EP0800335B1 - Circuit for operating electric lamps - Google Patents

Description

The invention relates to a circuit arrangement for operating electrical Lamps according to the preamble of claim 1.

Such a circuit arrangement is, for example, in the European one Patent EP 0 093 469 discloses. This document describes an inverter especially a self-oscillating half-bridge inverter with two alternating switching inverter transistors in their control circuit a time switch device is arranged in each case. These timers consist essentially of an auxiliary transistor and an RC element, whose ohmic resistance is caused by a Zener diode is bridged, and its capacitor parallel to the base-emitter path of the auxiliary transistor is switched. Because of the Zener diodes they have Time switch devices voltage-dependent time constants, the one Control of the frequency and duty cycle of the half-bridge inverter as well as setting defined heating and ignition conditions for which enable low pressure discharge lamps. A disadvantage here however, the large tolerance dependency of the electrode preheating, ignition and Operating parameters from the electronic components used. During the electrode preheating phase there is an asymmetrical control of the half-bridge inverter applied. Because of this, one delivers Circuit arrangement according to EP 0 093 469 with the same dimensions the load circuit components and with the same voltage on the lamps during the electrode preheating phase has a lower heating current than a comparable one Circuit arrangement with symmetrical control of the half-bridge inverter. This disadvantage of the circuit arrangement according to that in the aforementioned Circuit arrangement described occurs particularly in the so-called T2 and T5 fluorescent lamps, the comparatively sensitive electrodes possess. In order with the circuit arrangement according to EP 0 093 469 Adequate preheating of the electrode filaments also for the aforementioned lamp types To ensure a resonance capacitor with a comparatively large capacity can be used. However, this measure would become one higher load on the entire components of the circuit arrangement during the Burning operation of the lamps. In particular, the so-called pen current, that is the continuous heating current flowing through the lamp electrode filaments, which is additive from the current through the resonance capacitor arranged parallel to the lamp and from the one flowing over the discharge path of the lamp Electricity, increase so that with premature lamp failures, conditional due to excessive thermal stress on the electrode coils should be.

The published patent application DE 38 41 095 A1 describes a circuit arrangement of a Half bridge inverter for the ignition and AC operation of Discharge lamps. To ignite the lamps with preheated electrodes too enable, are parallel to the emitter resistances of the half-bridge inverter transistors Darlington transistors connected, one of the Darlington transistors is connected to a timer, the input of a threshold switch is connected to one of the control transformer and the output of the threshold switch the power supply of the other Darlington transistor switches.

The published patent application EP 0 093 469 A2 discloses a half-bridge inverter to ignite and power a discharge lamp. In line with the discharge lamp the primary winding of a transformer is switched. The secondary windings of the transformer are with a voltage-dependent elements having time switch of a control device for the half-bridge inverter transistors connected.

The published patent application EP 0 541 908 A1 describes a circuit arrangement for Operation of one or more low-pressure discharge lamps with a half-bridge inverter. Parallel to the basic series resistors of the half-bridge inverter transistors a parallel branch is connected, each consisting of one Threshold switch and an ohmic resistance to the aforementioned Transistors during the ignition phase of the lamps with an additional positive To supply basic electricity.

It is the object of the invention to provide a self-oscillating half-bridge inverter having circuit arrangement for operating electrical lamps with an improved one, tailored to the different phases of lamp operation Provide control of the inverter transistors. In particular, the Circuit arrangement according to the invention when operating the above-mentioned fluorescent lamps on the one hand, satisfactory preheating of the lamp electrodes ensure and on the other hand avoid an excessive increase in the pin current.

This object is achieved by the characterizing features of claim 1 solved. Particularly advantageous versions of the Invention are described in the subclaims.

The circuit arrangement according to the invention has a self-oscillating Half-bridge inverter, at the output of which is a resonant circuit trained load circuit is connected in which at least one electric lamp is arranged. The two inverter transistors have a control circuit, in each of which an auxiliary transistor is connected. According to the invention, these auxiliary transistors are in the control circuits of the Inverter transistors switched that the emitter or source resistance of these inverter transistors formed by a parallel connection is made up of at least one ohmic resistor and the parallel to it arranged control path of the corresponding auxiliary transistor. In addition, the control inputs of the two auxiliary transistors are according to the invention connected to the output of a common control circuit. These measures allow the effective emitter resistance or Source resistance of the half-bridge inverter transistors and thus the Feedback for the half-bridge inverter transistors depending of the different operating phases - these are for low-pressure discharge lamps: Preheating the lamp electrodes, ignition of the Lamp to switch lamp operation. This switching of Feedback changed for the half-bridge inverter transistors the duty cycle and / or the clock frequency of the half-bridge inverter. The resulting frequency detuning between the resonance frequency the load circuit and the clock frequency of the half-bridge inverter enables an optimal one for each of the three operating phases mentioned above Adaptation of the electrical parameters in the load circuit. The feedback the half-bridge inverter transistors can be changed by a suitable one Dimensioning of the ohmic resistances of the invention Parallel circuits, the emitter resistors or source resistors which form half-bridge inverter transistors, influence them within wide limits.

The parallel circuits according to the invention advantageously have the form the emitter resistances of the half-bridge inverter transistors, in each case at least one further ohmic resistance, which is in series with the Control path of the corresponding auxiliary transistor switched and parallel to the at least one ohmic resistance of the relevant parallel circuit is arranged. The dimensioning of these ohmic resistors is advantageously chosen such that for each of the invention, the Emitter resistance of a half-bridge inverter transistor Parallel connections the total resistance of the parallel to the control path of the auxiliary transistor arranged ohmic resistances by approximately one Order of magnitude greater than the total resistance of the series to that Auxiliary transistor is switched ohmic resistors. These measures ensure that the feedback of the half-bridge inverter in wide limits can be varied.

The auxiliary transistors are advantageously parallel to the control paths one capacitor each, to which in turn at least in each case a discharge resistor is connected in parallel. In addition, the exit is the Control circuit each with at least one charging resistor Control inputs of the auxiliary transistors connected. The resistance values of these charging resistors are smaller than the resistance values of the discharge resistors, so that the time constant for the discharge of the parallel capacitors connected to the auxiliary transistors considerably larger than is the time constant for the charging of these capacitors. It also takes place advantageously the connection in at least one auxiliary transistor to the output of the control circuit via at least one diode. These measures ensure reliable control of the auxiliary transistors from a common control circuit.

The half-bridge inverter transistors are advantageously bipolar transistors, while the auxiliary transistors advantageously field effect transistors are.

The preferred embodiment of the circuit arrangement according to the invention also has a voltage divider that has a tap is connected to a resonant circuit component in the load circuit and the voltage drop monitored on this component. The control input one of the Auxiliary transistors are connected to the latter, advantageously via a threshold value element Voltage divider connected. This voltage divider allows the electrical conductivity of the drain-source path of the aforementioned Auxiliary transistor depending on the voltage drop on the with Constantly vary voltage divider connected resonance circuit component. Thereby the effective emitter resistance of the corresponding one also changes Half-bridge inverter transistor steady. The above Voltage divider also offers the option of reducing the voltage to regulate on the resonant circuit component in a continuous manner.

The invention based on a preferred embodiment explained in more detail.

The figure shows the circuit arrangement according to the preferred embodiment. This circuit arrangement is used to operate a T5 fluorescent lamp LP, which is an electrical power consumption (nominal power) of approximately 35 W. Appropriate dimensioning of the electrical components of the preferred embodiment of the invention Circuit arrangement is given in the table.

This circuit arrangement has one with two npn bipolar transistors Q1, Q2 fitted self-oscillating half-bridge inverters. The Half-bridge inverter is supplied with a DC voltage that is on is usually obtained by rectification from the mains voltage. At the output M of the half-bridge inverter is a resonance circuit trained load circuit connected. It contains the primary winding RKa of a toroidal transformer, a resonance inductance L1, the electrode coil E1 of the lamp LP, a resonance capacitor C1 and the Electrode filament E2 of the fluorescent lamp LP. The discharge path of the Low pressure discharge lamp LP is parallel to the resonance capacitor C1 is switched. The resonance capacitor C1 is also across the electrode coil E2 to the center tap V1 between the two coupling capacitors C2, C3 connected, which in turn are parallel to the half-bridge inverter Q1, Q2 are arranged.

The half-bridge inverter is controlled using the Toroidal transformer, whose primary winding RKa is part of the load circuit is, and the secondary windings RKb, RKc each in one Control circuit of the half-bridge inverter transistors Q1, Q2 arranged are. To ensure that the half-bridge inverter starts up, the circuit arrangement has a starting device which essentially from the start capacitor C5, the diac DC, the diode D3 and the ohmic resistors R2, R12, R13, R14. The two bipolar transistors Q1, Q2 of the half-bridge inverter are each with a pre-run diode D1, D2 equipped parallel to the collector-emitter path of the corresponding transistors Q1, Q2 are connected. Parallel to the freewheeling diode D1 are arranged an ohmic resistor R1 and a capacitor C4. As far as the circuit arrangement corresponds to a self-oscillating, Half-bridge inverter like the one on pages 62-63 of the Book "Schaltnetzteile" by W. Hirschmann / A. Hauenstein, publisher Siemens AG is disclosed.

The control circuits of the two bipolar transistors Q1, Q2 each contain one Base series resistor R3 or R4, which has an inductance L2 or L3 with the secondary winding RKb or arranged in this control circuit RKc of the toroidal transformer is connected. The emitter resistance of the Bipolar transistor Q1 is made by one of the ohmic resistors R5, R6 and the auxiliary transistor T1 existing parallel circuit is formed. This Parallel connection is carried out in such a way that the lower resistance R6 is arranged in series with the drain-source path of the auxiliary transistor T1 and the higher impedance resistor R5 in parallel with this from the resistor R6 and the drain-source path of the auxiliary transistor T1 existing Series connection is switched. The emitter resistance of the Bipolar transistor Q2 from one of the ohmic resistors R7, R8 and the parallel transistor consisting of the auxiliary transistor T2. This parallel connection is also designed so that the lower resistance R8 arranged in series with the drain-source path of the auxiliary transistor T2 and the higher impedance resistor R7 is parallel to this from the resistor R8 and the drain-source path of the auxiliary transistor T2 existing Series connection is switched. The control circuits of the two half-bridge inverter transistors Q1, Q2 also each have a base-emitter parallel resistor R9 or R10, which is parallel to the base-emitter path of the corresponding bipolar transistor Q1, Q2 is switched and that Switching behavior of these two bipolar transistors Q1, Q2 improved.

The two auxiliary transistors T1, T2 are field effect transistors, which are controlled with the aid of the control circuit IC. To this Purpose is the output of the control circuit IC on the one hand via the ohmic Resistor R11 and diode D5 with the gate terminal of the field effect transistor T1 and on the other hand via the ohmic resistor R21 with the Gate connection of the field effect transistor T2 connected. Parallel to the gate of the field effect transistor T1 and T2 are a capacitor C6 and C7 and an ohmic resistor R15 or R16 switched. Besides, is parallel to the gate of each auxiliary transistor T1, T2, one each as overvoltage protection serving Zener diode Z1, Z2 arranged.

The circuit arrangement also has a voltage divider, which is essentially consists of resistors R17, R18 and R19. This voltage divider is across capacitor C8 and branch point V2 with one connection of the resonance capacitor C1 and with one connection the lamp electrode E1 connected, so that the voltage divider alternating current is connected in parallel to the resonance capacitor C1. The center tap V3 between the resistors R18, R19 of the voltage divider via a diode D6 and a Zener diode DZ with the gate terminal of Field effect transistor T2 connected. The Zener diode DZ and the diode D6 are polarized in opposite directions.

After switching on the circuit arrangement, the starting capacitor charges C5 through the resistors R12, R13 to the breakdown voltage of the Diacs DC on, which then triggers the base of the bipolar transistor Q2 generates and thereby the half-bridge inverter starts to oscillate causes. After the transistor Q2 is turned on, the starting capacitor Discharge C5 via resistor R2 and diode D3 until the diac DC does not generate any further trigger pulses. The two inverter transistors Q1, Q2 switch alternately, so that the center tap M the half bridge alternating with the positive or negative pole of the DC voltage supply connected is. As a result, between the taps M and V1 in the load circuit designed as a series resonant circuit is a medium frequency Generates alternating current, the frequency of which is the clock frequency of the Half-bridge inverter. The clock frequency of the half-bridge inverter is usually more than 20 kHz. The electronic Components of the circuit arrangement according to the invention are also dimensioned so that the clock frequency of the self-oscillating half-bridge inverter above the resonance frequency of the series resonance circuit L1, C1 lies. The auxiliary transistors T1, T2 are initially in the blocked state, so that as an emitter resistor for the bipolar transistors Q1, Q2 only the higher impedance resistors R5 and R7 are effective. These comparatively large emitter resistors R5, R7 cause one relatively strong negative feedback of the half-bridge inverter. Thereby the toroidal transformer already reaches within a comparatively short period of time its saturation magnetization, so that the clock frequency of the half-bridge inverter is correspondingly high. The clock frequency of the half-bridge inverter is initially so far above that Resonance frequency of the resonance circuit L1, C1, that of the resonance capacitor C1 build-up voltage drop is not sufficient to the Ignite fluorescent lamp LP. During this immediately after the start of the half-bridge inverter, the electrode preheating phase flows through the electrode filaments E1, E2 of the lamp LP and a medium-frequency heating current via the resonance capacitor C1, which the Electrode filaments E1, E2 heated. After the expiry of the control circuit IC predetermined preheating time, the control circuit IC switches its Output voltage from about 0 V to about 10 V to 12 V around, so that the Control voltage for switching the field effect transistor T2 over the Resistor R21 is built up on capacitor C7.

While transistor Q2 is on, that is, during center tap M of the half-bridge inverter is at ground potential analogous to this via the resistor R11 and the diode D5 on the capacitor C6 the control voltage for switching on the field effect transistor T1 on. While the bipolar transistor Q2 is turned on Capacitor C6 from the control circuit IC through the charging resistor R11 and via the diode D5 to the for switching on the auxiliary transistor T1 required control voltage is charged. Since the discharge resistor R15 has a considerably higher resistance value than the charging resistor R11, the time constant of the capacitor C6 is essential for the discharge process larger than for the charging process, so that the capacitor C6 too then the control voltage required for switching Auxiliary transistor T1 is present when the duty cycle of the bipolar transistor Q2 has already ended. In each switch-on phase of the bipolar transistor Q2 the capacitor C6 is recharged via the resistor R11 and the diode D5.

When the field effect transistors T1 are switched on, the effective emitter resistance is for the bipolar transistors Q1 through the total or equivalent resistance given the now connected resistors R5 and R6, if you look at the resistance of the drain-source path of the auxiliary transistor T1 refrains. The same applies in a similar way to the effective emitter resistance of the bipolar transistor Q2, which is turned on Auxiliary transistor T2 essentially from the equivalent resistance of the parallel resistors R7 and R8 results. Because of the significantly lower effective Emitter resistance of the bipolar transistors Q1, Q2 and the resulting ones resulting reduced negative feedback of the half-bridge inverter the clock frequency of the half-bridge inverter drops. The upset between the clock frequency of the half-bridge inverter and the Resonance frequency of the resonance circuit L1, C1 drops so far that on Resonance capacitor C1 through the method of resonance exaggeration ignition voltage required to ignite the lamp LP is generated.

After the lamp LP has been ignited, it is then electrically conductive Discharge path of the lamp LP shunts to the resonance capacitor C1 represents, so that only the operating voltage via the resonance capacitor C1 the lamp LP falls off.

Because of the sensitive electrodes E1, E2 of the lamp LP, the resonance circuit components are C1, L1 dimensioned in the preferred embodiment such that only a relatively small pin current through the electrodes E1, E2 flows. The resonant circuit of the preferred embodiment therefore has one a comparatively large resonance inductance L1 and one relative high goodness. Due to the high quality of the resonance circuit, the Build resonance circuit components C1, L1 a high voltage drop. The Voltage divider R17, R18, R19 now offers together with the Zener diode DZ and the diode D6 an additional way to measure the voltage drop in the Limit or regulate resonance circuit C1, L1.

At the tap V2 in the series resonance circuit this voltage divider the voltage drop across the resonance capacitor C1 or the lamp LP detected and according to the resistance values of the ohmic resistors R17, R18, R19 divided. As long as the amplitude of the resonant capacitor voltage a critical value by appropriate dimensioning the voltage divider resistors to a desired one Value can be set, remains below the Zener diode DZ and hence the current path, which starts from the gate of the field effect transistor T2 via the Zener diode DZ and the resistor R19 to the negative pole the DC voltage source leads, de-energized and the field effect transistor T2 maintains its full control signal. Reaches the amplitude of the resonant capacitor voltage this critical value, the negative half wave of the resonant capacitor voltage the voltage drop between the gate of field effect transistor T2 and the branch point V3 so far that the Zener diode DZ becomes conductive. That has As a result, the gate of the field effect transistor T2 is only a reduced one Control signal received because part of the coming from the control circuit IC Control signal via the now conductive Zener diode DZ and the voltage divider resistor R19 flows to the negative pole of the DC voltage source. The Rectifier diode D6 is polarized so that the Zener diode DZ only on the negative Half-wave of the resonance capacitor voltage reacts sensitively. On reduced control signal for the gate of the field effect transistor T2 reduced the conductivity of the drain-source path of the field effect transistor T2 and thus increases the effective emitter resistance of the bipolar transistor Q2. The effective emitter resistance of bipolar transistor Q2 is calculated in this Fall from the no longer negligible resistance of the drain-source path of the auxiliary transistor T2 and the resistance values of the ohmic Resistors R7 and R8. This increase in the effective emitter resistance of transistor Q2 causes a reduced duty cycle of Bipolar transistor Q2 and increases the clock frequency of the half-bridge inverter accordingly, causing the open circuit voltage across the resonance capacitor is reduced.

The invention is not limited to the exemplary embodiment explained in more detail above. For example, the circuit arrangement according to the invention can also be used for dimming the lamp LP. For this purpose, the control circuit IC is to be designed in such a way that it not only switches between two voltage stages 0 V and 12 V for driving the auxiliary transistors T1, T2, as described in the exemplary embodiment described above, but also provides a continuously variable output voltage after the lamp has been ignited , Dimensioning of the electrical components of the circuit arrangement according to the preferred embodiment R1 3.3 MΩ R2, R11 22 kΩ R3, R4 8.2 Ω R5 18 Ω R6, R8 1 Ω R7 15 Ω R9, R10 47 Ω R12, R13 560 kΩ R14 1 MΩ R15 220 kΩ R16 470 kΩ R17, R18 330 kΩ R19 56 kΩ R21 47 kΩ C1 3.3 nF C2, C3 200 nF C4 1.5 nF C5, C6, C7 100 nF C8 100 pF L1 4 mH L2, L3 10 µH D1, D2, D3, D5 1N4946GP D6 1N414B Z1, Z2 Zener diode, 12 V DZ Zener diode, 39 V DC diac Q1, Q2 BUF 620 T1, T2 STK14N05 IC Timer, IC 40106 RKa, RKb, RKc Toroidal core R8 / 4 / 3.8

Claims (6)

1. Circuit arrangement for operating electric lamps, the circuit arrangement having the following features:

   a free-running half-bridge inverter with two alternately switching inverter transistors (Q1, Q2),

   a first auxiliary transistor (T1) which is connected into the control circuit of the first half-bridge inverter transistor (Q1),

   the emitter or source impedance of the first half-bridge inverter transistor (Q1) is formed by a parallel circuit (R5, T1) which consists of at least one resistor (R5) and the control path, arranged in parallel therewith, of the first auxiliary transistor (T1),

   a second auxiliary transistor (T2) which is connected into the control circuit of the second half-bridge inverter transistor (Q2),

   the emitter or source impedance of the second half-bridge inverter transistor (Q2) is formed by a parallel circuit (R7, T2) which consists of at least one resistor (R7) and the control path, arranged in parallel therewith, of the second auxiliary transistor (T2),

   a load circuit which is connected to the output (M) of the inverter, is designed as a resonant circuit and into which at least one electric lamp (LP) is connected,

   characterized in that

   a capacitor (C6, C7) is in each case arranged in parallel with the control paths of the auxiliary transistors (T1, T2) and at at least one discharge resistor (R15, R16) is in each case connected in parallel with the capacitors (C6, C7),

   the control inputs of the two auxiliary transistors (T1, T2) are connected to the output of a common control circuit (IC) by the output of the control circuit (IC) in each case being connected via at least one charging resistor (R11, R21) to the control inputs of the auxiliary transistors (T1, T2), the resistances of these charging resistors (R11, R21) being smaller than the resistances of the discharge resistors (R15, R16), and wherein

   in the case of at least one auxiliary transistor (T1), connection to the output of the control circuit (IC) takes place via at least one diode (D5).
2. Circuit arrangement according to Claim 1, characterized in that the auxiliary transistors (T1, T2) are field-effect transistors.
3. Circuit arrangement according to Claim 1, characterized in that the two parallel circuits (R5, T1; R7; T2) in each case have at least one further resistor (R6; R8) which is connected in series with the control path of the corresponding auxiliary transistor (T1; T2) and in parallel with the at least one resistor (R5; R7) of the relevant parallel circuit (R5, T1; R7; T2).
4. Circuit arrangement according to Claim 1, characterized in that the control input of at least one auxiliary transistor (T2) is connected to a voltage divider (R17, R18, R19) which is connected, via a branch point (V2) in the load circuit, to a resonant circuit component (C1).
5. Circuit arrangement according to Claim 4, characterized in that the control input of the at least one auxiliary transistor (T2) is connected, via a threshold-value element (DZ), to the voltage divider (R17, R18, R19).
6. Circuit arrangement according to Claim 1, characterized in that, during normal operation of the lamp (LP), the control circuit (IC) produces a continuously variable output voltage.

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