Redundant LED lighting circuit

Abstract

The LED lighting circuit has a driver circuit divided into a set of driver modules and an LED configuration divided into separate LED sub-configurations. A selection circuit selects which LED sub-configurations should be active and which should be inactive. The selection circuit configures the LED sub-configurations as a first set of multiple active LED sub-configurations and a second set of at least one inactive LED sub-configuration depending on fault detection. In this manner, partial redundancy is provided, whereby certain driver modules and associated LED sub-configurations can be removed from operation to allow the remaining non-faulty modules and LED sub-configurations to function normally.

Description

[Technical Field]

[0001] The present invention relates to an LED lighting circuit. [Background technology]

[0002] Electronic products can be designed to achieve a desired lifespan by derating (operating the device below its rated maximum capability to extend the device's lifespan), however, some instances of early device failure and random failure are inevitable.

[0003] Figure 1 shows the so-called Weibull curve, which shows the mean time between failures. As can be seen, there is a relatively high early failure rate, a lower (random) failure rate during the design life (dotted line), and an increasing failure rate after the design life.

[0004] The present invention relates, inter alia, to LED lighting circuits. LEDs can fail by becoming short-circuited or open, and LED drivers can also fail.

[0005] Some suppliers propose a solution to address the driver failure issue by providing two drivers in parallel. This is equivalent to 100% driver redundancy. Therefore, this solution is not optimal from the perspective of cost and reliability. 100% redundancy is applied to the driver to cover only a partial risk of failure. This increases the amount of wasted electronics. It also only addresses driver failure, not LED failure. Summary of the Invention [Problem to be solved by the invention]

[0006] It would be interesting to address the failure mechanisms to extend the operational lifetime of LED drivers and LED modules in a cost-effective manner. [Means for solving the problem]

[0007] The invention is defined by the claims.

[0008] According to an example of an aspect of the present invention, there is provided an LED lighting circuit having a plurality of LED sub-arrangements, each of which comprises: A driver module; at least one LED, wherein the driver module is for driving the at least one LED; The LED lighting circuit a fault detection system for detecting a fault in the LED sub-configuration; a selection circuit for selecting which LED sub-configurations are to be active and which are to be inactive; An LED lighting circuit is provided, wherein the selection circuit is adapted to configure the LED sub-configurations as a first set of a plurality of active LED sub-configurations and a second set of at least one inactive LED sub-configuration depending on fault detection by the fault detection system.

[0009] The lighting circuit has fractional redundancy, meaning that one (or more) driver modules and their associated LEDs can be selected to be inactive. In particular, a driver module effectively becomes redundant if it is associated with an inactive LED sub-configuration. This approach covers the risk of early and random failures by dividing the entire circuit into a set of sections. If a failure is detected, the failed section is deactivated, i.e., removed from the electrical circuit. This configuration means that the remaining circuit provides compensation for the failed section.

[0010] The partial redundancy addresses the risk of early and random failures by dividing the entire circuit into a set of sections (each section having a driver module and a load). Multiple driver modules together function as a single driver. This entire single driver is therefore divided into many smaller modules. This allows for the use of thin components. Large, bulky components are more prone to failure due to their thermal expansion coefficients and large mass. Dividing the driver and LED load in this manner also allows for a scalable design without increasing SKUs.

[0011] The partial redundancy requires only a few additional components to ensure redundancy in the event of an early or random failure.

[0012] The fault detection system can detect, for example, open circuit faults and / or short circuit faults with high detection accuracy. If an LED sub-configuration has a short circuit, an alternative current path can be provided.

[0013] The second set may, for example, comprise a single inactive LED sub-configuration.

[0014] In this manner, redundancy is provided to allow continued operation if one LED sub-configuration fails. For example, there may be 5 to 50 active LED sub-configurations in a circuit. Thus, a partial redundancy of 1 / 5 to 1 / 50 allows continued circuit operation if a single LED sub-configuration fails. Of course, the lighting circuit can accommodate failures of more than one LED sub-configuration by providing a higher partial redundancy.

[0015] In one set of examples, the LED sub-configurations are in series and the selection circuit has a respective shorting transistor in parallel with each LED sub-configuration.

[0016] The series configuration allows for the use of lower voltage components since the input voltage is distributed to many driver modules connected in series. The shorting transistor is used to bypass a failed LED sub-configuration (thus also shorting the power supply to the driver module, rendering the driver module inactive as well).

[0017] The fault detection system may then comprise a fault detection unit for each LED sub-configuration. In this way, the fault location can be identified. This provides a robust fault detection method.

[0018] The fault detection unit may be configured to monitor, for example, one or more voltages of the associated driver module. To identify an error, the input or output voltage may be measured. In particular, an open circuit error may be obvious, whereas an individual LED short circuit fault may not be obvious, although such an individual short circuit fault may not be a problem for the overall device performance in any case.

[0019] The fault detection unit for each LED sub-configuration is, for example, powered by a power supply from a driver module associated with a different LED sub-configuration.

[0020] Therefore, an auxiliary power circuit is used to supply the fault detection system and the selection circuit. In the series configuration, when the LED sub-configuration has a fault, the local power supply to the driver module is shorted, and therefore a separate power supply is required to continue powering the fault detection system.

[0021] The fault detection system may comprise a single fault detection unit for measuring bus voltage, the lighting circuit further comprising a controller for locating a detected fault.

[0022] This provides simplified fault detection using a single centralized detection circuit that monitors only the bus voltage. When one of the series-connected LED sub-configurations fails (e.g., an open circuit), an increase in the bus voltage is detected. The controller can then operate the selection circuit in a scanning procedure to identify which LED sub-configuration has failed, for example, by monitoring the bus voltage. This has the advantage of lower hardware costs, but is less robust than separate detection circuits.

[0023] Each driver module includes, for example, a boost converter.

[0024] In another set of examples, the LED sub-configurations are in parallel, which allows for easier fault detection and selection of the active unit.

[0025] In that case, the selection circuit may include a respective isolation transistor in series with each LED sub-configuration, which causes the LED sub-configuration to be open-circuited and therefore unable to conduct current, with only the other parallel branch being active.

[0026] The fault detection unit is configured, for example, to monitor the LED current of each LED sub-configuration, which is used to detect errors in the current through the LED load.

[0027] The driver module may, for example, comprise a buck-boost converter.

[0028] In all examples, the fault detection system may include an OR circuit for detecting a fault in any of the individual LED sub-configurations. The fault detection circuit may include, for example, an error signal propagation circuit.

[0029] The present invention provides a method of implementing redundancy in an LED lighting circuit, the LED lighting circuit including a driver circuit having a set of driver modules and an LED configuration having a set of separate LED sub-configurations, each driver module for driving an associated LED sub-configuration, the method comprising: detecting a failure of an LED sub-configuration; and configuring the LED sub-configurations as a first set of a plurality of active LED sub-configurations and a second set of at least one inactive LED sub-configuration including the failed LED sub-configuration depending on the detected failure.

[0030] The LED sub-configurations may be in series, and the configuring step is performed by operating a selection circuit having a respective shorting transistor in parallel with each LED sub-configuration.

[0031] In another example, the LED sub-configurations may be in parallel, and the configuring step is performed by operating a selection circuit having a respective isolation transistor in series with each LED sub-configuration.

[0032] These and other aspects of the invention will be elucidated and elucidated with reference to the following embodiments. [Brief explanation of the drawings]

[0033] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: [Figure 1] 1 shows a Weibull curve showing the mean time between failures. [Figure 2] Shown are some common known examples of LED lighting circuits. [Figure 3] 1 shows a first example of an LED lighting circuit with modules in parallel. [Figure 4] 1 shows a first example of an LED lighting circuit with modules in series. [Figure 5]1 shows an example of a fault detection circuit for a series configuration. [Figure 6] 1 shows an example of a fault detection circuit for a parallel configuration. [Figure 7] 1 shows a simplified detection configuration for a series configuration. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention will be described with reference to the drawings.

[0035] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are 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 devices, 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.

[0036] The present invention provides an LED lighting circuit having a driver circuit divided into a set of driver modules and an LED configuration divided into separate LED subconfigurations. A selection circuit selects which LED subconfigurations should be active and which should be inactive. The selection circuit configures the LED subconfigurations as a first set of multiple active LED subconfigurations and a second set of at least one inactive LED subconfiguration depending on fault detection. In this manner, partial redundancy is provided, whereby certain driver modules and associated LED subconfigurations can be removed from operation to allow the remaining non-faulty modules and LED subconfigurations to function normally.

[0037] Figure 2 shows a conventional configuration of an LED driver 101 and LEDs. Mains power is supplied to the driver 101 via inputs 111 and 112. The driver 101 converts the input power into an appropriate output power to supply to an 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 arrangements of LEDs are applied in parallel branches.

[0038] 2 shows a first branch comprising series LEDs 102, 103, 104, ... 10m, a second branch comprising series LEDs 202, 203, 204, ... 20m, and an nth branch comprising series LEDs n02, n03, n04, ... n0m (so a total of n(m-1) LEDs in this example). The current distribution in the LED network depends on the total forward voltage of the LEDs and the total dynamic resistance of the series string of LEDs, such that the string with the lowest forward voltage will conduct the highest current, and vice versa.

[0039] Although such arrangements are frequently used, they have the disadvantage that driver failure results in no light output, and LED failures, such as short circuits, result in high levels of current imbalance. Building redundancy into such circuits complicates matters because the circuits are powered by a single driver. In such cases, failure of a single component can be expected to immediately or eventually lead to failure of the entire driver.

[0040] Figure 3 shows a first example of an LED circuit according to the invention with a series connection of LED driver sections, and Figure 4 shows a second example of an LED circuit according to the invention with a set of parallel LED driver sections, each parallel branch having a series connection of LEDs.

[0041] In both examples, a single driver and LED load is divided into multiple independent sections, and therefore multiple sections, with independent LED driver modules and LED sub-configurations, with one LED sub-configuration associated with each driver module.

[0042] The series example of Figure 3 includes first through nth driver modules 101, 201, n01. Each driver module is used to drive an associated series string of LEDs: module 101 drives LEDs 102, ... 10m, module 201 drives LEDs 202, ... 20m, and module n01 drives LEDs n02, ... n0m (so again, a total of n(m-1) LEDs).

[0043] The driver modules are in series, in other words the current through each driver module is the same, and therefore the same series current can flow through all the LED strings. This single series current is the current drawn from the power supply.

[0044] The parallel example of Figure 4 includes first through nth driver modules 101, 201, n01. Each driver module is used to drive an associated series string of LEDs: module 101 drives LEDs 102, ... 10m, module 201 drives LEDs 202, ... 20m, and module n01 drives LEDs n02, ... n0m (so again, a total of n(m-1) LEDs).

[0045] The driver modules are in parallel, in other words the current supplied by each driver module is in parallel with the other driver modules and therefore the currents may be different. The current drawn from the power supply is the sum of the parallel branch currents.

[0046] In each of Figures 3 and 4, the driver circuitry is divided into a set of driver modules, and the overall LED configuration has a set of separate LED sub-configurations, with each driver module for driving an associated LED sub-configuration.

[0047] 3 and 4 each schematically show a fault detection system 500 for detecting faults in LED sub-configurations and a selection circuit 502 for selecting which LED sub-configurations to activate and which to deactivate. The selection circuit configures the LED sub-configurations depending on the fault detection by the fault detection system.

[0048] The different sections are configured as a first set of multiple active LED sub-configurations and a second set of at least one inactive LED sub-configuration. In a preferred example, there is a single additional section that is used only if a fault is detected in one of the other sections. Thus, the second set has exactly one driver module and one LED sub-configuration. However, there may be more than two additional sections.

[0049] Dividing the driver architecture and the entire LED configuration into many sections provides partial redundancy, whereby one (or more) driver modules and their associated LED sub-configurations can be selected to be inactive. In particular, a driver module effectively becomes redundant when associated with an inactive LED sub-configuration. If a fault is detected, the failed section is deactivated, i.e., removed from the electrical circuit. The remaining circuit (including the redundant section) then provides compensation for the failed section. Thus, the redundant section then functions as a normal section. Partial redundancy addresses the risks of early failures and random failures. The fault detection system can detect, for example, open-circuit faults and / or short-circuit faults with high detection accuracy. If an LED sub-configuration has a short circuit, an alternative current path can be provided.

[0050] The series configuration is more complex in terms of control loop design and error signal propagation. However, it can allow for the use of lower voltage components because the input voltage is distributed among many drivers connected in series. The parallel configuration is simpler to implement.

[0051] The circuit redundancy ratio is given by 1 / n, where n is the number of independent driver modules and associated LED loads (i.e., LED sub-configurations). This assumes one additional normal redundant circuit.

[0052] In a preferred example, a fault detection circuit is provided for each section, and a selection circuit provides engagement / disengagement functions for each independent driver module and LED sub-configuration. The number of independent driver modules and associated LED sub-configurations (i.e., the number n) is, for example, in the range of 5 to 50, so the amount of additional circuitry is limited.

[0053] For the series configuration of FIG. 3, a short circuit failure of a single LED in a long string of LEDs (i.e., m is a large value, such as 20 or more) has an almost negligible impact, and therefore this failure mode can be discarded from fault detection.

[0054] In the series configuration, a fault is detected if the LED current is detected to be outside a predetermined operating window, which can be easily detected based on the resulting voltage.

[0055] FIG. 5 shows an example of a fault detection circuit for a series configuration.

[0056] The circuit has sections 100, 200, ... m00. Each section has a driver module and associated LED sub-configuration, shown together as nodes 1001, 2001, ... m001. The driver modules are shown as having a boost converter topology; other topologies are also applicable.

[0057] In this example, m section m00 may be considered a spare section. Thus, by default, m section m00 is inactive (and therefore redundant) until fault detection determines that m section m00 is needed. m section m00 is placed as the top section (i.e., at the high-voltage end of the series connection) for implementation of the auxiliary power circuitry described below.

[0058] In a series configuration, the faulty section must short itself out. For this purpose, each section has a shorting transistor 1002 in parallel with the node. The shorting transistor shorts out the power supply to the driver module, making it inactive.

[0059] Components for fault detection and selection are shown for all sections and are described with reference to section 100.

[0060] The shorting transistor is shown as 1002. The fault detection system is also divided into sections. For section 100, fault detection circuit 1004 is shown. Shorting transistor 1002 is driven by signal 1105 generated by fault detection circuit 1004.

[0061] Power to maintain the short circuit condition must be extracted from outside the section itself (since power to the section is shorted). In this particular example, auxiliary power is extracted from the section above. Thus, auxiliary power for section 100 is supplied from auxiliary section m00 by auxiliary power circuit 1005, and auxiliary power for section 200 is supplied from auxiliary section 100 by auxiliary power circuit 2005.

[0062] Auxiliary power circuit 1005 supplies power to detection circuit 1004 by line 1102. Because spare node m001 is shorted, the auxiliary power potential is shorted to supply node m101 and is therefore approximately equal to the node's own supply voltage at node 1101. In the event of an error in section 100, section 100 shorts itself, which allows spare section m00 to become active. Auxiliary power circuit 1005 is supplied from section m00.

[0063] Although there are many causes that can lead to a fault, a serious fault results in a mismatch in the input or output voltage of the boost converter. Therefore, the input voltage 1101 and output voltage of the boost converter are monitored for fault detection by a window comparator in the fault detection circuit 1004.

[0064] When an error condition is detected by the fault detection circuit 1004 , the faulty section 100 is shorted out by the parallel transistor 1002 .

[0065] A control signal 1005 to the shorting transistor provides an indication of when a fault has been detected. This control signal 1005 is fed to a monitor circuit 1003 which provides an OR function.

[0066] Each OR function is applied to (i) the output from the section below (line 1106 is the output of monitor circuit 2003 and the input to monitor circuit 1003) and (ii) the gate signal of the shorting transistor. Thus, the cascaded series of OR circuits propagates the error signal up to redundant section m00.

[0067] When the redundant section receives an indication that an error exists in one (or more) of the sections below, node m001 is activated by driver circuit m003.

[0068] Therefore, this configuration does not require a global controller for the redundancy function, although a global controller may be provided that, for example, monitors the status of the drivers and indicates, for example, how many redundant components are being used at any one time.

[0069] To prevent oscillation, the shorted transistor must remain conductive until the next power cycle. At each power-up, the circuit starts up normally until an error is detected. In particular, in series configurations that benefit from the use of low-voltage components, the error detection signal must propagate through a node at a higher potential to activate the spare node, which is located at the highest potential of the circuit as explained above.

[0070] Compared to the series circuit of FIG. 5, fault detection for the parallel configuration is much simpler.

[0071] Figure 6 shows a fault detection circuit for a parallel configuration. Two sections 1100, m00 are shown. The parallel sections are all supplied by direct current (DC) rails 1101 and 1104. In this example, each driver module is shown as a buck-boost converter.

[0072] In contrast to the series configuration, where voltage is used as a means to detect an error condition, error detection in the parallel configuration only senses the LED current. For this purpose, current sensing resistor 1003 is used.

[0073] At power up, if the auxiliary power supply 1005, 2005, 3005, etc. is present, all "normal" sections 100, 200, etc. are powered up by default by setting the series transistors 1002, 2002, 3002, etc. to a conductive state.

[0074] If the current through a node is not within a certain window, this particular node is removed from the circuit and the spare section m00 is activated. Compared to the normal section, the spare section includes an additional input 600 to the detection circuit m004, which receives an error signal from the fault node at the additional input 600. Since a fault can occur in any of the parallel circuits, the outputs of the individual fault detectors are combined with a wired OR circuit to generate the error signal 600.

[0075] The OR circuit simply combines the outputs from all the fault detection circuits (without requiring the more complex signal propagation technique of Figure 5).

[0076] Figures 5 and 6 are examples only.

[0077] Another approach is that all nodes, normal and spare, can be powered on by default. This is intended to apply uniform aging to all components. In the event of a failure, the faulty node is removed from the power rails 1101 and 1104, while the remaining nodes increase their output power to compensate for the removed faulty node.

[0078] The present invention is of particular interest with respect to serious errors, such as open circuit errors in the case of a series configuration and short circuit errors in the case of a parallel configuration, which can lead to a complete failure of the lighting system, which is prevented by the fault detection and selection features described above.

[0079] Instead of isolation transistors for the parallel configuration, fuses may be used.

[0080] 7 shows a simplified configuration for a series configuration. The centralized detection circuit 500 monitors only the bus voltage Vbus. When one of the series-connected cells fails (e.g., an open circuit), an increase in the bus voltage is detected. The central control circuit 504 then turns on each of the bypass transistors, e.g., 1002, in turn (as a scanning process) and identifies which cell has failed by monitoring Vbus while the bypass transistors are enabled.

[0081] When Vbus drops to a threshold level, the failed cell is identified and then bypassed, and a backup cell is enabled to resume operation. The backup cell can be any one of the series-connected cells.

[0082] The above solutions detect faulty LED outputs, including output faults caused by failures in the associated driver modules. Driver modules generally have built-in protection functions that generate signals that can also be used to detect faults (overvoltage protection OVP and overcurrent protection OCP).

[0083] The driver module's fault signal can also be OR-ed with the LED failure mechanism.

[0084] However, because the LED sub-configuration and driver module are lumped together, only detection of the failure of the entire combined unit is required (i.e., independent detection of a driver module failure offers little additional benefit, since a non-faulty LED sub-configuration would still not be available for use).

[0085] Those skilled in the art can understand and effect variations to the disclosed embodiments in practicing the claimed invention, from a study of the drawings, the specification and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the singular does not exclude a plurality.

[0086] 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.

[0087] It should be noted that when the term "adapted to" is used in the claims or the specification, the term "adapted to" is intended to be equivalent to the term "configured to." It should be noted that when the term "configuration" is used in the claims or the specification, the term "configuration" is intended to be equivalent to the term "system," and vice versa.

[0088] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. An LED lighting circuit having a plurality of LED sub-arrangements, each LED sub-arrangement comprising: A driver module; at least one LED, the driver module being for driving the at least one LED; The LED lighting circuit a fault detection system for detecting a fault in the LED sub-configuration; a selection circuit for selecting which LED sub-configurations are to be active and which are to be inactive; the selection circuitry is adapted to configure the LED sub-configurations as a first set of a plurality of active LED sub-configurations and a second set of at least one inactive LED sub-configuration dependent on a fault detection by the fault detection system; An LED lighting circuit in which the plurality of LED sub-configurations are coupled in series.

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

3. 3. A lighting circuit as claimed in claim 1 or 2, wherein the selection circuit comprises a respective shorting transistor in parallel with each LED sub-configuration.

4. 4. The lighting circuit of claim 3, wherein the fault detection system comprises a fault detection unit for each LED sub-configuration.

5. 5. A lighting circuit as claimed in claim 4, wherein the fault detection unit is configured to monitor one or more voltages of an associated driver module.

6. 6. A lighting circuit according to claim 4 or 5, wherein the fault detection unit for each LED sub-configuration is adapted to be powered by a power supply from a driver module associated with a different LED sub-configuration.

7. 7. A lighting circuit according to any preceding claim, wherein each driver module comprises a boost converter.

8. 1. A method of implementing redundancy in an LED lighting circuit, the LED lighting circuit having a plurality of LED sub-configurations, each LED sub-configuration having a driver module and at least one LED, the driver module for driving the at least one LED, the plurality of LED sub-configurations being coupled in series, the method comprising: detecting a failure of an LED sub-configuration; and configuring the LED subconfigurations as a first set of a plurality of active LED subconfigurations and a second set of at least one inactive LED subconfiguration including the failed LED subconfiguration depending on the detected failure.

9. the LED sub-configurations are connected in series and the configuring step is performed by operating a selection circuit having a respective shorting transistor in parallel with each LED sub-configuration; or 9. The method of claim 8, wherein the LED sub-configurations are connected in parallel, and the configuring step is performed by operating a selection circuit having a respective isolation transistor in series with each LED sub-configuration.

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