EP4684599A1

EP4684599A1 - Led lighting circuit with redundancy

Info

Publication number: EP4684599A1
Application number: EP24710789.9A
Authority: EP
Inventors: Karnekumar ARULANDU; Theo Gerrit Zijlman; Anteneh Alemu ABBO; Dalibor Cvoric
Original assignee: Signify Holding BV
Current assignee: Signify Holding BV
Priority date: 2023-03-21
Filing date: 2024-03-15
Publication date: 2026-01-28
Also published as: JP2026508688A; WO2024194202A1; CN120937502A

Abstract

A LED lighting circuit comprises a driver circuit divided into a set of driver modules and a LED arrangement divided into separate LED sub-arrangements. A selection circuit selects LED sub-arrangements to be active and LED-sub-arrangements to be inactive. The selection circuit configures the LED sub-arrangements in dependence on a failure detection, as a first set of a plurality of active LED sub-arrangements and a second set of at least one inactive LED sub-arrangement. In this way fractional redundancy is provided, whereby one driver module and associated LED sub-arrangement can be taken out of operation, to allow the remaining non-failed modules and LED sub-arrangements to function normally.

Description

LED lighting circuit with redundancy

FIELD OF THE INVENTION

This invention relates to LED lighting circuits.

BACKGROUND OF THE INVENTION

Electronic products can be designed to achieve a desired life-time by means of derating (operating a device at less than its rated maximum capability to prolong its life). However some instances of early device failure and random failures are unavoidable.

Figure 1 shows the so-called Weibull curve that shows the mean time between failures. As shown, there is a relatively high early failure rate, a lower (random) failure rate for times up to the designed lifetime (the dotted line) and increasing failure rate after the designed lifetime.

This invention relates, in particular, to LED lighting circuits. LEDs can fail by creating a short circuit or an open circuit. LED drivers can also fail.

Some suppliers have proposed solutions to counter driver failure issues by providing two drivers in parallel. This corresponds to 100% driver redundancy. This solution is therefore not optimal from a cost and reliability point of view. The 100% redundancy is applied to the driver to cover a only fractional risk of failure. This increases the amount of electronics that will be thrown away. This also only addresses driver failure and does not address LED failure.

It would be of interest to address failure mechanisms to extend the operation life of LED drivers and LED modules in a cost-effective manner.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided a LED lighting circuit comprising: a plurality of LED sub-arrangements, each LED sub-arrangement comprising: a driver module; at least one LED, wherein the driver module is for driving the at least one LED; the LED lighting circuit further comprising: a failure detection system for detecting failure of a LED sub-arrangement; and a selection circuit for selecting LED sub-arrangements to be active and LED- sub-arrangements to be inactive, wherein the selection circuit is adapted to configure the LED subarrangements, in dependence on the failure detection by the failure detection system, as a first set of a plurality of active LED sub-arrangements and a second set of at least one inactive LED sub-arrangement.

This lighting circuit has fractional redundancy, whereby one (or more) driver module and its associated LED may be selected to be inactive. In particular, a driver module is effectively redundant when it is associated with an inactive LED sub-arrangement. This approach covers risks of early and random failure by dividing the entire circuit into a set of sections. In the case that a failure is detected, the failed section is rendered inactive, i.e. excluded from the electrical circuit. The configuration means the remaining circuits provide compensation of the failed section.

The fractional redundancy addresses risks of early and random failure, by dividing the entire circuit into a set of sections (each section having a driver module and a load). The multiple driver modules together function as a single driver. This single overall driver is thus split into a number of smaller modules. This allows the use of low-profile components. Large bulky components are more prone to failures due to their coefficient of thermal expansion and their large mass. The splitting up of the driver and LED load in this way also allows scalable designs without an increase of SKUs.

The fractional redundancy only requires a fraction of added components to ensure redundancy in the event that early failures or random failures occur.

The failure detection system is for example able to detect open circuit failures and/or short circuit failures, with high degree of detection accuracy. If a LED subarrangement has a short, an alternative current path can be provided.

The second set for example comprises a single inactive LED sub-arrangement.

In this way, redundancy is provided to enable continued operation when there is a fault in one LED sub-arrangement. There may for example be between 5 and 50 active LED sub-arrangements in the circuit. Thus a fractional redundancy of between 1/5 and 1/50 allows continued circuit operation in the event of a single failed LED sub-arrangement. Of course, the lighting circuit could enable two or more failed Led sub-arrangements by providing a higher fractional redundancy.

In one set of examples, the LED sub-arrangements are in series, and the selection circuit comprises a respective shorting transistor in parallel with each LED subarrangement.

A series configuration allows low voltage components to be used because the input voltage is distributed amongst the number of driver modules that are connected in series. The shorting transistor is used to bypass a failed LED sub-arrangement (and hence it also shorts the power supply to the driver module, rendering it inactive as well).

The failure detection system may then comprise a failure detection unit for each LED sub-arrangement. In this way, the location of the failure can be determined. This provides a robust failure detection method.

The failure detection units are for example configured to monitor one or more voltages of the associated driver module. The input voltage or output voltage may be measured in order to determine an error. In particular, an open circuit error will be evident, whereas a short circuit failure of an individual LED may not be evident, but such individual short circuit failure may not in any case matter to the overall device performance.

The failure detection unit for each LED sub-arrangement is for example powered by a power supply from a driver module associated with a different LED subarrangement.

Thus, an auxiliary supply circuit is used to supply the failure detection system and the selection circuit. In the case of a series configuration, the local power supply to the driver module is shorted when the LED sub-arrangement has a failure, so that a separate supply is needed to continue to power the failure detection.

The failure detection system may comprise a single failure detection unit for measuring a bus voltage, and wherein the lighting circuit further comprises a controller for locating a detected failure.

This provides a simplified failure detection, using a single centralized detection circuit that monitors only a bus voltage. When one of the series connected LED sub-arrangements fails (e.g., open circuit), an increase in the bus voltage will be detected. The controller may for example then operate the selection circuit in a scan procedure to determine which LED sub-arrangement has failed by monitoring the bus voltage. This has the advantage of lower hardware cost, but is less robust than independent detection circuits.

Each driver module for example comprises a boost converter. In another set of examples, the LED sub-arrangements are in parallel. This enables simpler fault detection and selection of active units.

The selection circuit may then comprise a respective isolating transistor in series with each LED sub-arrangement. The isolating transistor renders the LED subarrangement open circuit and hence not able to conduct current. Only the other parallel branches are then active.

The failure detection system is for example configured to monitor the LED current of each LED sub-arrangement. This is used to detect a current error through the LED load.

Each driver module for example comprises a buck-boost converter.

In all examples, the failure detection system may comprise an OR circuit for detecting failure detection in any of the individual LED sub-arrangements. The failure detection circuit for example comprises an error signal propagation circuit.

The invention also provides a method of implementing redundancy in a LED lighting circuit, wherein the LED lighting circuit comprises a driver circuit having a set of driver modules and a LED arrangement having a set of separate LED sub-arrangements, wherein each driver module is for driving an associated LED sub-arrangement, wherein the method comprises: detecting a failure of a LED sub-arrangement; configuring the LED sub-arrangements, in dependence on the detected failure, as a first set of a plurality of active LED sub-arrangements and a second set of at least one inactive LED sub-arrangement including the failed LED sub-arrangement.

The LED sub-arrangements may be in series, and the configuring is performed by operating a selection circuit which comprises a respective shorting transistor in parallel with each LED sub-arrangement.

Alternatively, the LED sub-arrangements may be in parallel, and the configuring is performed by operating a selection circuit which comprise a respective isolating transistor in series with each LED sub-arrangement.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Fig. 1 shows the Weibull curve that shows the mean time between failures;

Fig. 2 shows a typical known example of a LED lighting circuit;

Fig. 3 shows a first example of a LED lighting circuit with modules in parallel; Fig. 4 shows a first example of a LED lighting circuit with modules in series; Fig. 5 shows an example of the failure detection circuit for the series arrangement;

Fig. 6 shows an example of the failure detection circuit for a parallel arrangement; and

Fig. 7 shows a simplified detection arrangement for the series arrangement.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention will be described with reference to the Figures.

It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

The invention provides a LED lighting circuit that comprises a driver circuit divided into a set of driver modules and a LED arrangement divided into separate LED subarrangements. A selection circuit selects LED sub-arrangements to be active and LED subarrangements to be inactive. The selection circuit configures the LED sub-arrangements in dependence on a failure detection, as a first set of a plurality of active LED sub-arrangements and a second set of at least one inactive LED sub-arrangement. In this way fractional redundancy is provided, whereby one driver module and associated LED sub-arrangement can be taken out of operation, to allow the remaining non-failed modules and LED subarrangements to function normally. Figure 2 shows a conventional arrangement of a LED driver 101 and LEDs.

Mains power is supplied to the driver 101 through inputs 111 and 112. The driver 101 converts the input power to a suitable output power to supply the LED load via output lines 114, 115. The LED load consists of a series/parallel arrangement of LEDs. In conventional LED lighting applications, the LEDs are connected in series and these series arrangement of LEDs are applied in parallel branches.

Figure 2 shows a first branch with series LEDs 102, 103, 104, . . . 10m, a second branch with series LEDs 202, 203, 204, . . . 20m, and an nth branch with series LEDs nOl, n02, n03, . . . nOm (so n(m-l) LEDs in total in this example). The current distribution within the LED network depends on the total forward voltage of LEDs and the total dynamic resistance of the series arrangements of LEDs, such that the arrangement with lowest forward voltage conducts highest current, and vice versa.

Even though such arrangements are frequently used, they have the disadvantage that a failing driver results in no light output, and that a LED failure as a short results in high level of current imbalance. Building redundancy into such a circuit makes matters complicated as it is powered by a single driver. A single component failure is in such case expected to cause a complete driver failure instantly or over time.

Figure 3 shows a first example of a LED circuit in accordance with the invention having a series connection of LED driver sections and Figure 4 shows a second example of a LED circuit in accordance with the invention with a set of parallel LED driver sections. Each parallel branch has a series connection of LEDs.

In both examples, the single driver and the LED load are split into a plurality of independent sections, hence with independent LED driver modules and LED subarrangements, with one LED sub-arrangement associated with each driver module.

The series example of Figure 3 has first to nth driver modules 101, 201, nOl. Each driver module is used to drive an associated series string of LEDs. Module 101 drives LEDs 102, ... 10m, module 101 drives LEDs 202, . . . 20m and module nOl drives LEDs n02, . . . nOm (hence again n(m-l) LEDs in total).

The driver modules are in series. In other words, the current through each driver module is the same and the same series current may therefore flow through all LED strings. This single series current is the current drawn from the supply.

The parallel example of Figure 4 has first to nth driver modules 101, 201, nOl. Each driver module is used to drive an associated series string of LEDs. Module 101 drives LEDs 102, ... 10m, module 101 drives LEDs 202, . . . 20m and module nOl drives LEDs n02, . . . nOm (hence again n(m-l) LEDs in total).

The driver modules are in parallel. In other words, the current delivered by each driver module is in parallel with the other driver modules so that the currents may be different. The current drawn from the supply is the sum of the parallel branch currents.

In each of Figures 3 and 4, the driver circuit is divided into a set of driver modules and the overall arrangement of LEDs comprises a set of separate LED subarrangements, wherein each driver module is for driving an associated LED sub-arrangement.

Figures 3 and 4 each schematically show a failure detection system 500 for detecting failure of a LED sub-arrangement and a selection circuit 502 for selecting LED sub-arrangements to be active and LED-sub-arrangements to be inactive. The selection circuit configures the LED sub-arrangements, in dependence on the failure detection by the failure detection system.

The different sections are configured as a first set of a plurality of active LED sub-arrangements and a second set of at least one inactive LED sub-arrangement. In preferred examples, there is a single additional section which is only used when a failure is detected in one of the other sections. Thus, the second set has exactly one driver module and one LED sub-arrangement. However, there could by more than one additional section.

The division of the overall driver architecture and LED arrangement into a number of sections provides fractional redundancy, whereby one (or more) driver module and its associated LED sub-arrangement may be selected to be inactive. In particular, a driver module is effectively redundant when it is associated with an inactive LED sub-arrangement.

When a failure is detected, the failed section is rendered inactive, i.e. excluded from the electrical circuit. The remaining circuits (including the redundant section) then provide compensation of the failed section. Thus, the redundant section then functions as a normal section. The fractional redundancy addresses risks of early and random failure. The failure detection system is for example able to detect open circuit failures and/or short circuit failures, with high degree of detection accuracy. If a LED sub-arrangement has a short, an alternative current path can be provided.

The series configuration is more complex in the sense of the control loop design, and error signal propagation. However, it can allow low voltage components to be used because the input voltage is distributed amongst the number of drivers that are connected in series. The parallel configuration is simpler to implement. The rate of redundancy of the circuit is given by 1/n, where n is the number of independent driver modules and associated LED load (i.e. LED sub-arrangement). This assumes one additional normally redundant circuit.

In preferred examples, a failure detection circuit is provided for each section and the selection circuit provides an engagem ent/ disengagement function per independent driver module and LED sub-arrangement. The number of independent driver modules and associated LED sub -arrangements (i.e. number n) is for example in the range 5 to 50 so that the amount of additional circuitry is limited.

For the series arrangement of Figure 3, a single LED short failure from a long string of LEDs (i.e. a large value of m such as 20 or more) has almost negligible impact, therefore this failure mode may be discarded from the failure detection.

For the series arrangement, a failure is detected when the LED current is detected to be outside a pre-defined operating window. This can be detected simply based on the resulting voltage.

Figure 5 shows an example of the failure detection circuit for the series arrangement.

The circuit comprises sections 100, 200, . . . mOO. Each section has a driver module and associated LED sub-arrangement, together shown as nodes 1001, 2001, . . . mOOl. The driver module is shown as having a boost converter topology. Other topologies also be applicable.

In this example, m^th section mOO may be considered to be a spare section. Thus, by default it is inactive (and hence redundant), until the fault detection determines that it is needed. It is positioned as the top section (i.e. at the high voltage end of the series connection) due to the implementation of an auxiliary supply circuit explained below.

In the series arrangement, a defective section needs to short circuit itself. For this purpose, each section has a shorting transistor 1002 in parallel with the node. The shorting transistor shorts power supply to the driver module rendering it inactive.

The components for the failure detection and selection are shown for all sections and they are explained with reference to section 100.

The shorting transistor is shown as 1002. The failure detection system is also divided into sections. For the section 100, a failure detection circuit 1004 is shown. The shorting transistor 1002 is driven by signal 1105 which is generated by the failure detection circuit 1004. The supply to maintain the short circuited condition needs to be extracted from outside the section itself (because the power supply to the section is shorted). In this particular example, auxiliary power is drawn from the section above. Thus, auxiliary power for section 100 is supplied from the spare section mOO by auxiliary power supply circuit 1005, and auxiliary power for section 200 is supplied from the section 100 by auxiliary power supply circuit 2005.

The auxiliary power supply circuit 1005 delivers power by line 1102 to the detection circuit 1004. As the spare node mOOl is short circuited, the auxiliary supply potential is shorted to the supply node mlOl and hence almost equal to the supply voltage of the node itself at node 1101. In the case of an error in section 100, it will short circuit itself which will enable the spare section mOO to become active. The auxiliary power supply circuit 1005 is supplied from section mOO.

There are many causes that could result in a failure, but a critical failure will result in a mismatch in input voltage or output voltage of the boost converter. Therefore, the input voltage, 1101, and the output voltage of the boost converter are monitored for failure detection by window comparators in the failure detection circuit 1004.

Once an error condition is detected by the failure detection circuit 1004, the defective section 100 is short circuited by the parallel transistor 1002.

The control signal 1005 to the shorting transistor provides an indication of when a fault has been detected. This control signal 1005 is supplied to a monitor circuit 1003 which provides an OR function.

Each OR function is applied to the (i) output from the section below (line 1106 is the output of the monitor circuit 2003 and is an input to the monitor circuit 1003) and (ii) . the shorting transistor gate signal. Thus, a cascaded series of OR circuit propagates an error signal up to the redundant section mOO.

When the redundant section receives an indication that there is an error in one (or more) of the sections below, the node mOOl is activated by the drive circuit m003.

This arrangement thus does not require an overall controller for the redundancy function. However, an overall controller may also be provided, for example monitoring the status of the driver, for example indicating how many redundant components are used at any point in time.

In order to prevent oscillation, the shorting transistor should remain in a conducting state until the next power cycle. At each power-up, the circuit starts up normally until an error is detected. Particularly in the series configuration that benefits from the use of low voltage components, the error detection signal needs to propagate through the higher potential nodes in order to activate the spare node, which is positioned at the highest potential of the circuit as explained above.

Compared to the series circuit of Figure 5, the failure detection for the parallel arrangement is far simpler.

Figure 6 shows the failure detection circuit for a parallel arrangement. Two sections 100, mOO are shown. The parallel sections are all supplied by the direct current (DC) rails 1101 and 1104. Each driver module is shown in this example as a buck-boost converter.

In contrast to the series arrangement, where voltage is used as a means to detect an error condition, the error detection in the parallel configuration only detects the LED current. A current sense resistor 1003 is used for this purpose.

At power up, all ‘normal’ sections 100, 200, etc. are powered on by default by setting the series transistors 1002, 2002, 3002 etc. into a conducting state once auxiliary supplies 1005, 2005, 3005 etc. are present.

If the current through a node is not within a specific window, this specific node is excluded from the circuit, and the spare section, mOO is activated. Compared to the normal sections, the spare section contains an additional input 600 to the detection circuit m004, on which it receives the error signal from a faulty node. Since the fault can occur in any of the parallel circuits, the individual fault detector outputs are combined with a wired- OR circuit to generate the error signal 600.

The OR circuit simply combines the outputs from all the failure detection circuits (and does not need the more complicated signal propagation approach of Figure 5).

Figures 5 and 6 are merely examples.

Another approach is that all nodes i.e., normal nodes and spare nodes may be powered on by default. This is intended to apply equal aging to all components. In an event of a failure, the defective node is excluded from the power rails 1101, and 1104, while the remaining nodes increase their output power to compensate for the for the excluded defective node.

The invention is of particular interest for crucial errors, such as an open circuit error for a series arrangement and a short circuit error for a parallel arrangement. Such errors may result in a complete failure of the lighting system. Such complete failures are prevented by the failure detection and selection functions described above.

Instead of an isolating transistor for the parallel arrangement, a fuse could be used. Figure 7 shows a simplified arrangement for the series arrangement. A centralized detection circuit 500 monitors only the bus voltage Vbus. When one of the series connected cells fails (open circuit), an increase in the bus voltage will be detected. Then a central control circuit 504 turns on each of the bypass transistors e.g. 1002 in turn (as a scanning process) to determine which cell has failed by monitoring Vbus while enabling the bypass transistor.

If Vbus drops to a threshold level, a faulty cell is determined and then bypassed. A backup cell is enabled to resume the operation. The backup cell can be any one of the series connected cells.

The solution above detects a faulty LED output, which includes an output fault resulting from a failure of the associated driver module. The driver modules typically have protection functions built in, and these protection functions generate signals that could also be used for detection of faults (overvoltage protection OVP, and overcurrent protection OCP).

The driver module fault signals could be also OR-ed with the LED failure mechanisms.

However, because the LED sub-arrangement and driver module are bound together, only any detection of overall failure of the combined unit is needed (i.e. there is little added benefit in independently detecting a driver module fault, since the non-failed LED sub-arrangement will still not be available for use.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

If the term "adapted to" is used in the claims or description, it is noted the term "adapted to" is intended to be equivalent to the term "configured to". If the term "arrangement" is used in the claims or description, it is noted the term "arrangement" is intended to be equivalent to the term "system", and vice versa.

Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A LED lighting circuit comprising: a plurality of LED sub-arrangements, each LED sub-arrangement comprising: a driver module (101, 201, nOl); at least one LED (102, 202, n02), wherein the driver module is for driving the at least one LED; the LED lighting circuit further comprising: a failure detection system (500) for detecting failure of a LED subarrangement; and a selection circuit (502) for selecting LED sub-arrangements to be active and LED-sub -arrangements to be inactive; wherein the selection circuit is adapted to configure the LED subarrangements, in dependence on the failure detection by the failure detection system, as a first set of a plurality of active LED sub-arrangements and a second set of at least one inactive LED sub-arrangement, wherein the plurality of LED sub-arrangements are coupled in series.

2. The lighting circuit of claim 1, wherein the second set comprises a single inactive LED sub-arrangement.

3. The lighting circuit of claim 1 or 2, wherein the selection circuit comprises a respective shorting transistor (1002) in parallel with each LED sub-arrangement.

4. The lighting circuit of claim 3, wherein the failure detection system comprises a failure detection unit (1004) for each LED sub-arrangement.

5. The lighting circuit of claim 4, wherein the failure detection units are configured to monitor one or more voltages of the associated driver module.

6. The lighting circuit of any one of claims 4 to 5, wherein the failure detection unit for each LED sub-arrangement is adapted to be powered by a power supply from a driver module associated with a different LED sub-arrangement.

7. The lighting circuit of any one of preceding claims, wherein each driver module comprises a boost converter.

8. A method of implementing redundancy in a LED lighting circuit, wherein the LED lighting circuit comprises a plurality of LED sub-arrangements, each LED subarrangement comprising a driver module and at least one LED, wherein the driver module is for driving the at least one LED, wherein the plurality of LED sub-arrangements are coupled in series and wherein the method comprises: detecting a failure of a LED sub-arrangement; configuring the LED sub-arrangements, in dependence on the detected failure, as a first set of a plurality of active LED sub-arrangements and a second set of at least one inactive LED sub-arrangement including the failed LED sub-arrangement.

9. The method of claim 8, wherein: the LED sub-arrangements are in series, and the configuring is performed by operating a selection circuit which comprises a respective shorting transistor in parallel with each LED sub-arrangement; or the LED sub-arrangements are in parallel, and the configuring is performed by operating a selection circuit which comprise a respective isolating transistor in series with each LED sub-arrangement.