EP1395094A1 - Apparatus and method for operating a lamp - Google Patents

Abstract

The device has an inverter device for supplying the lamp with alternating current with at least one transistor switching unit and a current limiter device connected to the at least one transistor switching unit to limit the current through the at least one transistor switching unit. The current limiter can drive the control electrode of the at least one transistor switching unit for current limiting. AN Independent claim is also included for the following: (a) a method of operating a lamp, especially a low pressure discharge lamp.

Description

Technical field

The present invention relates to a circuit device for operating a lamp, in particular a low-pressure discharge lamp, with an inverter device, the has at least one transistor switching unit for supplying the lamp with alternating current and a current limiting device connected to the at least one transistor switching unit is connected to limit the current through the transistor switching unit. About that In addition, the present invention relates to a corresponding method for operating a lamp.

Low-voltage discharge lamps are typically made using an electronic ballast (EVG) operated. It contains the alternating current necessary to operate the lamp usually generated by known half-bridge inverters. With the half bridge a load circuit comprising one or more lamps is operated. The load circuit includes inductive and capacitive elements, resulting in a predetermined load circuit resonance frequency results.

In the case of self-oscillating resonance circuits, depending on the circuit concept i.e. with the electronic ballast in the ignition phase of the lamp, an operation at the resonance frequency. In In this case, the resonance current is determined solely by the quality of the resonant circuit. at high quality, this leads to a very high component load, since very high currents occur.

State of the art

The ignition voltage for igniting a lamp by means of a resonance circuit and the thus connected reactive current before ignition can only be achieved by the saturation behavior of the Limit resonance inductance or by reducing the quality of the resonance circuit. So far the open circuit voltage was therefore limited by a resonance choke whose saturation was deliberately chosen low. This measure leads to an additional increase of the resonance current. The current may be limited by a deliberately deteriorated quality of the resonance circuit. However, this deterioration occurs Efficiency and is only practical for devices with lower power.

A further developed current limitation is from the European patent EP 0 798 952 B1 known. In the electronic ballast described there is one of the inverter transistors in the emitter line the control path of a transistor arranged. About the variable conductivity this control path becomes the effective emitter resistance of the inverter transistor changes continuously depending on the voltage drop at one of the resonance circuit components and thereby the clock frequency of the inverter increased so much that because of the now greater detuning from the resonant frequency of the resonant circuit a reduction the open circuit voltage in the resonance circuit with simultaneous current limitation becomes.

A similar current limiting circuit is known from European patent application EP 0 800 335 A2 known. In the control circuits of the half-bridge inverter transistors one auxiliary transistor each, so that the emitter resistance of each half-bridge inverter transistor is formed by a parallel connection consisting of at least one ohmic resistance and the parallel control path of the corresponding one Auxiliary transistor exists. As a result, the effective emitter resistance or Feedback of the half-bridge inverter depending on the operating phases of the Lamp switched and so the clock frequency of the half-bridge inverter in a simple manner within wide limits by dimensioning the resistances of the invention Parallel connection can be varied. Here, as in the previous case, the auxiliary transistor controlled by the lamp voltage, which in turn is the emitter line of a Controls half-bridge transistor.

Presentation of the invention

The object of the present invention is an improved type of current limitation by a transistor unit of an inverter device for the operation of Propose lamps.

According to the invention, this object is achieved by a switching device for operation a lamp, in particular a low-pressure discharge lamp, with an inverter device for supplying the lamp with alternating current, the at least one transistor switching unit and a current limiting device connected to the at least one transistor switching unit is connected to limit the current through the minimum a transistor switching unit flows, the control electrode with the current limiting device the at least one transistor switching unit can be controlled for current limitation.

Furthermore, the above-mentioned object is achieved according to the invention by a method for Operating a lamp, in particular a low-pressure discharge lamp, by generation an alternating current for supplying the lamp by means of at least one transistor switching unit and limiting the current through the at least one transistor switching unit, wherein to control the current, the control electrode of the at least one transistor switching unit is driven becomes.

The inverter device can be a half bridge from the at least one transistor unit and a further transistor unit. So the inverter can do a lot can be produced inexpensively from only two active components. If necessary, you can the transistor units each consist of MOSFET transistors.

The lamp is preferably operated in a load circuit connected to the inverter device connected. This load circuit preferably comprises an LC resonance circuit to operate the lamp with a defined resonance frequency and a Coupling capacitor to suppress DC components.

For a more cost-effective implementation, the circuit device includes an inverter device connected phaser to the operating frequency of the Inverter device to adapt to a resonance frequency of the load circuit. In order to a voltage surge necessary for the ignition process can be achieved. The For this purpose, phase setting device can be connected to a control electrode of the at least one transistor switching unit be connected so that the switching process in the transistors of the Inverter device is adapted to the load circuit resonance.

The current limiting device is advantageously parallel to the phase setting device on the control electrode of a transistor of the inverter device. So that will regulates the amplitude of the lamp current through the control electrode of the transistor by the switching frequency is adjusted.

It is also advantageous if the current limiting device comprises a switching device, by the at least one transistor switching unit depending on the current through which at least one transistor switching unit can be switched off. For example, as such a switching device, a transistor can be used, which in turn is the transistor switching unit the inverter device on or off.

Brief description of the drawings

Figur 1

die Einhüllende des Spannungsverlaufs an einer Lampe mit einem elektronischen Vorschaltgerät;

Figur 2

die Einhüllende des Strom- und Spannungsverlaufs an einer Lampe mit einem elektronischem Vorschaltgerät gemäß dem Stand der Technik

Figur 3

die Einhüllende des Strom- und Spannungsverlaufs an einer Lampe mit erfindungsgemäßem elektronischem Vorschaltgerät;

Figur 4

den Stromverlauf am Schalttransistor des Wechselrichters innerhalb eines Schaltzyklus; und

Figur 5

einen Schaltplan zu einer erfindungsgemäßen Schaltungsvorrichtung.

The present invention will now be explained in more detail with reference to the accompanying drawings, in which:

Figure 1

the envelope of the voltage curve on a lamp with an electronic ballast;

Figure 2

the envelope of the current and voltage curve on a lamp with an electronic ballast according to the prior art

Figure 3

the envelope of the current and voltage curve on a lamp with an electronic ballast according to the invention;

Figure 4

the current profile at the switching transistor of the inverter within a switching cycle; and

Figure 5

a circuit diagram for a circuit device according to the invention.

Preferred embodiment of the invention

The exemplary embodiments described below represent preferred embodiments of the present invention.

To illustrate the invention, the course of the envelope of the voltage is shown in FIG. 1 shown when igniting low-pressure discharge lamps. After switching on the voltage rises to the value at which the respective lamp ignites. This value is reached at time t1. The ignition phase is usually in less than a millisecond completed. After ignition, the voltage across the lamp drops to the level of the Glow discharge from. The glow phase can take times of one for non-preheated filaments Second. The voltage level during the glow discharge is clear above the level in rated operation UB .. At time t2, the lamp voltage drops to Operating level. If the lamp does not glow within a time, max in nominal operation switch, the safety shutdown of the device also responds in order to close the components protect.

If the lamp does not ignite, a protective circuit switches the electronic ballast from (see Fig. 2). This serves to protect the half-bridge or inverter transistors because these lead the high current only for a short time interval without permanent damage can. I.d.R. is the time intervals are ignition and glow, max in terms of circuitry linked, so that a protection-related short time also limits the glow phase. Furthermore, the electronic ballast must ensure that the open circuit voltage U0 does not exceed a limit set in the safety standards.

The component load is crucial for a reliable ignition and a good lamp life to minimize by low currents and thereby realize a long glow phase to be able to. At the same time, the open circuit voltage U0 must be within the safety standards be limited to favorable values. In conventional circuits, the ignition voltage limited by deliberately reducing the saturation limit of the resonance choke. However, this measure leads to high currents in the inverter. In Figure 2 is the use of saturation in current i is characterized by isat and in voltage u by usat.

According to the invention, the ignition voltage is therefore reduced in the ignition phase in such a way that the Current in the half-bridge drops and the ignition phase can be extended significantly without that the electronic ballast is damaged. This extension is in Figure 3 indicated. Here too, the voltage rises to U02 after switching on. This Value is significantly below the value of U01 according to the state of the art. Because of the non-linear current-voltage relationship increases when limited to U02 Current through the transistors only on I2. This significant current reduction allows one equally significant extension of the maximum duration of the ignition phase. The typically used Transistors do not suffer any damage even after t Zünd2, because they only do so a current of 12 flows. The electronic ballast is switched off at the latest after t Zünd2 switched off if the lamp does not ignite. If the lamp, however, at the latest ignites at point in time t2, the voltage drops from here to the glow voltage Uglimm ab. The ignition time, which is much longer than that of tünd1, also enables a proportional extended glow phase tglimm, max and lamps with glow phases from start safely over a second.

The circuit arrangement shown below in connection with FIG. 5 leads through active feedback to the desired current limitation with increased lamp efficiency. The circuit in FIG. 5 shows a lamp LA. It is crossed by a half bridge consisting of the MOSFET transistors T1 and T2 and the capacitor C1. The two transistors T1 and T2 are connected in series, while the capacitor C1 is connected in parallel to transistor T1. An inductor L1-A is between the connection point of the two transistors T1 and T2 and the capacitor C1. she forms together with the capacitor C1 a resonant circuit, the idle frequency or specifies the frequency in the ignition phase. The lamp LA is parallel to that Capacitor C1 connected, between the one electrode of the lamp LA and the one Electrode of the capacitor C 1, a coupling capacitor C2 is arranged, the DC components filtered out of the power supply. The characteristics of the load circuit of the half-bridge are determined in addition to the lamp LA by the components L1-A, C1, and C2.

The transistor T2 is connected to ground via a resistor R. This resistor R1 serves, among other control tasks, by detuning the resonant circuit L1, C1 to prevent a so-called resonance catastrophe, in which very high currents arise.

Between the gate of transistor T2 and ground is a so-called phase control circuit connected. This phase control circuit causes the frequency of the half bridge to Resonance frequency of the load circuit is adjusted. The phase controller circuit consists of a parallel connection of a resistor R2, a capacitor C2 and a coil L2. The phase shift results from the dimensioning of the reactances C2 and L2. In terms of the phase control circuit is referred to the European patent EP 0 781 077 B1.

The control voltage for the gate of transistor T2 is generated by a coil L1-B which is magnetically coupled to the coil L1-A and thus the one generated by the half-bridge Voltage is coupled into the gate circuit of transistor 2 to control it. The sink For this purpose, L1-B is connected between the resistor R2 and ground.

It is now important to control the transistor T2 via its gate so that the one flowing through it Current does not exceed a certain threshold. For this purpose, the bipolar transistor T3 used, the base of which is controlled by the voltage dropping across the resistor R1 becomes. Between the base of transistor T3 and resistor R1 is a zener diode D1 switched, which together with one connected between the base of transistor T3 and ground Capacitor C3 causes transistor T3 only in a higher current range, i.e. is active during the ignition phase and the transistor T2 in every switching cycle if necessary switches off prematurely. This causes an increase in the switching frequency. at lower voltages, i.e. during the glow and burn phase the transistor T3 not activated and therefore not the transistor T2 of the half bridge for current limitation off. The emitter of transistor T3 is connected to ground and the collector is on the center of two Zener diodes D2 and D3, which are parallel to the phase control circuit, i.e. are connected between the gate of transistor T2 and ground.

Figure 4 shows the current in the MOSFET transistor T2 in the ignition phase. A solid one Line describes the current profile without current limitation a dashed line describes the current profile with current limitation according to the invention. The frequency increase of the Half-bridge is reached by switching off at switching threshold 12 prematurely. The cycle time tz1 without limiter circuit is much longer than the cycle time tz2 with limiter circuit. So that the turn-off transistor T3 does not work in the linear range and so that the MOSFET transistor T2 turns off completely, the capacitor C3 is inserted. After the lamp LA has been ignited and then glow phase, the current drops through the transistor T2 well below the switching threshold 12, so that the current limiter circuit no longer intervenes during continuous lamp operation.

Overall, the operating frequency is thus seen in the circuit according to the invention the half bridge through the phase adjuster R2, C2, L2 to the resonance frequency of the load circuit L1-A, C1, C2, LA adjusted and the current flowing through transistor T2 through the gate of the transistor T2 through the current limiting circuit D1, D2, D3, T3, C3 during the Firing phase limited.

The gate of transistor T1 is also driven by a phase control circuit and the control voltage is also generated by a magnetically coupled inductor. A current limiting circuit as used to control the gate of transistor T2 is used, does not need to be used to control the gate of the transistor T1 because the discharge current from the coil L1-A is automatically limited when the charge current was limited. This can easily be deduced from the energy balance of the coil L1-A.

The current limitation is effected by the corresponding control of the gate of transistor 2 now, as already indicated, that the current through the transistors T1 and T2 limits is, so that their lifespan increases significantly, and that the ignition phase is extended can be. Lamps can also be ignited with the circuit according to the invention that have a significantly longer ignition phase than the maximum duration of the ignition phase of have conventional electronic ballasts.

Claims (12)

Switch device for operating a lamp (LA), in particular a low-pressure discharge lamp,
with an inverter device for supplying the lamp (LA) with alternating current, which has at least one transistor switching unit (T2), and
a current limiting device (D1, D2, D3, T3, C3), which is connected to the at least one transistor switching unit (T2), for limiting the current through the at least one transistor switching unit;
characterized in that
with the current limiting device (D1, D2, D3, T3, C3) the control electrode of the at least one transistor switching unit can be controlled for current limiting. Circuit device according to claim 1, wherein the inverter device Half bridge including at least one transistor unit (T2) and another Transistor unit (T1) comprises. Circuit device according to claim 2, wherein the at least one transistor unit (T2) comprises a MOSFET transistor. Circuit device according to one of claims 1 to 3, wherein the lamp (LA) in a load circuit, which is connected to the inverter device, can be operated. A circuit device according to claim 4, which is connected to the inverter device Phase setting device (R2, C2, L2) for adjusting the operating frequency of the inverter device to a resonance frequency of the load circuit. Circuit device according to claim 5, wherein the phase rotator (R2, L2, C2) connected to a control electrode of the at least one transistor switching unit (T2) is. Circuit device according to claim 5 or 6, wherein the phase setting device (R-2, L2, C2) connected in parallel to the current limiting device (D1, D2, D3, T3, C3) is. Circuit device according to one of claims 1 to 7, wherein the current limiting device (D1, D2, D3, T3, C3) comprises a switching device (T3) through which the at least one transistor switching unit (T2) depending on the current through the at least one transistor switching unit (T2) can be switched on and off. Method for operating a lamp, in particular a low-pressure discharge lamp
Generating an alternating current for supplying the lamp (LA) by means of at least one transistor switching unit (T2) and
Limiting the current through the at least one transistor switching unit (T2),
characterized in that
for current limitation, the control electrode of the at least one transistor switching unit (T2) is activated. A method according to claim 9, wherein the lamp (LA) is operated in a load circuit. The method of claim 10, wherein the frequency of the alternating current generated to a Resonance frequency of the load circuit is adjusted. Method according to one of claims 9 to 11, wherein the at least one transistor switching unit (T2) depending on the current flowing through it at a given one Threshold is switched off.

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