Device and method for providing power to gas discharge lamp

Abstract

A device (1) for providing an amount of power to a gas discharge lamp (2) comprises a control circuit (3) for controlling a supply circuit (4) for supplying the power according to a power versus voltage graph (10). A calculator (30) calculates a boundary voltage value as a function of a measured voltage value of a voltage signal that has been measured after a predefined time-interval from a cold start of the gas discharge lamp (2). A more accurate boundary voltage value results in more stability and in less time required to reach a steady state. The calculator (30) may be arranged for calculating the boundary voltage value as a function of a minimum voltage value of the voltage signal and of a steady state voltage value of the voltage signal. A memory (31) may store voltage values of the voltage signal and a processor (32) may update these voltage values.

Claims

1. A device for providing an amount of power to a gas discharge lamp, the device comprising: a control circuit for controlling a supply circuit for supplying the power to the gas discharge lamp, the control circuit configured to: from a cold start of the gas discharge lamp, supply a maximum current to the gas discharge lamp; when the power to the gas discharge lamp reaches a maximum amount of power, supply a decreasing current to maintain the power to the gas discharge lamp at the maximum amount of power; at a predefined time interval after the cold start of the gas discharge lamp, measure a non-steady state voltage value of a voltage signal across the gas discharge lamp; calculate a boundary voltage value as a function of the measured, non-steady-state voltage value of the voltage signal; and when the voltage signal reaches the boundary voltage value, supply an even more decreasing current to decrease the power to the gas discharge lamp.

2. The device as claimed in claim 1, wherein the control circuit comprises a calculator being arranged for calculating the boundary voltage value as a function of a minimum voltage value of the voltage signal and as a function of a steady state voltage value of the voltage signal.

3. The device as claimed in claim 2, the function of the measured, non-steady-state voltage value of the voltage signal comprising a first weighting factor, the function of the minimum voltage value of the voltage signal comprising a second weighting factor, and the function of the steady state voltage value of the voltage signal comprising a third weighting factor, a sum of the weighting factors being equal to a predefined value.

4. The device as claimed in claim 2, wherein the control circuit is further configured to, when the voltage signal reaches a steady state voltage value, supply a stable amount of power.

5. The device as claimed in claim 1, the control circuit comprising a memory for storing the measured, non-steady-state voltage value of the voltage signal and comprising a processor for updating the measured, non-steady-state voltage value stored in the memory.

6. The device as claimed in claim 1, wherein said predefined time-interval is not less than 2 seconds.

7. A method for providing an amount of power to a gas discharge lamp, the method comprising: from a cold start of the gas discharge lamp, supplying a maximum current to the gas discharge lamp; when the power to the gas discharge lamp reaches a maximum amount of power, supplying a decreasing current to maintain the power to the gas discharge lamp at the maximum amount of power; at a predefined time interval after the cold start of the gas discharge lamp, measuring a non-steady-state voltage value of a voltage signal across the gas discharge lamp; calculating the calculating a boundary voltage value as a function of the measured, non-steady-state voltage value of the voltage signal; and when the voltage signal reaches the boundary voltage value, supplying an even more decreasing current to decrease the power to the gas discharge lamp.

8. A computer program product, stored in a non-transitory computer readable medium, for performing the method as claimed in claim 7.

9. An electronic ballast for providing an amount of power to a gas discharge lamp, the ballast comprising: a supply circuit for supplying the power to the gas discharge lamp; a control circuit configured to: from a cold start of the gas discharge lamp, supply a maximum current to the gas discharge lamp; when the power to the gas discharge lamp reaches a maximum amount of power, supply a decreasing current to maintain the power to the gas discharge lamp at the maximum amount of power; at a predefined time interval after the cold start of the gas discharge lamp, measure a non-steady-state voltage value of a voltage signal across the gas discharge lamp; calculate a boundary voltage value as a function of the measured non-steady-state voltage value of the voltage signal; and when the voltage signal reaches the boundary voltage value, supply an even more decreasing current to decrease the power to the gas discharge lamp.

10. The ballast as claimed in claim 9, wherein the control circuit comprises a calculator arranged for calculating the boundary voltage value as a function of a minimum voltage value of the voltage signal and as a function of a steady state voltage value of the voltage signal.

11. The ballast as claimed in claim 9, wherein the control circuit comprises: a memory for storing the measured, non-steady-state voltage value of the voltage signal; and a processor for updating the measured, non-steady-state voltage value stored in the memory.

12. The ballast as claimed in claim 9, further comprising a memory for storing the measured, non-steady-state voltage value, wherein the control circuit and the memory are hardware units.

13. The ballast as claimed in claim 9, further comprising a memory for storing the measured, non-steady-state voltage value, wherein the control circuit and the memory are software units.

14. The method as claimed in claim 7, further comprising: comparing the measured, non-steady-state voltage value with a previous voltage value stored in a memory; replacing the previous voltage value stored in memory with the measured, non-steady-state voltage value.

15. The method as claimed in claim 7, further comprising calculating the amount of power to the gas discharge lamp by: presenting the measured voltage value U; presenting the calculated boundary voltage value U.sub.b; presenting a steady state voltage value U.sub.stst; determining a normalized voltage value U.sub.norm=(UU.sub.stst)/(U.sub.bU.sub.stst); and calculating a polynomial based on the normalized voltage value, the calculated polynomial corresponding to the power to the gas discharge lamp.

16. The method as claimed in claim 15, further comprising: defining a maximum power and a minimum power; and comparing the calculated polynomial to the maximum power and minimum power.

17. The method as claimed in claim 16, further comprising: providing the power corresponding to the calculated polynomial to the gas discharge lamp when the power corresponding to the calculated polynomial is between the maximum power and the minimum power; providing the minimum power to the gas discharge lamp when the power corresponding to the calculated polynomial is less than the minimum power; and providing the maximum power to the gas discharge lamp when the power corresponding to the calculated polynomial is more than the maximum power.

18. The method as claimed in claim 7, further comprising: storing in a memory the measured, non-steady-state voltage value; storing in the memory a minimum voltage value; and storing in the memory a steady state voltage value.

19. The method as claimed in claim 18, wherein calculating the boundary voltage value is based on one or more of the values stored in the memory.

20. The device of claim 1, wherein the pre-defined time interval is between two and ten seconds.

21. The device of claim 1, wherein the boundary voltage value is a turning point voltage value at which a bulb voltage starts rising after switching on the gas discharge lamp.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 shows a power versus voltage graph,

(3) FIG. 2 shows a system comprising a device,

(4) FIG. 3 shows a control circuit,

(5) FIG. 4 shows a power defining algorithm,

(6) FIG. 5 shows a boundary voltage as a function of a timed voltage,

(7) FIG. 6 shows a voltage as a function of a time for FIG. 5,

(8) FIG. 7 shows a boundary voltage as a function of a minimum voltage,

(9) FIG. 8 shows a voltage as a function of a time for FIG. 7,

(10) FIG. 9 shows a boundary voltage as a function of a steady state voltage,

(11) FIG. 10 shows a voltage as a function of a time for FIG. 9, and

(12) FIG. 11 shows a measured boundary voltage versus a calculated boundary voltage.

DETAILED DESCRIPTION OF EMBODIMENTS

(13) In the FIG. 1, a power versus voltage graph 10 of a gas discharge lamp is shown. The power versus voltage graph 10 defines a first state 11 for supplying a first amount of power. The power versus voltage graph 10 defines a second state 12 for supplying a second amount of power. The first state 11 ends at a boundary voltage value U.sub.b of a voltage signal and the second state 12 starts at the boundary voltage value U.sub.b. The first amount of power comprises an increasing amount of power during a first part of the first state 11 while supplying a maximum current I.sub.max to the gas discharge lamp. The first amount of power comprises a maximum amount of power P.sub.max during a second part of the first state 11. The second amount of power comprises a decreasing amount of power until a steady state voltage value U.sub.stst of the voltage signal has been reached. The power versus voltage graph 10 defines a third state 13 for supplying a third amount of power. The third state 13 starts at the steady state voltage value U.sub.stst. The third amount of power comprises a stable amount of power.

(14) In the FIG. 2, a system 6 is shown comprising a device 1. The system 6 further comprises a gas discharge lamp 2 connected to a supply circuit 4 for supplying an amount of power according to the power versus voltage graph 10 shown in the FIG. 1. Thereto, the supply circuit 4 supplies for example a current signal to the gas discharge lamp 2, which current signal results in a voltage signal across the gas discharge lamp 2. A combination of these current and voltage signals defines an amount of power. The supply circuit 4 is for example connected to a rectifier 5 for rectifying a mains voltage. Alternatively, a battery may be used. The device 1 comprises a control circuit 3 connected to the gas discharge lamp 2 (in parallel to the supply circuit 4) and for example connected to the rectifier 5 (in parallel to the supply circuit 4). A control output of the control circuit 3 is connected to a control input of the supply circuit 4. Between the gas discharge lamp 2 and the supply circuit 4, or in/near the gas discharge lamp 2, or in/near the supply circuit 4, an ignition circuit may be present (not shown).

(15) In the FIG. 3, the control circuit 3 is shown in greater detail. The control circuit 3 comprises a calculator 30 for calculating the boundary voltage value U.sub.b as a function of a measured voltage value U.sub.T of the voltage signal that has been measured after a predefined time-interval from a cold start of the gas discharge lamp 2. According to an option, the calculator 30 may further calculate the boundary voltage value U.sub.b as a function of a minimum voltage value U.sub.min of the voltage signal and as a function of a steady state voltage value U.sub.stst of the voltage signal. According to a further option, the function of the measured voltage value U.sub.T of the voltage signal comprising a first weighting factor A, the function of the minimum voltage value U.sub.min of the voltage signal comprising a second weighting factor B, and the function of the steady state voltage value U.sub.stst of the voltage signal comprising a third weighting factor C, a sum of the weighting factors being equal to a predefined value (A+B+C=D, D is for example equal to 1, without having excluded other predefined values).

(16) An output of the calculator 30 constitutes the control output of the control circuit 3 and an input of the calculator 30 is for example connected to a processor 32. The processor 32 is connected to a memory 31 and is for example connected to a voltage determining circuit 33 and a feeding circuit 34. The feeding circuit 34 for example feeds the calculator 30, the memory 31, the processor 32 and the voltage determining circuit 33. The voltage determining circuit 33 determines the measured voltage value U.sub.T of the voltage signal by for example measuring this voltage value after a predefined time-interval from a cold start of the gas discharge lamp 2 in response to an instruction from the processor 32. The voltage determining circuit 33 may further determine other voltage values of the voltage signal by for example measuring these voltage values and supplying the measured voltage values to the processor 32 to for example find the minimum voltage value U.sub.min of the voltage signal and the steady state voltage value U.sub.stst of the voltage signal by for example comparing the measured voltage values with each other. The processor 32 may thereto comprise an analog comparator or comparing function, alternatively this analog comparator or comparing function may be located inside the voltage determining circuit 33 etc. Alternatively, the voltage determining circuit 33 may comprise an analog to digital converter, and the processor 32 may then comprise a digital comparator or comparing function, alternatively this digital comparator or comparing function may be located inside the voltage determining circuit 33 etc. The calculator 30 may form part of the processor 32, or vice versa.

(17) The memory 31 stores the measured voltage value U.sub.T of the voltage signal and the processor 32 updates the measured voltage value U.sub.T stored in the memory 31. The memory 31 may further store the minimum voltage value U.sub.min of the voltage signal and the steady state voltage value U.sub.stst of the voltage signal and the processor 32 may further update these voltage values stored in the memory 31. After a start of the gas discharge lamp 2, one or more stored values may be used to calculate the boundary voltage value U.sub.b, and one or more recent values may be used for updating the stored values.

(18) The units 30-33 may be hardware units and/or software units and may form part of a computer or a microcontroller or analog and/or digital control circuitry etc.

(19) In the FIG. 4, a power defining algorithm is shown. At a block 40, a measured voltage value U is presented. At a block 41, a (calculated) boundary voltage value U.sub.b is presented. At a block 42, a (measured) steady state voltage value U.sub.stst is presented. At blocks 43 and 44 differences are determined, and at a block 45 a division is made such that at the output of the block 45 a normalized voltage value U.sub.norm is available:

(20) U.sub.norm=(UU.sub.stst)/(U.sub.bU.sub.stst). Other ways to normalize the voltage are not to be excluded. This normalized voltage value U.sub.norm is offered to a block 46 that for example calculates a polynomial 15 x.sup.3+13 x.sup.2+7 x+35 or any other kind of polynomial. At blocks 47 and 48, a maximum power P.sub.max and a minimum power P.sub.min are defined, and at a block 49, the information from the blocks 46, 47 and 48 is converted into an output power defined at a block 50 and to be provided to the gas discharge lamp 2. Thereby, according to an embodiment, as long as the calculated polynomial has a value between the maximum power P.sub.max and the minimum power P.sub.min this value is offered, if said value is larger than the maximum power P.sub.max, this maximum power P.sub.max is offered, and if said value is smaller than the minimum power P.sub.min, this minimum power P.sub.min is offered.

(21) In the FIG. 5, a boundary voltage U.sub.b (V) as a function of the measured voltage U.sub.T (V) is shown. The measured voltage value U.sub.T of the voltage signal is to be measured after a predefined time-interval T from a cold start of the gas discharge lamp 2. The FIG. 6 shows a voltage U (V) as a function of a time t (s) for the FIG. 5. Clearly, after having measured U.sub.T, U.sub.b can be calculated.

(22) In the FIG. 7, a boundary voltage U.sub.b (V) as a function of a minimum voltage U.sub.min (V) is shown. The FIG. 8 shows a voltage U (V) as a function of a time t (s) for the FIG. 7. Clearly, after having determined U.sub.min, U.sub.b can be calculated.

(23) In the FIG. 9, a boundary voltage U.sub.b (V) as a function of a steady state voltage U.sub.stst (V) is shown. The FIG. 10 shows a voltage U (V) as a function of a time t (s) for the FIG. 9. Clearly, after having determined U.sub.stst, U.sub.b can be calculated.

(24) In the FIG. 11, a measured boundary voltage U.sub.b,m (V) versus a calculated boundary voltage U.sub.b,c (V) is shown.

(25) A possible algorithm might be as follows. After the predefined time-interval T, such as for example five, six or seven seconds for a particular kind of gas discharge lamp 2, or such as for example for a more general kind of lamp any time value between two and ten seconds, the voltage value U.sub.T of the voltage signal is to be measured. This measured voltage value U.sub.T of the voltage signal is to be compared with a previous voltage value U.sub.T stored in the memory 31. In response to a first comparison result (non-cold start) the previous voltage value U.sub.T stored in the memory 31 is to be replaced by the measured voltage value U.sub.T of the voltage signal. In response to a different second comparison result (cold start) the previous voltage value U.sub.T stored in the memory 31 is to be replaced by a new voltage value U.sub.T depending on for example the measured voltage value U.sub.T of the voltage signal and one or more, such as for example 20, previously stored voltage values U.sub.T.

(26) After another predefined time-interval, such as for example 120 seconds for a particular kind of gas discharge lamp 2, the steady state voltage value U.sub.stst of the voltage signal is to be measured. This steady state voltage value U.sub.stst of the voltage signal is to be compared with a previous steady state voltage value U.sub.stst stored in the memory 31. In response to a first comparison result the previous steady state voltage value U.sub.stst stored in the memory 31 is to be replaced by the measured steady state voltage value U.sub.stst of the voltage signal. In response to a different second comparison result the previous steady state voltage value U.sub.stst stored in the memory 31 is to be replaced by a new steady state voltage value U.sub.stst depending on for example the measured steady state voltage value U.sub.stst of the voltage signal and one or more previously stored steady state voltage values U.sub.stst. With the updated voltage values, a new boundary voltage value U.sub.b is to be calculated, and the new boundary voltage value U.sub.b and the new steady state voltage value U.sub.stst can be used for a next calculation of the amount of power to be provided etc.

(27) Of course, in addition, after having measured/determined one of the voltage values U.sub.T and U.sub.stst, a measurement/determination result can be used for updating the (calculated) other one.

(28) After a cold start of an existing particular gas discharge lamp 2, U.sub.T and U.sub.stst can be updated. After a non-cold start of the existing particular gas discharge lamp 2, U.sub.T can be kept as it is and U.sub.stst can be updated. After a cold start of a novel particular gas discharge lamp 2, U.sub.T and U.sub.stst are to be determined. After a non-cold start of the novel particular gas discharge lamp 2, U.sub.T can be kept as it is and U.sub.stst can be updated.

(29) Summarizing, a device 1 for providing an amount of power to a gas discharge lamp 2 comprises a control circuit 3 for controlling a supply circuit 4 for supplying the power according to a power versus voltage graph 10. A calculator 30 calculates a boundary voltage value as a function of a measured voltage value of a voltage signal that has been measured after a predefined time-interval from a cold start of the gas discharge lamp 2. A more accurate boundary voltage value results in more accuracy and in less time required to reach a steady state. The calculator 30 may be arranged for calculating the boundary voltage value as a function of a minimum voltage value of the voltage signal and of a steady state voltage value of the voltage signal. A memory 31 may store voltage values of the voltage signal and a processor 32 may update these voltage values.

(30) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. For example, it is possible to operate the invention in an embodiment wherein different parts of the different disclosed embodiments are combined into a new embodiment.

(31) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.