EP0648068A1 - Circuit for operating electrical lamps - Google Patents

Abstract

The invention relates to a circuit arrangement for operating electric lamps, in particular fluorescent lamps. The circuit according to the invention preferably comprises a free-running half-bridge invertor 2, 3 which is provided with a disconnecting device which disconnects the invertor in the case of a faulty lamp L by cutting off the control signal from a transistor 3 of the half-bridge. The disconnecting device contains as essential elements a field effect transistor 23 which is connected in parallel with the control electrode of the transistor 3, a bistable multivibrator 17, 18 which drives the gate of the field effect transistor 23, and a threshold-value switch 26 which resets the bistable multivibrator 17, 18 in the case of a faulty lamp L, leading to the field effect transistor 23 switching on and thus the invertor being disconnected. <IMAGE>

Description

The invention relates to a circuit arrangement for operating electric lamps according to the preamble of patent claim 1.

Such a circuit arrangement is disclosed, for example, in EP 0 276 460 B1. It serves to operate a low-pressure discharge lamp and has an inverter which consists of two alternating switching transistors arranged in a half-bridge. This circuit arrangement has a safety shutdown which shuts down the inverter in the event of abnormal operation. The shutdown device consists essentially of a thyristor, which is connected in parallel to the control electrode of a switching transistor of the inverter, and a Zener diode, which controls the gate of the thyristor. In the event of an abnormal operating state, the thyristor switches through and withdraws the control signal from a switching transistor of the inverter and thus brings the circuit arrangement to a standstill. To implement this safety shutdown, a voltage-proof thyristor and several relatively large-volume ohmic resistors with a few watts of load capacity are required, which are used to limit the current in the event of a shutdown and to generate the thyristor holding current.

It is the object of the invention to provide a circuit arrangement for operating electrical lamps which has a safety shutdown which is as simple, universally applicable and inexpensive as possible and which reliably switches off the circuit arrangement in the event of an abnormal operating state.

This object is achieved by the characterizing features of claim 1. Particularly advantageous embodiments of the invention are described in the subclaims.

The circuit arrangement according to the invention has a switch-off device which switches off the operating device in the event of an abnormal operating state. This switch-off device consists essentially of a controllable electronic switch, in particular a field effect transistor, the switching path of which is connected in parallel with the control path of a transistor of the switching power supply, and a bistable multivibrator, from which an output with the control electrode of the electronic switch is connected, and from a threshold switch, which is connected to an input of the bistable multivibrator. If there is an abnormal operating state, for example in the case of a defective lamp, the threshold switch switches through and sets the bistable multivibrator, as a result of which the switching path of the controllable electronic switch becomes conductive and the control signal is thus withdrawn from a transistor in the switching power supply.

The circuit arrangement according to the invention takes up less space than the circuit disclosed in patent EP 0 274 460 B1 cited above as prior art, since the circuit according to the invention dispenses with large-volume ohmic resistors with a load capacity of a few watts. It is even possible to design the switch-off device of the circuit arrangement according to the invention to be extremely compact in SMD technology. In addition, this shutdown device can in principle be integrated into any inverter. The use of a bistable multivibrator in the shutdown device of the circuit arrangement according to the invention offers the further advantage that this circuit is prepared for an external switching on / off of the lamp operating device. The bistable multivibrator can also be controlled externally via an additional sensor system, for example a touch contact with a downstream evaluation logic, and the operating device can thus be switched on and off. This creates the possibility of switching individual lamps or lamp groups separately in a lighting system which comprises a larger number of lamps and operating devices.

Figur 1

Eine schematisierte Schaltskizze einer erfindungsgemäßen Schaltungsanordnung zum Betrieb einer Niederdruckentladungslampe

Figur 2

Ein detailliertes Schaltbild der erfindungsgemäßen Schaltungsanordnung zum Betrieb einer Niederdruckentladungslampe

In der Figur 1 ist das Prinzip der erfindungsgemäßen Schaltungsanordnung zum Betrieb einer Niederdruckentladungslampe anhand einer Schaltskizze schematisch dargestellt.The invention is explained below with reference to a preferred embodiment. Show it:

Figure 1

A schematic circuit diagram of a circuit arrangement according to the invention for operating a low-pressure discharge lamp

Figure 2

A detailed circuit diagram of the circuit arrangement according to the invention for operating a low-pressure discharge lamp

The principle of the circuit arrangement according to the invention for operating a low-pressure discharge lamp is shown schematically in FIG. 1 using a circuit diagram.

This circuit is a self-oscillating half-bridge inverter which is fed by a smoothing capacitor 1 which is parallel to the DC voltage input of the circuit. The half-bridge inverter essentially consists of two alternating switching transistors 2, 3, shown here as bipolar transistors, which form a half-bridge and are each provided with a control for the base connection and with flyback diodes 4, 5 parallel to their switching path. The bipolar transistors 2, 3 are controlled via a toroidal core transformer, the secondary windings 6b, 6c of which are each led via a series resistor 7, 8 to the base of a switching transistor 2, 3 and the primary winding 6a of which, on the one hand, with the center tap M of the half-bridge and, on the other hand is connected to a tap A via the lamp inductor 27 and the discharge path of the lamp L or via a resonance capacitance 28 connected in parallel with the lamp L. The tap A is led to the collector of the bipolar transistor 2 via a first coupling capacitor 10 and to the emitter of the bipolar transistor 3 via a second coupling capacitor 11. The inductance 27 and the capacitance 28 form a series resonance circuit which makes it possible, after the lamp electrodes on the capacitance 28 have been preheated sufficiently, to provide the starting voltage for the low-pressure discharge lamp L by increasing the resonance.

A resistor 12, a capacitor 13 and a diac 14 arranged in parallel to the capacitor 13 are used to start the half-bridge inverter and are led to the base of the transistor 3 via an ohmic resistor 15. An additional diode 16, which is connected to the node B between the resistor 12, capacitor 13, and diac 14 and to the center tap M, ensures that this starting circuit is shut down when the inverter is working.

As far as this circuit arrangement corresponds to a typical self-oscillating half-bridge circuit, as described, for example, in the book "Switching Power Supplies" by W. Hirschmann / A. Hauenstein, ed. Siemens AG, 1990 edition on page 63.

After switching on the circuit arrangement, the smoothing capacitor 1 charges to the full input voltage U. The transistors 2, 3 of the half bridge switch alternately with a switching frequency greater than 20 KHz. As a result, the center tap M is alternately connected to the positive or negative pole of the smoothing capacitor 1, while the tap A is located with a suitable dimensioning of the circuit components the potential U / 2. In this way, a medium-frequency alternating current (greater than 20 kHz) flows in the branch between the center tap M and the node A, the frequency of which is determined by the switching frequency of the transistors 2, 3.

Diac 14 is mainly responsible for starting the half-bridge inverter. Immediately after switching on the circuit arrangement, the breakover voltage of the diac 14 builds up on the capacitor 13, so that the diac 14 gives trigger pulses to the base of the transistor 3. After the start of the inverter, the capacitor 13 is discharged via the diode 16 to such an extent that no further trigger pulses can be generated by the diac 14.

The remaining elements 9 and 17 to 26 of the circuit arrangement, which have not yet been explained, belong to the shutdown device according to the invention, which shuts down the inverter if the lamp L is defective or if there is an abnormal operating state. The main component of this switch-off device is a bistable multivibrator, consisting of the bipolar transistors 17, 18 and the ohmic resistors 19 to 22, which drives the gate electrode of a field effect transistor 23. For this purpose, an output of the bistable multivibrator, i.e. the collector of transistor 17, is connected to the gate electrode of field effect transistor 23. The switching path, ie the drain-source path, of the field effect transistor 23 is parallel to the control electrode, ie to the base-emitter path, of the transistor 3. If the lamp L is defective or if there is an abnormal operating state, the bistable multivibrator switches over and closes the switching path of the field effect transistor 23, so that the base connection of the transistor 3 is present at the negative pole of the voltage source or the smoothing capacitor 1 and the control signal is withdrawn from the transistor 3. The Zener diode 9 protects the gate of the field effect transistor 23 against voltage overload.

In the circuit according to the preferred exemplary embodiment, an abnormal operating state is manifested by an excessive voltage drop across the smoothing capacitor 1 compared to the normal operating state , and scanned by means of a Zener diode 26. The zener diode 26 is arranged in parallel with the resistor 25 of the voltage divider and is connected to the set or reset input of the bistable multivibrator, that is to say to the base connection of the transistor 18. If it is defective The lamp builds up on the zener diode 26, so that it becomes conductive and sets the bistable multivibrator, which in turn turns on the field effect transistor 23, whereby the control signal is withdrawn from the transistor 3 of the half-bridge inverter.

FIG. 2 shows a detailed circuit diagram of a circuit arrangement according to the invention for operating a low-pressure discharge lamp, in particular for operating a fluorescent lamp with an electrical power consumption between 9 and 13 watts. A suitable dimensioning of the circuit components used can be found in the table. This circuit arrangement contains an integral part of a self-oscillating half-bridge inverter, which is fed by the DC voltage output of a voltage source V. The transistors T1, T2 of the half inverter are provided with a control device and with series resistors R3 to R6 as well as with flyback diodes D3, D4 arranged parallel to the switching paths of the transistors T1, T2. The transistors T1, T2 are driven via the secondary windings RK1b and RK1c of a toroidal core transformer, which are each connected to the base of a transistor T1, T2. The primary winding RK1a of the toroidal transformer is integrated in the series resonance circuit, which extends from the center tap M between the transistors T1, T2 via the primary winding RK1a, the resonance inductance LD, the coupling capacitor C10, the resonance capacitance C9 and the lamp electrode E2 to the collector terminal of the transistor T1 . The resonance capacitance C9 is connected in parallel to the discharge path of the low-pressure discharge lamp LP.

In addition, the circuit arrangement contains an electrode heating circuit which enables the electrode filaments E1, E2 of the lamp LP to be preheated and, in addition to the electrode filaments E1, E2, also includes the PTC thermistor R12, the capacitances C12, C15 and the diode D1. During the electrode preheating phase, the PTC thermistor R12 bridges the capacitance C15 lying parallel to it. The electrode E2 of the lamp LP is connected to the positive pole of the smoothing capacitor C6, which is connected in parallel with the switching paths of the transistors T1, T2 and in parallel with the DC voltage output of the voltage source V.

This circuit arrangement also contains an active harmonic filter, which enables sinusoidal mains current draw. The active harmonic filter consists of two diode pairs D11, D13 and D12, D14 and capacitors C8 and C13.

Both diode pairs are connected in the forward DC direction to the supporting capacitor C5, which is parallel to the DC output of the voltage source V, and are connected to the smoothing capacitor C6 via the electrode coil E2. The capacitor C13 is connected to a tap between the series connected diodes D12, D14 and to a node M1, which potentially corresponds to the center tap M, in the series resonant circuit, while the capacitor C8 is connected to a tap between the series connected diodes D11, D13 connected to another pair of diodes and to node M1 in the series resonant circuit.

A diac DK, a starting capacitor C7 and the resistors R2, R8 ensure that the half-bridge inverter starts to oscillate. The starting capacitor C7 is connected on the one hand to the negative pole of the smoothing capacitor C6 and on the other hand via the resistor R2 to the positive pole of the smoothing capacitor C6. The diac DK is connected in parallel to the starting capacitor C7 and connected to the base of the transistor T2. A tap M3 between the starting capacitor C7 and the resistor R2 is led via a resistor R15 and a diode D5 to the center tap M of the inverter. The resistor R8 is connected in parallel to the flyback diode D3. A capacitor C14 arranged in parallel with the flyback diode D4 reduces the power losses that occur when magnetizing the inductors by slowing down the voltage edges generated by the inverter.

The shutdown device of this circuit arrangement according to the invention comprises a bistable multivibrator, which is formed by the transistors T3, T4 and the ohmic resistors R9, R10, R11, R13, and a field effect transistor T5, two Zener diodes D2, D6 and a voltage divider R1, R7 and an ohmic resistor R14. The collector of the transistor T4 is connected on the one hand via the resistor R10 to the tap M3 and on the other hand to the gate electrode of the field effect transistor T5, and via the resistor R13 to the base of the transistor T3. Zener diode D2 is connected in parallel with the collector-emitter path of transistor T4 and the gate of field-effect transistor T5. It protects the gate of the low-voltage field effect transistor T5 against excessive input voltages. The collector of transistor T3 is led via resistor R9 to a node between resistors R2 and R10 and connected to the base of transistor T4 via resistor R11. The source connection of the field effect transistor T5 and the emitter connection of the transistors T3, T4 are with the negative pole of the smoothing capacitor C6. The voltage divider consisting of the ohmic resistors R1, R7 is parallel to the smoothing capacitor C6 and has a tap M4, which is led via the Zener diode D6 to the base of the transistor T3.

The functioning of this circuit arrangement largely corresponds to the functional principle of the circuit already explained above and shown in FIG. 1.

The transistors T1, T2 of the half-bridge inverter switch alternately at a frequency above 20 KHz, so that the center tap M is alternately connected to the positive or negative pole of the smoothing capacitor C6, while the coupling capacitor C10 carries the voltage U / 2, if that on the smoothing capacitor C6 applied voltage is denoted by U. As a result, an alternating current flows in the series resonance circuit, the frequency of which is determined by the switching frequency of the inverter. The inverter starts to oscillate through the diac DK, which gives trigger pulses to the base of the transistor T2 after the starting capacitor C7 has previously been charged to the breakover voltage of the diac DK. After the successful oscillation of the inverter, the starting capacitor C7 is discharged via the node M3, the resistor R15, the diode D5 and the switching path of the transistor T1 or T2 to such an extent that the breakdown voltage of the diac DK is not reached and this no further trigger pulses to the transistor T2 can give.

Before the low-pressure discharge lamp LP is ignited, a heating current first flows through the electrode filaments E1, E2, the capacitance C12 and the PTC thermistor R12. After sufficient electrode preheating, the PTC thermistor R12 becomes high-impedance, so that the ignition voltage required for the lamp LP is built up on the capacitances C12, C15, which are now connected in series and are arranged parallel to the lamp LP, in conjunction with the resonance inductance LD by means of resonance increase. The lamp LP ignites and the lower operating voltage is established across the lamp.

The mode of operation of the active harmonic filter consisting of the diodes D11 to D14 and the capacitors C8, C13 in combination with the resonance inductance LD and the capacitors C5, C6 is described in detail in DE 36 23 749 A1 and should therefore not be described in more detail here. The active harmonic writing and should therefore not be explained in more detail here. The active harmonic filter continuously pumps energy from the series resonance circuit back into the smoothing capacitor C6 with the aid of the capacitors C8, C9, C13, so that an approximately sinusoidal mains current drain is possible.

The bistable multivibrator, consisting essentially of the transistors T3, T4, is fed by the start capacitor C7. After the circuit arrangement has been switched on, the bistable multivibrator is reset in a defined manner with the voltage rising at the starting capacitor C7 in that the base-emitter voltage at the transistor T3 is delayed more than via the resistor R10 and the gate-source capacitance of the field-effect transistor T5 on transistor T4 so that transistor T3 blocks while transistor T4 conducts. The field effect transistor T5 also blocks. The breakover voltage of the diac DK builds up at the starting capacitor C7, so that it gives trigger pulses to the base of the transistor T2. If the inverter vibrates, the transistors T1, T2 switch alternately and the start capacitor C7 is discharged via the resistor R15, the diode D5 and the switching path of the transistor T1 or T2 to such an extent that the breakdown voltage of the diac DK is not reached and no further trigger pulses are generated . Transistors T3, T4 and T5 maintain their initial state.

An abnormal operating state of the half-bridge inverter manifests itself in the present circuit arrangement in an excessive voltage drop across the smoothing capacitor C6. If a threshold value defined by the zener diode D6, the voltage divider resistors R1, R7 and the transistor T3 is exceeded, a base current flows for the transistor T3 and the bistable multivibrator is reset, ie the switching path of the transistor T3 conducts and that of the transistor T4 blocks. The field-effect transistor T5 is now switched through by the bistable multivibrator, so that the control signal is withdrawn from the base of the half-bridge transistor T2 via the resistor R14 and via the now conductive source-drain path of the field-effect transistor T5. The inverter is de-energized and the voltage at the starting capacitor C7 remains below the breakover voltage of the diac DK due to the load from the resistor R9, which is now connected in parallel. This means that no trigger pulses are generated by the Diac DK. The inverter can only start to swing again when the bistable multivibrator is set again by interrupting the power supply.

The invention is not limited to the exemplary embodiment described in more detail above. The shutdown device according to the invention, consisting of the electrical components 9 and 17 to 26, can also be integrated into a circuit arrangement for operating low-voltage halogen incandescent lamps. The voltage divider 24, 25 is here, however, not connected in parallel to the input capacitor 1, but part of the load or lamp circuit. In the event of an abnormal operating condition, i.e. in the event of a short circuit, the short circuit current in the voltage dividing resistors causes an excessive voltage drop, which is detected by the Zener diode 26 and leads to the tripping device being triggered. The voltage divider 24, 25 can also be replaced in a circuit arrangement for low-voltage halogen incandescent lamps by a simple load or emitter resistor which is connected to the emitter connection of the half-bridge transistor 3 and the negative pole of the input capacitor 1 and to which the zener diode 26 is connected in parallel is.

Furthermore, in circuit arrangements in which the inverter is restarted after each grid half-wave, the field effect transistor can be dispensed with, since in these circuits only the trigger pulse from the diac that triggers the start of the inverter has to be suppressed.

In addition, the bistable multivibrator can be implemented as a space-saving integrated circuit using C-MOS technology. A D flip-flop, in which an undetermined output state cannot occur, is particularly suitable for the circuit arrangement according to the invention. This opens up the possibility of switching off the circuit arrangement externally via a sensor, for example a touch contact with a downstream evaluation logic, in that the clock input of the D flip-flop is controlled by the sensor.

The shutdown device according to the invention can also be integrated into a full-bridge inverter. Table 1 Dimensioning of the circuit according to FIG. 3 R1 2.2 MΩ, 1% R2 820 KΩ R3, R4 8.2 Ω R5, R6 0.56 Ω R7, R9 39 KΩ R8 510 KΩ R10, R11, R13 330 KΩ R14 0.22Ω R15 33 KΩ C5 47 nF C6 10 µF C7 100 nF, 63 V C8 3.3 nF C9 5.6 nF C10 150 nF C12 10 nF C13 4.7 nF C14 1.0 nF C15 3.3 nF DK N413M T3, T4 BC547C T5 BSS295 D2 BZX55 / C10 D6 BZX55B7V5 LD 3 mH, EF16

Claims (8)

Circuit arrangement for operating electric lamps, the circuit arrangement having the following features: - A switching power supply fed with direct voltage, which has at least two alternating switching transistors (2, 3; T1, T2), - A control for the transistors (2, 3; T1, T2) of the switching power supply - A smoothing capacitor (1; C6) arranged parallel to the switching paths of the transistors (2, 3; T1, T2) of the switching power supply a switch-off device which, in the event of an abnormal operating state of the circuit arrangement, shuts it down by removing the control signal for its control electrode from at least one transistor (3; T2) of the switching power supply, characterized in that the switch-off device has the following features: a controllable electronic switch (23; T5), the switching path of which is connected in parallel to the control electrode of a transistor (3; T2) of the switching power supply, - A bistable multivibrator (17, 18; T3, T4), an output of the multivibrator (17, 18; T3, T4) being connected to the control electrode of the electronic switch (23; T5) and the set or reset input of the multivibrator ( 17, 18; T3, T4) is connected to the output of a threshold switch (26; D6). Circuit arrangement for operating electric lamps according to claim 1, characterized in that the controllable electronic switch is a field effect transistor (23; T5). Circuit arrangement for operating electric lamps according to claim 1, characterized in that the switching power supply is a self-oscillating half-bridge inverter. Circuit arrangement for operating electric lamps according to claim 1, characterized in that the threshold switch (26; D6) is connected in parallel with a resistor (25; R7) of a voltage divider (24, 25; R1, R7), the voltage divider (24, 25 ; R1, R7) is arranged parallel to the smoothing capacitor (1; C6). Circuit arrangement for operating electric lamps according to claim 1, characterized in that the bistable multivibrator is an integrated circuit implemented in C-MOS technology. Circuit arrangement for operating electric lamps according to claim 5, characterized in that the bistable multivibrator is a D flip-flop. Circuit arrangement for operating electrical lamps according to claim 6, characterized in that the clock input of the D flip-flop is controlled by a sensor with downstream evaluation logic. Circuit arrangement for operating electric lamps according to claim 7, characterized in that the sensor is a touch contact.

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