Emergency lighting apparatus for driving a light source, especially an LED

0001The present invention relates to an emergency lighting device according to the preamble of claim 1, which is provided for operating a light source, in particular an LED.

0002Emergency lighting devices are essential to implement lighting systems in larger buildings or complexes, which provide sufficient lighting even in the event of a failure of the general power supply. Only if certain relevant premises or areas are still illuminated in the event of a power failure or other emergency, can evacuation or relief measures be carried out safely. Accordingly, such emergency lighting devices are used in particular for illuminating escape routes and the like.

0003Accordingly, emergency lighting devices of the generic type have an energy storage unit, in particular a battery or an accumulator, as the central element, which is charged by the general mains supply voltage during normal or charging operation. For this purpose, a charging circuit is provided which is connected on the input side to the mains supply voltage and, during the charging operation, continuously supplies the energy storage unit with energy, which stores it. Only in the event of an emergency occurring, which is usually automatically recognized by such devices by monitoring the mains supply voltage, is it switched to an emergency lighting mode in which the light source is activated and operated, for which purpose - if necessary - the energy provided by the energy storage unit is being used. Since the storage capacity of the energy storage unit is of course limited, light sources are preferably used which consume relatively little energy. Accordingly, such emergency lighting devices are preferably equipped with gas discharge lamps, in particular fluorescent tubes. However, light sources in the form of light-emitting semiconductors, in particular LEDs, are also being used increasingly, since these light sources also have a high degree of efficiency and can accordingly be used in an energy-saving manner.

0004The monitoring of the mains supply voltage, which is carried out in order to be able to initiate emergency lighting operation in good time, is usually carried out by a control unit which evaluates the signals supplied to it and uses these signals to assess the state of the mains supply voltage. In known circuits, the mains supply voltage itself is measured in an obvious manner for this purpose. This then results in the problem, however, that the sensor system for determining the state of the mains supply voltage is at mains potential and must be galvanically isolated from the other circuit areas of the emergency lighting device, which are at the voltage level of the energy storage unit or LED. The electrical isolation required for this is not only expensive, but also takes up a relatively large amount of space in the emergency lighting device.

0005The document <patcit id="pcit0001" dnum="US6502044B1"><text>6,502,044 B1</text></patcit> describes an electronic self-diagnosis system for emergency lights. The self-diagnosis system checks the circuits, the power supply, the charger, and the equipment of emergency lights for either manual or automatic triggering. The test functions are provided through the use of a programmable microprocessor, with a diagnostic circuit not only monitoring the operation of the charger, but also controlling the charger to enable alternative approaches to correcting a fault. In emergency lighting mode, a microprocessor-controlled two-stage inverter is not only used to operate an LED light source, but also to supply the microprocessor with power. The power supply of the microprocessor is controlled by the microprocessor itself and can be adjusted until the mains power is restored, which reduces the power consumption to zero.

0006The document "<nplcit id="ncit0001" npl-type="s"><text>Critical-Mode Control Stabilizes Switch-Mode Power Supplies "by Basso (EDN, Apr 23, 1998, page 171 ff</text></nplcit>.) shows an example of a power factor correction circuit using a switching funnel IC MC33364. The power factor correction circuit works in the so-called critical conduction mode (also called borderline mode). In this operating mode, the maximum input current consumed can be limited by zero cross detection. During the switch-on phase, the current flowing through the shunt then corresponds to the input current consumed. The measurement on an optocoupler, which is carried out on the secondary side of the circuit, only serves to record the output voltage and to keep the amplitude of the output voltage as constant as possible and then to adapt the control. The output voltage in the power factor correction circuit is only recorded for the purpose of stabilizing the output voltage, but no conclusion is drawn about the input voltage or other variables.

0007The document "<nplcit id="ncit0002" npl-type="s"><text>Evaluation of a low-cost permanent emergency lighting system based on high efficiency LEDs "by Rico-Secades and others (38th IEEE Industry Applications Conference, conference record of the IEEE Industry Applications Conference IAS annual meeting, October 12-16, 2003</text></nplcit>) describes a control circuit for emergency lighting that can detect an emergency. The control circuit is not connected to the charging circuit. The charging circuit is therefore controlled independently of the control of the control circuit for emergency lighting operation.

0008The document <patcit id="pcit0002" dnum="US20060001381A1"><text>US 2006/0001381 A1</text></patcit> describes a drive and control arrangement for supplying a desired switching current to a load with a chain of one or more electronic arrangements, the arrangement comprising: A voltage converter provided for connection to a power supply, said voltage converter being for converting voltage from the voltage supply from a first magnitude voltage to a second magnitude voltage, said voltage converter responding to a control signal; a dimming control arrangement arranged to receive said large-size voltage and to control the transmission of the second-size voltage to said chain, thereby controlling the activation of said chain; a voltage sensing arrangement electrically connected to the output of said voltage converter and intended to produce a first signal and a voltage sensing arrangement in series with said chain for generating a second signal indicative of the current flowing through said chain and ; a feedback arrangement electrically coupled to said voltage converter, said voltage sensing arrangement and said current sensing arrangement. The feedback arrangement is intended to receive the entire first and second signal and to supply the control signal to the voltage converter, said control signal being based on the first and second signals. The voltage converter changes the voltage of the second magnitude on the basis of the control signal received by the feedback arrangement. The dimming control arrangement is provided for receiving a switching signal and in response to the switching signal controls the transmission of the second quantity to the chain mentioned. The feedback arrangement further includes a feedback switch responsive to a duty cycle control signal, said feedback arrangement being adapted to generate the control signal based primarily on the first signal when said feedback switch is in an active state, and said one Feedback arrangement is provided to generate the control signal, specifically based on the second signal, when said feedback switch is in a deactivated state.

0009The document <patcit id="pcit0003" dnum="US7015654B1"><text>US 7,015,654 B1</text></patcit> describes a microcontroller and a boost converter circuit that transmit a constant current to an LED array. The microcontroller is connected to a semiconductor switch and the boost converter circuit measures the ability of a DC power supply to change an inductor. The operating cycles of the semiconductor switch are changed in accordance with the measurement in order to supply the LED arrangement with a substantially constant current through the inductor, regardless of the current battery voltage.

0010The present invention is based on the object of specifying an improved concept for an emergency lighting device in which the disadvantages described above are avoided.

0011This object is achieved by an emergency lighting device with the features of claim 1. Advantageous developments of the invention are the subject of the dependent claims.

0012The main idea of ​​the present invention is that, in contrast to known solutions, the mains supply voltage is now only monitored indirectly, in order to possibly initiate emergency lighting operation. For this purpose, only measured values ​​on the potential of the energy storage unit or LED are recorded and, on the basis of these measured values, conclusions are drawn on the state of the mains supply voltage with the aid of further information.

0013Accordingly, an emergency lighting device for operating a light source, in particular an LED, is proposed, the emergency lighting device having:<ul id="ul0001" list-style="bullet"><li>an energy storage unit,</li><li>a charging circuit to be supplied with a mains supply voltage for charging the energy storage unit during a charging operation of the emergency lighting device, the charging circuit having a potential separation, and</li><li>a driver circuit supplied by the energy storage unit during emergency lighting operation for operating the light source,</li></ul>wherein the device further has a control unit which is designed to monitor the state of the mains supply voltage during charging and to activate the emergency light mode when an emergency is detected. It is provided according to the invention that the control unit determines the state of the mains supply voltage on the basis of operating variables of the emergency lighting device measured on the output side of the charging circuit.

0014The measures according to the invention ensure that an emergency state affecting the voltage supply can still be reliably detected and, accordingly, emergency lighting operation can be initiated. At the same time, however, the necessary electrical isolation between the means for monitoring the mains supply voltage and the other components of the emergency lighting device is eliminated, so that the device as a whole can be implemented more cost-effectively and compactly.

0015The charging circuit preferably has a controllable switch and a transformer, it being possible for the charging circuit to be formed in particular by a so-called flyback converter. The controllable switch is controlled by the control unit of the emergency lighting device, wherein the control can take place here in particular via an optocoupler.

0016The state of the mains supply voltage is now determined, in particular, taking into account the duty cycle selected by the control unit for controlling the switch of the flyback converter or the charging circuit. Furthermore, the secondary voltage of the flyback converter or, in the case of other switched-mode power supply topologies, the charging power for the energy storage unit is taken into account. This charging power can be determined in a simple manner by the control unit during charging operation, that is to say when the light source is switched off, since the values ​​to be measured for this purpose, namely voltage and current of the energy storage circuit, relate to the same basic potential on which the other components of the emergency lighting device are based lie. The same applies to the secondary voltage to be measured if the flyback converter is used. In both cases, the galvanic separation between the measuring devices and the control unit required in the prior art can therefore be omitted.

0017Another advantageous development of the present invention relates to the measures for operating the light source, in particular the LED, during emergency lighting operation. For this purpose, the driver circuit is preferably designed as a switching regulator and accordingly has a further controllable switch, which in turn is controlled by the control unit. The control of the switch is such that the light source can be operated with a constant power or constant current regardless of the state of charge of the energy storage unit. This measure is of particular importance since the power of the energy storage unit naturally drops over time, which should not, however, affect the light intensity of the emergency lighting device.

0018In the case of using an LED as a light source, it would in turn be appropriate to detect the diode current itself, which determines the light output, in order to enable the desired power regulation. According to a particularly advantageous development of the present invention, it is provided that the measurement of the diode current is omitted and instead the current or the power of the light source is measured or estimated indirectly using other parameters. In particular, preferably only the voltage applied to the light source is determined and then the diode current is derived from further information, the power loss of the driver circuit in particular being taken into account. Using previously determined comparison tables stored in the control unit, the power of the light source can then be determined without a direct measurement of the diode current, so that an almost constant light output can be set by the control unit. The light output is regulated here in particular by appropriate clocking of the controllable switch of the driver circuit, since in this way the output with which the light source is operated can be set in a very simple and elegant manner.

0019This special measure for operating the light source at an almost constant power, whereby a direct measurement of the current is dispensed with, can also be used independently of the inventive idea of ​​indirect monitoring of the mains supply described at the beginning. Accordingly, this idea is also the subject of a further independent claim.

0020The invention will be explained in more detail below with reference to the accompanying drawing. Show it:<ul id="ul0002" list-style="none"><li><figref idref="f0001">Fig. 1</figref> schematically the circuit diagram of an embodiment of an emergency lighting device according to the invention;</li><li><figref idref="f0001">Fig. 2</figref> an example of an emergency lighting device;</li><li><figref idref="f0001">Fig. 3</figref> a graphic for determining the mains supply voltage on the basis of operating parameters measured on the output side of the charging circuit and</li><li><figref idref="f0001">Fig. 4</figref> another graphic for determining the secondary power of the charging circuit, which is taken into account for the indirect determination of the light source power.</li></ul>

0021This in <figref idref="f0001">Fig. 1</figref> The emergency light device according to the invention, shown in a simplified manner and generally provided with the reference number 1, is provided in the exemplary embodiment shown for operating an LED as an emergency light source. The emergency lighting device 1 is connected on the input side to a power supply network, which has a power supply voltage U_in provides and has as essential components a control unit 2, a charging circuit 3, an energy storage unit 4 in the form of a battery or an accumulator and a driver circuit 5. In the exemplary embodiment shown, the charging circuit 3 is formed by a so-called flyback converter, which on the one hand has a transformer T with a primary winding n1 and a secondary winding n2 and on the other hand a controllable switch S1. In a known manner, a corresponding alternating opening and closing of the switch S1, the from the mains supply voltage U_in The energy made available is transferred to the secondary side of the flyback converter 3 and used to charge the energy storage unit 4. The energy transfer takes place in the open state of the switch S1, with a diode D on the output side of the flyback converter 3₁ is provided. Such flyback circuits are widely used in such emergency lighting devices due to their simple structure and reliable function.

0022The controllable switch S1 is activated by the control unit 2 of the emergency lighting device, the activation being carried out, in particular, in an electrically isolated manner via an optocoupler 6. The control unit 2 controls the switch S1 alternately, the so-called duty cycle D1 for the switching operation of the switch S1 being calculated as follows:<maths id="math0001"><math display="block"><mi>D</mi><mo>⁢</mo><mn>1</mn><mo>=</mo><msub><mi>t</mi><mrow><mi mathvariant="italic">on</mi><mo>⁢</mo><mn>1</mn></mrow></msub><mo>/</mo><mfenced><mi>T</mi><mo>-</mo><msub><mi>t</mi><mrow><mi mathvariant="italic">on</mi><mo>⁢</mo><mn>1</mn></mrow></msub></mfenced></math><img file="EP2249458B1_D0001.tif" /></maths> t_onl corresponds to the switch-on time, while T denotes the total duration of a complete switching cycle for switch S1.

0023It is also conceivable that the control of S1 is a 'cantilever' and that the natural frequency of the 'cantilever' is influenced by the optocoupler 6 via the duty cycle.

0024During a charging operation of the emergency lighting device 1, usually only the charging circuit 3 is active in order to charge the battery 4 permanently. Only in the event that there is an emergency which is caused in particular by deviations in the mains supply voltage U_in is characterized by predetermined target values, an emergency lighting operation is initiated in which the driver circuit 5 is used to control the LED. For this purpose, the driver circuit 5 designed as a switching regulator has a further controllable switch S2, an inductance L and a diode D.₂ on. By alternately actuating the switch S2 by the control unit 2, a current is made available to the LED, via which the LED is operated. The duty cycle with which the switch S2 is controlled by the control unit 2 can be varied in order to set the level of the current supplied to the LED and thus the power at which the LED is operated. In this way it can be ensured in a very elegant way that the LED is operated with constant brightness despite everything, even with fluctuating battery power.

0025A first essential function of the emergency lighting device 1 thus consists in assessing the mains supply voltage U_in to recognize whether there is an emergency, in order to initiate emergency lighting operation if necessary. Up to now it was known to directly determine the value of the input voltage U_in to determine for the charging circuit 3, which, however, is associated with disadvantages for the reasons mentioned above.

0026According to the present invention, a direct measurement of the mains supply voltage U_in waived. Instead, it is planned to determine these indirectly. In particular, it is provided that only the sizes of operating parameters of the emergency lighting device 1 are measured on the secondary side of the charging circuit 3.

0027In the embodiment according to <figref idref="f0001">Fig. 1</figref> the voltage U present on the secondary side of the flyback converter or flyback converter 3_flb2 measured, for which in particular no electrical isolation is required, since this variable is at the same reference potential as the control unit 2, which evaluates the measured value. Now is the level of this secondary voltage U_flb2 known, it can be based on the level of the input voltage U_in be inferred. When switch S1 of flyback converter 3 is switched on, there is a connection between input voltage U_in and secondary voltage U_flb2, which is particularly dependent on the winding ratio between the two windings n1 and n2 of the transformer T and on the duty cycle of the switch S1. This relationship between the easy-to-measure secondary voltage U_flb2 and the input voltage U to be monitored_in is now stored in the form of a table of values ​​in the control unit 2, so that after measuring the secondary voltage U_flb2 in a simple manner the level of the input voltage U_in can determine without having to measure them directly. Now the control unit 2 determines that the input voltage U_in is outside certain target value ranges, this indicates an emergency state, which in turn will cause the control unit 2 to initiate an emergency operation.

0028The solution described thus enables very simple but effective monitoring of the status of the general power supply. There is also a particular advantage of the in<figref idref="f0001">Fig. 1</figref> illustrated embodiment in that the level of the input voltage U_in regardless of whether the emergency light LED is switched on or not. The diode D₁ causes a separation between the secondary voltage U by its blocking effect_flb2 and battery voltage U_Bat, so that the activity of the driver circuit 3 is not based on the above-described process of determining the input voltage U_in affects.

0029A more general example of an emergency lighting device is in <figref idref="f0001">Fig. 2</figref> shown. The structure of this corresponds essentially to that in<figref idref="f0001">Fig. 1</figref> shown emergency lighting device 1, but now the charging circuit 3 is not formed by a flyback converter but generally by a circuit arrangement which has a potential separation and a switch S1 controlled by the control unit 2.

0030In this more general form, there is not necessarily a known relationship between the input voltage U_in and the voltage on the output side of the charging circuit 3. Nevertheless, the level of the input voltage U_in can be determined indirectly, but now other farm sizes are measured.

0031On the one hand, this is the battery voltage U_asked as well as the battery current I_asked. Both variables can in turn be determined relatively easily, that is to say without galvanic isolation, since they, like the control unit 2, which evaluates these measured variables, are at the same reference potential. &lt;

0032> On the basis of these two measured variables U_asked and I_asked and the known duty cycle D1 for the switch S1 of the charging circuit 3 can then the input voltage U_in can be determined, since this is related to the three known quantities. This illustrates the graphic of<figref idref="f0001">Fig. 3</figref>which different characteristics of the secondary power P_flb2 shows the charging circuit 3 as a function of the duty cycle D1 for the switch S1. These characteristic curves are determined, for example, during the manufacture of the emergency lighting device and are in turn stored in the form of a table in the control unit 2. It can be seen that these characteristics in particular also depend on the input voltage U_in are dependent. So now the duty cycle D1 and the secondary power P_flb2 the charging circuit 3 known, as in the example of <figref idref="f0001">Fig. 1</figref> to the level of the input voltage U_in be closed back.

0033In the example shown by <figref idref="f0001">Fig. 3</figref> it is thus determined with which characteristic curve the known combination of duty cycle D1 and secondary power P_flb2 the charging circuit 3 which, when the driver circuit 5 is deactivated, the product of the battery voltage U_asked and battery power I_asked corresponds, agrees. In the measured values ​​shown, for example, this value lies on the characteristic curve for an input voltage U_in of 220 volts, which corresponds to a proper condition of the general mains supply. However, the determined value would lie on a characteristic curve, for example an input voltage U_in corresponds to 140 volts or 280 volts, this would in turn be interpreted by the control unit 2 in such a way that there is an error in the mains supply and accordingly initiate an emergency.

0034In both of the examples shown, the input voltage U can be measured reliably and without the need for a direct measurement_in determine whether the mains supply is OK or not. A limitation in the example of<figref idref="f0001">Fig. 2</figref> consists, however, in that the described determination of the input voltage U_in is only possible when the driver circuit 5 is switched off. In the example of<figref idref="f0001">Fig. 1</figref> however, as already mentioned, this restriction does not exist. Basically, however, the control unit 2 will activate the driver circuit 5 and accordingly switch the LED on if a fault is detected.

0035After the driver circuit 5 has been activated, the switch S2 can then be controlled at high frequency in the manner described above in order to operate the LED with a desired power. In this case, to ensure that the power of the LED is constant, it would be necessary to use both the LED voltage U_led as well as the LED current I_led to know to enable regulation. According to a particularly advantageous development, however, only the LED voltage U_led measured and the current I_led or the resulting power P_led indirectly determined by the control unit 2, which will be explained in more detail below.

0036To the diode current I_led To be able to determine indirectly, at least the quantities battery voltage U_asked, Battery current I_asked and - case of the example of <figref idref="f0001">Fig. 1</figref> - secondary voltage U_flb2 as well as the LED voltage U_led measured. From this, the further information that is used to regulate the LED current I_lea are required, are calculated, for which, however, further information is required, which is not recorded by actual value measurements, but rather is stored in the control unit 2 as value tables.

0037The first table of values ​​is the information already mentioned above with regard to the relationship between duty cycle D1, secondary voltage U_flb2 and input voltage U_in in the example of <figref idref="f0001">Fig. 1</figref> or between duty cycle D1, battery voltage U_asked, Battery current I_asked and input voltage U_in in the more general example of <figref idref="f0001">Fig. 2</figref>. Furthermore, in order to determine the diode current, the power loss P_lost the driver circuit 5, which is known from the difference between the measured LED voltage U_led and the battery voltage U also measured_asked is dependent, so that: <maths id="math0002"><math display="block"><msub><mi>P</mi><mi mathvariant="italic">lost</mi></msub><mo>=</mo><mi>f</mi><mo>⁢</mo><mfenced><msub><mi>U</mi><mi mathvariant="italic">led</mi></msub><mo mathvariant="italic">-</mo><msub><mi mathvariant="italic">U</mi><mi mathvariant="italic">asked</mi></msub></mfenced></math><img file="EP2249458B1_D0002.tif" /></maths>

0038Finally, the third information required is the secondary power P present in the case of an activated driver circuit_flb2 the charging circuit 3, which is a function of the duty cycle D1, the input voltage U_in and the battery voltage U_asked is. The relationship between these quantities is in<figref idref="f0001">Fig. 4</figref> shown, wherein it can be seen that the secondary power P_flb2 the charging circuit 3 primarily from the input voltage U_in and is dependent on the duty cycle D1 for the switch S1, but also because of the battery voltage U._asked can vary.

0039Is now due to the measures described above, the input voltage U_in (possibly in the example of <figref idref="f0001">Fig. 2</figref> were first determined with the driver circuit 5) switched off, then the relationship in <figref idref="f0001">Fig. 4</figref> the secondary power P even when the driver circuit 5 is activated_flb2 the charging circuit 3 can be determined. The measured quantities of battery voltage U are then known_asked, Battery current I_asked, possibly secondary voltage U_flb2 and LED voltage U_led, the duty cycle D1 specified by the control unit for the switch S1, and the further variables input voltage U determined on the basis of the stored value tables_in' Secondary power P_flb2 the charging circuit 3 and power loss P_lost the driver circuit 5.

0040Knowing these variables in turn enables the current I to be determined in accordance with the following relationship_flb2 on the secondary side of the charging circuit 3: <maths id="math0003"><math display="block"><msub><mi>I.</mi><mrow><mi mathvariant="italic">flb</mi><mo>⁢</mo><mn>2</mn></mrow></msub><mo>=</mo><msub><mi>P</mi><mrow><mi mathvariant="italic">flb</mi><mo>⁢</mo><mn>2</mn></mrow></msub><mo>/</mo><msub><mi>U</mi><mi mathvariant="italic">asked</mi></msub></math><img file="EP2249458B1_D0003.tif" /></maths>

0041Finally, the LED current I_led and the LED power P_led can be calculated according to the following equations: <maths id="math0004"><math display="block"><msub><mi>I.</mi><mi mathvariant="italic">led</mi></msub><mo>=</mo><mfenced><msub><mi>P</mi><mrow><mi mathvariant="italic">flb</mi><mo>⁢</mo><mn>2</mn></mrow></msub><mo>-</mo><msub><mi>U</mi><mi mathvariant="italic">asked</mi></msub><mo>⋅</mo><msub><mi>I.</mi><mi mathvariant="italic">asked</mi></msub><mo>-</mo><msub><mi>P</mi><mi mathvariant="italic">lost</mi></msub></mfenced><mo>/</mo><msub><mi>U</mi><mi mathvariant="italic">led</mi></msub></math><img file="EP2249458B1_D0004.tif" /></maths><maths id="math0005"><math display="block"><msub><mi>P</mi><mi mathvariant="italic">led</mi></msub><mo>=</mo><msub><mi>P</mi><mrow><mi mathvariant="italic">flb</mi><mo>⁢</mo><mn>2</mn></mrow></msub><mo>-</mo><msub><mi>U</mi><mi mathvariant="italic">asked</mi></msub><mo>⋅</mo><msub><mi>I.</mi><mi mathvariant="italic">asked</mi></msub><mo>-</mo><msub><mi>P</mi><mi mathvariant="italic">lost</mi></msub></math><img file="EP2249458B1_D0005.tif" /></maths>

0042Both equations apply in the event that the charging circuit 3 is still active, that is to say at least a certain power supply is still available. This can be the case, for example, if an emergency lighting operation has been initiated otherwise. However, in the event that the power supply fails completely and the emergency lighting operation is only maintained by the battery, the simplified equations apply:<maths id="math0006"><math display="block"><msub><mi>I.</mi><mi mathvariant="italic">led</mi></msub><mo>=</mo><mfenced><msub><mi>U</mi><mi mathvariant="italic">asked</mi></msub><mo>⋅</mo><msub><mi>I.</mi><mi mathvariant="italic">asked</mi></msub><mo>-</mo><msub><mi>P</mi><mi mathvariant="italic">lost</mi></msub></mfenced><mo>/</mo><msub><mi>U</mi><mi mathvariant="italic">led</mi></msub></math><img file="EP2249458B1_D0006.tif" /></maths><maths id="math0007"><math display="block"><msub><mi>P</mi><mi mathvariant="italic">led</mi></msub><mo>=</mo><msub><mi>U</mi><mi mathvariant="italic">asked</mi></msub><mo>⋅</mo><msub><mi>I.</mi><mi mathvariant="italic">asked</mi></msub><mo>-</mo><msub><mi>P</mi><mi mathvariant="italic">lost</mi></msub></math><img file="EP2249458B1_D0007.tif" /></maths>

0043Ultimately, the current actual value of the LED current I_led as well as the current power P_led indirectly determined and used for regulation. The corresponding calculations are carried out by the control unit 2.

0044The advantage of these indirect determinations of the actual values ​​required for regulation is that there is no need to measure an additional operating parameter of the emergency lighting device, which in turn leads to a further simplification of the device as a whole. Since this is partly based on the input voltage that has already been determined or measured parameters can be used, this indirect determination of the LED current thus represents a particularly advantageous development of the idea of ​​indirect determination of the input voltage described at the beginning. However, a corresponding indirect current and power determination for the light source could also be used in other devices, in which the first idea according to the invention has not been realized. For example, this procedure is among others useful for emergency lighting devices in which an emergency state can be signaled alternatively or in addition to monitoring the power supply. For example, in the emergency lighting device according to the invention, an emergency signal, for example from a fire alarm or another control device, could also be transmitted via a separate control input in order to initiate emergency lighting operation by means of an external signal.

0045Another development finally relates to the value tables mentioned above and stored in the control unit, which are required for the indirect determination of the input voltage and the diode current. As already mentioned, these value tables can already be saved in the control unit when the emergency lighting device is manufactured. Alternatively or in addition, it would also be conceivable to subsequently write this information or update at a later date. For this purpose, for example, a digital interface provided in the emergency lighting device could be used, which is usually used for error signaling and monitoring. With the help of this interface, new value tables could now be written into the control unit using an extended command set. This subsequent registration of new information is useful, for example, in order to Specify tolerance values ​​for the input voltage or adapt the information for determining the quantities that are not directly measured to the connected battery. As a result, the behavior of the emergency lighting device can be adapted to new circumstances at any time.

0046Overall, the present invention thus provides a new type of emergency lighting device which is distinguished by its simple and inexpensive construction and, despite everything, reliably enables an emergency to be determined by monitoring the general power supply. In addition, the advantageous regulation of the diode current ensures constant light output over the duration of an emergency operation.