# Patent

## Title
Device for measuring a chopped current

## Abstract

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.

## Background
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 and
        two 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, and
            preventing 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, and
        the 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 and
        the 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, and
        the 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, and
        a 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, and
            at 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, and
            the 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, and
        two 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, and
            prevent 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.



Other features and advantages of the invention will appear more clearly on reading the following description, given as an illustrative and non-restrictive example, and the accompanying drawings in which:
FIG. 1 represents a DC-DC converter circuit through which a chopped current flows including two transformers of a device for measuring the chopped current,
FIG. 2 schematically represents two demagnetizing circuits and two measuring circuits of the device for measuring the chopped current according to a first embodiment,
FIG. 3 schematically represents two demagnetizing circuits and two measuring circuits of the device for measuring the chopped current according to a second embodiment,
FIG. 4 is a more detailed representation of the demagnetizing circuits and measuring circuits of the device for measuring the chopped current in FIG. 2 according to the first embodiment,
FIG. 5 is a graph representing the temporal evolution of chopped currents in the primary circuits of two transformers respectively connected to a branch of the H-bridge structured converter,
FIG. 6 is a first example of a timing diagram representing the temporal evolution of the chopped currents in FIG. 5, and the pulse signals of the H-bridge branch switches,
FIG. 7 is a second example of a timing diagram representing the temporal evolution of chopped currents in the primary circuits of two transformers respectively connected to a branch of the H-bridge structured converter, and the pulse signals of the H-bridge branch switches, and
FIG. 8 schematically represents an example of comparators used after measuring an output voltage proportional to the input chopped current.



In these figures, identical elements bear the same references.
The invention relates to a device 1 for measuring a chopped current, in particular flowing inside a DC-DC converter 3.
Converter
Referring to FIG. 1, the converter 3 represented has an H-bridge structure having a first branch B1 and a second branch B2.
The first branch B1 comprises a first switch Mos1 and a second switch Mos2.
The second branch B2 comprises a first switch Mos3 and a second switch Mos4.
The switches Mos1 to Mos4 comprise, by way of a non-restrictive example, an N-type, field effect transistor known under the acronym MOSFET.
When the first branch B1 is controlled, the first switch Mos1 is turned on when the second switch Mos1 is blocked, and conversely the second switch Mos1 is turned on when the first switch Mos1 is blocked.
The same applies to controlling the second branch B2, the first switch Mos3 is turned on when the second switch Mos4 is blocked, and conversely the second switch Mos4 is turned on when the first switch Mos3 is blocked.
The offset between the two branches B1 and B2 depends on the H-bridge control logic.
Device for Measuring the Chopped Current
Referring again to FIG. 1, the device 1 for measuring the chopped current comprises two transformers 10B1 and 10B2 with a transformation ratio of mi. The two transformers 10B1 and 10B2 are arranged respectively on a branch B1 or B2 of the converter 3.
One transformer 10B1 or 10B2 includes a primary circuit 12 and a secondary circuit 14.
The primary circuit 12 of a first transformer 10B1 is connected to the first switch Mos1 of the first branch B1 of the converter 3. The primary circuit 12 of the second transformer 10B2 is connected to the first switch Mos3 of the second branch B2 of the converter 3.
The secondary circuit 14 of a transformer 10B1 or 10B2 comprises two output terminals 16 and 18.
When a chopped current ic flows in the converter 3, it is split in the two branches B1 and B2, so that a first chopped current iMos1 flows in the primary circuit 12 of the first transformer 10B1, and a second chopped current iMos3 flows in the primary circuit 12 of the second transformer 10B2.
When the primary circuit 12 of the first transformer 10B1 or of the second transformer 10B2 is closed, the chopped current iMos1 or iMos3 flowing in the primary circuit 12 of the first transformer 10B1 or of the second transformer 10B2 is non-zero, and the associated transformer 10B1 or 10B2 is magnetized.
A demagnetization of a transformer 10B1 or 10B2 takes place when the primary circuit 12 of the first transformer 10B1 or of the second transformer 10B2 is open, the chopped current iMos1 or iMos3 being zero, i.e. when there is no current to be measured.
And in addition, the device 1 can be used to measure the chopped current when the primary circuit 12 of the first transformer 10B1 or of the second transformer 10B2 is closed, the chopped current iMos1 or iMos3 flowing in the primary circuit 12 of the first transformer 10B1 or of the second transformer 10B2 being non-zero.
For this purpose, with reference to FIG. 2, the measuring device 1 further includes:
two demagnetizing circuits 20B1, 20B2 respectively associated with a transformer 10B1 or 10B2, and
two chopped current measuring circuits 22B1 and 22B2 respectively connected to the output terminals 16, 18 of the associated transformer 10B1 or 10B2.
According to the described embodiment, the demagnetizing circuits 20B1, 20B2 are separate from the measuring circuits 22B1 and 22B2.
Each demagnetizing circuit 20B1 and 20B2 is connected between the two output terminals 16 and 18 of the associated transformer 10B1 or 10B2.
Each demagnetizing circuit 20B1, 20B2 enables the demagnetization of the associated transformer 10B1 or 10B2 through a flow of a current in the demagnetizing circuit 20B1 or 20B2.
According to the embodiment illustrated in FIG. 2, a demagnetizing circuit 20B1 or 20B2 includes a first Zener diode 24 connected in series with a second Zener diode 26 between the output terminals 16 and 18. The Zener voltage is by way of an illustrative example of the order of 10 V.
The first Zener diode 24 and the second Zener diode 26 are mounted in opposite directions. As an example, the first Zener diode 24 may be connected via its cathode to the output terminal 16 and the second Zener diode 26 may be connected via its cathode to the other output terminal 18. The two Zener diodes 24 and 26 are then connected with one another via the anodes thereof.
Thus, the demagnetizing circuits 20B1, 20B2 are 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 circuit 22B1 is connected to the output terminals 16, 18 of the secondary circuit 14 of the first transformer 10B1 connected to the first branch B1 of the converter 3. The first measuring circuit 22B1 is connected in parallel with the first demagnetizing circuit 20B1.
A second measuring circuit 22B2 is connected to the output terminals 16, 18 of the secondary circuit 14 of the second transformer 10B2 connected to the second branch B2 of the converter 3. The second measuring circuit 22B2 is connected in parallel with the second demagnetizing circuit 20B2. The second measuring circuit 22B2 is further connected to the first measuring circuit 22B1.
The measuring circuits 22B1 and 22B2 respectively include at least one unit configured for:

    
    
        allowing the flow of a current imes1; imes2 induced by the chopped current, in the measuring circuit 22B1 or 22B2, when the primary circuit 12 of a transformer 10B1; 10B2 is closed; in this case the chopped current flowing in the primary circuit 12 is non-zero, either strictly positive or strictly negative, and
        preventing the flow of the demagnetizing current in the measuring circuit 22B1 or 22B2 when the primary circuit 12 of a transformer 10B1; 10B2 is open; in this case the chopped current flowing in the primary circuit 12 is zero.
    
    


According to the embodiment described, the two measuring circuits 22B1 and 22B2 respectively include a unit configured for allowing or preventing the flow of a current induced by the chopped current in the associated measuring circuit 22B1 or 22B2, and comprising a first switch and a second switch. The unit of the first measuring circuit 22B1 includes a first switch Ki1_HS and a second switch Ki1—LS. The unit of the second measuring circuit 22B2 includes a first switch Ki2_HS and a second switch Ki2_LS.
The first switches Ki1_HS and Ki2_HS are also called High Side switches.
The second switches Ki1_LS and Ki2_LS are also called Low Side switches.
The first and second switches Ki1_HS and Ki1_LS of the first measuring circuit 22B1 and the first and second switches Ki2_HS and Ki2_LS of the second measuring circuit 22B2 are formed, according to the example described, of MOSFET field effect transistors.
The first and second switches Ki1_HS and Ki1_LS of the first measuring circuit 22B1 in this example are connected in reverse. Similarly, the first and second switches Ki2_HS and Ki2_LS of the second measuring circuit 22B2 are connected in reverse.
Furthermore, with reference to FIGS. 3 and 4, the measuring circuits 22B1; 22B2 include at least one measuring resistor Rmes or Rmes′ connected via a first terminal to the ground.
The first switch Ki1_HS; Ki2_HS of a measuring circuit 22B1; 22B2 comprises a terminal connected to a second terminal of the measuring resistor Rmes or Rmes′, the first terminal of the measuring resistor Rmes or Rmes′ being connected to the ground. The second Ki1—LS switch; Ki2_LS of a measuring circuit 22B1; 22B2 in turn comprises a terminal connected to the ground.
More specifically, with regard to the first measuring circuit 22B1:
the drain of the first transistor Ki1_HS is connected to the first output terminal 16 of the first transformer 10B1 connected to the first branch B1 of the converter 3.
the source of the first transistor Ki1_HS is 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_HS is connected to the gate of the second transistor Ki1_LS of the first measuring circuit 22B1,
the drain of the second transistor Ki1_LS is connected to the second output terminal 18 of the first transformer 10B1, and
the source of the second transistor Ki1_LS is connected to the ground.
With regard to the second measuring circuit 22B2:
the drain of the first transistor Ki2_HS is connected to the first output terminal 16 of the second transformer 10B2 connected to the second branch B2 of the converter 3.
the source of the first transistor Ki2_HS is 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_HS is connected to the gate of the second transistor Ki2_LS of the second measuring circuit 22B2,
the drain of the second transistor Ki2_LS of the second measuring circuit 22B2 is connected to the second output terminal 18 of the second transformer 10B2,
the source of the second transistor Ki2_LS is connected to the ground.
In addition, the first transistors Ki1_HS and Ki2_HS must 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_HS and Ki1_LS of the first measuring circuit 22B1 and the transistors Ki2_HS and Ki2_LS of the second measuring circuit 22B2 are capable of being controlled according to the H-bridge control logic. Thus, when the primary circuit 12 of a transformer 10B1 or 10B2 is closed, the chopped current in the primary circuit 12 of the transformer 10B1 or 10B2 is non-zero, and the two transistors Ki1_HS and Ki1_LS or Ki2_HS and Ki2_LS of the associated measuring circuit 22B1 or 22B2 are in the on state. When the primary circuit 12 of the first transformer 10B1 or of the second transformer 10B2 is open, the chopped current is zero, and the two transistors Ki1_HS and Ki1_LS or Ki2_HS and Ki2_LS of the associated measuring circuit 22B1 or 22B2 are in the blocked state.
Thus, when the primary circuit 12 of a transformer 10B1 or 10B2 is closed, the chopped current iMos1 iMos3 in the primary circuit 12 of a transformer 10B1 or 10B2 being non-zero, and there is therefore a current to be measured, the two transistors Ki1_HS and Ki1_LS or Ki2_HS and Ki2_LS of the associated measuring circuit 22B1 or 22B2 must be controlled in the on state.
And, the demagnetization of a transformer 10B1 or 10B2 may be performed when the primary circuit 12 of the transformer 10B1 or 10B2 is open, the chopped current iMos1 or iMos3 being zero and there is no current to be measured, by blocking the two transistors Ki1_HS and Ki1_LS or Ki2_HS and Ki2_LS of the associated measuring circuit 22B1 or 22B2, so as to disconnect the demagnetizing circuit 20B1 or 20B2 from the measuring resistor Rmes or Rmes′ during the demagnetization of the corresponding transformer 10B1 or 10B2.
When the primary circuit 12 of the first transformer 10B1 or of the second transformer 10B2 is closed, a chopped current iMos1 or iMos3 flows in the primary circuit 12 of the associated transformer 10B1 or 10B2, and a current is induced in the secondary circuit 14 of the associated transformer 10B1 or 10B2. If the transistors Ki1_HS and Ki1_LS of the first measuring circuit 22B1, respectively if the transistors Ki2_HS and Ki2_LS, of the second measuring circuit 22B2, are turned on, a current imes1, respectively imes2, flows in the associated first or second measuring circuit 22B1 or 22B2.
According to a first embodiment illustrated in FIG. 2, the two measuring circuits 22B1 and 22B2 further comprise a common measuring resistor Rmes connected firstly via a first terminal to the ground and via a second terminal to the source of the first two transistors Ki1_HS and Ki2_HS. The source of the first transistor Ki2_HS of the unit capable of allowing or preventing the flow of a current induced by the chopped current in the first measuring circuit 22B1, is therefore connected to the source of the first transistor Ki2_HS of the unit capable of allowing or preventing the flow of a current induced by the chopped current in the second measuring circuit 22B2.
Thus, the currents imes1 and imes2 flowing respectively in the first measuring circuit 22B1 and in the second measuring circuit 22B2 are added together, so that the common measuring resistor Rmes is traversed by a current imes, corresponding to the sum of the currents imes1 and imes2.
According to the first embodiment, the chopped current measurement is done by measuring the voltage vmes at the terminals of the measuring resistor Rmes. Indeed, this voltage vmes is an image of the chopped current ie, according to formula (1):




  
    
      
        
          v
          mes
        
        =
        
          
            
              R
              mes
            
            
              m
              i
            
          
          ⁢
          
            i
            e
          
        
      
    
    
      
        (
        1
        )
      
    
  




where Rmes=measuring resistance common to the two measuring circuits 22B1 and 22B2,

vmes=voltage measured at the terminals of the measuring resistor Rmes,

mi=transformation ratio of a transformer 10B1 or 10B2.

Thus a direct measurement is obtained at the terminals of the measuring resistor Rmes connected to the ground.
On the other hand, during the phases of demagnetization of a transformer 10B1 or 10B2, the transistors of the associated measuring circuit 22B1 or 22B2 in the blocked state enable the measuring resistor Rmes to be decoupled from the demagnetizing circuit 20B1 or 20B2. Thus the measurement of the voltage Vmes is not affected.
As a variant, according to a second embodiment illustrated in FIG. 3, the two measuring circuits 22B1 and 22B2 each 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 circuit 22B1, 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_LS is connected to the ground.
With regard to the second measuring circuit 22B2, the measuring resistor Rmes2 is 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_LS is connected to the ground.
Thus, the two measuring circuits 22B1; 22B2 respectively include a measuring resistor Rmes′ connected via a terminal to the ground. The measuring resistor Rmes′ of the first measuring circuit 22B1 is 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_LS of the first measuring circuit 22B1. The measuring resistor Rmes′ of the second measuring circuit 22B2 is connected to the source of the first transistor Ki2_HS via one of the terminals thereof, and via the other of the terminals thereof to the source of the second transistor Ki2_LS of the second measuring circuit 22B2.
Whether it is the first embodiment in FIG. 2, or the second embodiment in FIG. 3, the common measuring resistor Rmes or each separate measuring resistor Rmes′ of the two measuring circuits and 22B1 and 22B2 is connected to the ground. This arrangement provides better immunity with respect to noise.
According to the second embodiment, the first measuring circuit 22B1 includes a first output resistor R connected to the source of the first transistor Ki1_HS and to the measuring resistor Rmes′.
Similarly, the second measuring circuit 22B2 includes a second output resistor R connected to the source of the first transistor Ki2_HS and to the measuring resistor Rmes′. The voltage Vmes can be measured at the common node between the two output resistors R.
In this case, these are the voltages vmes1 and vmes2 respectively at the terminals of the measuring resistors Rmes′ of the two measuring circuits 22B1 and 22B2 which are added together (see formula (2)):




  
    
      
        
          v
          mes
        
        =
        
          
            
              v
              
                mes
                ⁢
                
                  
                
                ⁢
                1
              
            
            +
            
              v
              
                mes
                ⁢
                
                  
                
                ⁢
                2
              
            
          
          2
        
      
    
    
      
        (
        2
        )
      
    
  




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




  
    
      
        
          v
          mes
        
        =
        
          
            1
            2
          
          ⁢
          
            
              R
              mes
              ′
            
            
              m
              i
            
          
          ⁢
          
            i
            e
          
        
      
    
    
      
        (
        3
        )
      
    
  




where Rmes′=measuring resistance of each measuring circuit 22B1 and 22B2,

vmes=voltage measured at the common node between the two output resistors R,

mi=transformation ratio of a transformer 10B1 or 10B2.

In a similar way to the first embodiment, these measuring resistors Rmes′ are decoupled from the associated demagnetizing circuit 20B1 or 20B2 during the demagnetization period of the associated transformer 10B1 or 10B2.
Moreover, if the value of the measuring resistor of each measuring circuit 22B1 and 22B2 is substantially equal to the value of the measuring resistor Rmes common to the two measuring circuits 22B1 and 22B2, a ratio of 1⁄2 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 circuit 22B1 and 22B2 must be chosen so that it is of the order of twice the value of the common measuring resistor Rmes according to the first embodiment, (see formula (4)):

Rmes′=2×Rmes  (4)

The first embodiment with the measuring resistor Rmes common to the two measuring circuits 22B1 and 22B2 provides measuring accuracy, since there are less resistors.
Furthermore, the diagram in FIG. 4 presents details of the measuring circuit 22B1 or 22B2 according to the first embodiment illustrated in FIG. 2. Of course, these additions or details also apply to the second embodiment illustrated in FIG. 3.
In the diagram in FIG. 4, it is seen that the first measuring circuit 22B1 also comprises a first resistor R11 and a second resistor R21 connected via a terminal common to the gates of the two transistors Ki1_HS and Ki1_LS of the measuring circuit 22B1, and secondly to a third switch Ki1. The third switch Ki1 of the first measuring circuit 22B1 is controlled by the control signal K2 which also controls the second switch Mos2 of the first branch B1.
Similarly, the second measuring circuit 22B2 also comprises a first resistor R12 and a second resistor R22, connected via a common node to the gates of the two transistors Ki2_HS and Ki2_LS of the measuring circuit 22B2, and secondly to a third switch Ki2. The third switch Ki2 of the second measuring circuit 22B2 is controlled by the control signal K4 which also controls the second switch Mos4 of the second branch B2.
The first resistor R11 or R12 is connected to a potential e.g. of 15 V and the second resistor R21 or R22 is connected to the ground.
The first and second resistors R11 and R21 or R12 and R22 ensure the correct switching of the first transistor Ki1_HS or Ki2_HS to the on state. More precisely, when the third switch Ki1 or Ki2 is 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_HS or Ki2_HS is greater than the threshold voltage of the transistor.
Otherwise, this voltage dependent on the values of the two resistors R11 and R21, respectively R12 and R22, is zero.
With reference to FIGS. 5 to 7, an example of control logic is described for the device 1 for 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. 5 represents an example of temporal evolution of the chopped currents iMos1 or iMos3 flowing in the primary circuits 12 of the transformers 10B1 et 10B2. The non-restrictive example illustrated in FIG. 5 has a high duty cycle.
On the graph in FIG. 5:
a first curve with round dots, represents the temporal evolution of the chopped current iMos1 in the primary circuit 12 of the first transformer 10B1 connected to the first branch B1 of the converter 3, and
a second curve with squares, represents the temporal evolution of the chopped current iMos3 in the primary circuit 12 of the second transformer 10B2 connected to the second branch B2 of the converter 3.
The chopped current iMos1 or iMos3 flowing in the primary circuit 12 of a transformer 10B1 or 10B2 is periodic and is capable of taking zero values and non-zero values. When the primary circuit 12 of a transformer 10B1 or 10B2 is open, the chopped current iMos1 or iMos3 flowing in the primary circuit 12 of the transformer 10B1 or 10B2 is zero, and the corresponding transformer 10B1 or 10B2 is demagnetized.
The offset between the chopped current iMos1 flowing in the primary circuit 12 of the first transformer 10B1 and the chopped current iMos3 flowing in the primary circuit 12 of the second transformer 10B2 depends on the offset between the branches B1 and B2.
Control of the First Measuring Circuit 22B1 
As mentioned previously, the first switch Mos1 of the first branch B1 is turned on when the second switch Mos1 of the first branch B1 is blocked, and conversely, the first switch Mos1 is blocked when the second switch Mos1 is turned on. In addition, according to the example of control logic illustrated in FIG. 6 or 7, a dead time tm is provided between two switchings.
The first transistor Ki1_HS and the second transistor Ki1_LS of the first measuring circuit 22B1 are controlled jointly.
The first transistor Ki1_HS and the second transistor Ki1_LS of the first measuring circuit 22B1 are turned on when the second switch Mos1 of the first branch B1 is blocked.
In other words, the unit Ki1_HS, Ki1_LS of the first measuring circuit 22B1 configured for allowing or preventing the flow of a current induced by the chopped current iMos1 in the first measuring circuit 22B1, is configured for being controlled by the inverse of the control signal, termed K2 of the second switch Mos1 of the first branch B1. It is therefore the inverse of the control signal of the second switch Mos2, termed K2, which controls the state of the transistors Ki1_HS and Ki1_LS of the first control circuit 22B1 (see FIG. 6 or 7).
Thus, when the second switch Mos1 of the first branch B1 is blocked, the primary circuit 12 of the first transformer 10B1 is closed, the chopped current iMos1 flowing in the primary circuit 12 of the first transformer 10B1 is non-zero and induces a current flowing in the secondary circuit 14 of the first transformer 10B1. Since the two transistors Ki1_HS and Ki1_LS of the first measuring circuit 22B1 are turned on, a current imes1 can freely flow in the measuring circuit 22B1 associated with the first transformer 10B1. On the other hand, no current flows in the demagnetizing circuit 20B1 because the second Zener diode 26 is not turned on, given that the voltage between the terminals 18 and 16 is variable and is not equal to the Zener voltage thereof.
When the second switch Mos1 of the first branch B1 is turned on and the first switch Mos1 is blocked, the primary circuit 12 of the first transformer 10B1 is open, the chopped current iMos1 takes a zero value. The two transistors Ki1_HS and Ki1_LS of the first measuring circuit 228i change to the blocked state, no longer allowing the flow of a current in the measuring circuit 22B1.
During this period, a demagnetizing current flows in the demagnetizing circuit 20B1, the potential difference between the terminals 18 and 16 of the secondary circuit 14 then being imposed by the Zener voltage of the second Zener diode 26 according to the example in FIGS. 2 and 3. The two transistors Ki1_HS and Ki1_LS of the first measuring circuit 22B1 in the blocked state, do not allow the flow of the demagnetizing current in the measuring circuit 22B1.
As long as the chopped current iMos1 is zero, the demagnetizing current decreases flowing in the demagnetizing circuit 20B1.
Control of the Second Measuring Circuit 22B2 
Similarly, the first switch Mos3 of the second branch B2 is turned on when the second switch Mos4 of the second branch B2 is blocked, and conversely, the first switch Mos3 is blocked when the second switch Mos4 is turned on. According to the example of control logic illustrated in FIG. 6 or 7, a dead time tm is also provided between two switchings.
The first transistor Ki2_HS and the second transistor Ki2_LS of the second measuring circuit 22B2 are controlled jointly.
The first transistor Ki2_HS and the second transistor Ki2_LS of the second measuring circuit 22B2 are turned on when the second switch Mos4 of the second branch B2 is blocked.
The unit Ki2_HS, Ki2_LS of the second measuring circuit 22B2 configured for allowing or preventing the flow of a current induced by the chopped current iMos3 in the second measuring circuit 22B2 is configured for being controlled by the inverse of the control signal, termed K4 of the second switch Mos4 of the second branch B2.
It is therefore the inverse of the control signal of the second switch Mos4, termed K4, which controls the state of the transistors Ki2_HS and Ki2_LS of the second measuring circuit 22B2 (see FIG. 6 or 7).
Thus, when the second switch Mos4 of the second branch B2 is blocked, the primary circuit 12 of the second transformer 10B2 is closed, the chopped current iMos3 flowing in the primary circuit 12 of the second transformer 10B2 is non-zero and induces a current flowing in the secondary circuit 14 of the second transformer 10B2. Since the two transistors Ki2_HS and Ki2_LS of the second measuring circuit 22B2 are turned on, a current imes2 can freely flow in the measuring circuit 22B2 associated with the second transformer 10B2. On the other hand, no current flows in the demagnetizing circuit 20B2 because the second Zener diode 26 is not turned on, given that the voltage between the terminals 18 and 16 is variable and is not equal to the Zener voltage thereof.
As soon as the second switch Mos4 of the second branch B2 is turned on and the first switch Mos3 is blocked, the primary circuit 12 of the second transformer 10B2 is open, the chopped current iMos3 takes a zero value. The two transistors Ki2_HS and Ki2_LS of the second measuring circuit 22B2 change to the blocked state, no longer allowing the flow of a current in the measuring circuit 22B2.
However, during this period, a demagnetizing current flows in the demagnetizing circuit 20B2, according to the example illustrated in FIGS. 2 and 3, the potential difference between the terminals 18 and 16 of the secondary circuit 14 then being imposed by the Zener voltage of the second Zener diode 26. As long as the chopped current iMos3 is zero, the demagnetizing current decreases flowing in the demagnetizing circuit 20B2. The two transistors Ki2_HS and Ki2_LS of the second measuring circuit 22B2 in the blocked state, do not allow the flow of the demagnetizing current in the measuring circuit 22B2.
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 transformers 10B1 and 10B2. Demagnetization is therefore independent of the duty cycle.
Thus, whatever the direction of the demagnetizing current, when the primary circuit 12 of the transformer 10B1 or 10B2 is open, the chopped current iMos1 or iMos3 takes the value zero, the device 1 enables the demagnetization of the associated transformer 10B1 or 10B2. In other words, given that the direction of the magnetizing current depends on the average value of the chopped current iMos1 or iMos3, whatever the average value of the chopped current iMos1 or iMos3, the device 1 enables the demagnetization of the associated transformer 10B1 or 10B2.
With regard to the measurement of the chopped current, this is accomplished by measuring the voltage vmes at the terminals of the measuring resistor Rmes according to the first embodiment illustrated in FIG. 2 or 4, or by measuring the voltage vmes at the common node between the output resistors R of the two measuring circuits 22B1 and 22B2 according to the second embodiment illustrated in FIG. 3, the voltage vmes being proportional to the chopped current ie, according to formula (1) for the first embodiment or according to formula (3) for the second embodiment.
Referring to FIG. 8, this measurement of the voltage vmes measured, for example, at the terminals of the measuring resistor Rmes, provides information on the average value of the input current ie absorbed by the converter 3, e.g. by means of a double RC filter for obtaining the voltage VIE corresponding 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.

## Claims

1. 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, the device comprising:
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; and
two 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, and
prevent 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.

2. The device according to claim 1, in which the first switch and the second switch are respectively implemented by a field effect transistor.

3. The device according to claim 1, wherein:
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.

4. The device according to claim 1, wherein:
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, and
the 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 and
the 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.

5. The device according to claim 1, wherein:
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, and
the 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.

6. The device according to claim 1, wherein a demagnetizing circuit is connected between the two output terminals of the secondary circuit of the associated transformer.

7. The device according to claim 6, in which a demagnetizing circuit comprises two Zener diodes mounted in series and in opposite directions.