Patent Application
20060214602
The present invention relates to a circuit arrangement for operating at least one first and one second lamp which can be inserted in said circuit arrangement, each lamp having a first and a second filament, having a drive circuit for the purpose of driving the at least one first and second lamp, the drive circuit being designed to operate the at least one first and second lamp using a radiofrequency signal.
Such a circuit arrangement is known from the prior art. If the drive circuit is now in the form of a remote-controlled electronic ballast, there is the risk of the removal of a lamp from the circuit arrangement during operation not being recognized if the corresponding load circuit is not monitored. The corresponding load circuit can then continue to operate in the so-called capacitive mode. Owing to the lack of damping by the lamp removed and given an unchanged operating frequency, the switches which are generally used as transistors in the drive circuit are no longer operated at the optimum time, at which the transistors are without voltage, but at times at which a voltage is present across the transistor and, at the same time, current flows through the transistor. The power loss which is thereby increased and is converted in the transistor may lead to heating of the transistor which may result in destruction of the transistor.
The object of the present invention therefore consists in developing the circuit arrangement mentioned initially such that damage which results when a lamp is removed in the prior art can be avoided in a reliable manner.
The invention is based on the knowledge that the abovedescribed problem can be counteracted if two voltage potentials are compared with one another, the difference between these two voltage potentials being dependent on whether a lamp has been removed from the circuit arrangement.
If the two voltage potentials are selected such that they are equal when all of the lamps are inserted, it is possible in a simple manner for further measures to be taken to protect the transistors in the drive circuit when a discrepancy between the two voltage potentials is established. According to the invention, a deactivation apparatus is accordingly also provided for the purpose of deactivating the drive circuit, the comparator circuit being designed to activate the deactivation apparatus if the difference between the first and the second voltage potential exceeds a predeterminable limit value. This measure automatically prevents operation of the drive circuit and thus a risk to the transistors used in the drive circuit if a lamp has been removed from the circuit arrangement.
The second voltage potential preferably depends on the voltage potential across each second filament of each lamp. If a half-bridge circuit is used in the drive circuit, the respective second filament of each lamp is connected to the center point of this half-bridge circuit via in each case one lamp inductor.
It is preferred if the difference between the first and the second voltage potential, if all of the lamps are inserted, is less than the predeterminable limit value and, if at least one lamp is not inserted, is greater than the predeterminable limit value.
The circuit arrangement preferably comprises a second voltage divider, at which the second voltage potential can be tapped off, the supply voltage of the second voltage divider being formed by the large number of voltages across the respective second filament of each lamp. As a result of the fact that each lamp thus contributes to the second voltage potential via its second filament, the removal of a lamp leads to mistuning which, given suitable dimensions, leads to the second voltage potential being changed such that the predeterminable limit value is exceeded.
Since the comparator circuit is designed for operating lamps using a radiofrequency signal, a time controller is preferably also provided which is designed to deactivate the deactivation apparatus over a predeterminable period of time, in particular during preheating and starting of the lamps. In one preferred embodiment, the time controller is therefore supplied with voltage via a DC path, which flows in series through the respective first filament of each lamp.
One particularly preferred embodiment is finally characterized by the fact that it also comprises a starting apparatus for the purpose of starting driving of the lamps by means of the drive circuit, the starting apparatus being supplied with voltage via a DC path, which flows in series through the respective first filament of each lamp, the circuit arrangement being designed such that at least one lamp inserted in the circuit arrangement is connected to a second voltage potential via the direct current flowing in each case through the second filament, said second voltage potential being different from the first voltage potential by less than the predeterminable limit value. This embodiment takes into account so-called “relamping”, i.e. starting of the circuit arrangement once a lamp has been reinserted without it being necessary to interrupt the power supply system. The DC ratio at the comparator circuit is accordingly of significance for relamping. The starting apparatus is accordingly only enabled again when every lamp is inserted. Since, however, a holding element, for example a capacitor of large magnitude which is charged via the difference between the first and the second voltage potential and whose discharge may last for a crucial period of time, is often used for stabilizing the trigger condition for the activation of the deactivation apparatus, in which case the circuit arrangement is designed such that even the presence of a lamp in the circuit arrangement in the DC case results in a second voltage potential which is different from the first voltage potential by less than the predeterminable limit value. The discharge of the holding element is thus triggered as early as when a lamp is removed, with the result that it can reliably be assumed that, when the new second lamp is inserted, the holding element is discharged and no longer represents an obstacle to starting the circuit arrangement.
Further preferred embodiments are described in the dependent claims.
An exemplary embodiment will now be described below with reference to the attached drawing, which shows a preferred exemplary embodiment of a circuit arrangement according to the invention.
Operation
During radiofrequency operation, the two voltage potentials U6 and U7 applied to the comparator circuit 10 are essentially identical. In this case, the voltage U6 results from the intermediate-circuit voltage UZW owing to a current flow through the coupling capacitor C1, the filament W11, and the resistor R3 via the voltage drop across the resistor R6. The voltage U7 results during radiofrequency operation from the intermediate-circuit voltage UZW owing to a current flow through the coupling capacitor C1, the filament W11, the filament W12 and the resistor R4, on the one hand, and the filament W21, the filament W22 and the resistor R5, on the other hand, owing to the voltage drop U7 across the resistor R7.
If one of the two lamps LP1, LP2 is now removed from the circuit arrangement, mistuning results, i.e. the difference between the two voltage potentials U7 and U6 is altered and, depending on the dimensions, exceeds a predeterminable limit value. The difference between the two voltages U6, U7 is applied to the output 20 of the comparator circuit 10 as a voltage UH and charges the capacitor CH. This voltage UH is supplied to the deactivation apparatus 16, which deactivates the drive circuit 18 via the line 22 as long as this voltage exceeds the predeterminable limit value. Since, during preheating and starting of the lamps, a voltage UH can also result which is above the predeterminable limit value, the time controller 14 is provided which deactivates the deactivation apparatus 16 during this period of time.
Following disconnection by means of the deactivation apparatus 16, the DC paths are critical, the voltage U6 in this case resulting owing to the voltage drop across the resistor R6 as a result of a current flow via R2, R3 and R6. The voltage U7 results owing to a current flow, on the one hand, via R1, L1, W12, R4 and, on the other hand, via a current flow via R1, L2, W22, R5 via the voltage drop U7 across the resistor R7. In this case, the resistors R2, R3, R6, on the one hand, and R1, R4, R5, R7, on the other hand, are dimensioned such that the voltage UH, which corresponds to the difference between the voltages U6 and U7, is smaller than the predeterminable limit value once the lamp LP1 or LP2 has been removed from the circuit arrangement, with the result that the deactivation of the deactivation apparatus 16 is cancelled. However, initially, the drive circuit 18 is not started again yet. Only when the first removed lamp LP1 or LP2 is inserted in the circuit arrangement again is a starting apparatus 12 supplied with current again, because it is arranged in series with the DC path of the current flowing through the respective first filament W11, W21 of each lamp LP1, LP2. As soon as the starting apparatus 12 is supplied with current again, a start signal is applied to the drive circuit 18 via the line 24, whereupon the drive circuit 18 again drives the switches S1, S2 using a radiofrequency signal. Once the lamp has been reinserted, the circuit arrangement according to the invention thus starts without it having been necessary to interrupt the power supply system.
In order that the voltage UH is always positive, an absolute-value generator function can be provided in the comparator circuit 10, and this function provides the absolute value for the difference between the voltages U6 and U7 at the output 20 of the comparator circuit 10. Without deviating from the principle of the invention, other switching elements, for example a digital holding element, may also be provided instead of the capacitor CH.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 013 898.5 | Mar 2005 | DE | national |
