GB2544562A

GB2544562A - LED light fitting and emergency power supply therefor

Info

Publication number: GB2544562A
Application number: GB1520666.7A
Authority: GB
Inventors: Hanslod Mohamed; Kola Sakilbabu; Horton Peter
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-11-23
Filing date: 2015-11-23
Publication date: 2017-05-24
Also published as: WO2017089755A1; GB201520666D0

Abstract

A backup power supply module 10 for an LED light fitting comprises an AC-DC converter 16, a DC-DC converter 50, a battery 40, a controller 100, sensing means 14, 114 to detect whether power is supplied to the AC-DC converter 16, and switching means 20, 22, 24 for switching the module between a passive state and an active state. The module switches from passive state to active state if power supply to the AC-DC converter 16 is lost. In the passive state, the AC-DC converter 16 charges the battery 40 and powers the controller 100, and the DC-DC converter 50 is disconnected from the battery 40 and/or the LEDs 4 of a light fitting 1. In the active state, the battery 40 powers the controller 100 and supplies power to the LEDs 4 via the DC-DC converter 50, and the controller 100 controls the DC-DC converter 50 to supply a substantially constant current to the LEDs 4.

Description

LED LIGHT FITTING AND EMERGENCY POWER STTPPT Y THEREFOR

Technical Field of the Invention

The present invention relates to emergency lighting, and particularly to backup power supplies for converting standard light fittings into emergency light fittings.

Background to the Invention

Emergency light fittings are fitted with a battery to provide a backup power supply to the light fitting during a mains power outage. The battery is charged by the mains power when available, and once power is lost the battery is typically required to power the light fitting for an extended period of time, such as several hours. Manufacturers often make light fitting designs available in both emergency lighting and standard formats, i.e. with or without a backup power supply. However, since many designs of light fitting are not offered as emergency lighting, backup power supplies may be retrofitted onto standard light fittings so that they too can function as emergency lighting. This allows architects and interior designers greater flexibility when selecting light fittings for public and commercial buildings.

Traditional fluorescent tube light fittings require an alternating current (AC) power supply, so their backup power supplies include an inverter powered by the battery. The inverter supplies AC power to the light fitting at the appropriate mains frequency. LED light fittings, which have grown in popularity in recent years, require direct current (DC) power supply and are typically fitted with an AC-DC converter for that purpose. A conventional backup power supply suitable for use with fluorescent tube lighting may be connected to the AC-DC converter of an LED unit, although this is rather inefficient because of switching losses in the inverter and the AC-DC converter.

Accordingly, objects of the invention include the provision of a backup power supply for LED light fittings that addresses the above problems and/or that provides a simple, inexpensive, efficient alternative to conventional retrofitted backup power supply modules.

Summary of the Invention

According to a first aspect of the invention, there is provided a backup power supply module for an LED light fitting, the module comprising an AC-DC converter, a DC-DC converter, a battery, a controller, sensing means arranged to detect whether there is a power supply to the AC-DC converter, and switching means for switching the module between a passive state and an active state, wherein the module is arranged to switch from the passive state to the active state in the event that power supply to the AC-DC converter is lost, and wherein: when the module is in the passive state, the AC-DC converter is arranged to charge the battery and to power the controller, and the DC-DC converter is disconnected from one or both of the battery and the LEDs of a light fitting; and when the module is in the active state, the battery is arranged to power the controller and to supply power to the LEDs of a light fitting via the DC-DC converter, and the controller controls the DC-DC converter to supply a substantially constant current to the LEDs of the light fitting.

Preferably, the module is arranged so that while the module is in its active state, the AC-DC converter is disconnected from the battery. The switching means may comprise a single switch arranged to connect the battery to the AC-DC converter when the module is in its passive state only and to the DC-DC converter when the module is in its active state only.

The module may comprise terminals for connection of a further AC-DC converter, may be arranged to connect the further AC-DC converter to the LEDs of the light fitting when the module is in the passive state, and may be arranged to disconnect the further AC-DC converter from the LEDs of the light fitting when the module is in the active state. The switching means may comprise a single switch arranged to connect the LEDs of the light fitting to the further AC-DC converter when the module is in the passive state only and to the DC-DC converter when the module is in the active state only. Conveniently, the module may comprise terminals for connection of the LEDs of the light fitting, wherein said LED terminals are located adjacent to the terminals for connection of the further AC-DC converter, such as within a few centimetres or millimetres of one another.

The DC-DC converter may comprise a boost converter, and may be controlled by the controller via pulse-width modulation. The module may comprise a current sensor arranged to provide a signal to the controller representing an input or output current of the DC-DC converter, and the module may be arranged to provide a feedback signal to the controller representing an output voltage of the DC-DC converter.

According to a second aspect of the invention, there is provided an emergency light fitting comprising a backup power supply according to the first aspect of the invention.

The light fitting may comprise a DC power supply arranged to power the LEDs of the light fitting when the module is in the passive state. Preferably, the module is arranged to disconnect the DC power supply from the LEDs when the module is in the active state.

According to a third aspect of the invention there is provided a method of converting an LED light fitting into an emergency light fitting, the method comprising the steps of providing a backup power supply module according to the first aspect of the invention, connecting the LEDs of the light fitting across a first pair of terminals of the module, and connecting a DC power supply of the light fitting across a second pair of terminals of the module.

Detailed Description of the Invention

In order that the invention may be more clearly understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a schematic representation of an LED emergency light fitting including a backup power supply; and

Figure 2 is a simplified circuit diagram of the backup power supply of Figure 1.

Referring to Figure 1, an LED light fitting 1 is shown in which the mains AC power supply 2 is connected to the built-in or manufacturer-supplied DC power supply unit 3 (LED PSU) that drives the LEDs 4. These components represent a standard, nonemergency light fitting 1 before the backup power supply 10 has been retrofitted. The remainder of the components represent the backup power supply 10 retrofitted to the light fitting 1 in order to provide an emergency lighting function.

In the backup power supply 10, the AC mains 12 is connected to a voltage sensor 14 and an additional DC power supply unit 16 (DC PSU) which charges a relay 20 and feeds a battery charging circuit 30 and a voltage regulator 18. The voltage regulator 18 powers the voltage sensor 14 and a microcontroller 100. The microcontroller 100 receives a signal 114 from the voltage sensor 14 indicating the presence or absence of mains AC power 12 and, when a power outage is detected, triggers the switching relay 20 in response. One switch 22 actuated by the relay 20 connects the battery 40 either to the charger 30 or, during a power outage, to the voltage regulator 18 that supplies the microcontroller 100 and to a boost converter 50 controlled by the microcontroller 100. Another switch 24 actuated by the relay 20 connects the LEDs 4 either to the original PSU 3 or, during a power outage, to the boost converter 50. Thus, when the switching relay 20 is tripped by a power outage, it simultaneously disconnects the LEDs 4 from the original PSU 3, disconnects the charger 30 from the battery 40, and connects the battery 40 to power the microcontroller 100 and, via the boost converter 50, the LEDs 4.

The microcontroller 100 drives the switching of the boost converter 50, controlling for feedback signals 154, 156 from the boost converter 50 indicating the output voltage and current. Thus, the LEDs 4 are supplied with constant current at a desired level of current, voltage, and/or power independently of the output of the original PSU 3.

For example, a typical 45W LED downlight may produce an output of around 3800 lumens when running on mains. However, when operating as an emergency light, it may need only to produce around 300 lumens or less in order to comply with relevant building regulations and safety standards. Thus, to preserve battery life during a power outage, the LEDs may be illuminated at less than 8% of their normal brightness.

The backup power supply module 10 of Figure 1 is shown in more detail in Figure 2. The mains AC 12 (L, N) powers the module’s internal PSU 16, which charges the battery 40 via series resistors 34, 36. A control signal 130 (Charge Enable) from the microcontroller 100 is operable via transistors 31, 33 (Ql, Q3) to bypass one ofthe series resistors 34, so that the charger 30 is switchable between higher and lower (trickle) charging rates.

The microcontroller 100 receives a feedback signal 140 representing the battery voltage. The battery voltage also powers an indicator LED 42 which can be switched on or off via a control signal 142 (EL On) from the microcontroller. The microcontroller 100 can thus indicate a fault, such as by blinking the indicator LED 42.

The microcontroller 100 receives from the mains voltage sensor 14 (U3) a signal 114 (Mains Sense) indicating the presence or absence of the mains AC supply 12. When a mains power outage is detected, the microcontroller 100 triggers a switching relay 20 (RLla) via a control signal 120 (Relay On) to transistor 26 (Q4). The relay 20 (RLla) actuates switches 22, 24 so that the backup power supply 10 is toggled between a charging state (NC) where the battery 40 is connected to the charger 30, and an operational state (NO) where the battery 40 powers the AC voltage sensor 14, the microcontroller 100, and the LEDs 4 of the lighting unit 1.

While in the charging state (NC), one of the relay switches 24 connects the LEDs 4 to the lighting unit’s original/built-in DC power supply unit 3 (PSU IN), bypassing the backup power supply module 10. Thus, in the charging state (NC), the LED lighting 1 operates as if the backup power supply 10 had not been installed, so that the circuitry supplying power to the LEDs 4 is effectively unmodified relative to the default configuration provided by the manufacturer.

Thus, the backup power supply 10 is not required to power the LEDs 4 at a level suitable for normal use. Rather, its design can be optimised purely to provide the low-level lighting output required for emergency lighting.

To power the LEDs 4 when the backup power supply 10 is in the operational state (NO), such as during a mains power outage, the relay switches 22,24 connect the battery 40 to the LEDs 4 of the lighting unit 1 via a boost converter 50. In the operational state (NO), the microcontroller 100 supplies a pulse-width modulated (PWM) control signal 152 (MOSFET Drive) to the transistor 52 (Q5) that modulates the boost converter 50. The PWM switching frequency and the various resistances, capacitances, and inductances of the boost converter 50 are selected to provide a constant-current power supply to the LEDs 4.

The microcontroller 100 receives feedback signals 154,156 (V Feedback, I Load) via a potential divider 54 and current sensor 56 (U2) respectively, representing the output voltage and current of the boost converter 50. While the backup power supply 10 is in its operational state (NO), the PWM is controlled so as to maintain a predefined level of output current, regardless of the depleting battery voltage and regardless of the variable voltage drop across the LEDs 4. In certain embodiments, the microcontroller 100 and boost converter 50 are arranged to provide a single, fixed level of output current.

This enables a wide range of different LED light fittings to be retrofitted with a single design of backup power supply—i.e. a one-size-fits-all solution—since, although the brightness of each type of light fitting will depend on the number and characteristics of its LEDs, a large number of different types of LED light fittings would nevertheless operate within a range that is deemed acceptable under building regulations and safety standards relating to the required luminance of emergency lighting.

For example, a single backup power supply module according to the invention has been developed that is compatible with LED lighting panels rated from 9W to 60W and with LEDs rated from 10V to 42 V. This covers a very substantial proportion of the types of architectural LED lighting commonly found in public and commercial buildings. The installer does not need to adjust or pre-select the desired output settings, as the module simply works across a very wide range of LED light fittings. Moreover, if the backup power supply module is provided with several different output currents, either as several individual models or as easily selectable current settings on a single model, a very limited number of current output options may provide a retrofit backup power supply suitable for almost all LED light fitting types, across a much wider range of power ratings and LED voltages.

These advantages allow architects and lighting designers to select almost any design of LED light fitting and convert it into an efficient, standards-compliant emergency light fitting. This provides a great deal of freedom, since it is therefore immaterial whether the manufacturer offers a matching unit as an emergency light.

During emergency operation, the LEDs are directly powered by the battery, with no power supplied to either PSU or to an inverter, unlike many conventional retrofitted backup power supplies. This provides a very substantial improvement in efficiency and battery life for a given battery size when compared with conventional inverter-based retrofit emergency power supplies. It also allows the provision of a significantly smaller, lighter, and less expensive backup power supply module when compared with conventional inverter-based retrofit emergency power supplies.

Installation of the backup power supply module is extremely simple, as it merely needs to be connected between the LED lighting circuit and its original/built-in DC power supply unit. Since the retrofit module according to the invention does not interact in any way with the original PSU, other than simply to connect and disconnect it with the LEDs, there is no need to support multiple types of PSU. This avoids the need for additional components, wiring, and interconnecting fittings typically required to safely connect a retrofit power supply unit to multiple types of PSU and to match its power requirements.

Emergency lighting can be categorised as ‘maintained’ or ‘non-maintained’ types. Maintained emergency lighting is operable as a normal light fitting while mains power is available; non-maintained lighting is arranged for emergency use only, such as to illuminate fire escapes. Whilst the embodiments described above are of the maintained type of emergency lighting, the backup power supply is equally usable for converting standard light fittings into non-maintained emergency lighting. In that case, the backup power supply module may optionally replace the original/built-in power supply rather than bypassing it.

In certain embodiments, the microcontroller comprises a data connection (not shown) that allows it to transmit its status and input signals to a remote device, and/or to allow its control signals to be remotely controlled, via a wired or wireless connection. For example, a building may comprise a central computer that monitors the battery level of each emergency light fitting unit and is centrally operable to remotely enable and disable battery charging, or to boost and restrict the battery charging rate, in each lighting unit. Alternatively, or in addition, the data connection may transmit information to a remote device, such as the presence or absence of mains AC supply, and the output voltage and/or current during emergency operation or safety testing. Such modules may, for example, be used to remotely diagnose faults with the battery, charger, or output and to disable or enable the emergency lighting capabilities of individual units so that spare units can be remotely swapped in or out.

The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention.

Claims

1. A backup power supply module for an LED light fitting, the module comprising an AC-DC converter, a DC-DC converter, a battery, a controller, sensing means arranged to detect whether there is a power supply to the AC-DC converter, and switching means for switching the module between a passive state and an active state, wherein the module is arranged to switch from the passive state to the active state in the event that power supply to the AC-DC converter is lost, and wherein: when the module is in the passive state, the AC-DC converter is arranged to charge the battery and to power the controller, and the DC-DC converter is disconnected from one or both of the battery and the LEDs of a light fitting; and when the module is in the active state, the battery is arranged to power the controller and to supply power to the LEDs of a light fitting via the DC-DC converter, and the controller controls the DC-DC converter to supply a substantially constant current to the LEDs of the light fitting.

2. A backup power supply module according to claim 1 arranged so that while the module is in its active state, the AC-DC converter is disconnected from the battery.

3. A backup power supply module according to claim 1 or claim 2 wherein the switching means comprises a single switch arranged to connect the battery to the AC-DC converter when the module is in its passive state only and to the DC-DC converter when the module is in its active state only.

4. A backup power supply module according to any preceding claim comprising terminals for connection of a further AC-DC converter.

5. A backup power supply module according to claim 4 arranged to connect the further AC-DC converter to the LEDs of the light fitting when the module is in the passive state.

6. A backup power supply module according to claim 4 or claim 5 arranged to disconnect the further AC-DC converter from the LEDs of the light fitting when the module is in the active state.

7. A backup power supply module according to any one of claims 4 to 6 wherein the switching means comprises a single switch arranged to connect the LEDs of the light fitting to the further AC-DC converter when the module is in the passive state only and to the DC-DC converter when the module is in the active state only.

8. A backup power supply module according to any preceding claim comprising terminals for connection of the LEDs of the light fitting, wherein said LED terminals are located adjacent to the terminals for connection of the further AC-DC converter.

9. A backup power supply module according to any preceding claim wherein the DC-DC converter comprises a boost converter.

10. A backup power supply module according to any preceding claim wherein the DC-DC converter is controllable by the controller via pulse-width modulation.

11. A backup power supply module according to any preceding claim comprising a current sensor arranged to provide a signal to the controller representing an input or output current of the DC-DC converter.

12. A backup power supply module according to any preceding claim arranged to provide a feedback signal to the controller representing an output voltage of the DC-DC ΛΛΜΤ 7Λ»4λ1*

13. A backup power supply module substantially as herein described with reference to the appended drawings.

14. An emergency light fitting comprising a backup power supply according any preceding claim.

15. An emergency light fitting according to claim 14 comprising a DC power supply arranged to power the LEDs of the light fitting when the module is in the passive state.

16. An emergency light fitting according to claim 14 or claim 15 wherein the module is arranged to disconnect the DC power supply from the LEDs when the module is in the active state.

17. An emergency light fitting substantially as herein described with reference to the appended drawings.

18. A method of converting an LED light fitting into an emergency light fitting, the method comprising the steps of: providing a backup power supply module according to any one of claims 1 to 13, connecting the LEDs of the light fitting across a first pair of terminals of the module, and connecting a DC power supply of the light fitting across a second pair of terminals of the module.

19. A method of converting an LED light fitting into an emergency light fitting, the method substantially as herein described with reference to the appended drawings.