage U _H. This signal is input to a pulse shaping unit 9, which forms a pulse signal therefrom. The ratio of pulse to pulse pause in nominal operation is approximately 1: 4. This signal in turn serves as an input signal for a driver stage 11 of a converter 10. The converter is preferably a class E converter, which has a transformer 15 and a switching element 13. The transformer 15 is embodied here as an autotransformer with a primary winding 15a and two secondary windings 15b and 15c. The first end of the primary winding 15 a is connected to the power supply, the second end is connected to the switch 13, which in turn is connected to its other end to ground. The first end of the primary winding 15 a is also connected to the first end of the first secondary winding 15 b, the other end of which is connected to a gas discharge lamp 50. The other end of the primary winding 15a is connected to the first end of the second secondary winding 15c, whose other end is connected to the gas discharge lamp 50. The power delivered to the load, in this case the gas discharge lamp 50, of the Class E converter depends on the one hand on the input voltage U _B, on the other hand on the frequency and the pulse / pause ratio of the class E converter, as shown below:

[20] At a constant pulse / pause ratio, the transformer is always energized per period for a constant time t ₀ N and absorbs the energy W ₀ N.

[21] W _0N = ¹ ^ * L * I _max ² ; In this case, L is the primary inductance of the transformer on winding a, that is to say the winding 15a.

[22] According to the law of induction, L:

[23] u _L = L * di / dt

[24] The voltage U _L at L is constant during t _0N and has the value U _B. The current i through L therefore increases linearly from zero to the value I _max . It follows:

[25] I _max = t _ON * U _B / L

[26] Thus W _0N = ¹ ^ L * (t _ON * U _B / L) ² = ^ t _ON ² * U _B / L

[27] For the average power P _ΣN applies: PIN = _O W N / T, where T = t N + t ₀ ₀ FF (t ₀ FF is in this case a kon ^¬ stante off).

[28] Thus: P _1N = (t _ON ² * U _B ) / (2 * L * T) = (Tt _0FF ) ² * U _B / (2 * L * T)

From this equation it can be seen that the

Power consumption at constant t ₀ N and T and L depends only on U _B. But it is also clear that the output power of the converter also strongly depends on the switch-on time t ₀ N.

[30] In order to minimize the dependence on the input voltage U _B , the auxiliary voltage supply 3 generates an auxiliary voltage U _H , which preferably has a linear dependence on the input voltage U _B. Characterized the frequency of the voltage controlled oscillator at modified input voltage U _B changes 7. The pulse shaping unit 9 generates from the signal of the voltage controlled oscillator 7, a drive signal for the converter 10, the ON time is identical to the period of the output signal of the voltage controlled oscillator 7 minus a constant switch-off time , The turn-off time in the present embodiment is about 2 μs. The switch-on time which the voltage-controlled oscillator 7 generates is dimensioned such that a power fluctuation at the converter, which occurs due to a variable input voltage U _B , is approximately compensated by the different switch-on time of the converter switching element 13. As can be seen clearly in the figure, this is done without a complex and expensive feedback with a control loop. The auxiliary voltage supply is rather dimensioned so that a forward control takes place, which keeps the power constant by suitable parameterization.

[31] FIG. 1b shows a start-up sequence 39, which is preferably used to start the lamp. In the graph, the control voltage VCO-IN of the voltage controlled oscillator is plotted against time. A small input voltage results in a large lamp power. At the beginning of the start sequence before the time point ti is coupled into the lamp a lot of power directly after switching on (the input voltage is very low). This is followed by a pause between the times ti and t ₂ , in which the power supply by means of the switch 17 is turned off. After the time t ₂ , a very small power is coupled into the lamp (the input voltage is high), which is successively increased slowly up to the rated power. By means of this start sequence, a gas discharge lamp with dielectrically impeded discharge used in the present exemplary embodiment can be started safely and reproducibly. The starting sequence 39 is thereby changed by the auxiliary voltage supply 3 from the time t ₂ so that the power to the lamp is substantially independent of the input voltage U _B. This is achieved by multiplying the entire curve shape with respect to the Y axis. In the case of the circuit arrangement according to the invention, this happens quite automatically, since the maximum of the curve shape of the start sequence 39 is generated from the auxiliary voltage U _H , and when the auxiliary voltage U _{H changes,} the entire curve shape changes proportionally.

FIG. 2 shows in a graph the required dependence of the auxiliary voltage on the input voltage (curve 31) and the simplified real voltage dependency of the auxiliary voltage on the input voltage (line 33). Since the required dependency 31 shows only a small nonlinearity, it can be replaced by a linear dependency 33 without implementing a larger control error.

[33] This linear dependence 33 can be achieved by a simple circuit arrangement, as shown, for example, in FIG. is is to be generated. The circuit arrangement consists of a first voltage divider 21, which generates a constant reference voltage U _Re f with a zener diode 23 which can be adjusted in this way. The resistor 24 is the load resistor of the adjustable Zener diode 23. This reference voltage U _Re f is now subtracted from the operating voltage U _B and the result U _B - U _Re f is input to the positive input of an operational amplifier 25 whose output voltage via a decoupling resistance 26 is guided. The voltage present behind the decoupling resistor 26 is then provided as an auxiliary voltage U _H. The auxiliary voltage U _H is routed via a second voltage divider 27 to the resistors R1 and R2 and input to the negative input of the operational amplifier. About this voltage divider 27, the voltage gain of the operational amplifier is set. The voltage gain is calculated as V = 1H--. The auxiliary voltage is calculated as U _H = v * (U _B -

[34] Fig. 3 is a graph showing the dependence of the lamp power P _L on the input voltage of a prior art transducer (curve 37) and a transducer according to the invention (trace 35). Both curves intersect at the nominal point of the input voltage U _B. It can clearly be seen that the circuit arrangement according to the invention shows a far smaller dependence of the lamp power P _L on the input voltage U _B. Reference sign list

3 Auxiliary voltage supply according to the invention with analog characteristic, depending on U _B

4 Static auxiliary power supply according to the prior art, independent of U _B

5 control circuit

6 activation switch

7 voltage-controlled oscillator 9 pulse shaping unit 10 converter circuit

11 driver level

13 transformer switch

15 converter transformer

17 Start sequence switch 21 Voltage divider for generating U _Ref

23 Adjustable reference diode

24 load resistor for the reference diode

25 operational amplifiers

26 Uncoupling resistor 27 Voltage divider for setting the gain 31 Uv should be 33 U _H

35 Lamp power in the circuit arrangement according to the invention 37 Lamp power in a circuit arrangement according to the prior art 39 Start sequence 50 gas discharge lamp

Claims

claims

1. Circuit arrangement for starting and operating a gas discharge lamp (50) with a converter (10) without a control loop whose output power (P _L ) depends on its input voltage (U _B ), characterized in that an auxiliary voltage (U _H ), the is dependent on the input voltage (U _B ), controls the transducer (10) in a manner that significantly reduces its input voltage dependence.

2. Circuit arrangement according to claim 1, characterized in that the auxiliary voltage (U _H ) has a linear dependence on the input voltage (U _B ).

3. Circuit arrangement according to claim 1 or 2, character- ized in that the gas discharge lamp

(50) is operated with a dielectrically impeded discharge.

4. Circuit arrangement according to one of the preceding claims, characterized in that it comprises the gas discharge lamp (50) by means of a start sequence

(39) starts.

5. Circuit arrangement according to one of the preceding claims, characterized in that the transducer (10) is a class E converter.

6. Circuit arrangement according to one of the preceding claims, characterized in that the transducer (10) emits a pulse-shaped voltage.

7. Circuit arrangement according to one of the preceding claims, characterized in that the duty cycle pulse to break at rated operation is about 1 to 4.

8. Circuit arrangement according to claim 6 or 7, characterized in that a power adjustment over the pulse length is accomplished while the pulse interval is constant.

9. Circuit arrangement according to claim 8, characterized in that the pulse length is adjusted by means of the frequency of a voltage-controlled oscillator (7).

10. Circuit arrangement according to claim 9, characterized in that a control voltage of the voltage-controlled oscillator (7) is proportional to the auxiliary voltage (U _H ).

11. A method for operating gas discharge lamps (50) with independent of the input voltage power, characterized in that one of the input voltage (U _B ) dependent auxiliary voltage (U _H ) is generated, the input voltage dependence of a transducer used (19) with respect its power output is significantly reduced.