FIELD OF INVENTION

[0001] The invention relates to an emergency ballast system.

BACKGROUND OF THE INVENTION

[0002] Current solution for emergency lighting, for example, in fluorescent lamp fixtures, involves relatively complicated system which includes both an emergency ballast and a regular ballast. Figure 1 illustrates an emergency ballast system 1 in the prior art. As shown in Figure 1, the emergency ballast system 1 includes an emergency ballast 10 and a regular ballast 20. Both the emergency ballast 10 and the regular ballast 20 are wired on the output side in a way that allows complete switching-over of the lamp from the regular ballast 20 to the emergency ballast 10, or vice visa. In the case of emergency, the emergency ballast 10 drives the lamp with the power from the battery 30. In most cases, relays are used for the switching-over.

[0003] In such a solution as shown in Figure 1, the wiring from the two ballasts to the lamp is very complicated, with a high probability of miss-wiring. In addition, the changed capacity of the output wires to the fixture can cause EMI interference. Each type of lamp need a special dedicated emergency ballast in order to run the lamp within the specification of the lamp (A universal emergency ballast generally can not operate the lamp properly, and may result in a very fast damage of the lamp). Moreover, the emergency ballast and the regular ballast each include an inverter for the high frequency operation of the lamp, which is relatively expensive. Furthermore, in such solutions, the usage of the emergency ballast in parallel to a dimmable ballast is almost impossible due to the high sensitivity to the wire capacities in the dimmable applications.

SUMMARY OF THE INVENTION

[0004] The invention is to provide an emergency ballast system which can solve one or more problems in the prior art. [0005] According to an embodiment of the invention, there is provided an emergency ballast system. The emergency ballast system includes a ballast unit having a DC/AC inverter, and further includes a signal preparing unit and an emergency unit. The ballast unit is adapted to power a load connected to the emergency ballast system by using power from a regular power source when the regular power source is in normal operation. The signal preparing unit is connected to the regular power source and is adapted to detect an operation condition of the regular power source, generate a detection signal reflecting the operation condition of the regular power source and output the detection signal to the emergency unit. The emergency unit comprises an emergency power source block. When the regular power source is in failure, in response to the detection signal reflecting the failure, the emergency power source block is adapted to power the DC/ AC inverter by using an emergency power source connected to the emergency unit.

[0006] The objects, features and advantages of the invention will be better understood from the following description of some embodiments of the invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic diagram illustrating an emergency ballast system in the prior art; [0008] Figure 2 is a schematic diagram illustrating an emergency ballast system according to an embodiment of the invention; [0009] Figure 3 is a schematic diagram illustrating an emergency ballast system according to another embodiment of the invention; and

[0010] Figure 4 is a schematic diagram illustrating an emergency ballast system according to another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Exemplary embodiments of the present invention are described in conjunction with the accompanying drawings hereinafter. For the sake of clarity and conciseness, not all the features of actual implementations are described in the specification. However, it is to be appreciated that, during developing of any of such actual implementations, numerous implementation-specific decisions must be made to achieve the developer's specific goals, for example, compliance with system-related and business-related constraints which will vary from one implementation to another. Moreover, it is also to be appreciated that, such a development effort might be very complex and time-consuming, but may nevertheless be a routine task for those skilled in the art having the benefit of this disclosure.

[0012] Figure 2 illustrates an emergency ballast system 100 according to an embodiment of the invention. The emergency ballast system 100 includes an emergency unit 110 including an emergency power source block 111, a ballast unit 120 including a DC/ AC inverter 121, and a signal preparing unit 130.

[0013] As shown, the ballast unit 120 is connected to a regular power source via wires Ll and N. When the regular power source is in normal operation, the ballast unit 120 powers a load(s) connected to the emergency ballast system by using the regular power source.

[0014] The signal preparing unit 130 is also connected to the regular power source via a wire L2 and is adapted to detect an operation condition (e.g. the voltage) thereof. In addition, the signal preparing unit 130 may generate a detection signal reflecting the operation condition of the regular power source and output the detection signal to the emergency unit 110 and/or the ballast unit 120.

[0015] The detailed structure of the signal preparing unit 130 is omitted. It shall be recognized by those skilled in the art that any structure that is capable of detecting the operation condition (e.g. the voltage) of a power source and generating and outputting a signal reflecting the operation condition may be used as the signal preparing unit. For example, the signal preparing unit may be a conversion unit for converting a high voltage line signal to a small signal (preferably DC) which is used as a driving signal for the logic in an AC/DC converter. In an embodiment, the signal preparing unit may be a voltage divider with rectification and output filter. Of course, it shall be appreciated by those skilled in the art that the signal preparing unit according to the invention shall not be limited to the examples and embodiments described herein.

[0016] During normal working condition when the inverter 121 of ballast unit 120 powers the load connected to the emergency ballast system by using the power from the regular power source, in response to the detection signal reflecting the normal condition generated by the signal preparing unit 130, the emergency power source block 111 is switched off and the output of the DC/ AC inverter 121 is adjusted to a nominal value. [0017] When the regular power source is in failure, the signal preparing unit 130 detects the failure and generates a detection signal reflecting the failure. In response to the detection signal reflecting the failure, the emergency power source block 111 of the emergency unit 110 is switched on so that the emergency unit 110 powers the inverter 121 by using an emergency power source connected to the emergency unit 110. In addition, in response to the detection signal reflecting the failure, the output of the DC/AC inverter 121 may be optionally adjusted to a lower level in order to reduce the consumption of energy delivered by the emergency power source. At the same time, the emergency power source block 111 may charge a bus voltage capacitor 122, connected between the inputs terminals of the DC/AC inverter 121, to a level required for the proper operation of the DC/ AC inverter 121. [0018] The bus voltage capacitor 122 is the part of the ballast to which the energy must be delivered from the external source in order to keep the inverter running in case of emergency.

[0019] When the regular power source recovers from the failure, the signal preparing unit 130 detects the recovery and generates a signal reflecting the recovery. In response to the signal reflecting the recovery, the emergency power source block 111 is switched off and the output of the DC/ AC inverter 121 is adjusted to a nominal value.

[0020] As can be seen, the emergency unit 110 is different from the emergency ballast unit 10 as shown in Figure 1 since the emergency unit 110 does not include an inverter for lamp operation. That is, in the case that the regular power source is in failure, the inverter 121 in the regular ballast unit 120 is still used to drive the load (e.g. a lamp).

[0021] This solution does not need special wiring or any switches at the output side of the emergency ballast system. The basic idea is to share the available circuit parts in the regular ballast for common function with the emergency unit. [0022] Figure 3 is illustrates an emergency ballast system 200 according to another embodiment of the invention.

[0023] As shown in Figure 3, the emergency ballast system 200 includes an emergency unit

210 and a ballast unit 220. The ballast unit 220 includes an APFC(Active Power Factor

Correction) or PPFC(Passive Power Factor Correction) block 223, a DC/AC inverter 221 and a signal preparing (Sig Prep) block 230. The emergency unit 210 includes a DC/DC power source block 211 and a DC/DC battery charger 212.

[0024] In some embodiments, both of the DC/DC power source block 211 and the DC/DC battery charger 212 can utilize the well known DC/DC topologies, such as boost converter, fly-back converter, Single-Ended Primary Inductance Converter (SEPIC) or buck-boost converter. For the DC/DC power source block 211, preferably a Boost converter can be used, alternatively a SEPIC. For the DC/DC battery charger 212, preferably a flyback or buck-boost converter can be used. While some examples of the two blocks have been described, it shall be recognized by those skilled in the art that any other structure that is capable of performing the functions of the two blocks described herein can be used. That is, the two blocks according to the invention shall not be limited to the particular embodiments and examples described herein.

[0025] In the embodiment, the Sig Prep block 230 has the same functions as those of the signal preparing unit 130 as shown in Figure 2. The structure of the emergency ballast system 200 is similar to that of the emergency ballast system 100 as shown in Figure 2, the difference lies in that the Sig Prep block is integrated in the ballast unit 220. In addition, a switch S may be used on the wire Ll to switch on or off the ballast unit.

[0026] In the embodiment, the emergency power source connected to the emergency unit is a battery. The emergency unit 210 maintains the energy of the battery and provides the energy to the inverter 221 of the ballast unit 220 in the case of emergency, independently from the regular power source, e.g. the power line. Of course, it shall be recognized by those skilled in the art that the emergency power source may be other types of available power sources other than the battery.

[0027] In the ballast unit 220, the most suitable part for providing energy for charging the battery is the bus voltage capacitor 222 which is adapted to store energy for the inverter of the ballast. As shown in Figure 3, the bus voltage capacitor 222 is connected between the two input terminals of the inverter of the ballast. In addition, one pole of the bus voltage capacitor 222 is connected to the emergency unit 210, and the other pole thereof is connected to the ground of the ballast. [0028] In addition, the bus voltage capacitor 222 is the part of the ballast to which the energy must be delivered from the external source in order to keep the inverter running in case of emergency. In the embodiment, the bus voltage capacitor (also referred to as Bus E-cap) may be charged by the APFC or PPFC to a certain relatively stable DC voltage (for example, typically 200-500V for the line applications) and therefore can store the energy for the DC/AC inverter. In addition, the bus E-cap can be used as an energy source of the DC/DC battery charger as described above.

[0029] Similarly, during normal working condition when the inverter 221 of ballast unit 220 powers the lamp by using the power from the power line, in response to a signal L2i reflecting the normal operation condition generated by the Sig Prep block, the DC/DC battery charger 212 is switched on so that the battery is charged by the battery charger using the energy available in the bus voltage capacitor 222. At the same time, in response to the signal L2i reflecting the normal operation condition, the DC/DC power source block 211 is switched off and the output of the DC/AC inverter 221 is adjusted to a nominal value.

[0030] In the case that the regular power source (i.e. the power line in the embodiment) is in failure, for example, when the power line loses its voltage, the Sig Prep block 230 detects the failure and generates a signal L2i reflecting the failure. In response to the signal L2i reflecting the failure, the DC/DC battery charger 212 is switched off, the DC/DC power source block 211 is switched on, and the output of the DC/AC inverter 221 is reduced to a lower level in order to reduce the consumption of energy delivered by the battery. By reducing the output power of the inverter, the operating time of the emergency ballast system can be extended significantly. At the same time, the DC/DC power source block 211 charges the bus voltage capacitor 222 to a level required for the proper operation of the DC/ AC inverter 221.

[0031] When the power line recovers from the failure, the Sig Prep block 230 detects the recovery and generates a signal reflecting the recovery. In response to the signal reflecting the recovery, the DC/DC power source block 211 is switched off, and the output of the DC/ AC inverter 221 is adjusted to a nominal value.

[0032] Figure 4 illustrates an emergency ballast system 300 according to another embodiment of the invention. The structure of the emergency ballast system 300 is similar to that of the emergency ballast system 200 as shown in Figure 3, except that the Sig Prep block in this embodiment is integrated in the emergency unit. In this case, the Sig Prep block must be connected to the regular power source (e.g. the power line in the embodiment) directly without any switch. The operation of the emergency ballast system 300 is the same as that of the emergency ballast system 200 as shown in Figure 3, and will not be repeated herein.

[0033] In the embodiments, the ballast unit is an electronic ballast.

[0034] As can be seen, in the above embodiments the wiring between the emergency ballast system and the load (e.g. the lamp) is very simple, without any change to the original wiring between a ballast and a lamp. The simple output wiring can reduce EMI interference compared with the prior art solution as shown in Figure 1.

[0035] Further, with the emergency ballast system according to the embodiments, no dedicated emergency ballast is required.

[0036] In addition, the emergency unit in the emergency ballast system according to the embodiments does not include an inverter, so that the cost of the system is reduced.

[0037] Furthermore, in the invention the output level of the inverter of the ballast may be adjusted in response to the signal which reflects the operation condition of the regular power source (e.g. the power line).

[0038] In addition, a dimmable ballast may be used in the invention. [0039] Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no way limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.