EP1492393B1 - Ballast for fluorescent lamp and method to detect eol - Google Patents

Description

The invention relates to a method for operating at least one low-pressure discharge lamp on an inverter according to the preamble of patent claim 1 and a Bethebsgerät for at least one low-pressure discharge lamp according to claim 9.

I. State of the art

Such an operating method is described, for example, in the international patent application with the publication number WO 99/56506 disclosed. This document describes the operation of a low-pressure discharge lamp on a circuit arrangement which has a half-bridge inverter with a load circuit connected thereto, in which the connections for the lamp are arranged. In order to detect the occurrence of the rectifier effect in the low-pressure discharge lamp, the voltage drop across the half-bridge capacitor is monitored, and when a predetermined upper limit value is exceeded or a predetermined lower limit value is exceeded, a shutdown device for the half-bridge inverter is activated.

The US 6,232,727 B1 discloses an operating method for a low-pressure discharge lamp with a power control and an automatic shutdown at the end of life of the low-pressure discharge lamp.

II. Presentation of the invention

It is the object of the invention to provide an operating method for at least one low-pressure discharge lamp, which enables a more reliable detection of the rectifying effect in the at least one low-pressure discharge lamp and in particular avoids disconnections of the operating device due to erroneous detection of the rectifier effect. In addition, it is the object of the invention to provide an operating device for at least one low-pressure discharge lamp for carrying out this method.

This object is achieved by the features of claim 1 and 9, respectively. Particularly advantageous embodiments of the invention are described in the dependent claims.

The method according to the invention for operating at least one low-pressure discharge lamp on an inverter is characterized in that for monitoring the occurrence of the rectifier effect in the at least one low-pressure discharge lamp, the DC voltage drop across the electrical terminals of the at least one low-pressure discharge lamp and the current through the at least one low-pressure discharge lamp or a thereto proportional size to be evaluated in order to define a criterion for the presence of the rectifier effect in the at least one low-pressure discharge lamp and thus a criterion for reaching the end of life of the at least one low-pressure discharge lamp. By monitoring and evaluating the aforementioned variables, the occurrence of the rectifier effect, regardless of the lamp used and the current dimming position can be determined with sufficient accuracy. The method according to the invention increases the reliability of the system consisting of the at least one low-pressure discharge lamp and the operating device, since the tolerance range for determining the end of life of the at least one low-pressure discharge lamp by means of the aforementioned variables can be specified more precisely and in this way a shutdown of the operating device due to an erroneous detection the rectifier effect is avoided.

For evaluating the above-mentioned variables, the product from the current through the at least one low-pressure discharge lamp and the DC voltage drop across the electrical terminals of the at least one low-pressure discharge lamp is advantageously compared with a predetermined power value, since this product directly measures the asymmetry of the emission behavior of the lamp electrodes and the Result provides a value for electrical power that can be directly compared to the maximum allowable value specified in the supplement to the IEC 61347-2-3 standard fluorescent lamps "under test 2" Asymmetric Power Dissipation. "This maximum value is 7.5 watts for T5 lamps and 5.0 watts for T4 lamps.

The comparison is repeated continuously throughout the lamp operation with updated values of the aforementioned magnitudes, in order to avoid overheating of the lamp electrodes in the event of the occurrence of the rectifier effect. In order to enable a reliable detection of the rectifier effect and thus does not lead to a random, exceeding the permissible maximum value to shutdown of at least one low-pressure discharge lamp, a counting operation is advantageously carried out depending on the result of the comparison and in the case of a counter overflow or when an upper Counter threshold one status bit set or reset. The status of the status bit is thus an indicator of whether the at least one low-pressure discharge lamp has already reached its end of life.

The evaluation is advantageously carried out with the aid of a microcontroller in which a corresponding program for carrying out the comparisons has been implemented. The microcontroller can additionally take over the control of the driver circuits for the transistor switches of the inverter. For evaluation, the values for the difference of a predefined power value and the product from the DC voltage drop across the electrical connections of the at least one low-pressure discharge lamp and the current through the at least one low-pressure discharge lamp or a variable proportional thereto are preferably added up at different times of the lamp operation.

The current through the at least one low-pressure discharge lamp or the variable proportional thereto is advantageously determined by means of a resistor which is connected in series with the at least one low-pressure discharge lamp during a half-wave of the current through the at least one low-pressure discharge lamp, for example during the positive half-wave. The current through the at least one low-pressure discharge lamp is determined from the voltage drop across this resistor, preferably after smoothing by means of a low-pass filter connected downstream of the resistor. The voltage drop across the aforementioned resistor can additionally: be used for brightness control of at least one Niederdruckentladungslainpe. The same measured values can therefore be evaluated, for example with the aid of a microcontroller, both for controlling the brightness and for detecting the end of life of the at least one low-pressure discharge lamp.

• einen Halbbrückenwechselrichter, an den ein Lastkreis angeschlossen ist, in dem elektrische Anschlüsse für mindestens eine Niederdruckentladungslampe und mindestens ein Halbbrückenkondensator angeordnet sind,
• eine erste Messvorrichtung zur Messung einer ersten Spannung, die proportional zu dem Strom durch die mindestens eine Niederdruckentladungslampe ist,
• eine zweite Messvorrichtung zur Messung einer zweiten Spannung, die proportional zu dem Spannungsabfall an dem mindestens einen Halbbrückenkondensator ist,
• eine dritte Messvorrichtung zur Messung einer dritten Spannung, die proportional zur Versorgungsspannung des Halbbrückenwechselrichters ist, und
• eine Auswertungseinheit, die mit den Ausgängen der Messvorrichtungen verbunden ist, einen programmgesteuert arbeitenden Mikrocontroller umfasst und die zur Auswertung der ersten, zweiten und dritten Spannung sowie zur Steuerung des Halbbrückenwechselrichters in Abhängigkeit von dem Ergebnis der Auswertung dient.

The operating device according to the invention for at least one low-pressure discharge lamp has the following features:

• a half-bridge inverter, to which a load circuit is connected, in which electrical connections for at least one low-pressure discharge lamp and at least one half-bridge capacitor are arranged,
• a first measuring device for measuring a first voltage, which is proportional to the current through the at least one low-pressure discharge lamp,
• a second measuring device for measuring a second voltage that is proportional to the voltage drop across the at least one half-bridge capacitor,
• a third measuring device for measuring a third voltage which is proportional to the supply voltage of the half-bridge inverter, and
• an evaluation unit which is connected to the outputs of the measuring devices, comprises a program-controlled operating microcontroller and which serves to evaluate the first, second and third voltage and to control the half-bridge inverter depending on the result of the evaluation.

The operating device described above makes it possible to carry out the operating method according to the invention.

III. Description of the Preferred Embodiment

Figur 1

Eine Schaltskizze der Schaltungsanordnung des erfindungsgemäßen Betriebsgerätes zur Durchführung des erfindungsgemäßen Betriebsverfahrens in schematischer Darstellung

Figur 2

Ein Flussdiagramm des erfindungsgemäßen Betriebsverfahrens

The invention will be explained in more detail below with reference to a preferred embodiment. Show it:

FIG. 1

A circuit diagram of the circuit arrangement of the operating device according to the invention for carrying out the operating method according to the invention in a schematic representation

FIG. 2

A flow chart of the operating method according to the invention

At the in FIG. 1 schematically illustrated operating device according to the invention is an electronic ballast for the operation of two parallel-connected low-pressure discharge lamps, in particular T5 fluorescent lamps FL1, FL2. This ballast in particular also allows brightness regulation of the fluorescent lamps FL1, FL2.

The ballast has two mains voltage terminals 1, 2, a downstream mains voltage rectifier GL, which also includes a filter circuit and optionally a boost converter and at the voltage output, the supply voltage for the downstream half-bridge inverter is provided. The half-bridge inverter has two half-bridge transistors T1, T2, at whose center tap M a load circuit formed as a series resonant circuit is connected, which comprises the resonance inductance L 1 and the resonance capacitor C 1. Parallel to the resonance capacitor C1, a parallel circuit consisting of two fluorescent lamps FL1, FL2 is arranged. This parallel circuit has two half-bridge capacitors C2, C3, which are each arranged in series with one of the fluorescent lamps FL1 and FL2. In addition, in each branch of the parallel circuit, a winding N1 or N2 of a balancing transformer L2 is connected, which serves to balance the lamp currents in the two branches. The high-potential terminal A2 of the first half-bridge capacitor C2 is connected through the winding N2 of the transformer L2, the electrode E2 of the first fluorescent lamp FL1 and the resistor R1 to the positive DC voltage output of the mains voltage rectifier GL. Analogously, the high-potential terminal A3 of the second half-bridge capacitor C3 is connected to the positive DC voltage output of the mains voltage rectifier GL via the winding N 1 of the transformer L2, the electrode E4 of the second fluorescent lamp FL2 and the resistor R2. The low potential Terminals of the half-bridge capacitors C2, C3 are respectively connected to the negative DC voltage output of the mains voltage rectifier GL and the ground potential. The terminal A1 of the resonance capacitor C1 is connected to the electrode E1 of the first fluorescent lamp FL1 and the electrode E3 of the second fluorescent lamp and connected via the resonance inductor L1 to the center tap M of the half-bridge inverter. The other terminal of the resonant capacitor C1 is connected to the negative DC voltage output of the mains voltage rectifier GL and the ground potential. In addition, the terminal A1 is connected via the electrode E1 and the resistor R3 to the positive DC voltage output of the mains voltage rectifier GL. The in the FIG. 1 only schematically illustrated heater H is inductively coupled to all electrodes E1, E2, E3, E4 of the two fluorescent lamps FL1, FL2 and is used to heat the lamp electrodes before the ignition of the gas discharge or during the dimming operation of the lamps. Details of this heater H are, for example, in the published patent application EP 0 748 146 A1 described. The resistors R0, R1, R2 and R3 serve to adjust the potentials at the taps A1, A2 and A3. In particular, by means of the abovementioned resistors, the corresponding electrical voltages can build up on the capacitors C1, C2 and C3 immediately after switching on the operating device and before igniting the gas discharge in the lamps FL1, FL2.

The control of the half-bridge transistors T1, T2 takes place with the aid of the programmatically operating microcontroller MC and the driver circuits TR for the transistors T1, T2. By alternately switching the transistors T1, T2, the center tap M is alternately connected to the negative and the positive DC output of the mains voltage rectifier GL. Since the half-bridge capacitors C2, C3 are charged to half the supply voltage of the half-bridge inverter flows during lamp operation between the taps M and A2 and A3, a high-frequency alternating current whose frequency is determined by the switching clock of the transistors T1, T2. For igniting the gas discharge in the fluorescent lamps FL1, FL2, the switching clock of the half-bridge transistors T1, T2 is changed such that the frequency of the alternating current in the load circuit is close to the resonance frequency of the series resonant circuit L1, C1. As a result, a sufficiently high voltage is generated at the resonance capacitor C 1 in order to ignite the gas discharge in the fluorescent lamps FL1, FL2. After igniting the gas discharge in the fluorescent lamps FL1, FL2, the series resonant circuit L1, C1 is attenuated by the parallel connection of the fluorescent lamps FL1, FL2. The brightness control of the fluorescent lamps FL1, FL2 also takes place by changing the frequency of the alternating current in the load circuit and in the parallel connection of the fluorescent lamps FL1, FL2.

For measuring the current I through the parallel connection of the lamps FL1, FL2 serve the resistor R14, the two rectifier diodes D3, D4 and the low-pass filter R15, C10. Due to the polarity of the two diodes D3, D4, a voltage which is proportional to the positive half-wave of the current 1 is measured at the resistor R14. By means of the low-pass filter R15, C10 connected downstream, a value U 1 of this voltage averaged over one or more half-waves is supplied to the terminal A 11 of the microcontroller MC for evaluation. The time-averaged voltage U 1 is therefore proportional to the time average I _{+ of} the positive half-wave of the current I through the parallel-connected lamps FL1, FL2. The voltage U1 detected at the terminal A11 is also used to control the brightness of the two fluorescent lamps FL1, FL2.

Parallel to the DC voltage output of the mains voltage rectifier GL, the voltage divider R6, R7 is arranged with the capacitor C5 connected in parallel with the resistor R7. At the tap A6 between the resistors R6, R7, which is connected to the corresponding terminal A6 of the microcontroller MC, the voltage U2 is measured, which is proportional to the supply voltage of the half-bridge inverter. Parallel to the half-bridge capacitor C3, the voltage divider R8, R9 is arranged with the parallel to the resistor R9 connected capacitor C6. At the tap A7 between the resistors R8, R9, which is connected to the corresponding terminal A7 of the microcontroller MC, the voltage U3 is measured, which is proportional to the voltage drop across the half-bridge capacitor C3. Similarly, parallel to the half-bridge capacitor C2 the voltage divider R10, R11 is arranged with the capacitor C7 connected in parallel with the resistor R11. At the tap A8 between the resistors R10, R11, which is connected to the corresponding terminal A8 of the microcontroller MC, the voltage U4 is measured, which is proportional to the voltage drop across the half-bridge capacitor C2.

The voltage applied to the terminals A6, A7, A8 and A11 voltages U1 to U4 are converted by analog-to-digital converters into digital values and evaluated by the microcontroller MC using a program implemented in the microcontroller to the driver circuit TR by an appropriate controller the half-bridge transistors T1, T2 to ensure a brightness control of the fluorescent lamps FL1, FL2 and a detection of the end of life of the lamps FL1, FL2. The end of life of the lamps FL1, FL2 is detected by monitoring the occurrence of the rectifier effect in the fluorescent lamps FL1 FL2. For this purpose, by means of the microcontroller MC, the DC voltage _drop U _dc1 or U _dc2 across the electrical connections of the fluorescent lamps FL1, FL2 and the current through the fluorescent lamps FL1, FL2, that is, the total current 1 through the parallel connection of the lamps FL1, FL2. evaluated. The mean value I ₊ over the positive half wave of this current I is calculated from the voltage U1 and the resistance R14 to: $$I_{+}=\frac{U1}{R14}$$

The DC voltage _drop U _dc1 across the electrical terminals of the fluorescent lamp FL1 is calculated from the difference of half the supply voltage of the half-bridge inverter and the voltage drop across the half-bridge capacitor C2 and can therefore be determined from the voltages U2 and U4. $$U_{\mathit{de}1}=\frac{1}{2}\cdot U2\cdot \frac{R6+R7}{R7}-U4\cdot \frac{R10+R11}{R11}$$

Analogously, the DC voltage _drop U _dc2 across the electrical connections of the fluorescent lamp FL2 is calculated from the difference of the half Supply voltage of the half-bridge inverter and the voltage drop across the half-bridge capacitor C3 and can therefore be determined from the voltages U2 and U3. $$U_{\mathit{de}2}=\frac{1}{2}\cdot U2\cdot \frac{R6+R7}{R7}-U3\cdot \frac{R\mathrm{8th}+R9}{R9}$$

berechnet werden, wobei der Korrekturfaktor p von der Kurvenform abhängt und sich aus dem Formfaktor k und dem Tastverhältnis τ ergibt zu: $$p=\frac{k^2}{\tau }$$

From the above variables I ₊ and U _dc1 , or U _dc2 can for both fluorescent lamps FL1 and FL2, the power P1 or P2 by means of the formula $$P1=I_{+}\cdot \left|U_{\mathit{de}1}\right|\cdot p\mathrm{respectively}\mathrm{,}P2=I_{+}\cdot \left|U_{\mathit{de}2}\right|\cdot p$$

the correction factor p depends on the curve shape and results from the form factor k and the duty cycle τ: $$p=\frac{{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">k</figure-callout>}}^2}{\tau }$$

For a sinusoidal signal with a duty cycle of 0.5, the correction factor p has the value 1.11. The values of the outputs P 1 or P 2 can be directly compared with the maximum permissible limit P _max of 7.5 W for the lamp power at T5 listed in the "Test 2: Asymmetric Power Dissipation" of the supplement to the standard IEC 61347-2-3 Lamps are compared to monitor the end of life of the two fluorescent lamps FL1, FL2. This comparison is cyclically repeated by the microcontroller MC during lamp operation for both lamps FL1, FL2.

In order for the comparative evaluation in the microcontroller, the second multiplication in the formulas (4a, 4b) to save, the correction factor p is taken into account in the comparison value P _max and deposited with this value in the nonvolatile memory. During operation, this stored value is then compared cyclically with the product of I ₊ and the amount of U _dc1 and U _dc2 , respectively.

The following is the procedure for monitoring the end of life of the two T5 fluorescent lamps FL1, FL2 using the method described in US Pat FIG. 2 illustrated flowchart explained in more detail.

At the beginning of the cyclical process, by means of the program implemented in the microcontroller MC, the measured values for the variables U1, U2 and U3 or U4 are updated sequentially for both lamps FL1 and FL2 according to the above formulas for the powers P1 and P2 calculated and compared respectively with the maximum allowable power P _max . If the power P1 or P2 is less than the maximum allowable power P _max and the count of the counter variables Z 1 and Z2 for the lamp FL1 and FL2 is equal to zero, the current cycle for the lamp FL1 or FL2 is exited. If the power P1 or P2 is smaller than the maximum permissible power P _max and the counter reading of the counter variables Z1 or Z2 for the lamp FL1 or FL2 is greater than zero, the counter Z1 or Z2 is decremented by the value 1. Thereafter, when the count is zero, the status bit S1 or S2 for reaching the end of life of the lamp FL1 or FL2 is deleted, otherwise the new count Z1 or Z2 is stored and leave the current cycle for the lamp FL1 or FL2 , If the power P1 or P2 but not smaller than the maximum allowable power P _max , the counter Z1 or Z2 is increased by 1. Thereafter, if the value of the counter Z1 or Z2 exceeds the upper counter threshold ZSW, then the status bit S1 or S2 is set, that is, the lamp FL1 or FL2 has reached its end of life. If the value of the counter Z1 or Z2 is not greater than the upper counter threshold ZSW, the new counter reading Z1 or Z2 is stored and then the current cycle for the lamp FL1 or FL2 is exited. The value of the upper counter threshold ZSW can be specified.

In the event that the status bit S1 or the status bit S2 is set, the operating device is switched off.

The invention is not limited to the embodiment explained in more detail above. For example, the lamps FL1, FL2 may also be interrogated alternately instead of one after the other in the same cycle. Furthermore, the counter readings Z1, Z2 be increased or decreased by a value greater than 1 in the event of a high overshoot or undershoot of the permissible limit value. Instead of switching off the operating device or the lamps FL1, FL2 when the permissible maximum limit value is exceeded, it is also possible to operate the lamps FL1, FL2 with considerably reduced power until the permissible limit value is again permanently undershot.

Claims (9)

1. Method for operating at least one low-pressure discharge lamp using a half-bridge inverter (T1, T2), to which a load circuit (L1, C1) is connected, in which electrical connections for at least one low-pressure discharge lamp (FL1, FL2) and at least one half-bridge capacitor (C2, C3) are arranged, during the operation of the at least one low-pressure discharge lamp (FL1, FL2) the occurrence of a rectifier effect in the at least one low-pressure discharge lamp (FL1, FL2) being monitored in order to determine the end of its life, characterized in that, for the purpose of monitoring the rectifier effect of the at least one low-pressure discharge lamp (FL1, FL2), the DC voltage drop (U_dc1, U_dc2) across the electrical connections of the at least one low-pressure discharge lamp (FL1, FL2) and the current (I) through the at least one low-pressure discharge lamp (FL1, FL2) or a variable proportional thereto are evaluated by virtue of a first voltage (U1) being measured, which is proportional to the current (I) through the at least one low-pressure discharge lamp (FL1, FL2), and the DC voltage drop (U_dc1, U_dc2) being calculated from the difference between half the supply voltage of the half-bridge inverter (T1, T2) and the voltage drop across the at least one half-bridge capacitor (C3, C2) by means of a measured second voltage (U3, U4), which is proportional to the voltage drop across the at least one half-bridge capacitor (C3, C2), and a measured third voltage (U2), which is proportional to the supply voltage of the half-bridge inverter (T1, T2).
2. Method as claimed in Claim 1, characterized in that the product of the DC voltage drop (U_dc1, U_dc2) across the electrical connections of the at least one low-pressure discharge lamp (FL1, FL2) and the current (I) through the at least one low-pressure discharge lamp (FL1, FL2) or a variable proportional thereto is compared with a predetermined power value (P_max).
3. Method as claimed in Claim 2, characterized in that the comparison is repeated cyclically during the lamp operation.
4. Method as claimed in Claim 1, characterized in that the DC voltage drop (U_dc1, U_dc2) across the electrical connections of the at least one low-pressure discharge lamp (FL1, FL2) and the current through the at least one low-pressure discharge lamp (FL1, FL2) or a variable proportional thereto are determined from measured values which are supplied to a microcontroller (MC), and an evaluation is carried out in a program-controlled manner by means of the microcontroller (MC).
5. Method as claimed in one or more of Claims 2, 3 or 4, characterized in that a counting operation (Z1, Z2) is carried out as a function of the result of the comparison, and, in the event of a counter overflow, a status bit (S1, S2) is set or reset.
6. Method as claimed in one or more of Claims 1 to 5, characterized in that the values, which are determined at different points in time in the lamp operation, for the difference between a predetermined power value (P_max) and the product of the DC voltage drop (U_dc1, U_dc2) across the electrical connections of the at least one low-pressure discharge lamp (FL1, FL2) and the current through the at least one low-pressure discharge lamp (FL1, FL2) or a variable proportional thereto are totaled and evaluated.
7. Method as claimed in Claim 1, characterized in that the current through the at least one low-pressure discharge lamp (FL1, FL2) or the variable proportional thereto is determined by means of a resistor (R14) which, during a half-cycle of the current through the at least one low-pressure discharge lamp (FL1, FL2), is connected in series with the at least one low-pressure discharge lamp (FL1, FL2).
8. Method as claimed in Claim 7, characterized in that the voltage drop across the resistor (R14) is evaluated by means of a low-pass filter (R15, C10).
9. Operating device for at least one low-pressure discharge lamp (FL1, FL2) having

   - a half-bridge inverter (T1, T2), to which a load circuit (L1, C1) is connected, in which electrical connections for at least one low-pressure discharge lamp (FL1, FL2) and at least one half-bridge capacitor (C2, C3) are arranged,

   - a first measuring apparatus (R14, R15, D3, D4, C10) for measuring a first voltage (U1), which is proportional to the current through the at least one low-pressure discharge lamp (FL1, FL2),

   - a second measuring apparatus (R8, R9, C6; R10, R11, C7) for measuring a second voltage (U3, U4), which is proportional to the voltage drop across the at least one half-bridge capacitor (C3, C2),

   - a third measuring apparatus (R6, R7, C5) for measuring a third voltage (U2), which is proportional to the supply voltage of the half-bridge inverter, and

   - an evaluation unit (MC, TR), which is connected to the outputs of the measuring apparatuses, and comprises a program-controlled microcontroller (MC),

   - the microcontroller (MC) being programmed in such a way that, for the purpose of monitoring the rectifier effect in the at least one low-pressure discharge lamp (FL1, FL2), the first voltage (U1) and the DC voltage drop (U_dc1, U_dc2) across the electrical connections of the at least one low-pressure discharge lamp (FL1, FL2) are evaluated and, depending on the result of the evaluation, the half-bridge inverter (T1, T2) is controlled by virtue of the DC voltage drop (U_dc1, U_dc2) being calculated from the difference between half the supply voltage of the half-bridge inverter (T1, T2) and the voltage drop across the at least one half-bridge capacitor (C3, C2) by means of the measured second voltage (U3, U4) and the measured third voltage (U2).

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