EP2184956A2 - Electronic pre-switching device, lighting device and method for operating same - Google Patents

Abstract

The electronic ballast has a center tap arranged between a switch and another switch. An inductor and a capacitor are coupled in series at the center tap. A limiting circuit is provided to vary signal sloping at shunt (R1) for gaining given signal level at a measuring input (CS). An independent claim is included for a method for operating electronic ballast of an illuminator.

Description

The present invention relates to an electronic ballast for operating at least one lamp, preferably a gas discharge lamp, with a center tap arranged between a first and a second switch to which a choke and a first capacitor are coupled in series, preferably with a further lying at a reference potential Capacitor, wherein the first capacitor is preferably connected directly to a terminal for the lamp, as well as having a measuring input having IC, which is provided for controlling the ballast, wherein the measuring input between a connected to the reference potential shunt and a switch is coupled. Furthermore, the invention relates to a lighting device with a corresponding electronic ballast and a method for operating this, in which a IC having a measuring input a Mittenabgriff a preferably a bridge circuit, in particular a half-bridge circuit ballast by means of a first and a second switch switches to an alternating Potential to apply to a choke and a first capacitor and to supply via this one pole of a lamp, wherein over the measuring input of the IC a voltage drop across a shunt is measured, in particular to detect a dead time for switching on one of the switches and / or trigger a switch-off ,

Generic ballasts are equipped with ICs that often bring features such as automatic deadtime detection or saturation control for the lamp inductor according to the manufacturer. Also is often an additional Switch-off threshold implemented for faults in preheated ECGs. The necessary measuring input is in this case designed to measure the current via one, preferably the second switch or a voltage drop across the shunt coupled to the reference potential. A problem may arise if the magnitude of the ignition voltage is adjusted or programmed via the half-bridge shunt. If high ignition voltages are required, for example for series-connected bulbs, the shunt is due to the high current during the ignition phase in the resonant circuit to dimension correspondingly low. The lower the resistance, the higher the set ignition voltage. However, the resistance falls below a certain value, the dead time detection via the measuring input no longer works, because the triggering threshold for switching on the (eg MOSFET) transistor or switch is no longer achieved. If, on the other hand, higher-impedance shunts are used, too rapid a shutdown takes place in the ignition phase due to the reaching of the shutdown level threshold.

In addition, in dimmable devices, there is the additional difficulty that in certain dimming ranges, the current felt in the shunt is so low that the minimum value for the implied turn-off threshold for current-preheated devices is no longer reached. Just as in the first problem case, which can lead to power surges, a protection shutdown is activated in the latter case.

It is an object of the present invention to improve the described prior art in terms of its disadvantages. The same applies to a method according to the preamble of claim 8.

Starting from a preamble of claim 1, the object is achieved by an object which further developed according to the characterizing part of the claim is. According to the invention training and further developments are dependent dependent claims and the following description.

It is provided according to the invention that the signal dropping at the shunt is varied in its amplitude by means of a circuit, in particular a limiting circuit. As a variation serves in particular and in the following a limitation of the maximum amplitude value, which can be seen at the measuring input. In other forms or in addition, it may also be an at least partial stretch or other change in amplitude. The measuring input thus does not directly see the signal dropping at the shunt of the circuit, which is preferably in the form of a half-bridge, but a signal provided with an example of a reduced maximum amplitude. The limiting circuit, which can advantageously be tuned to the circuit and / or adapted configured, thus serves the revision of the falling signal / signal level at the shunt, or the voltage dropping at the shunt such that the necessary and for the individual functions of the IC thresholds are achieved. These thresholds may be predetermined or predetermined depending on the IC used. be adjustable. The signal dropping at the shunt can be changed in a linear or nonlinear way. The limiting circuit is coupled between the measuring input and the shunt in the circuit, and switched in particular from the measuring input to the present between shunt and one of the switch line, preferably between shunt and the reference potential switching to the center tap switch or coupled.

Advantageously, the limiting circuit is connected to a diode connected to the reference potential or the like. Provided barrier effect circuit, which is coupled into the conduction path between shunt and measuring input. The diode presents a very simple and inexpensive way to form a limiting circuit. Here, the forward voltage of the diode already serves a voltage drop, so that the measuring input "sees" a lower signal compared to the signal applied to the shunt.

Compared to conventional applications, it is therefore possible to use a relatively high-impedance shunt in which a signal is present in the ignition phase whose level is significantly above the ignition voltage control threshold of the IC, which is not seen by the measuring input. At the measuring input, the signal is in the range of the control threshold. An ignition is thus possible despite a high-impedance shunt, since the scheme takes effect later. At the same time, the selected polarity of the diode ensures that the negative signal components at the shunt are forwarded to the measuring input. The diode blocks the negative signal components against reference potential.

Furthermore, the shunt can be dimensioned sufficiently large to generate a sufficient measurement signal at the measuring input even with dimmable devices in which only a small current flows. The limiting circuit according to the invention thus provides a balance between the actually required for an ignition voltage low-resistance (half-bridge) shunt and a sufficiently large-sized shunt for dead time detection.

Instead of a diode having a defined forward voltage, another blocking device which is permeable on one side can be part of the limiting circuit as a component of a plurality of individual components. It is essential here that, due to the blocking of the signal components, either in the direction of plus or in the direction of minus, the signal for deadtime detection which arrives above or falls above the shunt actually reaches the switch-on threshold.

The object is achieved according to the mandatory also by a method according to the preamble of claim 8, which is characterized in that the voltage applied to the measuring input signal varies in amplitude by means of a limiting circuit and is limited in particular. Relatively high-impedance shunts can be used since the positive signal components applied to the measuring input do not correspond to the signal applied to the shunt and the ignition voltage control threshold is accordingly reached later. At the same time can be achieved via the limiting circuit that the signal is locked in one direction to provide a sufficient signal in the event of deadtime detection available. It can be assumed here that the relevant signal component dropping off at the shunt during the ignition phase has a different polarity than the signal component for detecting a dead time. The negative signal components are fully applied to the measurement input, while the positive ones are limited in their amplitude applied to the measurement input. Such a method for operating an electronic ballast can be used especially for a ballast according to one of claims 1 to 6 or for a lighting device according to claim 7.

The advantages and advantages of the electronic ballast described above and described can also be transferred to a lighting device operated with such a device, so that this too solves the problem posed at the outset.

Advantageously, the signal components falling at the shunt are referred to as negative signal components by means of a diode or the like. Barrier having device locked to reference potential. In addition to the one-sided on-state effect of the diode via this also a voltage drop for positive signal components, which is caused by the sloping at the diode forward voltage to reference potential. A prescribed electronic ballast or the inventive method are then developed particularly advantageous if the voltage applied to the shunt signal is supplied to the measuring input via a voltage divider of the limiting circuit of the electronic ballast. This improves the setting options of the electronic ballast or the adaptation of the method to already known electronic ballasts and special circuits for the operation of particular with high ignition voltages to be operated lamps.

In a further advantageous embodiment of the invention, the limiting circuit has a arranged in the line branch of the diode additional resistance. This may be part of the voltage divider or without such as part of the limiting circuit for reducing the signal applied to the measuring input of the IC signal. The resistance arranged in the line branch between the line path (between the shunt and the measuring input) and the reference potential is preferably pre-coupled to a diode arranged in the same line branch. However, he can also be linked to this.

Preferably, the limiting circuit further comprises a resistor arranged in the conduction path between shunt and measuring input, which preferably has a resistance value which is greater than that of the shunt. For example, the resistor can form a voltage divider with the additional resistor assigned to a diode. The resistance arranged in the conduction path between the shunt and the measuring input is preferably greater by a factor of at least 50 than the resistance of the shunt, particularly preferably by a factor in the region of 100. In the case of such dimensioning, the resistance in the conduction path between Shunt and measuring input arranged resistors can be used a variety of conventional IC such as the ICB2FL01 G (Infinion) not only for static ballasts but also for dimmable ballasts.

Furthermore, it is advantageous for the invention if a capacitance is connected in parallel with the diode or in a series circuit comprising the diode in order to act as a filter against high-frequency interference. The capacitance is arranged between the measuring input and the reference potential.

Instead of the above-described voltage divider based on ohmic resistors, it can alternatively or additionally also be designed as a capacitive voltage divider and correspondingly be part of the limiting circuit. This is particularly advantageous when certain DC sources of the signal are to be filtered.

Fg.1

eine Schaltungsanordnung eines Beleuchtungsgeräts nach dem Stand der Technik,

Fig. 2

einen erfindungsgemäß weitergebildeten Gegenstand gemäß Fig. 1 in aus- schnittsweiser Darstellung,

Fig. 3

einen Vergleich zwischen dem am Shunt des Gegenstands nach Fig. 1 anfallenden Signal mit dem des am Messeingang anliegenden Signal,

Fig. 4

einen erfindungsgemäßen Gegenstand in einer weiteren Ausbildung.

Further advantages and details of the invention can be taken from the following description of the figures. In a schematic representation shows:

FG.1

a circuit arrangement of a lighting device according to the prior art,

Fig. 2

an inventively further developed article according to Fig. 1 in a detailwise representation,

Fig. 3

a comparison between that at the shunt of the object Fig. 1 resulting signal with that of the signal applied to the measuring input,

Fig. 4

an article of the invention in a further embodiment.

Equal or similar parts are provided with identical reference numerals, if appropriate. Individual technical features of the exemplary embodiments described below can also lead to developments of the invention with the features of the above-described embodiments.

An electronic ballast known from the prior art comprises an IC 1 to be used as a control unit, which in a known manner drives a first switch S1 and a second switch S2 in a half-bridge arrangement ( Fig. 1 ). The switches S1 and S2 are arranged between reference, ie preferably ground potential and the intermediate circuit voltage UZ. Between the two switches S1 and S2, a half-bridge center M is formed. From this leads a conduction path via an inductance L1 and a coupling capacitor C1 to a pole of a lamp La. Another pole of the lamp La is connected to the reference potential. Another capacitor C2 is connected as a resonant circuit capacitor with the inductance L1 and the coupling capacitor C1 and on the other hand with reference potential. In addition to the control terminals 2 (for switch S2) and 3 (for switch S1), the IC 1 also has a measuring input CS, via which the current flow through the switch S2 or the voltage dropping at the shunt R1 is recorded and evaluated. Depending on the design of the IC, an ignition voltage control and / or a dead time detection can be realized via this evaluation, which, however, identify the above-described disadvantages of the prior art. In the IC's design as Infinion's ICB2FL01 G, features such as automatic deadtime detection and a shutdown threshold for power preheat ECG faults are implemented. Important for the correct Functioning of these functions is that the triggering threshold U _tot for the dead time detection at the measuring input CS is safely undercut as soon as the half-bridge voltage at point M has fallen to ground potential. However, if the measuring shunt R1 is dimensioned relatively low in order to achieve high ignition voltages, it can no longer be ensured with sufficient certainty that the voltage dropping there will actually approach the triggering threshold U _tot for the deadtime control.

When switching off the switch S1, the voltage applied to the bridge point M drops to zero or reference potential, with a residual current flows through the snubber capacitor C3. If the voltage has dropped to zero potential at the point M, due to the energy stored in the coil L1 via the freewheeling diode of the switch S2, a current which is connected to a voltage drop at R1 flows. This can be detected via the measuring input CS. S2 is switched only when the triggering threshold for the dead time detection is reached. The dead time is stored and is subsequently also used for the switch-off process of the S2 or the switch-on of the S1.

However, if the resistance R1 falls below a certain value, as described above, the dead time detection does not work, which can lead to current peaks. In this case, the half-bridge driver IC may detect an error case if necessary and activate the protective shutdown. In addition, in stromvorgeheizten electronic ballasts of the half-bridge shunt felt current when reducing the lamp power to 50%, for example, so low that the shutdown threshold for stromvorgeheizte equipment is no longer achieved. Also in this case, the protection shutdown would be activated.

In an embodiment of the invention according to Fig. 2 the limiting circuit acting as an additional or limiting circuit comprises an arranged in the conduction path between R1 and CS additional resistance R3, as well as a coupled to the conduction path between R3 and CS line branch with a further resistor R5 and a diode D1. The signal applied at the measuring point P during the ignition phase corresponds to the dot-dash line Uzü (FIG. Fig. 3 ) and is therefore above the also the Fig. 3 removable voltage regulation threshold U _R. Due to the additional circuit of the line path leading to the measuring input acting as a limiter, however, only the signal corresponding to the dashed line U _CS in FIG. In operation mode (run mode), the curve of the voltage at the measuring input corresponds to the solid line U _CSB .

Out Fig. 3 is also apparent that the triggering threshold U _tot is sufficiently undershot due to the sufficiently large-sized R1 in a degree .DELTA.V, for example, 0.2 volts, so that the switch S2 is closed correctly. Safe switching of the switch is ensured.

If the shunt resistor R1 is sufficiently large, for example 2 ohms, to ensure deadtime detection, the required ignition voltage would possibly no longer be able to be achieved, since the ignition voltage control threshold would be exceeded too quickly. In such a case, the additional circuit of R3, R5 and D1 causes the voltage dropping across the half-bridge shunt R1 to be divided down and the half-bridge driver IC to be biased to a lower ignition voltage. As a result, the ignition voltage is correspondingly higher and operation of the device is still ensured. R3 and R5 are preferably substantially larger than R1 and are particularly preferably in a ratio between R3 / R5 ≈ 10 to each other. Depending on the systemic and For component-specific requirements, this value can preferably be in a range between 2 and 100.

In a further advantageous embodiment of the invention, the limiting circuit in addition to the resistor R3 and R5, a further resistor R4 for forming a voltage divider with R3 and a capacitor C4, which causes the filtering of HF components. The Halbbrückenshunt can be supplemented to reduce the individual power losses by another resistor R2, wherein R1 and R2 can then be dimensioned accordingly ( Fig. 4 ).

Claims (10)

Electronic ballast for operating at least one lamp (La), preferably a gas discharge lamp, with a center tap (M) arranged between a first (S1) and a second switch (S2), to which in series a choke (L1) and a first capacitor ( C1), preferably with a further capacitor (C2) located at a reference potential, wherein the first capacitor (C1) is preferably connected to a terminal for the lamp (La) and to an IC (1) having a measuring input (CS) ), which is provided for the operation of the ballast, wherein the measuring input (CS) between a connected to the reference potential shunt (R1) and a switch (S2) is coupled, characterized in that a limiting circuit is provided, which at the shunt (R1 ) falling signal to reach predetermined signal level at the measuring input (CS) varies, preferably limited in its amplitude. Electronic ballast according to claim 1, characterized in that the limiting circuit has a connected to the reference potential diode (D1) or the like. Blocking effect having circuitry which is coupled into the conduction path between shunt (R1) and measuring input (CS). Electronic ballast according to claim 1 or 2, characterized in that the limiting circuit comprises a in the line branch of the diode (D1) arranged additional resistance (R5). Electronic ballast according to one of the preceding claims, characterized in that the limiting circuit comprises a in the conduction path between shunt (R1) and measuring input (CS) arranged resistor (R3), whose resistance value is preferably greater than that of the shunt (R1). Electronic ballast according to one of the preceding claims, characterized in that a capacitor (C4) is connected in parallel with a diode (D1) or with a series circuit comprising at least one diode (D1). Electronic ballast according to one of the preceding claims, characterized by a capacitive voltage divider coupled to the shunt (R1). Lighting device, characterized by an electronic ballast according to one of the preceding claims. Method for operating an electronic ballast and / or a lighting device having such a device, wherein an IC (1) having a measuring input (CS) has a center tap (M) of a ballast preferably having a bridge circuit by means of a first (S1) and a second Switch (S2) switches to apply an alternating potential to a choke (L1) and a first capacitor (C1) and to supply via this the pole of a lamp (La), via the measuring input (CS) of the IC (1) of the Voltage drop at a shunt (R1) is measured, in particular to detect a dead time for switching on one of the switches (S1, S2) and / or to achieve a control or shutdown threshold, characterized in that the signal applied to the measuring input (CS) ( U _cs , U _CSB ) is varied in amplitude by means of a limiting circuit for reaching predetermined signal levels and in particular limited. A method according to claim 8, characterized in that negative signal components from the shunt (R1) by means of a diode (D1) or the like. Blocking device having the measuring input are supplied. Method according to Claim 8 or 9, characterized in that the signal present at the shunt (R1) is supplied to the measuring input (CS) via a voltage divider.

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