EP3554196A1 - Temperature-monitored led module - Google Patents

Abstract

The invention relates to an LED module for connection to a separate electronic ballast, electronic ballast, the LED module having at least one row of LEDs connected in series, which are supplied with a supply current when connected to an electronic ballast, one or more of the LEDs are bridged in at least one of the rows with at least one thermal switch, and the thermal switch is set up to short-circuit the at least one or more bridged LEDs when a predetermined temperature is exceeded.

Description

The present invention relates to an LED module, which is supplied with power by a separate electronic ballast and in particular has a temperature monitoring.

In the prior art, the temperature monitoring of LED modules is achieved in various ways. The temperature monitoring can be done by the electronic ballast, short electronic ballast. This requires a connection between the ECG and a temperature sensor in the LED module. The ECG evaluates the signal from the temperature sensor, which is usually transmitted as an analog voltage, in order to infer the possible overheating of the LED module and possibly reduce the supply current. However, the evaluation of the analog signal is localized because the monitoring becomes inaccurate with increasing line length. In contrast, a digital signal would be relatively expensive. On the other hand, there is the possibility that the LED module is separated from the electronic ballast by means of a bimetallic switch. However, this solution has the disadvantage that in case of overheating the entire LED module is turned off. Therefore, monitoring from the TOE is preferred in the art. However, this leads to problems with longer line connections.

Object of the present invention is to provide an LED module for power supply with a separate ECG, which allows temperature monitoring in the simplest possible way.

The object is achieved by an LED module according to claim 1 and by an LED module in conjunction with an electronic ballast according to claim 10.

A particularity of the LED module of the present invention is that the thermal switch bridges only a portion of the LEDs in the one or more rows of LEDs in the LED module to short only that portion of LEDs when a predetermined temperature is exceeded. If, when the predetermined temperature is exceeded, only a portion of the LEDs is switched off by short-circuiting, this is generally sufficient to reduce the operating temperature of the LED module to such an extent that thermal failure can be prevented. On the other hand, there is an advantage in that the LED module is not completely disconnected from the supply current. Even when the thermal switch is activated, light is still generated by the remaining part of LEDs, so that at least one emergency lighting is still present.

According to a preferred embodiment, at least two LED groups are bridged, each with a thermal switch, each group comprising at least one LED. In particular, the thermal switches may have different predetermined temperatures at which they short-circuit the respectively bridged LED group. This allows different staggered temperatures to be defined for shutting off the groups of LEDs. By way of example, when a first temperature threshold is exceeded, a smaller group of LEDs can be switched off, so that the deactivation of some LEDs does not occur in the overall illumination intensity. Only when a second higher temperature threshold is exceeded, a larger group of LEDs is additionally short-circuited to avoid damage. However, according to the invention remains in this Condition still a part of the LEDs left, which are still supplied with power, so that at least one emergency lighting is maintained. It can also be bridged more than just two groups of LEDs, each with a thermal switch.

According to a development of the aforementioned embodiments, the at least two LED groups comprise only LEDs from the same row. Since the current through the LED row remains constant due to the supply of the electronic ballast, when the LEDs are short-circuited in one or both groups, the remaining LEDs are supplied with the same supply current as before. This prevents the non-shorted LEDs from receiving a higher supply voltage to avoid overheating these LEDs.

According to a preferred embodiment, a bridged with a thermal switch LED group, which has one or more LEDs, surrounded on all sides by a plurality of LEDs in a planar arrangement. The surrounding LEDs may be LEDs that are not bridged by another thermal switch, or may be LEDs that are bridged with another thermal switch, which preferably triggers at a higher temperature than the first thermal switch. As a result, in operation, when a predetermined temperature is exceeded, the bridged LED group is first switched off and the surrounding LEDs continue to light up. However, heat generation is reduced because the center LEDs, which receive the most waste heat from the surrounding LEDs, are turned off first. If the temperature rises further, the other LEDs may also be switched off. The advantage, however, is that initially the centrally located LEDs are turned off, so that no heat test within the areal arrangement of the LEDs arises. Preferably the plurality of LEDs, which surround the LED group bridged by a thermal switch on all sides, connected in series with the bridged LED (s) of the LED group in the same row. This avoids that when shorting a group of LEDs, the remaining LEDs are supplied with a higher voltage because the ECG keeps the current constant through the row of all LEDs.

According to a development of the last-mentioned embodiments, at least some of the several LEDs surrounding the LED group bridged on all sides by the thermal switch are not themselves bridged in a thermal switch. Since these LEDs have a larger average distance from each other due to the arrangement around the circumference of the bridged LED group, the risk of overheating of these LEDs when the LED group is switched off is low.

In another aspect, the invention includes an LED module as previously described and an ECG connected to the LED module to provide it with a constant current. The ECG is arranged separately from the LED module. It can be arranged in the same luminaire, for example a same luminaire housing. It may also be spaced from the LED module by at least one meter. Since the thermal monitoring of the LED module takes place in the LED module itself, the proper operation of the LED module is ensured even with a larger cable length between the ECG and the LED module. Since the electronic ballast provides a constant current, the voltage drop across the line resistance of the supply lines for the electronic ballast is also compensated. The LED module is always supplied with the desired current to achieve the desired illuminance. The constant current can for To achieve a desired dimming to a predetermined value in the ECG be set.

Figur 1

zeigt ein Schaltbild einer ersten Ausführungsform der Erfindung.

Figur 2

zeigt ein Schaltbild einer zweiten Ausführungsform der Erfindung, wobei die Anordnung der LEDs innerhalb der Schaltung die räumliche Anordnung der LEDs zueinander wiedergibt.

Figur 3

zeigt eine symbolische Darstellung einer weiteren Ausführungsform der Erfindung.

Other features and advantages of the present invention will be apparent from the following description of preferred embodiments, taken in conjunction with the figures. The figures show the following:

FIG. 1

shows a circuit diagram of a first embodiment of the invention.

FIG. 2

shows a circuit diagram of a second embodiment of the invention, wherein the arrangement of the LEDs within the circuit reflects the spatial arrangement of the LEDs to each other.

FIG. 3

shows a symbolic representation of another embodiment of the invention.

In the FIG. 1 is a block diagram of an embodiment of the present invention is shown. An ECG 2 is connected to an LED module, which in the embodiment according to FIG. 1 only a row of LEDs 4 has. The LEDs are all connected in series in the series and connected to the ECG 2. In the schematic diagram after FIG. 1 It should be understood that the electrical connection between the ECG and the row of LEDs 4 can be much longer compared to the chain row. The electronic ballast supplies the LED module with a constant current I. In the row of LEDs 4, two LED groups 8 of two LEDs or of a single LED each with a thermal switch 6 are bridged. The thermal switches 6 have a predetermined temperature at which they trip to short the bridged LEDs or the single bridged LED. Preferably, the two in the FIG. 1 shown thermal switch on a different trip temperature. For example, at a lower temperature initially only the single LED and only at a higher temperature, the group 8 of two LEDs 4 are shorted. Due to the short circuit, the LEDs 4 are no longer supplied with power, so that the operating temperature of the LED module is lowered when the temperature is exceeded. Since the entire series of LEDs are supplied with a constant current I through the ECG, the voltage drop in each non-shorted LED remains the same regardless of the number of shorted LEDs. The brightness of the individual LEDs is therefore always the same except for the shorted LEDs. Shorting the LEDs merely causes a few of the LEDs in the row to fail to meet thermal conditions. However, even if one or both predetermined triggering temperatures of the thermal switches are exceeded, at least four LEDs are still obtained in the embodiment which achieve the desired lighting task.

In FIG. 2 an alternative embodiment is shown in which the LED module comprises a series of seven LEDs 4. In the LED series, an LED group 8 of only a single LED with a thermal switch 2 is bridged. A special feature of this embodiment is that the bridged LED is arranged in the middle of the unbridged LEDs. When the trip temperature of the thermal switch 6 is exceeded, therefore, the central LED is turned off. Since the middle LED is deliberately switched off, a better power distribution of the remaining LEDs under unfavorable ambient temperature can be achieved. The heat test in the middle of the LED group is turned off, so that the power density is reduced. Turning off a LED on Edge would have less effect on the thermal load within the LED module. The short-circuiting of the central LED is therefore advantageous in order to switch off the LED which is subject to the highest thermal stress in the planar arrangement of the LEDs.

The FIG. 3 shows another embodiment similar to in FIG. 2 , In this embodiment, five LED groups 8 are included, which are distributed in the same manner as the individual LEDs in the FIG. 1 , It is to be understood that each LED group 8 may consist of one or more LEDs. The groups 8 are connected to each other in series (in the FIG. 3 not shown) and within each LED group, the LEDs are also connected in series. There is provided a single thermal switch 6, which shorts the middle group 8 when a predetermined temperature is exceeded, as in the previously described embodiments.

Numerous modifications may be made to the above-described embodiments without departing from the scope of the invention, which is defined by the claims. In particular, a plurality of LED groups of different sizes can be provided, which are individually short-circuited at preferably different triggering temperatures by the thermal switch. Furthermore, it is also possible to provide a plurality of parallel rows of LEDs, wherein groups of a plurality of LEDs within the rows are preferably short-circuited with one thermal switch each.

As a thermal switch according to the invention is preferably a bimetallic switch. This can be provided directly on a board on which the LEDs are arranged in the LED module. Alternatively, electronic switches come into consideration, which make temperature measurements and means an electronic switch, in particular a semiconductor device, short-circuit the bridged LED group.

LIST OF REFERENCE NUMBERS

2

electronic ballast, electronic ballast

4

LED

6

thermal switch

8th

LED group

Claims (10)

LED module for connection to a separate electronic ballast (2), electronic ballast,
wherein the LED module has at least one series of series-connected LEDs (4) which are supplied with a supply current (I) when connected to an electronic ballast (2),
wherein one or more of the LEDs (4) are bridged in at least one of the rows with at least one thermal switch (6), and the thermal switch (6) is arranged to switch the at least one or more bridged LEDs (4) when a predetermined temperature is exceeded. kurzuschalten. LED module according to claim 1, wherein at least two LED groups (8) are each bridged with a thermal switch (6), wherein each group comprises at least one LED (4). LED module according to claim 2, wherein the two thermal switches (6) are arranged to short-circuit the respective bridged LEDs (4) when different predetermined temperatures are exceeded. LED module according to claim 2 or 3, wherein the at least two groups (8) have different numbers of LEDs (4). LED module according to one of claims 2 to 4, wherein the at least two LED groups comprise only LEDs (4) from the same row. LED module according to one of the preceding claims, wherein a with a thermal switch (6) bridged LED group (8), which comprises one or more LEDs (4) is surrounded on all sides by a plurality of LEDs (4) in a planar arrangement. LED module according to claim 6, wherein the plurality of LEDs (4) which surround the LED group (8) bridged by a thermal switch (6) on all sides, with the bridged LEDs (4) of the LED group (8) in the same row are connected in series. LED module according to claim 6 or 7, wherein the plurality of LEDs surrounding the LED group (8) bridged on all sides with a thermal switch (6) are themselves not bridged with a thermal switch. LED module according to one of the preceding claims in conjunction with an electronic ballast, electronic ballast, (2) which is connected to the LED module, and provides a constant supply current (I). LED module in conjunction with an electronic ballast according to claim 9, wherein the electronic ballast (2) is adapted to provide different constant currents (I) for the LED module in response to a desired dimming of the LED module.

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