IGNITOR-ARRANGEMENT

Abstract

The invention describes an ignitor arrangement (1) for a high-intensity discharge lamp (2), which ignitor arrangement (1) comprises a first pair of input terminals (101, 102) for applying an ignition voltage to the ignitor arrangement (1); a second pair of input terminals (101, 103) for applying an input drive voltage to the ignitor arrangement (1); and a discharge resistor (10) arranged in the interior (100) of the ignitor arrangement (1) and connected across the first input terminal pair (101, 102), which discharge resistor (10) is realised as a temperature-dependent resistor (10). The invention also describes a lamp driver (3) realised to drive a high-intensity discharge lamp (2); a lighting arrangement (4); and a method of driving a high-intensity discharge lamp (2).

Claims

1.-15. (canceled)

16. An ignitor arrangement for a high-intensity discharge lamp, which ignitor arrangement comprises a first pair of input terminals for applying an ignition voltage to the ignitor arrangement; a second pair of input terminals for applying an input drive voltage to the ignitor arrangement; and a discharge resistor arranged in the interior of the ignitor arrangement and connected across the first input terminal pair, characterized in that the discharge resistor is realised as a temperature-dependent resistor, and in that a resistance of the discharge resistor relates to a temperature (T.sub.100) in the interior of the ignitor arrangement.

17. The ignitor arrangement according to claim 16, wherein the temperature-dependent discharge resistor comprises any of: a negative temperature coefficient thermistor; a positive temperature coefficient thermistor; a silistor.

18. The ignitor arrangement according to claim 16, wherein the temperature-dependent discharge resistor is chosen on the basis of a temperature in the ignitor interior at a nominal lamp power.

19. The ignitor arrangement according to claim 16, comprising a housing realised to incorporate electrical components of an ignitor circuit, and wherein the housing comprises a lamp interface for connecting to the high-intensity discharge lamp, and a driver interface for connecting the input terminals to a lamp driver.

20. A lamp driver realised to drive the high-intensity discharge lamp via the ignitor arrangement of claim 16, the lamp driver comprising ignition circuitry realised to apply the ignition voltage across the first pair of input terminals of the ignitor arrangement; drive circuitry realised to apply the input drive voltage across the second pair of input terminals of the ignitor arrangement; a temperature evaluation unit realised to determine the temperature (T.sub.100) in the interior of the ignitor arrangement; and a control unit for regulating an operating power of the high-intensity discharge lamp on basis of the temperature (T.sub.100) in the interior of the ignitor arrangement.

21. The lamp driver according to claim 20, wherein the temperature evaluation unit is realised to measure a current (I.sub.10) through the temperature-dependent discharge resistor of the ignitor arrangement and to determine the temperature (T.sub.100) in the interior of the ignitor arrangement on basis of the measured current (I.sub.10).

22. The lamp driver according to claim 20, wherein the temperature evaluation unit is realised to measure a voltage (V.sub.10) across the temperature-dependent discharge resistor of the ignitor arrangement and to determine the temperature (T.sub.100) in the interior of the ignitor arrangement on basis of the measured voltage (V.sub.10).

23. The lamp driver according to claim 20, wherein the control unit is realised to continuously monitor the temperature (T.sub.100) in the interior of the ignitor arrangement.

24. A lighting arrangement comprising the ignitor arrangement according to claim 16, arranged in a housing; and the high-intensity discharge lamp mounted onto the housing.

25. A method of driving the high-intensity discharge lamp via the ignitor arrangement of claim 16, which method comprises the steps of connecting the high-intensity discharge lamp to the ignitor arrangement; applying the ignition voltage across the first pair of input terminals of the ignitor arrangement in order to ignite the high-intensity discharge lamp; applying, after ignition, the input drive voltage across the second pair of input terminals of the ignitor arrangement; determining the temperature (T.sub.100) in the interior of the ignitor arrangement on basis of an altered resistance of the temperature-dependent discharge resistor across the first pair of input terminals of the ignitor arrangement; and regulating an operating power of the high-intensity discharge lamp on basis of the temperature (T.sub.100) in the interior of the ignitor arrangement.

26. The method according to claim 25, comprising a step of measuring a current (I.sub.10) through the temperature-dependent discharge resistor of the ignitor arrangement during a steady-state operation of the high-intensity discharge lamp.

27. The method according to claim 25, comprising a step of measuring a voltage (V.sub.10) across the temperature-dependent discharge resistor of the ignitor arrangement during a steady-state operation of the high-intensity discharge lamp.

28. The method according to claim 25, wherein the input drive voltage comprises a low-frequency square-wave voltage, and the step of determining the temperature (T.sub.100) in the interior of the ignitor arrangement is performed during one half cycle of the input drive voltage.

29. The method according to claim 25, wherein the step of regulating the operating power is performed such that the temperature (T.sub.100) in the interior of the ignitor arrangement is maintained below an upper temperature limit (T.sub.max).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 shows an embodiment of a lighting arrangement according to the invention;

[0027] FIG. 2 shows an embodiment of a lamp driver according to the invention;

[0028] FIG. 3 shows a first embodiment of a temperature evaluation unit in the lamp driver of FIG. 2;

[0029] FIG. 4 shows a second embodiment of a temperature evaluation unit in the lamp driver of FIG. 2;

[0030] FIG. 5 shows graphs of ignitor temperature vs. lamp power for different ambient temperatures;

[0031] FIG. 6 shows a prior art arrangement with a lamp driver and a lighting arrangement incorporating an asymmetrical ignitor.

[0032] In the drawings, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] FIG. 1 shows an embodiment of a lighting arrangement 4 according to the invention, with a HID lamp burner 2 mounted to and electrically connected to an ignitor arrangement 1 according to the invention. The ignitor arrangement 1 is realised as an asymmetrical automotive ignitor 1, and the lamp 2 can be a HID burner 2 for a front lighting application. The lighting arrangement 4 can be realised, for example, as a D1 or D3 application. The ignitor arrangement 1 has a pair of input terminals 101, 102 to which an ignition voltage is applied (by a lamp driver, not shown here), and another pair of input terminals 101, 103 to which a drive voltage is applied. A first terminal 101 is shared, and an ignition terminal 102 is only required during ignition of the lamp 2. A HID lamp requires a brief intense voltage pulse to establish a discharge arc between the electrode tips, which face each other across a short gap in the discharge vessel 20 of the burner 2. The ignitor arrangement 1 comprises various electrical components to generate such a brief intense pulse to the lamp 2, which is connected by means of its electrode leads 200, 201 to the ignitor arrangement. Here, the components comprise a transformer 12, a spark gap 13, an ignition capacitor 11, and a discharge resistor 10. An ignition voltage is initially applied across the shared and ignition terminals 101, 102. Voltage builds up across the ignition capacitor 11, and therefore across the spark gap 13, until the voltage has reached a level which causes a breakdown across the spark gap 13. As soon as current flows (even if only briefly) through the primary winding of the transformer 12 and across the spark gap 13, current also flows through the secondary winding of the transformer 12, so that a high voltage ignition pulse appears across the electrodes of the lamp 2, and a discharge arc is established. At this point, the ignition terminal 102 is no longer required, the spark gap is once again non-conductive, and the ignition capacitor 11 can discharge through the discharge resistor 10 if the ignitor 1 is disconnected from the lamp driver. The diagram also shows a clipping diode arrangement 14 which serves to clip high voltage pulses between the second pair of input terminals to protect the lamp driver.

[0034] The components of the ignitor arrangement 1 are generally enclosed in a compact housing to which the lamp 2 is mounted. The burner of a Xenon HID lamp can easily reach temperatures in the range of 700 C. during operation at rated power, and this temperature can increase further when the lamp is driven above rated power (for example if more light is desired in a certain driving situation). Since the burner 20 is in close physical proximity to the ignitor housing, the temperature in the interior 100 of the ignitor will increase accordingly, and the components 10, 11, 12, 13, 14 will be exposed to high temperatures and may ultimately fail as a result of heat damage. Temperatures in the ignitor interior 100 reaching or exceeding 150 C. are critical for ignitors of the type described herein.

[0035] The inventor realised that a thermistor 10 could be used as a discharge resistor 10, so that its discharge function can still be fulfilled, while the temperature dependency of the thermistor's resistivity could be used to good effect in order to determine the temperature in the interior 100 of the ignitor housing. A lamp driver is connected to the ignitor arrangement 1 via the terminals 101, 102, 103, and can measure the thermistor resistivity by applying an appropriate voltage across the first input terminal pair 101, 102 even during normal steady-state operation of the lamp 2, since the first terminal 101 is shared and the ignition terminal 102 is not required during steady-state operation. FIG. 2 shows an embodiment of a lamp driver 3 according to the invention connected to the ignitor arrangement 1 of FIG. 1, to which an HID lamp 2 is securely mounted by means of a lamp interface 151. The diagram shows that the known type of connection interface 152 between ignitor arrangement 1 and lamp driver 3 need not be changed in any way. The lamp driver 3 can be connected to an external power source (not shown) by means of terminals 301, 302 and comprises the usual arrangement of functional units, namely an input circuit 30 for lamp driver protection and for filtering the higher frequencies that are generated by a DC-DC converter; a DC-DC converter 31 for converting the input voltage to a suitable level; a DC-AC converter 32 for generating a low-frequency square wave in the range of 200-1000 Hz; and an auxiliary ignition module 33 for applying a suitable DC voltage across the first pair of input terminals 101, 102 to the ignition arrangement 1. The lamp driver 3 also comprises a control circuit 34 for regulating the power applied to the lamp during steady-state operation. In this exemplary embodiment, the control unit 34 is provided with an additional control input 340 to allow the lamp power to be adjusted as desired by an external module (not shown). In this exemplary embodiment of the lamp driver 3 according to the invention, an additional module 35 is realised as a temperature evaluation unit 35, whose function is to determine or estimate the temperature in the interior 100 of the ignitor housing 15. Since the spark gap is non-conductive during steady-state operation, the only current path available between the first terminal 101 and the ignition terminal 102 is through the discharge resistor. The ignition terminal 102 is not required during the steady-state operation of the lamp 2, so that the temperature evaluation unit 35 can incorporate the thermistor 10 into an evaluation circuit to which a known voltage is applied, and the resulting voltage can be measured between the ignition terminal 102 and another suitable node. The temperature evaluation unit 35 can then calculate the momentary resistance of the thermistor 10, estimate the momentary temperature T.sub.100 in the ignitor interior 100, and provide the control unit with a value of the estimated temperature T.sub.100.

[0036] FIG. 3 shows an embodiment of a temperature evaluation unit 35 for the lamp driver shown in FIG. 2. The simplified diagram only indicates the relevant elements of the lamp driver 3, and only the thermistor 10 of the ignitor arrangement 1 is shown. During steady-state operation, a low-frequency square wave is applied across the drive terminals 101, 103 of the ignitor as shown in FIG. 1. During one half-wave, which can persist for several milliseconds, the voltage at the shared terminal 101 is essentially constant. During this time, the current I.sub.10 through the thermistor 10 can be measured without interfering with the operation of the lamp.

[0037] Here, the temperature evaluation unit 35 makes use of the fact that a known voltage is applied to the terminals 101, 102 by the DC-AC converter 32 and the auxiliary ignition module 33. In this exemplary embodiment, the temperature evaluation unit 35 comprises a current monitoring unit 350 which can measure the current I.sub.10 through the thermistor 10. A memory 351 storing a look-up table relating current values to temperature values is included in the temperature evaluation unit 35. In this way, an estimated temperature value T.sub.100 can quickly be obtained and forwarded to the control circuit of the lamp driver.

[0038] FIG. 4 shows another embodiment of a temperature evaluation unit 35 for the lamp driver of FIG. 2. Again, this simplified diagram only indicates the relevant elements of the lamp driver 3, and only the thermistor 10 of the ignitor arrangement 1 is shown. In this exemplary embodiment, the temperature evaluation unit 35 comprises a voltage monitoring unit 352 which can measure the voltage V.sub.10 across the thermistor 10. Here also, a memory 351 storing a look-up table is used, in this case a look-up table relating voltage values to temperature values. The estimated temperature value T.sub.100 is again forwarded to the control circuit of the lamp driver.

[0039] As mentioned above, the temperature in the ignitor housing will be affected to some extent by the ambient temperature. This in turn can affect the power levels at which the lamp can be driven. FIG. 5 shows graphs of ignitor temperature (in degrees Kelvin) vs. lamp power (in Watt) for three different ambient temperatures T.sub.amb1, T.sub.amb2, T.sub.amb3. The lowest ambient temperature T.sub.amb1 is associated with the highest maximum lamp power P.sub.max3, while the highest ambient temperature T.sub.amb3 is associated with the lowest maximum lamp power P.sub.max1. The maximum ignitor temperature T.sub.max is essentially constant, since this is the temperature above which the ignitor components may suffer damage. A typical maximum ignitor temperature is about 150 C. The control unit of the lamp driver according to the invention will regulate the lamp power such that the temperature within the ignitor housing does not exceed this maximum ignitor temperature T.sub.max. Since the temperature in the ignitor housing depends to some extent on the ambient temperature, the temperature in the ignitor can be different for different ambient temperatures even if the lamp power is the same in each case. Here, an exemplary power level P.sub.x is associated with three different interior ignitor temperatures T.sub.1, T.sub.2, T.sub.3. These different temperatures might be observed in the interior of an ignitor when used in a relatively cold environment; a normal environment, and a relatively hot environment, respectively. Therefore, the maximum power P.sub.max1, P.sub.max2, P.sub.max3 at which the lamp can be driven depends also on the ambient temperature T.sub.amb1, T.sub.amb2, T.sub.amb3, and a lamp driver according to the invention can take this into account be regulating the lamp power in response to an estimated ignitor interior temperature as described above.

[0040] FIG. 6 shows a prior art arrangement with an asymmetrical ignitor 60 for connection to a lamp driver 61. The lamp driver 61 comprises most of the modules 30, 31, 32, 33, 34 already described above. Here, a temperature sensor 603 is arranged inside the asymmetrical ignitor 60 so that it is in close proximity to the components of the ignitor 60, for example close to the conventional fixed-value discharge resistor or to the ignition capacitor. To access feedback from the temperature sensor 603, electrical connections 601, 602 are required. The driver 61 also needs corresponding connections 611, 612 so that some suitable temperature evaluation module 610 can obtain the feedback and evaluate it. The necessity of altering the known driver and ignitor designs to accommodate the temperature sensor 603 and the electrical connections 601, 602, 611, 612 result in an increased overall cost and a reduction in compatibility.

[0041] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0042] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements. The mention of a unit or a module does not preclude the use of more than one unit or module.