Abstract:
An AC/DC converter includes a first terminal and a second terminal to receive an AC voltage and a third terminal and a fourth terminal to deliver a DC voltage. A rectifying bridge is provided in the converter. A controllable switching or rectifying element has a control terminal configured to receive a control current. A first switch is coupled between a supply voltage and the control terminal to inject the control current. A second switch is coupled between the control terminal and a reference voltage to extract the control current. The first and second switches are selectively actuated by a control circuit.

Description:
PRIORITY CLAIM 
       [0001]    This application claims the priority benefit of French Application for Patent No. 1552983, filed on Apr. 7, 2015, the contents of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law. 
       TECHNICAL FIELD 
       [0002]    The present disclosure generally relates to electronic devices and, more specifically, to alternating current to direct current (AC/DC) converters. The present disclosure generally applies to any system using a rectifying bridge, for example, circuits for controlling electric motors, electric chargers, switched-mode power supplies, etc. 
       BACKGROUND 
       [0003]    Many AC/DC converter architectures based on rectifying elements, which may be controllable (thyristors, for example) or not (diodes, for example), assembled as a rectifying bridge, powered with an AC voltage and delivering a DC voltage, this DC voltage being possibly itself converted back into an AC voltage, are known. 
         [0004]    The power consumption at stand-by, that is, the power consumption while the converter is powered with an AC voltage but no load extracts power from the output, is generally desired to be minimized. 
         [0005]    Further, the inrush current, that is, the current peaks which occur for each halfwave of the AC voltage as long as the voltage across a capacitor at the output of the rectifying bridge has not reached a sufficient level and, this, particularly, in starting phases, is generally desired to be limited. 
         [0006]    U.S. Pat. No. 5,715,154, United States Patent Application Publication No. 2002/0080630, and Japanese Publication No. JPS62135269 describe examples of AC/DC converters (all references incorporated by reference). 
       SUMMARY 
       [0007]    An embodiment overcomes all or part of the disadvantages of usual power converter control circuits. 
         [0008]    An embodiment provides a converter starting circuit solution where stand-by losses are decreased. 
         [0009]    Thus, an embodiment provides an AC/DC converter comprising: a first terminal and a second terminal, intended to receive an AC voltage; a third terminal and a fourth terminal, intended to supply a first DC voltage; a rectifying bridge having input terminals respectively connected to the first and second terminals; and having either: output terminals respectively coupled by a controllable switching element to the third terminal and connected to the fourth terminal, or output terminals respectively connected to the third and fourth terminals, two controllable rectifying elements of the bridge respectively coupling the first and second terminals to the third terminal. 
         [0010]    According to an embodiment, an electrode for controlling the switching element or electrodes for controlling the rectifying elements are coupled, by a first switch, to a terminal for supplying a positive potential and, by a second switch, to the fourth terminal. 
         [0011]    According to an embodiment, the converter further comprises a circuit for supplying said positive potential, coupled by at least one diode to the first terminal. 
         [0012]    According to an embodiment, the converter further comprises a microcontroller for controlling the first and second switches, powered from said positive potential. 
         [0013]    According to an embodiment, the first switch is a PNP-type bipolar transistor or a P-channel MOS transistor, the second switch being an NPN-type bipolar transistor or an N-channel MOS transistor. 
         [0014]    According to an embodiment, the switching element is a triac. 
         [0015]    According to an embodiment, the switching element is a cathode-gate thyristor capable of being controlled by injection of current into the gate and by extraction of current from the gate. 
         [0016]    According to an embodiment, the controllable switching elements are cathode-gate thyristors capable of being controlled by injection of current into the gate and by extraction of current from the gate. 
         [0017]    An embodiment provides a method of controlling a converter, wherein the first switch injects a current into the gate of the switching element or of the rectifying elements in a first phase, after which the second switch extracts a gate current from the switching element or from the rectifying elements in a second phase. 
         [0018]    According to an embodiment, in the second phase, the switching element or the rectifying elements are controlled in phase angle to limit the inrush current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    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, wherein: 
           [0020]      FIG. 1  shows an embodiment of an AC/DC converter; 
           [0021]      FIGS. 2A, 2B, 2C, 2D, and 2E  illustrate, in timing diagrams, the operation of the converter of  FIG. 1 ; 
           [0022]      FIG. 3  shows another embodiment of an AC/DC converter; 
           [0023]      FIG. 4  shows a detail of another embodiment of an AC/DC converter; 
           [0024]      FIG. 5  is a simplified cross-section view of an embodiment of a cathode-gate thyristor having a positive gate current; and 
           [0025]      FIG. 6  is a simplified cross-section view of an embodiment of a cathode-gate thyristor having a negative gate current. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    The same elements have been designated with the same reference numerals in the different drawings. In particular, the structural and/or functional elements common to the different embodiments may be designated with the same reference numerals and may have identical structural, dimensional, and material properties. 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, the circuits powered by the power converter have not been detailed, the described embodiments being compatible with usual applications. In the disclosure, term “connected” designates a direct connection between two elements, while terms “coupled” and “linked” designate a connection between two elements which may be direct or via one or a plurality of other elements. When reference is made to terms “about”, “approximately”, or “in the order of”, this means to within 10%, preferably to within 5%. 
         [0027]      FIG. 1  schematically shows an embodiment of an AC/DC converter. 
         [0028]    Two input terminals  12  and  14  are intended to receive an AC voltage Vac, for example, the voltage of the electric distribution network (for example, 230 or 120 volts, 50 or 60 Hz). Terminal  12  is connected to a first rectifying input terminal  32  of a rectifying bridge  3  (for example, fullwave) having its second rectifying input terminal  34  connected to terminal  14 . A first rectified output terminal  36  of bridge  3  is coupled, via a switch, in this example, a triac T, to a first output terminal  16  supplying the high potential of a DC voltage Vdc. A second rectified output terminal  38  of bridge  3  is connected to a second output terminal  18  supplying the low potential of DC voltage Vdc. In the example of  FIG. 1 , terminals  38  and  18  define a reference potential (the ground) of the assembly, output voltage Vdc then being positive. A storage and smoothing capacitor C 0  couples terminals  16  and  18 . 
         [0029]    Rectifying bridge  3  is, in this example, formed of four diodes D 31 , D 33 , D 35 , and D 37 . Diodes D 31  and D 33  respectively couple terminals  32  and  34  to terminal  36  (cathodes of diodes D 31  and D 33  on the side of terminal  36 ) and diodes D 35  and D 37  respectively couple terminals  32  and  34  to terminal  38  (anodes of diodes D 35  and D 37  on the side of terminal  38 ). Voltage Vr between terminals  36  and  38  corresponds to rectified and non-filtered voltage Vac. 
         [0030]    Triac T has the function of controlling the output power supply. It is controlled in pulse mode, that is, a control circuit  2  applies a pulse on its gate for each halfwave of AC voltage Vac. Triac T then remains conductive until the current that it conducts disappears. 
         [0031]    Control circuit  2  comprises a digital circuit  22 , for example, a microcontroller (μC), in charge of generating control pulses of triac T. Microcontroller  22  receives different reference values CT or measurements to generate the pulses at the right times according, among others, to the needs of the load powered by the converter. Microcontroller  22  is powered by bridge  3 , that is, it is not necessary to provide an auxiliary circuit sampling the supply power directly from voltage Vac. In the shown example, a power supply circuit  24  (PW) is series-connected with a capacitive element C 1 , between terminals  36  and  38 . Two terminals  222  and  224  for powering microcontroller  22  are connected across capacitor C 1  delivering its power supply voltage Vdd. Circuit  24  has the function of regulating voltage Vdd so that it remains compatible with the power supply needs of the microcontroller. In practice, voltage Vdd is a low voltage as compared with voltages Vac, Vr, and Vdc. Typically, voltage Vdd is lower than 10 volts. 
         [0032]    As an example, circuit  24  may be a switched-mode power supply. It is then formed of a MOS transistor controlled by an integrated circuit regulating voltage Vdd. Such a MOS transistor generally controls an inductance or a primary of a magnetic transformer. 
         [0033]    Microcontroller  22  controls a first transistor T 1  coupling terminal  222  (at potential Vdd) to the gate of triac T. In the example of  FIG. 1 , transistor T 1  is a PNP-type bipolar transistor having its emitter connected to terminal  222  and having its collector coupled, via a diode D 1  in series with an optional resistor R 1 , to the gate of triac T. The base of transistor T 1  is coupled, optionally via a resistor R 2 , to a first output of microcontroller  22 . 
         [0034]    Microcontroller  22  also controls a second transistor T 2  for controlling triac T. In the example of  FIG. 1 , transistor T 2  is an NPN-type bipolar transistor having its emitter connected to ground  38  and having its collector connected, via a resistor R 3 , to the gate of triac T. The base of transistor T 2  is coupled, optionally via a resistor R 4 , to a second output of microcontroller  22 . 
         [0035]      FIGS. 2A, 2B, 2C, 2D, and 2E  are timing diagrams illustrating the operation of the converter of  FIG. 1  at the start-up.  FIG. 2A  shows an example of the shape of voltage Vac.  FIG. 2B  shows the corresponding shape of voltage Vdd.  FIG. 2C  shows the shape of gate current Ig of triac T.  FIG. 2D  shows the shape of current Iac sampled from the AC power supply.  FIG. 2E  shows the corresponding shape of voltage Vdc. 
         [0036]    Initially, capacitor C 0  is discharged, as well as capacitor C 1 . Microcontroller  22  is thus not powered and triac T is off. 
         [0037]    When AC power supply Vac is applied between terminals  12  and  14  (for example, via a power-on switch, not shown), capacitor C 1  is charged by power supply block  24  until it reaches voltage Vdd required for the operation of microcontroller  22 . 
         [0038]    However, since capacitor C 0  is discharged, no current can be drawn in the branch of transistor T 2  to start triac T. A positive gate current should thus be applied to the triac to make it conductive and start charging capacitor C 0 . This is the function of transistor T 1 . At the end of a first halfwave of voltage Vac (or more generally at the end of a halfwave where the microcontroller is powered but where capacitor C 0  is discharged), the microcontroller controls the turning-on of transistor T 1  by drawing a base current onto it for a short time period (pulse for example lasting from 1 μs to approximately 1 ms). This causes the injection of a positive current Ig into the gate of triac T and the turning-on thereof until the end of the halfwave. Capacitor C 0  is then charged during this halfwave end. To limit the inrush current, the turning-on of transistor T 1 , and thus of triac T, is caused in the vicinity of the end of the halfwave. 
         [0039]    As soon as voltage Vdc across capacitor C 0  is sufficient, microcontroller  22  controls, for each halfwave and in pulse mode, transistor T 2  to draw current into the triac gate (negative gate current Ig) and cause the progressive charge of capacitor C 0  (voltage Vdc progressively increasing from one halfwave to the next one). 
         [0040]    To respect a soft start and limit current inrushes, microcontroller  22  controls transistor T 2  in phase angle, that is, it starts turning on the triac in the decreasing portion of the halfwave and progressively sooner and sooner according to the charge level of capacitor C 0 . As soon as capacitor C 0  is sufficiently charged, the triac can be controlled by a DC or pulse signal. In the case of a pulse control, the control is synchronized as well as possible with the time when the capacitor is to be recharged for each halfwave (that is, when voltage Vdc becomes lower than voltage Vac). 
         [0041]    The number of cycles required to start the charge of capacitor C 0  (number of conduction periods of transistor T 1 ), and thus to wake up the system, as well as the number of cycles required for the starting (until capacitor C 0  is charged) depends on the application and on the possible downstream power consumption at the start. 
         [0042]    In practice, a single period is most often sufficient to sufficiently charge capacitor C 0  to have a voltage sufficient to supply the gate current required to turn on the triac by controlling transistor T 2 . Transistor T 1  is thus in this case only used once per converter start. 
         [0043]    An advantage is that all the references of the power supplies and of the control signals are common (the ground). Elements of optocoupler, transformer, or the like types are thus avoided, conversely, for example, to the solution of document JP 62135269. 
         [0044]    Another advantage is that it is no longer necessary to use a resistive element to limit the inrush current at the starting of the converter, since triac T can be used in phase control from as soon as the first halfwave. 
         [0045]      FIG. 3  shows another embodiment where triac T is replaced with two cathode-gate thyristors Th 1  and Th 2 . Actually, this amounts to replacing diodes D 31  and D 33  of bridge  3  with thyristors Th 1  and Th 2  to integrate the control in the bridge. To allow the power supply of circuit  24 , at least one diode D 2  coupling terminal  12  to circuit  24  is then provided. In the example of  FIG. 3 , the power supply rectification of microcontroller  22  is halfwave, which is generally sufficient due to the low required power. As a variation, another diode (D 3  in dotted lines in  FIG. 3 ) coupling terminal  14  to circuit  24  is provided to perform a fullwave rectification. 
         [0046]    The operation of the circuit of  FIG. 3  can be deduced from the operation discussed in relation with  FIG. 1 . Thyristors Th 1  and Th 2  are however formed to be controlled both by a negative gate current and by a positive gate current. This amounts, in a way, to using a half-triac to keep the rectifying character of the thyristor. 
         [0047]      FIG. 4  partially shows an embodiment of a converter. 
         [0048]    As compared with the assembly of  FIG. 1 , triac T is replaced with a thyristor Th. Indeed, the bidirectional character of the conduction of the triac is not used herein. What matters is to be able to control the switch placed between terminals  12  and  16  with a positive or negative gate current. As for the embodiment of  FIG. 3 , the cathode-gate thyristor should be able to be controlled by drawing a current onto its gate. 
         [0049]      FIGS. 5 and 6  are simplified cross-section views of embodiments of cathode-gate thyristors respectively with a positive gate current or a current injection (most current case) and with a negative gate current or a current extraction. 
         [0050]    According to these examples, the thyristor is formed in an N-type substrate  51 . At the rear surface, a P-type layer  52  defines an anode region, anode electrode A being obtained by a contacting metallization  53  of region  52 . A P-type well  54  is formed at the front surface. An N-type cathode region  55  (N 1 ) is formed in well  54  and a contacting metallization  56  of this region  55  defines cathode electrode K. 
         [0051]    In the case of  FIG. 5 , a gate contact  57  is formed at the level of P-type well  54 . Thus, the injection of a gate current starts the thyristor if it is properly biased (positive anode-cathode voltage). 
         [0052]    In the case of  FIG. 6 , an N-type region  58  (N 2 ) is added under gate contact  57 . Region  58  allows a turning-on by a negative gate current (that is, flowing from the gate to the cathode) by allowing an electron injection into N-type substrate  51 , which corresponds to the base of the NPN-type bipolar transistor formed by regions  52 - 51 - 54 . 
         [0053]    Region N 2  is divided into at least two regions  58  and  58 ′ to allow a direct contact of region  54  on the gate. This embodiment, called “short-circuit hole”, enables to improve the immunity to transient disturbances of the thyristor and the control by a positive gate current (that is, flowing from gate G to cathode K 1 ). This embodiment thus enables the thyristor to be used to form thyristors Th 1  and Th 2  in the circuit of  FIG. 3 , or thyristor Th in  FIG. 4 . 
         [0054]    Various embodiments have been described. Various alterations, modifications, and improvements will occur to those skilled in the art. For example, a current source may be used instead of resistor R 3  to be sure of drawing a gate current from components T, Th 1 , Th 2 , and Th which remains approximately constant whatever the voltage across capacitor C. Further, the practical implementation of the described embodiments is within the abilities of those skilled in the art based on the functional indications given hereabove. In particular, the programming of the microcontroller depends on the application and the described embodiments are compatible with usual applications using a microcontroller or the like to control a converter. Further, the forming of a component acting as a normally-on switching element (triac) or rectifying element (thyristor), controllable to be turned on by a positive or negative pulse applied on a control electrode, is within the abilities of those skilled in the art based on the indications given hereabove. 
         [0055]    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.