DE3327189A1 - Circuit arrangement for the starting and brightness control of fluorescent lamps - Google Patents

Abstract

A circuit arrangement for the starting and brightness control (dimmer mode) of fluorescent lamps is intended to be designed to lead to a stable operation and reliable starting even in low environmental temperatures and, in particular, also to make possible a dimmer mode, even in the case of modern, power-saving, thin fluorescent tubes. For this purpose, an interrupter switch (9) is connected in series with the heating circuits (6) and hence in parallel with the fluorescent tube starting electrodes (5), which interrupter switch (9) can be driven from a phase shifter (depending on the desired operating brightness). In that the inductive heating current (i3 = i1) via the series connection of the heating circuits (6) and the switch (9), which is initially closed, is opened abruptly, a starting voltage (uZ) is set across the switch (9), and hence across the starting electrodes (5), which is very steep and very high, determined by the preceding heating current, and which leads to reliable starting and stable light operation in every light time interval (a) which is predetermined by the phase shifter (8) and even when the fluorescent tube (2) is at very low operating temperatures. <IMAGE>

Description

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5 DIEHL GMBH & CO., D-8500 Nuremberg

Circuit arrangement for the ignition and for the brightness control of Fluorescent lamps

The invention relates to a circuit arrangement according to the Preamble of claim 1.

A generic circuit arrangement is known from DE-AS 21 41 097. The control circuit points there for the Series connection of the two fluorescent tube heating circuits on a triac, which within each heating period the phase shifter is ignited. The fluorescent tube is used for the remaining part of the heating season are deleted and the heating circuits are connected in series to the mains until the next zero crossing, i.e. until the end the current heating season, the triac goes out again. The fluorescent tube therefore ignites and lights up until to the occurrence of the triac activation for the following heating period.

It is claimed that when a base load phase shift circuit is used parallel to the phase shifter that can be set for the brightness control, that control circuit is also used for stable operation of longer fluorescent tubes with low brightness is suitable. However, it has been shown that the modern energy-saving thin fluorescent tubes (diameter 26 mm compared to 38 mm for dimmer operation suitable standard fluorescent tubes) cannot be dimmed with such a previously known control circuit common dimmer control circuits for the standard lighting

Fabric tubes (38 mm diameter) are not suitable for use in conjunction with these modern, thin fluorescent tubes. The latter are therefore offered by the manufacturers with the express advice that they are not suitable for dimmer operation (and for operation at low ambient temperatures); for such applications, the previous fluorescent tubes with a diameter of 38 mm should still be used (cf. OSRAM printed matter 866/5 of April 1982 "Light for inside and outside", there pages 24 and 30). On the other hand, on the installation sector a great interest in generellem use only modern thin fluorescent tubes because they are more economical and because the _{Lagerhaitung}} would be to different tube diameters for constant light operation and dimmers, much simpler and cheaper. In addition, there is the weight saving with smaller and with lower power consumption - that is, fluorescent tubes working with smaller throttle weights, which is of particular interest when used to illuminate passenger cabins in aircraft.

In recognition of these circumstances, the invention is based on the object of a generic circuit arrangement designed for igniting and dimming fluorescent lamps in such a way that they are particularly suitable for the operation of modern, thin fluorescent tubes are suitable, which were previously generally regarded as non-dimmable and, moreover, especially at very low working temperatures, with the for it sold starters (opening of the heating circuit series connection after a certain heating period has elapsed after switching on the fluorescent tube to the power supply) are not always reliably ignitable.

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According to the invention, this object is essentially achieved in that the generic circuit arrangement additionally has the partial features according to the characterizing part of claim 1.
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According to this solution, the heating current is periodically, namely in each case at the ignition point that can be specified via the phase shifter, abruptly interrupted; with the result that due to the self-induction effect of the upstream Choke coil builds up a steep and very high cut-off voltage peak between the heating circuits, which is used as the ignition voltage acts between the fluorescent tube ignition electrodes. The time behavior and level of this ignition voltage peak are therefore no longer due to the time behavior of the mains voltage period given, but by suddenly switching off a powerful inductive heating current. Because the heating current the greater, the shorter the lighting period (i.e. the smaller The brightness emitted by the fluorescent tube is the result of the critical working method with low brightness a particularly strong ignition voltage pulse, i.e. again reliable ignition and more stable Operation of the fluorescent tube. So you can say that the circuit automatically adjusts the pulse height of its ignition voltage to the critical operating conditions of the fluorescent tube adapts. It also follows from this that this circuit arrangement applies equally to thin and conventional fluorescent tubes is applicable; with conventional, more easily ignitable fluorescent tubes there is a lower ignition pulse than with the modern tubes with a diameter of only 26 mm.

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For the implementation of the circuit breaker in the series circuit For the heating circuits, it is particularly useful to use a diode bridge circuit with an electronic interrupter switching path to be used in the bridge diagonal, in which there is always only one direction of current flow for both mains voltage half-waves occurs. At the same time, damage caused by excessive ignition voltage peaks can be easily prevented by that at least two of the, with respect to this switching path diametrically opposite, bridge diodes as Zener diodes are realized whose Zener or breakdown voltages act as a voltage limiter for the ignition voltage peaks.

Additional developments and alternatives as well as further features and advantages of the invention emerge from the subclaims and from the following description of a preferred exemplary embodiment for the solution according to the invention, shown in simplified form in the drawing with restriction to the essentials.
It shows:

1 shows the complete circuit arrangement for the ignition and for the brightness control in a block diagram in particular thin fluorescent tubes with a control circuit according to the invention,

2 shows an implementation example for the interrupter switching path in the control circuit according to FIG. 1,

3 shows the current profiles in a highly abstracted representation in the division by the fluorescent tube and by the control circuit and

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FIG. 4 corresponds to the amplitude-time representation of FIG 3 shows the time-related course of the voltage across the fluorescent tube.

According to the basic block diagram of FIG. 1, a network 1 is converted into a fluorescent tube 2 by means of a control circuit 3 operated via a power switch 4. The control circuit 3 is used to ignite and control the brightness of the Fluorescent tube 2. The ignition electrodes 5 of the fluorescent tube 2 are given by their two heating circuits 6. The control circuit 3 is parallel to the fluorescent tube 2, that is, parallel to its ignition electrodes 5, on the network 1; i.e. the heating circuits 6 are fed in series from the network 1 when the control circuit 3 is switched through - during this short circuit over the ignition electrodes 5 is canceled when the control circuit 3 is no longer switched through and the ignition and discharge voltage (tube voltage u2) build up in the fluorescent tube 2 can. Furthermore, a choke 7 is connected in series between the network 1 and the fluorescent tube 2, its inductance the heating current limitation and an adjustment of the phase control curve shape to the sinusoidal curve shape of the voltage of the Network 1 (to reduce the interference feeds from the control circuit 3 into the network 1); but especially the generation of a high, pulsed glow discharge ignition voltage uZ at points in time recurring with the periodicity of the network 1, which can be set by a phase shifter 8 are (as explained in more detail below).

in the control circuit 3 is between the heating circuits 6 and thus arranged in the shunt to the electrodes 5 of the fluorescent lamp 2, a controllable breaker switch 9, the

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is normally switched through to switch on the heating circuits 6. However, depending on the periodicity of the course of the mains voltage u1, the interrupter switch 9 is opened for a lighting period a which can be set on the phase shifter 8; so that the ignition voltage uZ builds up between the heated electrodes 5, which collapses with the use of the glow discharge (brightness radiation from the fluorescent tube 2) on the tube voltage u2, as known from the physics of electrical glow discharges. If namely at the ignition time ta for the remainder of the period (or ₃ according to FIG. 3 _; the half period) according to the phase setting on the phase shifter 8 by opening the circuit breaker 9, the heating current i3 is abruptly interrupted through the heating circuits 6, flows due to the effect of the high inductance value of the choke 7, the current line current i1 continues, namely now inevitably as tube current i2 between the electrodes 5. Due to the high resistance of the fluorescent tube 2, which is not yet ignited at this moment, this corresponds to the very steep, high formation of an ignition voltage uZ between the during of the previous part of the (heating) period heated electrodes 5/6. This constellation leads to the reliable ignition of the gas path in the fluorescent tube 2 and thus to the collapse of the ignition voltage uZ to the gas discharge burning voltage u2 during the lighting period a; until the breaker switch 9 is closed again _; and as a result, the series connection of the heating circuits 6 is short-circuited again by the shunt of the control circuit 3 by short-circuiting the tube voltage u2 (cf. FIG. 4 in conjunction with FIG. 3) until the next ignition.

The controllable breaker switch 9 is preferably made essentially from a diode bridge circuit 10 with

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electronic interrupter switching section 11 in the bridge diagonal 12 between two oppositely interconnected diode cathodes 13 on the one hand and two oppositely on the other hand interconnected diode anodes 14. The connections 15 for the series connection of the heating circuits 6 are therefore between two diodes of the bridge circuit 10 connected in series in the same direction. This ensures that in each Half-wave of the AC voltage network 1 during the partial periods, Since the heating circuits are fed, the current flow direction across the bridge diagonal 12 is always identical. This simplifies the implementation of the interrupter switching path 11 by simply using a bipolar or field effect transistor 16 (see. Fig. 2), the potential-free - for example via an optocoupler 17 - from a conventional, with the mains voltage u1 fed phase shifter 8 can be periodically controlled.

Within the interrupter switch 9 of the control circuit 3 can, in principle, be used as an electronically controllable switching speech 11 also used other electronic components will; such as, for example, an anti-parallel connection of GTO thyristors, which is not only achieved by the loss of the anode-cathode voltage go out, but also by a switch-off signal to their gate (namely in the present case for Time ta) can be deleted. However, additional technical effort is then required, especially for reclosing of the heating circuits 6 after the next zero crossing of the current i1 fed in from the network 1. Besides, the In Fig. 1 shown circuit implementation for the interrupter switch 9 is therefore of particular advantage, because the diode bridge circuit 10 is a particularly simple protective measure against excessive pulses of the Ignition voltage uZ can be realized; by simply at least

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two with respect to the diagonal 12 diametrically opposite one another of the diodes are used as Zener diodes 18, the breakdown voltage of which limits the level of the ignition voltage uZ.

Contrary to the, in the interest of clarity in FIG. 3 provided ^ lighting period immediately before the expiry of each half cycle of the input current drawn from network 1 i1 can also be provided, the lighting time period a symmetrically around an extreme of the current i1 or symmetrically at the respective current zero crossing. Always determines the time span in which there is no current i3 across the shunt flows in the form of the control circuit 3, the lighting period a; and during the remainder of each half period the heating circuits 6 are connected in series to the ignition electrodes 5 until the next interruption and ignition point ta heat up again.

Less clear current-time relationships than those on which the explanation is based in FIG. 3 arise when these Switching on the heating circuits 6 via the control circuit 3 additionally has a smoothing throttle 19. This provides however, the advantageous effect of increasing the input current 11 independently of the ignition point ta that has just been set Approximate sinusoidal shape and thereby, in coordination with the inductance of the choke 7> Interference from the switching operation of the control circuit 3 in the network 1 is essential to be able to reduce.

Surprisingly, it has been shown that this circuit arrangement not only for stable dimmer operation of both conventional and modern (thin) fluorescent tubes is suitable, but also the possible uses of the thin fluorescent tubes at significantly lower levels Operating temperatures extended. During namely after

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the manufacturer's data sheets guarantee that the thin fluorescent tubes will only ignite up to ambient temperatures of minus 25 ^° C. and adapted thermal insulation is required at lower temperatures, these modern, thin fluorescent tubes ignite reliably even at minus when the circuit arrangement according to the invention is used without any additional measures 5O ⁰ C operating temperature. This is of particular interest when used in lighting systems for passenger compartments of vehicles that are parked outdoors at night, for example, and should be ready for use the next morning without malfunctions even after exposure to low night temperatures.

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List of reference symbols

a light period (of 2)

i current curve

u voltage curve

Z ignition

ta ignition timing

1 network (to supply 2)

2 fluorescent tubes (with 6-6)

3 control circuit (for 6-6 and 5/5)

4 power switches (between 1 and 2)

5 ignition electrodes (of 2)

6 heating circuits (of 2; as 5)

7 throttle (between 1 and 2)

8 phase shifters (in 3)

9 circuit breakers (parallel to 2, controlled from 8)

10 diode bridge circuit (in 9 for 11)

11 Interrupter switching path (between 6-6)

12 bridge diagonals (with 11 between 13-14)

13 Cathode counter-circuit (at 12)

14 anode counter-connection (at 12)

15 connections (from 9/11 to 6/5)

16 transistor (in 9 as 11)

17 optocouplers (between 8 and 9/16)

18 zener diodes (in 10 for uZ)

19 smoothing choke (between 6 and 3/9)

Claims (5)

Expectations . Circuit arrangement for ignition and for brightness control of fluorescent lamps, especially thin fluorescent tubes (2), their ignition electrodes (5) by two in series with an adjustable phase shifter control circuit (3) and an upstream throttle (7) are provided, heating circuits (6), characterized, that between the heating circuits (6) an interrupter which can be periodically controlled from an adjustable phase shifter (8) Switch (9) is arranged. 2. Circuit arrangement according to claim 1, characterized in that that the interrupter switch (9) is constructed as a diode bridge circuit (10), in which in the bridge diagonal (12) between oppositely interconnected diode-cathodes (13) and oppositely interconnected diode anodes (14) an electronically controllable interrupter switching path (11) is formed. 20th 3. Circuit arrangement according to claim 2, characterized in that that the interrupter switching path (11) as a transistor (i6) is formed, which can be driven potential-free from the phase shifter (8). ... 11 4. Circuit arrangement according to claim 2 or 3, characterized in that that at least two with respect to the diagonal switching path (11) diametrically opposite diodes of the bridge circuit (10) are designed as Zener diodes (18). 5. Circuit arrangement according to one of the preceding addresses, characterized, that with the heating circuits (6) and the breaker switch (9) the control circuit (3) is additionally connected in series with a smoothing choke (19).