EP1715729A1 - Electronic ballast for a lamp - Google Patents

Abstract

The ballast has a signal evaluation unit (20), where direct current (DC) voltage reference potential for the unit is implemented in a value range, whose limit is defined by mass and voltage potentials. A control unit (14) and the unit (20) are designed such that with a difference of the DC voltage of the signals of the unit (20) the unit (14) does not control switches or controls the switches to reduce the output power of the ballast.

Description

Technical area

The present invention relates to an electronic ballast for a lamp, in particular an electronic ballast having a bridge circuit comprising at least a first and a second switch, which are coupled between a terminal for a supply voltage and a terminal for a ground potential, wherein between the first and second the second switch is defined a center point of the bridge circuit, a first and a second terminal for a lamp, wherein the first terminal is coupled via an inductance to the center of the bridge circuit, and a signal evaluation unit, wherein the signal evaluation unit comprises a first and a second input, wherein the first input is coupled to a signal that is at the DC level of the first terminal for the lamp, and wherein the second input is coupled to a signal that is at the gate voltage level of the second terminal for the lamp pe is.

State of the art

Such an electronic ballast for a lamp is known. In this case, in a signal evaluation unit, which is connected to the ground potential as a reference potential, the difference between the DC voltage level of the first terminal for the lamp and the second terminal for the lamp is determined and evaluated to make statements about the remaining life of the lamp. In particular, upon detection of an imminent end of the lamp (EoL = End of Life), the control of the bridge circuit is switched off in order to avoid damage in the electronic ballast. The DC voltage useful signal is a DC voltage equal to the DC potential of the center of the bridge circuit superimposed. Since the voltage dividers and comparator circuits necessary for the evaluation are subject to the usual tolerances, this leads to a voltage divider typically causing 1% tolerance when using resistors +/- 4% of the potential at the midpoint of the bridge circuit can be generated as an error in the measured value. The supply voltage is for example 450 V; Therefore, the potential at the midpoint of the bridge circuit is about 225 V. With an error of +/- 4%, the error in the measured value is thus about +/- 9 V. Since the DC voltage useful signal for detecting an "EoL situation" usually in the order of 10 to 20 V, therefore, a reliable EoL detection is not possible.

Presentation of the invention

The object of the present invention is to further develop the aforementioned electronic ballast in such a way that a more reliable EoL detection is possible.

This object is achieved by an electronic ballast having the features of claim I.

The present invention is based on the finding that a less error-prone evaluation of the DC useful signal in the EoL detection can be achieved if, in the evaluation, the DC reference potential for the signal evaluation unit does not represent the ground potential, but a potential that is variably executed in a range of values, whose limits are defined by the ground potential and the supply voltage potential. The smaller the DC voltage component which is superimposed on the DC useful signal, the lower the error in the measurement result.

A particularly advantageous embodiment is therefore characterized in that the DC voltage reference potential for the signal evaluation unit is essentially the potential of the center point of the half-bridge circuit. In the case of such a dimensioned "floating" EoL detection, therefore, the DC useful signal is not superposed by any disturbing DC voltage. The measurement error due to component tolerances is therefore minimal, the reliability of the result maximum.

A preferred embodiment further comprises a control unit for controlling the first and the second switch, wherein the control unit has a shutdown or Abregeleingang which is coupled to the signal evaluation unit, wherein the control unit and the signal evaluation unit are designed to cooperate such that at a difference of DC voltage component of the signals at the two inputs the signal evaluation unit, the signal evaluation unit controls the control unit via the shutdown or Abregeleingang such that no control of the first and / or the second switch is made or the first (S1) and / or the second switch (S2) are controlled in such a way in that the output power of the electronic ballast is reduced. By this measure, damage to the electronic ballast is reliably prevented upon detection of an EoL situation. If a lamp continues to operate in an EOL situation, there is also the risk of lamp overheating, which can lead to breakage or melting of the lamp and thus to danger to persons in the vicinity of the lamp.

In a further preferred embodiment, the control unit has a supply voltage connection and is connected to the ground potential as a DC voltage reference potential. The signal evaluation unit comprises a latch and is designed to activate the latch when the difference in the DC component of the signals at the two inputs of the signal evaluation unit is above a predetermined limit, wherein the output of the latch on the series circuit of a diode and a resistor to the Supply voltage terminal of the control unit and / or the signal evaluation unit is coupled. In this variant, the signal evaluation unit is realized as an active circuit, wherein the supply voltage of the control unit and / or the signal evaluation unit, which is usually of the order of 15 V and thus in the order of magnitude of the EoL DC utility signal, is used in a skilful manner for the evaluation. If the output signal of the signal evaluation unit is linked in this way with the supply voltage of the control unit and / or the signal evaluation unit, the signal which can be tapped off at the connection point between the diode and the ohmic resistance, the so-called EoL signal, is characterized by the fact that it is intact Lamp is a signal of constant amplitude, whereas this signal is a rectangular signal when the lamp is defective. The difference between the DC signal and the square wave signal can be evaluated in a very simple way. As a result, an extremely cost-effective and reliable EoL detection can be realized.

In a realization of the signal evaluation unit by passive components, this has a capacitor which is arranged such that a voltage drops across it, which decreases the difference of the Gkichspannungsanteils the signals at the two inputs of the signal evaluation unit corresponds, wherein the capacitor is coupled via the series circuit of a diode and a resistor at the supply voltage terminal of the control unit. If, in turn, the so-called EoL signal at the connection point between the diode and the ohmic resistance is considered, an intact lamp can now be detected by a positive square-wave signal. A defective lamp is characterized by a signal of constant amplitude in the case of a positive direct-voltage useful signal, while a negative direct-voltage signal produces a rectangular-shaped EoL signal which, in contrast to the square-wave signal with an intact lamp, also has negative amplitude components. These three signals are also quite easy to distinguish from each other and allow a cost-effective and reliable EoL detection of a lamp.

Preferably, therefore, the connection point between the diode and the ohmic resistance is coupled to a shutdown or Abregeleingang the control unit.

The signal evaluation unit can comprise a comparator unit for carrying out a comparison of the voltage components of the signals at its two inputs.

Further preferred embodiments emerge from the subclaims.

Brief description of the drawings

Figur 1

in schematischer Darstellung einen Ausschnitt aus einem erfindungsgemäßen elektronischen Vorschaltgerät;

Figur 2

einen detaillierteren Ausschnitt aus Figur 1 bei einer Realisierung der Signalauswertungseinheit mit aktiven Bauelementen;

Figur 3a

den zeitlichen Verlauf des EoL-Signals bei einer Realisierung der Signalauswertungseinheit gemäß Figur 2 und defekter Lampe;

Figur 3b

den zeitlichen Verlauf des EoL-Signals bei einer Realisierung der Signalauswertungseinheit gemäß Figur 2 und intakter Lampe;

Figur 4

einen detaillierteren Ausschnitt aus Figur 1 bei einer Realisierung der Signalauswertungseinheit mit passiven Bauelementen;

Figur 5a

den zeitlichen Verlauf des EoL-Signals bei einer Realisierung der Signalauswertungseinheit gemäß Figur 4 im Falle eines positiven Gleichspannungsnutzsignals;

Figur 5b

den zeitlichen Verlauf des EoL-Signals bei einer Realisierung der Signalauswertungseinheit gemäß Figur 4 im Falle eines negativen Gleichspannungsnutzsignals; und

Figur 5c

den zeitlichen Verlauf des EoL-Signals bei einer Realisierung der Signalauswertungseinheit gemäß Figur 4 bei intakter Lampe.

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

FIG. 1

a schematic representation of a section of an electronic ballast according to the invention;

FIG. 2

a more detailed section of Figure 1 in a realization of the signal processing unit with active components;

FIG. 3a

the time profile of the EoL signal in a realization of the signal evaluation unit according to Figure 2 and defective lamp;

FIG. 3b

the time course of the EoL signal in a realization of the signal evaluation unit according to Figure 2 and intact lamp;

FIG. 4

a more detailed section of Figure 1 in an implementation of the signal evaluation unit with passive components;

FIG. 5a

the time profile of the EoL signal in a realization of the signal evaluation unit according to Figure 4 in the case of a positive DC voltage useful signal;

FIG. 5b

the time profile of the EoL signal in a realization of the signal evaluation unit according to Figure 4 in the case of a negative DC voltage useful signal; and

FIG. 5c

the time course of the EoL signal in a realization of the signal evaluation unit according to Figure 4 with an intact lamp.

Preferred embodiment of the invention

Figure 1 shows an inventive electronic ballast for a lamp in a schematic representation. Since such electronic ballasts are well known, for the sake of clarity, only the part relevant to the invention is shown schematically. In this case, a first S1 and second switch S2, which define a center M between them, are acted upon by the so-called intermediate _circuit voltage U _ZW . The center M is coupled via an inductance L1 to a first terminal A1 of a lamp La. The terminal A1 is also connected via a coupling capacitor C1 to the ground potential. The second terminal A2 for the lamp La is coupled via a coupling capacitor C2 to the ground potential. Between the center M of the half-bridge circuit and the first terminal A1 for a lamp, an inductor L1 is coupled. The electronic ballast comprises a control unit 14 which activates the switch S1 via an output 10 and the switch S2 in a push-pull manner via an output 12 in a known manner with an e-hole frequency square wave signal. At the input 16 of the control unit 14, the supply voltage U _{V of} the control unit 14 is applied. U _v is 15 V. The supply voltage U _V is generated from the voltage U _M at the midpoint of the bridge circuit by a bootstrap circuit comprising a capacitor C3 and a diode D1. The potential at the capacitor C3 is applied to an input 1S of the control unit 14 and serves to supply a arranged in the control unit 14 driver circuit (not shown) for the signal at the output 10 of the control unit 14. The electronic ballast according to the invention further comprises a Signahuswertungseinheit 20th of at its input 22, a signal is supplied to the the DC level of the terminal A2 for the lamp La is located. At the input 24, the signal evaluation unit 20 is supplied with a signal which is at the DC voltage level of the terminal A1 for the lamp La. At its output 26, the control unit 20 provides a so-called EoL signal, which is coupled to the input 25 of the control unit 14. The input 25 of the control unit 14 is also connected via a resistor R1 to the supply voltage U _v for the control unit 14. Via an optional line 29, the signal evaluation unit 20 is coupled to the capacitor C3. The signal evaluation unit 20 is supplied with the potential at C3 as a supply voltage and not the voltage U _V , which serves to supply the control unit 14, since the voltage U _{V is} a permanently connected to the ground potential voltage and the signal evaluation unit 20 according to their mitschwingendem reference potential also a resonant Supply voltage required. The line 29 is needed in an interpretation of the signal evaluation unit 20 with active components, while it is omitted in a realization of the signal evaluation unit 20 with passive components. The potential at the midpoint M of the bridge circuit, which is coupled to the signal evaluation unit 20 via the input 24, serves as DC reference potential for the signal evaluation unit 20.

Figure 2 shows a more detailed view of a detail of Figure 1, wherein the signal evaluation unit 20 is realized as an active circuit. It comprises a signal processing unit 30 which determines the difference in track voltage between the two signals applied to the inputs 22 and 24. It further comprises a delay unit 32, to which the output signal of the signal processing unit 30 is supplied. wherein the delay unit 32 serves to prevent premature shutdown due to only a short-term fulfillment of the shutdown condition. In particular, thereby shutdown states that last shorter than about 0.5 s, filtered out. The output signal of the delay unit 32 is fed to a memory unit 34, in particular a latch memory. Between the output of the memory unit 34 and the output 26 of the signal evaluation unit 20, a diode D2 is arranged. After a lamp failure, the latch accumulates, so that the voltage provided at the output of the memory unit 34 corresponds to the voltage U _M. U _M alternates between ground potential, ie 0 V, and the intermediate _circuit voltage U _ZW . The memory unit 34 is designed so that it provides a "low" signal at its output in the activated state. Due to the fact that the reference potential of the signal evaluation unit 20 is the voltage U _M , when the storage unit is activated, ie when the EoL situation has been established, the voltage U ₃₄ at the output is, therefore, the output Memory unit 34, the voltage U _M on. At the times when the voltage U ₃₄ relative to ground potential 0 V, the diode becomes conductive and the EoL signal is neglecting the diode voltage U _D2 to 0 V. If U _{34 is} equal to U _ZW , locks the diode D2 and the EoL signal is U _V equal to 15 V. In this context, reference is made to the representation in Figure 3a.

When the lamp is intact, the memory unit 34 provides a "high" signal at its output, ie U ₃₄ is therefore U _M + U _V. Regardless of the changes of U _M between 0 and U _ZW , therefore, the potential at the cathode of the diode D2 is always equal to U _V , so that the diode D2 always blocks. The EoL signal is therefore the same constant U _V , see the illustration in Figure 3b.

FIG. 4 shows a section from FIG. 1 corresponding to FIG. 2 when the signal evaluation unit 20 is realized by passive components. The signal at the input 24 of the signal evaluation unit 20 is supplied to the parallel connection of a capacitor C4 and an ohmic resistor R3, while the signal at the input 22 of the signal evaluation unit 20 is coupled via an ohmic resistor R2 to the series circuit of the capacitor C4 with the ohmic resistor R3. Diode D2 is present as in the embodiment of FIG. Referring to Figure 5, different states may occur depending on the DC difference between the signals at the inputs 22 and 24: where U _{C4 is} the voltage between the terminal of the capacitor C4 connected to the diode D2 and the ground potential.

Figure 5a: This figure shows the time course of the EoL signal, ie the voltage at the input 25 of the control unit 14, with a positive DC voltage useful signal. As long as the voltage U _{C4 is} greater than or equal to U _V plus U _M , the diode D2 blocks and the EoL signal corresponds to the voltage U _v , which is effected via the high-resistance resistor R1. If the voltage U _{C4 is} greater than U _M and less than U _v plus U _M. the diode D2 turns off at the times when U _{M is} equal to U _ZW . At the times when U _M is 0, the diode D2 becomes conductive and transmits the voltage U _C4 to the EoL input of the control unit 14. The voltage U _v is suppressed due to the high-resistance resistor R1 and does not come into play.

FIG. 5b: This figure shows the time profile of the EoL signal with a negative direct voltage useful signal. The capacitor C4 is therefore charged negatively. At times when U _{M is} equal to U _ZW , this negative charge will impact as a result of the greens Voltage U _ZW not off, the diode D2 turns off and the EoL signal is equal to U _V. At times when U _M equals 0, diode D2 becomes conductive and the negative voltage to which C4 is charged dominates the EoL signal because R1 is high impedance.

Figure 5c: This figure shows the time course of the EoL signal with an intact lamp. Accordingly, U _C4 is equal to U _M , so that the diode becomes conductive at U _M equal to 0V and the EoL signal is also 0 V. When U _{M is} equal to U _ZW , diode D2 turns off and the EoL signal is equal to U _V.

A corresponding evaluation of the EoL signal is realized in the control unit 14. Depending on the result of the evaluation, the switches S1 and S2 are correspondingly driven via the outputs 10 and 12 of the control unit 14.

Claims (7)

Electronic ballast for a lamp with - A bridge circuit comprising at least a first (S1) and a second (S2) switch, which are coupled between a terminal (A1) for a supply voltage and a terminal (A2) for a ground potential, wherein between the first (S1) and the second (S2) switch is defined as a midpoint (M) of the bridge circuit; - A first (A1) and a second (A2) terminal for a lamp (La), wherein the first terminal (A1) via an inductance (L1) to the center (M) of the bridge circuit is coupled; and - A signal evaluation unit (20), wherein the signal evaluation unit (20) comprises a first (24) and a second (22) input, wherein the first input (24) is coupled to a signal which is at the DC level of the first terminal (24). for the lamp (La), and wherein the second input (22) is coupled to a signal which is at the DC level of the second terminal (A2) for the lamp (La), characterized,
that the DC voltage reference potential for the signal evaluation unit (20) is made variable in a range of greater than or equal to the ground potential and less than or equal to the supply voltage potential. Electronic ballast according to claim 1,
characterized,
that the DC voltage reference potential for the signal evaluation unit (20) is substantially the potential (U _M) of the center point (M) of the bridge circuit. Electronic ballast according to one of claims 1 or 2.
characterized,
in that it furthermore comprises a control unit (14) for controlling the first (S1) and the second (S2) switch, wherein the control unit (14) has a cut-off or cut-off input which is coupled to the signal evaluation unit (20), wherein the control unit (14) and the signal evaluation unit (20) are designed to cooperate in such a way that, in the event of a difference in the DC voltage component of the signals at the two inputs (22, 24) of the signal evaluation unit over a predefinable limit value, the signal evaluation unit (20) controls the control unit (14) via the Switching or Abregeleingang such controls that no control of the first (S1) and / or the second (S2) switch is made or the first (S1) and / or the second switch (S2) are controlled such that the output power of the e electronic ballast is reduced. Electronic ballast according to claim 3,
characterized,
that the control unit (14) has a supply voltage connection and is connected to the ground potential as a DC voltage reference potential, the signal evaluation unit (20) comprises a latch and is designed to activate the latch if the difference for the DC component of the signals at the two inputs (22, 24 ) of the signal evaluation unit (20) is above a predeterminable limit value, wherein the output (26) of the latch on the series circuit of a diode (D2) and an ohmic resistance (R1) to the supply voltage terminal (16) of the control unit (14) and / or the signal evaluation unit (20) is coupled. Electronic ballast according to claim 3,
characterized,
in that the control unit (14) has a supply voltage connection and is connected to the ground potential as reference potential, the signal evaluation unit (20) has a capacitor (C4) which is arranged such that a voltage drops across it which corresponds to the difference in the DC voltage component of the signals the two inputs (22, 24) of the signal evaluation unit (20), wherein the capacitor (C4) via the series circuit of a diode (D2) and an ohmic resistance (R1) to the supply voltage terminal (16) of the control unit (14) is coupled , Electronic ballast according to claim 4 or 5,
characterized,
in that the connection point between the diode (D2) and the ohmic resistance (R1) is coupled to a turn-off or turn-off input of the control unit (14). Electronic ballast according to one of the preceding claims,
characterized,
in that the signal evaluation unit (20) comprises a comparator unit.

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