GB2541470A

GB2541470A - Controlled mains changeover in an emergency LED converter

Info

Publication number: GB2541470A
Application number: GB1515277.0A
Authority: GB
Inventors: Frankland James
Original assignee: Tridonic GmbH and Co KG
Current assignee: Tridonic GmbH and Co KG
Priority date: 2015-08-19
Filing date: 2015-08-19
Publication date: 2017-02-22
Anticipated expiration: 2035-08-19
Also published as: GB2541470B; GB201515277D0

Abstract

A device 1 for driving an emergency lighting means 2 comprises a first drive means 9 for driving the emergency lighting means, a first terminal 5 for connecting to an input of a second drive means 4 and a second terminal 6 for connecting to an output of the second drive means. A first switching means 7.1 selectively connects a mains power supply 3 to the second drive means. A second switching means 7.2 switches either the first drive means or the second terminal to an output 8 to the emergency lighting means. In case of a mains power failure, a control means 20 initiates a switching sequence by first controlling the first switching means to disconnect the first terminal from the mains power supply and, after a predetermined time delay interval has elapsed, controlling the second switching means to connect the output of the first drive means to the output of the device for driving the emergency lighting means.

Description

CONTROLLED MAINS CHANGEOVER IN AN EMERGENCY LED CONVERTER

The present invention relates to a device for driving an emergency lighting means. In particular the invention relates to a method for controlling a switchover from a first converter to a second converter for driving an emergency lighting means in an emergency LED converter. A luminary can include lighting means including for example one or more light emitting diodes (LED) and a power supply device for driving the lighting means by using either mains supply or supply by an energy storage. A known emergency lighting luminary monitors the mains power supply at its mains power supply input and activates an emergency lighting mode when the mains power supply is unavailable or malfunctions. The power supply device includes a conventional maintained LED converter for driving the LED when mains power supply is available and an emergency LED converter for driving the LED from an energy storage device when a mains failure is detected. A maintained emergency lighting system includes lighting means which are continuously lit and continue to work even in case of a mains power failure. This requires an alternate source of energy, for example an energy storage from which a dedicated emergency drive means is supplied with energy for driving the emergency lighting means.

Contrary thereto emergency lighting can be provided by a non-maintained emergency lighting system. A non-maintained emergency lighting system is configured to switch on a dedicated emergency lighting means in case of a mains power failure. A known power supply device of a luminary includes an emergency LED converter and terminals for connecting a conventional LED converter. The emergency LED converter output and the conventional LED converter output are connected to the respective inputs of an output relay (load relay) of the device. The inputs of the output relay can be alternatively connected to the output of the device for driving a lighting means, in particular an LED or a string of LEDs. The known power supply device further includes an input relay (ballast relay) which in a connected state can supply mains power to the conventional LED converter via one of the terminals. In case of a mains power failure the input relay will be controlled so as to disconnect the mains power supply, while the output relay will connect the emergency LED converter output to the output of the device for driving the LED in an emergency mode of operation.

Hence either the conventional LED converter or the emergency LED converter are connected to the output of the power supply device via the output relay. In case of a mains failure the input relay is switched to cut-off the failed mains power supply to the input of the maintained LED converter and the output relay switches the output of the power supply device from being driven by the maintained LED converter to being driven by the emergency LED converter.

The input relay and the output relay of known systems may switchover at any time relative to each other in case a mains supply failure (mains power failure) is determined. In case that the output relay by chance switches before the input relay switches large voltages and/or currents may be encountered at an output terminal of the power supply device. Large voltages at the output terminal may potentially damage the LED emergency converter. Large voltages at the output terminal also violate the safety of the power supply device.

The known power supply device employs a robust input relay and output relay in order to cope with such a situation and to maintain product reliability and product safety even in case of a mains power failure. The known power supply device uses relays which have to fulfill high requirements and are therefore expensive and bulky.

Therefore improving the known power supply device with respect to cost and dimensions while simultaneously maintaining a high degree of product safety is desirable.

The device for driving an emergency lighting means according to independent claim 1 and the corresponding method for operating the device driving an emergency lighting means provide a solution to the technical problem.

The problem is solved by a device for driving an emergency lighting means according to claim 1. The device comprises a first drive means for driving the emergency lighting means, a first terminal for connecting an input of a second drive means for driving the emergency lighting means and a second terminal for connecting an output of the second drive means. A first switching means of the device is configured to connect or disconnect a mains power supply to the first terminal and a second switching means of the device is configured to connect either the second terminal or an output of the first drive means to an output to the emergency lighting means. The inventive device for driving an emergency lighting means further comprises a control means configured to control the first switching means so as to disconnect the first terminal from the mains power supply first and, after a predetermined time interval has elapsed, to switch the second switching means so as to connect the output of the first drive means to the output of the device in case of a mains power failure.

Due to the control means disconnecting mains power supply to the second drive means by switching the first 'switching means prior to connecting an output of the first drive means to the output of the device to the emergency lighting means, any energy stored in the second drive means will be continued to be fed to the emergency lighting means as a load. Energy may, for example, still be stored in coils or capacities of the second drive means when a mains power failure occurs, for example when using a flyback converter as the second drive means.

After a predetermined time has elapsed the control means controls the second switching means to disconnect the output of the second drive means and to connect the output of the first drive means to the output of the device. Thus the control means ensures a defined switching sequence of the first and second switching means with respect to the respective switching points in time. Energy stored in the second drive means will thus be consumed in the time interval between switching the first and the second switching means. The risk of generating a voltage spike at the output terminals of the power supply device caused by synchronous switching of the first and second switching means is reduced. The voltage spike at the output terminal of the device acting as a power supply may be detrimental to lighting means to be connected via the output of the device. Furthermore a potential damage to the first drive means by an excessive voltage at the output terminal of the device is avoided by controlling the time sequence of disconnecting the mains power supply by the first switching means and thereafter of connecting the first drive means to the output by switching the second switching means according to the invention.

Further advantageous embodiments of the invention form part of the dependent claims . A preferred embodiment of the device for driving an emergency lighting means comprises a power supply means for supplying electrical power to the first switching means and the second switching means.

Thus the power supply means ensures that the first and second switching means are supplied with the required electrical power for executing the predetermined switching sequence according to the invention.

An advantageous device for driving an emergency lighting means according to an embodiment comprises the control means being configured to control the power supply means to supply electrical power to the first switching means and the second switching means for a further predetermined time interval.

The device for driving an emergency lighting means according to an embodiment includes an energy storage means adapted to supply power to the power supply means and the control means. Thus the power supply means is adapted to provide the required power to the first switching means and the second switching means even in case of a mains power failure.

Preferably each of the first switching means and the second switching means are relays.

According to an embodiment of the invention the first drive means is an emergency converter and the second drive means is a converter, preferably a flyback converter.

The problem is also solved by a method for operating a device for driving an emergency lighting means. The device comprises a first drive means for driving an emergency lighting means, a first terminal for connecting an input of a second drive means for driving the emergency lighting means and a second terminal for connecting an output of the second drive means, a first switching means configured to connect or disconnect a mains power supply to the first terminal and a second switching means configured to connect either an output of the first drive means or the second terminal to an output of the device to the emergency lighting means. The method for operating a device for driving an emergency power supply is characterized by, in case of a mains power supply failure, performing steps of controlling the first switching means so as to disconnect the first terminal from the mains power supply first and, after a predetermined time interval has elapsed, to switch the second switching means so as to connect the output of the first drive means to the output to the emergency lighting means.

The method for controlling a device for driving an emergency lighting means according to a preferred embodiment further comprises a step of supplying electric power to the first switching means and the second switching means, in case of the mains power failure.

Embodiments of the invention will be described now with reference to the accompanying drawings in which

Fig. 1 shows an arrangement of a known power supply device according to prior art,

Fig. 2 shows an arrangement of a power supply device according to an embodiment of the invention,

Fig. 3 shows a flowchart of a method for operating a power supply device according to the invention.

In the figures same numerals denote the same elements and a description of the same elements is not necessarily repeated in the following description of the figures.

Fig. 1 shows schematically an arrangement of a power supply device for driving an emergency lighting means 2 according to prior art.

The power supply device according to prior art comprises a first drive means 9 for driving the emergency lighting means 2 in an emergency lighting operation mode and a first terminal 5 and a second terminal 6 for connecting a second drive means 4 for driving the emergency lighting means 2 in a regular mains operation mode.

The second drive means 4 for mains operation can also be referred to as an offline LED driver or as a standard LED driver, which feeds the emergency lighting means 2 when an AC voltage is applied to a mains power supply input 3.

Fig.l shows that a first current path starting from the mains power supply input 3 leads via a first switching means 7.1, the first terminal 5 to the input of the second drive means 4, then from the output of the second drive means 4 via the second terminal 6 of the device to an input of a second switching means 7.2. From an output of the second switching means 7.2 the first current path leads via the output 8 of the device to the emergency lighting means 2. This first current path passes partially through the device (emergency lighting device). The first current path serves the purpose of driving the lighting means 2 in the regular mains operation mode.

The first and second switching means 7.1, 7.2 are designed to switch over the emergency lighting means 2 as a load from the second drive means 4 for operation by mains power supply to a first drive means 9 for emergency operation when a mains power supply voltage fails. Mains power supply failure may include the mains power supply voltage moving out of a predetermined voltage range or the mains power supply voltage falling below a (first) predetermined threshold value or exceeding a (second) predetermined threshold value.

Fig. 1 also shows that the mains power supply charges an energy storage means 10 during normal operation via a charging means 11. For example the second drive means 4 provides the charging means 11 with a DC voltage and the charging means 11 charges the energy storage means 10.

The energy storage means 10 provides electrical power to the first drive means 9 during the emergency lighting operation mode. The first drive means 9 supplies for example a drive current to the emergency lighting means 2 via the second switching means 7.2 and the output 8 of the device. Hence the energy storage means 10, the first drive means 9, the second switching means 7.2 and the output 8 of the device constitute a second current path for driving the emergency lighting means 2 in the emergency lighting operation mode.

An indicator means 12, which can be actuated via an indicator driver not shown in fig. 1, provides visual and/or acoustic signaling of an emergency lighting operation mode and/or a regular operation mode to a user. The indicator means 12 may additionally or alternatively be adapted to communicate a charging status of the energy storage means 10 and/or a charging mode visually and/or acoustically to a user.

The device as shown in fig. 1 for driving an emergency lighting means 2 dispenses with details on extra-low voltage isolation barriers for galvanic isolation which nevertheless can be integrated into the device. Reference is made to the contents of international application WO 2014/030062 A2 which is incorporated by reference for the details of galvanic isolation and high voltage protection in the device for driving an emergency lighting means 2.

Fig. 1 also shows a control means 13, which determines, whether switching into an emergency lighting operation mode is required. The control means 13 can for example detect indirectly or directly the mains power supply voltage, for example by means of a measurement of the voltage on a secondary side of a first electrical isolation element of the charging means 11. Thus the control means 13 may directly identify a failure of the mains power supply or a discrepancy between the mains power supply voltage and a predetermined voltage value or a deviation of the mains power supply voltage from a predetermined voltage range. The control means 13 can be configured to receive a signal indicating a request for switching from the regular mains operation mode to the emergency lighting operation mode and thereby indirectly identify a mains power supply failure.

The control means 13 is adapted to actuate switching of the first and second switching means 7.1, 7.2 via a switch control signal 15 in case the mains power supply failure is detected.

The device can include a relay rail 14 for supplying electrical energy to the first switching means 7.1, the second switching means 7.2 and the control means 13. The relay rail 14 can be supplied with electrical energy by the second drive means 4.

The control means 13 can further be adapted to provide clock signals for controlling the switching timing of a second electrical isolation element of the first drive means 9, and therefore the power, the current and/or the voltage output by the device to supply the emergency lighting means 2 during the emergency lighting operation mode.

The control means 13 can measure and regulate a current output by the energy storage means 10 or an output voltage of the energy storage means 10 and optionally control the operation of the indicator means 12.

Preferably, the control means 13 regulates or controls a current output by the energy storage means 10 or the output voltage or power or else control the power, current and/or voltage which is used to supply the emergency lighting means 2 in the emergency lighting operation mode. The control means 13 may perform controlling the current by means of an actuation of an actively controlled switch in an emergency LED converter employed as the first drive means 9.

The control means 13 may be implemented by a microcontroller (pC) , an integrated circuit (IC) and/or an application specific integrated circuit (ASIC).

Fig. 2 shows an arrangement of a power supply device 1 according to an aspect of the invention. The design of the charging means 11, the energy storage means 10, the second drive means 4 and the first drive means 9 (emergency LED driver) can be substantially identical to the respective means (units) in fig. 1. The components provided with the same reference numerals are substantially identical in terms of design and function as well. The inventive device 1 for driving an emergency lighting means 2 of fig. 2 further comprises a control means 20 specifically adapted according to an aspect of the invention.

The control means 20 of figure 2 is to be understood in a functional manner. The functions of the control means 20 can be implemented at least partially in form of dedicated circuitry. The functions of the control means 20 can also be implemented in a microcontroller. The functions of the control means 20 can be implemented in a distributed manner in plural subunits of the device 1. For example the indicator means 12 can include drive means to switch on or to switch off the indicator means 12 in order to communicate a corresponding mode of operation of the device 1, such as the emergency lighting operation mode and the regular mains operation mode.

The control means 20 is adapted to determine if the mains power supply to the mains power supply input 3 is in a state of failure, thus to determine a mains power failure. A state of failure may particularly be determined if the power supply voltage at the mains power supply input 3 drops below a predetermined threshold voltage value.

If the control means 20 determines a mains power supply failure or is informed about such power failure, the control means 20 initiates the inventive procedure for a controlled changeover from mains driven power supply by the second drive mains 4 to a battery driven power supply by the first drive means 9 in order to drive the emergency lighting means 2. Thus the control means 20 controls . a switching process from the regular mains operation mode to the emergency lighting operation mode.

If the control means 20 according to an embodiment of the invention determines a mains power supply failure, the control means 20 can control a low voltage power supply switch 11 via a supply voltage switch control signal 16. The low voltage power supply switch 11 is controlled to connect a low voltage power supply means 17 (LVPS) to the relay rail 14 if a mains power supply failure is determined. The low voltage power supply means 17 corresponds to a power supply means 17. By supplying the relay rail 14 with a DC voltage, the first switching means 7.1 and the second switching means 7.2 receive a required electrical power for securely executing the switching process. Thus even in case of a mains power supply failure the relay rail 14 is provided with sufficient electrical power for a required minimum time interval for performing the mains changeover process according to the invention. This is essential in an embodiment in which the mains power supply failure may also affect the second drive means 4 and its ability of feeding the relay rail 14.

The low voltage power supply means 17 is preferably supplied by the energy storage means 10 with a supply voltage 18 and generates one or more low voltages as required by individual subunits (means) of the device 1. Besides generating a low voltage, for example 12 V, for driving the relay rail 14, the low voltage power supply means 17 can generate further low voltages. For example the low voltage power supply means 17 can provide a further supply voltage 27 to supply the control means 20. Thus the low voltage power supply means 17 ensures a stable power supply to the control means 20 while the control means 20 controls the defined inventive switching sequence to achieve a controlled changeover in case of mains power failure.

The inventive control means 20 controls the first switching means 7.1 by a first switch control signal 19 to disconnect the mains power supply input 3 from the first terminal 5. In particular the first switch control signal 19 actuates the first switching means 7.1 to disconnect an output 30 of the first switching means 7.1 from an input 21 of the first switching means 7.1. The input 21 of the first switching device 7.1 is electrically connected to the mains power supply input 3 of the device 1. The output 30 of the first switching means 7.1 is connected to the first terminal 5. Thus the mains power supply input 3 can be disconnected from the first terminal 5 by actuating the first switching means 7.1. An input of the second drive means 4 is accordingly also disconnected from being fed with mains power supply by switching the first switching means 7.1. Hence the second drive means 4, for example a maintained converter, is forced to cease feeding a lighting means drive signal via the second terminal 6 to a first input 22 of the second switching means 7.2.

In the regular mains operation mode the second switching means 7.2 connects the first input 22 of the second switching means 7.2 to an output 23 of the second switching means 7.2.

When the control means 20 controls the first switching means 7.1 to disconnect the mains power supply input 3, the second switching means 7.2 continues to hold the first input 22 of the second switching means 7.2 in an electrically connected state with the output 23 of the second switching means 7.2. Any energy left in capacities and/or coils of the second drive means 4 or elsewhere continues to be fed to the output 8 of the device 1 and thus to the emergency lighting means 2.

After a predetermined time interval has elapsed from switching of the first switching means 7.1 so as to disconnect the mains power supply input 3 from the first terminal 5, the control means 20 proceeds by issuing a second switch control signal 25 to the second switching means 7.2. The second switch control signal 25 controls the second switching means 7.2 to disconnect the first input 22 of the second switching means 7.2 from the output 23 of the second switching means 7.2. The second switch control signal 25 further controls the second switching means 7.2 to connect the second input 24 of the second switching means 7.2 to the output 23 of the second switching means 7.2. Thereby the second switching means 7.2 disconnects the second drive means 4 from the output 23 of the second switching means 7.2. The second switching means 7.2 thus connects the output of the first drive means 9 to the output 23 of the second switching means 7.2. The output 23 of the second switching means 7.2 is electrically connected the output 8 of the device 1 for driving an emergency lighting means 2. Thus the first drive means 9 now drives the emergency lighting means 2.

The first drive means 9 is supplied by the energy storage means 10 with the necessary input power and is thereby independent from mains power supply for a given time.

The control means 20 according to the invention now terminates the switching procedure for a controlled mains changeover in the device 1 for driving an emergency lighting means 2. The low voltage power supply means 17 may terminate switching procedure after a further predetermined time interval has elapsed. During the further predetermined time interval the control means 20 is provided with power by the low voltage power supply 17 via the closed low voltage power supply switch 16. The further predetermined time interval will preferably be of a longer duration than the predetermined time interval between switching times of the second switching means 7.2 and the first switching means 7.1 in order to ensure a secure switching of both the first and second switching means 7.1, 7.2.

The predetermined time interval will be preferably selected having a time duration which is sufficiently long to ensure that any energy remaining in coils of a converter is fed to the emergency lighting means 2 before the second switching means 7.2 disconnects the second drive means 4 from the output of the device 1. The predetermined time interval may for example be selected to be 200 ms.

Waiting the predetermined time interval after disconnecting mains power supply by the first switching means 7.1, and, after the predetermined time interval has elapsed, disconnecting the output of the second drive means 4, allows in particular a LED drive current to subside and prevents large voltages and/or currents being generated at the output 8 of the device 1. Thus the possibility of damaging the device 1, in particular the first drive means 9 in case of a mains failure is efficiently reduced. The first and second switching means 7.1, 7.2 need not to be designed to cope with respectively excessive voltages and/or currents. Hence the first and second switching means 7.1, 7.2 may be designed or selected to satisfy reduced requirements with respect to dielectric strength. Required device space and manufacturing cost can be expected to be lower for the inventive device 1 for driving an emergency lighting means 2 when compared to the state of the art.

The control means 20 may further be adapted to receive a charging state signal 26 from the energy storage means 10 and/or the charging means 11 which signals a charging state of the energy storage means 10 and/or a charging mode of operation of the charging means 11 to the control means 20. For example the control means 20 can include a functionality of controlling the indicator means 12 to signal a charging state of the energy storage means 10 visually and/or acoustically.

The second drive means 4 can further be adapted to provide a low voltage 27 via a low voltage feed line to the relay rail 14 in the regular mains operation mode of the device 1.

The relay rail 14 can supply the charging means 11 with the electrical energy for charging the energy storage means 10.

Fig. 3 shows a flowchart depicting method steps for operating a device 1 according to an embodiment of the invention. In a step SI the mains power supply input 3 is monitored. If in a step S2 succeeding to step SI a mains failure is determined to be present, the method succeeds to step S3. If the step S2 of determining a mains power failure determines no mains failure to be present, the monitoring of the mains power supply is continued by returning to step SI.

If a mains power failure is determined in step S2, the method continues to step S3 and disconnects the mains power supply input 3 by switching the first switching means 7.1. By the first switching means 7.1 disconnecting the mains power supply input 3 from the first terminal 5, the input of the second drive means 4 is brought into a defined state in which no further electrical energy is fed to the second drive means 4. After disconnecting the mains power supply input 3 in step S3, the method proceeds to a step S4 and waits until a predetermined time interval has elapsed. After having waited until the predetermined time interval has elapsed, the method continues with a step S5 of switching the second switching means 7.2. In step S5 in particular the output 23 of the second switching means 7.2 is switched from being fed via the first input 22 of the second switching means 7.2 by the second drive means 4 to being fed via the second input 24 of the second switching means 7.2 by the first drive means 9. After having switched the second switching means 7.2 when the predetermined time interval has elapsed, the inventive method of operating the device 1 is terminated. The device 1 for driving an emergency lighting means 2 is accordingly switched from driving the emergency lighting means 2 by the second drive means 4 fed via mains power supply to driving the emergency lighting means 2 by the first drive means 9 fed by the energy storage means 10 in a time-controlled manner. By avoiding any race condition when switching, possibly detrimental voltages at the output 8 of the device 1 are successfully suppressed.

The invention is of particular advantage when employed in non-maintained emergency LED converters or fluorescent converters.

All single features of the discussed embodiments described and illustrated in the accompanying figures just by way of example, may also be combined in an appropriate and advantageous manner without prejudice to the underlying principles of the invention as defined in the appending claims.

Claims

CLAIMS :

1. A device for driving an emergency lighting means (2), the device comprising a first drive means (9) for driving the emergency lighting means (2), a first terminal (5) for connecting an input of a second drive means (4), and a second terminal (6) for connecting an output of the second drive means (4) for driving the emergency lighting means (2), a first switching means (7.1) configured to connect or disconnect a mains power supply to the first terminal (5), a second switching means (7.2) configured to connect either the second terminal (6) or an output of the first drive means (9) to an output (8) to the emergency lighting means (2), and characterized in that the device further comprises a control means (20) configured to control the first switching means (7.1) so as to disconnect the first terminal (5) from the mains power supply first and, after a predetermined time interval elapsed, to switch the second switching means (7.2) so as to connect the output of the first drive means (9) to the output (8) of the device, in case of a mains power failure.

2. The device for driving an emergency lighting means (2) according to claim 1, characterized in that the device comprises a power supply means (17) for supplying electrical power to the first switching means (7.1) and the second switching means (7.2).

3. The device for driving an emergency lighting means (2) according to claim 1 or 2, characterized in that in case of mains power failure, the control means (20) is configured to control the power supply means (17) to supply electric power to the first switching means (7.1) and the second switching means (7.2) for a further predetermined time interval.

4. The device for driving an emergency lighting means (2) according to any one of claims 1 to 3, characterized in that the device comprises an energy storage means (10) configured to supply power to the power supply means (17) and the control means (20).

5. The device for driving an emergency lighting means (2) according to any one of claims 1 to 4, characterized in that the first switching means (7.1) and the second switching means (7.2) are relays.

6. The device for driving an emergency lighting means (2) according to any one of claims 1 to 5, characterized in that the first drive means (9) is an emergency converter and the second drive means (4) is a converter.

7. A method for controlling a device for driving an emergency lighting means (2), the device comprising a first drive means (9) for driving the emergency lighting means (2), a first terminal (5) for connecting an input of a second drive means (4) for driving the emergency lighting means (2) and a second terminal (6) for connecting an output of the second drive means (4), , a first switching means (7.1) configured to connect or disconnect a mains power supply to the first drive means (9), a second switching means (7.2) configured to connect either the second terminal (6) or an output of the first drive means (9) to an output (16) to the emergency lighting means (2), and characterized in that the method comprises steps of, in case of a mains power failure, controlling the first switching means (7.1) so as to disconnect the first terminal (5) from the mains power supply first and, after a predetermined time interval elapsed, to switch the second switching means (7.2) so as to connect the output of the first drive means (8) to the output (8) of the device.

8. The Method for driving a device for driving a emergency lighting means (2) according to claim 7, characterized in that the method comprises a step of supplying electric power to the first switching means (7.1) and the second switching means (7.2), in case of the mains power failure.