EP0378992B1 - Circuitry for driving discharge lamps - Google Patents

Description

The invention relates to a circuit arrangement for high-frequency operation of one or more low-pressure discharge lamps connected in series in accordance with the preamble of claim 1.

Such a circuit arrangement for igniting a low-pressure discharge lamp is listed in DE-OS 34 41 992. The circuit arrangement includes a further capacitor in parallel with the PTC thermistor.

When a mains voltage is applied to the circuit arrangement, the PTC thermistor has a low resistance and thus enables a preheating current to flow through the two electrodes of the lamp. The PTC thermistor is heated by the current flow and changes into a high-resistance state after a period of time characteristic of the respective PTC thermistor. This interrupts the preheating of the electrodes and the lamp can be ignited by the resonance circuit. The PTC thermistor enables sufficient and quick preheating of the electrodes and reliable ignition of the lamp.

However, it is disadvantageous that the PTC thermistor is heated for the entire duration of the lamp after the ignition. This results in relatively high energy losses due to the long burning times for fluorescent lamps. The permanent heating of the PTC thermistor represents an additional thermal load on the circuit arrangement, which can lead to premature failure of a circuit part, in particular the PTC thermistor itself.

The object of the invention is to provide a circuit arrangement which prevents further heating of the PTC thermistor after the low-pressure discharge lamp or lamps have been ignited, so as to keep the power loss of the circuit arrangement low. The number of circuit elements required for this shutdown should be as small as possible so that the circuit arrangement can also be easily integrated into small device housings.

The object is achieved by the characterizing features of claim 1. Further advantageous refinements of the circuit arrangement can be found in the subclaims.

The relay uses the switch to deactivate the PTC thermistor if the electrodes have been preheated sufficiently. So far, it has been known to control complex contacts, such as e.g. RC circuits to use as a timer. The circuit arrangement according to the invention does not require such circuits, since the PTC thermistor to be switched off itself - by transition to the high-resistance state - serves as a time constant element for the normally closed contact relay.

To generate the required DC voltage, the relay is connected in parallel with the PTC thermistor in the heating circuit via a rectifier. It is also in a the supply lines between the PTC thermistor and the AC input of the relay rectifier, a capacitor is used to set the relay switching voltage. Another capacitor in parallel with the DC output of the relay rectifier has the task of screening the DC voltage if low-noise direct current is required to operate the relay.

When operating several low-pressure discharge lamps connected in series, for optimal ignition it is necessary that all electrodes are preheated. The electrodes that are not connected to the center tap between the two transistors or to the positive and / or negative pole must therefore undergo additional preheating. This is advantageously done by a separate heating circuit which connects these electrodes to one another and in which a secondary winding on the resonance inductor is additionally integrated. With the help of another switch in this additional heating circuit, which is also integrated in the break contact relay listed above, this heating circuit can then be deactivated at the same time as the heating circuit of the outer electrodes.

By using the PTC thermistor in multiple functions as a preheating element and time constant element, an optimal preheating time, a quick and glow phase-free lamp ignition and a high system efficiency are achieved in the circuit arrangement according to the invention. The relay remains switched on during the operating period of the lamp or lamps, ie as long as the push-pull frequency generator oscillates. The PTC thermistor cools down immediately after being switched off by the relay when starting the lamp. Thus, if the device is switched off within a few minutes and then switched on again, a new preheating with subsequent good ignition is guaranteed. These properties therefore also enable the circuit arrangement to be used in short-term operating applications.

Figur 1

zeigt eine erfindungsgemäße Schaltungsanordnung zum Betrieb einer Niederdruckentladungslampe

Figur 2

zeigt eine erfindungsgemäße Schaltungsanordnung zum Betrieb von zwei in Reihe geschalteten Niederdruckentladungslampen

Im Ausführungsbeispiel der Figur 1 ist eine Schaltungsanordnung zum Betrieb einer Leuchtstofflampe LP wiedergegeben. Die Schaltung beinhaltet ein Hochfrequenzfilter 1, eine Gleichrichteranordnung 2, einen Glättungskondensator C1 und einen Gegentaktfrequenzgenerator mit zwei alternierend schaltenden Transistoren T1, T2, Emitterwiderständen R1, R2 sowie einer Ansteuerschaltung 3. Der Gegentaktfrequenzgenerator ist selbststeuernd, wobei die Steuerspannung von einem Ringkerntrafo TR mit einer Primärwicklung im Betriebsstromkreis und je einer Sekundärwicklung in den Basissteuerungen der Transistoren T1, T2 erhalten wird. Außerdem weist die Schaltungsanordnung einen Serienresonanzkreis mit einer Induktivität L1, einem Kopplungskondensator C2 und einem Resonanzkondensator C3 auf. Die Resonanzinduktivität L1 und der Kopplungskondensator C2 sind in Reihe zum Ringkerntrafo TR in den Betriebsstromkreis zwischen den Mittenabgriff M und die erste Elektrode E1 der Lampe LP und der Resonanzkondensator C3 in den Heizkreis der Lampe LP gelegt. Die zweite Elektrode E2 der Niederdruckentladungslampe LP ist netzseitig mit dem Pluspol der Gleichrichteranordnung 2 verbunden.The circuit arrangement is illustrated in more detail with reference to the following figures.

Figure 1

shows an inventive circuit arrangement for operating a low-pressure discharge lamp

Figure 2

shows a circuit arrangement according to the invention for the operation of two low-pressure discharge lamps connected in series

In the exemplary embodiment in FIG. 1, a circuit arrangement for operating a fluorescent lamp LP is shown. The circuit includes a high-frequency filter 1, a rectifier arrangement 2, a smoothing capacitor C1 and a push-pull frequency generator with two alternating switching transistors T1, T2, emitter resistors R1, R2 and a control circuit 3. The push-pull frequency generator is self-controlling, the control voltage being generated by a toroidal transformer TR with a primary winding is obtained in the operating circuit and one secondary winding each in the basic controls of the transistors T1, T2. In addition, the circuit arrangement has a series resonance circuit with an inductance L1, a coupling capacitor C2 and a resonance capacitor C3. The resonance inductor L1 and the coupling capacitor C2 are connected in series to the toroidal transformer TR in the operating circuit between the center tap M and the first electrode E1 of the lamp LP and the resonance capacitor C3 in the heating circuit of the lamp LP. The second electrode E2 of the low-pressure discharge lamp LP is connected on the network side to the positive pole of the rectifier arrangement 2.

The exact circuit structure and the mode of operation of such a circuit arrangement can be found in the book "Electronics Circuits" by W. Hirschmann (Siemens AG), 1982, page 148 and will not be described in more detail here.

In series with the resonance capacitor C3, a PTC thermistor KL and a switch S of a relay RL are placed in the heating circuit. A relay rectifier GL with its AC inputs is connected in parallel with the PTC thermistor KL and the switch S, a capacitor C4 also being placed in a supply line. The DC outputs of the relay rectifier GL are connected to the relay RL, in which the switch S is integrated. In addition, a capacitor C5 is connected in parallel with the DC output of the relay rectifier GL.

When a mains voltage is applied to the circuit arrangement, a preheating current flows through the heating circuit via the two electrodes E1, E2. The PTC thermistor is initially low-resistance and, due to the current flow, changes to the high-resistance state after a certain preheating time. Now the capacitor C4 can charge until the DC voltage output of the relay rectifier GL requires the relay RL Switching voltage is present. If this voltage is reached, the switch S is opened by the relay and de-energizes the PTC thermistor KL. At the same time, the lamp LP is ignited. The PTC thermistor KL remains switched off during the entire burning time of the lamp LP, since the relay RL keeps its normally closed contact switch S open by permanent excitation. If the circuit arrangement is switched off by switching off the mains voltage, the normally closed contact switch S closes again. If the circuit arrangement is reconnected to the mains, the process begins again.

C1 :

10 µF/450 V-

T1, T2 :

MJE 13007

R1, R2 :

0,39Ω

TR :

Ringkern (10x6x4) primär 9 Windungen sekundär je 3 Windungen

L1 :

EF25, 1,4 mH

C2 :

100 nF/250 V∼

KL :

Kaltleiter 65Ω (1,5 A)

GL :

B 250, C 800

RL :

24 V DC/1400Ω , Ruhekontakt 2 A/250 V∼

C3 :

2,2 nF/630 V-

C4 :

0,47 nF/1000 V-

C5 :

0,1 µf/100 V-

In Figur 2 ist eine erfindungsgemäße Schaltungsanordnung zum Betrieb von zwei in Reihe geschalteten Leuchtstofflampen LP1, LP2 wiedergegeben. Der Aufbau der Grundschaltung und des Schaltkreises für die Abschaltung des Kaltleiters KL entsprechen der in Figur 1 aufgeführten Schaltung, wobei hier die erste Elektrode E1 der ersten Lampe LP1 mit dem Mittenabgriff M und die zweite Elektrode E2′ der zweiten Lampe LP2 mit dem Pluspol der Gleichrichteranordnung 2 verbunden ist. Zusätzlich sind die beiden mittleren Elektroden E2 und E1′ der Lampe LP1 bzw. Lampe LP2 zu einem eigenen Heizkreis zusammengefaßt, der durch eine Sekundärwicklung L2′ an der Resonanzinduktivität L1′ die Elektroden mit Strom versorgt. Der Heizkreis beinhaltet außerdem einen im Relais RL integrierten Schalter S′, der durch das Relais RL geöffnet wird. Dadurch ist es möglich, mit dem Relais RL, das durch den Kaltleiter KL gesteuert wird, die Vorheizströme sämtlicher Elektroden gleichzeitig zu unterbrechen, wenn eine für die Zündung der Lampe ausreichende Vorheizung erfolgt ist.In the following equipment list, the circuit elements used for the circuit arrangement according to the invention in accordance with FIG. 1 for the operation of a 58 W fluorescent lamp on 220 V AC voltage are summarized:

C1:

10 µF / 450 V-

T1, T2:

MJE 13007

R1, R2:

0.39Ω

TR:

Toroid (10x6x4) primary 9 turns secondary 3 turns each

L1:

EF25, 1.4 mH

C2:

100 nF / 250 V∼

KL:

PTC thermistor 65Ω (1.5 A)

GL:

B 250, C 800

RL:

24 V DC / 1400Ω, normally closed contact 2 A / 250 V∼

C3:

2.2 nF / 630 V-

C4:

0.47 nF / 1000 V-

C5:

0.1 µf / 100 V-

FIG. 2 shows a circuit arrangement according to the invention for operating two series connected Fluorescent lamps LP1, LP2 reproduced. The structure of the basic circuit and the circuit for switching off the PTC thermistor KL correspond to the circuit shown in Figure 1, here the first electrode E1 of the first lamp LP1 with the center tap M and the second electrode E2 'of the second lamp LP2 with the positive pole of the rectifier arrangement 2 is connected. In addition, the two middle electrodes E2 and E1 'of the lamp LP1 or lamp LP2 are combined to form a separate heating circuit which supplies the electrodes with current through a secondary winding L2' at the resonance inductor L1 '. The heating circuit also includes a switch S 'integrated in the relay RL, which is opened by the relay RL. This makes it possible to interrupt the preheating currents of all electrodes at the same time with the relay RL, which is controlled by the PTC thermistor KL, if a preheating sufficient for the ignition of the lamp has taken place.

Claims (5)

1. Circuit arrangement for the high-frequency operation of a low-pressure discharge lamp (LP) or of a plurality of low-pressure discharge lamps (LP1, LP2) connected in series, in which the circuit has the following features:

   - a rectifier arrangement (2);

   - a push-pull frequency generator connected to the direct-current output of the rectifier arrangement (2) and comprising two alternately switching transistors (T1, T2), a drive circuit (3) and a smoothing capacitor (C1), a central tap (M) being provided between the two transistors;

   - terminal leads for the low-pressure discharge lamp (LP) or lamps (LP1, LP2), one lead connecting the first electrode (E1) of the lamp (LP) or of the first lamp (LP1) to the central tap (M) between the two transistors (T1, T2) and a further lead connecting the second electrode (E2; E2') of the lamp (LP) or of the last lamp (LP2) to the positive and/or negative terminal of the rectifier arrangement (2);

   - a series resonance circuit comprising resonance inductance (L1, L1'), coupling capacitor (C2) and resonance capacitor (C3), the resonance inductance (L1, L1') and the coupling capacitor (C2) being connected in series between the central tap (M) and the first electrode (E1) of the lamp (LP) or of the first lamp (LP1) and the resonance capacitance (C3) being connected in the heater circuit in parallel with the lamp (LP) or with the lamps (LP1, LP2),

   - and a positive temperature coefficient resistor (KL) in series with the resonance capacitor (C3) in the heater circuit,

   characterised in that the switching circuit comprises a relay (RL) with which the positive temperature coefficient resistor (KL) can be disconnected from the circuit by means of a switch (S) in series with the positive temperature coefficient resistor (KL), the positive temperature coefficient resistor (KL) also serving as timing element for controlling the relay (RL).
2. Circuit arrangement according to Claim 1, characterised in that the power terminals of the relay (RL) are connected to the direct voltage output of a relay rectifier (GL) and the alternating current inputs of the relay rectifier (GL) are connected to the positive temperature coefficient resistor (KL).
3. Circuit arrangement according to Claim 1 and/or 2, characterised in that a capacitor (C4) is connected in one of the two alternating current connecting leads between positive temperature coefficient resistor (KL) and relay rectifier (GL).
4. Circuit arrangement according to one or more of Claims 1 to 3, characterised in that a capacitor (C5) is connected in parallel with the direct current output of the relay rectifier (GL).
5. Circuit arrangement according to one or more of Claims 1 to 4, characterised in that, during the operation of a plurality of low-pressure discharge lamps (LP1, LP2) connected in series, the electrodes (E2, E1') which are not connected to the central tap (M) or to the positive and/or negative terminal are connected in series to a secondary winding (L2') on the resonance inductor (L1') to form a further heater circuit and a switch (S') with which the further heater circuit can be interrupted by means of the relay (RL) is incorporated in said heater circuit.

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