DE102005014857B4 - Luminaire, in particular for installation in or for attachment to a piece of furniture or a showcase, with a cold cathode tube - Google Patents

Abstract

Luminaire with a cold cathode tube (12, 38) as illuminant and with an electrical circuit (50) connected upstream of the cold cathode tube (12, 38) in an electrical ballast (14, 40) which regulates the current supply to the cold cathode tube (12, 38), wherein the electrical circuit (50) comprises a current control loop which regulates the operating current applied to the cold cathode tube (12, 38) in response to a detected actual current flow or current voltage, and between the electrical circuit (50) and the Cold cathode tube (12, 38) is a power switching stage (52) is provided, which is the input side connected to the output of a regulator (56) of the current control loop, and the power switching stage (52) comprises a full bridge converter in resonance technology, characterized by a design for installation in or Attachment to a piece of furniture or a showcase, in a lamp housing (10, 30) both the cold cathode tube (12) and the elec trical ballast (14, 40) are housed, and by a resistance sensor (54) which is directly connected to the cold cathode tube (12, 38); and about which of the ...

Description

The The present invention relates to a luminaire with a cold cathode tube according to the preamble of claim 1.

to Interior lighting of showcases, drawers or cupboards will be used as light sources so-called cold cathode tubes, in comparison to develop little heat to other bulbs. Only by This low heat makes it possible to put the bulb in a small, locked room like a drawer, a display case or to integrate a cabinet, even if the one produced by the cold cathode tube Heat in Nevertheless, individual cases can lead to considerable temperatures. These in the closed drawer, showcase or in the closed Cabinet pent-up heat can lead to cracking in the wood and / or damage to the cold cathode tube. In extreme cases the cold cathode tube burst and possibly the furniture catch fire, especially if an electrode defect occurs.

To avoid overheating of such cold cathode tubes is in the DE 101 01 275 C2 proposed to regulate the operating current based on the temperature present at the cold cathode tube. It should be achieved by adjusting the operating current, a constant temperature in the cold cathode tube.

From the AT 407 461 B is a control for a discharge lamp is known, in which the operating current applied by means of pulse width and / or pulse packet modulation to the cold cathode lamp, wherein in determining the operating current, a dependent of the lamp temperature correction factor is taken into account according to the lamp-specific correlation of luminance, lamp current and lamp temperature is determined.

From the US 5,408,162 A are a power supply and a control circuit for operating a fluorescent tube by a power source that provides a low DC current, such as a battery known. An inverter converts the low DC voltage into a higher AC voltage for operating the fluorescent tube. The lamp is received in a feedback loop which includes a circuit for generating a feedback signal indicative of the magnitude of the current passed through the lamp. A regulated regulator generates a regulated lamp intensity.

From the US 5,384,516 A An information processing apparatus is known in which a liquid crystal display and a fluorescent lamp are used to backlight the screen of the liquid crystal display. A lighting circuit for supplying the fluorescent lamp with alternating current receives an input power either from a commercial AC power source or from a DC battery. The level of power provided to the fluorescent lamp is determined based on a determination of whether the input power is from a conventional power source or from the battery.

The DE 200 09 428 U1 relates to an electronic ballast for cold cathode lamps with resonant circuit for high voltage generation, wherein the series resonant circuit is excited by an oscillator or chopper circuit, the cold cathode lamp is connected in parallel to the series inductance or in parallel to the series capacitance and wherein for stabilization of the operating point a ballast capacitor is connected in series with the cold cathode lamp , The ballast can turn off when no cold cathode lamp is connected. The circuit can also be protected by a varistor from damaging overvoltages.

The DE 299 11 536 U1 describes a furniture radiator with cold lamps in a housing also receiving an electrical circuit, wherein a substantially flat parallelepiped housing in a plane next to each other has a lamp housing part for a tortuous cold cathode tube or for a light-emitting diode array and a circuit housing part.

Of Further, the document "AN-01, Resonant Fashion CCFL Inverters "by Monolithic Power Systems (Monolithic Power Systems, Inc., 983 University Avenue, Building D, Los Gatos, CA 95032 USA, AN-01 Rev 1.4, 08/11/02). This concerns the use of cold cathode fluorescent tubes in liquid crystal displays. In this case, an embodiment is provided as a full bridge circuit.

From that The present invention is based on the object, to provide a lamp of the type mentioned, in which the Cold cathode tube not overheated and has a long life.

there the invention is based on the finding that such after the Gas discharge principle working cold cathode tubes as constant as possible Need operating current, to burn optimally. Deviations from the ideal current of usually 5 mA can significantly reduce the life of a cold cathode tube.

As a technical solution to this problem, a luminaire according to the features of claim 1 is proposed according to the invention. Advantageous developments of this lamp are the respective Subclaims refer.

A formed according to this technical teaching lamp has the advantage that over the current loop permanently (within the usual Tolerances) constant operating current applied to the cold cathode tube can be, resulting in a long life of the cold cathode tube. there allows the direct detection of the actual current and / or the actual voltage a fast response to abnormal operating conditions, so that the operating current can be kept within a narrow tolerance range.

The Use of a resistance sensor for Detection of the actual current and / or the actual voltage has on the cold cathode tube the advantage that captures both measured values with a resistance sensor can be and that the values are very precise be recorded. At the same time, such a resistance sensor is inexpensive and space-saving.

The Attachment of the resistance sensor directly on the cold cathode tube has the advantage that this results in a very direct and unadulterated detection of Measured values is reached.

According to the invention is between This circuit and the cold cathode tube, a power switching stage provided that a full bridge converter in resonance technology. This has the advantage that hereby in cheaper Way a precise adjustable power supply can be realized.

One Another advantage of the resistance sensor is that over the measured at the resistance sensor Current or voltage drop can be detected, whether a defect is present at the lamp, in particular whether the cold cathode tube is defective or not. If the current control circuit detects such a defect, the power supply to the cold cathode tube is interrupted immediately. hereby will be another power supply and any associated overheating the cold cathode tube avoided. Another advantage is that the cold cathode tube is now is no longer under power and thus exchanged safely can.

One Operating procedure for a cold cathode tube, which keeps the operating current constant, has the advantage that thereby the cold cathode tube ideal is operated, resulting in a long life of the cold cathode tube. It is understood that any performance adjustments, for example overheating the cold cathode tube, by changing the operating voltage so that the operating current in these cases can be kept constant.

Further Advantages of the lamp according to the invention emerge from the attached Drawing and the embodiments described below. Likewise, the The above-mentioned and the still further features according to the invention in each case be used individually or in any combination with each other. The mentioned embodiments are not as final enumeration but rather have an exemplary character. It demonstrate:

1 a schematic representation of a first embodiment of a lamp according to the invention;

2 a schematic representation of a second embodiment of a lamp according to the invention;

3 a schematic diagram of a circuit according to the invention.

In 1 a luminaire according to the invention is shown in which in a lamp housing 10 both the cold cathode tube 12 , as well as an electric ballast 14 In this case, the electrical connection between the circuit 14 and the cold cathode tube 12 over extremely short cables or over an appropriate track 16 on the board 18 respectively.

In close proximity to the cold cathode tube 12 is a measuring resistor 20 arranged, whose resistance increases with increasing temperature. Furthermore, in the case 10 a non-contact switch 22 provided, with which the cold cathode tube can be switched on and off.

By using the electric ballast 14 for controlling the power supply to the cold cathode tube 12 It is possible to build everything very small and all components in the housing 10 accommodate. This is the case 10 around a closed housing, to facilitate the installation of this lamp in a piece of furniture or a showcase. This light then only needs to be connected to a 12 V, 110 V or 230 V power source. This eliminates the known from the prior art laying a cable between the electric ballast and the cold cathode tube and the associated expense.

Due to the compact design of the electrical circuit, the housing 10 also be made very compact. In the in 1 illustrated embodiment, the housing 10 rectangular in cross-section and has an edge length of 10 mm by 10 mm.

At the in 2 illustrated light is an alternative embodiment. In this embodiment, the housing 30 from a soil 32 and a lid 34 which are lockable to each other. In this case is on a holding plate 36 a meandering curved cold cathode tube 38 , an electric ballast 40 , a temperature measuring resistor 42 and a non-contact switch 44 assembled. Again, it is due to the compact design of the electrical circuit 44 It is possible to mount everything in the smallest space and in a very compact housing 30 to integrate. In this case, the housing has 30 a height of about 8 mm and a diameter of about 70 mm.

In 3 is an electrical circuit 50 shown, for example, in the electric ballast 14 according to the lamp 1 or in the electric ballast 40 according to the lamp 2 is used. This electrical circuit 50 controls a power switching stage 52 connected to the cold cathode tube 12 . 38 connected is. In this case, the power switching stage comprises 52 a full-bridge transducer in resonance technology, as known from the prior art. Furthermore, the electrical circuit comprises 50 a regulator 56 and a limit memory 58 , as well as a voltage divider 60 , The following is the operation of the electric circuit 50 as described in more detail below:
The temperature measuring resistor 20 . 42 permanently measures the existing temperature. The current temperature is proportional to the resistance. In the limit memory 58 is stored a temperature limit, which was determined experimentally. Now raises the temperature in the housing 10 . 30 so strong that the resistance in the temperature measuring resistor 20 . 42 increases so much that the limit is reached, so controls the controller 56 the power switching stage 52 to the effect that the power supply to the cold cathode tube 12 . 38 for a predetermined time T is reduced by 10% to 95%, preferably 80%. This process is repeated until the temperature at the cold cathode tube 12 . 38 fell below the threshold.

At the same time, the electrical circuit is detected 50 over the resistance sensor 54 the current flow or the voltage at the cold cathode tube 12 . 38 , For example, in the case that the cold cathode tube 12 . 38 is defective, the current or voltage drop at the resistance sensor increases 54 drastically, so that the limit provided for this is exceeded. This recognizes the electrical circuit 50 in that there is a defect and interrupts the power supply to the cold cathode tube 12 . 38 Completely. Since the lamp is no longer under power / voltage now required repair work can be carried out without risk.

In another, not shown embodiment is the electrical Circuit designed such that when reaching a limit in memory stored temperature upper limit of, for example, 80 ° C, the power supply to the cold cathode tube is lowered by 10% to 95%, preferably 80%. The remains Reduced power supply maintained until the temperature a likewise stored in the limit memory temperature lower limit of for example, reaches 50 ° C. Has. In this case, then the power supply to the old value returned, until the temperature reaches the upper temperature limit has reached again. This procedure can be repeated as often as desired and as a result, the temperature at the cold cathode tube is always remains in a predetermined temperature interval.

In yet another embodiment, not shown here will be the power supply after reaching the lower temperature limit not to the original one Height, but only 90% of the original Power up. Should the heat build on the cold cathode tube despite only 90% power also to a temperature increase up to the temperature upper limit to lead, so the process described above is repeated, if necessary several times.

In another operating procedure is at the resistance sensor 54 the current operating current is measured and in the controller 56 with a predetermined limit value from the limit memory 58 compared. If the two values deviate from one another beyond the usual tolerances, the controller regulates 56 the operating current accordingly.

In yet another operating procedure is at the resistance sensor 54 the current operating voltage measured and in the controller 56 with a predetermined limit from the limit memory 58 compared. If the two values deviate from one another beyond the usual tolerances, the controller regulates 56 the operating current accordingly.

In the event that the cold cathode tube 12 . 38 should overheat once, the operating voltage of the cold cathode tube 12 . 38 lowered and the operating current kept constant at 5 mA. As a result, the power of the cold cathode tube can be throttled at a constant operating current, so that the cold cathode tube cools.

10

casing

12

Cold cathode tube

14

electrical ballast

16

conductor path

18

circuit board

20

Temperature-sensing resistor

22

switch

30

casing

32

ground

34

blanket

36

Retaining plate

38

Cold cathode tube

40

electrical ballast

42

Temperature-sensing resistor

44

switch

50

electrical circuit

52

Power switching stage

54

RTD

56

regulator

58

limit memory

60

voltage divider

Claims (3)

Luminaire with a cold cathode tube ( 12 . 38 ) as a light source and with one of the cold cathode tubes ( 12 . 38 ) upstream, electrical circuit ( 50 ) in an electric ballast ( 14 . 40 ), which supplies the power to the cold cathode tube ( 12 . 38 ), whereby the electrical circuit ( 50 ) has a current control loop that the on the cold cathode tube ( 12 . 38 ) adjusts operating current as a function of a detected actual current flow or a detected actual voltage, and between the electrical circuit ( 50 ) and the cold cathode tube ( 12 . 38 ) a power switching stage ( 52 ) is provided, the input side to the output of a controller ( 56 ) of the current control loop, and the power switching stage ( 52 ) comprises a full-bridge converter in resonant technology, characterized by a design for installation in or for mounting to a piece of furniture or a showcase by placing in a lamp housing ( 10 . 30 ) both the cold cathode tube ( 12 ) as well as the electrical ballast ( 14 . 40 ), and by a resistance sensor ( 54 ), which on the cold cathode tube ( 12 . 38 ) is directly connected; and over which the electrical circuit ( 50 ) detects the actual current flow and / or the actual voltage. Luminaire according to claim 1, characterized by a design of the electrical circuit ( 50 ) with one for an increase of the current or voltage drop at the resistance sensor ( 54 ) such that, when the limit value is exceeded, the electrical circuit ( 50 ) a power supply to the cold cathode tube ( 12 . 38 ) completely interrupts. Luminaire according to claim 1 or 2, characterized in that in the lamp housing ( 10 . 30 ) a non-contact switch ( 22 . 44 ) for switching on and off the cold cathode tube ( 12 . 38 ) is arranged.