Abstract:
Circuit arrangement for operation of discharge lamp comprising an input for connecting a supply alternating current voltage. A startup supply device is provided with an input and an output, where the input is connected to an input of a control circuit and the output is connected to another input of the control circuit. The startup supply device provides a startup supply voltage at the output of the startup supply device and hence reduces the stand-by losses.

Description:
RELATED APPLICATIONS 
     The present application is a national stage entry according to 35 U.S.C. §371 of PCT application No.: PCT/EP2007/054532 filed on May 10, 2007. 
     BACKGROUND 
     The present invention relates to a circuit arrangement for the operation of at least one discharge lamp with an input for connecting an AC supply voltage, a rectifier, which is coupled to the input and has a first output terminal and a second output terminal for providing a DC supply voltage, an inverter, which includes at least a first switch and a second switch, which are coupled in series between the first output terminal and the second output terminal of the rectifier, a control circuit which is at least designed to drive the first switch and the second switch, with a first input for receiving a control signal, and a second input for feeding a voltage for supplying the control circuit, the second input being connected to an operational supply apparatus, which is designed to couple an operational supply voltage to the second input of the control circuit during operation of the inverter and a control line, which is coupled firstly to the input for connecting an AC supply voltage and secondly to the first input for receiving a control signal, a third switch being arranged in the control line. The invention moreover relates to a method for the operation of at least one discharge lamp using such a circuit arrangement. 
     Circuit arrangements, in particular electronic ballasts, which are switched on and off via a control input, have a power consumption in the switched-off state of up to 1 W, which is referred to as standby losses. The cause of these losses is primarily the internal control circuit, which needs to be supplied with voltage even in the “off” state, in order to be able to react to the next “on” command. The losses caused by the internal control circuit make up approximately 60% of the standby losses. 30% of the standby losses are produced by the filament monitoring, and 10% of the losses by the switched-mode power supply. 
     For a more detailed illustration of the problem on which the invention is based, reference is first made to  FIG. 1 , which shows a circuit arrangement of the generic type known from the prior art. Said circuit arrangement has an input E 1 , E 2  for connecting an AC supply voltage U N . Connected thereto are a first X capacitor Cx 1 , two inductances L 1   a , L 1   b , which are coupled to one another, a rectifier  10  and a second X capacitor Cx 2 . A discharge lamp La is connected via an inductance L 3  to the half-bridge center point HM of an inverter, which includes a first switch Q 2  and a second switch Q 3 . A capacitor C 3  is arranged in parallel with the lamp La. The circuit arrangement includes a control circuit  12 , which in this case solves various problems. Firstly, the first switch Q 2  of the inverter is driven via a control output HSG of the control circuit  12 , and the switch Q 3  of the inverter is driven via a control output LSG of the control circuit  12 . An input Line is used for measuring the system voltage, which input evaluates the voltage across a nonreactive resistor R 2  of a voltage divider including the nonreactive resistors R 1  and R 2 . The resistor R 1  is coupled to the voltage provided at the capacitor Cx 2 . Using the inductances L 2   a , L 2   b , which are coupled to one another, and the nonreactive resistor R 8 , a zero crossing of the current is determined by the inductance L 2   a  via an input ZC in order to drive a switched-mode power supply, which includes a transistor Q 1 , a diode D 1 , the inductances L 2   a , L 2   b , a nonreactive resistor R 8  and a capacitor C 1 , in a suitable manner via an output PFG. In this case, the transistor Q 1 , the diode D 1  and the capacitor C 1  form a PFC (power factor correction) apparatus. Using the nonreactive resistors R 3  and R 4 , which together form a voltage divider, the amplitude of the so-called intermediate circuit voltage U ZW  is measured via an input Bus. The clock signal produced by a pushbutton T 1  which in this case is coupled to the input E 2 , is converted via a pulse-shaping apparatus  14 , which includes the nonreactive resistors R 9  and R 10  and a diode D 4  and a capacitor C 6 , into a pulse, which is coupled to the input Cntrl of the control circuit  12  via the section  16  of a control line St. Via a nonreactive resistor R 7 , which is coupled to the intermediate circuit voltage U ZW , the control circuit  12 , after reception of an off signal at the Cntrl input, continues to be supplied with voltage via the input SS in order to be reception-ready for the next on command at the Cntrl input. During operation of the discharge lamp La, the control circuit  12  is supplied with voltage via an operational supply apparatus, the operational supply apparatus including the capacitor C 2 , the diodes D 2  and D 3  and the capacitor C 5 . In this case, the voltage U VCC  is provided across the capacitor C 5 , which is coupled to the input VCC of the control circuit  12 . This input VCC is furthermore used for determining, using the nonreactive resistors R 5  and R 6  and the capacitor C 4 , whether a discharge lamp La has been inserted. 
     Details regarding operation: The circuit arrangement illustrated in  FIG. 1  is part of an electronic ballast, which can be switched on and off via a pushbutton T 1 . In this case, the system voltage U N  is present across the circuit arrangement even in the off state. It is only the internal control circuit  12  which is stopped, with the result that the PFC transistor Q 1  and the inverter, which includes the switches Q 2  and Q 3 , are no longer driven. The internal control circuit  12  needs to continue to be supplied with voltage via the nonreactive resistor R 7  in order to be reception-ready for the next on command. The internal control circuit  12  in this case, together with its supply via the nonreactive resistor R 7 , causes the majority of the standby losses. 
     Furthermore, a plurality of current paths which produce the measured values for the various functions of the electronic ballast increase the standby losses: Particular mention should be made of the filament monitoring, which includes the two nonreactive resistors R 5  and R 6 , which are connected in series with an electrode of the fluorescent lamp La and only allows a current to flow from the so-called intermediate circuit, i.e. the line of the circuit arrangement across which the intermediate circuit voltage U ZW  is provided, to the internal control circuit  12  when the fluorescent lamp La is inserted. The filament monitoring ensures that the electronic ballast can start only when the fluorescent lamp La is inserted, that the electronic ballast, which is automatically shut down once a lamp fault has been identified, remains shut down, and that the electronic ballast automatically restarts (relamping) once a defective fluorescent lamp has been replaced. 
     The switched-mode power supply, which includes the inductances L 2   a  and L 2   b , the nonreactive resistor R 8  and the PFC apparatus, which has the transistor Q 1 , the diode D 1  and the capacitor C 1 , is controlled in such a way that the intermediate circuit voltage U ZW  is kept at a constant value in a load-independent manner, and that the system current drawn is sinusoidal. For this purpose, a control signal is used which is proportional to the product of the control discrepancy between the intermediate circuit voltage U ZW  and the present value of the system voltage U N . For this purpose, the system voltage U N  is interrogated via the nonreactive resistors R 1  and R 2 , and the intermediate circuit voltage U ZW  is interrogated via the nonreactive resistors R 3  and R 4 , by the internal control circuit  12 . 
     SUMMARY 
     Various embodiments provide a circuit arrangement of the generic type such that it has reduced standby losses. 
     Various embodiments are based on the knowledge that the abovementioned reduced standby losses can be achieved with a circuit arrangement of the generic type if the off signal on the control line is used to completely shut down the electronic ballast, including the internal control circuit. The “on” signal triggered by the next depression of the pushbutton T 1  serves not only as the control signal “on”, but at the same time to supply the internal control circuit until the electronic ballast is started and the supply to the internal control circuit again functions via the known operational supply apparatus. 
     Therefore, a circuit arrangement according to the invention furthermore includes a startup supply apparatus with an input and an output, its input being coupled to the first input of the control circuit, and its output being coupled to the second input of the control circuit, the startup supply apparatus being designed to provide a startup supply voltage at the output of the startup supply apparatus in the event of an on signal at the input of the startup supply apparatus when the control circuit has no supply and therefore is switched off. 
     By virtue of this measure, the control circuit can be shut down completely until the reception of a new on signal, i.e. a supply as is provided in the prior art via the resistor R 7  is not provided in this phase. The control circuit therefore does not cause any standby losses during standby operation. 
     In a preferred embodiment, the operational supply apparatus includes a first capacitor, which is coupled to the second input of the control circuit, the startup supply apparatus being designed to couple the on signal at its input, as startup supply voltage, to the first capacitor, in order to charge the latter. Thus, the same capacitor and the same input of the control circuit are used for the startup supply as for the operational supply, which results in an extremely favorable embodiment. 
     Preferably, the circuit arrangement includes a second capacitor, which is coupled between the DC supply voltage and a first terminal for the discharge lamp, and a third capacitor, which is coupled between the second terminal for the discharge lamp and the reference potential, the startup supply apparatus being designed to convert the charging current of the third capacitor, which charging current occurs once a discharge lamp has been inserted, into a voltage pulse and to provide this voltage pulse at the output of the startup supply apparatus. Thus, the relamping function is made possible, i.e. a control pulse, which is sufficient for startup of the control circuit, is provided at the input VCC of the control circuit once a lamp has been inserted. Owing to the fact that the first input of the control circuit is coupled to the second input of the control circuit via the startup supply apparatus, the charging current of the third capacitor can therefore also be applied to the first input of the control circuit in order thus to provide an on signal at the control circuit. As a result, the charging current of the third capacitor is used during relamping firstly for providing a supply voltage for the control circuit, and secondly as an on signal for the control circuit. 
     Particularly preferably, in this case the circuit arrangement furthermore has a charging-current amplification apparatus, which is designed to amplify the charging current of the third capacitor, the charging-current amplification apparatus being coupled between the DC supply voltage and the reference potential. As a result of the dimensioning of the charging-current amplification apparatus, it is therefore possible to ensure that the charging current of the third capacitor is also always sufficient during relamping to supply the internal control circuit with sufficient voltage. 
     Preferably, a nonreactive resistor is connected in parallel with the third capacitor. This measure ensures rapid discharge of the third capacitor when the lamp is removed. 
     It is furthermore preferable for the startup supply apparatus to include a coupling apparatus, which is arranged in such a way that the second input of the control circuit can be coupled to the DC supply voltage via the coupling apparatus, the coupling apparatus having a control input, which is coupled to the input of the startup supply apparatus. Therefore, the DC supply voltage is “tapped” to supply the control circuit only when an on signal has been received at the input of the startup supply apparatus. In a particularly preferred embodiment, in this case the coupling apparatus comprises a fourth and a fifth switch and at least one nonreactive resistor, which are arranged in such a way that, by driving of the fourth switch with the signal at the input of the startup supply apparatus, a current flow through the nonreactive resistor is made possible, with the voltage drop produced thereby across the nonreactive resistor being coupled to the control path of the fifth switch, in order to switch the fifth switch into the on state, as a result of which the fifth switch, which is coupled to the DC supply voltage, applies the DC supply voltage to the output of the startup supply apparatus. 
     Preferably, in this case the first input of the control circuit is coupled, through the control circuit, to the input of the startup supply apparatus. Here, holding elements can be provided in order to provide a pulse-shaped on signal at the first input of the control circuit as a permanent on signal at the input of the startup supply apparatus. As a result, the filament monitoring is activated during operation of the discharge lamp. 
     Preferably, the third switch is in the form of a pushbutton. Without actuation of the third switch, startup of the control circuit during so-called relamping is produced by a discharge lamp being inserted. 
     The preferred embodiments and advantages thereof set forth with reference to a circuit arrangement according to the invention apply correspondingly, if appropriate, to the method according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which: 
         FIG. 1  shows a schematic illustration of a circuit arrangement known from the prior art for the operation of at least one discharge lamp; 
         FIG. 2  shows a schematic illustration of a first exemplary embodiment of a circuit arrangement according to the invention; 
         FIG. 3  shows a schematic illustration of a second exemplary embodiment of a circuit arrangement according to the invention; and; 
         FIG. 4  shows a schematic illustration of a third exemplary embodiment of a circuit arrangement according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. 
     The components introduced with reference to  FIG. 1  and the reference symbols thereof apply, insofar as they relate to identical or similar components, to the exemplary embodiments of circuit arrangements according to the invention illustrated in  FIGS. 2 to 4  as well. They are therefore not introduced again, with the result that the description below substantially provides details on the differences from the prior art illustrated in  FIG. 1 . 
     The first exemplary embodiment illustrated schematically in  FIG. 2  of a circuit arrangement according to the invention has a startup supply apparatus  18 , which has an input E 3  and an output A 1 . The input E 3  is coupled to the first input Cntrl of the control circuit  12 , and the output A 1  is coupled to the second input VCC of the control circuit  12 . The startup supply apparatus  18  includes a line  20 , which is designed to produce an on signal on the control line  16  for charging the capacitor C 5  and therefore for providing a startup supply voltage at the input VCC of the control circuit  12 . For this purpose, the startup supply apparatus  18  furthermore comprises two diodes D 7  and D 8 . 
     Although  FIG. 2  illustrates an embodiment with a pushbutton T 1 , with which the system voltage U N  can be switched to the control input Cntrl of the control circuit  12 , the present invention can be used in all control methods which operate with non-potential-free control signals. In the exemplary embodiment shown, a brief depression of the pushbutton T 1  results in the electronic ballast in which a circuit arrangement according to the invention is implemented being switched on and switched off, and a long depression of the pushbutton serves the purpose of changing the dimming setting alternately upwards or downwards. 
     The internal control circuit  12  is in this case only supplied with voltage as long as the electronic ballast is in operation. A charge pump, which includes the capacitor C 2  and the diodes D 2  and D 3 , is used in this case for the operational supply. This operational supply draws its power from an electronic-ballast-internal AC voltage signal, for example from the lamp voltage. An off signal at the control input St, produced by a depression of the pushbutton T 1 , stops the control circuit  12  and therefore the circuit arrangement according to the invention. The control circuit  12  then no longer has a supply. The next depression of the pushbutton T 1  is firstly interpreted as an on signal at the input Cntrl of the control circuit  12  and is secondly used, via the diode D 7 , for charging the capacitor C 5 . The control circuit  12  is thus started and supplied with voltage from the capacitor C 5  until the circuit arrangement according to the invention has been started up and the operational supply via the charge pump C 2 , D 2 , D 3  functions again. 
     It is not necessary for the shutdown to be stored after a lamp defect has been identified in the case of a circuit arrangement according to the invention since the circuit arrangement does not start up again independently, but only after an on signal from the pushbutton T 1 . 
     If, during relamping, a new lamp La is inserted, the charging current of the capacitor C 11  produces a voltage pulse across C 4 , which charges the capacitor C 5  via the diodes D 7  and D 8  and thus supplies the control circuit  12  with voltage until the circuit arrangement has started up and the operational supply via the charge pump C 2 , D 2 , D 3  functions again. At the same time, this voltage pulse via the diode D 8  and the line  20  acts as an on signal at the input Cntrl of the control circuit  12 . The resistor R 11 , which is connected in parallel with the capacitor C 11 , ensures rapid discharge of the capacitor C 11  when the lamp La is removed. This results in rapid generation of the starting conditions after relamping. 
     Thus, the filament monitoring, as has been described with reference to  FIG. 1 , is not required. The standby losses which have resulted in the prior art from the filament monitoring, therefore likewise do not occur in the case of a circuit arrangement according to the invention as shown in  FIG. 2 . 
     A further reduction in the standby losses can be achieved by modification of the switched-mode power supply. Said switched-mode power supply can dispense with the measurement of the system voltage, as was carried out in the circuit arrangement shown in  FIG. 1  using the resistors R 1  and R 2 , if the switch-on time of the transistor Q 1  of the PFC apparatus is only dependent on the control discrepancy of the intermediate circuit voltage U ZW , and no longer on the system voltage U N . In order furthermore to achieve a sinusoidal current consumption, the X-capacitor Cx 2  then needs to be connected upstream of the rectifier  10 , however. 
     A further reduction in standby losses results if the intermediate circuit voltage U ZW  is determined from the peak-to-peak voltage across the inductance L 2   b , which indicates the current zero crossing, via the peak-to-peak rectifier, which includes the components C 8 , D 6 , D 5 . The voltage divider R 3 , R 4  therefore no longer needs to be connected to the intermediate circuit voltage U ZW  and therefore no longer produces any standby losses. 
     A second exemplary embodiment of a circuit arrangement according to the invention is illustrated schematically in  FIG. 3 . In this exemplary embodiment, the input Cntrl of the control circuit  12  is coupled through the control circuit  12 , to the output S 0  of the control circuit  12 . The signal present at the output S 0  is coupled to the input E 3  of the startup supply apparatus  18 , the output A 1  of the startup supply apparatus  18  again being coupled to the capacitor C 5 . In this case, the startup supply apparatus  18  comprises a coupling apparatus, which includes a switch Q 4 , a switch Q 5  and two nonreactive resistors R 12  and R 13 . In this case, the input of the switch Q 5  is coupled to the input E 3  of the coupling apparatus  18 , and therefore to the output S 0  of the control circuit  12 . If the switch Q 5  is switched into the on state by an on signal at the output S 0  of the control circuit  12 , a current flow through the nonreactive resistors R 12  and R 13  thus results. The voltage drop across the nonreactive resistor R 13  is applied to the control path of the switch Q 4 , as a result of which said switch is switched into the on state and supplies the intermediate circuit voltage U ZW , via the resistor R 5 , and electrode of the lamp La and the nonreactive resistor R 6 , to the capacitor C 5  in order to charge said capacitor and therefore to provide a startup supply voltage to the control circuit  12  via the input VCC thereof. The measurement of the intermediate circuit voltage U ZW  is likewise dependent on the switching state of the switch Q 4 , with the result that a measurement of the intermediate circuit voltage takes place via the resistors R 3  and R 4  only when the switch Q 4  is switched on. This does not result in any standby losses, in contrast to the arrangement for measuring the intermediate circuit voltage shown in  FIG. 1 . 
     Instead of the signal at the input Cntrl of the control circuit  12  being passed on internally to the output S 0  of the control circuit  12 , this can be achieved easily by virtue of an external line  22 , as is illustrated by dashed lines in  FIG. 2 . 
     In the embodiment shown in  FIG. 4 , a charging-current amplification apparatus  24  is provided which is used to amplify the charging current of the capacitor C 11  if said charging current is insufficient during relamping for supplying the internal control circuit  12  with sufficient voltage. For this purpose, the charging current is passed via a nonreactive resistor R 14 , which applies a voltage to the control path of a switch Q 6 . Owing to the voltage drop across the nonreactive resistor R 14 , the switch Q 6  is switched into the on state, with the result that the intermediate circuit voltage U ZW  is applied to the capacitor C 5  via the diodes D 8  and D 7 . In this case, a zener diode D 9  protects the internal control circuit  12  against overvoltage. 
     While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.