Abstract:
A rectifying circuit including: between a first terminal of application of an AC voltage and a first rectified voltage delivery terminal, at least one first diode; and between a second terminal of application of the AC voltage and a second rectified voltage delivery terminal, at least one first anode-gate thyristor, the anode of the first thyristor being connected to the second rectified voltage delivery terminal; and at least one first stage for controlling the first thyristor, including: a first transistor coupling the thyristor gate to a terminal of delivery of a potential which is negative with respect to the potential of the second rectified voltage delivery terminal; and a second transistor connecting a control terminal of the first transistor to a terminal for delivering a potential which is positive with respect to the potential of the second rectified voltage delivery terminal, the anode of the first thyristor being connected to the common potential of voltages defined by said positive and negative potentials.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit of French patent application number 15/62393, filed on Dec. 15, 2015, the content of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law. 
       BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present disclosure generally relates to electronic circuits and, more specifically, to the forming of a rectifying bridge based on diodes and thyristors. 
         [0004]    Description of the Related Art 
         [0005]    Many implementations of controllable rectifying bridges, based on the use of thyristors, are known. 
         [0006]    For example, U.S. Pat. No. 6,493,245 describes a rectifying bridge having two cathode-gate thyristors provided in the upper portion of the bridge, that is, with the cathodes connected to the positive potential of the rectified voltage. 
       BRIEF SUMMARY 
       [0007]    An embodiment overcomes all or part of the disadvantages of usual rectifying bridges with thyristors. 
         [0008]    Another embodiment more specifically provides a controllable rectifying bridge having a simplified control. 
         [0009]    Another embodiment provides a controllable rectifying bridge compatible with applications where the current of the load controlled by the bridge varies by significant proportions. 
         [0010]    Thus, an embodiment provides a rectifying circuit comprising:
       between a first terminal of application of an AC voltage and a first terminal of delivery of a rectified voltage, at least one first diode;   between a second terminal of application of the AC voltage and a second terminal of delivery of the rectified voltage, at least one first anode-gate thyristor, the anode of the first thyristor being connected to the second rectified voltage delivery terminal; and   at least one first stage for controlling the first thyristor, comprising:   a first transistor coupling the gate of the thyristor to a terminal of delivery of a potential negative with respect to the potential of the second terminal of delivery of the rectified voltage; and   a second transistor connecting a control terminal of the first transistor to a terminal of delivery of a potential which positive is with respect to the potential of the second rectified voltage delivery terminal,   the anode of the first thyristor being connected to the common potential of voltages defined by said positive and negative potentials.       
 
         [0017]    According to an embodiment, the circuit further comprises:
       between the second terminal of application of the AC voltage and the first terminal of delivery of the rectified voltage, at least one second diode;   between the first terminal of application of the AC voltage and the second terminal of delivery of the rectified voltage, at least one second anode-gate thyristor, the anode of the second thyristor being connected to the second terminal of delivery of the rectified voltage; and   at least one second stage for controlling the second thyristor, comprising:   a third transistor coupling the gate of the second thyristor to said terminal of delivery of said negative potential; and   a fourth transistor connecting a control terminal of the third transistor to said terminal of delivery of said positive potential.       
 
         [0023]    An embodiment provides a rectifying circuit comprising:
       a first terminal and a second terminal, intended to receive an AC voltage;   a third terminal and a fourth terminal, intended to deliver a rectified voltage;   a rectifying bridge having input terminals respectively connected to the first and second terminals, and having   output terminals respectively connected to the third terminal, and connected by a first anode-gate thyristor to the fourth terminal; and   a stage for controlling the thyristor comprising:   a first transistor coupling the gate of the first thyristor to a terminal of delivery of a potential which is negative with respect to the potential of the second terminal of delivery of the rectified voltage; and   a second transistor connecting a control terminal of the first transistor to a terminal of delivery of a potential which is positive with respect to the potential of the second rectified voltage delivery terminal,   the anode of the first thyristor being connected to the common potential of voltages defined by said positive and negative potentials.       
 
         [0032]    According to an embodiment, the second or the second and fourth transistors are controlled by a digital circuit. 
         [0033]    According to an embodiment, a resistive element is interposed between the gate of the first or of each thyristor and the first transistor or each of the first and third transistors. 
         [0034]    According to an embodiment, a resistive element is interposed between the base of the first or of each of the first and third transistors and the second or each of the second and fourth MOS transistors. 
         [0035]    According to an embodiment, the first or the first and third transistors are bipolar transistors, preferably of NPN type. 
         [0036]    According to an embodiment, the second or the second and fourth transistors are MOS transistors. 
         [0037]    According to an embodiment, the control circuit is powered with a positive voltage delivered by a power supply circuit connected to the first rectified voltage delivery terminal, a capacitor connecting the power supply circuit to the second rectified voltage delivery terminal. 
         [0038]    According to an embodiment, said negative potential is obtained, from the power supply circuit, by a charge pump circuit. 
         [0039]    According to an embodiment, at least one diode series-connected with a resistive element connects the second terminal of delivery of the rectified voltage to one of the terminals of application of the AC voltage. 
         [0040]    The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0041]      FIG. 1  is an electric diagram of an example of a known rectifying bridge with thyristors; 
           [0042]      FIG. 2  is a block diagram of an embodiment of a controllable rectifying circuit with thyristors; 
           [0043]      FIG. 3  is an electric diagram of an embodiment of the circuit of  FIG. 2 ; 
           [0044]      FIG. 4  illustrates an example of a circuit for generating a negative voltage for the rectifying bridge of  FIGS. 2 and 3 ; 
           [0045]      FIG. 5  illustrates a starting circuit for the controllably rectifying circuit shown in  FIGS. 2 and 3 ; 
           [0046]      FIG. 6  is an electric diagram illustrating an alternative embodiment of a starting circuit; and 
           [0047]      FIG. 7  is a block diagram illustrating a controllable rectifying circuit utilizing diodes. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    The same elements have been designated with the same reference numerals in the different drawings. For clarity, only those steps and elements which are useful to the understanding of the described embodiments have been shown and will be detailed. In particular, what use is made of the rectified voltage has not been detailed, the described embodiments being compatible with usual applications of such a rectified voltage. Further, the circuits for generating control signals from a microcontroller have not been detailed either, the described embodiments being here again compatible with usual control signal generation circuits. For simplification, in the following explanations, forward voltage drops will be neglected in the diodes and the thyristors. 
         [0049]      FIG. 1  is an electric diagram of an example of a controllable rectifying bridge with thyristors of the type described in above-mentioned document U.S. Pat. No. 6,493,245. This bridge is a fullwave bridge and comprises two parallel branches between two terminals  11  and  12  of delivery of a rectified voltage Vout. Each branch comprises a thyristor Th 1 , respectively Th 2 , connected to a diode D 1 , respectively D 2 , the diode anodes being on the side of terminal  12  which defines the most negative potential (generally the ground or reference potential) of rectified voltage Vout. The respective junction points of the thyristors and of the diodes define two terminals  13  and  14  of application of an AC voltage Vac to be rectified. A capacitive element C is generally connected between terminals  11  and  12  to smooth the rectified voltage. 
         [0050]    Thyristors Th 1  and Th 2  are cathode-gate thyristors intended to be controlled from a signal CT. 
         [0051]    In such a controllable rectifying bridge, a control voltage directly originating from a microcontroller cannot be applied, neither can, more generally, a voltage directly referenced to reference potential  12 , due to the reference of the cathodes of thyristors Th 1  and Th 2 , which is on the side of the most positive potential (terminal  11 ) of the rectified voltage. This imposes using a conversion element  15  of galvanic isolation transformer or optocoupler type to convert the reference of the control signal. 
         [0052]    Such an embodiment increases the production costs of a controllable rectifying bridge. 
         [0053]      FIG. 2  schematically shows in the form of blocks an embodiment of a controllable rectifying circuit (rectifying bridge with thyristors). This circuit comprises a rectifying bridge having two parallel branches between two terminals  21  and  22  of delivery of a rectified voltage Vout, terminal  22  representing a reference potential, such as ground GND. Each branch comprises a diode D 3 , respectively D 4 , connected to a thyristor TH 3 , respectively TH 4 , between terminals  21  and  22 , the thyristors having anodes connected to terminal  22  and the diode cathodes being connected to terminal  21 . The respective midpoints of the two branches define terminals  23  and  24  of application of an AC voltage Vac to be rectified, terminal  23  being connected to the anode of diode D 3  and to the cathode of thyristor TH 3 , terminal  24  being connected to the anode of diode D 4  and to the cathode of thyristor TH 4 . A filtering capacitive element C is preferably connected between terminals  21  and  22 . 
         [0054]    Thyristors TH 3  and TH 4  are anode-gate thyristors. The respective gates of thyristors TH 3  and TH 4  receive control signals from a control circuit  3  of digital control circuit or microcontroller type (CTRL), via control stages  4  and  5 . Control circuit  3  is for example a microcontroller or an integrated circuit powered from a low positive voltage (for example, having a value in the range from 3.3 volts to 12 volts). Low positive voltage Vdd is provided between a terminal  25  at a positive potential Vdd and terminal  22 . Voltage Vdd is low as compared with voltage Vout (in the range from some ten volts to several hundreds of volts). 
         [0055]    For a current to flow in one of thyristors TH 3  and TH 4 , the anode voltage should be greater than the cathode voltage and it should be activated by the drawing of a current onto its gate. Since the anodes of thyristors TH 3  and TH 4  are connected to terminal  22 , to draw a current onto their respective gates, the latter have to be taken to a negative potential with respect to ground. To be able to directly process (with no optocoupler or the like) the control signals received from control circuit  3 , control stages  4  and  5  are powered from positive potential Vdd (terminal  25 ). However, to be able to take the gates to a negative potential, the reference (low potential) of control stages  4  and  5 , instead of being the ground, is a negative potential −Vdd′ provided on a terminal  26 . The absolute values of potential Vdd and −Vdd′ may be identical or different according to the positive and negative voltages adapted to the application and to the components and circuits used. 
         [0056]      FIG. 3  is an electric diagram of an embodiment of the circuit of  FIG. 2 .  FIG. 3  details, in particular, examples of the forming of control stages  4  and  5  and of generation of positive voltage Vdd. 
         [0057]    Each control stage  4 ,  5  comprises a resistor, respectively R 4 , R 5 , in series with a bipolar transistor T 4 , T 5 , of type NPN, between the gate of thyristor TH 3 , respectively TH 4 , and terminal  26  at potential −Vdd, the emitter terminals of transistors T 4  and T 5  being connected to terminal  26 . The base of transistor T 4 , respectively T 5 , is connected via a MOS transistor M 4 , respectively M 5 , series-connected with a resistor R 4 ′, respectively R 5 ′, to terminal  25  at potential Vdd. Transistor M 4 , respectively M 5 , is on the side of terminal  25 . The gates of transistors M 4  and M 5  are connected to outputs of control circuit  3  providing DC control signals. Control circuit or microcontroller  3  may, on the other hand, receive information from other circuits, not shown. 
         [0058]    The gates of transistors M 4  and M 5  are, in the quiescent state, at potential Vdd. Thus, transistors M 4  and M 5  are off, as well as transistors T 4  and T 5 . Thyristors TH 3  and TH 4  are then off and the rectifying bridge is off. 
         [0059]    To turn on one of thyristors TH 3  or TH 4 , circuit  3  takes its output connected to the gate of the corresponding transistor M 4  or M 5  to ground. Thus, transistor M 4 , respectively M 5 , turns on. A base current is then injected into the base of transistor T 4 , respectively T 5 , which turns it on. A gate current is then drawn onto the gate of the concerned thyristor TH 3  or TH 4  and the corresponding branch of the bridge is thus on. 
         [0060]    In practice, thyristor TH 4  is turned on during positive halfwaves of input voltage Vac and thyristor TH 3  is turned on during negative halfwaves. 
         [0061]    Resistors R 4 ′, R 5 ′, R 4 , and R 5  enable to set the current in the respective bases of transistors T 4  and T 5  and in the respective gates of thyristors TH 3  and TH 4 . 
         [0062]    As a variation, MOS transistors M 4  and M 5  are replaced with bipolar transistors, for example, if control circuit  3  can provide a current control. Similarly, bipolar transistors T 4  and T 5  may be replaced with MOS transistors. 
         [0063]    Positive voltage Vdd may originate from an external power supply source but is, preferably, generated by a power supply circuit  6  (DC/DC) from voltage Vout. A capacitive element Ca is connected between power supply circuit  6  and terminal  22 . Power supply circuit  6  is of voltage regulator type to provide a power supply voltage adapted to control circuit  3 . 
         [0064]    Preferably, negative voltage −Vdd′ is obtained, indirectly from voltage Vout, by a circuit  7  (NS) generating, from voltage Vdd, voltage −Vdd′. 
         [0065]      FIG. 4  shows an example of a circuit  7  for generating a negative voltage −Vdd′. 
         [0066]    In this example, circuit  7  has the shape of a capacitive charge pump and comprises, between terminals  26  and  22 , a first capacitor C 71  and, in parallel, two series-connected diodes D 72  and D 73 , the anode of diode D 72  being coupled to terminal  26 . Junction point  74  of diodes D 72  and D 73  (anode of diode D 73  and cathode of diode D 72 ) is connected, by a second capacitor C 75  in series with a resistor R 76 , to a terminal  77  of application of a train of pulses at potential Vdd. Terminal  77  is for example connected to an output terminal of digital control circuit  3 . The operation of a charge pump circuit such as illustrated in  FIG. 4  is usual per se. 
         [0067]    Other structures of generation of a negative power supply voltage may be provided, for example with a plurality of capacitive stages. 
         [0068]    An advantage of the described embodiments is, as compared with the circuit of  FIG. 1 , that it is no longer necessary to use a conversion element of optocoupler or galvanic insulation transformer type to apply the control signals to the thyristors. This considerably simplifies the forming of a controllable rectifying bridge and decreases the cost thereof. 
         [0069]    In an embodiment where voltages Vdd and −Vdd′ are provided by external circuits, the control signals may be provided by control circuit  3 , even with an initially-discharged capacitor C. 
         [0070]    In the embodiment of  FIG. 3  where voltages Vdd and −Vdd′ are obtained from voltage Vout, a starting aid should be provided. 
         [0071]      FIG. 5  partially illustrates an embodiment of a starting circuit. 
         [0072]    According to this example, an inductive element L is provided between one of terminals  23  and  24  (in  FIG. 5 , terminal  23 ) and the input of the bridge (e.g., the mid-point between diode D 3  and thyristor TH 3  and/or the mid-point between diode D 4  and thyristor TH 4 ) having this terminal connected thereto. The effect of this inductance is to slow down the growth of the current sampled from terminals  23  and  24  when thyristors TH 3  and TH 4  are turned on while capacitor C is not charged or is only very lightly charged. 
         [0073]    Additionally or alternatively, an inductive element (not shown) may be placed at the output, between, for example, terminal  21  and the common point of the two anodes of thyristors TH 3  and TH 4 . This inductive element may be placed upstream or downstream of capacitor C. This type of element may be used, for example, in a switched power supply circuit used to correct the power factor of the current sampled from the network. 
         [0074]      FIG. 6  partially illustrates a variation of a starting circuit. 
         [0075]    According to this example, a diode D 6  connects one of the input terminals (for example, terminal  24 ) to ground  22  via a resistor R 6 . Another diode D 7  may connect the other input terminal (for example,  23 ) to resistor R 6  to start in fullwave mode. The effect of this resistor (which generally has a temperature variation coefficient) is to enable capacitor C to charge on powering-on, while control circuit  3  is not powered yet and thus cannot control thyristors TH 3  and TH 4 , which are thus in the off state (otherwise preventing any charge of C). Such an embodiment enables to power control circuit  3  while avoiding an inductive element at the bridge input. 
         [0076]      FIG. 7  partially illustrates another embodiment where the rectifying bridge is a fullwave bridge only formed of diodes D 1 , D 2 , D 3 , and D 4 . This amounts to replacing thyristors TH 3  and TH 4  with diodes D 1  and D 2 . The bridge is then controlled by a single anode-gate thyristor TH connected between the common anodes of diodes D 1  and D 2  and terminal  22 . Thyristor TH is controlled by a control stage circuit  4 . 
         [0077]    Various embodiments have been described. Various alterations, modifications, and improvements will occur to those skilled in the art. In particular, although the embodiments have been described in relation with an example of a fullwave rectifying bridge, a halfwave bridge may be provided by using a single thyristor. A multiphase network with as many thyristor-diode arms as there are phases (for example, three thyristors and three diodes for a three-phase network) may also be provided. Further, the generation of the control signals capable of controlling the rectifying bridge depends on the application and is within the abilities of those skilled in the art according to this application. Further, the practical implementation of the embodiments which have been described is within the abilities of those skilled in the art based on the functional indications which have been described hereabove. 
         [0078]    The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.