WO2010115687A1 - Circuit assembly and method for operating at least two different types of discharge lamps - Google Patents

Abstract

The present invention relates to a circuit assembly for operating at least two different types of discharge lamps, for the operation of which different lamp currents are required. The discharge lamp is connected in series to a coupling capacitor (CK1). The AC voltage component at the coupling capacitor (CK1) is used to regulate the required lamp current.

Description

 description

Circuit arrangement and method for operating at least two different types of discharge lamps

Technical area

The present invention relates to a circuit arrangement for operating at least two different types of discharge lamps, the operation of which requires a different lamp current, having an input with a first and a second input terminal for coupling to a DC voltage source, a bridge circuit having a first and a second electro wherein the first and second electronic switches are serially coupled to form a first bridge center between the first and second input terminals, the first and second electronic switches each having a control electrode, a reference electrode, and a working electrode An output having a first and a second output terminal for providing an operating voltage for the at least one discharge lamp, a lamp inductor connected in series between the first bridge center and the first output terminal coupled, a resonant capacitor which is coupled between the first output terminal and the second input terminal, a coupling capacitor which is coupled between the second output terminal and the second input terminal, an evaluation device having an input and an output, wherein the input of the evaluation device with a decoupling point is coupled and the evaluation device is designed to provide at its output a correlated with the lamp current size, and a control Device having a first input and a first and a second output, wherein the first input of the control device is coupled to the output of the evaluation device, wherein the first output of the Steuerervorr- with the control electrode of the first electronic switch and the second output of the control device is coupled to the control electrode of the second electronic switch, wherein the control device is designed to regulate the lamp current by varying at least the frequency of the signals provided at its first and second output. It also relates to a corresponding method for operating at least one discharge lamp on such a circuit arrangement.

State of the art

High and low pressure discharge lamps are operated for effective operation on electronic ballasts. These devices ensure that the lamp is ignited and then operated with the characteristic of the lamp current. Multi-lamp devices are designed for the operation of different lamps, which means that it is possible to choose lamps with different operating data and then operate them on one and the same electronic circuit-breaker. Different principles are known from the prior art, according to which such multi-lamp devices work:

In fixed-frequency operation, after detection of the lamp type, for example by passing through a measuring routine, a fixed operating frequency assigned to the detected lamp type is applied to the switches of the bridge circuit. posed. These are then controlled in the sense of a control, that is without feedback, with a fixed operating frequency. As a result of the dependence of the lamp current provided at the output of the multi-lamp device on the operating frequency so a certain lamp current can be adjusted. As a result of tolerances of the operating parameters of a single lamp, however, there are unwanted fluctuations in the lamp current. Moreover, this fixed-frequency operation only works with high DC link voltage when lamp currents in a range of 100% to 300% of a minimum lamp current are needed. A high DC link voltage requires appropriately designed components, which is associated with additional costs and undesirably high losses.

According to a second principle, a shunt resistor is arranged serially to the coupling capacitor or to the discharge lamp, wherein the voltage drop across the shunt resistor represents a measure of the lamp current. Since the voltage drop across the shunt resistor must be subjected to rectification before being further processed in the control device, care should be taken to ensure that this voltage is greater than 0.7 V, since only then does the rectification function via diodes. The signal obtained after the rectification is then used to control the lamp current, that is, the control device varies the operating frequency at which the switches of the bridge circuit are driven with respect to the measured lamp current. Due to the comparatively high voltage which must drop at the shunt resistor in order to operate this principle, a loss-making rich measurement and especially at high lamp currents a poor overall efficiency.

According to a third known principle, the lamp current is regulated by means of an AC current measuring amplifier. For this purpose, the voltage dropping across a shunt resistor is first supplied to an AC amplifier, with the result that the shunt resistor can be dimensioned smaller. This results in fewer losses. Subsequently, the output of the AC amplifier is rectified. Since the amplifier must have a large bandwidth for this purpose, which covers in particular frequencies in the range of 10 kHz to 150 kHz, resulting in a high cost, which is associated with high costs.

Presentation of the invention

Therefore, the object of the present invention is to develop a circuit arrangement mentioned above in such a way that it enables reliable operation of different lamp types, that is to say lamp types which require a different lamp current, at low costs.

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 9.

The present invention is based on the finding that this object can be achieved if the voltage drop across the coupling capacitor is evaluated to determine a value correlated with the lamp current. This is called Auskoppelpunkt, with the input the evaluation device is coupled, the connection of the coupling capacitor selected, which is coupled to the second output terminal of the circuit arrangement. The voltage swing at the coupling capacitor, ie the AC voltage component, is proportional to the lamp current. The smaller the selected coupling capacitor, the greater the voltage drop across the coupling capacitor. Usually, it is completely unproblematic to find a dimensioning for the coupling capacitor, which leads to a voltage swing on the coupling capacitor, which allows a rectification without the interposition of an amplifier. Thus, the present invention allows control of the lamp current and thus the avoidance of fluctuations in the lamp current without the use of a complex amplifier and without the use of a shunt resistor. It therefore enables the operation of different lamp types on one and the same electronic ballast with high reliability and at low cost.

Particularly preferably, the decoupling point represents the point at which the second output terminal is coupled to the coupling capacitor. As a result, a maximum voltage swing at the coupling capacitor can be achieved.

Preferably, the evaluation device comprises a rectifier, which is coupled between the decoupling point and the first input of the control device. This allows the rectification of the decoupled signal. Preferably, a decoupling capacitor is further provided between the decoupling point and the rectifier. This can be very small, for example, 3.3 nF. As a result, only the ripple voltage proportional to the lamp current, that is, only the alternating current Voltage component, detected at the coupling capacitor and used to determine a proportional to the lamp current size.

To adapt the decoupled signal to the desired input level of the control device, a voltage divider can furthermore be provided. The evaluation device preferably further comprises an averaging device coupled serially to the rectifier. Thus, the control device is supplied with a signal which is proportional to the average value of the lamp current. Thus, the lamp current can be measured very reliably and thus regulated.

The rectifier preferably comprises a first and a second diode, the voltage divider comprises a first and a second ohmic resistance and the mean value forming device the second ohmic resistance of the voltage divider and an auxiliary capacitor, wherein a series circuit of Auskoppelkondensator, first ohmic resistance and first diode is coupled in parallel to the coupling capacitor wherein between the connection point of the first ohmic resistor to the first diode on the one hand and the first input of the control device, the second diode is coupled, wherein a series circuit of the second ohmic resistor and the Hilfskonden- sensor is coupled parallel to the first input of the control device. As a result of this measure, the second ohmic resistance can be used on the one hand for the voltage divider and on the other hand for the mean value forming device, resulting in a particularly low-effort and low-loss realization. According to a preferred development, the circuit arrangement further comprises a boost converter with a boost switch, a boost inductance and a boost diode, wherein the boost converter is coupled between the input of the circuit arrangement and the bridge circuit, wherein the voltage provided at the output of the boost converter the intermediate circuit voltage is where a signal correlated with the intermediate circuit voltage is coupled to a second input of the control device, wherein the control device has a third output which is coupled to the boost switch, and the control device is designed to increase the lamp current by varying the intermediate circuit voltage regulate. This refinement makes it possible to regulate the lamp current not only via the operating frequency with which the switches of the bridge circuit are actuated, but also via the intermediate circuit voltage. In particular, fluctuations of the mains voltage can thus be compensated.

Further advantageous embodiments will become apparent from the dependent claims.

Short description of the drawing (s)

In the following, an embodiment of a circuit arrangement according to the invention will now be described in more detail with reference to the accompanying drawings. Show it:

Fig. 1 in a schematic representation of an embodiment of a circuit arrangement according to the invention; and Fig. 2 shows the time course of the applied to the switches of the bridge circuit of Fig. 1 signals.

Preferred embodiment of the invention

1 shows a schematic representation of an embodiment of a circuit arrangement according to the invention. This comprises an input with a first El and a second input terminal E2, between which a mains voltage U _{N is} applied. The input E1, E2 is followed by a rectifier GL, which is designed to rectify the mains voltage U _N. After the rectifier GL, a boost converter is provided which comprises a boost choke L _B , a boost diode D _B and a boost switch S _B. At the output of the boost converter, a storage capacitor Cl is provided, which supplies the subsequent circuit part with an intermediate circuit voltage U _Zw . The following circuit part comprises a half-bridge circuit having a first Sl and a second half-bridge switch S2. Between the switches Sl and S2, a first half-bridge center BM1 is formed. A lamp inductor L _{D is} coupled between the half-bridge center BM1 and a first output terminal A1 of the circuit arrangement. Between the first output terminal Al and a second output terminal A2, between which an output voltage U _{A is} provided, a discharge lamp La is coupled, which is flowed through in operation by the lamp current IL _a . The first lamp terminal Al is coupled to a reference potential via a resonance capacitor C _R , while the second lamp terminal A 2 is likewise coupled to the reference potential via a coupling capacitor C _K i. The coupling capacitor C _K i is flowed through by a current I _C κi, which substantially corresponds to the lamp current I _La . Between the high-potential terminal of the switch Sl and the second output terminal A2, a second coupling capacitor C _K 2 can optionally be provided.

The voltage U _C κi dropping across the capacitor C _K i is supplied to an evaluation device 10 whose output is coupled to a microcontroller 12. The evaluation device 12 comprises a decoupling capacitor C _m , which ensures that only the AC voltage component of the voltage U _C κi is coupled out. This AC voltage component of the voltage U _C κi the lamp current I _La proportional. This AC voltage component is subsequently divided down using a voltage divider R3, R4 and rectified by means of a half-wave rectifier comprising the diodes D1 and D2. A capacitor C2, which is connected in parallel with the resistor R4, makes it possible to realize averaging.

The microcontroller 12 is designed to calculate a value from the signal applied to its input TE1, from which the value of the lamp current I _La results. This is shown in more detail below. On the basis of the determined lamp current I _La , it activates the switches S1 and S2 of the half-bridge via its outputs TA1, TA2. In particular, the microcontroller 12 is designed to increase the frequency fi of the signals provided at the outputs TAI, TA2 for controlling the lamp current I _La to the nominal value of the lamp current which is relevant for the type of discharge lamp La connected to the output A1, A2 vary. For this purpose, a corresponding look-up table is provided in the microcontroller 12, in which for different lamp types at least the nominal value of the lamp current is entered.

In the present case, a size is also provided to the microcontroller 12 using a voltage divider with the ohmic resistors R 1, R 2 at its input TE 2, from which the actual value of the intermediate circuit voltage U _Zw results. The microcontroller 12 is furthermore designed to continue to vary the intermediate circuit voltage U _Zw by varying the frequency _{2 2 of} the signal provided at its output TA 3 in view of the type of the lamp La.

Fig. 2 shows a schematic representation of the time course of the signals at the switch Sl or S2. The switch-on time t _on and the switch-off time t _O ff are entered. On this basis, the lamp current ILa can be estimated as follows:

^' UCKlAC '* La ~ * CKl ^~

^' UCKlAC'

where U _C KIA _{C represents} the AC voltage component of the voltage U _C κi.

From Fig. 2 follows:

f- \

This results in:

Mit K = K-C_1n folgt I_La »I_an = ^{K 'U<xlÄC} t„„ + 1 off

With K = KC _1n , I _La 'I _an = ^{K' U <xlÄC} t "" + 1 off

U _TEl calculates to:

TT _ ^ CKXAC ^' R ^

^TEl 2 • 1.11 • (R3 + R4)

where the factor 1/2 due to the one-way rectification with the diodes Dl and D2 results. The factor 1 / 1.11 takes into account the transition from the sinusoidal current to the mean value of the current. The factor R4 / (R3 + R4) takes into account the influence of the voltage divider R3, R4.

M ^Ll i ± t LU ^ J CKlAC - -I ¹ La ^ ° " ⁺ " ^

Ä

surrendered:

_ττ I _Lg -R4- {t _on + t _off )

^TEl K-2 - \, U- (R3 + R4)

R4- (t _on + t _off )

K ^■ 2 ^■ 1.11 • (R3 + R4)

Claims

claims A circuit arrangement for operating at least two different types of discharge lamps, the operation of which requires a different lamp current, comprising: - an input having a first (El) and a second input terminal (E2) for coupling to a DC voltage source (U _Zw ); a bridge circuit having a first (Sl) and a second electronic switch (S2), the first (Sl) and the second electronic switch (S2) forming a first bridge center (BMl) serially between the first (El) and the second Input terminal (E2) are coupled, wherein the first (Sl) and the second electronic switch (S2) each having a control electrode, a reference electrode and a working electrode; - An output with a first (Al) and a second output terminal (A2) for providing an operating voltage for the at least one discharge lamp (La); - A lamp inductor (L _D ), which is serially coupled between the first bridge center (BMl) and the first output terminal (Al); a resonant capacitor (C _R ) coupled between the first output terminal (Al) and the second input terminal (E2); a coupling capacitor (C _K i) coupled between the second output terminal (A2) and the second input terminal (E2); - An evaluation device (10) having an input and an output, wherein the input of the evaluation device (10) is coupled to a decoupling point and the evaluation device (10) is designed to provide at its output a correlated with the lamp current (I _La ) size; and - A control device (12) comprising a first input (TEI) and a first (TAI) and a second output (TA2), wherein the first input (TEI) of the control device (12) coupled to the output of the evaluation device (10) is, wherein the first output (TAI) of the control device (12) to the control electrode of the first electronic switch (Sl) and the second output (TA2) of the Steuervorrrich- device (12) to the control electrode of the second electronic switch (S2) is coupled wherein the control device (12) is adapted to control the lamp current (IL _a ) by varying at least the frequency (fi) of the signals provided at its first (TAI) and second output (TA2); characterized in that the decoupling point, with which the input of the evaluation device (10) is coupled to the terminal of the coupling capacitor (C _K i) is coupled, which in turn is coupled to the second output terminal (A2). 2. A circuit arrangement according to claim 1, characterized in that the decoupling point represents the point at which the second output terminal (A2) to the coupling capacitor (Cκi) is coupled. 3. Circuit arrangement according to one of claims 1 or 2, characterized in that the evaluation device (10) further comprises a rectifier (Dl, D2) which is coupled between the decoupling point and the first input (TEl) of the control device (12). 4. A circuit arrangement according to claim 3, characterized in that the evaluation device (10) further comprises a decoupling capacitor (C _m ), which is coupled between the decoupling point and the rectifier (Dl, D2). 5. Circuit arrangement according to claim 4, characterized in that the evaluation device (10) further comprises a voltage divider (R3, R4). 6. Circuit arrangement according to claim 5, characterized in that the evaluation device (10) further comprises a mean value forming device (R4, C2), which is serially coupled to the rectifier (Dl, D2). 7. The circuit arrangement as claimed in claim 6, characterized in that the rectifier (D1, D2) has a first (D1) and a second diode (D2), the voltage divider (R3, R4) has a first (R3) and a second ohmic resistance. (R4) and the mean value forming device (R4, C2) comprises the second ohmic resistor (R4) and an auxiliary capacitor (C2), wherein a series circuit of decoupling capacitor (C _m ), first ohmic resistor (R3) and first diode (Dl) is coupled in parallel to the coupling capacitor (Cκi), wherein coupled between the connection point of the first ohmic resistance (R3) with the first diode (Dl) on the one hand and the first input (TEl) of the control device (12), the second diode (D2) is, wherein a series circuit of the second ohmic resistor (R4) and the auxiliary capacitor in parallel with the first input (TEl) of the control device is coupled (12). 8. Circuit arrangement according to one of the preceding claims, characterized in that the circuit arrangement further comprises a boost converter with a boost switch (S _B ), a boost inductance (L _B ) and a boost diode (D _B ), wherein the Boo s t converter is coupled between the input of the circuit arrangement and the bridge circuit, wherein the voltage provided at the output of the boost converter is the intermediate circuit voltage (U _Zw ), wherein a signal correlated with the intermediate circuit voltage (U _Zw ) to a second input (TE2) of the control device (12) is coupled, wherein the control device (12) has a third output (TA3) which is coupled to the boost switch (S _B ), and the control device (12) is designed, the lamp current ( I _La ) by variation of further the intermediate _{circuit voltage} (U _Zw ) to regulate. 9. A method for operating at least two different types of discharge lamps, the operation of which a different lamp current is required, to a circuit arrangement having an input with a first (El) and a second input terminal (E2) for coupling to a DC voltage source (U _Zw ); a bridge circuit having a first (Sl) and a second electronic switch (S2), the first (Sl) and the second electronic switch (S2) forming a first bridge center (BMl) serially between the first (El) and the second input terminal (E2) are coupled, wherein the first (Sl) and the second electronic switch (S2) each have a control electrode, a reference electrode and a working electrode; an output having a first (Al) and a second output terminal (A2) for providing an operating voltage for the at least one discharge lamp (La); a lamp inductor (L _D ) serially coupled between the first bridge center (BMl) and the first output terminal (Al); a resonance capacitor (C _R ) coupled between the first output terminal (Al) and the second input terminal (E2); a coupling capacitor (C _K i) coupled between the second output terminal (A2) and the second input terminal (E2); an evaluation device (10) having an input and an output, wherein the input of the evaluation device (10) is coupled to a decoupling point and the evaluation device (10) is designed to provide at its output a correlated with the lamp current (I _La ) size ; a control device (12) having a first input (TE1) and a first (TAI) and a second output (TA2), wherein the first input (TE1) of the control device (12) is coupled to the output of the evaluation device (10), the first output ( TAI) of the control device (12) to the control electrode of the first electronic switch (Sl) and the second output (TA2) of the control device (12) is coupled to the control electrode of the second electronic switch (S2), wherein the control device (12) is designed to regulate the lamp current (I-L _a ) by varying at least the frequency (fi) of the signals provided at its first (TAI) and second output (TA2); characterized by the following steps: a) decoupling the voltage (U _C κi) across the coupling capacitor (C _K i); and b) coupling a signal correlated with the decoupled voltage (U _C κi) to the first input of the evaluation device (10).