Thyristor control

Abstract

Embodiments of the present disclosure relate to thyristor control. A rectifier bridge has a thyristor coupled in series with a rectifying element between a first rectified output terminal of the rectifier bridge circuit and a second rectified output terminal of the rectifier bridge circuit. A diode is coupled in series with a DC voltage source between the gate of the thyristor and the second rectified output terminal.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the priority of French Patent Application No. 1906487, filed on June 17, 2019, the content of which is incorporated herein by reference in its entirety to the maximum extent permitted by law. Technical Field

[0003] The present disclosure generally relates to electronic circuits, and more particularly to circuits configured to be coupled to an AC voltage source, such as a power distribution system. The present disclosure is more particularly applied to the control of thyristors in the rectifier bridge of a power converter. Background Art

[0004] Many applications use power converters, for example, to convert the energy sampled from a power distribution system into a voltage that can be used by an electrical or electronic circuit. Such converters most often perform the rectification of the AC voltage of the mains, which can be associated with the correction of the power factor before supplying a DC voltage to a load. The load itself is often a DC / DC or DC / AC conversion circuit of the switched-mode power supply type.

[0005] Controlled bridges or hybrid bridges are increasingly often used, which enable bypassing the inrush current limiting resistor for starting once the converter is in a steady state.

[0006] The presence of switches (usually thyristors) in the rectifier bridge conventionally requires an auxiliary power supply to control the thyristors for the upper half bridge. Due to different reference voltages, this also requires generating an auxiliary power supply voltage in addition to the voltage already required by the power factor correction circuit. This increases the volume and cost of the converter.

[0007] There is a need to overcome all or part of the disadvantages of conventional hybrid bridges or controlled bridges. Summary of the Invention

[0008] An embodiment provides a circuit including: a rectifier bridge having at least one first thyristor in series between a first terminal of the bridge and a second rectified output terminal with a first rectifying element; and at least one diode in series between the gate of the thyristor and the second terminal with a DC voltage source.

[0009] According to one embodiment, the circuit further includes a switch coupled between the output terminals.

[0010] An embodiment provides a method of controlling a circuit as described above, the method including the step of turning on the switch at the rate of a half-wave of the AC voltage.

[0011] According to one embodiment, the switch is turned on near the zero crossing of the AC voltage applied to the input of the rectifier bridge.

[0012] According to one embodiment, conduction of the switch is triggered when the AC voltage drops below a value greater than the DC voltage delivered by the source.

[0013] According to one embodiment, conduction of the switch is triggered with a delay relative to the time when the AC voltage drops below a value greater than the DC voltage delivered by the source.

[0014] According to one embodiment, a first resistor couples the cathode of the diode to the gate of the first thyristor.

[0015] According to one embodiment, a second thyristor of a rectifier bridge in series with a second rectifying element between the output terminals has its gate coupled to the diode via a second resistor.

[0016] According to one embodiment, a power factor correction circuit is coupled to the output terminals.

[0017] According to one embodiment, a capacitor couples the output terminals of the bridge.

[0018] According to one embodiment, a surge current limiting resistor can be bypassed by the thyristor(s).

[0019] According to one embodiment, an AC capacitor couples the two input terminals of the rectifier bridge.

[0020] According to one embodiment, when a disconnection of the AC voltage is detected, a discharge circuit capable of discharging the AC capacitor via at least a switch is turned on.

[0021] An embodiment provides a power converter including a circuit such as described.

[0022] According to one embodiment, the converter further includes a power factor correction circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In the following description of specific embodiments given by way of illustration and not limitation, the foregoing and other features and advantages will be described in detail with reference to the accompanying drawings, in which:

[0024] Figure 1 A power converter is shown;

[0025] Figure 2 An embodiment of a power converter is shown;

[0026] Figure 3 Another embodiment of a power converter is shown;

[0027] Figure 4 Is shown in detail Figure 3Power factor correction circuit of the converter;

[0028] Figures 5A - 5B Illustrates the operation of the converter under power supply and charging conditions Figure 3 of the converter;

[0029] Figures 6A - 6B Illustrates the operation of the converter under another power supply and charging conditions Figure 3 of the converter;

[0030] Figures 7A - 7B Illustrates the operation of the converter under another power supply and charging conditions Figure 3 of the converter;

[0031] Figure 8 Illustrates the operation of the converter under another power supply and charging conditions Figure 3 of the converter; and

[0032] Figure 9 Shows Figure 3 a variant of the power converter. Detailed Description

[0033] In the various figures, similar features have been denoted by similar reference numerals. In particular, structural and / or functional features common among the various embodiments may have the same reference numerals and may be arranged with the same structural, dimensional, and material characteristics.

[0034] For clarity, only the operations and elements useful for understanding the embodiments described herein have been illustrated and described in detail. In particular, the generation of the signals for controlling the power factor correction circuit has not been described in detail, and the described embodiments are compatible with conventional circuits and the conventional control of such circuits.

[0035] Unless otherwise indicated, when referring to two elements connected together, this represents a direct connection without any intermediate element other than a conductor; and when referring to two elements coupled together, this represents connecting or coupling the two elements via one or more other elements.

[0036] In the following disclosure, unless otherwise indicated, when referring to absolute position modifiers such as the terms "front", "rear", "top", "bottom", "left", "right", etc., or relative position modifiers such as the terms "above", "below", "higher than", "lower than", etc., or orientation modifiers such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figures.

[0037] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "on the order of" mean within 10%, preferably within 5%.

[0038] Figure 1 An example of a conventional power converter 1 is shown.

[0039] Such a converter 1 is based on half - wave or full - wave rectification of the AC supply voltage Vac, followed by power factor correction (PFC), to supply a load (Q) that may have DC / DC or DC / AC conversion.

[0040] Schematically, the AC voltage Vac is applied between two input terminals 11 (L) and 13 (N), which are typically coupled via an AC filter 2 (ACF) or an EMI filter to the AC input terminals 21 and 23 of a rectifier bridge 3. The voltage Vac is, for example, a 230V AC voltage or mains voltage at 50Hz or 60Hz, or a 110V AC voltage or mains voltage of a power distribution system at 50Hz or 60Hz. Typically, the terminals 11 and 13 are formed by the pins of a connection plug that connects the converter 1 to an electrical outlet.

[0041] The rectified output terminals 25 and 27 of the rectifier bridge are coupled to the input terminals 51 and 53 of a power factor correction circuit 5 (PFC). The output terminals 55 and 57 deliver the supply voltage to the load 7 (Q). A capacitor C1 is coupled (preferably, connected) between the terminals 25 and 27.

[0042] In the target application of the present disclosure, the converter 1 includes at least one controllable half - bridge 4 in addition to the rectifier bridge 3.

[0043] The rectifier bridge 3, which is, for example, a full - wave rectifier circuit, is formed by four branches that couple each of the two - by - two input terminals to each output terminal, and there is a rectifying element (usually a diode) in each branch.

[0044] The controllable half - bridge 4 is a rectifying half - bridge in which two branches couple the two input terminals 21 to 23 to the terminal 51, and there is a switch, usually a thyristor or SCR, in each branch.

[0045] Such a half - bridge 4 typically equips the power conversion system as a supplement to an uncontrollable bridge to bypass a surge current limiting resistor Ricl once the system has been started.

[0046] According to the described embodiment, the rectifier bridge 3 is a full - wave bridge associated with the controllable half - bridge 4, or a hybrid bridge associated with the same diode half - bridge.

[0047] In Figure 1In the example of, the bridge 3 includes: two diodes D1 and D2 that couple (preferably, connect) the terminals 21 and 23 to the first terminal of the resistor Ricl respectively, and the other terminal of the resistor Ricl is coupled (preferably, connected) to the terminal 25, and the anodes of the diodes D1 and D2 are on one side of the terminals 21 and 23; and two diodes D3 and D4 that couple (preferably, connect) the terminals 21 and 23 to the terminal 27 respectively, and the anodes of the diodes D3 and D4 are on one side of the terminal 27. The bridge 4 includes: two thyristors T1 and T2, where the thyristors T1 and T2 have cathode gates, and the two thyristors T1 and T2 couple (preferably, connect) the terminals 21 and 23 to the terminal 25 respectively, and the anodes of the thyristors are on one side of the terminals 21 and 23.

[0048] At circuit startup, i.e., when it is powered up with the voltage Vac, the thyristors T1 and T2 are not controlled, and the rectification of the voltage Vac is performed by the bridge 3 and the resistor Ricl. Once the circuit has started up and is in a steady state, the thyristors T1 and T2 are alternately controlled according to the half-waves of the voltage Vac and perform the function of the upper rectifying bridge. At each half-wave, a single one of the two thyristors (the forward-biased thyristor) conducts. The thyristors are pulse-controlled, that is, their gates receive current pulses at each half-wave of the voltage Vac. The term pulse means a signal with a duration much shorter than the duration of the half-wave of the voltage Vac, preferably with a ratio of at least 10. The use of thyristors enables bypassing the resistor Ricl and performing phase-angle control when the system is in a steady state.

[0049] The power factor correction circuit 5 generally includes at least one inductive winding ( Figure 1 not shown in), which is switched at a frequency much higher than the frequency of the voltage Vac (the ratio is in the range of 1,000 to 10,000). As a variant, the circuit 5 is a switched-mode power supply circuit.

[0050] The presence of the thyristors T1 and T2 in the upper part of the bridge requires the ability to generate gate current, and the voltage reference of the gate current is much higher than the reference potential of the converter (i.e., the potential of the terminal 27 (ground)). In particular, injecting current into the cathode gates of the thyristors T1 and T2 requires the potential of the thyristor cathode to be less than the potential of its gates G1 and G2. The thyristors are controlled, for example, by the circuit 6 (CTRL) to generate gate current according to the half-waves of the AC voltage Vac. Then, it is necessary to generate the positive low voltage VDD1 of the circuit 6 referenced to the terminal 25 to power the circuit 6. Usually, the circuit 6 receives the information ZV of the zero-crossing point of the input voltage of the bridge to generate the gate control signal.

[0051] The generation of voltage VDD1 typically requires an inductive transformer (not shown) that has a primary winding downstream of terminal 25 and a secondary winding that generates voltage VDD1 referenced to the potential of terminal 25. The need for such a transformer adversely affects the volume, cost, and simplicity of the converter.

[0052] Figure 2 An embodiment of a power converter is shown.

[0053] One can find: input terminals 11 and 13 to which an AC power supply voltage Vac is applied; a rectifier bridge 3, e.g., a full-wave rectifier bridge, whose AC input voltages 21 and 23 are coupled to terminals 11 and 13 respectively. A power factor correction circuit 5 (PFC) or a DC / DC or DC / AC converter, whose input terminals 51 and 53 are coupled (preferably, connected) to the output terminals 25 and 27 of the bridge 3, and whose output terminals 55 and 57 supply power to a load 7 (Q); a controllable upper half-bridge 4, coupled between terminals 21 and 23 and the positive rectified output terminal 25 of the half-bridge 4, for short-circuiting the diode half-bridge D1, D2 of the bridge 3 and associated with a surge current limiting resistor Ricl; optionally, an AC filter 2 between terminals 11 and 13 and terminals 21 and 23; and optionally, a capacitor C1 coupled (preferably, connected) to terminals 25 and 27.

[0054] In Figure 2 the example, the figure takes the form of a hybrid bridge that has a lower half-bridge formed by diodes D3 and D4 and an upper half-bridge formed by thyristors T1 and T2 and an upper half-bridge of diodes D1 and D2 associated with the resistor Ricl.

[0055] According to this embodiment, the gates of thyristors T1 and T2 are coupled via respective resistors R1 and R2 to the cathode of a diode D5, whose anode is coupled (preferably, connected) to a low DC voltage VCC (source 8) referenced to a ground 27 (GND). The low voltage means a voltage less than 30 volts, e.g., on the order of 20 volts or lower.

[0056] The function of this circuit component is that for each half-wave of voltage Vac, when the output voltage VDC of the bridge becomes less than voltage VCC (within the voltage drops of diode D5 and resistors R1 and R2 in the conducting state), current flows from voltage source 8 through diode D5, resistors R1 and R2, the gates of thyristors T1 and T2, and capacitor C1. Thus, capacitor C1 is used at the end of each half-wave and at the start of the next half-wave to allow the circulation of gate current. The value of voltage VCC regulates the voltage threshold around the zero-crossing of the voltage between terminals 51 and 53 during the period when current flows.

[0057] Therefore, it is no longer necessary to generate the voltage of the reference terminal 25 to control the thyristors T1 and T2. The voltage VCC can also be easily generated based on the voltage VDC. In fact, the absence of this voltage when starting the system is not disturbing because once the system is in a stable state, it is not necessary to control the thyristors T1 and T2 to bypass the resistor Ricl.

[0058] In this simplified embodiment, control is not required and the thyristors conduct automatically. However, the discharge of the capacitor C1 must be sufficient and / or the load must consume power sufficiently downstream as the voltage (voltage Vac) between terminals 11 and 13 approaches zero for the system to operate. For a stable consuming load, it is only necessary to size the resistors R1 and R2 and the diode D5 in a suitable manner to deliver the gate current necessary to trigger the thyristors T1 and T2. However, this embodiment is not most suitable for very low variable loads, for which, if the capacitor C1 is present in the circuit, the capacitor C1 will not discharge sufficiently. If there is no capacitor C1, then in this case, the equivalent impedance of the circuit 5 seen between terminals 51 and 53 is very high.

[0059] Figure 3 Another embodiment of the power converter is shown.

[0060] According to this embodiment, Figure 2 the circuit is completed by circuit components that force the capacitor C1 to discharge at the end of each half-wave to ease the flow of the gate current. For a circuit that does not include the capacitor C1, in the case where the impedance of the components downstream of terminals 51 and 53 is too high to generate the conduction of the thyristor T1 or T2 at the beginning of the half-wave, then the circuit can force the conduction of the diode D5 to allow the gate current to flow through the thyristors T1 and T2.

[0061] Therefore, a transistor Q1 (e.g., a bipolar transistor) is provided in series with a resistor R3 between terminals 25 and 27. For example, the emitter of the NPN bipolar transistor Q1 is coupled (preferably, connected) to ground 27. The collector of the transistor Q1 is coupled to terminal 25 through the resistor R3. The base or control terminal of the transistor Q1 receives a control signal from the circuit 9 via a resistor R4, for example.

[0062] The circuit 9 is preferably powered by a voltage VCC (between the terminals VCC and GND) and generates rectangular pulses for controlling the transistor Q1 near each zero crossing of the rectified voltage VDC (i.e., around it). For example, the input IN of the circuit 9 is coupled (preferably, connected) to the junction of two resistors R5 and R6, and the resistors R5 and R6 are coupled (preferably, connected) between the terminals 25 and 27. This series association forms a voltage divider bridge that enables triggering the switching of its output OUT between a high level and a low level at the level of the circuit 9. When the output OUT is at the high level, the transistor Q1 conducts, which forces the capacitor C1 (if present) to discharge through dissipation in the resistor R3 and forces current conduction in one of the diodes D5, the resistors R1 and R2, and one of the thyristors T1 and T2, depending on the presence of the capacitor C1.

[0063] The operation of the circuit components depends on the power consumption of the load connected downstream of the converter. In fact, if the load has a low power consumption, the current in the bridge and thus the current at the thyristor anode will become zero before the gate current for turning on the thyristor is sufficient. In this case, the resistor Ricl is not bypassed and dissipates energy at each half-wave. Therefore, the described solution is particularly advantageous when the load connected downstream of the circuit 5 consumes sufficient current such that the current in the thyristors T1 and T2 reaches its cut-off threshold at the beginning of each half-wave. The concept of sufficient current depends on the application but is, for example, at least 10% of the nominal power of the application.

[0064] Figure 4 is shown in detail Figure 3 an example of a power factor correction circuit of a

[0065] Figure 4 is a local representation. In particular, the rectifier bridge 3 is not shown, and only one branch (thyristor T1 or T2) of the half-bridge 4 is shown, associated with its gate resistor R1 or R2.

[0066] The power factor correction circuit 5 includes, for example: an inductor L in series with a diode D between the terminals 51 and 55; a switch M1, such as a MOS transistor, that couples (preferably, connects) the terminal 53 to the junction of the inductor L and the diode D; an output capacitor C that couples (preferably, connects) the terminals 55 and 57; and a circuit 9', such as a microcontroller (μC) for controlling the switch M1. The microcontroller 9' is powered, for example, by the voltage VCC or a voltage extracted from the voltage VCC.

[0067] The switch M1 is controlled at a high frequency (e.g., at a frequency of several hundred kHz) with a ratio of at least 1,000 with respect to the frequency of the voltage Vac. The operation of the power factor correction circuit 5 itself is conventional.

[0068] Figures 5A - 5B , Figures 5A - 6B , Figures 7A - 7B and Figure 8 The timing diagram illustrates the operation of the converter for multiple power supply voltages Vac and multiple power consumption levels of the load powered by the converter. Figure 3 These figures take as an example the unfavorable case where the thyristors T1 and T2 are turned off, that is, the power factor correction circuit operates in discontinuous current mode, where the inductor L ( Figure 4 ) becomes zero at each switching cycle of transistor M1.

[0069] The figures show examples of the shape of the VDC voltage across the capacitor C1, of the voltage VQ1 across the switch Q1 (its conduction period during which the capacitor C1 is partially discharged is illustrated), and of the cathode current I in the forward biased thyristor T1 or T2 (transistor T1 during the positive half-wave of the voltage Vac and transistor T2 during the negative half-wave of the voltage Vac). The discharge of the capacitor C1 is performed until the current I reaches the cut-off of the thyristor that has been turned on.

[0070] Figures 5A - 5B Pictured Figure 3 The converter is designed for operation with a voltage Vac of 110 volts and a frequency of 50 Hz and a load of 25% (ie the load 7 absorbs a power equal to 25% of the nominal power of the converter).

[0071] Figure 5A shows two half-waves of the voltage Vac, and Figure 5B This is an enlarged view of the vicinity of the zero crossing of the voltage VDC.

[0072] As shown in the timing diagram, when the circuit 9 detects that the voltage VDC drops below the threshold value adjusted by the resistors R5 and R6 (e.g., below 20 volts), the transistor Q1 is turned on (time t11, Figure 5B ). The capacitor C1 is discharged and maintained at a level of at least the voltage VCC by circulation from the power supply 8. At the beginning of the next half-wave, the gate current becomes sufficient to turn on the thyristor T1 or T2, and the cathode current I reaches the cut-off threshold of the thyristor T1 or T2. It should be noted that the current I in the figure includes the gate current flowing from the gate to the cathode (the cathode current I corresponds to the sum of the gate current and the cathode current). Therefore, at the disconnection of the switch Q1 (time t13), the thyristor T1 or T2 remains turned on until the end of the half-wave. As Figure 5BAs shown in the left - hand part of, no current flows through thyristor T1 or T2 at the end of the half - wave. This is due to the fact that the load does not require energy during the entire supply cycle. However, one of the thyristors conducts at the very end of the half - wave (the region marked by arrow 15) and then turns off when the capacitor C1 discharges to the VCC level.

[0073] Figures 6A - 6B The figure shows Figure 3 operation of the converter of at 110 Vrms voltage Vac and 50 Hz frequency and 100% load, that is, the load absorbs power equal to the nominal value of the converter.

[0074] Figure 6A Two half - waves of the voltage Vac are shown, while Figure 6B is an enlarged view near the zero - crossing of the voltage VDC.

[0075] Compared with Figures 6A - 6B the situation of, since the load permanently consumes power here, the thyristor T1 or T2 that has already conducted at the start of the half - wave remains conducting until the end of the half - wave ( Figure 6B left - hand part of).

[0076] Figures 7A - 7B The figure shows Figure 3 operation of the converter of at 230 Vrms voltage Vac and 50 Hz frequency and 50% load, that is, the load absorbs power equal to 50% of the nominal value of the converter.

[0077] Figure 7A Two half - waves of the voltage Vac are shown, while Figure 7B is an enlarged view near the zero - crossing of the voltage VDC.

[0078] In such a case, the transistor Q1 does not conduct at the end of the half - wave but only at the start of the next half - wave (time t12) to control the transistor Q1 only at the right time, that is, when the voltage Vac starts to increase back, which also enables the cathode current to reach the cut - off threshold faster compared to the initial time when the transistor Q1 starts to conduct. This delay in the conduction of the transistor Q1 makes it possible to reduce its conduction time to a useful part (the duration between time t11 and the time when VDC becomes larger than the steady - state VCC is actually useless), thus reducing the power consumption in the resistor R3.

[0079] Figure 8 The figure shows Figure 3 operation of the converter of at 230 Vrms voltage Vac and 50 Hz frequency and 25% load, that is, the load Q absorbs power equal to 25% of the nominal value of the converter.

[0080] Figure 8The representation is an enlarged view near the zero-crossing of the voltage VDC.

[0081] Such a situation is an extreme case where, although the discharge of the capacitor C1 forced by the transistor Q1 between times t12 and t13 allows the generation of a gate current and the conduction of one of the thyristors, the low power consumption of the load causes a reduction of the current I below the cut-off threshold of the thyristor, and thus, when the gate current becomes zero, the cut-off of the thyristor until the end of the half-wave. The resistor Ricl then ensures the continuity of the current supply from the voltage Vac to the converter.

[0082] Figure 9 A variant of the converter is shown.

[0083] According to this variant: the AC capacitor Xcap couples (preferably, connects) the terminals 11 and 13 and forms an AC filter; the transistor Q1 is controlled according to a circuit component that can provide a delay of the control pulses applied thereto to provide the operation described in FIG. 7; the resistor Ricl is suppressed (i.e., removed from the circuit).

[0084] The voltage VCC that cannot be supplied by the resistor Ricl at the start is then delivered by the auxiliary converter 95, which is preferably isolated, whose input terminals are coupled (preferably, connected) to the common cathode of the diodes D1 and D2 and has an output terminal for delivering the voltage VCC, where the converter 95 is self-powered according to the voltage VCC generated by it.

[0085] Once the voltage VCC is generated, the thyristors T1 and T2 are controlled with a conduction delay (the delay gradually decreasing) to ensure the gradual charging of the capacitor C1 (if present) and other capacitors (e.g., capacitor C, Figure 4 ) located downstream of the power factor correction circuit.

[0086] Such control is ensured by circuit assembly 100, which includes: a circuit 101 for detecting the zero crossing of voltage Vac, whose input terminal IN is coupled to the midpoint of a resistive voltage divider bridge formed by resistors R102 and R103 connected in series between terminal 11 (or terminal 13, or both via a rectifier) and ground 27, and circuit 101 is powered by voltage VCC between terminal VCC and GND; an NPN bipolar transistor Q2, whose collector is coupled to terminal 55 through resistor R104 and whose collector is coupled (preferably, connected) to ground terminal 27, and the base of transistor Q2 is coupled to the output terminal OUT of circuit 101 through resistor R105; and an NPN bipolar transistor Q3, whose collector is coupled to the base of transistor Q1 through resistor R107 and whose emitter is coupled (preferably, connected) to ground 27, and the base of transistor Q2 is coupled to the output terminal OUT of circuit 101 through resistor R108.

[0087] Here transistor Q1 is a PNP transistor, whose collector is coupled (preferably, connected) to the anode of diode D5, whose emitter receives voltage VCC, and whose base is coupled to the junction between resistor R106 and resistor R107 between the collector of transistor Q3 and the terminal for delivering voltage VCC.

[0088] Transistor Q1 enables the control of thyristors T1 and T2 near (i.e., around) the zero crossing of the mains voltage in a steady state, or with a delay with respect to the zero crossing time of voltage Vac detected by circuit 101. The pulses for controlling transistors Q3 (and thus Q1) and Q2 can have variable durations during the startup phase from one half-wave to the other half-wave, and can have different durations when in a steady state.

[0089] Then the presence of switches Q1 and Q2 can be utilized so that when voltage Vac disappears, capacitor Xcap is discharged by continuously conducting switches Q1 and thyristors T1 and T2.

[0090] Such a discharge is desirable for electrical safety reasons.

[0091] The advantages of the described embodiments are that, except for Figure 3 the embodiments, except for the power supply for controlling the power factor correction circuit that is already available for power circuit 9', their implementation does not require an auxiliary power supply.

[0092] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations can be combined, and other variations will occur to those skilled in the art. In particular, the disclosed solution for controlling switch Q1 near the zero crossing of voltage VDC is merely an example, and other solutions can be provided, such as a microcontroller using a power factor correction circuit. Additionally, although embodiments based on a full-wave bridge have been described, these embodiments can be easily swapped for a half-wave rectifier circuit.

[0093] Finally, based on the functional descriptions provided above, the actual implementation of the embodiments and variations described herein is within the capabilities of those skilled in the art. In particular, depending on the application under consideration, the selection of the duration and delay of the square pulse used to control the conduction of transistor Q1 depends on the application and can be determined based on the above disclosure.

[0094] Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to fall within the spirit and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The invention is defined only by the following claims and their equivalents.

Claims

1. A circuit, comprising: a rectifier bridge having a first thyristor serially coupled with a first rectifying element between a first rectifying output terminal and a second rectifying output terminal of the rectifier bridge; and a first diode serially coupled with a DC voltage source between the gate of the first thyristor and the second rectifying output terminal.

2. The circuit according to claim 1, further comprising a transistor switch coupled between the first rectifying output terminal and the second rectifying output terminal, wherein the transistor switch is selectively actuated to force current conduction from the DC voltage source through the first diode.

3. The circuit according to claim 1, further comprising a transistor switch coupled between the first rectifying output terminal and the second rectifying output terminal, wherein the transistor switch is selectively actuated at the rate of a half-wave of an AC voltage applied to the input of the rectifier bridge.

4. The circuit according to claim 1, further comprising a transistor switch coupled between the first rectifying output terminal and the second rectifying output terminal, wherein the transistor switch is selectively actuated near the zero-crossing of an AC voltage applied to the input of the rectifier bridge.

5. The circuit according to claim 4, wherein when the AC voltage drops below a value greater than the DC voltage delivered by the DC voltage source, conduction of the transistor switch is triggered.

6. The circuit according to claim 4, wherein after a delay after the time when the AC voltage drops below a value greater than the DC voltage delivered by the DC voltage source, conduction of the switch is triggered.

7. The circuit according to claim 1, further comprising a first resistor coupling the cathode of the first diode to the gate of the first thyristor.

8. The circuit according to claim 1, further comprising a power factor correction circuit coupled to the first rectifying output terminal and the second rectifying output terminal.

9. The circuit according to claim 1, further comprising a capacitor coupled between the first rectifying output terminal and the second rectifying output terminal of the rectifier bridge.

10. The circuit according to claim 9, further comprising a transistor switch coupled between the first rectifying output terminal and the second rectifying output terminal, wherein the transistor switch is selectively actuated to discharge the capacitor.

11. The circuit according to claim 10, wherein the selective actuation of the transistor switch occurs near the zero-crossing of an AC voltage applied to the input of the rectifier bridge.

12. The circuit according to claim 1, further comprising a surge current limiting resistor, and wherein actuation of the first thyristor bypasses the surge current limiting resistor.

13. The circuit according to claim 1, wherein The rectifier bridge further has a second thyristor, the second thyristor being serially coupled with a second rectifying element between the first rectified output terminal and the second rectified output terminal, and wherein the first diode is serially coupled with the DC voltage source between the gate of the second thyristor and the second rectified output terminal.

14. The circuit according to claim 13, further comprising a second resistor that couples the cathode of the first diode to the gate of the second thyristor.

15. The circuit according to claim 1, further comprising an AC capacitor coupled between the input terminals of the rectifier bridge.

16. The circuit according to claim 15, further comprising: a transistor switch coupled between the first rectified output terminal and the second rectified output terminal; and a discharge circuit configured to discharge the AC capacitor via at least the switch, the discharge circuit being turned on when a disconnection of the AC voltage is detected.

17. The circuit according to claim 1, further comprising a power conversion circuit coupled to the first rectified output terminal and the second rectified output terminal.

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