EP0411618B1 - Electronic ballast for gas discharge lamps - Google Patents

Abstract

An electronic ballast (1) for gas discharge lamps (2), having an input circuit part (10, 11) for producing an intermediate-circuit DC voltage (Uz) from a supply voltage (L1,N), having an oscillator circuit part (4,8,S1,S2), supplied from the intermediate circuit DC voltage (Uz) for generating an alternating signal (uw) which can be supplied to the gas discharge lamp (2), having a bistable switch-off latching circuit part (3) which supplies a switch-off signal (us) in its first and second stable state to the oscillator circuit part (4,8,S1,S2), and hence releases the oscillator circuit part (4,8,S1,S2) or switches it off, a first signal (u1), derived from the alternating signal (uw), driving the switch-off latching circuit part (3) from its first into its second stable state in the event of a predetermined value being exceeded, and generating the switch-off signal (us), is to be designed such that its operating reliability is further improved. This is achieved in that a further signal (u2), derived from the intermediate circuit DC voltage (Uz), produces the switch-off signal (us) when the intermediate circuit DC voltage (Uz) exceeds a predetermined maximum value. <IMAGE>

Description

The invention relates to an electronic ballast (EVG) for gas discharge lamps according to the preamble of claim 1.

Such a device is known, for example, from EP 0 146 683. There, a converter is switched off by means of a bistable switching device if the gas discharge lamp used is permanently unwilling to start, that is to say repeated unsuccessful start attempts. This is achieved by short-circuiting a secondary shutdown winding of a saturation transformer, the primary winding of which is connected to the lamp circuit. In the operating state of the electronic ballast, this saturation transformer generates base voltages with further secondary windings, by means of which two alternating switching transistors generate an alternating voltage signal. If the voltage induced in the secondary switch-off winding rises above the breakdown voltage of a trigger diode, a tyristor is ignited, which short-circuits the switch-off winding via two single-use diodes. In this way, further base voltages for the alternating switching transistors can no longer be generated by the saturation transformer. The inverter is and will remain in the switched-off state until it is interrupted by switching off the electronic ballast or removing the gas discharge lamp that does not ignite.

It is also known from FR-A 2,625,642 to additionally monitor the intermediate circuit voltage and to control the voltage converter by means of the signals obtained. In order to achieve a lamp power that is as constant as possible, the voltage converter is interrupted or the intermediate circuit voltage capacitor is briefly discharged. However, it is not intended to switch the device off completely if this lamp control malfunctions.

The invention has for its object to design an electronic ballast of the type mentioned so that its operational safety is further increased.

The object is achieved by the features specified in the characterizing part of claim 1.

The invention makes use of the idea of expanding the shutdown mechanism by at least one additional branch, which monitors the intermediate circuit voltage. This measure according to the invention avoids excessive thermal loads on sensitive components, for example the rectifier or the output transistors, which may be a result of excessive DC link voltage.

Another advantage of the electronic ballast (EVG) according to the invention is the now available security against neutral interruptions.

A development of the solution specified in claim 1 or an alternative solution is the subject of claim 7. This is based on detecting the load current and triggering the shutdown of the oscillator circuit part when a predetermined maximum value is exceeded.

Fig. 1

ein erfindungsgemäßes elektronisches Vorschaltgerät (EVG) mit entweder einem einzelnen Ausgang für eine Gasentladungslampe oder, in Tandemschaltung, mit zwei Ausgängen für zwei Gasentladungslampen;

Fig. 2

ein Blockschaltbild eines erfindungsgemäßen EVG mit einer einzelnen Gasentladungslampe als Last:

Fig. 3

ein Detail-Schaltbild mit einer erfindungsgemäßen Abschaltvariante des Oszillator-Schaltungsteiles;

Fig. 4

eine erfindungsgemäße Abschalt-Halteschaltungsanordnung zum Abschalten bzw. Sperren des Oszillatorschaltungsteiles;

Fig. 5

beispielhaft einen erfindungsgemäßen Leistungsschalter mit Stromshunt zur Teil-Erfassung des Laststromes;

Fig. 6

ein Teil- Schaltbild eines erfindungsgemäßen EVG mit disjunktiver Verknüpfung zweier Überspannungssignale und eines Überstromsignals.

The invention is explained in more detail below on the basis of exemplary embodiments. Show it:

Fig. 1

an inventive electronic ballast (EVG) with either a single output for a gas discharge lamp or, in tandem, with two outputs for two gas discharge lamps;

Fig. 2

a block diagram of an electronic ballast according to the invention with a single gas discharge lamp as a load:

Fig. 3

a detailed circuit diagram with a shutdown variant of the oscillator circuit part according to the invention;

Fig. 4

a shutdown-hold circuit arrangement according to the invention for switching off or locking the oscillator circuit part;

Fig. 5

an example of a circuit breaker according to the invention with a current shunt for partial detection of the load current;

Fig. 6

a partial circuit diagram of an electronic ballast according to the invention with disjunctive linking of two overvoltage signals and one overcurrent signal.

1 shows an electronic ballast 1, hereinafter referred to as EVG for short, which can be connected to a 220V household network or directly to a DC voltage, for example a battery. One or two gas discharge lamps 2 can be connected to this electronic ballast. A directly heated gas discharge lamp 2 has four connections which are connected to the electronic ballast 1. One connection each of two opposing heating coils 22, 23 is connected via a heating capacitor C _H.

FIG. 2 shows a block diagram of an electronic ballast 1 according to FIG. 1. The mains input voltage is supplied via a rectifier 10 with a possible step-up converter connected downstream (in particular in the case of battery operation). Its output signal is fed to a smoothing device 11 with a smoothing capacitor (DC link capacitor) C _Z , which provides a DC link voltage U _Z. The intermediate circuit voltage U _Z is fed to an inverter 4, which provides an alternating signal u _W for at least one gas discharge lamp 2 at its output connections. A shutdown-hold circuit arrangement 3 on the one hand one of the output alternating voltage u _{W of} the inverter 4 is amplitude-proportional voltage u 1 and on the other hand a voltage u 2 proportional to the intermediate circuit direct voltage U _Z is supplied. It receives its supply and holding current via the series connection of a resistor R 1 and 22 of the two heating coils 22, 23 from the positive output connection + of the inverter 4 or the rectifier 10. The supply voltage of the switch-off and holding circuit part 3 is thus when the gas discharge lamp 2 is removed interrupted from their bracket. The circuit arrangement 3 generates a switch-off or release signal u _S , via which the inverter 4 switches on or off. can be switched off. This shutdown signal u _S is generated by an OR operation of the two measured signals u₂ and u₁, if necessary after rectification and smoothing.

Fig. 3 shows a detailed circuit diagram of the logical OR operation in connection with other modules essential to the function. The intermediate circuit capacitor C _Z has already been explained. The load circuit arranged between the positive output connection + and the series circuit comprising two circuit breakers S1 and S2 has, in addition to the usual gas discharge lamp 2 with heating capacitor C _H, the series circuit comprising an oscillating circuit inductance L _O and an oscillating circuit capacitance C _O. It is also a saturation transformer Ü with primary winding n1 and secondary windings n2, n2 'the load circuit can be connected in series. This serves (as an oscillator circuit arrangement 8) for generating the base voltage signals of the circuit breakers S1 and S2. The series connection of the power semiconductors S1 and S2 connects the positive output connection + to the negative output connection -, these two connections correspond to the positive and negative connection of the smoothing capacitor C _{Z of} the smoothing device 11.

An AC voltage is now decoupled or measured from the load circuit between the resonant circuit capacitance C _O and the one connection of the other heating coil 23. This is ensured by a series connection of a capacitor C₁, a first resistor R₂ and a second resistor R₃ against the negative output terminal. Between the resistors R₂ and R₃ occurs with respect to the negative output terminal - a first signal u₁. At this point the anode of a first diode D₂ is connected, the cathode of which is connected via a resistor R₆ to the negative output terminal. The resistor R₆ is a capacitance C₆ connected in parallel.

The intermediate circuit capacitor C _Z is bridged with the series connection of a third resistor R4 and a fourth resistor R₅. This voltage divider provides a second signal u₂ proportional to the intermediate circuit direct voltage U _{Z in} parallel with the fourth resistor R5. The anode of another diode D₄ is connected at the connection point between the resistors R₄ and R₅, its cathode is connected to the resistor R₆ like the cathode of the diode D₂. At R₆ is therefore always the greater voltage of the voltages u₁ and u₂.
For better decoupling of the signals to be linked u₁ and u₂, the diodes D₂ and D₄ each have a resistor R₁₈, R₁₃ can be connected in series.

The voltage signal which arises at the resistor R₆, with a possible parallel capacitor C₆ with respect to the negative supply connection - is now supplied to the switch-off / hold circuit arrangement 3. It is explained in more detail in Fig. 4.

Fig. 4 shows, as an alternative to the disjunctive link described in Fig. 3 in diode transistor logic, an OR gate, the three signals u₁, u₂ and u₃ can be supplied. The first signal u₂ and second signal u₂ correspond to the derived from the load voltage and rectified signal u₁ shown in FIG. 3 and the derived from the intermediate circuit voltage by a division ratio second signal u₂. Both are coupled to resistor R6. The third signal u 3 shown here can alternatively be coupled either via the OR gate 6 or directly into the shutdown-hold circuit arrangement. It is a switch-off signal dependent on the load current.

The output signal u _s ' of the OR circuit 6, which corresponds to the signal u _s ' present at resistor R 'according to FIG. 3, is supplied to a diac 7 (trigger diode) via a low-pass circuit. The low pass consists of either Series connection of a resistor R₁₀ and C₁₁ or from a parallel connection of a capacitor C₁₁ and a resistor R₁₁. The connected to the capacitor C₁₁ trigger diode 7 controls the gate terminal of a thyristor 5. It specifies a threshold voltage with which the response threshold of the shutdown-hold circuit arrangement 3 is adjustable. This response threshold is predetermined in terms of amplitude, but can be delayed in time by the low-pass circuit, so that on the one hand any amplitude can be set and on the other hand any response speed can be specified. The amplitude is set via the divider ratio R₄ / R₅ or via the divider ratio R₁₀ / R₁₁. The time delay can be set either by the capacitor C₆ or the capacitor C₁₁.

The different shutdown signals u₁, u₂ or u3 different response speeds and response amplitudes can be assigned. For example, the coupling of the current-dependent signal u₃ via the series circuit of a diode D₁₂ and a resistor R12 directly to the gate terminal of the (forming a bistable shutdown element) thyristor 5 is shown. Different response amplitudes are achieved through the different threshold voltages.

The anode circuit of the thyristor 5 also has a holding current generating resistor R₁₄, which is connected with its one connection via the first heating coil 22 of the gas discharge lamp 2 to the positive connection of the intermediate circuit capacitor C _Z and the second connection of which is connected to the anode of the thyristor 5. This connection point between the holding current generating resistor R14 and the anode of the thyristor 5 is the oscillator 8 to switch off its oscillation or to prevent base voltages for the Semiconductor switches S1 and / or S2 supplied. This can be done either by short-circuiting an n2 'of the several secondary windings n2, n2', the saturation transformer Ü which can be inserted into the load circuit (self-oscillating inverter) or, in the case of a separate, non-load-current-controlled oscillator (freely oscillating inverter), by blocking the basic control signals for the power semiconductors S1 and / or S2.

Fig. 5 shows a detailed circuit diagram of one of the power semiconductors S1 and S2, as they are driven either by the oscillator 8 directly or via a saturation transformer Ü with a primary winding n1 and a plurality of secondary windings n2, n2 '. For example, the power semiconductor S2 has the series circuit comprising a power transistor and an emitter resistor R _E. Its base potential is generated depending on the load current via one of the several secondary windings n2 of the saturation transformer Ü via the series connection of a small choke and a diode. At the resistor R _E , a voltage proportional to the load current u₃ with respect to the negative terminal - of the intermediate circuit capacitor C _{Z is} now measurable. You can now optionally be supplied via the disjunctively linking OR gate 6, via a circuit arrangement R₂, R₃ and D₂ according to FIG. 3 or via the series connection of a diode D₁₂ and a resistor R₁₂ and a separate input of the shutdown-hold circuit arrangement 3 .

FIG. 6 shows a partial circuit diagram of an electronic ballast 1 according to FIG. 1 with a single gas discharge lamp 2 as a load. There are already described components of the rectifier 10, the intermediate circuit capacitor C _Z , the circuit breaker S1, S2, the oscillator 8 and the holding circuit via resistor R₁₄. A rectifier 10 is connected upstream of the rectifier 10 with the capacitor C _X. The capacitor C _Z is connected in parallel from the resistor R₄ and the resistor R₅. At the center tap between these two Resistors with respect to the negative connection - the intermediate circuit capacitor C _Z, an intermediate circuit voltage-dependent signal u₂, as described, is coupled via the series circuit of diode D₄ and an additional resistor R₁₃ to the capacitor C₆. At the same time, an AC voltage component coupled out of the load circuit via the capacitor C₁ is coupled via the second disjunctive linking branch, the series circuit comprising diode D₂ and additional resistor R₁₈, onto the same capacitor C₆. The voltage across the capacitor C₆ u _s ' controls via the series connection of the resistors R15, R16, R17 to the negative supply connection - and the resistor R₁₅ connected in parallel trigger diode 7 the resistor R₁₇ connected in parallel gate circuit of the turn-off thyristor 5th

Fig. 6 also shows a further variant in which the load current-dependent signal u₃ over a in the negative supply line between the switch S1 and the negative supply connection - of the electronic ballast to gain measuring resistor R _Sh . It is fed directly to the gate circuit of the thyristor with the series circuit of diode D₃ and resistor R₁₉. To set the threshold voltage, several diodes are to be connected in series instead of one diode D₃.

With the present circuit arrangement, a safe mode of operation is achieved, a longer operation with a high intermediate circuit voltage U _Z and consequently high thermal loads on the transistors S1, S2 is avoided by the possibly time-delayed shutdown. The response threshold of this overvoltage shutdown measure is set according to the following table. In the present case, it is effective at mains voltages of greater than 280V _eff .

Claims (9)

1. Electronic ballast (1) for gas discharge lamps (2), having an input circuit part (10, 11) for generating an intermediate circuit d.c. voltage (U_Z) from a power supply voltage (L₁, N)
   having an oscillator circuit part (4, 8, S1, S2) fed by the intermediate circuit d.c. voltage (U_Z) for generating an a.c. signal (u_w) which can be supplied to the gas discharge lamp (2),
   having a bistable tripping-holding circuit part (3) which, in its first and second stable condition, respectively, supplies a tripping signal (u_s) to the oscillator circuit part (4, 8, S1, S2) and thereby releases or trips the oscillator circuit part (4, 8, S1, S2),
   wherein a first signal (u₁) derived from the a.c. signal (u_w) directs the tripping-holding circuit part (3) from its first to its second stable condition and generates the tripping signal (u_s), when a pre-determined value is exceeded,
   characterised in that
   a further signal (u₂) derived from the intermediate circuit d.c. voltage (U_Z) generates the tripping signal (u_s) when the intermediate circuit d.c. voltage (U_Z) exceeds a pre-selected maximum value, and in that
   there are provided devices by means of which any desired response rates can be pre-selected for the respective signals (u₁, u₂).
2. Electronic ballast according to claim 1, characterised in that the further signal (u₂) is formed from the intermediate circuit d.c. voltage (U_Z) by way of a voltage divider (R₄, R₅).
3. Electronic ballast according to claim 1 or 2, characterised in that the first signal (u₁) and the further signal (u₂) can be supplied to an OR gate arrangement (6), and the output signal (u_s') thereof can be supplied to the tripping-holding circuit part (3) for generating the tripping signal (u_s) for the oscillator circuit part (4, 8, S1, S2).
4. Electronic ballast according to claim 3, characterised in that the OR gate arrangement (6) is constructed as an integrated OR gate or with discrete components (R₆, D₄, R₂, D₂ ) in resistor-diode logic and the tripping-holding circuit arrangement (3) has a thyristor (5).
5. Electronic ballast according to one of claims 2 to 4, characterised in that the maximum value of the intermediate d.c. voltage (U_Z) can be set by way of the divider ratio (R₄/R₅) of the voltage divider and a threshold voltage (breakdown voltage), in particular of a diac or a triggering diode (7).
6. Electronic ballast according to one of the preceding claims, characterised in that the first signal and/or the further signal (u₁, u₂) are delayed by way of a low pass circuit.
7. Electronic ballast according to claim 1 or according to the preamble of claim 1 alone, characterised in that an additional signal (u₃) derived from a load current flowing through the gas discharge lamp (2), generates the tripping signal (u_s) when the load current exceeds any pre-selected maximum value.
8. Electronic ballast according to claim 7, characterised in that the additional signal (u₃) is formed by way of a current transformer in the lamp circuit (2), or as a measuring signal proportional to the current at an emitter resistor (R_E) of a power transistor (S2) of the oscillator circuit part (3), or by means of a resistor (R_Sh) in the negative power supply line of the ballast.
9. Electronic ballast according to claim 7 or 8, characterised in that the first signal (u₁), the further signal (u₂) and the additional signal (u₃) can be supplied as alternative tripping signals (u_s) to the oscillator circuit part (4, 8, S1, S2) by way of an OR gate arrangement and the triggering-holding circuit part (3).

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