Device for measuring a chopped current

A device for measuring a chopped current capable of flowing in a circuit having an H-bridge structure including a first branch and a second branch is disclosed. The device includes two transformers respectively connected to a branch and each comprising a primary circuit configured for the flow of a chopped current and a secondary circuit, two demagnetizing circuits, and two measuring circuits respectively connected to the terminals of the secondary circuit of an associated transformer, and respectively including at least one unit which comprises two switch connected in reverse, the two switches being respectively implemented by a transistor and being capable of being controlled. The measuring circuits include a common measuring resistor connected via a terminal to the ground, and via another terminal to the source of the first transistor of the first measuring circuit and to the source of the first transistor of the second measuring circuit.

The present invention relates to a device for measuring a chopped current.

Such a measuring device is particularly applicable to measuring a chopped current flowing to the input of a DC-DC converter.

Such a measuring device may comprise a pulse transformer. The transformer comprises a primary circuit in which the chopped current flows, and a secondary circuit in which an output current flows that is proportional to the chopped current. The secondary circuit of the transformer includes two output terminals between which a circuit is connected for measuring the output current. The measuring circuit generally includes a resistor.

Sometimes it is necessary to measure a chopped current with a non-zero average value, e.g. for measuring the chopped current flowing in a DC-DC converter, connecting two power supply batteries of different voltages.

Accordingly, it is necessary to regularly demagnetize the pulse transformer. Indeed, as a first approximation, the imperfections of the pulse transformer can be modelled by a magnetizing inductance arranged between the output terminals of the secondary circuit. The measuring device comprises for this purpose means for demagnetizing the transformer. By way of example, the demagnetization takes place e.g. by passing the magnetizing current through a demagnetizing circuit so that the energy stored in the magnetizing inductance can thus be released.

The current to be measured may also comprise positive, negative or zero instantaneous values. To this end, according to a known solution, the measuring circuit comprises a switch and means for synchronizing this switch with the chopped current, for enabling the output current to flow in the measuring circuit when the chopped current is non-zero (positive or negative) and for preventing any current flow in the measuring circuit when the chopped current is zero.

The switch enables the output current to flow in both directions in the measuring circuit.

The demagnetizing circuit generally includes a Zener diode mounted in series with one diode arranged in the opposite direction to the Zener diode.

The demagnetizing operation is performed during ‘freewheel’ periods when the chopped current is zero.

The demagnetizing phase is therefore dependent on the freewheel period. However, this period depends on the duty cycle, and may not be long enough to allow the demagnetization of the transformer.

The invention aims to at least partially overcome these drawbacks of the prior art, by providing a device for measuring a chopped current, capable of measuring a bidirectional current, while ensuring a sufficient time for demagnetization.

To this end, the subject matter of the invention is a device for measuring a chopped current capable of flowing in a circuit having an H-bridge structure including a first branch and a second branch, characterized in that it comprises:two transformers respectively connected to a branch of the H-bridge, the transformers respectively comprising a primary circuit configured for the flow of a chopped current and a secondary circuit,two demagnetizing circuits for the two transformers andtwo measuring circuits respectively connected to the terminals of the secondary circuit of an associated transformer, the measuring circuits respectively including at least one unit configured for:allowing the flow of a current induced by the chopped current, in the measuring circuit when the primary circuit of the associated transformer is closed, andpreventing the flow of a demagnetizing current in the measuring circuit when the primary circuit current of the associated transformer is open.

Thus, the presence of a transformer in each branch of the H-bridge always enables having half an operating period for demagnetizing the transformer. The demagnetizing time is known which becomes constant and is no longer dependent on the duty cycle.

According to one aspect of the invention, a unit configured for allowing or preventing the flow of a current induced by the chopped current in a measuring circuit comprises a first switch and a second switch connected in reverse, the two switches being capable of being controlled so as to allow the flow of a current induced by the chopped current, in the measuring circuit when the primary circuit of the associated transformer is closed and to prevent the flow of the current in the measuring circuit when the primary circuit of the associated transformer is open.

According to one embodiment, the first switch and the second switch are respectively implemented by a transistor, e.g. a field effect transistor.

According to another aspect of the invention, the measuring circuits include at least one measuring resistor connected via a first terminal to the ground.

According to one example:

the first switch of a measuring circuit comprises a terminal connected to a second terminal of the measuring resistor, the first terminal of the measuring resistor being connected to the ground; and

the second switch of a measuring circuit comprises a terminal connected to the ground.

According to a first embodiment, the measuring circuits include a common measuring resistor connected:

via a first terminal to the ground, and

via a second terminal to the source of the first transistor of the first measuring circuit and to the source of the first transistor of the second measuring circuit.

According to a second embodiment, the measuring circuits respectively include a measuring resistor connected via a terminal to the ground,

the measuring resistor of the first measuring circuit is connected via one of the terminals thereof to the source of the first transistor and to the source of the second transistor of the first measuring circuit via the other of the terminals thereof, and

the measuring resistor of the second measuring circuit is connected to the source of the first transistor via one of the terminals thereof and to the source of the second transistor of the second measuring circuit via the other of the terminals thereof.

According to one example of embodiment, the first measuring circuit includes a first output resistor and the second measuring circuit includes a second output resistor, such that the two output resistors are in series. In this case, a measuring voltage can be measured at the common node between the two output resistors.

According to another aspect of the invention:the branches of the circuit respectively include a first switch and a second switch,the first transformer is connected to the first switch of the first branch and the second transformer is connected to the first switch of the second branch, andthe unit of the first measuring circuit configured for allowing or preventing the flow of a current induced by the chopped current in the first measuring circuit is configured for being controlled by the inverse of the control signal of the second switch of the first branch andthe unit of the second measuring circuit configured for allowing or preventing the flow of a current induced by the chopped current in the second measuring circuit is configured for being controlled by the inverse of the control signal of the second switch of the second branch.

According to one example of embodiment:the first measuring circuit comprises a first resistor and a second resistor, the terminal common to the two resistors being connected to the gate of the first transistor and of the second transistor of the first measuring circuit, andthe second measuring circuit comprises a first resistor and a second resistor, the terminal common to the two resistors being connected to the gate of the first transistor and of the second transistor of the second measuring circuit.

According to another aspect of the invention, the demagnetizing means respectively comprise a demagnetizing circuit connected between the two output terminals of the secondary circuit of the associated transformer.

A demagnetizing circuit comprises, for example, two Zener diodes mounted in series and in opposite directions.

The invention also relates to a device for measuring a chopped current capable of flowing in a branch of a circuit, characterized in that it comprises:a transformer connected to said branch, the transformer comprising a primary circuit configured for the flow of the chopped current, and a secondary circuit,a demagnetizing circuit for the transformer, anda measuring circuit connected to the terminals of the secondary circuit of the transformer, the measuring circuit including:at least one unit comprising a first switch and a second switch connected in reverse, the two switches being capable of being controlled so as to allow the flow of a current induced by the chopped current, in the measuring circuit when the primary circuit of the transformer is closed and to prevent the flow of a demagnetizing current in the measuring circuit when the primary circuit of the transformer is open, andat least one measuring resistor connected via a first terminal to the ground, such that:the first switch of the measuring circuit comprises a terminal connected to a second terminal of the measuring resistor, andthe second switch of the measuring circuit comprises a terminal connected to the ground.

The measuring device may have any one of the previously described features that are compatible therewith, in particular those relating to a transformer, a demagnetizing circuit, and/or a measuring circuit. Particularly, the device may comprise any one of the following features:the branch of the circuit including a first switch and a second switch, the transformer is connected to the first switch of the branch, and the unit of the measuring circuit configured for allowing or preventing the flow of a current induced by the chopped current in the measuring circuit is configured for being controlled by the inverse of the control signal of the second switch of the branch;the first switch and the second switch are respectively implemented by a transistor, e.g. a field effect transistor;the measuring circuit comprises a first resistor and a second resistor, the terminal common to the two resistors being connected to the gate of the first transistor and of the second transistor of the measuring circuit;the demagnetizing circuit is connected between the two output terminals of the secondary circuit of the transformer;the demagnetizing circuit comprises two Zener diodes mounted in series and in opposite directions.

The invention also relates to a device for measuring a chopped current capable of flowing in a circuit having an H-bridge structure including a first branch and a second branch, characterized in that it comprises:two transformers respectively connected to a branch of the H-bridge, the transformers respectively comprising a primary circuit configured for the flow of a chopped current, and a secondary circuit,two circuits for demagnetizing the two transformers, andtwo measuring circuits respectively connected to the terminals of the secondary circuit of an associated transformer, the measuring circuits respectively including at least one unit which comprises a first switch and a second switch connected in reverse, the two switches being respectively implemented by a transistor and being capable of being controlled so as to:allow the flow of the current induced by the chopped current, in the measuring circuit when the primary circuit of an associated transformer is closed, andprevent the flow of the demagnetizing current in the measuring circuit when the primary circuit of an associated transformer is open;

the measuring circuits including a common measuring resistor connected via a first terminal to the ground, and via a second terminal to the source of the first transistor of the first measuring circuit and to the source of the first transistor of the second measuring circuit.

The device may have any one of the previously described features that are compatible therewith.

In these figures, identical elements bear the same references.

The invention relates to a device1for measuring a chopped current, in particular flowing inside a DC-DC converter3.

Converter

Referring toFIG. 1, the converter3represented has an H-bridge structure having a first branch B1and a second branch B2.

The first branch B1comprises a first switch Mos1and a second switch Mos2.

The second branch B2comprises a first switch Mos3and a second switch Mos4.

The switches Mos1to Mos4comprise, by way of a non-restrictive example, an N-type, field effect transistor known under the acronym MOSFET.

When the first branch B1is controlled, the first switch Mos1is turned on when the second switch Mos1is blocked, and conversely the second switch Mos1is turned on when the first switch Mos1is blocked.

The same applies to controlling the second branch B2, the first switch Mos3is turned on when the second switch Mos4is blocked, and conversely the second switch Mos4is turned on when the first switch Mos3is blocked.

The offset between the two branches B1and B2depends on the H-bridge control logic.

Device for Measuring the Chopped Current

Referring again toFIG. 1, the device1for measuring the chopped current comprises two transformers10B1and10B2with a transformation ratio of mi. The two transformers10B1and10B2are arranged respectively on a branch B1or B2of the converter3.

One transformer10B1or10B2includes a primary circuit12and a secondary circuit14.

The primary circuit12of a first transformer10B1is connected to the first switch Mos1of the first branch B1of the converter3. The primary circuit12of the second transformer10B2is connected to the first switch Mos3of the second branch B2of the converter3.

The secondary circuit14of a transformer10B1or10B2comprises two output terminals16and18.

When a chopped current icflows in the converter3, it is split in the two branches B1and B2, so that a first chopped current iMos1flows in the primary circuit12of the first transformer10B1, and a second chopped current iMos3flows in the primary circuit12of the second transformer10B2.

When the primary circuit12of the first transformer10B1or of the second transformer10B2is closed, the chopped current iMos1or iMos3flowing in the primary circuit12of the first transformer10B1or of the second transformer10B2is non-zero, and the associated transformer10B1or10B2is magnetized.

A demagnetization of a transformer10B1or10B2takes place when the primary circuit12of the first transformer10B1or of the second transformer10B2is open, the chopped current iMos1or iMos3being zero, i.e. when there is no current to be measured.

And in addition, the device1can be used to measure the chopped current when the primary circuit12of the first transformer10B1or of the second transformer10B2is closed, the chopped current iMos1or iMos3flowing in the primary circuit12of the first transformer10B1or of the second transformer10B2being non-zero.

For this purpose, with reference toFIG. 2, the measuring device1further includes:

two demagnetizing circuits20B1,20B2respectively associated with a transformer10B1or10B2, and

two chopped current measuring circuits22B1and22B2respectively connected to the output terminals16,18of the associated transformer10B1or10B2.

According to the described embodiment, the demagnetizing circuits20B1,20B2are separate from the measuring circuits22B1and22B2.

Each demagnetizing circuit20B1and20B2is connected between the two output terminals16and18of the associated transformer10B1or10B2.

Each demagnetizing circuit20B1,20B2enables the demagnetization of the associated transformer10B1or10B2through a flow of a current in the demagnetizing circuit20B1or20B2.

According to the embodiment illustrated inFIG. 2, a demagnetizing circuit20B1or20B2includes a first Zener diode24connected in series with a second Zener diode26between the output terminals16and18. The Zener voltage is by way of an illustrative example of the order of 10 V.

The first Zener diode24and the second Zener diode26are mounted in opposite directions. As an example, the first Zener diode24may be connected via its cathode to the output terminal16and the second Zener diode26may be connected via its cathode to the other output terminal18. The two Zener diodes24and26are then connected with one another via the anodes thereof.

Thus, the demagnetizing circuits20B1,20B2are bidirectional, i.e. they enable demagnetization in both directions of flow of the magnetizing current, according to whether the average value of the chopped current is positive or negative.

A first measuring circuit22B1is connected to the output terminals16,18of the secondary circuit14of the first transformer10B1connected to the first branch B1of the converter3. The first measuring circuit22B1is connected in parallel with the first demagnetizing circuit20B1.

A second measuring circuit22B2is connected to the output terminals16,18of the secondary circuit14of the second transformer10B2connected to the second branch B2of the converter3. The second measuring circuit22B2is connected in parallel with the second demagnetizing circuit20B2. The second measuring circuit22B2is further connected to the first measuring circuit22B1.

The measuring circuits22B1and22B2respectively include at least one unit configured for:allowing the flow of a current imes1; imes2induced by the chopped current, in the measuring circuit22B1or22B2, when the primary circuit12of a transformer10B1;10B2is closed; in this case the chopped current flowing in the primary circuit12is non-zero, either strictly positive or strictly negative, andpreventing the flow of the demagnetizing current in the measuring circuit22B1or22B2when the primary circuit12of a transformer10B1;10B2is open; in this case the chopped current flowing in the primary circuit12is zero.

According to the embodiment described, the two measuring circuits22B1and22B2respectively include a unit configured for allowing or preventing the flow of a current induced by the chopped current in the associated measuring circuit22B1or22B2, and comprising a first switch and a second switch. The unit of the first measuring circuit22B1includes a first switch Ki1_HSand a second switch Ki1—LS. The unit of the second measuring circuit22B2includes a first switch Ki2_HSand a second switch Ki2_LS.

The first switches Ki1_HSand Ki2_HSare also called High Side switches.

The second switches Ki1_LSand Ki2_LSare also called Low Side switches.

The first and second switches Ki1_HSand Ki1_LSof the first measuring circuit22B1and the first and second switches Ki2_HSand Ki2_LSof the second measuring circuit22B2are formed, according to the example described, of MOSFET field effect transistors.

The first and second switches Ki1_HSand Ki1_LSof the first measuring circuit22B1in this example are connected in reverse. Similarly, the first and second switches Ki2_HSand Ki2_LSof the second measuring circuit22B2are connected in reverse.

Furthermore, with reference toFIGS. 3 and 4, the measuring circuits22B1;22B2include at least one measuring resistor Rmesor Rmes′ connected via a first terminal to the ground.

The first switch Ki1_HS; Ki2_HSof a measuring circuit22B1;22B2comprises a terminal connected to a second terminal of the measuring resistor Rmesor Rmes′, the first terminal of the measuring resistor Rmesor Rmes′ being connected to the ground. The second Ki1—LSswitch; Ki2_LSof a measuring circuit22B1;22B2in turn comprises a terminal connected to the ground.

More specifically, with regard to the first measuring circuit22B1:

the drain of the first transistor Ki1_HSis connected to the first output terminal16of the first transformer10B1connected to the first branch B1of the converter3.

the source of the first transistor Ki1_HSis connected via a terminal to the second terminal of the measuring resistor Rmes(FIG. 2) or Rmes′ (FIG. 3), the first terminal of the measuring resistor Rmes(FIG. 2) or Rmes′ (FIG. 3), being connected to the ground, and

the gate of the first transistor Ki1_HSis connected to the gate of the second transistor Ki1_LSof the first measuring circuit22B1,

the drain of the second transistor Ki1_LSis connected to the second output terminal18of the first transformer10B1, and

the source of the second transistor Ki1_LSis connected to the ground.

With regard to the second measuring circuit22B2:

the drain of the first transistor Ki2_HSis connected to the first output terminal16of the second transformer10B2connected to the second branch B2of the converter3.

the source of the first transistor Ki2_HSis connected via a terminal to the second terminal of the measuring resistor Rmes(FIG. 2) or Rmes′ (FIG. 3), the first terminal of the measuring resistor Rmes(FIG. 2) or Rmes′ (FIG. 3), being connected to the ground, and

the gate of the first transistor Ki2_HSis connected to the gate of the second transistor Ki2_LSof the second measuring circuit22B2,

the drain of the second transistor Ki2_LSof the second measuring circuit22B2is connected to the second output terminal18of the second transformer10B2,

the source of the second transistor Ki2_LSis connected to the ground.

In addition, the first transistors Ki1_HSand Ki2_HSmust be such that the voltage between the gate and the source is greater than the threshold voltage of the transistor for activating the transistor.

The transistors Ki1_HSand Ki1_LSof the first measuring circuit22B1and the transistors Ki2_HSand Ki2_LSof the second measuring circuit22B2are capable of being controlled according to the H-bridge control logic. Thus, when the primary circuit12of a transformer10B1or10B2is closed, the chopped current in the primary circuit12of the transformer10B1or10B2is non-zero, and the two transistors Ki1_HSand Ki1_LSor Ki2_HSand Ki2_LSof the associated measuring circuit22B1or22B2are in the on state. When the primary circuit12of the first transformer10B1or of the second transformer10B2is open, the chopped current is zero, and the two transistors Ki1_HSand Ki1_LSor Ki2_HSand Ki2_LSof the associated measuring circuit22B1or22B2are in the blocked state.

Thus, when the primary circuit12of a transformer10B1or10B2is closed, the chopped current iMos1iMos3in the primary circuit12of a transformer10B1or10B2being non-zero, and there is therefore a current to be measured, the two transistors Ki1_HSand Ki1_LSor Ki2_HSand Ki2_LSof the associated measuring circuit22B1or22B2must be controlled in the on state.

And, the demagnetization of a transformer10B1or10B2may be performed when the primary circuit12of the transformer10B1or10B2is open, the chopped current iMos1or iMos3being zero and there is no current to be measured, by blocking the two transistors Ki1_HSand Ki1_LSor Ki2_HSand Ki2_LSof the associated measuring circuit22B1or22B2, so as to disconnect the demagnetizing circuit20B1or20B2from the measuring resistor Rmes or Rmes′ during the demagnetization of the corresponding transformer10B1or10B2.

When the primary circuit12of the first transformer10B1or of the second transformer10B2is closed, a chopped current iMos1or iMos3flows in the primary circuit12of the associated transformer10B1or10B2, and a current is induced in the secondary circuit14of the associated transformer10B1or10B2. If the transistors Ki1_HSand Ki1_LSof the first measuring circuit22B1, respectively if the transistors Ki2_HSand Ki2_LS, of the second measuring circuit22B2, are turned on, a current imes1, respectively imes2, flows in the associated first or second measuring circuit22B1or22B2.

According to a first embodiment illustrated inFIG. 2, the two measuring circuits22B1and22B2further comprise a common measuring resistor Rmesconnected firstly via a first terminal to the ground and via a second terminal to the source of the first two transistors Ki1_HSand Ki2_HS. The source of the first transistor Ki2_HSof the unit capable of allowing or preventing the flow of a current induced by the chopped current in the first measuring circuit22B1, is therefore connected to the source of the first transistor Ki2_HSof the unit capable of allowing or preventing the flow of a current induced by the chopped current in the second measuring circuit22B2.

Thus, the currents imes1and imes2flowing respectively in the first measuring circuit22B1and in the second measuring circuit22B2are added together, so that the common measuring resistor Rmesis traversed by a current imes, corresponding to the sum of the currents imes1and imes2.

According to the first embodiment, the chopped current measurement is done by measuring the voltage vmesat the terminals of the measuring resistor Rmes. Indeed, this voltage vmesis an image of the chopped current ie, according to formula (1):

vmes=Rmesmi⁢ie(1)
where Rmes=measuring resistance common to the two measuring circuits22B1and22B2,
vmes=voltage measured at the terminals of the measuring resistor Rmes,
mi=transformation ratio of a transformer10B1or10B2.

Thus a direct measurement is obtained at the terminals of the measuring resistor Rmesconnected to the ground.

On the other hand, during the phases of demagnetization of a transformer10B1or10B2, the transistors of the associated measuring circuit22B1or22B2in the blocked state enable the measuring resistor Rmesto be decoupled from the demagnetizing circuit20B1or20B2. Thus the measurement of the voltage Vmesis not affected.

As a variant, according to a second embodiment illustrated inFIG. 3, the two measuring circuits22B1and22B2each comprise a separate measuring resistor Rmes′. The two measuring resistors Rmes′ are substantially equal in value according to the example described.

According to the second embodiment, with regard to the first measuring circuit22B1, the measuring resistor Rmes′ is connected between the two sources of the first transistor Ki1_HS, and of the second transistor Ki1_LS. In addition, the source of the second transistor Ki1_LSis connected to the ground.

With regard to the second measuring circuit22B2, the measuring resistor Rmes2is connected between the two sources of the first transistor Ki2_HS, and of the second transistor Ki2_LS. In addition, the source of the second transistor Ki2_LSis connected to the ground.

Thus, the two measuring circuits22B1;22B2respectively include a measuring resistor Rmes′ connected via a terminal to the ground. The measuring resistor Rmes′ of the first measuring circuit22B1is connected via one of the terminals thereof to the source of the first transistor Ki1_HS, and via the other of the terminals thereof to the source of the second transistor Ki2_LSof the first measuring circuit22B1. The measuring resistor Rmes′ of the second measuring circuit22B2is connected to the source of the first transistor Ki2_HSvia one of the terminals thereof, and via the other of the terminals thereof to the source of the second transistor Ki2_LSof the second measuring circuit22B2.

Whether it is the first embodiment inFIG. 2, or the second embodiment inFIG. 3, the common measuring resistor Rmesor each separate measuring resistor Rmes′ of the two measuring circuits and22B1and22B2is connected to the ground. This arrangement provides better immunity with respect to noise.

According to the second embodiment, the first measuring circuit22B1includes a first output resistor R connected to the source of the first transistor Ki1_HSand to the measuring resistor Rmes′.

Similarly, the second measuring circuit22B2includes a second output resistor R connected to the source of the first transistor Ki2_HSand to the measuring resistor Rmes′. The voltage Vmescan be measured at the common node between the two output resistors R.

In this case, these are the voltages vmes1and vmes2respectively at the terminals of the measuring resistors Rmes′ of the two measuring circuits22B1and22B2which are added together (see formula (2)):

According to this second embodiment, the measurement of the chopped current is done by measuring the voltage vmesat the common node between the two output resistors R. Indeed, this voltage vmesis an image of the chopped current ie, according to formula (3):

vmes=12⁢Rmes′mi⁢ie(3)
where Rmes′=measuring resistance of each measuring circuit22B1and22B2,
vmes=voltage measured at the common node between the two output resistors R,
mi=transformation ratio of a transformer10B1or10B2.

In a similar way to the first embodiment, these measuring resistors Rmes′ are decoupled from the associated demagnetizing circuit20B1or20B2during the demagnetization period of the associated transformer10B1or10B2.

Moreover, if the value of the measuring resistor of each measuring circuit22B1and22B2is substantially equal to the value of the measuring resistor Rmescommon to the two measuring circuits22B1and22B2, a ratio of ½ is found in the transfer function.

In this case, if it is desired to work with the same gain for the two embodiments, the value of the resistor Rmes′ of each circuit22B1and22B2must be chosen so that it is of the order of twice the value of the common measuring resistor Rmesaccording to the first embodiment, (see formula (4)):
Rmes′=2×Rmes(4)

The first embodiment with the measuring resistor Rmescommon to the two measuring circuits22B1and22B2provides measuring accuracy, since there are less resistors.

Furthermore, the diagram inFIG. 4presents details of the measuring circuit22B1or22B2according to the first embodiment illustrated inFIG. 2. Of course, these additions or details also apply to the second embodiment illustrated inFIG. 3.

In the diagram inFIG. 4, it is seen that the first measuring circuit22B1also comprises a first resistor R11and a second resistor R21connected via a terminal common to the gates of the two transistors Ki1_HSand Ki1_LSof the measuring circuit22B1, and secondly to a third switch Ki1. The third switch Ki1of the first measuring circuit22B1is controlled by the control signal K2which also controls the second switch Mos2of the first branch B1.

Similarly, the second measuring circuit22B2also comprises a first resistor R12and a second resistor R22, connected via a common node to the gates of the two transistors Ki2_HSand Ki2_LSof the measuring circuit22B2, and secondly to a third switch Ki2. The third switch Ki2of the second measuring circuit22B2is controlled by the control signal K4which also controls the second switch Mos4of the second branch B2.

The first resistor R11or R12is connected to a potential e.g. of 15 V and the second resistor R21or R22is connected to the ground.

The first and second resistors R11and R21or R12and R22ensure the correct switching of the first transistor Ki1_HSor Ki2_HSto the on state. More precisely, when the third switch Ki1or Ki2is blocked, the voltage VG1, respectively VG2, at the gates of the transistors, is positive, e.g. of the order of 10 V. The value of 10 V enables obtaining the condition according to which the voltage between the source and the gate of a first transistor Ki1_HSor Ki2_HSis greater than the threshold voltage of the transistor.

Otherwise, this voltage dependent on the values of the two resistors R11and R21, respectively R12and R22, is zero.

With reference toFIGS. 5 to 7, an example of control logic is described for the device1for measuring the chopped current according to one or other of the previously described embodiments.

Operation of the Measuring Device

Temporal Evolution of the Chopped Current

FIG. 5represents an example of temporal evolution of the chopped currents iMos1or iMos3flowing in the primary circuits12of the transformers10B1et10B2. The non-restrictive example illustrated inFIG. 5has a high duty cycle.

On the graph inFIG. 5:

a first curve with round dots, represents the temporal evolution of the chopped current iMos1in the primary circuit12of the first transformer10B1connected to the first branch B1of the converter3, and

a second curve with squares, represents the temporal evolution of the chopped current iMos3in the primary circuit12of the second transformer10B2connected to the second branch B2of the converter3.

The chopped current iMos1or iMos3flowing in the primary circuit12of a transformer10B1or10B2is periodic and is capable of taking zero values and non-zero values. When the primary circuit12of a transformer10B1or10B2is open, the chopped current iMos1or iMos3flowing in the primary circuit12of the transformer10B1or10B2is zero, and the corresponding transformer10B1or10B2is demagnetized.

The offset between the chopped current iMos1flowing in the primary circuit12of the first transformer10B1and the chopped current iMos3flowing in the primary circuit12of the second transformer10B2depends on the offset between the branches B1and B2.

Control of the First Measuring Circuit22B1

As mentioned previously, the first switch Mos1of the first branch B1is turned on when the second switch Mos1of the first branch B1is blocked, and conversely, the first switch Mos1is blocked when the second switch Mos1is turned on. In addition, according to the example of control logic illustrated inFIG. 6 or 7, a dead time tmis provided between two switchings.

The first transistor Ki1_HSand the second transistor Ki1_LSof the first measuring circuit22B1are controlled jointly.

The first transistor Ki1_HSand the second transistor Ki1_LSof the first measuring circuit22B1are turned on when the second switch Mos1of the first branch B1is blocked.

In other words, the unit Ki1_HS, Ki1_LSof the first measuring circuit22B1configured for allowing or preventing the flow of a current induced by the chopped current iMos1in the first measuring circuit22B1, is configured for being controlled by the inverse of the control signal, termedK2of the second switch Mos1of the first branch B1. It is therefore the inverse of the control signal of the second switch Mos2, termedK2, which controls the state of the transistors Ki1_HSand Ki1_LSof the first control circuit22B1(seeFIG. 6 or 7).

Thus, when the second switch Mos1of the first branch B1is blocked, the primary circuit12of the first transformer10B1is closed, the chopped current iMos1flowing in the primary circuit12of the first transformer10B1is non-zero and induces a current flowing in the secondary circuit14of the first transformer10B1. Since the two transistors Ki1_HSand Ki1_LSof the first measuring circuit22B1are turned on, a current imes1can freely flow in the measuring circuit22B1associated with the first transformer10B1. On the other hand, no current flows in the demagnetizing circuit20B1because the second Zener diode26is not turned on, given that the voltage between the terminals18and16is variable and is not equal to the Zener voltage thereof.

When the second switch Mos1of the first branch B1is turned on and the first switch Mos1is blocked, the primary circuit12of the first transformer10B1is open, the chopped current iMos1takes a zero value. The two transistors Ki1_HSand Ki1_LSof the first measuring circuit228ichange to the blocked state, no longer allowing the flow of a current in the measuring circuit22B1.

During this period, a demagnetizing current flows in the demagnetizing circuit20B1, the potential difference between the terminals18and16of the secondary circuit14then being imposed by the Zener voltage of the second Zener diode26according to the example inFIGS. 2 and 3. The two transistors Ki1_HSand Ki1_LSof the first measuring circuit22B1in the blocked state, do not allow the flow of the demagnetizing current in the measuring circuit22B1.

As long as the chopped current iMos1is zero, the demagnetizing current decreases flowing in the demagnetizing circuit20B1.

Control of the Second Measuring Circuit22B2

Similarly, the first switch Mos3of the second branch B2is turned on when the second switch Mos4of the second branch B2is blocked, and conversely, the first switch Mos3is blocked when the second switch Mos4is turned on. According to the example of control logic illustrated inFIG. 6 or 7, a dead time tmis also provided between two switchings.

The first transistor Ki2_HSand the second transistor Ki2_LSof the second measuring circuit22B2are controlled jointly.

The first transistor Ki2_HSand the second transistor Ki2_LSof the second measuring circuit22B2are turned on when the second switch Mos4of the second branch B2is blocked.

The unit Ki2_HS, Ki2_LSof the second measuring circuit22B2configured for allowing or preventing the flow of a current induced by the chopped current iMos3in the second measuring circuit22B2is configured for being controlled by the inverse of the control signal, termedK4of the second switch Mos4of the second branch B2.

It is therefore the inverse of the control signal of the second switch Mos4, termedK4, which controls the state of the transistors Ki2_HSand Ki2_LSof the second measuring circuit22B2(seeFIG. 6 or 7).

Thus, when the second switch Mos4of the second branch B2is blocked, the primary circuit12of the second transformer10B2is closed, the chopped current iMos3flowing in the primary circuit12of the second transformer10B2is non-zero and induces a current flowing in the secondary circuit14of the second transformer10B2. Since the two transistors Ki2_HSand Ki2_LSof the second measuring circuit22B2are turned on, a current imes2can freely flow in the measuring circuit22B2associated with the second transformer10B2. On the other hand, no current flows in the demagnetizing circuit20B2because the second Zener diode26is not turned on, given that the voltage between the terminals18and16is variable and is not equal to the Zener voltage thereof.

As soon as the second switch Mos4of the second branch B2is turned on and the first switch Mos3is blocked, the primary circuit12of the second transformer10B2is open, the chopped current iMos3takes a zero value. The two transistors Ki2_HSand Ki2_LSof the second measuring circuit22B2change to the blocked state, no longer allowing the flow of a current in the measuring circuit22B2.

However, during this period, a demagnetizing current flows in the demagnetizing circuit20B2, according to the example illustrated inFIGS. 2 and 3, the potential difference between the terminals18and16of the secondary circuit14then being imposed by the Zener voltage of the second Zener diode26. As long as the chopped current iMos3is zero, the demagnetizing current decreases flowing in the demagnetizing circuit20B2. The two transistors Ki2_HSand Ki2_LSof the second measuring circuit22B2in the blocked state, do not allow the flow of the demagnetizing current in the measuring circuit22B2.

Thus over a period T of operation, there is always a half period when the chopped current is zero, so that the demagnetization time is constant and ensures the demagnetization of the transformers10B1and10B2. Demagnetization is therefore independent of the duty cycle.

Thus, whatever the direction of the demagnetizing current, when the primary circuit12of the transformer10B1or10B2is open, the chopped current iMos1or iMos3takes the value zero, the device1enables the demagnetization of the associated transformer10B1or10B2. In other words, given that the direction of the magnetizing current depends on the average value of the chopped current iMos1or iMos3, whatever the average value of the chopped current iMos1or iMos3, the device1enables the demagnetization of the associated transformer10B1or10B2.

With regard to the measurement of the chopped current, this is accomplished by measuring the voltage vmesat the terminals of the measuring resistor Rmesaccording to the first embodiment illustrated inFIG. 2 or 4, or by measuring the voltage vmesat the common node between the output resistors R of the two measuring circuits22B1and22B2according to the second embodiment illustrated inFIG. 3, the voltage vmesbeing proportional to the chopped current ie, according to formula (1) for the first embodiment or according to formula (3) for the second embodiment.

Referring toFIG. 8, this measurement of the voltage vmesmeasured, for example, at the terminals of the measuring resistor Rmes, provides information on the average value of the input current ieabsorbed by the converter3, e.g. by means of a double RC filter for obtaining the voltage VIEcorresponding to the average value of the voltage Vmes.

In addition, it may be desired to monitor the peak value of the instantaneous current ie. Two comparators may be provided for this purpose. The first comparator being, for example, provided for limiting the current, and the second comparator for fault detection.