DE102010002227A1 - Protection of LEDs against overheating and high through-current - Google Patents

Abstract

In order to protect LEDs (2) or groups (5) of LEDs against overheating and the overcurrent causing them, a circuit arrangement is proposed which is characterized by an LED connected in parallel to the LED (2) or group of LEDs (5). Protector (4) which contains a temperature sensor (9), a logic circuit part (6) and a bypass element (7), the logic circuit part (6) evaluating the temperature measured by the temperature sensor (9) and the bypass element (7 ) causes the LED (2) or group of LEDs (5) to be bridged or their through current to be reduced if the measured temperature exceeds a predetermined switch-off threshold value.

Description

The invention relates to a method for protecting an LED or a group of LEDs against overheating and high through-current and a circuit arrangement for carrying out such a method. The invention also relates to an LED lamp with such a circuit.

The LEDs can u. a. be organic and / or inorganic LEDs.

LEDs are usually grouped together because of their low operating voltage (3-5 volts) and because of the relatively low light output through series and parallel connection. If, in a series connection, an LED fails due to an interruption failure, then the function of the whole group is inevitably affected. To counteract this undesirable effect is from the EP 2009 960 A2 a protective circuit is known, which takes over their current flow at an interruption defect of an associated LED. For this purpose, the protection circuit is provided with a bridging circuit part for the LED, which is controlled by a trigger circuit part in the form of a zener diode.

The present invention is concerned with another problem encountered with LEDs or groups of LEDs, namely with overheating, highlighted, for example, by overcurrent, damage to the LED, etc.

The object of the invention is to counteract the occurrence of the above influencing variables.

The object is solved by the features of the independent claims. The dependent features relate to expedient embodiments of the invention.

In one aspect, the invention proposes a method for protecting an LED or a group of LEDs, in particular against overheating and high throughput current. The temperature of the LED or the group of LEDs is detected indirectly or directly. When the sensed temperature exceeds a predetermined shutdown threshold, the LED or group of LEDs is electrically bypassed and / or their feedthrough current is reduced.

In this case, in the simplest embodiment, the protection mode (bridging or the reduction of the through-current) can be canceled again if the detected, for example, measured temperature falls below a switch-on threshold again. The turn-on threshold may be different than the turn-off threshold, here equal to or preferably less than the turn-off threshold. The criteria for canceling this protection mode are preferably more complex, so that it may not be necessary to fall short of the switch-off threshold. For example. This may require that the temperature reaches an operating setpoint or a defined value between the setpoint and the switch-off threshold. The temperature threshold for canceling the protection mode can therefore be lower than the value for switching on the protection mode (hysteresis control).

Otherwise, the temperature could again be measured just below the shutdown threshold, then the override would be removed and after a short time the temperature could possibly rise above the shutdown threshold again and the system might shut down because of multiple overshoots. The cancellation of the protection mode can therefore be regulated by a hysteresis.

The bridging or reduction of the passage current can be maintained for a certain minimum time.

The bridging time, or the time of reduction of the through-current, can be made longer than the time required for the cooling of the LED or the group of LEDs.

The bridging or reduction of the through-current can be permanently maintained if the measured temperature repeatedly exceeds the switch-off threshold, in particular within a given time window.

The bridging or the reduction of the through-current can be permanently maintained if the occurrence of the overheating case meets predetermined switch-off criteria.

• – Die Frequenz des Auftretens, also die Anzahl des Auftretens in einer bestimmten Zeiteinheit. Nach Ablauf der Zeiteinheit ohne Überhitzungsfall oder ohne Erreichen einer vorgegebenen Anzahl von Überhitzungsfällen innerhalb der Zeiteinheit kann somit ein Zähler wieder auf Null gestellt werden („Reset”),
• – Die absolute Anzahl des Auftretens. Dabei kann ein Überhitzungsereignis-Zähler bei bestimmten Ereignissen (Neueinschalten, etc.) zurückgesetzt werden (”Reset”).

The mentioned shutdown criteria can be, for example:

• - The frequency of occurrence, ie the number of occurrences in a certain time unit. After expiration of the time unit without Überhitzungsfall or without reaching a predetermined number of overheating cases within the time unit thus a counter can be reset to zero ("Reset"),
• - The absolute number of occurrences. In this case, an overheating event counter can be reset ("reset") for certain events (restarting, etc.).

The bridging or reduction of the through-current can be displayed in the form of, for example, an acoustic or visual error signal. It can also be a message via a bus line to a control center.

The optical display can be realized by activating an LED, preferably a red LED, in the bypass path or the current reduction path.

When the LED or group of LEDs is part of an overall circuit comprised of a plurality of LEDs or groups of LEDs, the protection mode may be restricted to a portion of the LEDs or groups of LEDs of the plurality.

The temperature measurement can be done by means of a temperature sensor.

The bridging can be done by a thyristor.

The invention also relates to a circuit arrangement for protecting an LED or a group of LEDs, comprising: an LED protector connected in parallel with the LED or group of LEDs, which contains a temperature sensor, a logic circuit part and a bypass element, wherein the logic circuit part from the temperature sensor (thus generally: element for direct or indirect temperature detection) evaluates measured temperature and causes the bypass element to bridge the LED or group of LEDs or reduce their through-current when the measured temperature exceeds a predetermined switch-off threshold.

The bypass element can be a thyristor.

The logic circuit part may be programmed to switch the bypass element to a non-conductive state and thus to cancel the bypass when the measured temperature falls below the one turn-on threshold again, the turn-on threshold being from the off-state Threshold can differ, d. H. especially lower may be chosen.

The logic circuit part may be programmed to maintain bridging the LED or group of LEDs or reducing their through current for a certain minimum time.

The logic circuit part may be programmed such that the time of the bypass or the reduction of the through-current is made longer than the time required for the cooling of the LED or the group of LEDs.

The logic circuit portion may be programmed to permanently maintain the bypass current reduction when the measured temperature repeatedly exceeds the shutdown threshold.

The logic circuit part may be programmed so that the bypass or the reduction of the through-current is permanently maintained if the occurrence of the overheating case meets predetermined switch-off criteria.

• – Die Frequenz des Auftretens, also die Anzahl des Auftretens in einer bestimmten Zeiteinheit. Nach Ablauf der Zeiteinheit ohne Überhitzungsfall oder ohne Erreichen einer vorgegebenen Anzahl von Überhitzungsfällen innerhalb der Zeiteinheit kann somit ein Zähler wieder auf Null gestellt werden (”Reset”),
• – Die absolute Anzahl des Auftretens. Dabei kann ein Überhitzungsereignis-Zähler bei bestimmten Ereignissen (Neueinschalten, etc.) zurückgesetzt werden („Reset”).

The mentioned shutdown criteria can be, for example:

• - The frequency of occurrence, ie the number of occurrences in a certain time unit. After expiration of the time unit without Überhitzungsfall or without reaching a predetermined number of overheating cases within the time unit thus a counter can be reset to zero ("Reset"),
• - The absolute number of occurrences. In this case, an overheating event counter can be reset ("reset") for certain events (restarting, etc.).

Means for generating an error signal may be provided which become effective with the lock-up.

The means for generating an error signal may have a - preferably red - LED or other lighting means arranged in the bridging path or current reduction path.

When the LED or group of LEDs is part of an overall circuit comprised of a plurality of LEDs or groups of LEDs, the protection circuitry may be provided only on a portion of the LEDs or groups of LEDs of the plurality.

The invention also relates to an LED lamp, comprising a protective circuit of the type mentioned above and at least one LED illuminant, preferably at least one white LED.

The LED lamp can be, for example, a retrofit LED lamp, an LED module, an LED spot, etc.

Generally speaking, the solution is that the through-current is reduced by an LED or group of LEDs to be protected or brought to zero by bridging, if directly or indirectly, but preferably by a true temperature measurement, an increase of the operating temperature over a predetermined shutdown threshold is detected. This inevitably results in a cooling of the LED or the group of LEDs.

The reduction should preferably be maintained for a minimum time such that cooling below a turn-on threshold is safely achieved. The turn-on threshold may be less than or equal to the turn-off threshold.

If a repeated overheating is detected after switching off the reduction or bridging, then a new and now permanent shutdown or bridging can be made.

In order to detect overheating, the temperature of the LED or the group of LEDs should be measured and the measurement result used to control the switch-off or bridging time.

In order to recognize the effect to be counteracted from the outside, an error signal is preferably generated simultaneously with the reduction or bridging, which can be signaled to a control center via a bus line, for example. But it is also possible to limit the error signal locally and generate it as an optical or acoustic signal.

If one of the LEDs or groups of LEDs considered here is part of an overall circuit with many LEDs or groups of LEDs into which they are connected in series, it is sufficient if only a partial number of LEDs or groups of LEDs is protected in the manner previously described , This is because the reduction of the passage current of the number of partitions of LEDs or groups of LEDs inevitably also results in a reduction of the through-current of the overall circuit.

The circuit according realization of the inventive concept described above is possible with
a current protector connected in parallel with the LED or group of LEDs to be protected,
a temperature sensor,
a logic circuit part and
a bypass element,
wherein the logic circuit portion evaluates the temperature sensed by the temperature sensor and causes the by-pass element to bypass the LED array of LEDs or reduce their through current when the measured temperature exceeds a predetermined shutdown threshold.

As a bypass element, for example, a thyristor is suitable, which is switchable between a conducting and a non-conducting state. The bypass or current reduction takes place when the thyristor is controlled by the logic circuit part in the conductive state. If the LED or group of LEDs to be protected for dimming is operated by means of PWM operation ("PWM" means pulse width modulation), it is also possible to cancel the bridging or current reduction with a thyristor.

The temperature sensor should be physically in close contact with the LED or group of LEDs to be protected in order to ensure good heat transfer.

To indicate a fault is again an LED, which is inserted in the bypass path, such that it is supplied with activation of the bypass element with a sufficiently high operating voltage.

Embodiments of the invention are described below with reference to the drawing.

Show it:

1 a series connection of individual LEDs, one of which is connected to a protection circuit shown schematically;

2 a group of LEDs connected to a more detailed protection circuit.

In the 1 Series connection shown consists of three LEDs 1 . 2 and 3 of which only the middle LED 2 to be protected against overheating or against the overheating causing overcurrent. These LEDs (or even OLEDs) can be white LEDs and / or monochromatic LEDs.

To the LED 2 is an LED protector 4 connected in parallel. This causes the detection of overheating of the LED 2 that the LED 2 is bridged, so that the current flowing through the LED series circuit through-current through the LED protector 4 flows because it is very low in the activated state and the LED to be protected 2 practically short circuits. This bridging condition is maintained at least until the LED 2 safely cooled down again. The reconnection can be done automatically when cooling below a switch-on threshold temperature detection, but also targeted for a predetermined or adaptive (eg, dependent on the previous history) minimum time delay.

Then results in the monitoring of the operating temperature of the LED 2 that these are up again has cooled to a normal state, then the LED protector 4 switched back to its inactive state.

The LED protector 4 can be kept in its activated low-resistance state after detection of overheating a predetermined minimum time, which is such that a cooling is guaranteed with certainty.

In the event that the occurrence of overheating case meets certain criteria, the LED protector 4 be programmed so that a new switch to the inactive high-impedance state is excluded.

• – Die Frequenz des Auftretens, also die Anzahl des Auftretens in einer bestimmten Zeiteinheit. Nach Ablauf der Zeiteinheit ohne Überhitzungsfall oder ohne Erreichen einer vorgegebenen Anzahl von Überhitzungsfälllen innerhalb der Zeiteinheit kann somit ein Zähler wieder auf Null gestellt werden („Reset”),
• – Die absolute Anzahl des Auftretens. Dabei kann ein Überhitzungsereignis-Zähler bei bestimmten Ereignissen (Neueinschalten, etc.) zurückgesetzt werden („Reset”).

The mentioned criteria (switch-off criteria) can be, for example:

• - The frequency of occurrence, ie the number of occurrences in a certain time unit. After expiration of the time unit without Überhitzungsfall or without reaching a predetermined number of Überhitzungsfälllen within the time unit thus a counter can be reset to zero ("Reset"),
• - The absolute number of occurrences. In this case, an overheating event counter can be reset ("reset") for certain events (restarting, etc.).

It is also possible to use the LED protector 4 be designed so that it can not only switch between two extreme states (high-resistance and low-resistance), but that it depends on the degree of overheating reduction of the through-current through the LED to be protected 2 causes.

The in 2 shown more specifically implemented LED protector 4 is here parallel to a group 5 switched by LEDs, which are arranged on a common substrate. It contains a logic circuit part 6 , a temperature sensor 9 , a thyristor 7 and an error LED 8th ,

The temperature sensor 9 is in close thermoconductive contact with the group 5 of LEDs carrying substrate. That of the temperature sensor 9 generated measuring signal is the logic circuit part 6 supplied and from this to control the thyristor 7 evaluated. When the of the temperature sensor 9 measured temperature of the substrate carrying the LEDs exceeds a predetermined threshold, controls the logic circuit part 6 the previously non-conducting thyristor 7 in the conductive state. The thyristor 7 lies in a bridging path to the group 5 of LEDs, thereby forming practically a bypass element.

Looking at the function of in 2 initially shown circuit arrangement without the error indication LED 8th (think of them as completely conductive), so flows the current, previously through the group 5 of LEDs flowed and heated, with the activation of the thyristor 7 now via the bridging path with the thyristor 7 , The above related to 1 described functions relating to the activation time can by appropriate programming of the logic circuit part 6 will be realized.

In the 2 displayed error LED 8th is with the thyristor 7 connected in series. When the thyristor 7 becomes conductive, so in the bypass path is only the resistance of the error LED 8th effective. Above the error LED 8th Now a sufficiently high voltage drops, so that it lights up and thus signals the error optically. The light she creates falls through a window 10 and is from outside the LED protector 4 visible, noticeable.

Due to the presence of the error LED 8th in the bridging path, the current is through the group 5 of LEDs only reduced, but not completely redirected. That's also enough to cool the group down 5 of LEDs. The LEDs of the group 5 light up in the activated state of the thyristor 7 no more.

Because of the presence of the error LED 8th in the bridging path the group 5 is not completely short-circuited by LEDs, the logic circuit part can remove its operating voltage in the manner shown from the bridging path.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2009960 A2 [0003]

Claims (16)

Method for protecting an LED ( 2 ) or a group of LEDs ( 5 ) against overheating and high through-current at which the temperature of the LED ( 2 ) or the group of LEDs ( 5 ) is detected indirectly or directly, and then - when the detected temperature exceeds a predetermined switch-off threshold - the LED ( 2 ) or the group of LEDs ( 5 ) is electrically bypassed or its throughput current is reduced. The method of claim 1, wherein the bridging or the reduction of the through-current is canceled when the detected, for example. Measured temperature again falls below a switch-on threshold that is equal to or preferably less than the switch-off threshold. Method according to one of the preceding claims, wherein the bridging or reduction of the through-current is maintained for a certain minimum time. Method according to one of the preceding claims, in which the bridging time or the time of the reduction of the through-current is dimensioned longer than that for the cooling of the LED ( 2 ) or the group of LEDs ( 5 ) necessary time. Method according to one of the preceding claims, in which the bridging or the reduction of the through-current is permanently maintained if the occurrence of the overheating case fulfills predetermined switch-off criteria. Method according to one of the preceding claims, in which the bridging or reduction of the through-current is displayed in the form of an error signal. Method according to one of the preceding claims, in which - if the LED ( 2 ) or the group of LEDs ( 5 ) Part of one of a plurality of LEDs ( 1 - 3 ) or groups of LEDs ( 5 ) existing overall circuit is / are - only for a part of the LEDs ( 2 ) or groups of LEDs ( 5 ) is applied from the plurality. Method according to one of the preceding claims, wherein the temperature measurement by means of a temperature sensor ( 9 ) he follows. Circuit arrangement for protecting an LED ( 1 - 3 ) or a group of LEDs, comprising: one to the LED ( 2 ) or group of LEDs ( 5 ) parallel LED protector ( 4 ), a temperature sensor ( 9 ), a logic circuit part ( 6 ) and a bypass element ( 7 ), wherein the logic circuit part ( 6 ) from the temperature sensor ( 9 ) and the bypass element ( 7 ), the LED ( 2 ) or group of LEDs ( 5 ) or to reduce their through current when the measured temperature exceeds a predetermined shutdown threshold. Circuit arrangement according to Claim 9, characterized in that the logic circuit part ( 6 ) is programmed to bypass the bypass element ( 7 ) switches to a non-conductive state and thus overrides the current reduction when the measured temperature falls below a turn-on threshold equal to or preferably less than the turn-off threshold. Circuit arrangement according to one of Claims 9 or 10, characterized in that the logic circuit part ( 6 ) is programmed to bypass the LED ( 2 ) or group of LEDs ( 5 ) or the reduction of their passage current maintains a certain minimum time. Circuit arrangement according to one of claims 9 to 11, characterized in that the logic circuit part ( 6 ) is programmed so that the time of bridging or the reduction of the through-current is made longer than that for the cooling of the LED ( 2 ) or the group of LEDs ( 5 ) necessary time. Circuit arrangement according to one of Claims 12 to 16, characterized in that the logic circuit part ( 6 ) is programmed so that the bridging or reduction of the through-current is permanently maintained if the occurrence of the overheating case meets predetermined switch-off criteria. Circuit arrangement according to one of Claims 9 to 13, characterized by means ( 8th ) for generating an error signal activated with the bypass. Circuit arrangement according to one of claims 9 to 14, characterized in that - if the LED ( 2 ) or the group of LEDs ( 5 ) Is part of a total of one of a plurality of LEDs or groups of LEDs overall circuit is / are - the circuit arrangement only a part of the LEDs ( 2 ) or groups of LEDs ( 5 ) is provided from the plurality. LED lamp, comprising a circuit arrangement according to one of claims 9 to 15, and at least one LED lighting means.

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