Abstract:
A rectifying circuit includes a first diode coupled between a first terminal configured to receive application of an A.C. voltage and a first terminal configured to deliver a rectified voltage; and an anode-gate thyristor coupled between a second terminal configured to receive application of the A.C. voltage and a second terminal configured to deliver the rectified voltage, wherein an anode of the anode-gate thyristor is connected to the second terminal configured to deliver the rectified voltage.

Description:
PRIORITY CLAIM 
     This application claims the priority benefit of French Patent application number 1459993, filed on Oct. 17, 2014, the contents of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law. 
     TECHNICAL FIELD 
     The present disclosure generally relates to electronic circuits and, more specifically, to the implementation of a rectifying bridge based on diodes and on thyristors. 
     BACKGROUND 
     Many solutions of controllable rectifying bridges, based on the use of thyristors, are known. 
     For example, U.S. Pat. No. 6,493,245 (incorporated by reference) 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. 
     SUMMARY 
     An embodiment overcomes all or part of the disadvantages of usual rectifying bridges with thyristors. 
     Another embodiment provides a controllable rectifying bridge, which can be controlled in simplified fashion. 
     Another embodiment provides a rectifying bridge directly controllable by a microcontroller. 
     Thus, an embodiment provides a rectifying circuit comprising: between a first terminal of application of an A.C. voltage and a first terminal of delivery rectified voltage, a first diode; and between a second terminal of application of the A.C. voltage and a second terminal of delivery of the rectified voltage, a first anode-gate thyristor, the anode of the first thyristor being connected to the second rectified voltage delivery terminal. 
     According to an embodiment, the circuit further comprises, between the second terminal of application of the A.C. voltage and the first terminal of delivery of the rectified voltage, a second diode. 
     According to an embodiment, the circuit further comprises, between the first terminal of application of the A.C. voltage and the second terminal of delivery of the rectified voltage, a second anode-gate thyristor, the anode of the second thyristor being connected to the second rectified voltage delivery terminal. 
     According to an embodiment, the circuit further comprises, between the cathode of the first thyristor and each terminal of application of the A.C. voltage, a diode. 
     According to an embodiment, the circuit further comprises at least one stage for controlling the thyristor or one of the thyristors, comprising: a diode connecting the thyristor gate to the second terminal of delivery of the rectified voltage; and a capacitive element in series with a resistive element connecting the thyristor gate to a control pulse generation circuit. 
     According to an embodiment, each thyristor is associated with a control stage. 
     According to an embodiment, the control circuit generates pulse trains at a frequency in the order of from 10 to 100 times greater than the frequency of the A.C. voltage. 
     According to an embodiment, the control circuit is powered with a 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. 
     According to an embodiment, a switch controlled by the control circuit is interposed between the second rectified voltage delivery terminal and a node of interconnection of the anode of the thyristor or of the anodes of the thyristors, of the cathode of the diode of the control stage or of the cathodes of the diodes of the control stages, of a reference terminal of the control circuit, and of the capacitor. 
     According to an embodiment, the circuit further comprises a capacitive element between the two terminals of delivery of the rectified voltage. 
     According to an embodiment, a switch controlled by the control circuit is interposed between the second rectified voltage delivery terminal and a node of interconnection of two capacitors forming said capacitive element, a diode connecting said node to a terminal for supplying the control circuit. 
     According to an embodiment, at least one diode in series with a resistive element connects the second rectified voltage delivery terminal to one of the terminals of application of the A.C. voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is an electric diagram of an example of a usual rectifying bridge with thyristors; 
         FIG. 2  is an electric diagram of an embodiment of a rectifying bridge with thyristors; 
         FIG. 3  is an electric diagram of an alternative embodiment of a controllable rectifying bridge; and 
         FIG. 4  is an electric diagram of another embodiment of a rectifying bridge with thyristors. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
       FIG. 1  is an electric diagram of an example of a controllable rectifying bridge with thyristors of the type described in above-mentioned 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 the diodes define two terminals  13  and  14  of application of an A.C. voltage Vac to be rectified. A capacitive element C is generally connected between terminals  11  and  12  to smooth the rectified voltage. Possibly, an inductive element (not shown) may be interposed at the bridge input (for example, between terminal  13  and the junction point of thyristor Th 1  and diode D 1 ). Such an element is particularly used to filter the current drawn from the bridge input. An inductive element may also be placed at the output, between, for example, terminal  11  and the common point of the two anodes of thyristors Th 1  and Th 2 . This inductive element may be placed upstream or downstream of capacitor C. This type of element may be used, for example, in a switched-mode power supply circuit used to correct the power factor of the current drawn from the network. 
     Thyristors Th 1  and Th 2  are cathode-gate thyristors intended to be controlled from a signal CT. 
     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. 
     Such an embodiment increases the production costs of a controllable rectifying bridge. 
       FIG. 2  is an electric diagram of an embodiment of a controllable rectifying circuit. This circuit comprises a rectifying bridge having two parallel branches between two terminals  21  and  22  of delivery of a rectified voltage Vout. Each branch comprises a diode D 3 , respectively D 4 , connected to a thyristor T 1 , respectively T 2 , between terminals  21  and  22 , the thyristor anodes being 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 A.C. voltage Vac to be rectified, terminal  23  being connected to the anode of diode D 3  and to the cathode of thyristor T 1 , terminal  24  being connected to the anode of diode D 4  and to the cathode of thyristor T 2 . A filtering capacitive element C preferably connects terminals  21  and  22 . 
     Thyristors T 1  and T 2  are anode-gate thyristors. The respective gates of thyristors T 1  and T 2  receive control signals from a circuit  27  of digital control circuit or microcontroller (CTRL) type, via stages  25  and  26 . Each stage is formed of a diode D 25 , respectively D 26 , connecting the gate of thyristor T 1 , respectively T 2 , to terminal  22 , the anode of diode D 25  or D 26  being on the gate side of thyristor T 1  or T 2 , and of a series association of a capacitive element C 25 , respectively C 26 , and of a resistive element R 25 , respectively R 26 , connecting the respective gates of thyristors T 1  and T 2  to circuit  27 . 
     Control circuit  27  is for example a microcontroller or an integrated circuit powered from a low voltage (for example, of a value in the range from 3.3 volts to 12 volts) generated by a power supply circuit  28  (DC/DC) from voltage Vout. A capacitive element Ca is connected between circuit  28  and terminal  22 . Such a circuit, of voltage regulator type, delivers a power supply voltage adapted to circuit  27 . The microcontroller may on the other hand receive data from other circuits, not shown. 
     A difference with respect to the circuit of  FIG. 1  is 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. 
     The bridge operates as follows. Thyristor T 2  is turned on during positive halfwaves of the input voltage and thyristor Ti is turned on during negative halfwaves. 
     For current to flow through one of thyristors T 1  and T 2 , the anode potential thereof should be greater than its cathode potential and be activated by drawing a current on its gate. For simplification, in the following explanations, forward voltage drops will be neglected in the diodes and the thyristors. 
     According to an embodiment, to turn on one of the thyristors, circuit  27  generates a pulse train at a frequency greater than the frequency of voltage Vac (for example, approximately from 10 to 100 times greater). 
     During a positive halfwave, for each (positive) pulse generated by circuit  27 , a current flows through resistor R 26 , through capacitance C 26 , and through diode D 26 , which causes the charge of capacitance C 26 . When the output signal of circuit  27  is lowered to a low level (generally, the level of reference terminal  22 ), an inverse current flows by the discharge of capacitance C 26  through resistor R 26 , circuit  27  (in practice, the low transistor of its output stage, not shown), and the gate of thyristor T 2 . As soon as the cathode potential of thyristor T 2  becomes lower than its anode potential, that is, the rectified amplitude of voltage Vac becomes greater than the voltage across capacitance C, thyristor T 2  turns on at the falling edge of the next control pulse generated by circuit  27 . This amounts to drawing a current into this gate and turns on transistor T 2 , which remains on until its current becomes zero. 
     It should be noted that the higher the frequency of the pulses generated by circuit  27 , the shorter the delay between the time when the anode-cathode voltage of thyristor T 2  becomes positive and the turning-on of thyristor T 2 . 
     A similar operation takes place during negative halfwaves with thyristor T 1  and stage  25 . 
     According to an alternative embodiment which requires for circuit  27  to monitor respective voltage levels Vac and Vout, a single control pulse is generated per halfwave of voltage Vac when the other conduction conditions are complied with. 
     At the circuit starting, that is, when capacitor C is initially discharged, circuit  27  is not powered if it is not connected to another power source. 
     To allow the starting, an inductive element may then be provided between one of terminals  23  and  24  and the input of the bridge having this terminal connected thereto. The effect of this inductance is to slow down the growth of the current drawn from terminals  23  and  24  when thyristors T 1  and T 2  are turned on while capacitor C is not or is only very lightly charged. 
     According to a variation which will be discussed hereafter in relation with  FIG. 3 , an initial charge (at the starting) of capacitor  27  is ensured by one or a plurality of additional diodes as well as a resistive element, between one of terminals  23  and  24  and terminal  22  of the bridge. 
       FIG. 3  shows the electric diagram of an alternative embodiment. 
     As compared with the embodiment of  FIG. 2 , a single anode-gate thyristor T is used. The cathode of this thyristor T is connected to respective anodes of diodes D 5  and D 6 , respectively connected in the same bridge arms as diodes D 3  and D 4 , the junction points of diodes D 3  and D 5 , respectively D 4  and D 6 , being connected to terminals  23  and  24 . Such an embodiment adds a voltage drop in the rectifying bridge but enables to use a single anode-gate thyristor to control the two halfwaves. Control stage  29  of thyristor T is formed of a diode D 29 , of a capacitor C 29 , and of a resistor R 29  in the same way as stages  25  and  26  of  FIG. 2 . 
       FIG. 3  illustrates another variation aiming at enabling to initially charge capacitor C. To achieve this, a diode D 7  connects one of the input terminals (for example, terminal  24 ) to ground  22  via a resistor R. Another diode D 8  may connect the other input terminal (for example,  23 ) to resistor R to start in fullwave mode. The effect of this resistance (which generally has a temperature variation coefficient) is to enable capacitor C to charge on powering-on, while circuit  27  is not powered yet and thus cannot control thyristors T 1  and T 2 , which are thus in the off state (otherwise preventing any charge of C). Such a variation enables to power circuit  27  while avoiding an inductive element at the bridge input. 
     This variation enabling to initially charge capacitor C may be combined with the embodiment of  FIG. 2 . 
     According to another variation shown in  FIG. 3 , a switch T 3  (for example, a MOS transistor) is interposed between terminal  22  and a node, noted  22   a , representing the common connection of the anode of thyristor T, of the cathode of diode D 29 , of the reference terminal of circuit  27 , and of capacitor Ca. Switch T 3  is controlled by circuit  27  and is off at the starting. It enables for the charge current, powering circuit  28  through resistor R, not to charge capacitor C, but only capacitor Ca, when the controlled rectifying bridge (formed of elements D 3 , D 4 , D 5 , D 6 , and T, or of elements D 3 , D 4 , T 1 , and T 2 ) is deactivated. This embodiment enables to decrease losses consumed in standby mode by the complete circuit and the circuits connected between terminals  21  and  22 . In this embodiment, an inductive element may be useful to progressively charge capacitor C at the starting when switch T 3  is turned on, by turning on thyristors T 1  and T 2  at the end of a halfwave of the mains voltage (voltage Vac) and by progressively increasing the conduction time of thyristors T 1  and T 2  until capacitor C is fully charged to a value close to the peak value of the A.C. voltage. This variation may here again be combined with the embodiment of  FIG. 2 . 
       FIG. 4  shows still another embodiment according to which, as compared with the embodiment of  FIG. 2 , capacitive element C is formed of two capacitors C 1  and C 2  having their junction point connected, by a diode D (anode of the diode connected to the junction point of capacitors C 1  and C 2 ), to the power supply terminal of circuit  27 , that is, to the positive electrode of capacitor Ca. A switch T 3 ′ connects the anode of diode D to terminal  22 . The embodiment of  FIG. 4  also illustrates the presence of diodes D 7  and D 8  and of resistor R, as well as of an inductance L between terminal  23  and the anode of diode D 3  (cathode of thyristor T 1 ). At the starting, switch T 3 ′ is off and capacitors C 1 , C 2 , and Ca are charged through resistor R and diodes D 7  and D 8 . The values of capacitors C 2  and Ca are lower than the value of capacitor C 1 . Accordingly, the voltage thereacross increases more rapidly than the voltage across capacitor C 1 . As soon as the voltage across capacitor Ca is sufficient, control circuit  27  starts operating and turns on switch T 3 ′. Thus, in steady state, the charge current of capacitor C 1  is deviated from capacitor C 2  which is not sized to withstand strong currents. This variation also applies to the case of  FIG. 3  with a single thyristor T. 
     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 one of diodes D 3  and D 4  and a single one of thyristors T 1  and T 2  (diode D 3  and thyristor T 2  or diode D 4  and thyristor T 1 ). 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. 
     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.