EP2484184A1

EP2484184A1 - Circuit arrangement for operating at least one discharge lamp

Info

Publication number: EP2484184A1
Application number: EP10784291A
Authority: EP
Inventors: Markus Heckmann
Original assignee: Osram GmbH
Current assignee: Osram GmbH
Priority date: 2009-12-09
Filing date: 2010-11-22
Publication date: 2012-08-08
Also published as: DE102009047714A1; WO2011069813A1; AU2010330179A1; CN203072233U

Abstract

The invention relates to a circuit arrangement for operating at least one discharge lamp (La) having an input having a first (E1) and a second input connection (E2) for coupling to a DC supply voltage (UZw); an output having a first (A1) and a second output connection (A2) for coupling to the at least one discharge lamp (La); a bridge circuit having at least one first (S1) and one second electronic switch (S2), wherein a series circuit of the first (S1) and the second electronic switch (S2) is coupled between the first (E1) and the second input connections (E2) forming a first bridge center point (HBM); an LRC resonance load circuit of at least the second degree having a lamp throttle (L1) coupled between the first bridge center point (HBM) and the first output connection (A1), and having at least one trapezoidal capacitor (Ct) coupled in parallel to one of the electronic switches (S1, S2), and a control device (10) for actuating at least the first (S1) and the second electronic switch (S2) by means of an actuating signal (AH, AL), wherein the actuating signal (AH, AL) comprises an operating frequency (f) for operating the LRC resonance load circuit in the frequency range having inductive phase position; wherein the circuit arrangement further comprises: A detection device (L2) designed for detecting the time derivative of the current (Is2) by at least one of the electronic switches (S1, S2); and a comparison device (R2, D3, R3, S3, C1, R4) coupled to the detection device (L2) and designed for comparing the value of the time derivative of the current (Is2) through at least one of the electronic switches (S1, S2) to a predefinable threshold value, wherein the comparison device (R2, D3, R3, S3, C1, R4) is further designed for actuating the control device (10) upon determining that the predefinable threshold value has been exceeded, such that said control device increases the operating frequency (f) of the actuating signal (AH, AL). The invention further relates to a corresponding method for operating at least one discharge lamp (La) of such a circuit arrangement.

Description

description

Circuit arrangement and method for operating at least one discharge lamp

Technical area

The present invention relates to a circuit ^arrangement for operating at least a discharge lamp with an input having a first and a second single input terminal for coupling to a DC supply voltage, an output having a first and a second output terminal for coupling to the at least ei ^¬ NEN discharge lamp, a bridge circuit having at least a first and a second electronic switch, a series circuit of the first and the second electronic switch to form a first bridge center point between the first and the two ^¬ th e i ngang s terminal coupled is an LRC resonant load circuit at least second order with a lamp inductor, which is coupled between the first bridge center and the first output terminal, and min ^¬ least one, parallel to one of the electronic switch coupled trapezoidal capacitor, and a control device for controlling at least he and the second electronic switch with a Ansteuersig- signal, the Ans has teuersignal an operating frequency for operating the LRC resonant load circuit in the frequency range with inductive phase position. It also relates to a corresponding method for operating at least ei ^¬ ner discharge lamp. State of the art

Typical load circuits for discharge lamps, in particular low-pressure discharge lamps, are LRC (L = inductance, R = resistance, C = capacitance) resonant circuits, which are operated at frequencies above their resonance frequency. Half-bridge or bridge circuits are commonly used as drivers of such load circuits.

In order to ensure a soft switching, a so-called soft switching, the switch of the bridge circuit, that is, a lossless switching, it is necessary to provide a certain amount of reactive power. With an appropriate design of the circuit overload conditions, component tolerances, fluctuations in the DC supply voltage and the lamp temperature and, moreover, the modification of various parameters due to the lamp aging must be considered. This leads to ^¬ that in normal operation, that is, in operation far away from the worst case, usually large amounts of Blindleis ^¬ tion are available. The transmission of these large amounts of reactive power causes unwanted losses. If not enough reactive power ^¬ is present in the circuit arrangement, the switches of the bridge circuit switch hard, so-called hard switching, thereby causing undesirable high current peaks, losses and elekt ^¬ romagnetische disorders. An operation near the resonance frequency of the LRC load circuit is desirable over ^¬ this, since then a maximum of energy can be transmitted to the LRC load circuit. Presentation of the invention

The object of the present invention is therefore to ^{weiterzu ¬} form a generic circuit arrangement or a generic method such that a soft switching with as little reactive power to be transmitted and largely independent of various boundary conditions, such as lamp temperature, lamp aging, component tolerances, is possible.

This object is achieved by a circuit arrangement having the features of patent claim 1 and by a method having the features of patent claim 10.

The present invention is based on the finding that during commutation of the current from a first to a second electronic switch of the bridge circuit, first a current flows through the freewheeling diode of the switch to be turned on, before this switch itself is turned on. The period during which both switches are switched off is called dead time. The second switch is turned on in the period during which current flows through its freewheeling diode to ensure smooth switching. This period is greater the more reactive power is present in the load circuit. Part of the reactive power is used to reload the trapezoidal capacitor. The further excess of reactive power is fed back into the supply via the freewheeling diodes.

If there is no longer sufficient reactive power, a recharging of the trapezoidal capacitor fails, as a result of which the switch to be switched conductive is hard-wired. The present invention is based in particular on the invention. know that a hard switching by a peak in the current through the conductive switch is recognizable. This indicates that the operating frequency of the drive signal for the switches of the half-bridge is too close to the resonance frequency, that is, tends to sink from the inductive range into the capacitive range.

The present invention therefore includes a Determined ^¬ averaging device, which is designed, the temporal derivation of the stream to determine at least one of the electronic switch by. It further comprises a comparator, coupled to the determining device and configured to compare the value of the time from ^¬ line of the current through at least one of the electronic switch to see a predeterminable threshold value. If exceeding this predetermined threshold determined, which Vergleichsvorrich ^¬ tung the control device in such a way that this increases the operating frequency of the drive signal ^¬ Be. As a result, the load circuit is operated again in the inductive range, whereby the mentioned peaks and thus a hard switching of the switches is avoided. By doing so, operation of the circuitry close to the resonant frequency but on the inductive side thereof is possible. This results in that the Schaltungsanord ^¬ tion can be operated with minimal reactive power. As a result, the power components, such as coils, capacitors, switches and so on, can be made smaller. In addition, simpler circuit concepts can be realized, for example the integration of preheating into the lamp inductor. In a preferred embodiment, the control device is designed to increase the operating frequency. This can be done by fine dimensioning predefinable steps in digital implementation or by stepless control in an analog implementation. In order for an operation of the circuit arrangement is made possible close to the optimum, that is, in view of the present Prob ^¬ lematics with minimal reactive power, yet a soft switching can be guaranteed. In a further preferred embodiment, the control device is designed to reduce the operating frequency on the basis of a predefinable initial value, in particular in predefinable steps or steplessly, as long as no exceeding of the predefinable threshold value is determined by the value of the time derivative of the current through at least one of the electronic switches , This measure serves to gradually lower the operating frequency starting from a value at which certainly exists sufficiently reactive ^¬ power in the load circuit to achieve the optimization mums in critical areas. Here, too, a fine dimensioning of vorgebba ^¬ ren steps allows reliable finding of the optimum, regardless of the above-mentioned varying operating parameters. Preferably, the detection device comprises a shunt resistor coupled serially to the first or second electronic switch. In order to determine the time derivative of the current through at least one of the electronic switches, the voltage drop across the shunt resistor must therefore be differentiated. Therefore, the determination device further preferably comprises a differential discriminating device which is designed to ermit ^¬ the time derivative of the current through the shunt resistor.

However, it is particularly preferred if the determining device comprises an inductance which is coupled in series to the first or second electronic switch. This variant makes use of the fact that the voltage drop across the inductance voltage of the zeitli ^¬ chen derivative of the current through the inductance is proportional, that is, U = L x di / dt. An additional differentiating device as in the evaluation of the current through a shunt resistor, therefore, can be omitted in the embodiment ^¬ ser.

In a preferred embodiment, the comparison device comprises a voltage divider, which is connected in parallel at least the inductance, wherein the Ab ^¬ grip point of the voltage divider is coupled to the control electrode of a controllable resistor. By means of this measure, it is possible in a simple manner to determine the predefinable threshold value for the time derivative of the current through at least one of the electronic switches. Preferably, the arrangement is designed so that the steu ^¬ newable resistance when exceeding the threshold mentioned vorgeb ^¬ cash, the control device such ansteu ^¬ ert that this increases the operating frequency.

The voltage divider may comprise a diode further, the diode between the inductance gekop ^¬-coupled terminal of the voltage divider and the tap ^¬ point of the voltage divider is coupled. This measure can take account of the fact that ne control tasks of the control device, the determination of the current through one of the electronic switches is needed, that is not its time derivative. If now for this purpose, a shunt resistor coupled in series with the inductance, in particular such that the coupled in ^¬ productivity between the second electronic switch and the shunt resistor, the voltage drop across the shunt resistor can be taken into account when maximum current through the diode and therefore does not disturb the evaluation of the time derivative of this current by a comparison device designed as mentioned.

In a preferred embodiment, a device for averaging is coupled between the working electrode of the controllable resistor and the control device. Thus, pulses at the input of the controllable resistor are not transmitted to its output, which is coupled to the control device.

Further advantageous embodiments will become apparent from the dependent claims. The preferred embodiments presented with reference to the circuit ^arrangement according to the invention and their advantages apply correspondingly, as far as applicable, to the method according to the invention.

Short description of the drawing (s)

In the following, an embodiment of the present invention with reference to the beigefüg ^¬ th drawings will now be described in more detail. These show: 1 shows a schematic representation of an embodiment of a circuit arrangement according to the invention;

FIG. 2 is a more detailed view of a portion of the guide shown in FIG. 1; FIG. and

3a to 3c show the time profile of the current through the second electronic switch of the embodiment shown in FIG. 1 different operating frequencies

Preferred embodiment of the invention

Fig. 1 shows a schematic representation of an embodiment of an inventive Schaltungsanord ^¬ tion. The circuit arrangement comprises an input with a first El and a second input terminal E2, between which a DC supply voltage is applied, in particular the so-called intermediate circuit voltage U _Zw . Between the input terminals El, E2 a Brü ^¬ bridge circuit is coupled, which mainly comprises a first switch Sl and a second switch S2. The actual switch is connected in antiparallel in each case one freewheeling diode Dl or D2, where vorlie ^¬ quietly is expressed by the dashed outline that in a MOSFET the respective freewheel diode ^¬ is realized by the respective body diode. In contrast, when using bipolar transistors for the switches Sl, S2 would provide a separate freewheeling ^¬ diode. Between the switches Sl, S2 a Halbbrückenmittel ^¬ point HBM is formed, which is coupled via a lamp inductor LI with a first output terminal AI. Between the first output terminal AI and the second output terminal A2, a discharge lamp La is coupled. Pa ^¬ rallel to the discharge lamp La is a resonant capacitor C _R coupled. Between the second output terminal A2 and the second input terminal E2, a coupling capacitor C _{K is} coupled. Parallel to the second switch S2, a trapezoidal capacitor C _{T is} coupled.

As will be apparent to those skilled in the art, other embodiments of LRC resonant circuits are possible. By way of example only, the number and position of the trapezoidal capacitor (s), coupling capacitor (s), and resonant capacitor (s) may be varied without affecting the present invention.

For measuring the current through the second switch S2, a Shun t resistor Rl is provided which is serially coupled to the switch S2. Tand between the switch S2 and the shunt resis Rl is an inductance L2 gekop ^¬ pelt. The drop across the inductance L2 voltage U _L 2 is proportional to the time derivative of the current I _S 2 through the inductance L2. The voltage U _L 2 is just ^¬ as the voltage U _R i, which drops across the shunt resistor Rl, a processing device 12 which is designed, at its output AL a drive signal for the switch S2 and at its output AH To provide drive signal for the switch Sl. The Ansteuersig- signals have an operating frequency f, which can be varied. In the processing device 12, a comparison device is provided, the voltage U _L 2 is supplied. It is designed to compare the voltage U _L 2 against a predefinable threshold, causing the processing device 12 to determine the operating frequency f of the control signals for the scarf ^¬ ter Sl, S2 upon detection of exceeding the predetermined threshold value.

FIG. 2 shows a more detailed representation of an embodiment of the embodiment of a circuit ^arrangement according to the invention shown in FIG. 1. NEN is how to recognize, the voltage drop across the inductor L2 voltage U _L 2 is supplied to a voltage divider D3 summarizes the resistors R2 and R3 and a diode to ^¬. Its tapping point is coupled to the control electrode ei ^¬ nes transistor S3, which is operated here as a controllable resistor. Parallel to the path working ^¬ electrode reference electrode of the transistor S3 is a Kon ^¬ capacitor Cl coupled, which represents a device for averaging together with an ohmic resistor R4. The processing device 12 further comprises a control device 10. The ohmic resistance R4 is coupled to an input of the control device 10.

For operation: If the switch Sl conductive scarf ^¬ tet, initially the current flows in the circle Sl, LI, La. If the switch Sl is now switched to blocking, the lamp choke LI continues to drive the current. As a result, first the trapezoidal capacitor C _{T is} reloaded. When it is recharged, the diode D2 becomes conductive, causing the voltage across the switch S2 to become almost zero. The switch S2 must be turned on during the phase during which the diode D2 conducts, to ensure a soft switching to ge ^¬ . If the switch S2 is turned on, the current first flows through the switch S2, the lamp inductor LI and the discharge lamp La. In this case, the capacitor C _{R is} charged. The potential at the half-bridge center HBM drops to nearly 0 V. Since the potential at point N due to the charged capacitor C _{R is} greater than 0 V, then a current flows from the discharge lamp La via the point N, the lamp inductor LI through the switch S2. To as much power to the discharge lamp to carry ^¬, the operating frequency f of the driving signals for the switches Sl, S2 is as far as possible lowered in the direction of the resonant frequency of the LRC load circuit. As a result, there is little excess reactive energy in the load circuit, resulting in only minor losses.

However, this means that after the Sperrendschalten of the switch Sl, the current through the lamp inductor LI is so small that it is not sufficient to completely reverse the charge of the trapezoidal ^¬ capacitor C _T. As a result, at the time when the switch S2 is turned on, the voltage at the half-bridge center HBM is not equal to zero. As a consequence, the switch S2 is switched hard.

In this context, reference is made to FIG. 3. FIG. 3a firstly shows the time profile of the current I _S 2 through the switch _S 2 and of the current I _D 2 through the diode D 2 when the operating frequency f is dimensioned greater than the resonant frequency f ₀ of the diode load circuit. It can be seen that a current I _{D2 flows} through the diode D2 over a period of time ti, that is to say the long period of time ti is available for the Leitendschalt the switch S2.

Now, if the operating frequency f is lowered to a range in the vicinity of f ₀ , but still on the inductive side of the resonant frequency, that is f> «f ₀ , see Fig. 3b, so is the period during which the switch S2 soft conductively connected can be shrunk to the period t ₂ ·

A still further lowering of the operating frequency f leads to the representation in Fig. 3c, in which the Betriebsfre ^acid sequence f "is _f0. Here there is no longer a period in which a current would flow through the diode D2. The circuit is operated at the resonant frequency f ₀ . In this case, so little reactive energy present in the load circuit, that the peak of the current I _s2 single ^¬ Lich flowing in the circuit of the switch S2 and the trapezoidal capacitor C _T. Since the voltage across the switch S2 is at the time of the peak equal to zero, all stored in the Tra ^¬ pezkondensator C _T energy is converted into heat. The switch S2 is switched hard.

Accurate setting of the operating frequency f to obtain a result as shown in Fig. 3b, is not possible in practice, since both the DC ^link voltage U _Zw varies, the temperature of the discharge lamp La and as a result of aging of the discharge lamp La whose Brenn ^¬ voltage , According to the invention will now be provided to detect the loading ^¬ operating frequency at which the peak of the current I _s2 shown in Fig. 3c is formed. For this purpose, the voltage U _L 2, which drops above the inductance L2, evaluated. For these, U _L 2 = _L 2 * di _S 2 / dt; It thus directly reflects the time derivative of the current I _s2 . If it is now established that the time derivative of the current I _s2 exceeds a predefinable threshold, the operating frequency of the switches S 1, _{S 2} is changed in such a way that it continues to be in the inductive range, ie is increased. This more inductive reactive power in the load circuit for Availability checked ^¬ supply is provided so that a reliable reoscillation and soft switching can be ensured.

Is as shown in FIG. 2, the sum of U _L 2 and U _R i supplied to the comparison means, so this is unschäd ^¬ Lich, since at the time of the peak of I _s2, see Fig. 3c, the current through the resistor Rl very small and therefore irrelevant.

In a preferred embodiment, a device was used for the drive device 12, which is designed so that it increases the operating frequency of the drive signals at its outputs AH and AL, the more current from the terminal to which the ohmic resistor R4 is connected via the ohmic resistor R4 flows through the transistor S3.

Claims

claims

1. Circuit arrangement for operating at least one discharge lamp (La) with

- An input with a first (El) and a second Eingangsanschlus s (E2) for coupling with a _DC supply voltage (U _Zw );

an output having a first (AI) and a second output terminal (A2) for coupling to the at least one discharge lamp (La);

- A bridge circuit having at least a first (Sl) and a second electronic switch (S2), wherein a series circuit of the first (Sl) and the second electronic switch (S2) to form a first bridge center point (HBM) between the first (El) and the second input terminal (E2) is coupled;

- an LRC resonant load circuit at least second Ord ^¬ voltage having a lamp inductor (LI), the (HBM) and the first off ^¬ is between the first bridge center point coupled to input terminal (AI), and at least one (parallel to one of the electronic switch S, S2) coupled trapezoidal capacitor (C _T ); and

- A control device (10) for controlling at least the first (Sl) and the second electronic switch (S2) with a drive signal (AH, AL), wherein the drive signal (AH, AL) a Betriebsfre ^¬ frequency (f) for the operation of the LRC -Resonanzlastkreises in the frequency range with inductive phase position has; characterized,

that the circuit arrangement further comprises: - A determination device (L2), which is designed to determine the time derivative of the current (Is ₂ ) by ^{¬ at} least one of the electronic switches (Sl, S2); and

- A comparison device (R2, D3, R3, S3, Cl, R4), which is coupled to the determination device (L2) and adapted to the value of the time derivative of the current (Is ₂ ) by at least one of the electronic ^¬ African switch (Sl , S2) to compare with a predefinable threshold value, wherein the comparison device (R2, D3, R3, S3, Cl, R4) is further designed to control the control device (10) upon detection of exceeding the predetermined threshold value such that the operating frequency ( f) of the drive signal (AH, AL) increases.

2. Circuit arrangement according to claim 1,

characterized,

that the control device (10) is adapted to increase the loading ^¬ operating frequency (f).

3. Circuit arrangement according to one of claims 1 or 2,

characterized,

that the control device (10) is adapted to the loading ^¬ operating frequency (f), starting to decrease from a predetermined initial value as long as no exceeding of the predetermined threshold value for the value of the time derivative of the current (Is ₂₎ by at least one of the electronic switches (Sl, S2) is detected.

4. Circuit arrangement according to one of the preceding claims,

characterized,

the determination device (L2) comprises a shunt resistor (R1) coupled serially to the first (S1) or second electronic switch (S2).

5. Circuit arrangement according to claim 4,

characterized,

in that the determining device (L2) further comprises a differentiating device which is designed to determine the time derivative of the current (Is ₂ ) through the shunt resistor (Rl).

6. Circuit arrangement according to one of claims 1 to 4, characterized

in that the determining device comprises an inductance (L2) which is coupled in series to the first (S1) or second electronic switch (S2).

7. Circuit arrangement according to claim 6,

characterized,

the comparison device (R2, D3, R3, S3, C1, R4) comprises a voltage divider (R2, D3, R3) which is connected in parallel with at least the inductance (L2), the tapping point of the voltage divider (R2, D3, R3) is coupled to the control electrode of a controllable resistance ^¬ (S3).

8. Circuit arrangement according to claim 7,

characterized, includes that the voltage divider (R2, D3, R3) includes a diode (D3), said diode (D3) between the productivity with the in ^¬ (L2) coupled to the terminal of the voltage ^¬ divider (R2, D3, R3) and the tapping point of the Voltage divider ^¬ (R2, D3, R3) is coupled.

9. Circuit arrangement according to claim 8,

characterized,

in that a device (R4, C1) for averaging is coupled between the working electrode of the controllable ^resistor (S3) and the control device (10).

10. A method for operating at least a discharge lamp (La) at a circuit arrangement comprising an input having a first (El) and a second input terminal (E2) for coupling to a supply ^¬ DC voltage (Uzw); an output with a first (AI) and a second output terminal (A2) for Kop ^¬ PelN with the at least one discharge lamp (La); a bridge circuit having at least a first (Sl) and a second electronic switch (S2), wherein a series connection of the first (Sl) and the second electronic switch (S2) to form a first bridge center (HBM) between the first (El) and the second input terminal (E2) is coupled; an LRC resonant load circuit at least second order having a lamp inductor (LI), which is between the first bridge center point (HBM) and the ers ^¬ th output terminal (AI) is coupled and Minim ^¬ least one, parallel to one of the electronic switches (Sl, S2) coupled trapezoidal capacitor (C _T ); and a control device (10) for controlling at least the first (Sl) and the second electronic switch (S2) with a drive signal (AH, AL), where ^¬ in the drive signal (AH, AL) an operating frequency (f) for operating the LRC Resonant load circuit in Fre ^¬ frequency range with inductive phase position having;

characterized by the following steps:

a) determining the time derivative of the current (Is ₂ ) by at least one of the electronic switches (Sl, S2);

b) comparing the value of the time derivative of the current (Is ₂ ) by at least one of the electronic switch ^¬ (Sl, S2) against a predetermined threshold value; and

c) increasing the operating frequency (f) of the Ansteuersig- signals (AH, AL) upon detection of exceeding the predetermined threshold in step b).