DE10127135B4 - Dimmable electronic ballast - Google Patents

Abstract

dimmable electronic ballast for operating at least one fluorescent lamp, comprising a first module (2) for radio interference suppression and rectification of the Mains voltage and a second module (3) with a half-bridge converter for operating the fluorescent lamp (1) with a high-frequency alternating voltage and at least one load-side series resonant circuit (4) for adjustment the operating point of the fluorescent lamp (1) and for generating the ignition voltage and comprising a drive circuit (5) for driving the half-bridge converter and having a transformer (7) for the production of the lamp filaments necessary heating voltage, its primary winding with a coupling capacitor (6) connected in series, characterized characterized in that the coupling capacitor (6) in conjunction with a further capacitor (8) via a controllable switch (9) can be supplemented to form a capacitive voltage divider, that the primary winding of the transformer (7) on one side with the center tap of the capacitive voltage divider and on the other side connected to a measuring circuit (12) which is through the transformer (7) flowing primary current recorded and that this measured value ...

Description

The The present invention is based on one according to the preamble of the main claim designed dimmable electronic ballast to operate from at least one fluorescent lamp.

such Facilities are usually designed for fluorescent lighting to operate. To fluorescent lamps a long life or a size To reach number of switching games, it is necessary before the ignition to preheat the lamp filaments. For dimmable ballasts have to that too during of the burning operation of the fluorescent lamp, the lamp filaments with a sufficient heating voltage are supplied, so that they are not premature wear out. A common way the needed Heating voltage for providing the lamp filaments is the primary winding a comparatively small transformer over one Coupling capacitor to the half-bridge center to switch. The transformer usually has a number of secondary windings which corresponds to the number of lamp filaments associated with the Heating voltage to be supplied.

By the EP 0 748 146 A1 is a the preamble of the main claim corresponding circuit arrangement for lamp filament preheating of fluorescent lamps known. On the part of the users of electronic ballasts, there is often a desire that the fluorescent lamp can be ignited as soon as possible after switching on the mains voltage, ie that the intermediate phase of the preheating takes only very little time (about 0.5 sec). In order to be able to supply the necessary pre-heating energy to the lamp filaments in such a short time, the preheating currents must be correspondingly high. Technically, it is not a problem to interpret the transmission ratio of the transformer so that there are sufficiently high heating voltages available.

When Result of it flow but also after ignition the fluorescent lamp continues to heat currents through the lamp filaments, in their height while of the combustion operation disproportionately high are and thus generate at least an unnecessarily high power loss, the efficiency of the overall arrangement (fluorescent lamp / ballast) considerably decreases. If the fluorescent lamp on such an electronic ballast not only operated in their nominal range, but optionally also can be dimmed to lower brightnesses, so on the one hand is a minimized heating operation of the lamp filaments or on the other hand a heating operation with certain, from the lamp manufacturer predetermined or resulting from standard data sheets heating currents desirable. If the filament temperature is too low, the electron-emitting Coating on the lamp filaments quickly eroded, resulting in the life expectancy of Fluorescent lamp can significantly lower. It also lies At the same time, users often wish to have one such dimmable electronic ballast short circuit cases, caused z. B. by an installation error, by a faulty fluorescent lamp etc., to know for sure so that it does not become disproportionate Heating current generation of the transformer comes. Due to a disproportionate high heating current can namely to damage on the ballast or the total failure of the electronic ballast, which is not acceptable.

Furthermore, by the US Pat. No. 5,920,155 an electronic ballast with a capacitive voltage divider become known, to which the primary winding of a Heizspannungsübertragers is connected. However, this voltage divider can not be connected via a controllable switch.

In addition, through the DE 197 08 792 A1 and the EP 490 330 A1 in each case an electronic ballast with a measuring circuit for detecting the current flowing through the transformer primary current has become known.

Of the present invention is based on the object, a dimmbares electronic ballast to realize which short circuit cases z. Due to installation errors, faulty fluorescent lamps, etc. safely recognizes and in such a Trap causes its automatic shutdown and which on the one hand high heating voltages during the Preheat time to allow a short preheating phase, as well as during the Burning operation suitable heating voltages for the lamp filaments for dimming the fluorescent lamp up to low brightness levels for disposal provides, resulting in an economical operation with long life expectancy the fluorescent lamp and at the same time a high level of operational safety is realized.

According to the invention Task specified by the characterizing part of the main claim Characteristics solved.

It is particularly advantageous that the controllable switch only has to be switched on once after expiration of the preheating time and then remains conductive during the entire firing operation of the fluorescent lamp, whereby a very simple and inexpensive favorable control of this switch is realized.

Furthermore It is particularly advantageous that disproportionate in such a dimmable electronic ballast high heating current generation, z. B. caused by a short circuit, is detected safely and automatically leads to the shutdown of the ballast, so that in a simple way damage to the electronic ballast are largely excluded.

at Half-bridge converters in electronic ballasts it is often common a capacity of Half-bridge center point to put against the ground line of the supply voltage. This capacity slows down the transhipment process of the half-bridge center while the short dead time, in which both circuit breakers of the half bridge lock. As a result, flows a large Part of the Umladestromes by the described capacity instead through the parasitic capacities the half-bridge circuit breaker, where he due to the parasitic resistors in series with the parasitic capacitances a power loss would produce. Since the load circuit during the charge phase represents a power source, arise in a not with such high series resistances affected additional capacity much lower losses. Therefore, it is still in accordance with the present invention advantageous in that the capacitive voltage divider consists of a coupling capacitor and another capacitor which are dimensioned that this is a suitable capacitive load on the output of the Form half-bridge converter, the while the burning operation of the fluorescent lamp a low-loss switching the circuit breaker ensures.

Further advantageous embodiments of the subject invention are in the dependent claims specified. Based on two embodiments becomes the subject of the invention described in more detail, show:

1 : a block diagram according to the first embodiment;

2 : A block diagram according to the second embodiment.

As can be seen from the figures, such a circuit arrangement or such a dimmable electronic ballast for operating at least one fluorescent lamp 1 essentially a first assembly 2 for radio interference suppression and rectification of the mains voltage, a second module 3 with a half-bridge converter for operating the fluorescent lamp 1 with a high-frequency alternating voltage and at least one load-side series resonant circuit 4 for setting the operating point and for generating the ignition voltage for the fluorescent lamp 1 on. In addition, a drive circuit 5 for controlling the second module 3 and a coupling capacitor 6 and a transformer 7 for generating the for the lamp filaments 14 . 15 necessary heating voltage provided.

The coupling capacitor 6 is in connection with another capacitor 8th via a controllable switch 9 can be supplemented to a capacitive voltage divider. The controllable switch 9 in turn is via its control terminal to the drive circuit 5 in connection. The activation of the controllable switch 9 thus takes place as needed on the drive circuit 5 , The primary winding of the transformer 7 is with the other capacitor 8th and with a measuring circuit 12 connected, which by the transformer 7 recorded flowing primary current. This detected measured value is used to check the permissibility of the flowing primary current one in the drive circuit 5 existing comparator element 13 fed. The lamp filaments 14 . 15 the fluorescent lamp 1 On the one hand are formed as capacitors impedances 10 . 11 on the other hand, with the secondary side of the transformer 7 keep in touch.

In the burning operation, a significant reduction in the heating voltage at the secondary windings of the transformer 7 to effect, there is a corresponding control of the controllable switch 9 via the drive circuit 5 , Thus, also by the lamp filaments 14 . 15 flowing heating currents are reduced as needed. Ie. the heating current required during the preheating phase becomes suitable for the dimming value of the fluorescent lamp in the firing mode 1 adapted, so that always a sufficiently high heat output of the lamp filaments 14 . 15 is present, but the high heating power required during the preheating, undergoes a significant reduction. Too low heat output of the lamp filaments 14 . 15 However, it is also effectively excluded. For this purpose, the controllable switch 9 during the preheating phase, which during the preheating phase of the lamp filaments 14 . 15 necessary high heating current is generated so that sufficient Wendelvorheizung within a very short time (about 0.5 sec) takes place. Upon completion of the preheat phase becomes the controllable switch 9 by driving by means of the drive circuit 5 closed as well as during the burning operation of the fluorescent lamp 1 kept permanently closed. This is effectively achieved that during the burning operation of the fluorescent lamp 1 the lamp filaments 14 . 15 only be charged with much lower adjusted heating currents. This training is a on the one hand fast preheating, so that the ignition process can be done virtually without delay very quickly after switching on the mains voltage. On the other hand, it is achieved that in the burning operation, a targeted lowering of the heating currents takes place, so that easily dimming operations of the fluorescent lamp 1 can be made up to very low brightness values, this results in a much lower power consumption and at the same time operation of the fluorescent lamp 1 which leads to a long life expectancy. The capacitive loading of the second module designed as a half-bridge converter 3 is with closed controllable switch 9 , due to an adapted dimensioning of the coupling capacitor 6 and the other capacitor 8th suitable for a particularly low-loss switching of the transistors of the second module 3 to realize.

As in particular from 1 this is apparent in the drive circuit 5 existing comparator element 13 executed as a comparator. This offers z. B. the advantage that a particularly cost-effective implementation of the above functions is possible.

As in particular from 2 indicates, the control circuit 5 a microcontroller provided with an A / D converter 16 on which also the comparator element 13 includes. This offers z. B. the advantage is a microcontroller 16 In such dimmable electronic ballasts already for other reasons that this can be used to represent the prescribed functions readily with.

Claims (6)

Dimmable electronic ballast for operating at least one fluorescent lamp, comprising a first assembly ( 2 ) for radio interference suppression and rectification of the mains voltage and a second assembly ( 3 ) with a half-bridge converter for operating the fluorescent lamp ( 1 ) with a high-frequency AC voltage and at least one load-side series resonant circuit ( 4 ) for adjusting the operating point of the fluorescent lamp ( 1 ) and for generating the ignition voltage and having a drive circuit ( 5 ) for driving the half-bridge converter and having a transformer ( 7 ) for generating necessary for the lamp filaments heating voltage whose primary winding with a coupling capacitor ( 6 ) is connected in series, characterized in that the coupling capacitor ( 6 ) in conjunction with another capacitor ( 8th ) via a controllable switch ( 9 ) can be added to a capacitive voltage divider, that the primary winding of the transformer ( 7 ) on one side with the center tap of the capacitive voltage divider and on the other side with a measuring circuit ( 12 ) connected by the transformer ( 7 ) detected, and that this measured value for checking the permissibility of the flowing primary current to a in the drive circuit ( 5 ) existing comparator element ( 13 ) can be fed. Dimmable electronic ballast according to claim 1, characterized in that in the drive circuit ( 5 ) existing comparator element ( 13 ) is designed as a comparator. Dimmable electronic ballast according to claim 1, characterized in that the drive circuit ( 5 ) a, provided with an A / D converter, microcontroller ( 16 ), which also contains the comparator element ( 13 ). Dimmable electronic ballast according to claim 3, characterized in that the control of the controllable switch ( 9 ) via the microcontroller ( 16 ) of the drive circuit ( 5 ) is feasible. Dimmable electronic ballast according to one of claims 1 to 4, characterized in that the dimming process for the at least one connected fluorescent lamp ( 1 ) by varying the operating frequency of the half-bridge converter ( 3 ) is feasible. Dimmable electronic ballast according to one of claims 1 to 5, characterized in that in front of the lamp filaments ( 14 . 15 ) of the fluorescent lamp ( 1 ) formed as capacitors impedance ( 10 . 11 ) available.