EP0648068B1 - Circuit for operating electrical lamps - Google Patents

Description

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

Such a circuit arrangement is disclosed, for example, in EP 0 276 460 B1. It is used to operate a low-pressure discharge lamp and has an inverter on that of two alternately switching, arranged in a half-bridge Transistors. This circuit arrangement has a safety shutdown, which shuts down the inverter during abnormal operation. The shutdown device consists essentially of a thyristor, which is parallel to the control electrode Switching transistor of the inverter is switched, and from a Zener diode that the Gate of the thyristor controls. 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 causes the circuit arrangement to be shut down. To realize this Safety shutdown will be a voltage-proof thyristor and several relative large-volume ohmic resistors with a few watts of load capacity required for Current limitation in the event of a shutdown and for generating the thyristor holding current to serve.

It is the object of the invention to provide a circuit arrangement for operating electrical Provide lamps that are as simple, universally applicable and cost-effective as possible Has safety shutdown, which the circuit arrangement at a reliably switches off the abnormal operating state.

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

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the controllable electronic Switch is conductive and thus a transistor of the switching power supply Control signal is withdrawn.

The circuit arrangement according to the invention takes up less space than that in Circuit disclosed above as prior art patent EP 0 274 460 B1 the circuit according to the invention on large-volume ohmic resistors with some Watts resilience waived. It is even possible to switch off the device according to the invention Circuit arrangement extremely compact in SMD technology. In addition, this switch-off device can in principle in any inverter to get integrated. The use of a bistable multivibrator in the shutdown device the circuit arrangement according to the invention offers the further advantage that this circuit on an external switching on / off of the lamp operating device is prepared. Via additional sensors, for example a touch contact with a subsequent evaluation logic, the bistable multivibrator can too externally controlled and thus the control gear can be switched on and off. In order to the possibility is created in a lighting system that has a larger Number of lamps and operating devices, individual lamps or lamp groups to switch separately.

Figur 1

Eine schematisierte Schaltskizze einer erfindungsgemäßen Schaltungsanordnung zum Betrieb einer Niederdruckentladungslampe

Figur 2

Ein detailliertes Schaltbild der erfindungsgemäßen Schaltungsanordnung zum Betrieb einer Niederdruckentladungslampe

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 is shown in FIG Operation of a low-pressure discharge lamp using a circuit diagram schematically shown.

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

A resistor 12, a capacitor, is used to start the half-bridge inverter 13 and a diac 14 arranged parallel to the capacitor 13, which via a ohmic resistor 15 is guided to the base of transistor 3. An additional diode 16, with the node B between resistor 12, capacitor 13, and Diac 14 and connected to the center tap M ensures that it is shut down Start switching 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 W.'s book "Schaltnetzteile" Hirschmann / A. Hauenstein, ed. Siemens AG, 1990 edition on page 63 is.

After the circuit arrangement has been switched on, the smoothing capacitor 1 charges to the full input voltage U. Switch transistors 2, 3 of the half bridge alternating with a switching frequency greater than 20 KHz. This means that the center tap is located M alternately on the positive or negative pole of the smoothing capacitor 1 while tap A with suitable dimensioning of the circuit components the potential U / 2 is thus flowing in the branch between the center tap M and the node A a medium frequency alternating current (greater than 20 KHz), the frequency of which is determined by the switching frequency of transistors 2, 3.

Diac 14 is mainly responsible for starting the half-bridge inverter. Immediately after switching on the circuit arrangement builds on Capacitor 13 the breakover voltage of the diac 14, so that the diac 14 trigger pulses on the base of transistor 3 there. After starting the inverter the capacitor 13 discharged via the diode 16 so far 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, the inverter if the lamp L is defective or if there is an abnormal operating state switches off. The main component of this shutdown 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. To for this purpose is an output of the bistable multivibrator, i.e. the collector of the Transistor 17, connected to the gate electrode of the field effect transistor 23. The Switching path, i.e. the drain-source path, of the field effect transistor 23 lies in parallel to the control electrode, i.e. to the base-emitter path of the transistor 3. If defective Lamp L or in the event of an abnormal operating state switches on bistable multivibrator and closes the switching path of the field effect transistor 23, so that the base connection of the transistor 3 at the negative pole of the voltage source or the smoothing capacitor 1 is applied and the control signal is withdrawn from the transistor 3 becomes. The zener diode 9 protects the gate of the field effect transistor 23 Voltage overload.

An abnormal operating condition manifests itself in the circuit according to the preferred one Embodiment by an excessive compared to the normal operating state Voltage drop across the smoothing capacitor 1. The voltage across the smoothing capacitor 1 is made with the help of one consisting of ohmic resistors 24, 25 Voltage divider, which is connected in parallel to the smoothing capacitor 1, and by means of a Zener diode 26 sampled. The Zener diode 26 is parallel to the resistor 25 of the Arranged voltage divider and with the set or reset input of the bistable Multivibrators, i.e. connected to the base terminal of transistor 18. In the event of a defect Lamp builds up on the breakdown voltage at the Zener diode 26, so that this becomes conductive and sets the bistable multivibrator, which in turn is the field effect transistor 23 turns on, causing the transistor 3 of the half-bridge inverter the control signal is withdrawn.

Figure 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 be removed. This circuit arrangement contains an essential component a self-oscillating half-bridge inverter from the DC voltage output a voltage source V is fed. The transistors T1, T2 of the half inverter are with a control device and series resistors R3 to R6 and arranged parallel to the switching paths of the transistors T1, T2 Return diodes D3, D4 provided. The transistors T1, T2 are activated via the secondary windings RK1b and RK1c of a toroidal 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 resonant circuit, the 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 connection of the Transistor T1 extends. The resonance capacitance C9 is parallel to the discharge path the low-pressure discharge lamp LP switched.

The circuit arrangement also contains an electrode heating circuit which preheats of the electrode filaments E1, E2 of the lamp LP and in addition to the electrode filaments E1, E2 also the PTC thermistor R12, the capacitances C12, C15 and the Diode D1 includes. The PTC thermistor bridges during the electrode preheating phase R12 is 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 parallel to the switching paths of the transistors T1, T2 and parallel to the DC voltage output of the voltage source V is switched.

This circuit arrangement also contains an active harmonic filter, which is a sinusoidal one Mains current drain enabled. The active harmonic filter consists of two Diode pairs D11, D13 and D12, D14 and from the capacitors C8 and C13.

Both diode pairs are in the forward DC direction on the parallel to the DC output connected to the voltage source V supporting capacitor C5 and connected to the smoothing capacitor C6 via the electrode coil E2. Of the Capacitor C13 is tapped between the diodes connected in series D12, D14 and with a node M1, which is potentially the center tap M corresponds, connected in the series resonance circuit, while the capacitor C8 with one tap between the diodes D11, D13 of the other connected in series Diode pair connected and led to node M1 in the series resonance circuit is.

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

The shutdown device according to the invention comprises this circuit arrangement a bistable multivibrator made by transistors T3, T4 and ohmic Resistors R9, R10, R11, R13 is formed, 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 transistor T4 is on the one hand via the resistor R10 with the tap M3 and on the other hand with the gate electrode of the field effect transistor T5 connected, and via the resistor R13 to the base of the transistor T3 led. Parallel to the collector-emitter path of transistor T4 and to the gate of the field effect transistor T5, the zener diode D2 is connected. It protects the gate of the low-voltage field-effect transistor T5 before input voltages are too high. Of the The transistor T3 collector is connected to a node via the resistor R9 passed between the resistors R2 and R10 and with the resistor R11 connected to the base of transistor T4. The source 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 one from the ohmic resistors R1, R7 existing voltage divider is parallel to the smoothing capacitor C6 and has a tap M4, which leads to the base of the transistor T3 via the Zener diode D6 is.

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

The transistors T1, T2 of the half-bridge inverter switch alternately a frequency above 20 kHz, so that the center tap M alternately with the positive or negative pole of the smoothing capacitor C6 is connected during the Coupling capacitor C10 carries the voltage U / 2 when connected to the smoothing capacitor C6 applied voltage is denoted by U. As a result, flows in the series resonance circuit an alternating current whose frequency is determined by the switching frequency of the inverter is determined. The inverter swings through the diac DK, which gives trigger pulses to the base of transistor T2 after the starting capacitor C7 has previously charged to the breakdown voltage of the Diac DK. After this the starting capacitor C7 is successfully started the node M3, the resistor R15, the diode D5 and the switching path of the Discharge transistor T1 or T2 so far that the breakdown voltage of the diac DK falls below and this will not give any further trigger pulses to transistor T2 can.

Before the low-pressure discharge lamp LP ignites, it first flows through the Electrode coils E1, E2, the capacitance C12 and the PTC thermistor R12 a heating current. After sufficient electrode preheating, the PTC thermistor R12 becomes high-resistance, so that to the now connected in series, arranged parallel to the lamp LP Capacities C12, C15 in interaction with the resonance inductance LD by means of Exaggerated resonance builds up the ignition voltage required for the lamp LP. The Lamp LP ignites and the lower operating voltage arises above the lamp a.

The mode of operation of the diodes D11 to D14 and the capacitors C8, C13 existing active harmonic filter 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 explained in more detail here. The active harmonic writing and should therefore not be explained in more detail here. The active harmonic filter pumps energy from the. with the help of the capacitors C8, C9, C13 Series resonance circuit in the smoothing capacitor C6 back, so that an approximate sinusoidal mains current draw is possible.

The bistable multivibrator, consisting essentially of transistors T3, T4, is fed by the start capacitor C7. After switching on the circuit arrangement becomes the bistable multivibrator with that rising at the start capacitor C7 Voltage defined by resetting that through resistor R10 and the gate-source capacitance of the field effect transistor T5, the base-emitter voltage at the transistor T3 is delayed more than that at transistor T4, so that transistor T3 turns off while transistor T4 conducts. The field effect transistor T5 also blocks. The breakover voltage of the diac DK builds up at the start capacitor C7, so that this Trigger pulses on the base of transistor T2 there. If the inverter vibrates, so the transistors T1, T2 switch alternately and the start capacitor C7 is switched over the resistor R15, the diode D5 and the switching path of the transistor T1 or T2 discharged so far that the breakdown voltage of the diac DK is undershot and no further trigger pulses are generated. Keep transistors T3, T4 and T5 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. Becomes a through the Zener diode D6, the voltage divider resistors R1, R7 and the transistor T3 defined threshold value exceeded, flows Base current for transistor T3 and the bistable multivibrator is reset, i.e. the switching path of transistor T3 conducts and blocks that of transistor T4. Of the Field effect transistor T5 is now switched through by the bistable multivibrator, see above that the base of the half-bridge transistor T2 through the resistor R14 and through the now conductive source-drain path of the field effect transistor T5 the control signal is withdrawn. The inverter is de-energized and the voltage at the starting capacitor C7 remains due to the load due to the resistance now connected in parallel R9 below the breakover voltage of the Diac DK. There are therefore no trigger pulses generated by the Diac DK. The inverter can only start again when the bistable multivibrator set again by interrupting the power supply becomes.

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, also in a circuit arrangement for Operation of low-voltage halogen bulbs can be integrated. 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 divider resistors have an excessive voltage drop from the zener diode 26 is detected and leads to the triggering of the shutdown device. Of the Voltage divider 24, 25 can be used in a circuit arrangement for low-voltage halogen incandescent lamps can also be replaced by a simple load or emitter resistor, with the emitter connection of the half-bridge transistor 3 and the negative pole of the Input capacitor 1 is connected, and to which the Zener diode 26 is connected in parallel is.

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

In addition, the bistable multivibrator can save space as one in C-MOS technology implemented integrated circuit can be realized. For the invention Circuit arrangement is particularly suitable for a D flip-flop in which an indefinite one Initial state cannot occur. This opens up the possibility the circuit arrangement via a sensor, for example a touch contact with downstream evaluation logic, to be switched off externally by 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. 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)

1. Circuit arrangement for operating electric lamps, the circuit arrangement having the following features:

   a switched-mode power supply which is fed with DC voltage and has at least two alternatingly switching transistors (2,3; T1, T2),

   a drive circuit for the transistors (2,3; T1, T2) of the switched-mode power supply,

   a smoothing capacitor (1; C6) arranged in parallel with the switching paths of the transistors (2, 3; T1, T2) of the switched-mode power supply,

   an interrupting device which stops the circuit arrangement operating when the latter is in an anomalous operating state by withdrawing from- at least one transistor (3; T2) of the switched-mode power supply the control signal for the control electrode thereof,

   characterized in that the interrupting device has the following features:

   a controllable electronic switch (23; T5) whose switching path is connected in parallel with the control electrode of a transistor (3; T2) of the switched-mode power supply, and

   a bistable multivibrator (17, 18; T3, T4), one 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) being connected to the output of a threshold value switch (26; D6).
2. Circuit arrangement for operating electric lamps according to Claim 1, characterized in that the controllable electronic switch is a field effect transistor (23; T5).
3. Circuit arrangement for operating electric lamps according to Claim 1, characterized in that the switched-mode power supply is a self-oscillating half-bridge inverter.
4. Circuit arrangement for operating electric lamps according to Claim 1, characterized in that the threshold value 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) being arranged in parallel with the smoothing capacitor (1; C6).
5. Circuit arrangement for operating electric lamps according to Claim 1, characterized in that the bistable multivibrator is an integrated circuit designed using C-MOS technology.
6. Circuit arrangement for operating electric lamps according to Claim 5, characterized in that the bistable multivibrator is a D flip-flop.
7. Circuit arrangement for operating electric lamps according to Claim 6, characterized in that the clock input of the D flip-flop is controlled by a sensor having a downstream evaluation logic circuit.
8. Circuit arrangement for operating electric lamps according to Claim 7, characterized in that the sensor is a direct contact.

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