EP0616752B1 - Circuit for operating one or more low-pressure discharge lamps - Google Patents

Description

The invention relates to a circuit arrangement for operating one or several low pressure discharge lamps according to the preamble of the claim 1.

These circuits are part of so-called electronic ballasts for low pressure discharge lamps and enable one gentle warm start - i.e. an ignition of the lamp with preheated Electrodes - the low-pressure discharge lamps, increasing their lifespan is extended.

Such a circuit arrangement is for example in EP-PS 93 469 disclosed. This circuit can be controlled by controlling the frequency and the duty cycle of the half-bridge inverter and set ignition conditions for the low-pressure discharge lamps. However, the large tolerance dependence of the have a disadvantage Heating, ignition and operating parameters of the components used and the high switching effort.

In addition, for example from EP-PS 185 179 is a circuit arrangement known that the load circuit of the half-bridge inverter between Preheating the electrodes and igniting the lamp switches. This will a PTC thermistor is used, which after the Heating time the resonance capacity of the series resonance circuit toggles.

However, the use of a PTC thermistor has the disadvantage that this component in the firing mode the low pressure discharge lamp a power loss from approx. 0.5 W to 1 W per lamp. Also needed the PTC thermistor has a cooling time of a few 10 seconds to minutes is enough for one gentle warm start of the lamps when switched on again to ensure.

Furthermore, in DE-A-39 01 111 is a circuit arrangement with a heating circuit for the electrodes of the Low pressure discharge lamps disclosed, being in the heating circuit in addition to a resonance capacity, a PTC thermistor and a relay are integrated. The PTC thermistor serves here as a timer for controlling the relay and in turn, after sufficient preheating the lamp electrodes, through the relay contact of the Circuit disconnected so that after ignition the low pressure discharge lamps no longer through the PTC thermistor flows. This circuit arrangement has compared to the circuit disclosed in EP-PS 185 179 the advantage that in the PTC thermistor during Burning operation of the lamps no power loss implemented becomes. However, the PTC thermistor also has here which is particularly annoying with short switching cycles Cooling time, so that no gentle lamp start can be done. This circuit configuration also requires a precise coordination of the components, if a cold start of the lamp avoided, on the other hand that Relay should turn off the PTC thermistor safely.

DE-A-3 901 111 is based on the preamble of claim 1.

It is the object of the invention to provide a circuit arrangement for operation to provide one or more low pressure discharge lamps, which with a sufficient circuit preheating the Electrodes of the low-pressure discharge lamps, and so one gentle warm start of the lamps as well as low power losses in the Heating circuit guaranteed.

This object is achieved by the characterizing features of claim 1 solved. Advantageous embodiments of the invention are set out in the subclaims.

As further advantages of the circuit arrangement according to the invention be listed:

The circuit arrangement according to the invention enables a controlled Preheat the lamp electrodes, matched to each one Electrode type adapted voltage value. In particular, the preheating phase of the electrodes largely independent of the tolerances of the mains voltage and the component parameters, since the voltage drop is direct used over the electrode coils to evaluate the electrode heating becomes. The heating voltage across the electrodes is so low (maximum a few tens of volts) that none in the low-pressure discharge lamp glow discharge can damage the lamp. Also be in the first two embodiments by the relay contacts, when Transition from the preheating phase to the ignition phase of the lamps, the heating circuits interrupted, so that in the burning operation of the low-pressure discharge lamps no current flows through the heating circuit. With that the power losses converted in the electrodes are reduced. With circuits with several low-pressure discharge lamps connected in parallel is the use of a relay with multiple relay contacts particularly inexpensive.

Figur 1

das Prinzip der erfindungsgemäßen Schaltungsanordnung für eine Niederdruckentladungslampe,

Figur 2a

ein genaues Schaltbild des in Figur 1 mit gestrichelten Linien umrahmten Schaltungsteils, insbesondere die Relaisansteuerung S, gemäß eines ersten Ausführungsbeispiels,

Figur 2b

ein detailliertes Schaltbild des in Figur 1 mit gestrichelten Linien umrahmten Schaltungsteils, insbesondere die Relaisansteuerung S, gemäß eines zweiten Ausführungsbeispiels,

Figur 3

das vollständige Schaltbild einer erfindungsgemäßen Schaltungsanordnung zum Betrieb zweier parallel geschalteter Niederdruckentladungslampen,

The invention is explained in more detail below with the aid of several exemplary embodiments. Show it:

Figure 1

the principle of the circuit arrangement according to the invention for a low-pressure discharge lamp,

Figure 2a

2 shows a precise circuit diagram of the circuit part framed in FIG. 1, in particular the relay control S, in accordance with a first exemplary embodiment,

Figure 2b

2 shows a detailed circuit diagram of the circuit part framed in FIG. 1, in particular the relay control S, according to a second exemplary embodiment,

Figure 3

the complete circuit diagram of a circuit arrangement according to the invention for operating two low-pressure discharge lamps connected in parallel,

Figure 1 illustrates the principle of the circuit arrangement according to the invention for operating a low-pressure discharge lamp LP.

An essential part of the circuit is a push-pull frequency generator, consisting of two bipolar transistors T1, T2, which act as half-bridge inverters are connected, with a schematically shown in Figure 1 Control device A and a DC voltage supply. The Control device A is, for example, in the book "Electronics Circuits" by W. Hirschmann (Siemens AG), on pages 147-148 and should therefore not be explained in more detail here. It also contains one Starting device for the circuit according to the invention.

The push-pull frequency generator supplies a series resonance circuit, which on Center tap M1 is connected between the transistors T1, T2 and from a coupling capacitor C3, a resonance inductor LD and a resonance capacitance C1 and a low-pressure discharge lamp LP exists with a high frequency (greater than 20 kHz) AC voltage. A connection the resonance capacitance C1 is here to the negative pole (Ground) of the DC voltage supply. The low pressure discharge lamp LP is at the connection point M connecting, parallel to the resonance capacity C1 switched. It has two with emitter material slurry electrode coils E1, E2, the together with a relay contact K1 in a heating circuit are integrated, with a connection of the electrode E2 with the negative pole (ground) of the DC voltage supply connected is.

At a tap M2 in the series resonance circuit is also a rectifier via a current limiting capacitor C5 GL connected with its input 2. Of the Input 1 of the rectifier GL is to the negative pole (Ground) of the DC power supply. Parallel to the DC output of the rectifier GL a smoothing capacitor C4. From the rectifier GL becomes a controllable electronic switch S, the controls the relay coil RL belonging to the relay contact K, supplied with DC voltage.

The principle of operation of this circuit can be as follows understand:

When switching on the half-bridge inverter or the circuit arrangement is the relay contact K initially closed so that through the electrode coil E1, the relay contact K and the electrode coil E2 via the strongly damped series resonance circuit high-frequency heating current flows through the electrodes E1 and E2 heated up. The voltage drop across the lamp is just the sum during this preheating phase from the voltage drop at the electrode coil E1 and on the electrode coil E2, that is, with the same type Electrodes E1, E2 equal to twice the heating voltage an electrode coil.

Since the rectifier GL with its inputs 1, 2 is connected in parallel to the lamp LP, during the preheating phase on him also the high frequency Heating voltage of the electrode coils E1, E2. This high-frequency voltage is from the rectifier GL in a pulsating DC voltage transforms and from Smoothing capacitor C4, which is parallel to the DC output of the rectifier GL is switched, smoothed so that the controllable electronic Switch S the rectified and smoothed heating voltage of the electrode coils E1, E2.

With increasing heating of the electrode coils E1, E2 also increases their ohmic resistance and thus the Heating voltage, i.e. the voltage drop across the electrodes E1, E2 and the voltage drop on the electronic Switch S. When a critical is exceeded The electronic switch S opens the voltage value relay contact K via the relay coil RL

Opening the relay contact K causes an interruption of the heating circuit, so that any further current flow prevented by the electrode coils E1, E2 becomes. It also increases the quality of the series resonance circuit on, since the resonance capacitance C1 is no longer bridged by the heating circuit and an attenuation of the series resonance circuit by the Resistance of the electrode coils E1, E2 is eliminated. Consequently can the ignition voltage at the resonance capacitance C1 provided for the low pressure discharge lamp LP will. After ignition of the lamp LP flows only the quiescent or holding current through the relay coil RL, which is required to switch the relay contact K keep open. Only after switching off the lamp LP or the circuit arrangement becomes the relay contact K closed again so that when it is again Switching on the lamp LP the preheating phase for the Electrodes E1, E2 starts again.

The controllable electronic switch S can be used as Threshold or be designed as a timer.

In FIG. 2a, according to the first exemplary embodiment, the controllable electronic switch S is designed as a threshold switch.
The electronic switch S here consists of a Zener diode DZ, a voltage divider with the resistors R17, R18 and a thyristor Th, which is connected in series with the relay coil RL and whose gate is controlled by the Zener diode DZ.
During the preheating phase, that is when the relay contact K is closed, the zener diode DZ and the thyristor Th block, so that no current flow takes place through the relay coil RL. With increasing heating of the electrode filaments E1, E2, the voltage drop at the electrode filaments E1, E2 and at the Zener diode DZ increases. When the breakdown voltage of the Zener diode DZ is exceeded, it becomes conductive and also controls the switching path of the thyristor Th into the conductivity via the voltage drop across the resistor R18. This results in a current flow through the relay coil RL and an opening of the relay contact K. Since the ignition and the operating voltage of the low-pressure discharge lamp LP are greater than the heating voltage at the electrode filaments E1, E2, the switching path of the thyristor Th remains in the conductive state, so that after the lamp LP has been ignited, the holding current flows through the relay coil RL, which is required is to keep the relay contact K open.

The freewheeling diode D1, parallel to the relay coil, is used only to protect the thyristor Th from the induction voltage the relay coil RL.

By appropriate dimensioning of the components, in particular C4, DZ, R17 and R18 can be the duration of the preheating phase optimally set for each electrode type will.

2b shows, according to the second exemplary embodiment, the controllable electronic switch S as Time switch trained. The electronic switch S consists of an RC element with the resistor R20 and the capacitor C20 and a thyristor Thl, which is connected in series to the relay coil RL1. There is an ohmic resistor in parallel with capacitor C20 R21 arranged. It is used to discharge the capacitor C20 after switching off the circuit arrangement and to set a defined preheating time at restart.

The capacitor C20 is opened via the resistor R20 charged the threshold voltage that is required by the switching distance of the thyristor Thl over the Control gate connection in conductivity, which a current flow through the relay coil RL1, similar to in the first embodiment in FIG. 2a becomes.

The rectifier GL2, the smoothing capacitor C7 as well as the thyristor Th1 and the relay coil RL1 the freewheeling diode D2 have the same function as that corresponding components of the first embodiment according to Figure 2a. The duration of the preheating phase Electrode coils E1, E2 is here by the time constant of the RC element and through the resistor R21 determined, which in turn of course for each type of electrode can be optimized (see FIG. 2b).

Figure 3 shows a detailed circuit diagram of an inventive Circuit arrangement for the operation of two low-pressure discharge lamps connected in parallel LP1, LP2 according to a particularly preferred embodiment.

As an essential component, the circuit contains a push-pull frequency generator, consisting of two bipolar transistors T3, T4 arranged in a half-bridge with a control device A 'shown only schematically here and a DC voltage supply G, to whose output a backup capacitor C8 is connected in parallel. A precise description of such a control device A 'can be found, for example, in the book "Electronics Circuits" by W. Hirschmann (Siemens AG), on pages 147-148 and in EP-OS 276 460. Parallel to the switching paths of the alternating switching transistors T3, A first smoothing capacitor C6 is connected to T4. The transistors T3, T4 also each have an emitter resistor R5 or R6 and a flyback diode D3 or D4 to protect their switching path. At the center tap M1 'between the two bipolar transistors T3, T4, two series resonant circuits lying in parallel to one another are connected via the coupling capacitor C10 and the primary winding RKla of a toroidal transformer.
The first series resonance circuit consists of the resonance inductance LD1, the resonance capacitance C91 and the low-pressure discharge lamp LP1, the lamp LP1 and the resonance capacitance C91 being connected in parallel with one another in terms of alternating current. Analogously to this, the second series resonance circuit C92 and the low-pressure discharge lamp LP2, the lamp LP2 and the resonance capacitance C92 also being connected in parallel with one another in terms of alternating current.

Both lamps LP1, LP2 have a heating circuit that each of the electrode coils E10, E20 and the electrode coils E11, E21 of the corresponding Lamps LP1 and LP2 and a relay contact K1 or K2 is formed. The two relay contacts K1, K2 are switched simultaneously by the relay coil RL '.

The relay coil RL 'is from the switching path of the in Series to thyristors Th 'arranged to it, the gate of thyristor Th 'in turn from the Zener diode DZ 'and the voltage divider controlled from the resistors R17 ', R18' becomes. At the Zener diode DZ 'and the voltage divider R17 ', R18' is that of the second smoothing capacitor C4 'smoothed output voltage of the rectifier GL' on. The rectifier DC output GL ', the smoothing capacitor C4', the Zener diode DZ ', the voltage divider R17', R18 ', the relay coil RL ', the freewheeling diode D1' and the thyristor Th ' completely analogous to the first embodiment, the is shown in Figure 2a, connected. The connection 1 of the rectifier GL 'is on the tap M3 to the positive pole of the first smoothing capacitor C6 performed while connection 2 of the rectifier GL 'via a first current limiting capacitor C17 with a tap M4 in the first series resonance circuit and via a second current limiting capacitor C18 with a tap M5 in the second series resonance circuit connected is.

Via the tap M3 is also a connection of the Electrode coils E20 and E11 to the positive pole of the first Smoothing capacitor C6 performed, so that the AC input 1, 2 of the rectifier GL 'parallel to both lamps LP1 and LP2 is switched.

The circuit arrangement also has an active one Harmonic filter, which is a sinusoidal mains current draw enables. This harmonic filter consists of the diodes D13, D14, D15, D16 and the capacitors C13, C81, C82 and the two resonance capacities C91, C92. A detailed functional description of a such harmonic filters can be found in the US-PS 4 808 887 and should therefore not be reproduced here will.

The one shown in FIG. 3 has not yet been mentioned Component R8, which, like the primary winding RKla of the toroidal transformer to the control device A 'heard and therefore not explained here shall be.

The mode of operation of the circuit arrangement according to the invention 3 can be described as follows:

After switching on and starting the push-pull frequency generator flows from the center tap M1 'over the Coupling capacitor a high frequency (larger than 20 kHz) alternating current, which is at the tap M2 'in the branches into two series resonance circuits, so that over the resonance inductance LD1 and the tap M4 Heating current through the heating circuit of the low pressure discharge lamp LP1, consisting of the electrode coils E10, E20 and the closed relay contact K1, for Tap M3 flows where it deals with the heating current through the heating circuit of the second low-pressure discharge lamp LP2, consisting of the electrode coils E11, E21 and the closed relay contact K2, flows, united.

The two lamps LP1, LP2 are Fluorescent lamps with a power consumption of approx. 9 W and with similar electrode coils E10, E20 and E11, E21.

The voltage drop during the preheating phase just twice the heating voltage above each lamp LP1, LP2 an electrode coil E10, E20, E11, E21.

Because the rectifier GL 'parallel to the fluorescent lamps LP1 and LP2 is switched between the Taps M6 and M7 approximately the peak of rectified and through the second smoothing capacitor C4 'smoothed double electrode coil voltage on.

With increasing heating of the electrode filaments E10, E20, E11, E21, their ohmic resistance and thus the voltage drop across the lamps LP1, LP2 and also the voltage drop between the taps M6, M7 also increase.
If the voltage drop across the electrode filaments E10, E20, E11, E21 exceeds a critical value, the zener diode DZ 'becomes conductive and also controls the switching path of the thyristor Th' via its gate and the voltage drop across resistor R18 'into the conductivity. As a result, a current flows through the relay coil RL 'and the relay contacts K1, K2 are opened so that both heating circuits are interrupted.

This ends the preheating phase for electrodes E10, E20, E11, E21. The resonance capacities are C91, C92 no longer bridged by the heating circuits, so that due to the higher quality of the series resonance circuits at the resonance capacitances C91, C92 the ignition voltage provided for the fluorescent lamps LP1, LP2 can be.

After the lamps LP1, LP2 have been ignited, the relay coil RL 'is still supplied with the holding or quiescent current which is sufficient to hold the relay contacts K1, K2 in the open position. Only when the lamps LP1, LP2 are switched off are the relay contacts K1, K2 closed again.
The functional principle is therefore completely analogous to that of the first exemplary embodiment according to FIG. 2a.

Table I indicates a suitable dimensioning of the components for the exemplary embodiment according to FIG. 3. C81, C82 2.2 nF C91, C92 4.7 nF C13 6.8 nF C17, C18 470 pF DZ ' BZX55 / C24 LD1, LD2 3.1 mH R5, R6 0.47 W. R17 ', R18' 1.8 kW C4 ' 10 mF Th ' 2N5061 D1 ' 1N4148

The invention is not limited to the exemplary embodiments described, but can also be used, for example, to operate several in parallel switched low-pressure discharge lamps can be used. It is natural also possible in the circuit arrangement according to the invention Figure 3 shows the control of the relay coil RL 'by means of a timer to execute according to Figure 2b.

The circuit arrangement according to the invention is also suitable for several Series of switched low pressure discharge lamps. In this case they would be Electrode filaments of all lamps integrated in a single heating circuit, and the relay had as many relay contacts as there were lamps would be, these relay contacts also integrated in the heating circuit would be and would switch simultaneously (controlled by the same relay coil). The relay contacts would then be at the end of the preheating phase Interrupt the heating circuit so that the electrical connection between the electrode filaments belonging to the same lamp would be interrupted.

In addition, instead of an electromechanical relay, a so-called electronic relays are used that come from an optocoupler and an electronic switch, e.g. a thyristor.

Claims (6)

1. Circuit arrangement for operating one or more low-pressure discharge lamps, comprising

   a push-pull frequency generator having a drive device (A, A') and a DC power supply (G),

   at least one series resonance circuit, to which a radio frequency signal is applied by the push-pull frequency generator, and which includes at least one resonance inductor (LD, LD1, LD2) and at least one resonance capacitor (C1, C91, C92),

   terminals for at least one low-pressure discharge lamp (LP, LP1, LP2) having electrode filaments (E1, E2, E10, E20, E11, E21), each electrode filament (E1, E2, E10, E20, E11, E21) having two terminals,

   at least one heating circuit for preheating the electrode filaments (E1, E2, E10, E20, E11, E21) of the low-pressure discharge lamp (LP) or of the low-pressure discharge lamps (LP1, LP2), having switching means (K, K1, K2) for closing and opening the heating circuit or the heating circuits, it being the case that these switching means (K, K1, K2) switch the heating circuit or the heating circuits between a low-resistance state and a high-resistance state, and that the quality of the series resonance circuit or of the series resonance circuits is increased with respect to the preheating phase, with the result that at the end of this electrode preheating phase the starting voltage for the low-pressure discharge lamp (LP) or the low-pressure discharge lamps (LP1, LP2) can be provided at the resonance capacitor or at the resonance capacitors (C1, C91, C92),

   a rectifier (GL, GL', GL1),

   a controllable electronic switch (S, S') which is constructed as a threshold-value or time switch, is connected to the DC output of the rectifier (GL, GL', GL1) and which actuates the switching means (K, K1, K2) as a function of the ohmic resistance of the electrode filaments (E1, E2, E10, E20, E11, E21) which increases with the heating up,

   characterized in that the electronic switch (S, S') is fed a heating voltage which is rectified by the rectifier (GL, GL', GL1) and drops during the preheating phase between the two terminals of at least one electrode filament (E1, E2, E10, E20, E11, E21).
2. Circuit arrangement according to Claim 1, characterized in that the circuit arrangement includes at least two low-pressure discharge lamps (LP1, LP2) which are connected in parallel with one another and each have a heating circuit for preheating their electrodes (E10, E20, E11, E21), and the switching means are constructed as a relay whose relay contacts (K1, K2) are each integrated into a heating circuit.
3. Circuit arrangement according to Claim 1, characterized in that the circuit arrangement includes at least two series-connected low-pressure discharge lamps, the electrode filaments of these lamps being integrated in a common heating circuit for preheating the electrode filaments.
4. Circuit arrangement according to Claim 1, characterized in that the switching means are constructed as a relay and the controllable electronic switch (S) has a thyristor (Th, Th') as well as a zener diode (DZ, DZ'), the zener diode (DZ, DZ') being connected to the gate of the thyristor (Th, Th') and the thyristor (Th, Th') being connected in series with the relay coil (RL, RL') of the relay.
5. Circuit arrangement according to Claim 1, characterized in that the switching means are constructed as a relay, and the controllable electronic switch (S) has a thyristor (Th1) and an RC element (R20, C20), the RC element (R20, C20) being connected to the gate of the thyristor (Th1), and the thyristor (Th1) being connected in series with the relay coil (RL1) of the relay.
6. Circuit arrangement according to Claim 1, characterized in that the circuit arrangement has at least one current-limiting capacitor (C5, C17, C18) which is connected to the AC input of the rectifier (GL, GL', GL1).

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