EP0389847B1 - Circuit - Google Patents

Abstract

A circuit arrangement is specified for the high-frequency operation of one or more low-pressure discharge lamps connected in parallel with one another. The circuit arrangement has a mains rectifier with a downstream active harmonic filter, a downstream smoothing capacitor and a high-frequency generator allocated to each low-pressure discharge lamp. The high-frequency generator is a single-ended high- frequency generator which has one switching transistor (T1), one switching inductor (L1) and an oscillator capacitor (C1) and which is operated on the smoothing capacitor (C0), decoupled from the mains via two diodes (D5, D6). <IMAGE>

Description

The invention relates to a circuit arrangement for the high-frequency operation of one or more low-pressure discharge lamps connected in parallel to one another according to the preamble of the main claim.

Such circuit arrangements are known per se (DE-OS 36 23 749, DE-OS 36 11 611 and DE-OS 37 00 421). Although these circuits can feed a low-pressure discharge lamp at a high frequency and meet the existing regulations regarding the form of the mains current, they still require a considerable amount of components. The desired circuit effects in the known circuits are based on the function of a push-pull output stage in conjunction with at least four diodes and three capacitors.

WO 87/04891 relates to a ballast for fluorescent tubes, which comprises a low-pass filter, a bridge rectifier, a smoothing capacitor and circuit devices, the low-frequency mains voltage being filtered and rectified and a high-frequency AC voltage being generated by periodically opening and closing the circuit devices for operating the lamp.

The object of the invention is to provide a circuit arrangement for the high-frequency operation of low-pressure discharge lamps, which manages with a minimum of components.

This object is achieved by the features specified in the characterizing part of the main claim.

The circuit arrangement according to the invention manages with fewer components than the known circuit arrangements, since the high-frequency generator is constructed as a single-ended high-frequency generator which has only one switching transistor, one switching inductance and one oscillating capacitor. By combining this single-ended high-frequency generator with the active harmonic filter, which has a series inductance, a pump capacitor and two decoupling diodes, an approximately sinusoidal mains current can be achieved, and on the other hand, a lamp current and a lamp voltage result that are suitable for operating the low-pressure discharge lamp.

The switching transistor switches the pump capacitor between the series inductance and one of the decoupling diodes against the reference potential. With this active harmonic filter, the mains current is modulated sinusoidally with every lamp cycle. Each time the lamp is switched on, an amount of energy proportional to the instantaneous value of the line voltage is drawn from the network and fed to the smoothing capacitor via one of the two decoupling diodes. This ensures a sinusoidally modulated mains current consumption through the harmonic filter.

According to an advantageous embodiment of the circuit arrangement according to the invention, the pump capacitor is connected in parallel with the switching inductance via the two decoupling diodes, so that the amplitude of the negative current half-wave in the lamp is reduced and the crest factor of the lamp current is improved.

According to a further advantageous embodiment of the circuit arrangement according to the invention, the pump capacitor is connected from the collector or drain connection of the switching transistor via the one decoupling diode in parallel to the switching inductance and the other decoupling diode, the rise in voltage at the switching transistor due to the resonance behavior, determined by the switching inductance and the pump capacitor. It is also advantageous if the single-ended high-frequency generator is operated in resonance frequency, determined by the switching inductance and the pump capacitor. This switching of the switching transistor creates an advantageous switch-off relief network.

According to a further advantageous embodiment of the circuit arrangement according to the invention, the switching transistor is controlled by an electronic control circuit which advantageously has an electronic oscillator and a pulse width modulator. The electronic control circuit forms an electronic interface. The electronic oscillator and the pulse width modulator can be started and stopped electronically and their pulse width or frequency can be set via an electronic control signal. This creates an interface that is desired for various user options.

wobei :
   P (ges) = Lampenleistung
   T (Netz) = Netzfrequenz (Periodenzeit)
   T (Lampe) = Lampenfrequenz (Periodenzeit)
   û = Spitzenwert der Netzspannung (Amplitude)
   ω = Kreisfrequenz
   U_O = Gleichspannung am Glättungskondensator
berechneten Maximalwert nicht überschreitet, wird gewährleistet, daß die aus dem Netz aufgenommene Leistung in dem Lampengenerator durch Lampenleistung und Schaltverluste abgenommen wird. Eine überschüssige Energiespeicherung und damit eine unzulässige Überhöhung der Spannung am Glättungskondensator werden somit vermieden.If the capacitance of the pump capacitor is according to the formula

in which :
P (tot) = lamp power
T (grid) = grid frequency (period time)
T (lamp) = lamp frequency (period time)
û = peak value of the mains voltage (amplitude)
ω = angular frequency
U _O = DC voltage at the smoothing capacitor
does not exceed the calculated maximum value, it is ensured that the power drawn from the network in the lamp generator is reduced by lamp power and switching losses. Excess energy storage and thus an impermissible increase in the voltage across the smoothing capacitor are thus avoided.

Another improved circuit arrangement enables starting with preheated electrodes and also offers corresponding safety functions and protection against overvoltage and overcurrents, such as those e.g. if a lamp fails. For this purpose, the switching inductance has two additional secondary windings which, depending on the lamp voltage, are switched to the respective heating coil of the lamp via a thyristor and heat the heating coil with their voltages.

According to a further advantageous embodiment of the circuit arrangement according to the invention, the control electronics are designed such that each time the circuit is started up for the first time, the switching frequency of the single-ended high-frequency converter is first increased, in order then to be reduced continuously to the actual clock frequency in the 1/10 second range, so that an increased heating current is available for each new start-up.

According to a further advantageous embodiment of the circuit arrangement according to the invention, both the voltage at the collector of the switching transistor and the electronics intrinsic supply voltage are detected in their respective levels and, if overvoltage occurs, by firing a thyristor used to short-circuit the start-up circuit and the control of the switching transistor. This enables a safe shutdown of the circuit.

According to a further advantageous embodiment of the circuit arrangement according to the invention, there is a resistor in series with the emitter of the switching transistor, the voltage drop of which in the event of overcurrents leads to the switching transistor being switched off and thus preventing current overload.

According to a further advantageous embodiment of the circuit arrangement according to the invention, an electronic supply voltage is derived from the rectified mains voltage via a series resistor, which is switched through with a thyristor when the maximum permissible limit value for the electronic supply voltage is reached, so that the thyristor can hold its own via the electronic supply current. With this circuit, the first electronics supply can be implemented with minimal effort until the clock-dependent self-supply can take over the power supply.

According to a further advantageous embodiment of the circuit arrangement according to the invention, there is a further secondary winding either on the switching inductance or on the protective inductance, via which an AC voltage is tapped. This AC voltage - rectified with a one-way rectifier circuit - then provides the electronics supply voltage.

Fig. 1

ein Blockschaltbild der Schaltungsanordnung mit Oberschwingungsfilter für eine Niederdruckentladungslampe;

Fig. 2

ein Schaltbild einer Schaltungsanordnung mit Heizkondensator und mit Oberschwingungsfilter zum Betrieb einer Niederdruckentladungslampe;

Fig. 3

ein Schaltbild einer Schaltungsanordnung mit Heizkondensator und mit Oberschwingungsfilter zum Betrieb mit zwei parallel geschalteten Niederdruckentladungslampen;

Fig. 4

ein Schaltbild einer Schaltungsanordnung mit Heizwicklung und mit Oberschwingungsfilter zum Betrieb einer Niederdruckentladungslampe;

Fig. 5

Liniendiagramme für Netzstrom und -spannung in der Schaltungsanordnung nach Fig. 2;

Fig. 6

die harmonische Analyse des Netzstromes;

Fig. 7

Lampenstrom und -spannung in der Schaltungsanordnung nach Fig. 2;

Fig. 8

ein Blockschaltbild eines weiteren Ausführungsbeispiels der Schaltungsanordnung mit den einzelnen Schaltungsabschnitten;

Fig. 9

ein Schaltbild der Schaltungsanordnung der zwei zusätzlichen Sekundär-Heizwicklungen mit Thyristoraufschaltung auf die Heizwendeln und die Überstromerfassung;

Fig. 10

ein Schaltbild der Schaltungsanordnung zur Erfassung der Überspannung am Kollektor des Schalttransistors und an der Elektronikversorgung; und

Fig. 11

ein Schaltbild der Schaltungsanordnung zur Erzeugung der Elektronik-Eigenversorgungsspannung.

Embodiments of the invention will now be described with reference to the accompanying drawings. The same reference numerals have been chosen for the same parts. Show it:

Fig. 1

a block diagram of the circuit arrangement with harmonic filter for a low-pressure discharge lamp;

Fig. 2

a circuit diagram of a circuit arrangement with a heating capacitor and with harmonic filter for operating a low-pressure discharge lamp;

Fig. 3

a circuit diagram of a circuit arrangement with heating capacitor and with harmonic filter for operation with two low-pressure discharge lamps connected in parallel;

Fig. 4

a circuit diagram of a circuit arrangement with heating winding and with harmonic filter for operating a low-pressure discharge lamp;

Fig. 5

Line diagrams for mains current and voltage in the circuit arrangement according to FIG. 2;

Fig. 6

the harmonic analysis of the mains current;

Fig. 7

Lamp current and voltage in the circuit arrangement according to Fig. 2;

Fig. 8

a block diagram of another embodiment of the circuit arrangement with the individual circuit sections;

Fig. 9

a circuit diagram of the circuit arrangement of the two additional secondary heating windings with thyristor connection to the heating coils and the overcurrent detection;

Fig. 10

a circuit diagram of the circuit arrangement for detecting the overvoltage on the collector of the switching transistor and on the electronics supply; and

Fig. 11

a circuit diagram of the circuit arrangement for generating the electronics self-supply voltage.

The block diagram in FIG. 1 shows the basic structure of the circuit arrangement for the high-frequency operation of a low-pressure discharge lamp LL1.

The circuit arrangement includes a high-frequency filter 1, a mains rectifier 2, a single-ended high-frequency generator with a switching transistor T1 and an electronic control circuit 6 for controlling the single-ended high-frequency generator, as well as a smoothing capacitor 4 and an active harmonic filter 3.

The harmonic filter 3 consists of a series inductor L2, a pump capacitor C2, the decoupling diodes D6 and D5 and the switching transistor T1 of the single-ended high-frequency generator.

FIG. 2 shows the circuit diagram of a circuit arrangement with the harmonic filter 3 for operating the low-pressure discharge lamp LL1. The high-frequency filter 1 is located at the input of the network, followed by the network rectifier 2 in a 2-pulse, uncontrolled bridge circuit. The single-ended high-frequency generator operated via an electronic control circuit 6 consists of the switching transistor T1, a switching inductance L1 and a resonant capacitor C1.

The electrodes of the lamp LL1 are connected on one side E1, H1 to the switching inductance L1, and the smoothing capacitor CO and on the other side E2, H2 to the oscillating capacitor C1. The electrodes of the heating circuits H1 and H2 can, as shown in FIG. 2, be connected via a heating capacitor C3; or a heating winding can be connected separately with E1-H1 and E2-H2 as part winding of the switching inductance L1, as shown in FIG. 4.

The high-frequency single-ended converter supplies a portion of the positive current half-wave of the lamp via the oscillating capacitor C1 from the positive pole of the smoothing capacitor C0 when the switching transistor is conductive. At the same time, the switching inductance L1 charges an energy part proportional to the switch-on time of the switching transistor T1. In the switched-off state of the switching transistor T1, an oscillating circuit is formed via the lamp, the resonance capacitor C1 and the switching inductance L1, which initially produces the negative current half-wave of the lamp with the same current direction in the switching inductance L1 and then when the current direction is reversed in the switching inductance L1 by discharging the oscillation capacitor C1 the positive current half-wave generated in the lamp. The smoothing capacitor CO is decoupled from the mains voltage via the decoupling diode D6.

The circuit arrangement also has an active harmonic filter, which consists of the series inductor L2 located in the positive line, the pump capacitor C2 and the decoupling diodes D5 and D6.

The mode of operation of the active harmonic filter in conjunction with the high-frequency single-ended lamp generator is explained in more detail below.

When the switching transistor T1 is switched "on", the pump capacitor C2 is charged via the series inductor L2 up to the voltage level at the smoothing capacitor C0. The charging current is taken from the network. An energy part is thus stored in the longitudinal inductance L2 and is emitted to the single-ended high-frequency generator, the lamp and the smoothing capacitor CO after charging of the pump capacitor C2 has ended. The amount of energy per cycle is proportional to the voltage time area at the series inductor L2 and is determined by the difference between the instantaneous mains voltage values and the voltage at the pump capacitor C2, which is present in negative polarity due to the preceding "switch-off" cycle. certainly. Due to the influence of the line voltage instantaneous values, the line current is modulated sinusoidally with each lamp cycle. The energy output of the longitudinal inductor L2 takes place by demagnetizing the longitudinal inductor L2. For this purpose, the voltage at the series inductor L2 reverses and reaches a voltage value equal to the difference between the voltage at the smoothing capacitor C0 and the respective instantaneous value of the mains voltage.

With the "switching off" of the switching transistor T1, a second phase begins in the action of the pump capacitor C2. The current flowing in the switching inductance L1 commutates from the switching transistor T1 partly to the pump capacitor C2 as a discharge and reversing current and partly to the oscillating capacitor C1 and the low-pressure discharge lamp, which thus receives its negative current half-wave. The pump capacitor C2 thus acts as a switch-off relief network for the switching transistor T1. The voltage at the collector or drain connection of the switching transistor T1 can therefore only change as quickly as the pump capacitor C2 with its resonance frequency, determined by the capacitance of the pump capacitor C2 and the inductance value of the switching inductance L1, is recharged. This limitation of the rise in voltage at the switching transistor T1 considerably reduces its turn-off losses.

The negative current half-wave in the oscillating capacitor C1 and the low-pressure discharge lamp LL1 is reduced by the current part which commutates from the switching inductance L1 as the charge-reversal current to the pump capacitor C2. This improves the crest factor of the lamp current and thus the service life of the low-pressure discharge lamp.

The electronic control circuit 6 of the switching transistor consists of an electronic oscillator and a pulse width modulator, which can be started and stopped electronically, and its pulse width or frequency via an electronic one Control signal is adjustable. This enables an electronic interface to be implemented, as is required for various user options.

3 shows a circuit arrangement for the high-frequency operation of two low-pressure discharge lamps LL1 and LL2 connected in parallel. The circuit part assigned to the low-pressure discharge lamp LL1 consists of the decoupling diodes D5.1 and D6.1, the switching inductance L1.1, the oscillating capacitor C1.1. and the heating capacitor C3.1. The circuit part assigned to the low-pressure discharge lamp LL2 consists of the decoupling diodes D5.2 and D6.2, the switching inductance L1.2, the oscillating capacitor C1.2 and the heating capacitor C3.2.

FIG. 4 shows a modified exemplary embodiment of the circuit from FIG. 2. For heating the low-pressure discharge lamp LL1, two heating winding sections L3, L4 are provided, each of which lies between the connections E1 and H1 or E2 and H2 of the low-pressure discharge lamp LL1. In this circuit arrangement, the current path leads, when the low-pressure discharge lamp LL1 is inserted, from the diode D6 via the connections H1 and E1 of the low-pressure discharge lamp LL1, the switching inductance L1 and the diode D5 to the switching transistor T1. When the low-pressure discharge lamp LL1 is removed from the circuit, the path E1-H1 is bridged by the heating winding, while on the other hand the energy present at the switching inductance L1 can no longer be discharged. A further diode D7 is therefore provided as no-load protection, which lies between the switching inductance L1 and the smoothing capacitor C0 and interrupts the inrush current path.

5 to 7 show current and voltage diagrams of an actually implemented circuit arrangement according to FIG. 2. FIG. 5 is an ozillogram for mains voltage and mains current of the circuit according to FIG. 2. Current curve I shows an approximately sinusoidal curve of the mains current. Without that Harmonic filter in the circuit of Fig. 2 results in a current during 1/10 to 1/15 of the half wave. Such a current spike would lead to grid repercussions, which have to be limited due to legal regulations. Due to the harmonic filter, the maximum of the current is reduced and the current is distributed over the entire half-wave, so that the desired approximation to a sinusoidal current curve results.

FIG. 6 shows the harmonic analysis of the mains current shown in FIG. 5. The harmonic component of the mains current is far below the limit values permitted by VDE / IEC.

FIG. 7 shows lamp current and lamp voltage of a circuit arrangement according to FIG. 2. The curves of lamp current I and lamp voltage U each show a peak superimposed on a sine curve on the positive half-wave. This peak corresponds to the turn-on time of transistor T1. In practice, it has been shown that the low-pressure discharge lamp can be operated with such a current or such a voltage without there being any disadvantageous side effects or a shorter service life.

The block diagram in FIG. 8 shows the basic structure of a further circuit arrangement for the high-frequency operation of a low-pressure discharge lamp LL1. Reference numerals a - j in FIG. 8 are also used in FIGS. 9-11 to show the connection points of the various circuit blocks in FIG. 8. The circuit arrangement includes a high-frequency filter 10, a mains rectifier 12, an active harmonic filter 13, a smoothing capacitor 14, a single-ended high-frequency lamp generator 15, control electronics 16, a driver circuit 17, an overvoltage monitor 18, a starting circuit 19 and an electronics supply 20.

Fig. 9 shows the circuit diagram of the circuit arrangement of the two additional secondary heating windings L3 and L4, which are connected to the heating coils E2, H2 and E1, H1 with the thyristors Q4 and Q5. The connection depends on the operating state of the lamp. A lamp which has not yet been ignited or is in the starting process shows an increased operating and ignition voltage, which is also available as a secondary voltage and is also available in the form of a winding on the windings L3 and L4 and is used as a trigger voltage. The ignition point for the thyristors Q4 and Q5 is derived via the voltage divider R1 / R2 and R3 / R4.

At the nominal operating voltage of the lamp, the trigger voltage is no longer reached, so that the heating remains switched off. If the operating voltage of the lamp increases, e.g. B. at low operating temperatures or with a dimmed lamp, the trigger voltage is reached, whereby the heating of the filaments automatically switches on. If the heating coils fail due to an interruption, the diodes D12 and D13 prevent an impermissibly high current load on the voltage divider resistors.

The starting behavior can be further improved by increasing the switching frequency of the single-cycle high-frequency lamp generator, because each switching cycle delivers a heating current pulse. The frequency is increased depending on the first time the electronics supply voltage is applied to the control electronics.

FIG. 9 also shows the overcurrent detection of the emitter current from T1 via the voltage drop across the resistor RO, which is connected in series with the emitter. If a certain current limit value is reached, the corresponding voltage drop acts on the control electronics 16 in such a way that the driver circuit 17 is switched off and thus the switching transistor T1 is switched off. This circuit arrangement thus acts as an electronic overcurrent protection.

10 shows a circuit section of the circuit arrangement for overvoltage detection. The collector voltage of the switching transistor is switched to the trigger diode Q1 via the voltage divider R5 / R6 and the diode D15. In a logical "OR" combination, the trigger diode Q1 can also be switched via the diode D16 depending on the level of the electronics supply voltage. The capacitor C13 prevents the trigger circuit from responding to voltage spikes that only occur for a short time and, when the trigger diode is switched through, provides the required ignition current for the thyristor Q2. If the thyristor Q2 is ignited by means of a trigger pulse, it drops into a latched state via the resistor R7.

At the same time, it short-circuits the output of the control electronics via diode D17 and the output of the start-up circuit via diode D18. The single-ended high-frequency lamp generator is now switched off. The lamp cannot be restarted until the mains have been disconnected, i.e. by canceling the latching of the thyristor current Q2.

11 shows the circuit section of the circuit arrangement for the starting circuit 19 and for the electronic self-supply 20. Each time the mains voltage is switched on, the capacitor C14 is charged via the resistor R10 and the diode D10. A maximum permissible voltage value at C14 is specified via the voltage divider R8 / R9, at which the thyristor Q3 connects this voltage to the electronics supply.

This allows the single-ended high-frequency lamp generator to oscillate and take over the electronics self-supply according to the flyback converter principle via the magnetically coupled coils L1-L5 or alternatively L6-L5. The voltage stabilization takes place in block 20 (FIG. 8) in a simple manner with the aid of a series transistor.

Claims (13)

1. A circuit for the high-frequency operation of one or more low-pressure discharge lamps connected in parallel, the circuit comprising a mains rectifier (2) followed by an active harmonic filter (3), followed by a smoothing capacitor (C0) and a high-frequency generator associated with each low-pressure discharge lamp (LL1), characterised in that the high-frequency generator is a single-cycle high-frequency generator comprising a switching transistor (T1), a switching inductance (L1) and an oscillating capacitor (C1),
   the active harmonic filter (3) comprises a series inductance (L2), a pump capacitor (C2) and two
   decoupling diodes (D5, D6),
   the first decoupling diode (D5) being situated between the oscillating capacitor (C1) and the switching transistor (T1) and
   the second decoupling diode (D6) being disposed between the smoothing capacitor (C0) and the mains voltage, and the pump capacitor (C2) being charged directly from the mains with the switching on of the switching transistor (T1).
2. A circuit according to claim 1, characterised in that the pump capacitor (C2) is connected in parallel to the switching inductance (L1) via the two decougling diodes (D5, D6).
3. A circuit according to claim 1 or 2, characterised in that the re-rise of the voltage at the switching transistor (T1) is determined by the resonance characteristic governed by the switching inductance (L1) and the pump capacitor (C2).
4. A circuit according to any one of claims 1 to 3, characterised in that the single-cycle high-frequency generator is operated at resonance frequency governed by the switching inductance (L1) and the oscillating capacitor (C1).
5. A circuit according to any one of claims 1 to 4, characterised in that the switching transistor (T1) is controlled by an electronic control circuit (6).
6. A circuit according to claim 5, characterised in that the electronic control circuit (6) forms an electronic interface.
7. A circuit according to claim 6, characterised in that the control circuit (6) comprises an electronic oscillator and a pulse-width modulator.
8. A circuit according to any one of claims 1 to 7, characterised in that the switching inductance (L1) comprises two additional secondary windings (L3) and (L4) each switched to the associated lamp filament via a thyristor (Q4, Q5) in dependence on the lamp voltage.
9. A circuit according to claim 8, characterised in that by means of an electronic control unit (16), whenever the circuit is operated for the first time, the switching frequency of the single-cycle high-frequency generator is increased and then continuously reduced to the actual clock frequency in the 1/10 second range.
10. A circuit according to claim 8 or 9, characterised in that both the overvoltage at the collector of the switching transistor (T1) and the overvoltage of an electronic power supply (10) are used, via a voltage divider (R5/R6) and a third diode (D15), in the case of the former, and via a fourth diode (D16) in the case of the latter, for triggering via a trigger diode (Q1) of another thyristor (Q2) which in turn renders inoperative a starting circuit (19) and the control circuit (16) of the switching transistor.
11. A circuit according to claim 8 or 9, characterised in that to protect the circuit from overcurrents, the emitter current of the switching transistor (T1) is detected as a voltage field at a protective resistor (RO) and a signal corresponding to the voltage drop is fed to the control circuit (16) which switches off the switching transistor when the voltage drop exceeds a predetermined value.
12. A circuit according to claim 8 or 9, characterised in that when the mains voltage is applied the circuit automatically builds up the electronic power supply voltage to the maximum permissible limit via a build-up resistor (R10) and a build-up diode (D10), at a capacitor (C14), in order then to be switched to the electronic power supply (20) by means of an additional thyristor (Q3).
13. A circuit according to any one of claims 8 to 12, characterised in that on each lamp cycle an AC voltage is tapped off via another secondary winding (L5) on the switching inductance (L1) or on a protective inductance (L6 ) and is made available as an internal electronic power supply via rectifier (D19).

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