WO2009019647A1

WO2009019647A1 - Control of ignition of a gas discharge lamp

Info

Publication number: WO2009019647A1
Application number: PCT/IB2008/053104
Authority: WO
Inventors: Gerlach C. P. M. Emmen; Ferdinand J. P. M. Seuren; Jozef P. E. De Krijger; Ronald P. F. Hendriks
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-08-07
Filing date: 2008-08-04
Publication date: 2009-02-12

Abstract

In a method of controlling ignition of a gas discharge lamp, an ignition voltage is provided to the lamp in at least one ignition attempt. A time or number of ignition attempts is counted. The count of time and/or number of ignition attempts is limited, and the count of time and/or number of ignition attempts is reset at subsequent time intervals to a predetermined lower count.

Description

Control of ignition of a gas discharge lamp

FIELD OF THE INVENTION

The present invention relates to a method for controlling ignition of a gas discharge lamp. The present invention also relates to an electronic ballast for a gas discharge lamp. A gas discharge lamp may be of a high intensity discharge (HID) type, such as high pressure mercury, high pressure sodium, metal halide, high pressure metal vapor, or low pressure sodium types.

BACKGROUND OF THE INVENTION

A gas discharge lamp typically requires a high voltage for ignition. The voltage may be several kilo volts. The ignition voltage may be generated in different ways, and the high voltage is applied to the lamp. An ignition voltage generator is activated after (AC) power is applied to a ballast connected to the lamp.

In the operation of a gas discharge lamp, the application of an ignition voltage basically is only appropriate when the lamp is not yet ignited. Therefore, the operation of the ignition voltage generator is limited in time by a time counter (or timer), which allows the ignition voltage generator to operate during a predetermined, limited time normally sufficient for the lamp to ignite, and thereafter disables the operation of the ignition voltage generator. Instead of a time counter, or in combination with a time counter, also a counter of ignition attempts may be used, which allows the ignition voltage generator to operate a predetermined, limited number of (i.e. one or more) times, and thereafter disables the operation of the ignition voltage generator. Therefore, in this specification the term counting will be used to indicate counting time and/or number of ignition attempts. The time and number of ignition attempts is limited to prevent the circuitry involved and the lamp from premature failure. In the prior art, so-called self-stopping ignition circuits (also referred to as shut-off type ignition circuits) are known, e.g. from US-A-5 070 279. The ignition circuit comprises a timer set to activate an ignitor for a short, predetermined period after power is first applied to the ballast circuit, and to thereafter disable operation of the ignitor until line power has been removed and then reapplied, which resets the timer. This shut-off type ignition scheme does not reignite the gas discharge lamp when a supply voltage dip (transient) occurs sufficient to turn off the lamp but not low enough to reset the timer. Consequently, an extinction of the lamp due to such a supply voltage dip leads to the lamp being off as long as the supply voltage sustains. This is a serious problem, in particular when the lamp is located in public and/or unattended and/or unobserved places, such as streets, car parks, shopping areas and the like.

Various solutions to this problem have been proposed, including circuitry to reset the ignitor timer when a current is detected flowing through the lamp after ignition has taken place (e.g. GB-A-I 598 450), or circuitry to reset the ignitor timer based on the output voltage being insufficient to light the lamp load to automatically reignite the lamp when the output voltage momentarily drops below a level sufficient for lighting the lamp load followed by restoration of an output voltage sufficient for lighting the lamp load (e.g. US-A-5 424 617).

The application of ignition pulses is not appropriate when the gas discharge lamp approaches the end of its life. Under such circumstances, the necessary voltage to be applied to the lamp to keep it working increases from its nominal value to a higher value. In addition, the arc voltage becomes higher so that a working threshold voltage may exceed a value above which the lamp extinguishes. However, when the lamp thereafter cools, it may be ignited again when the ignition circuit provides ignition pulses and said threshold voltage decreases due to the decrease of temperature. This process may be repeated towards the end of the life of the lamp, and is known as cycling. US-A-4 665 346 discloses an ignition control circuit with a cycling detection function, so that if the lamp extinguishes due to an increase of its working threshold voltage without interruption of the supply voltage, no ignition pulses will be generated and the defective lamp will remain extinguished indicating a need for replacement. In the past, also other End Of Life (EOL) protections have been devised.

While the above and other provisions to protect a gas discharge lamp from receiving ignition pulses where this is inappropriate may be adequate in most situations, in practice lamps may still be off or be extinguished while there is no function or mechanism provided to turn them on again, although the lamp may be fit for normal operation.

OBJECT OF THE INVENTION

It is desirable to provide a method and an electronic ballast for ignition of a gas discharge lamp to ensure operation of the lamp as much as possible while the lamp operating conditions would be normal and a supply voltage is present. SUMMARY OF THE INVENTION

In an embodiment of the present invention, a method of controlling ignition of a gas discharge lamp is provided. According to the method, an ignition voltage (e.g. a resonant voltage, a DC voltage, one or more voltage pulses, one or more multi-pulse voltage pulses) is provided to the lamp in at least one ignition attempt, while counting a time or number of ignition attempts. The count of time (which may relate to one ignition attempt or a plurality of ignition attempts) and/or number of ignition attempts is limited to extend the lifetime of an ignition circuit and the lamp. The count of time and/or number of ignition attempts is reset to a predetermined lower count at subsequent time intervals.

A problem that when the lamp is extinguished, and at the same time a count of time and/or number of ignition attempts up to a predetermined limit is reached, the lamp will not be (re-)ignited, is solved by the features above in that after a time interval, the count of time and/or the number of ignition attempts is reset to a predetermined lower count below the limit thereof (i.e. reset to zero, or any other value below said limit), thereby enabling one or more new ignition attempts. The reset as such, and/or the amount of reset may be made dependent from a lamp operating condition, e.g. whether the lamp is extinguished or not, whether a lamp operating condition is well within boundaries or near a boundary, whether a lamp operating condition indicates an EOL condition, etc. In a further embodiment of the present invention, the method further comprises sensing at least one lamp operating parameter, during lamp operation; determining whether the sensed lamp operating parameter indicates a normal lamp operating condition; and resetting the count of time and/or number of ignition attempts at subsequent time intervals to a predetermined lower count, if a normal lamp operating condition has been determined. Examples of lamp operating parameters are a lamp voltage, a lamp current, and a lamp power.

In such an embodiment, a reset of the count of time and/or a number of ignition attempts, and thereby the enablement of one or more ignition attempts is conditional, and will only take place when the lamp operating condition is sensed as being normal. In a further embodiment of the present invention, an electronic ballast for a gas discharge lamp is provided. The ballast comprises a lamp ignition driver circuit for providing an ignition voltage to a lamp in at least one ignition attempt. The lamp ignition driver circuit comprises at least one of an ignition attempt time counter disabling the lamp ignition driver circuit when an ignition attempt time count is exceeded, and an ignition attempt number counter disabling the lamp ignition driver circuit when an ignition attempt number count is exceeded. The ballast further comprises a reset control circuit for resetting the count of the ignition attempt time counter and/or the ignition attempt number counter at subsequent time intervals to a predetermined lower count. In a further embodiment of the present invention, the ballast further comprises a sensing circuit coupled to the reset control circuit. The sensing circuit is configured to sense at least one lamp operating parameter during lamp operation, and to determine whether the sensed lamp operating parameter indicates a normal lamp operating condition. The reset control circuit is configured to reset the count of the ignition attempt time counter and/or the ignition attempt number counter at subsequent intervals to a predetermined lower count, if the lamp operating parameter has indicated a normal lamp operating condition. The claims and advantages will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a block diagram of a circuit arrangement of a ballast for a gas discharge lamp in an embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLES

Fig. 1 shows a circuit arrangement of a ballast B for a gas discharge lamp in an embodiment of the present invention, connected to a gas discharge lamp L. The ballast B includes input terminals Tl and T2 for connection to a power source (e.g. to a mains AC voltage). The ballast B includes a lamp ignition driver circuit LIDC for providing an ignition voltage to the lamp L in at least one ignition attempt. The lamp ignition driver circuit LIDC includes at least one of an ignition attempt time counter TC and an ignition attempt number counter NC. The ballast B further includes a reset control circuit RCC coupled to the ignition attempt time counter TC (if present in the circuit) and the ignition attempt number counter NC (if present in the circuit). A sensing circuit SC is coupled to the reset control circuit RCC. It is noted that the reset control circuit RCC and/or the sensing circuit SC may be functionally part of the ballast B, but may physically be located outside the ballast B.

The ignition attempt time counter TC is configured to disable the lamp ignition driver circuit LIDC when a predetermined ignition attempt time count is exceeded. The ignition attempt number counter NC is configured to disable the lamp ignition driver circuit LIDC when a predetermined ignition attempt number count is exceeded. The reset control circuit RCC is configured to reset the count of the ignition attempt time counter TC and/or the count of the ignition attempt number counter NC at subsequent time intervals to a lower count, i.e. to a count of zero or more, but below said predetermined time count and/or number count.

The sensing circuit is configured to sense at least one lamp operating parameter, such as a lamp operating voltage, a lamp operating current, and/or a lamp operating power, during a steady state operation of the lamp, and to determine whether the sensed lamp operating parameter indicates a normal lamp operating condition. The lamp operating parameter(s) is/are compared to threshold values stored in a memory (not shown) coupled to, or incorporated in the reset control circuit RCC. If the comparison indicates that the lamp operates within a normal working range, then a condition indicator indicating normal operation of the lamp is stored in the memory. If the comparison indicates that the lamp operates outside a normal working range, e.g. as a result of the operating voltage increasing near the end of the life of the lamp, then said condition indicator stored in the memory will indicate an abnormal operation of the lamp. As an example, the condition indicator may be a flag or bit having a value "0" when the lamp operates in its normal working range, and having a value "1" when the lamp operates outside its normal working range (i.e. in an abnormal working range). The memory should retain its information without supply of power.

In an embodiment, the reset control circuit RCC is configured to reset the count of the ignition attempt time counter TC and/or the count of the ignition attempt number counter NC to a lower count (below said predetermined limit count) at subsequent regular or irregular time intervals, and independently from other functions of the lamp ignition driver circuit LIDC or ballast B. In an embodiment, the condition indicator is not taken into account. However, if the lamp L is in a condition to operate, and the lamp L would have been extinguished without the lamp ignition driver circuit LIDC having any other function or mechanism to reignite the lamp L, then in this embodiment the lamp L will be reignited after expiry of a time interval, provided a supply voltage is present.

In a further embodiment, the reset control circuit RCC is configured to reset the count of the ignition attempt time counter TC and/or the count of the ignition attempt number counter NC to a lower count (below said predetermined limit count) at subsequent time intervals, provided that the condition indicator indicates a normal operation of the lamp L. In this embodiment, if the lamp L would have been extinguished without the lamp ignition driver circuit LIDC having any other function or mechanism to reignite the lamp L, then the lamp L will only be reignited if the condition indicator indicates a previous operation of the lamp L in its normal working range, and after expiry of a time interval, provided a supply voltage is present. A lamp L approaching the end of its life will have a condition indicator indicating a lamp operation outside the normal operating range, and consequently the ignition attempt time counter TC and/or the ignition attempt number counter NC will not be reset for such lamp L.

The subsequent time intervals may be regular, each time interval having the same length, or a group of subsequent time intervals having regular different lengths. The subsequent time intervals may also each have a random length, possibly within certain minimum and maximum limits.

The lamp ignition driver circuit LIDC, the reset control circuit RCC, and the sensing circuit SC may have the functions explained above implemented in hardware, in software, or in a combination thereof.

Detailed embodiments of the present invention have been disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting, but rather to provide an understandable description of the invention.

The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. The terms program, software, and the like as used herein, are defined as a sequence of instructions designed for execution on a computer system. A program, computer program, or software application may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system.

Claims

CLAIMS:

1. A method of controlling ignition of a gas discharge lamp, comprising: providing an ignition voltage to the lamp in at least one ignition attempt, while counting a time or number of ignition attempts; limiting the count of time and/or number of ignition attempts; and - resetting the count of time and/or number of ignition attempts at subsequent time intervals to a predetermined lower count.

2. The method according to claim 1, further comprising: during lamp operation, sensing at least one lamp operating parameter; - determining whether the sensed lamp operating parameter indicates a normal lamp operating condition; resetting the count of time and/or number of ignition attempts at subsequent time intervals to a predetermined lower count, if a normal lamp operating condition has been determined.

3. The method according to claim 2, wherein the lamp operating parameter is at least one of a lamp voltage, a lamp current, and a lamp power.

4. The method according to claim 1, wherein the subsequent time intervals are regular.

5. An electronic ballast for a gas discharge lamp, the ballast comprising: lamp ignition driver circuit for providing an ignition voltage to a lamp in at least one ignition attempt, the lamp ignition driver circuit comprising at least one of: - n ignition attempt time counter disabling the lamp ignition driver circuit when a predetermined ignition attempt time count is exceeded, and a ignition attempt number counter disabling the lamp ignition driver circuit when a predetermined ignition attempt number count is exceeded; reset control circuit for resetting the count of the ignition attempt time counter and/or the ignition attempt number counter at subsequent time intervals to a predetermined lower count.

6. The ballast according to claim 5, further comprising a sensing circuit coupled to the reset control circuit, the sensing circuit being configured to sense at least one lamp operating parameter during lamp operation, and to determine whether the sensed lamp operating parameter indicates a normal lamp operating condition, wherein the reset control circuit is configured to reset the count of the ignition attempt time counter and/or the ignition attempt number counter at subsequent intervals to a predetermined lower count, if the lamp operating parameter has indicated a normal lamp operating condition.