EP2498584A1 - Pre-switching device for high pressure gas discharge lamps - Google Patents

Abstract

The arrangement (10) e.g. full bridge circuit arrangement, has a half-bridge inverter (12) connected to a gas discharge lamp (11) e.g. high-pressure discharge lamp. An impulse train (F1) of frequency reverses polarity of lamp current (iL) with low frequency. Another impulse train (F2) of higher frequency controls a level of the current, and control circuits (29- 31) control the inverter and the latter impulse train in an operating mode during impulse of the former impulse train to constantly raise the level of the current opposite to end of the impulse. An independent claim is also included for a method for operating a circuit arrangement for operating a discharge lamp.

Description

The invention relates to an operating method and a circuit arrangement for a ballast, which is particularly suitable for the operation of high-pressure gas discharge lamps.

High-pressure gas discharge lamps are usually operated on full bridge circuits, such as those from the US 4,170,747 are known. Each bridge branch contains two electronic switches and thus forms an inverter half-bridge. Between both inverter half-bridges, the bridge diagonal is connected to the high-pressure discharge lamp and a series-connected, current-limiting choke.

The electronic switches of this bridge circuit are controlled by a control circuit, which thus dictates the operating regime of the bridge and the gas discharge lamp. With a first low frequency, e.g. diagonally opposite electronic switches are each activated to determine the direction of current flow. At a second higher frequency, one of the two activated electronic switches is clocked to limit the current flowing through the lamp.

The principle of controlling electronic switches with two different frequencies, on the one hand to apply to the high-pressure gas discharge lamp with an alternating current without DC component and on the other hand to limit the current with the aid of a relatively small throttle, is also applicable to half-bridge inverters. This suggests the EP 1 994 805 B1 to replace the electronic switches of a bridge branch with capacitors. The operating regime of the two electronic switches is to alternate with the low frequency alternately to clock the upper or the lower electronic switch of the bridge branch with high frequency.

High-pressure gas discharge lamps require reliable ionization for stable operation. During heating, the plasma recombines rapidly, so that it can spontaneously come to extinction of the lamp. That's why the beats EP 1 994 805 B1 the monitoring of the lamp voltage and readjustment of the lamp current before. When the lamp voltage increases, which means rapid high resistance, the current is increased to promote ionization and restore the lamp to low impedance.

However, it has been found that attempting to increase the current upon detection of an increase in lamp voltage may be too late for critical lamp types.

It is an object of the invention to provide a concept with which high-pressure gas discharge lamps can be operated safely even in difficult operating phases.

• Die erfindungsgemäße Schaltungsanordnung umfasst mindestens eine Wechselrichterhalbbrücke zur Speisung der Gasentladungslampe, wobei eine Steuerschaltung die Wechselrichterhalbbrücke mit einer ersten Impulsfolge mit einer ersten niedrigen Frequenz zur Umpolung der Lampe und mit einer zweiten Impulsfolge einer zweiten höheren Frequenz zur Steuerung des Lampenstroms angesteuert wird. Die Steuerschaltung variiert die zweite Impulsfolge dabei so, dass der Betriebsstrom vor dem mit niedriger Frequenz erfolgenden Umpolen des Lampenstroms vorzugsweise erhöht wird. Zumindest aber wird ein insbesondere bei Halbbrückenwechselrichtern vor dem Umpolen auftretendes Absinken des Lampenstroms verhindert. Somit wird Löschungsereignissen vorgebeugt, die sonst insbesondere beim mit der niedrigen Frequenz erfolgenden Umpolen mit einiger Wahrscheinlichkeit eintreten können. Der Erfinder hatte erkannt, dass insbesondere das Umpolen kritisch ist. Mit dem erfindungsgemäßen Konzept kann auf eine auf der Lampenspannungsüberwachung basierende schnelle Regelung des Lampenstroms verzichtet werden, was auch zu stabilerer flackerarmer oder flackerfreier Lichterzeugung führt.

This object is achieved with the circuit arrangement according to claim 1 and the method according to claim 11:

• The circuit arrangement according to the invention comprises at least one inverter half bridge for feeding the gas discharge lamp, wherein a control circuit, the inverter half bridge with a first pulse train with a first low frequency for reversing the lamp and a second pulse train of a second higher frequency is controlled to control the lamp current. The control circuit varies the second pulse train in such a way that the operating current is preferably increased before the low-frequency polarity reversal of the lamp current. At least, however, a decrease in the lamp current occurring in particular in the case of half-bridge inverters before the polarity reversal is prevented. Thus, cancellation events are prevented, which may otherwise occur with some likelihood, especially at the low frequency reverse polarity. The inventor had recognized that, in particular, the polarity reversal is critical. With the inventive concept can be dispensed based on the lamp voltage monitoring rapid control of the lamp current, which also leads to more stable flackerarmer or flicker-free light generation.

By this measure, the constant current or current increase immediately before the polarity reversal, the degree of ionization of the existing plasma is maintained or increased, especially in the vicinity of the electrodes, so that it can not come to the extinction of the gas discharge even in adverse operating conditions. In particular, the heating operation of the gas discharge lamp and / or operation with reduced power can thus be made safer.

The invention is particularly applicable to inverter half-bridges in which the end of the lamp branch remote from the inverter half-bridge is connected to a capacitive voltage divider. The potential of the voltage divider point gradually shifts to ground or to the operating voltage, respectively, in response to the low reverse pole frequency during a low frequency pulse. This has a reduction of over the throttle dropping voltage and thus a reduction in the lamp current result. By suitable variation of the pulses of the second pulse train this tendency can be counteracted, so that the operating current does not decrease towards the end of a pulse of the first pulse train, but remains constant or even increased.

The measure according to the invention can thus be used to make the operation of the gas discharge lamp less susceptible to unintentional extinguishment of the same, in particular in those operating phases in which the plasma recombines relatively easily, which is the case during heating or power reduction. In addition, the measure according to the invention can be used to reduce the necessary capacitance of the capacitors of the capacitive voltage divider, which contributes to a reduction of the size and the construction costs of the ballast.

In the circuit arrangement according to the invention, at least one inductive choke component is preferably arranged in series with the gas discharge lamp in the lamp branch, one end of the lamp branch being connected to the inverter half-bridge. The other end of the lamp branch may be connected to a further inverter half-bridge, so that the ballast operates in full-bridge circuit. In this case, for example, with a first low frequency in the bridge, diagonally opposite electronic switches may each be activated to determine the direction of current flow. At a second higher frequency, one of the two activated electronic switches is clocked to limit the current flowing through the lamp.

In any case, the electronic switches of the half bridges, regardless of whether the ballast in Half-bridge or full-bridge circuit is designed to be any type of suitable electronic switch, such as MOS transistors, bipolar transistors, IGBTs, JFETs, HEXFETs, both in P-channel technology and in N-channel technology. In particular, in a half-bridge both transistors of the same conductivity type as well as complementary transistors (eg npn and pnp or p-channel combined with n-channel) can be used.

In the preferred embodiment, the ballast operates in a half-bridge circuit with only two electronic switches in one bridge branch and two capacitors in the other bridge branch. The capacitors are at least sized so that they can absorb the amount of charge flowing through the lamp branch during a pulse of low frequency. The control circuit operates to open and close the electronic switches of the inverter half-bridge (s) in accordance with the first low and second higher frequency operating regimes. For example, the control circuit alternately releases the upper and lower switches of the inverter half bridge alternately with the first one, lower ones. The released switch is acted upon by a pulse train of higher frequency than the drive signal. Switching whether the upper or the lower switch is clocked, takes place with the lower frequency. According to the invention, the second pulse train, which has the higher frequency, in each case varies so that shortly before the polarity reversal a current drop is avoided or the increase of the lamp current is achieved. This can be done for example by raising a current setpoint towards the end of a pulse of the first frequency. The increase can be sudden, step-like, ramped following a steady function or similar. The magnitude of the increase in the current setpoint can be determined by external conditions, such as temperature, mean lamp voltage, lamp age, operating time that has elapsed since the power is turned on, desired lamp power and the like are made dependent and optionally readjusted. If the increase of the current setpoint is made dependent on the lamp voltage, this is averaged over at least one, preferably several periods of the first frequency, in order to avoid too fast and thus flickering control.

The operation of the ballast according to the invention is particularly suitable for the operation of critical lamp types, which otherwise have a strong tendency to extinguish.

• Fig. 1 eine erfindungsgemäße Schaltungsanordnung in schematisierter Darstellung;
• Fig. 2 Strom- und Spannungsverläufe der Schaltungsanordnung nach Fig. 1 zur Verdeutlichung der Funktion der Steuerschaltung;
• Fig. 3 und 4 Strom- und Spannungsverläufe von Vorschaltgeräten mit abgewandelten Betriebsregimes und
• Fig. 5 eine abgewandelte Schaltungsstruktur der erfindungsgemäßen Schaltungsanordnung.

Further details of advantageous embodiments of the invention are described in connection with an embodiment or will become apparent from the drawings or subclaims. Show it:

• Fig. 1 a circuit arrangement according to the invention in a schematic representation;
• Fig. 2 Current and voltage curves of the circuit according to Fig. 1 to clarify the function of the control circuit;
• 3 and 4 Current and voltage characteristics of ballasts with modified operating regime and
• Fig. 5 a modified circuit structure of the circuit arrangement according to the invention.

In Fig. 1 the circuit arrangement 10 for a ballast for a high-pressure gas discharge lamp 11 is illustrated schematically and partly as a block diagram. The high-pressure gas discharge lamp 11 may be an HID gas discharge lamp (metal halide lamp) or other gas discharge lamp, for example, a sodium vapor gas discharge lamp, mercury vapor gas discharge lamp, or the like. Although the invention is illustrated here for the example of the ballast for a high-pressure gas discharge lamp, it can also be applied to other gas discharge lamps.

The circuit arrangement 10 is designed as a half-bridge inverter circuit. It comprises an inverter half-bridge 12, which is arranged between an operating voltage-carrying line 13 and a ground potential-carrying line 14. The operating voltage may be in the range of a few hundred volts (e.g., 400V) and is provided by a feed circuit 15. This can e.g. be the connection of a power rectifier and a boost converter. Alternatively, the operating voltage on line 13 may also be provided by other means.

The inverter half-bridge 12 includes an upper switch 16 which is connected to the operating voltage leading line 13, and a lower switch 17 which is connected to the ground-carrying line 14. The switches 16, 17 are connected to one another at a circuit point 18 to which the lamp circuit 19 is connected. The switches 16, 17 may be any type of controlled electronic switch, e.g. MOSFETs, IGBTs or the like. They can have the same or opposite polarity.

The lamp circuit 19 includes a current limiting inductor 20 connected in series with the high pressure gas discharge lamp 11 is switched. The remote from the inverter half-bridge 12 end of the lamp circuit 19 is connected to a voltage divider point 21 of a capacitive voltage divider 22. This comprises an upper capacitor 23 and a lower capacitor 24. The capacitors 23, 24 are preferably poled capacitors of higher capacity, for example, switch-resistant electrolytic capacitors with eg some 100 uF. The upper capacitor 23 is connected to the operating voltage leading line 13. The lower capacitor 24 is connected to the ground potential leading line 14. At the voltage divider point 21, both capacitors 23, 24 are connected with their respective other end.

The circuit arrangement 10 can contain further capacitors 25, 26 leading from the lamp circuit 19 to ground and / or operating voltage, which serve, for example, for generating a resonance peak during ignition, for suppressing interference or for other purposes.

The electronic switches 16, 17 are each bridged by diodes 27, 28, which are poled in the rest state in the reverse direction and which may also be formed internally in the switches 16, 17. When you take the lamp current you take over each of the freewheeling current driven by the throttle 20.

For driving the switches 16, 17 is a driver circuit 29, the bases, gates or other control electrodes of the switches 16, 17 corresponding to a first low frequency f1 (see Fig. 2 ) and a second higher frequency f2 (see also Fig. 2 ). The driver circuit 29 provides the drive signals in the required form and power available. The driver circuit 29 uses the pulse sequence F1 with the first Frequency f1 to enable or disable each one of the switches 16 or 17. It then uses the pulse train F2 of the second frequency f2 to turn the enabled switch 16 or 17 on and off according to the pulses I2 of the pulse train F2. The pulse train F2 receives the driver circuit 29 from a pulse supply circuit, which includes, for example, a pulse width modulator 30, which is also referred to as a PWM circuit. The pulse width modulator 30 generates signals of varying duty cycle. This can be done at constant frequency or at changing frequency.

The pulse break ratio, i. the duty cycle of the generated signal of the frequency f2, is predetermined by a manipulated variable S, which is supplied by a control unit 31. The control unit 31 may, for example, also supply the first frequency f1 and forward it to the driver circuit 29.

• In Betrieb wird über die Speiseschaltung 15 Betriebsspannung an der Leitung 13 bereitgestellt, so dass diese gegen die Leitung 14 eine Spannung, beispielsweise 400 Volt, aufweist. Entsprechend sind die Kondensatoren 23, 24 jeweils etwa auf die halbe Betriebsspannung aufgeladen, so dass an dem Spannungsteilerpunkt 21 z.B. 200 Volt bereitstehen.

The circuit arrangement 10 described so far operates as follows:

• In operation, 15 operating voltage is provided to the line 13 via the supply circuit, so that it against the line 14 has a voltage, for example, 400 volts. Accordingly, the capacitors 23, 24 are each charged approximately to half the operating voltage, so that at the voltage divider point 21, for example, 200 volts are available.

After the ignition of the gas discharge lamp 11, the switches 16, 17 according to the pulse scheme of Fig. 2 driven. For clarity, first the upper transistor 16 is activated. The upper diagram in Fig. 2 illustrates that the first pulse I1a of the frequency f1 the switch 16 releases. The pulse train I2 with the frequency f2 illustrated below is thus applied to the transistor 16. The transistor 17 remains inactive.

The pulse train I2 of the frequency f2 is evidently a pulse width modulated signal. Towards the end of the first pulse I1a, ie approaching time t1, the pulse / pause ratio of the pulse train F2 is increased. This is done by specifying a control signal S, which in Fig. 2 below and provided in this manner by the control circuit 31. Due to the flowing lamp current, the capacitor 24 gradually charges, the capacitor 23 discharges and the potential at the voltage dividing point 21 increases. The lamp current would thereby tend to decrease. Due to the significant increase of the control signal S when approaching the switching time t1, however, this tendency is counteracted. The lamp current i _L is thereby kept constant or even slightly increased when approaching the switching time t1.

At time t1, the first pulse I1a of the slow pulse train F1 of the frequency f1 ends. Thus, the switch 16 is deactivated, ie initially switched off permanently. The switch 17 is activated. Now, during the pulse I1b, it receives the pulse sequence F2 of the frequency f2, which, according to the control signal S, first begins with a low pulse pause ratio. When approaching the next switching time t2, the control signal S rises again, whereby the pulse / pause ratio of the pulse train F2 increases again accordingly. The current flowing in the negative direction lamp current i _L is thereby increased again. The decreasing tendency of the voltage across the voltage divider 21 caused by the flow of current is thus counteracted. As can be seen, the current i _{L has a} low frequency f1 towards the end of the second pulse I1b of the pulse sequence F1 largest, but at least no reduced value.

As can be seen, the lamp current i _L is raised in each case shortly before the polarity reversal, whereby extinction of the high-pressure gas discharge lamp 11 during polarity reversal is prevented.

Fig. 3 illustrates the current and voltage curves of a modified embodiment of a ballast according to the invention. The modification lies in the operating regime of the control unit. The control signal S is initially kept constant during a pulse I of the slow pulse train F1 for a certain time t0 and then rises toward the end of the pulse I, eg in steps. As Fig. 4 shows the control signal S towards the end of the pulse I also increase steadily. It arises in both cases in the bottom diagram in Fig. 4 idealized illustrated current flow i _L.

In Fig. 5 a circuit variant is shown, which differs from the presented circuit only by changing the mass reference. The lines 13 and 14 carry positive and negative operating voltage with respect to ground. The ground is connected to the voltage divider point 21. The provisioning circuit also has a voltage-related ground reference. Otherwise, the above description applies accordingly.

The natural current profile of a half-bridge circuit 12 with capacitive bridge branch 22 contains a decreasing current characteristic within a half-period of the low-frequency square-wave signal. This can complicate the commutation of the high-pressure gas discharge lamp 11 and lead to an increased Wiederzündspannung. It may come to extinguish the lamp. In the method proposed here according to the invention is by a step, linear or otherwise Raising the output from the control unit 31 manipulated variable S for the lamp current i _L influenced so that it comes within a half-period I1a to an increasing profile of the lamp current i _L. As a result, the electrodes of the lamp are additionally heated prior to commutation, which facilitates the commutation and leads to the reduction of Wiederzündspannung. As a result, the extinction of critical lamps can be avoided.

LIST OF REFERENCE NUMBERS

10

circuitry

11

High-pressure gas discharge lamp

12

Inverter half bridge

13

Operating voltage leading line

14

Earth leading pipe

15

feed circuit

16

Upper switch

17

Lower switch

18

circuit point

19

lamp circuit

20

throttle

21

Voltage dividing point

22

Capacitive voltage divider

23

Upper capacitor

24

Lower capacitor

25, 26

capacitors

27, 28

diodes

29

driver circuit

30

Pulse width modulator

31

control unit

F1

Impulsfoge first, low frequency

I1

Pulse (s) of the first pulse train F1

I1a, b ...

Single pulse of the first pulse train F1

F2

Impulsfoge second, high frequency

I2

Pulse (s) of the second pulse train F2

f2

First frequency, e.g. 500Hz ... 40kHz

S

Control values / current setpoint

t1

End of the first pulse of the pulse train F1

t2

End of the second pulse of the pulse train F1

t0

Time span within the pulses of the first sequence F1

Claims (11)

Circuit arrangement (10) for operating a discharge lamp (11), in particular a high-pressure discharge lamp,
with at least one inverter half bridge (12) connected to the gas discharge lamp (11) for supplying a lamp current (i _L ) therethrough,
with a control circuit (29, 30, 31) for controlling the inverter half bridge (12) with: - A first pulse train (F1) of a first frequency for reversing the lamp current (i _L ) with a first, low frequency (f1), and with a second pulse train (F2) of a second, higher frequency (f2) for controlling the size of the lamp current (i _L ), wherein the control circuit (29, 30, 31) in at least one mode of operation varies the second pulse train (F2) during a pulse (I1a) of the first pulse train (F1) to reduce the magnitude of the lamp current (i _L ) during the pulse (I1a) first pulse train (F1) towards the end of the pulse (I1a) to hold constant or raise. Circuit arrangement according to Claim 1, characterized in that the gas discharge lamp (11) is arranged in series in a lamp branch (19) with an inductive choke component (20), one end of the lamp branch (19) being connected to the inverter half bridge (12). Circuit arrangement according to claim 2, characterized in that another end of the lamp branch (19) is connected to an at least temporarily constant potential. Circuit arrangement according to claim 2, characterized in that another end of the lamp branch (19) is connected to a second inverter half-bridge. Circuit arrangement according to Claim 1, characterized in that another end of the lamp branch (19) is connected to a capacitor half-bridge (22). Circuit arrangement according to Claim 1, characterized in that the control circuit (29, 30, 31) sets the second pulse sequence (F2) in accordance with a current setpoint (S) which is increased at least once during a pulse of the first pulse sequence (F1). Circuit arrangement according to claim 6, characterized in that the current setpoint (S) is increased several times during a pulse. Circuit arrangement according to claim 6, characterized in that the current setpoint (S) during each pulse (I1a, I1b ...) of the pulse train (F1) is increased starting from a value. Circuit arrangement according to claim 1, characterized in that the current setpoint (S) in each pulse of the pulse train (F1) at the beginning of the respective pulse has a reduced value. Circuit arrangement according to claim 1, characterized in that the operating mode is heating operation and / or reduced-power operation. Method for operating a circuit arrangement (10) for a discharge lamp (11), in particular a high-pressure discharge lamp,
with at least one inverter half bridge (12) connected to the gas discharge lamp (11) for supplying a lamp current (i _L ) therethrough,
with a control circuit (29, 30, 31) for controlling the inverter half bridge (12): - A first pulse train (F1) of a first frequency for reversing the lamp current (i _L ) with a first, low frequency (f1), and - generates a second pulse train (F2) of a second, higher frequency (f2) for controlling the size of the lamp current (i _L ) wherein the control circuit (29, 30, 31) in at least one mode of operation varies the second pulse train (F2) during a pulse (I1a) of the first pulse train (F1) to reduce the magnitude of the lamp current (i _L ) during the pulse (I1a) first pulse train (F1) towards the end of the pulse (I1a) to hold constant or raise.

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