EP0895443A1 - Inrush current limiting circuit - Google Patents

Abstract

The lamp (L) is series-connected, across the AC e.g. mains supply (P,N), with a single-pole switch and a peak-lopping circuit based on two MOSFET transistors (M1,M2). The load-carrying current connection between MOSFETs includes a resistance (Rm) providing current-related input levels to bipolar transistors (T1,T2) controlling the MOSFETs. Bypass diodes (D1,D2) ensure one MOSFET is inoperative during positive current half-cycles. The other during negative half-cycles. The series resistor provides current measurement for the relevant control transistor in both half-cycles. In one variant, a single peak-lopper is used, with a full-wave rectifier. In another, a MOSFET is used in a chopping mode. Optionally, IGBTs replace MOSFETs.

Description

The present invention relates to the field of lamps with filament and, more particularly, incandescent lamps or halogens, especially high voltage.

Figure 1 shows the classic electrical diagram for connecting an L lamp, for example incandescent, to the electrical network supplying an alternating voltage Vac, by example of 230 volts efficient. L lamp is connected in series with a switch K for commissioning between two terminals P, N of application of the Vac voltage. Usually switch K is inserted between the phase P terminal of the alternating voltage single phase and the L lamp. A protection device, generally a fuse or a circuit breaker, from the electrical panel of the installation is inserted between the line of the electrical network and the circuit shown in Figure 1.

Each time the lamp is turned on by closing the switch K, there appears a current call whose value instantaneous is several times greater than current nominal operating. The amplitude of the peak of the inrush current varies depending on the temperature of the lamp filament L and of the instantaneous value of the Vac voltage at the closing instant. When cold and at the top of alternating voltage Vac, this inrush current can reach up to fifteen times the current in nominal speed. The stresses then undergone by the filament of the lamp will shorten its life. Filament lamps have generally a maximum lifespan of around 1000 hours.

FIG. 2 illustrates, in the form of chronograms, the shape of the voltage V _L at the terminals of the lamp L and of the current I _L in the filament of the lamp L. In FIG. 2, it has been assumed that the switch K at an instant t ₁ . A peak of the current I _L appears at time t ₁ and this peak puts several alternations to be damped so that the current in the lamp oscillates between the nominal peak values Inom and -Inom.

This phenomenon is mainly related to the variation of the value of the resistance of the filament of the lamp L as a function of the temperature. When cold, the resistance of the filament is minimal, the nominal power of the lamp corresponding to the value of the resistance of the hot filament, once the lamp is on. As a specific example, for a Vac voltage of 230 volts efficient, a 60 watt bulb has a resistance value of filament of the order of 880 ohms hot. Cold, if the value of the resistance is divided by 10 which corresponds to a proportion usual and if the ignition takes place at the peak of the voltage Vac, i.e. 340 instantaneous volts, the same lamp and the line of the network see an instantaneous power peak of more than 1200 watts.

Besides the fact that these power peaks cause that most incandescent lamps break, i.e. the filament breaks on power up, an arc may appear between a free end of the filament and the base of the bulb, and this arc is likely to cause disjunction of the protection fuse concerned, therefore maintenance costs of the installation.

The same phenomenon is observed on halogen lamps provided with a filament, in particular, for halogen lamps high voltages, i.e. which are not supplied by via a step-down transformer.

Another disadvantage of current spikes on ignition of a filament lamp is that these disturbances on the line lamp power supply may damage other devices connected on the same circuit, i.e. downstream of the same fuse.

A classic solution to overcome these drawbacks is to provide, in series with the lamp, a coefficient thermistor negative, i.e. a resistance whose value decreases with the temperature. Such a solution presents several disadvantages. First, the thermistor affects the performance of the lighting installation because its heat resistance remains non negligible and therefore causes energy dissipation. We have to indeed choose thermistors with very cold values high enough to limit the current peak sufficiently. It follows that the power actually restored by the lamp does not does not correspond to its nominal value. Second, a thermistor cools more slowly than a filament lamp filament incandescence. Therefore, thermistor protection is ineffective in the event of repeated lighting of the lamp, in brief time intervals.

In other applications, it has already been proposed to limit peaks of inrush current to the commissioning of a device, by means of an electronic control circuit controlling the energization so that it intervenes at a zero crossing of the alternating voltage. Such a solution is however unsuitable for filament lamps. In fact, if such a solution would make it possible to reduce the amplitude of the current peak when the switch K is closed (instant t ₁ ), the current in the lamp would however exceed the nominal values for several half-waves and would then no longer be limited. , the time that the filament heats up enough for its resistance to reach its nominal value. In addition, the implementation of such a solution requires a complex electronic circuit requiring, most often, the generation of a low bias voltage of the electronic components constituting it.

The present invention aims to propose a new solution to limit the inrush current in a filament lamp.

The invention aims, in particular, to propose a device which maintains the current in the lamp between the values ratings for which the lamp is designed.

The invention also aims to propose a device which either simple and inexpensive.

The present invention also aims to ensure that this device can be powered without the need for power specific.

The present invention further aims to provide a device small footprint.

To achieve these objects, the present invention provides a circuit for limiting the inrush current of a filament lamp, intended to be connected in series between the filament and a power switch by an alternating voltage, and comprising at least one controllable active element, limiting the current at a predetermined threshold value, polarized, outside periods of limitation, by a resistor connected between a power terminals of this element and its control terminal.

According to an embodiment of the present invention, said threshold value is fixed by means of a measuring resistor current in the lamp.

According to an embodiment of the present invention, the circuit includes at least one limiting element in series with said measurement resistor, an element control terminal of limitation being connected to a control means, detecting the voltage across the measurement resistor.

According to an embodiment of the present invention, said means consists of a bipolar transistor, between base and transmitter from which the measurement resistor, the element is connected limit being controlled in linear mode.

According to an embodiment of the present invention, said means consists of a comparator of the voltage across the terminals of the measurement resistance with respect to a reference value predetermined, the limiting element being controlled in cutting.

According to an embodiment of the present invention, said active element is mounted as a unidirectional limiter and is associated with a rectifier bridge.

According to an embodiment of the present invention, the circuit has two limiting elements, to limit the current in the lamp at the predetermined threshold value, each element being mounted as a one-way limiter.

According to an embodiment of the present invention, the circuit includes two MOS field effect transistors, mounted in series between the switch and the filament, the resistance of measure being inserted between these two transistors and the path current comprising, at each alternation of the supply voltage, a stray diode from one of the two effect transistors field.

The present invention also relates to a bulb filament comprising, in its base, a current limiting circuit.

les figures 1 et 2 qui ont été décrites précédemment sont destinées à exposer l'état de la technique et le problème posé ;

la figure 3 représente un schéma de principe d'un circuit limiteur de courant associé à une lampe à filament selon la présente invention ;

la figure 4 illustre, sous forme de chronogrammes, le fonctionnement d'un circuit limiteur de courant selon la présente invention ;

la figure 5 représente un premier mode de réalisation d'un circuit limiteur de courant selon la présente invention ;

la figure 6 représente un deuxième mode de réalisation d'un circuit limiteur de courant selon la présente invention ;

la figure 7 représente la caractéristique courant-tension d'un élément limiteur de courant selon la présente invention ; et

la figure 8 représente un troisième mode de réalisation d'un circuit limiteur de courant selon la présente invention.

These objects, characteristics and advantages, as well as others of the present invention will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

Figures 1 and 2 which have been described above are intended to show the state of the art and the problem posed;

FIG. 3 represents a block diagram of a current limiting circuit associated with a filament lamp according to the present invention;

FIG. 4 illustrates, in the form of timing diagrams, the operation of a current limiting circuit according to the present invention;

FIG. 5 represents a first embodiment of a current limiting circuit according to the present invention;

FIG. 6 represents a second embodiment of a current limiting circuit according to the present invention;

FIG. 7 represents the current-voltage characteristic of a current limiting element according to the present invention; and

FIG. 8 represents a third embodiment of a current limiting circuit according to the present invention.

The same elements have been designated by the same references to the different figures. For reasons of clarity, the timing diagrams of Figures 2 and 4 and the characteristic of the Figure 7 is not to scale.

FIG. 3 schematically represents a circuit ignition of a filament lamp L from a voltage alternative Vac, for example, the mains voltage, according to a embodiment of the invention. Conventionally, the lamp L is connected in series with a switch K between two terminals P, N of alternative power supply.

A characteristic of the present invention is to connect, in series with the lamp L and, preferably, between the switch K and the lamp L, a current limiting circuit 1, bidirectional, whose role is to clip the current I _L taken from the power supply at a predetermined threshold value.

According to the present invention, the device 1, symbolized in FIG. 3 by means of two unidirectional limiting elements 2, 3 controllable, consists, at least in part, of active components. Each element 2, 3 is intended to clip the current by limiting it to a threshold value Ilim and the elements 2 and 3 operate in turn according to the alternation of the voltage Vac.

FIG. 4 illustrates, in the form of timing diagrams representing the voltage V _L at the terminals of the lamp L and the current I _L passing therethrough, the operation of the circuit represented in FIG. 3. It is assumed that the switch K is closed at an instant t ₁ during a positive alternation of the Vac voltage. As the resistance of the filament of the lamp L is very low, the current I _L increases suddenly and is limited to the threshold value Ilim by the element 3. During this first alternation which follows the closing of the switch K, the current I _L remains maintained at the value Ilim as long as the voltage at the terminals of the lamp L has not become sufficiently low for the resistance of the filament of the lamp to be sufficient for the current I _{L to} be less than the value Ilim ( instant t ₂ ). The same operation is repeated at the next alternation (negative) by the action of element 2 because the filament of the lamp does not have time to heat up enough during an alternation for its resistance to reach its value nominal. This operation therefore reproduces at the following alternations as long as this resistance of the filament of the lamp is not sufficient to maintain the current I _L between Ilim and -Ilim.

In the example shown in Figure 4, we have considered the case of an Ilim value corresponding to the current value nominal in the lamp once the filament is warm. Note however that the current Ilim is preferably fixed at a value slightly higher than the nominal lamp current, in particular, to take into account the tolerances of the Vac voltage (generally ± 15%) so that elements 2 and 3 are not in permanent limitation operation.

An advantage of the present invention is that it avoids any power peak in the lamp L when it is switched on. The the life of the filament lamp is increased.

Another advantage of the present invention is that the device 1 protects the filament of the lamp L, even during nominal operation, for example, in the event of an accidental overvoltage alternative food.

Another advantage of the present invention is that it eliminates any risk of damage to another electrical device powered from the same fuse, in particular, in the case the fuse is oversized.

Another advantage of the present invention is that it prevents, in the event of a filament break, the propagation of a peak current linked to the appearance of an arc between a free end of the filament and the base of the bulb.

FIG. 5 represents a first embodiment of a limiter circuit according to the present invention.

The device comprises, between the switch K and the lamp L, two MOS field effect transistors M1, M2, preferably N channel, mounted in adjustable current sources, and between the sources of which a measurement resistance Rm is interposed current. The drain of transistor M1 is connected to the terminal of the switch K, on the lamp side, and the drain of the transistor M2 is connected to a first lamp terminal including the second terminal is connected, for example, to neutral N of the AC power supply. The source of each transistor M1, M2 is also connected to the base of a bipolar transistor T1, T2 including the collector is connected to the gate of the corresponding transistor M1, M2 and, via a polarization resistor R1, R'1, to the drain of this transistor M1, M2. The emitter of transistor T1 is connected to the source of transistor M2, and the emitter of the transistor T2 is connected to the source of transistor M1. Transistors T1 and T2 detect the voltage across the resistor Rm and control, respectively, the transistors M1 and M2.

A feature of the invention is that each element limiter (here, the transistors M1 and M2) is associated with a polarization resistive element (here, resistors R1 and R'1) connected between one of its power terminals and its ordered.

This resistive element serves as a local power supply and avoids the generation of a bias voltage by a complex circuit.

The limit value Ilim depends on the value of the resistor Rm. As long as the voltage drop across the resistor Rm is less than the base-emitter junction voltage of the bipolar transistor T1 or T2, this transistor remains off and the transistor MOSFET M1 or M2 associated with it is maintained, by being polarized by the resistance R1, R'1, in conduction in its operating zone where its gate-source voltage (VgsON) is approximately equal to its drain-source voltage (VdsON ), and therefore has a low voltage drop. When the current I _L becomes such that the voltage drop across the resistor Rm is greater than the junction voltage of one of the transistors T1, T2, the corresponding transistor M1, M2 then operates in linear mode, that is ie in its current limiting region.

In the assembly of FIG. 5, the transistors M1, T1 and resistance R1 intervenes during positive half-waves, and the transistors M2, T2 as well as the resistance R2 intervene during negative alternations. The resistance Rm serves as current measurement resistance whatever the alternation considered.

During positive half-waves, the stray diode D2 of the transistor M2 is forward biased and the resistance Rm is is therefore connected to the lamp L, neglecting the voltage drop (about 0.7 volts) in the stray diode D2. During the work-study program negative, a similar role is played by the stray diode D1 of transistor M1 and resistor Rm is therefore connected to switch K by neglecting the voltage drop in this stray diode.

Note that other current limiting components unidirectionals may be used in place of transistors M1 and M2. For example, we could use two transistors IGBT. However, in this case, care should be taken to add diodes D1, D2 in parallel on the IGBT transistors to allow the bidirectional operation of the limiting circuit.

Figure 6 shows a second embodiment of the present invention in which a diode bridge D3, D4, D5 and D6 is used to make a limiting circuit bidirectional unidirectional, for example, one of the circuits of the figure 5.

Two alternative input terminals 4, 5 of the diode bridge are respectively connected to an output terminal of the switch K and to an arbitrarily called input terminal of the lamp L. A limiting circuit 8, unidirectional, is connected between two output terminals 6, 7 of the diode bridge, i.e. between the anodes of the diodes D3 and D4 and the cathodes of the diodes D5 and D6.

This limiter circuit 8 includes, as before, a measuring resistance Rm in series with a limiting element, here an IGBT transistor 9, between the switch K and the lamp L, here between terminals 6 and 7. The gate of the IGBT transistor is connected to the collector of a bipolar control transistor T whose transmitter is connected to terminal 7 and whose base is connected to the emitter of the IGBT transistor, that is to say that the resistance Rm is placed in parallel between the base and the emitter of transistor T. A bias resistor R1 is connected between terminal 6 and the collector of transistor T.

The operation of the assembly of FIG. 6 is deduced of the operation described in relation to FIG. 5. During the positive half-waves, the current flows in the diode D3, in transistor 9, in resistor Rm and in diode D5. When negative half-waves, the current flows in the diode D4, in transistor 9, in resistor Rm and in diode D6.

Other components or assemblies than those exposed in relationship with Figures 5 and 6 can be used to constitute the unidirectional current limiting circuit according to the present invention. For example, we could use a technology bipolar combination and cascode type MOSFET, or bipolar transistors mounted in Darlington.

The current-voltage characteristic which a unidirectional limiting element (M1, M2, FIG. 5 - 9, FIG. 6) must comply with according to the present invention is shown in FIG. 7. As long as the current I _L remains below the limit value Ilim , the limiting element behaves like a resistance of very low value (corresponding to the value of the series resistance of a MOSFET transistor in conduction or of an IGBT transistor). As soon as the current I _L reaches the limitation value fixed by the resistor Rm, the element limits the current I _L to this value, whatever the voltage Vac, provided that this remains below a limit value Vbr d ' avalanche of the limiting element (MOSFET transistors M1, M2 or IGBT transistor).

The value Vs of the threshold voltage between the two modes of operation of the device corresponds, in the embodiment of Figure 6, at the voltage drop in two diodes of the bridge, increased by the voltage drop in the resistance Rm and of the series voltage drop in the limiting element 9.

An advantage of the present invention is that the circuit limiter has few components and is easily preferably integrated into the base of an incandescent bulb or in the socket of a luminaire. The integration of a the limiting circuit in the base of the bulb has the advantage to be able to link the current limit to the power of the lamp. This avoids permanent dissipation by the device limitation, linked to its permanent operation in limitation mode, if the bulb has a higher power than that for which the device is dimensioned.

Such integration is facilitated by the fact that the limiting element is polarized, outside the limitation periods, by a simple resistive element which avoids the need for a third circuit access point. So a characteristic of the invention is that the limiter circuit is a "2-wire" circuit and can therefore be connected in series with the filament of the lamp without requiring connection to the two terminals of the power supply alternative.

As a particular embodiment, for a 60 watt incandescent lamp with nominal resistance (i.e. hot) filament is around 880 ohms for a voltage of 230 volts rms, the nominal current of operating (i.e. maximum operating intensity nominal) is around 370 mA. A limiting circuit according to the invention, dimensioned with a resistance Rm of 1.2 ohms, peak current from around 500 mA and thus allow correct functioning and minimal dissipation even in case of variation of the supply voltage within the tolerance range (± 15%) of supply of the AC mains voltage.

FIG. 8 represents a third embodiment of a current limiting circuit according to the present invention. This circuit always consists of at least one active element, by example a MOSFET M transistor or an IGBT transistor, controllable to limit the current to a predetermined threshold value. The transistor M is connected in series with a measurement resistance of the current and the limiter circuit includes a means for detecting the voltage across this measurement resistor to control transistor M.

A characteristic of this embodiment is that the transistor M is controlled in switching mode, that is to say that it is opened as soon as the current in the resistor Rm reaches the fixed threshold value and that it is restored. in conduction after a short time interval. This amounts, by resuming the shape of the current I _L of FIG. 4, to chop this current between the instants t ₁ and t ₂ . An advantage is that this reduces dissipation during limitation periods. This advantage is particularly noticeable in the case of a limiting circuit connected upstream of the bulb, for example in the socket of the luminaire, since the dissipation is reduced if the bulb has a power greater than that for which the device is sized. .

As with the other embodiments, the transistor M is associated with a bias resistor R1 allowing to put it in conduction. In the example shown in the figure 8, the limiter circuit is unidirectional and is associated with a diode bridge D3, D4, D5, D6 so as to make it bidirectional, the transistor M in series with the resistance Rm being connected between terminals 6 and 7 of the bridge. Detection means here consists of a comparator 10, for example an amplifier differential, an inverting input of which is connected to the point middle of the series association of transistor M and resistance Rm. The non-inverting input of comparator 10 receives a reference voltage fixed, for example, by a diode D7 whose cathode is connected to terminal 7 and the anode of which is connected, via a resistor R2 at the non-inverting input. The output of comparator 10 is connected to the grid of the transistor M and, via a resistor R3, to its non-inverting input. The divider bridge made up of resistors R2 and R3 condition a hysteresis around the reference voltage fixed by diode D7, so that the assembly oscillates. The comparator 10 is supplied by means of an associated capacitor C to a diode D8, the resistor R1, the diode D8 and the capacitor C being connected in series between terminals 6 and 7. A resistor R4 connects the cathode of diode D8 (the midpoint of the interconnection between diode D8 and capacitor C) to the anode of diode D7 which is thus always polarized in direct.

When the voltage across the resistor Rm (proportional to the current I _L ) becomes greater than the reference voltage, the output of the comparator 10 is drawn to its low power supply, and the gate of the transistor M is found substantially at the terminal potential 7. The transistor M is therefore immediately open. The current in the lamp is canceled. The comparator then switches almost immediately to its high power supply, which causes the transistor M to go back into conduction. However, the transistor M conduction is slightly delayed by the time constant introduced by the resistor R1 associated with the gate capacitance of transistor M. This chopping operation is repeated as long as the current I _L is, on each conduction, greater than the fixed threshold value. When hot, that is to say when the resistance of the filament of the lamp has reached its nominal value, the operation described above is reproduced in relation to FIG. 5, the output of the comparator remaining at its high supply.

It will be noted that the limiting circuit exposed in relation with figure 8 also applies to the case where two elements limiters are used without righting bridge. We use then two comparators (one for each alternation).

Of course, the present invention is capable of various variants and modifications which will appear to the man of art. In particular, other components than those indicated in relationship with Figures 5, 6 and 7 could be used to carry out the limitation function, provided that they comply with the features described above. In addition, the sizing respective components of the limiting device are within the reach of the skilled person according to the power of the lamp. In addition, elements other than resistors may be used to supply local food to the limiting element by polarizing it outside of the limitation periods. We could, for example, use a transistor or any another element mounted as a resistive element.

Claims (9)

Lamp current limiting circuit (L) with filament, intended to be connected in series between the filament and an AC power switch (K) (Vac), characterized in that it comprises at least one active element (M1, M2; 9; M) controllable, limiting the current to a predetermined threshold value (Ilim), polarized outside periods of limitation by a resistive element (R1, R'1) connected between a power terminals of the limiting element and its terminal ordered. Current limiting circuit according to claim 1, characterized in that said threshold value (Ilim) is fixed to by means of a resistance (Rm) for measuring the current in the lamp (L). Current limiting circuit according to claim 2 characterized in that it comprises at least one limiting element (M1, M2; 9; M) in series with said measurement resistor (Rm), a control terminal of the limiting element being connected to a control means (T1, T2; T; 10), detecting the voltage across the measurement resistor. Current limiting circuit according to claim 3, characterized in that said means consists of a transistor (T1, T2; T) bipolar, between base and transmitter of which is connected the measurement resistance (Rm), the limiting element (M1, M2; 9) being controlled in linear mode. Current limiting circuit according to claim 3, characterized in that said means consists of a comparator (10) of the voltage across the measurement resistor (Rm) with respect to a predetermined reference value, the element limiter being controlled in switching mode. Current limiting circuit according to any one claims 1 to 5, characterized in that said element active (9; M) is mounted as a unidirectional limiter and is associated to a rectifier bridge (D3, D4, D5, D6). Current limiting circuit according to any one of claims 1 to 5, characterized in that it comprises two limiting elements (M1, M2), to limit the current in the lamp (L) at the predetermined threshold value (Ilim), each element being mounted as a one-way limiter. Current limiting circuit according to claim 7, characterized in that it comprises two effect MOS transistors field (M1, M2), mounted in series between the switch (K) and the filament, the measurement resistance (Rm) being inserted between these two transistors and the current path including, at each alternating supply voltage, a stray diode (D1, D2) of one of the two field effect transistors. Filament bulb, characterized in that it comprises, in its base, a current limiting circuit according to one any of claims 1 to 8.

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