EP1962565B1 - Ballast with power commutation - Google Patents

Abstract

The ballast (1) has half bridge inverters (4, 8) provided with a frequency-control input (17), and a line circuit (26) e.g. mechanical single-pole switch, for activating or deactivating a resonance capacitor (25). An evaluating circuit (18) detects activation or deactivation of the resonance capacitor and influences the frequency-control input. The inverters are operated with operating frequencies and switched between the operating frequencies. The line circuit switches the inverters from one operating frequency to another operating frequency.

Description

The invention relates to an electronic ballast, which is switchable in its performance.

For fluorescent lamps and other gas discharge lamps electronic ballasts are increasingly used. These are usually fed on the mains side and ensure the power supply of the gas discharge lamp and, if necessary, for the generation of ignition pulses. Other functions, such as. Error monitoring, dimming, etc., are common.

Frequently fluorescent lamps are equipped with electrodes that are preheated prior to ignition to facilitate the ignition process. But there are also ballasts that ignite ordinary or specially designed fluorescent lamps without electrode preheating. Such ballasts are referred to as cold start ballasts. They usually work with a fixed predetermined and neither during ignition nor otherwise in operation changing inverter frequency of, for example, 30 kHz. On the output side, they are provided with a current-limiting inductor, which is associated with at least one resonance capacitor. In the case of an unlit lamp, this leads to a resonance increase in the voltage applied to the lamp, which leads to lamp ignition. After ignition of the lamp due to the caused by the lamp damping of the resonant circuit disappears, the voltage overshoot.

Due to the fixed predetermined operating frequency of such a ballast, the output side choke has a certain impedance, whereby the lamp current is fixed. Lamps that require a different lamp current are therefore not operable.

The DE 2005 022 592 A1 describes a circuit arrangement for operating a discharge lamp with a resonance capacitor, which can be connected via a controlled switching element parallel to the discharge lamp. The switching element is switched by an unspecified control circuit. During a preheating or ignition phase of the discharge lamp, the resonant capacitor can be switched in parallel to the discharge lamp by closing the switching element. After ignition of the lamp, the switching element is opened again. During dimming of the lamp, the switching element is opened and the parallel branch is separated with the resonance capacitor in order to reduce the lamp current.

It is an object of the invention to provide an electronic ballast for cold starting discharge lamps, in particular Fluorescent lamps, with which a performance adjustment in a simple and comfortable way is possible.

• Das erfindungsgemäße Vorschaltgerät weist nach Anspruch 1 einen Wechselrichter auf, der einen Frequenz-Steuereingang aufweist. An dem Frequenz-Steuereingang kann die Frequenz des Wechselrichters durch ein anliegendes Signal geändert werden. Im einfachsten Fall kann die Wechselrichterfrequenz zwischen zwei Sollfrequenzen umgeschaltet werden. Damit ergeben sich dann bei verschiedenen Wechselrichterfrequenzen verschiedene Lampenströme, wodurch Lampen verschiedener Leistung an ein und dasselbe Vorschaltgerät angeschlossen werden können.

This object is achieved in particular with the ballast according to claim 1, but also with the ballast according to claim 2:

• The ballast according to the invention comprises according to claim 1 to an inverter having a frequency control input. At the frequency control input, the frequency of the inverter can be changed by an applied signal. In the simplest case, the inverter frequency can be switched between two setpoint frequencies. This then results in different inverter frequencies at different lamp currents, which lamps of different power can be connected to one and the same ballast.

In the case of the ballast according to the invention, it is also ensured in this case that the desired voltage resonance peaks for the ignition of the cold fluorescent lamp are generated at the different operating frequencies. For this purpose, at least one resonance capacitor is provided, which can be activated or deactivated. Activation or deactivation occurs e.g. by setting or interrupting a line connection.

In the ballast according to the invention, an evaluation unit ensures that the activation or deactivation of the resonance capacitor is detected and the frequency control input of the inverter is influenced accordingly. This ensures that the inverter is always operating at the frequency that is substantially equal to the resonant frequency of the resonant circuit, that of the output choke and the resonance capacitors is formed. If, for example, the resonance frequency is reduced by activating an (additional) resonant capacitor, the evaluation unit automatically adjusts the operating frequency of the inverter by lowering it. The activatable and deactivatable resonance capacitor is tuned in its effect on the resonant frequency of the output circuit of the ballast to the desired frequency change. Likewise, a frequency-determining component, for example a frequency-determining capacitor, can be activated and deactivated on the inverter and tuned to the same frequency change.

This concept allows the ballast to be frequency and hence power adjusted by setting or breaking a single line connection. The independent setting of the operating frequency of the inverter and the resonant frequency of the lamp output circuit is not possible. Rather, the frequency adjustment of the resonance output circuit of the ballast via the evaluation unit is firmly linked to the frequency change of the inverter.

In the ballast according to the invention according to claim 1, the operator takes a manual action on the resonant circuit of the ballast whereupon the inverter automatically adjusts its operating frequency. However, it is also the reverse procedure possible, as it is realized in the ballast according to claim 2. There, the operator makes a frequency adjustment action on the inverter, whereupon the evaluation unit deactivates or activates a corresponding resonance capacitor. Here, too, the basic idea is realized that a Frequenzeinstellmaßnahme a component of the overall arrangement a automatic frequency adjustment of another component of the circuit results.

In principle, it is possible to provide a plurality of independently activatable or deactivatable Resonanzkondenstoren and adjust the inverter to several different frequencies accordingly. However, in most cases, it is sufficient if the ballast is switchable between two different resonant frequencies and operating frequencies. In any case, regardless of the number of possible operating frequencies is guaranteed in each case in the invention that a switching of the resonant frequency automatically has a switching of the operating frequency result (and vice versa).

For activating or deactivating the resonance capacitor or for otherwise influencing the frequency of the resonance circuit, a line branch is preferably provided which can be cut, for example. This may be a suitably trained Leiterzug, a circuit board, a wire bridge, a plug-in contact or the like. Alternatively, to activate or deactivate a resonant capacitor or other frequency-determining component, a wire bridge can also be provided which is to be plugged into corresponding sockets or terminals or which is to be used in another suitable way for bridging two contacts. Also, simple switches or the like, e.g. find application through fusible conductor areas.

Further details of advantageous embodiments of the invention will become apparent from the drawings and the accompanying description or subclaims. The description is limited to essential aspects of the invention and other conditions. The drawing is to be used as a supplement.

• Fig. 1 ein Vorschaltgerät mit angeschlossener Lampe in schematischer Darstellung;
• Fig. 2 eine erste Ausführungsform einer Auswerteeinheit in schematischer Darstellung;
• Fig. 3 eine zweite Ausführungsform einer Auswerteeinheit in schematischer Darstellung;
• Fig. 4 bis 9 weitere Ausführungsformen des erfindungsgemäßen Vorschaltgerätes jeweils in schematischer Darstellung.

In the drawings, embodiments of the invention are illustrated. Show it:

• Fig. 1 a ballast with a connected lamp in a schematic representation;
• Fig. 2 a first embodiment of an evaluation in a schematic representation;
• Fig. 3 a second embodiment of an evaluation in a schematic representation;
• Fig. 4 to 9 further embodiments of the ballast according to the invention in each case in a schematic representation.

In FIG. 1 is a ballast 1 illustrated, to which a gas discharge lamp 2 is connected. The ballast 1 is connected via not further illustrated components to an electrical supply network. These electrical components provide a DC voltage, for example, in the amount of 300 V at a node 3 ready. Such components are, for example, a line filter, a mains rectifier, a step-up converter, for example in the form of a flux converter and possibly a storage capacitor for screening the DC voltage provided by the 300 V exemplified. In addition, suitable circuit means may be present to provide an operating voltage of, for example, 12 or 15 V or other desired height. Such may be necessary to supply components of the ballast 1 with operating voltage.

To the ballast 1 includes an inverter, which is formed by an inverter half bridge 4 in the above embodiment. This consists of two electronic switches 5, 6, for example. In the form of field effect transistors which are connected in series and alternately open and close. The series circuit is connected at one end to the node 3 and at its other end to ground 7. To control these switches 5, 6, these are connected via their control inputs to a half-bridge driver 8, which is usually formed by an integrated circuit. The half-bridge driver opens and closes the switches 5, 6 alternately at an operating frequency fixed by an RC circuit 9. To the connected to the half-bridge driver 8 RC circuit 9 includes a frequency-determining resistor 10 and in the present example, two frequency-determining capacitors 11, 12. The resistor 10 is connected to terminals 13, 14. With The terminal 14 is also the series circuit of the capacitors 11, 12 connected, which is grounded at its other end.

The connection point 15 between the capacitors 11, 12 forms a frequency control point at which the operating frequency of the half-bridge driver 8 can be influenced. If the capacitor 12 is bypassed, only the capacitor 11 is effective. The half-bridge driver 8 then operates at a first lower frequency. However, if the connection point 15 is left free, the series connection of both capacitors 11, 12 is active. The effective total capacity is lower and the operating frequency of the inverter half-bridge 8 rises to a second value.

At the connection point 15, an electronic switch 16 such as. A bipolar transistor can be connected, which is grounded with its emitter. Its control input 17, i. specifically, for example, its base is connected to an evaluation circuit 18. This can selectively open or close the switch 16 so that it shorts or releases the capacitor 12.

At the connection point of the switches 5, 6 of the inverter half bridge 4, a lamp branch is connected, which includes a resonant circuit 19. This includes, for example, a throttle 20 which is connected at one end to the inverter half-bridge 4 and at its other end to a coupling capacitor 21. To the series circuit of the inductor 20 and the coupling capacitor 21, an electrode 22 of the lamp 2 is connected, the other electrode 23 is connected to ground. Alternatively, the coupling capacitor 21 can be omitted and the electrode 23 on a capacitive voltage divider be connected. It is also possible to provide a second inverter half-bridge, which is connected in push-pull to the existing inverter half bridge 4 and connected to the electrode 23. In this case, the electronic ballast 1 has a full-bridge inverter.

To ignite the lamp 2, a resonance capacitor 24 is provided. This is connected in parallel to the lamp 2. He determines together with the throttle 20 a first resonant frequency.

The resonance capacitor 24, a further resonance capacitor 25 is connected in parallel. The parallel connection of the resonance capacitors 24, 25 establishes a different resonance frequency together with the inductor 20. The resonance capacitor 25 can be activated or deactivated via a suitable technical means. For this purpose, for example, a severable line connection 26 can serve, which connects a connection of the resonance capacitor 25 to the electrode 22. This severable line connection may be an exposed trace of a printed circuit board to be severed with a mounting tool, a wire bridge to be removed or severed with a side cutter or other suitable tool, a solder bump that may be removed with the soldering iron, or the like. Instead of the severable line connection 26, a manufacturable line connection can be provided, for example, two sockets can be provided which can receive a connecting wire bridge, two pins on which a connector can be placed, which can be connected by wire or with each other, for example to be twisted by a pair of pliers, to connect. Other appropriate means such as simple switches or the like can be used.

The evaluation unit 18 is connected with its input 27 to the non-ground end of the resonance capacitor 25 and serves to detect whether the resonance capacitor 24 has been activated or whether it has been deactivated.

FIG. 2 illustrates a simple embodiment of the evaluation unit 18. at its input 278, at least one preferably connects a plurality of high-resistance resistors 28, 29, which are connected in series. The resistors 28, 29 are dimensioned so large that they do not substantially attenuate the resonant circuit consisting of the choke 20 and the resonance capacitors 24, 25. Connected to the resistors 28, 29 is a voltage doubler rectifier circuit 30. The output signal of this voltage doubler rectifier circuit 30 is zero when no AC voltage is applied to the capacitor 25. If AC voltage is applied to resonant capacitor 25, it is significantly greater than zero. It is then sufficient to make the switch 16 current-conducting, ie to close.

An alternative evaluation unit is in FIG. 3 illustrated. It consists of a one-way rectifier circuit with high impedance input resistance and a capacitor which is connected to the base of the subsequent switching transistor.

The ballast 1 described so far operates as follows:

It is assumed that initially a lamp 2 high power is to operate. This lamp 2 requires a high lamp current. The line connection 26 is present. This is when switching on the power and the incipient operation of the inverter half-bridge 4 on the Kondenstor 25 an AC voltage present. The evaluation unit 18 detects this and makes the switch 16 electrically conductive. Thus, only the capacitor 11 is active. The capacitor 12 is short-circuited. The half-bridge driver 8 thus operates at a relatively low frequency. This operating frequency coincides with the resonance frequency, which results from the sum of the capacitances of the resonance capacitors 24 and 25 and the inductance of the inductor 20. Thus, a resonance-elevated voltage arises at the electrode 22. The lamp 20 lights. By the ignition of the lamp, the resonance of the lamp output circuits or resonant circuit consisting of the choke 20 and the resonance capacitors 24, 25 is attenuated. The throttle 20 limits the lamp current and the arrangement goes into continuous operation.

If the operator wants to use the same ballast 1 for a lamp 2 of lesser power, it cuts through the line connection 26. Thereupon, the operation of the ballast 1 is as follows:

When switching on the ballast 1, the inverter half-bridge 4 starts operating. However, no AC voltage appears at the resonance capacitor 25. The evaluation unit 18 outputs no signal at its output. Thus, the switch 16, ie the transistor in question remains non-conductive. Now, the series connection of the capacitors 11, 12 frequency determining. The half-bridge driver 8 therefore operates at a higher (second) operating frequency. This agrees with the resonance frequency, which results from the capacity of the resonance capacitor 24 and the inductance of the inductor 20. Thus, in turn, a sufficient voltage overshoot to ignite the (weaker) lamp 2 is present. If this is ignited, the arrangement is in normal operation, in which the inductor 20 now limits the current due to the higher operating frequency of the inverter half-bridge 4 to a lower value.

The ballast 1 described so far can be modified. For example, the resonant capacitors 24, 25, such as FIG. 4 shows, to be connected in series. The activation or deactivation of the resonance capacitor 25 can be accomplished by a bridge connection 26, which is connected in parallel with the resonance capacitor 25. In FIG. 4 For this purpose, a jumper is indicated. In this device, the inverter half bridge 8 is set to a lower frequency when the line connection 26 is present, while being set to a higher frequency when the line connection 26 is absent. The evaluation unit 18 contains in this case in addition to the in FIG. 2 illustrated circuit, a signal-inverting device or other circuitry measures that cause the switch 16 is conductive when no input to the input 27 AC voltage. Otherwise, due to the structure and function of the ballast 1 after FIG. 4 refer to the above description.

Another variation illustrates FIG. 5 , There, the resonant capacitor 25 is activated or deactivated by establishing or disconnecting its ground connection via the line connection 26. Again this condition becomes monitored by the evaluation unit 18. Because of function and structure otherwise refer to the above description.

Another modification shows FIG. 6 , This reverses the above-described functional principle. The disconnectable line connection 26 now activates or deactivates the frequency-determining capacitor 12 of the RC circuit 9. The inverter half bridge 8 accordingly operates at a higher or lower frequency. It can now activate or deactivate the resonance capacitor 25 in that its ground connection is designed as a fuse 31. The half-bridge driver 8 now has a logic function that detects the removal of the line connection 26. This can be done either by internal evaluation of the self-adjusting operating frequency or by a separate line connection 32, via which the line connection 26 is controlled. If the half-bridge driver 8 detects the interruption of the line connection 26, it increases its operating frequency to the operating frequency which is now determined solely by the capacitor 11. But first, it changes its frequency to a value at which an excessive resonance current occurs at the resonance capacitor 25, so that the fuse 31 melts. Thereafter, the half-bridge driver transitions to an operating frequency corresponding to the resonant frequency of the reactor 20 in conjunction with the resonant capacitor 24.

FIG. 7 illustrates another modified embodiment of the circuit according to the invention. For the description, reference is made to the previous description with reference to the same reference numerals. The circuit of the ballast 1 after FIG. 7 differs from the above-described embodiments by the type of frequency determination of the half-bridge driver 8. Here are as frequency-determining Components resistors 11 ', 12', 10 'are provided. Otherwise, the function is as described above.

In the embodiment according to FIG. 8 a modified design of the resistor network is provided for frequency determination. Again, the frequency switching is done by activating or deactivating a frequency-determining device, here the resistor 12 ".

FIG. 9 illustrates the application of the invention in a ballast for fluorescent lamps with preheated electrodes. The resonance-determining capacitor 24 'sits here between the ends of the preheatable electrodes whose other ends are connected via the coupling capacitor 21 and the inductor 20 to the inverter half bridge 4 and to ground. Again, a line connection 26 is provided, via which, in addition to the capacitor 24 ', the further capacitor 25' can be activated or deactivated.

A ballast for cold ignited fluorescent lamps has an inverter with at least two different frequencies. A frequency control input allows switching from the one operating frequency. On the output side, it has a resonant circuit with two resonance frequencies. Between the resonance frequencies, for example, a capacitor 25 is switched over by activation or deactivation of a resonant component. An evaluation unit detects the activation or deactivation of the resonant component 25 and outputs a corresponding signal to the frequency control input of the inverter so that it operates with the respectively appropriate operating frequency.

LIST OF REFERENCE NUMBERS

1

ballast

2

lamp

3

circuit point

4

Inverter half bridge

5

switch

6

switch

7

Dimensions

8th

Half-bridge driver

9

RC circuit

10

resistance

11

capacitor

12

capacitor

13

connection

14

connection

15

junction

16

switch

17

control input

18

evaluation

19

resonant circuit

20

throttle

21

coupling capacitor

22

electrode

23

electrode

24

Resonant capacitor

25

Resonant capacitor

26

line connection

27

entrance

28

resistance

29

resistance

30

Voltage doubler rectifier circuit

31

fuse

32

line connection

Claims (10)

1. Ballast (1), in particular for fluorescent lamps,
   with an inverter (4, 8) with a frequency control input (17),
   with a resonant circuit connected to the inverter (4, 8) on the output side with at least one resonant capacitor (25),
   with at least one switching element (26) for activating or deactivating the resonant capacitor (25),
   characterised in that
   an evaluation unit (18) is provided, which is connected at its input to the unearthed end of the resonant capacitor (25), and which detects the activation or deactivation of the resonant capacitor (25) and emits a corresponding signal to the frequency control input (17) of the inverter (4, 8), so that this operates with a respectively appropriate operating frequency.
2. Ballast (1), in particular for fluorescent lamps,
   with an inverter (4, 8), which can be operated with a first and with a second operating frequency,
   with at least one switching element (26) for switching over the inverter (4, 8) from the first to the second operating frequency and vice versa,
   with a first resonant capacitor (24),
   with a second resonant capacitor (25),
   characterised by
   an evaluation unit (8, 32) for detecting whether the inverter is operated with the first or second operating frequency and for activating or deactivating the second resonant capacitor (25) accordingly for automatic frequency adjustment of a resonant frequency of a resonant circuit, so that the resonant frequency substantially corresponds to the operating frequency of the inverter.
3. Ballast according to claim 2, characterised in that the earth connection of the second resonant capacitor (25) is configured as a safety fuse (31), wherein the deactivation of the second resonant capacitor (25) occurs by means of the inverter (4, 8) by it changing its frequency to a value for generating an oversize resonant current, as a result of which the safety fuse (31) melts.
4. Ballast according to claim 1, characterised in that the inverter (4, 8) can be switched over between at least two different operating frequencies.
5. Ballast according to claim 1, characterised in that the resonant capacitor (25) or the resonant capacitor (25) and a further resonant capacitor (24) together with a choke (20) define a resonant frequency, which is the same as one of the operating frequencies of the inverter (4, 8).
6. Ballast according to claim 5, characterised in that a further resonant capacitor (24) is provided, which with the choke (20) defines a resonant frequency, which is the same as another operating frequency of the inverter (4, 8).
7. Ballast according to claim 1, characterised in that the switching element (26) is a separable conductor.
8. Ballast according to claim 1, characterised in that the switching element (26) is a jumper.
9. Ballast according to claim 1, characterised in that the switching element (26) is a mechanical single-pole switch.
10. Ballast according to claim 1, characterised in that the evaluation unit (18) has an a.c. voltage-sensitive input (27) and a switching signal output, which is connected to the frequency control input (17).

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