Electronic circuit

Abstract

Embodiments of the present disclosure generally relate to the discharge of an AC capacitor. A circuit includes two thyristors coupled in inverse series. The AC capacitor has a first electrode and a second electrode coupled to two different electrodes of the two thyristors, respectively. The first electrode and the second electrode are coupled to receive an AC voltage. A control circuit detects an interruption of the AC voltage applied to the AC capacitor and, in response to detecting the interruption, applies the same gate current to the two thyristors simultaneously. The residual voltage stored on the AC capacitor is released through current paths of the two thyristors, one conducting current in the forward mode and the other conducting current in the reverse mode.

Description

[0001] Priority

[0002] This application claims the benefit of priority of French Patent Application No. 1905816, filed on May 31, 2019, the entire 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 source. More specifically, the present disclosure applies to circuits including an AC capacitor. Background Art

[0004] In many applications, the power received by a device from a power distribution network is filtered by an AC capacitor upstream of a voltage conversion and / or power factor correction circuit. The capacitor is generally directly connected to the line and neutral conductor of the AC power supply (or between two phases).

[0005] When the device is disconnected from the network, the presence of the capacitor requires it to be discharged. In fact, for electrical safety reasons, when the device is disconnected, the charge it contains should be discharged or dissipated. This need will be greater due to the higher power.

[0006] Although there are many solutions to this problem, these solutions are generally complex and / or expensive.

[0007] There is a need in the art for a simple and inexpensive AC capacitor discharge circuit. Summary of the Invention

[0008] One embodiment overcomes all or some of the drawbacks of the AC capacitor discharge circuit.

[0009] In one embodiment, the circuit includes two thyristors in inverse series and an AC capacitor having two electrodes respectively coupled to two different electrodes of the thyristors. The circuit includes a control circuit configured to simultaneously apply the same gate current to the two thyristors to effect a process for operation when the circuit detects the absence of an AC voltage across the AC capacitor.

[0010] According to one embodiment, one of the thyristors conducts in the opposite direction in response to the application of the gate current.

[0011] According to one embodiment, the gate current is applied to discharge the AC capacitor when the application of the AC voltage to the electrodes of the capacitor is stopped for a period longer than a first threshold (at least one half-cycle of the AC voltage).

[0012] According to one embodiment, if the circuit does not detect that the input voltage becomes less than the second threshold for a period greater than the third threshold, the application of the gate current is stopped, where the third threshold is greater than the first threshold.

[0013] According to one embodiment, the period during which the gate current is applied is longer than half a cycle of the AC voltage configured to be applied to the two electrodes of the capacitor.

[0014] According to one embodiment, the period during which the gate voltage is applied ranges from several tens of milliseconds to several hundreds of milliseconds.

[0015] According to one embodiment, the gate current is applied continuously.

[0016] According to one embodiment, the gate current is applied in pulses.

[0017] According to one embodiment, the thyristor is controlled by a circuit that operates to detect the absence of voltage between the terminals to which the AC voltage is applied.

[0018] According to one embodiment, the thyristor forms part of a bridge for rectifying the AC voltage.

[0019] According to one embodiment, in the presence of the AC voltage, the thyristor is controlled using pulses to rectify the AC voltage.

[0020] According to one embodiment, the thyristor receives simultaneous control pulses for each half-wave of the AC voltage.

[0021] According to one embodiment, each thyristor receives control pulses for one half-wave of two AC voltages of the AC voltage.

[0022] According to one embodiment, the output of the bridge supplies power to a switched-mode power supply, and the gate current is generated under the control of a circuit for controlling the switched-mode power supply.

[0023] According to one embodiment, the thyristor is a cathode-gate thyristor.

[0024] According to one embodiment, the thyristor is an anode-gate thyristor. Description of the Drawings

[0025] In the following non-limiting description of specific embodiments in conjunction with the drawings, the foregoing and other features and advantages will be discussed in detail, where:

[0026] Figure 1 An example of a power conversion system is shown;

[0027] Figure 2 An embodiment of a power conversion system or circuit equipped with an AC capacitor discharge function is schematically shown;

[0028] Figures 3A to 3B illustrates the reverse conduction phenomenon of a thyristor;

[0029] Figures 4A to 4E illustrates Figure 2 the operation of the system in response to the disappearance of the AC power supply voltage;

[0030] Figure 5 schematically shows another embodiment of a power conversion system or circuit equipped with an AC capacitor discharge function;

[0031] Figure 6 schematically shows yet another embodiment of a power conversion system or circuit equipped with an AC capacitor discharge function; and

[0032] Figure 7 schematically shows yet another embodiment of a power system or circuit equipped with an AC capacitor discharge function. Detailed Description

[0033] In the different figures, the same elements have been denoted by the same reference numerals. In particular, structural and / or functional elements common to different embodiments may be denoted by the same reference numerals and may have the same structure, dimensions, and material properties.

[0034] For clarity, only those steps and elements that contribute to an understanding of the described embodiments have been shown and described in detail. In particular, the DC / AC or DC / DC power converters powered by the described circuits and the control of such power converters have not been described in detail, and the described embodiments are compatible with conventional converters and the conventional control of such converters.

[0035] Throughout this disclosure, the term "connected" is used to denote a direct electrical connection between circuit elements without intermediate elements other than conductors, while the term "coupled" is used to denote an electrical connection between circuit elements that may be direct or may be via one or more intermediate elements.

[0036] In the following description, when referring to terms that define absolute positions such as "front", "rear", "top", "bottom", "left", "right", etc., or terms that define relative positions such as "above", "below", "upper", "lower", etc., or terms that define directions such as "horizontal", "vertical", etc., unless otherwise specified, the orientation of the drawings is referred to.

[0037] The terms "about", "substantially", "approximately" are used herein to denote a tolerance of plus or minus 10% (preferably plus or minus 5%) of the value being discussed.

[0038] Figure 1An example of a power conversion system 1 is shown. Such a conversion system 1 is based on half-wave or full-wave rectification of the AC supply voltage Vac followed by DC / DC or DC / AC conversion to supply power to a load (Q).

[0039] Schematically, the AC voltage Vac is applied between two input terminals 11 (L) and 13 (N) that are coupled to the AC input terminals 21 and 23 of a rectifier bridge 3. The voltage Vac is, for example, the AC voltage or supply voltage of a 230V / Hz or 60Hz, or 110V / Hz or 60Hz power distribution network. Typically, the terminals 11 and 13 are formed by the pins of a plug that connects the system 1 to an electrical outlet of an electrical installation.

[0040] The rectified output terminals 25 and 27 of the rectifier bridge are coupled to the input terminals 51 and 53 of a DC / DC or DC / AC conversion circuit 5. The (DC or AC, according to the embodiment) output terminals 55 and 57 of the circuit 5 supply the supply voltage to the load 7 (Q). A DC capacitor Cdc couples (preferably connects) the terminals 25 and 27 to smooth the rectified voltage and convey the rectified voltage at the input of the circuit 5.

[0041] In the applications targeted by the present disclosure, an AC capacitor Xcap couples (preferably connects) to the terminals 11 and 13 upstream of any element of the conversion system 1 (and in particular upstream of the bridge 3). The function of the capacitor Xcap is to filter the AC voltage Vac, in particular to remove possible high-frequency interferences (frequencies greater than the frequency of the AC voltage Vac).

[0042] For safety reasons, the presence of the AC input capacitor Xcap requires that the capacitor be discharged when the system is disconnected from the electrical installation, to prevent contact of the user with the terminals 11 and 13 when the system is disconnected. This need is greater due to the high power of the system. In fact, the electrical power stored in the capacitor has the risk of being discharged by the body of a user touching the two terminals.

[0043] Many solutions have been provided for discharging the AC capacitor when the AC input voltage disappears.

[0044] The first category of solutions uses passive components, where the capacitor Xcap subsequently forms part of an AC filter that has a low-value resistor connected in parallel with the capacitor and dissipates the power it contains when the system is disconnected. The drawback of such a solution is the permanent power dissipation in the application.

[0045] The second category of solutions uses active components to control the discharge of the AC capacitor when the supply voltage Vac disappears. Such solutions generally require additional circuits and components, which increases the cost of the system or application.

[0046] According to the described embodiments, provided is a power conversion system equipped with a specific rectifier bridge structure, namely, a hybrid bridge or a controllable bridge.

[0047] (e.g., full-wave) The rectifier bridge is formed by four branches that couple every two input terminals to each output terminal, and there is a rectifying element (usually a diode) in each branch.

[0048] The controllable bridge is a rectifier bridge in which two or four branches (hybrid bridge) include switches (usually thyristors or SCRs) instead of diodes.

[0049] Such a bridge generally equips the power conversion system as a supplement to the non-controllable bridge, so as to short-circuit the inrush current limiting resistor once the system is started, or ensure the gradual charging (soft start) of the output capacitor. Such a bridge can also be used without an inrush current limiting resistor, but when using the controllable elements of the bridge during the startup of the system to gradually charge the downstream capacitor.

[0050] According to the described embodiments, provided is to use the bridge thyristor to discharge the AC capacitor when the system is disconnected from the power network.

[0051] Then advantages are obtained from the specific characteristics of the thyristor, namely, when the circuit device is reverse-biased but a gate current is applied, the circuit device has a significant leakage current.

[0052] Figure 2 Embodiments of a power conversion system or circuit equipped with an AC capacitor discharge function are shown very schematically.

[0053] It includes: input terminals 11 and 13 to which the AC power supply voltage Vac is applied; an AC capacitor Xcap coupled (preferably connected) to terminals 11 and 13; a (e.g., full-wave) rectifier bridge 3 having AC input terminals 21 and 23 respectively coupled to terminals 11 and 13, and rectified output terminals 25 and 27 respectively coupled (preferably connected) to the input terminals 51 and 53 of a DC / DC or DC / AC converter 5; and one or more DC capacitors Cdc coupled (preferably connected) to terminals 25 and 27.

[0054] In Figure 2In the example, it is assumed that there are AC filters ACF (shown by dashed lines) between terminals 11 and 21, and between terminals 13 and 23. Such optional filters generally include inductive and capacitive elements, and such optional filters are used to remove electrical noise presented on the lines of the power distribution network. For example, inductor L1 couples (preferably connects) terminals 11 and 21, and inductor L2 couples (preferably connects) terminals 13 and 23. Capacitor C1 couples (preferably connects) terminal 21 to ground, and capacitor C2 couples (preferably connects) terminal 23 to ground.

[0055] Preferably, converter 5 is a switched-mode power supply controlled at a frequency much higher (in a ratio of approximately 1000 to 10000) than the frequency of voltage Vac.

[0056] According to the described embodiment, rectifier bridge 3 is a full-wave bridge associated with a controllable half-bridge, or a hybrid bridge associated with a diode half-bridge (which is the same).

[0057] In Figure 2 the example, bridge 3 includes: two diodes D1 and D2 that respectively couple (preferably connect) terminals 21 and 23 to the first terminal of inrush current limiting resistor Ricl, and the other terminal of inrush current limiting resistor Ricl is coupled (preferably connected) to terminal 25; two diodes D3 and D4 respectively couple (preferably connect) terminals 21 and 23 to terminal 27; and two thyristors T1 and T2, here having cathode gates, that respectively couple (preferably connect) terminals 21 and 23 to terminal 25.

[0058] At circuit startup, that is, when powered by voltage Vac, thyristors T1 and T2 are uncontrolled, and the rectification of voltage Vac is through resistor Ricl. Once the circuit has been started and is in the steady state, thyristors T1 and T2 are controlled alternately according to the half-wave of voltage Vac, and the rectification function of the upper half-bridge is ensured. At each half-wave, a single thyristor of the two thyristors (the forward-biased thyristor) is conducting. The thyristors are controlled with pulses, that is, the gates of the thyristors receive current pulses for each half-wave of voltage Vac. In this context, the term "pulse" means a signal having a duration (preferably at least in a ratio of 10) shorter than the half-wave duration of voltage Vac. When the system is in the steady state, the use of thyristors enables resistor Ricl to be short-circuited. When the resistor and diodes D1 and D2 are not in use, thyristors T1 and T2 can be activated to perform phase angle control to provide progressive charging of (a plurality of) capacitors Cdc.

[0059] The operation of the system in the startup and steady states is itself unremarkable. It should be noted that due to the hybrid bridge and the specifically described control, the circuit does not include a resistor in parallel with the AC capacitor Xcap.

[0060] When the circuit is turned off, for example, when the circuit is disconnected from the supply voltage Vac, continuous control of the bridge 3 is provided, but with a specific control, namely, a DC gate current is simultaneously applied to both thyristors. With respect to the pulse signal, the application of the continuous control signal means maintaining a state for a period of time that is at least equal to (preferably greater than) half a wave of the voltage Vac. Thus, in response to the simultaneously applied control signal, one of the thyristors T1 and T2 conducts when forward-biased, while the other thyristor, although reverse-biased, still has a non-negligible leakage current. Since the two thyristors are anti-connected in series (interconnected by electrodes of the same nature, i.e., they have a common anode or a common cathode), it can be considered that the AC capacitor Xcap is short-circuited by the thyristors T1 and T2.

[0061] If the bias of the capacitor Xcap is positive on the terminal 11 side (turned off under the positive half-wave according to the convention in the figure), the discharge current of the capacitor Xcap flows from its electrode on the terminal 11 side to its electrode on the terminal 13 side: if present, through the inductor L1 of the filter ACF; in the forward direction through the thyristor T1 in the on state; in the reverse direction through the thyristor T2; and if present, through the inductor L2 of the filter ACF.

[0062] If the bias of the capacitor Xcap is negative on the terminal 13 side (turned off under the negative half-wave according to the convention in the figure), the discharge current of the capacitor Xcap flows from its electrode on the terminal 13 side to its electrode on the terminal 11 side: if present, through the inductor L2 of the filter ACF; in the forward direction through the thyristor T2 in the on state; in the reverse direction through the thyristor T1; and if present, through the inductor L1 of the filter ACF.

[0063] Thus, the capacitor Xcap is discharged, and its power is dissipated by discharging into the series resistors of the thyristors T1 and T2, and possibly into the inherent resistors of the inductors L1 and L2. Although the resistance is small, this resistance is sufficient to discharge the capacitor Xcap. In practice, a current of a few milliamperes is sufficient to discharge the capacitor Xcap quickly enough (within a few milliseconds to tens of milliseconds).

[0064] At the disconnection of the voltage Vac, the control of thyristors T1 and T2 is ensured by circuit 9 (DET), which operates to detect the disappearance of voltage Vac and generate a gate current that is commonly applied to the gates G1 and G2 of thyristors T1 and T2. Typically, in the example of a cathode-gate thyristor, current is injected into its gate. However, the example described is compatible with a cathode-gate thyristor that is controllable by extraction of its gate current. Circuit 9 is coupled (preferably connected) to terminals 21 and 23 (or to terminals 11 and 13) to detect, for example, the zero-crossing of voltage Vac. In the absence of such a zero-crossing, circuit 9 can detect the disappearance of voltage Vac.

[0065] A low DC voltage is used to power circuit 9 and the control circuit of converter 5 (not shown in Figure 2 . Examples for providing the DC voltage will be presented subsequently in conjunction with Figure 6 and Figure 7 .

[0066] Figures 3A to 3B Illustrates the phenomenon of reverse conduction of the thyristor. Figure 3A Illustrates an example of the shape of the reverse current Ir (or leakage current) according to the reverse voltage Vr (cathode potential minus anode potential) across the thyristor when no gate current Ig is applied to the thyristor. Figure 3B Illustrates an example of the shape of the reverse current Ir according to the reverse voltage Vr for multiple values of the gate current Ig.

[0067] As illustrated in Figure 3A , when no gate current (Ig = 0 mA) is applied, the leakage current Ir is typically on the order of several hundred microamps. The reverse current increases slightly according to the reverse voltage Vr. In most applications using such a power conversion system, such a leakage current level is completely negligible, since the currents used to implement the application typically range from several tens of milliamps to several tens of amps.

[0068] However, the result of such a leakage current is not sufficient to discharge capacitor Xcap quickly enough. Typically, several seconds are required, which is unacceptable in terms of the user's electrical safety.

[0069] As illustrated in Figure 3B , when a gate current Ig of approximately several milliamps is applied, the reverse current Ir increases by a factor of approximately 10 to 20. For example, the reverse current Ir is: approximately 2 mA for a gate current of approximately 6 mA; approximately 4 mA for a gate current of approximately 8 mA; approximately 6 mA for a gate current of approximately 12 mA; and approximately 10 mA for a gate current of approximately 16 mA.

[0070] The reverse current Ir increases slightly with the increase of the reverse voltage Vr, but increases by about 10% to 20% between 100 - 400V in the main target range of the supply voltage. Therefore, the discharge of the capacitor Xcap can be performed faster, and additionally, there is sufficient current during the longest part of the discharge range (up to dozens of volts).

[0071] It should be noted that, different from the start control of the forward - biased thyristor which can be performed with pulses (pulses of several microseconds per half - wave voltage Vac are sufficient to turn on the thyristor), the gate current should be continuously applied to utilize reverse conduction.

[0072] Figures 4A to 4E illustrates Figure 2 the operation of the Figure 4A shows an example of the shape of the voltage VXcap across the capacitor Xcap. Figure 4B shows an example of the shape of the gate current Ig1 of the thyristor T1. Figure 4C shows an example of the shape of the gate current Ig2 of the thyristor T2. Figure 4D illustrates an example of the shape of the current IA1 in the thyristor T1. Figure 4E illustrates an example of the shape of the current IA2 in the thyristor T2.

[0073] By convention, it is assumed that: the voltage VXcap is the potential difference between the electrode on the terminal 11 side and the electrode on the terminal 13 side; and the gate current Ig1 or Ig2 is positive when current is injected into the gate of the relevant thyristor; the current IA1 or IA2 in the thyristor is positive when the current IA1 or IA2 enters through the anode of the relevant thyristor.

[0074] In the steady state, for each positive half - wave of the AC voltage Vac, that is, when the voltage VXcap is positive, the thyristor T1 is turned on; and for each negative half - wave of the voltage Vac, that is, when the voltage VXcap is negative, the thyristor T2 is turned on. Figures 4A to 4E The example assumes that the thyristor starts at zero voltage, that is, a positive gate - current pulse is applied at the start of each half - wave to start the relevant thyristor. In Figures 4A to 4E the example, for simplicity, neither the filter ACF nor other possible sources of phase shift between voltage and current are considered. It is also assumed that the converter 5 absorbs current in phase with the supply voltage, which is the case when the converter 5 also ensures the function of power - factor correction of the complete circuit. In this case, the currents IA1 and IA2 have positive and negative half - waves. When the voltage across the thyristor is reversed, when the current flowing through the thyristor becomes zero, the conduction of the thyristor stops.

[0075] The control of thyristors T1 and T2 in the steady state is provided by a control circuit (preferably synchronized on the voltage Vac). Such a circuit (not shown in Figure 2 ) may be a dedicated circuit, a microcontroller or may be included in circuit 9.

[0076] In the steady state, the voltage VXcap reverses for each half-wave (which follows the voltage Vac), and thus becomes zero twice per cycle of the voltage Vac.

[0077] It is assumed that at time t0, the voltage Vac disappears ( Figure 4A dashed line in ). Such a disappearance causes the voltage VXcap to suddenly decrease (faster than the decrease in the voltage Vac) due to the operation of converter 5 continuously absorbing the current provided by capacitor Xcap. Then, when the voltage across converter 5 drops below a given threshold, converter 5 suddenly stops operating, and the discharge of capacitor Xcap accordingly stops.

[0078] However, capacitor Xcap is typically kept charged at a level corresponding to a value between 100 and 200 volts. In the case where the voltage Vac is disconnected and converter 5 is slightly charged, the voltage can remain equal to the supply voltage at the time of disconnection (i.e., between 0 and 320 volts for a 230 volt rms voltage).

[0079] Circuit 9 monitors the voltage Vac to detect its disappearance. For example, circuit 9 uses a zero-crossing detection circuit to detect that the voltage across capacitor Xcap, or between terminals 11 and 13, or between terminals 21 and 23, does not become equal to zero for a period of time exceeding at least one half-cycle (preferably, from one cycle to several cycles) of the voltage Vac.

[0080] In the Figures 4A - 4E example, at time t1 after the period T of disappearance of the voltage Vac (i.e., after the period during which the voltage VXcap does not take on zero), circuit 9 triggers the generation of the gate current in the two thyristors. In the Figures 4A - 4E example, thyristor T1 is forward-biased and thus is turned on. Thyristor T2 is reverse-biased but conducts a negative leakage current IA2. The amplitude of the gate current limits the amplitude of the leakage current and thus limits the speed and duration of the discharge of capacitor Xcap. When the capacitor is discharged (time t2), the current in thyristor T1 disappears causing it to turn off. Circuit 9 detects that the voltage VXcap across capacitor Xcap has become zero and stops the generation of the thyristor gate signal.

[0081] Figure 5 Another embodiment of a power conversion system or circuit equipped with an AC capacitor discharge function is very schematically shown.

[0082] This embodiment uses the principle of a rectifier diode bridge associated with a controllable half-bridge. Elements common to Figure 2 the embodiments will not be described again.

[0083] Unlike Figure 2 the embodiments, a surge current limiting resistor Ricl is inserted between the common anode of diodes D3 and D4 and terminal 27. Another difference is that the controllable half-bridge is a lower half-bridge formed by two anode-gate thyristors T1' and T2'. The common anode of thyristors T1' and T2' is coupled (preferably connected) to terminal 27. The cathode of thyristor T1' is coupled (preferably connected) to terminal 23. The cathode of thyristor T2' is coupled (preferably connected) to terminal 21. Compared with cathode-gate thyristors, anode-gate thyristors are generally turned on by extracting current from their gates G1 or G2. Therefore, the circuit 9 that detects the disappearance of the voltage Vac can pull the current on gates G1 and G2. As a variant, anode-gate thyristors that can be controlled by injecting current into their gates are used.

[0084] Figure 5 The operation of the circuit of

[0085] can be inferred from the operation described in connection with the previous figures.

[0085] According to another embodiment, surge current limiting resistors are provided in the upper and lower parts of the circuit, which is equivalent to combining Figure 2 and Figure 5 the embodiments, and in addition to providing a complete bridge of four diodes, a complete controllable bridge of four thyristors is also provided.

[0086] According to other embodiments, when the thyristors are turned on, the thyristor control is controlled for a start without current peaks. This requires adaptive control of the thyristors at startup (by a phase angle with a gradually decreasing delay), but this avoids the resistor Ricl.

[0087] Figure 6 Yet another embodiment of a power conversion system or circuit equipped with an AC capacitor discharge function is very schematically shown.

[0088] According to this embodiment, the rectifier bridge 3 is formed only by a hybrid bridge, which includes an upper half-bridge with cathode-gate thyristors T1 and T2 and a lower half-bridge with diodes D3 and D4. The absence of the system startup inrush current limiting resistor is compensated by the specific control of thyristors T1 and T2 to ensure the gradual charging of the capacitor Cdc. Then the presence of the microcontroller 8 (MCU) is advantageously used to control the switch-mode converter 5 (DC / DC or AC) using the microcontroller to generate the control signals for gates G1 and G2.

[0089] Figure 6 Embodiments illustrate another variant related to the generation of a low DC voltage adapted to a control signal (low voltage means a voltage less than 20 volts, preferably a few volts) and a voltage reference. In particular, the injection current into the cathode gates of thyristors T1 and T2 requires the potential (GND1) of the thyristor cathode to be less than the potentials (VDD1) of its gates G1 and G2. In addition, the microcontroller 8 is powered by a low voltage VDD2 (the potential (GND2) of reference terminal 27). Therefore, the generation of the gate control signals G1 and G2 requires a change in the voltage reference. For this purpose, the output I / O of the microcontroller 8 that transmits a digital state signal (taking one of the potentials VDD2 and 0, within the voltage drop range in the output transistor in the on state) may be applied via a resistor RD to the photodiode PD82 (anode d’) of the optocoupler 82. The (e.g., bipolar) phototransistor PT82 of the optocoupler 82 has its collector coupled (preferably connected) to a power supply terminal at potential VDD1. The emitter of the phototransistor PT82 may be coupled to the gates G1 and G2 of the thyristors T1 and T2 via resistors RG1 and RG2.

[0090] In Figure 6 the example, the voltages VDD1 and VDD2 are obtained from a transformer 6 having a first winding or primary 61, the first terminal of the transformer 6 being coupled (preferably connected) to the cathodes of two rectifier diodes D5 and D6, the anodes of the rectifier diodes D5 and D6 being coupled (preferably connected) to terminals 11 and 13 respectively. The other end of the first winding 61 is coupled to its first end on the one hand through a diode D7 (the anode of the diode D7 on the second end side), and on the other hand, to terminal 27 (potential GND2) through a MOS transistor M. The transistor M is controlled by a signal provided by a system on / off block 63. A capacitor C62 may couple the cathode of the diode D7 to terminal 27.

[0091] The (first) secondary winding 65 of the transformer 6 provides a voltage VDD2 referenced to potential GND2. The first end of the winding 65 is coupled via a diode D8 (anode on the first end side of the winding 65) to the first terminal of a capacitor C64 that provides the potential VDD2, and its other terminal is coupled (preferably connected) to the second end of the winding 65 and terminal 27 (GND2).

[0092] The (second) secondary winding 67 of the transformer 6 delivers a voltage VDD1 referenced to potential GND1. The first end of the winding 67 is coupled via a diode D9 (anode on the first end side of the winding 67) to the first terminal of a capacitor C66 that provides the potential VDD1, and its other terminal is coupled (preferably connected) to the second end of the winding 67 and terminal 25 (GND1).

[0093] The microcontroller 8 receives information ZV indicating the presence or absence of voltage Vac at the digital input / output terminal I / O. The binary information ZV indicating zero voltage (and thus no voltage Vac) at the system input enables the microcontroller 8 to trigger both thyristors T1 and T2 in pulse mode at the zero-crossing point of voltage Vac (when present), and to control the discharge of capacitor Xcap by forcing one of the thyristors to conduct forward and the other to conduct in reverse when the signal ZV no longer crosses the threshold representing the zero level of voltage Vac for a period equivalent to at least one half-cycle (preferably several half-waves) of voltage Vac. In Figure 6 the example, simultaneous control of thyristors T1 and T2 in pulse mode is provided, which is not disturbed because the pulses are short enough to avoid generating an extended reverse conduction of the reverse-biased thyristor.

[0094] The signal ZV is obtained, for example, by means of circuit 4 based on optocoupler 42. The anode of the emitting photodiode PD42 of optocoupler 42 is coupled (e.g., connected) to one of terminals 11 and 13 (e.g., terminal 11) through one or more resistors R4. The cathode of diode PD42 is coupled (preferably connected) to the other of terminals 11 and 13 and its own anode through diode D42. Resistor R4 reduces the voltage driving photodiode PD42. The phototransistor PT42 of optocoupler 42 is coupled (preferably connected) to terminal 27 (ground GND2) through its emitter, and is coupled to resistor R6, the other terminal of which is coupled (preferably connected) to the terminal at potential VDD2. The signal ZV is sampled from the junction of resistor R6 and the junction of phototransistor PT42. As long as the voltage between terminals 11 and 13 is not zero, photodiode PD42 energizes phototransistor PT42, thereby pulling the state of signal ZV to the low state (usually less than 2 volts). When voltage Vac is zero (or at each zero-crossing point), transistor PT42 turns off, and the level of signal ZV is pulled to the high state (VDD2) via resistor R6 (pull-up resistor). When the level ZV does not exhibit further transitions between the high and low states during the selected period T( Figure 4A )), the microcontroller 8 causes the continuous generation of gate current.

[0095] Figure 7 A further embodiment of a power conversion system or circuit equipped with an AC capacitor discharge function is shown very schematically.

[0096] With Figure 6Compared with the embodiments of Figure 6 ), the thyristors T1' and T2' are anode-gate thyristors that replace the diodes D3 and D4 in the lower part of the bridge 3'. The thyristors T1 and T2 are replaced by the diodes D1 and D2 in the upper part of the bridge 3'. This reduces the number of DC low voltages to be generated to a single voltage VDD, since the gate signals G1 and G2 can be referenced to the same reference potential GND as the microcontroller 8. Thus, the transformer 6' can be simplified to two windings 61 and 65, and the winding 65 provides the low voltage VDD to power the microcontroller 8 and the optocoupler 4. In addition, the optocoupler 82( Figure 6 ) is not required, and the gate control signal power output I / O can be directly coupled (preferably connected) to the resistors RG1 and RG2. Figure 7 The remaining circuit of Figure 6 is similar to the circuit of

[0097] Figure 6 and Figure 7 The embodiments of

[0098] combine the advantages of discharging the AC capacitor via the thyristor and using a hybrid bridge to avoid the inrush current limiting resistor Ricl. In addition, they are able to use the same microcontroller as that used by the switch-mode converter 5 and that can be used for thyristor control during the soft-start phase.

[0098] An advantage of the described embodiments is that their implementation only requires the generation of specific control of the thyristors of the hybrid bridge.

[0099] An advantage of the described embodiments is that the discharge of the AC capacitor Xcap is particularly simple and uses a low-complexity circuit.

[0100] Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these different embodiments and variants can be combined, and other variations will be conceived by those skilled in the art. In particular, the solution for discharging the capacitor Xcap by reverse-conduction turn-off in the thyristor is compatible with any conventional system, and the provided rectifier bridge includes two upper thyristors and / or two lower thyristors, and thus, they are anti-connected in series with a common electrode (common anode or common cathode) coupled to the rectified output terminal of the bridge.

[0101] In addition, although the simultaneous continuous control of the thyristors T1 and T2 has been referenced to ensure the discharge of the capacitor Xcap, control can also be performed by simultaneous pulses, provided that the duration and / or frequency of the pulses are much higher than the frequency and / or duration of the AC voltage Vac (the ratio is at least 10) to sufficiently ensure that the reverse-biased thyristor is reverse-conducted for a period of time sufficient to discharge the capacitor Xcap.

[0102] Furthermore, it can be provided that if the input voltage, assumed to be an AC voltage (between terminals 11 and 13), does not become lower than a (second) threshold during a period of time greater than a (third) threshold (e.g., from several hundred milliseconds to several seconds), the simultaneous control of the thyristors is stopped. Such a variant makes it possible to distinguish the absence of an AC voltage from the presence of a DC input voltage and to disconnect the circuit in the event of a power supply or DC power connection failure. This is equivalent to providing simultaneous control of thyristors T1 and T2 during a time window ranging from a first threshold, for example, of several tens or hundreds of milliseconds, to a third threshold, for example, several hundreds of milliseconds or several seconds greater than the first threshold. The second threshold is a voltage threshold and corresponds, for example, to several volts.

[0103] Finally, based on the functional indications given above, the actual practice of the described embodiments and variants is within the capabilities of a person skilled in the art. In particular, the choice of the period of time during which the voltage Vac disappears before the capacitor Xcap discharges can vary, provided that it is compatible with the maximum period of time required for the capacitor Xcap to discharge (usually set by a standard). A period of time ranging from several tens of milliseconds to several hundreds of milliseconds is a preferred choice (more preferably on the order of 40 ms to 300 ms).

Claims

1. A circuit, comprising: A rectifier circuit for rectifying an AC voltage; Two thyristors, anti - serially coupled to the rectifier circuit; An AC capacitor having a first electrode and a second electrode, the first electrode and the second electrode being respectively coupled to two different electrodes of the two thyristors, and the first electrode and the second electrode being respectively coupled to two different electrodes of the rectifier circuit, and the AC capacitor being further configured to receive the AC voltage; And A control circuit configured to detect an interruption in the received AC voltage at the first electrode and the second electrode of the AC capacitor, and in response to detecting the interruption, simultaneously apply the same gate current to the two thyristors to provide a circuit path for discharging the voltage across the AC capacitor; Wherein in the presence of the AC voltage, the two thyristors are also controlled by pulses to rectify the AC voltage.

2. The circuit according to claim 1, wherein a first thyristor of the two thyristors conducts in the reverse direction in response to the simultaneous application of the gate current.

3. The circuit according to claim 1, wherein if the interrupted reception of the AC voltage lasts for a period longer than a first threshold, the control circuit detects the interruption in the reception of the AC voltage, wherein the first threshold is at least one half - cycle of the AC voltage.

4. The circuit according to claim 3, wherein if the input voltage becomes less than a second threshold for a period greater than a third threshold, the control circuit also stops the application of the gate current, wherein the third threshold is longer than the first threshold.

5. The circuit according to claim 1, wherein the control circuit applies the gate current for a period longer than a half - cycle of the AC voltage.

6. The circuit according to claim 5, wherein the period ranges from tens of microseconds to hundreds of microseconds.

7. The circuit according to claim 5, wherein the gate current is applied continuously.

8. The circuit according to claim 5, wherein the gate current is applied in pulses.

9. The circuit according to claim 1, wherein the rectifier circuit includes a first rectifier diode and a second rectifier diode, and the terminals of the first rectifier diode and the second rectifier diode are connected to the terminals of the two thyristors.

10. The circuit according to claim 9, wherein the first rectifier diode and the second rectifier diode form part of a bridge for rectifying the AC voltage.

11. The circuit according to claim 9, wherein the first rectifier diode and the second rectifier diode connected to the two thyristors form a bridge for rectifying the AC voltage.

12. The circuit according to claim 1, wherein the pulses for rectification comprise: Pulses applied to the thyristors corresponding to a half - wave of the AC voltage.

13. The circuit according to claim 1, wherein each thyristor receives the pulse in only one half - wave of the two half - waves of the AC voltage.

14. The circuit according to claim 1, wherein the output of the rectifier circuit powers a switched-mode power supply, and wherein the control circuit is further operative to control the switched-mode power supply.

15. The circuit according to claim 1, wherein the two thyristors are cathode-gate transistors.

16. The circuit according to claim 1, wherein the two thyristors are anode-gate thyristors.

17. A circuit comprising: a surge current limiting resistor; a rectifier bridge circuit including a first diode coupled between a first input node and a first terminal of the surge current limiting resistor, a second diode coupled between a second input node and the first terminal of the surge current limiting resistor, a third diode coupled between the first input node and an output node, and a fourth diode coupled between the second input node and the output node, wherein the first input node and the second input node are coupled to receive an AC voltage; a first thyristor coupled between the first input node and a second terminal of the surge current limiting resistor; a second thyristor coupled between the second input node and the second terminal of the surge current limiting resistor; an AC capacitor having a first electrode and a second electrode coupled to the first input node and the second input node, respectively; and a control circuit configured to detect an interruption in the received AC voltage at the first electrode and the second electrode of the AC capacitor, and in response to detecting the interruption, simultaneously apply the same gate current to the first thyristor and the second thyristor to provide a circuit path for discharging the voltage across the AC capacitor.

18. The circuit according to claim 17, wherein one of the first thyristor and the second thyristor conducts in the reverse direction in response to the simultaneous application of the gate current.

19. The circuit according to claim 17, wherein the gate current is applied continuously.

20. The circuit according to claim 17, wherein the gate current is applied in pulses.

21. The circuit according to claim 17, wherein in the presence of the AC voltage, the first thyristor and the second thyristor are also controlled by pulses to rectify the AC voltage.

22. The circuit according to claim 17, wherein the first thyristor and the second thyristor are cathode-gate thyristors.

23. The circuit according to claim 17, wherein the first thyristor and the second thyristor are anode-gate thyristors.

24. The circuit according to claim 17, wherein if the interrupted reception of the AC voltage lasts longer than a first threshold period, wherein the first threshold is at least one half-cycle of the AC voltage, the control circuit detects the interruption in the received AC voltage.

25. A circuit comprising: A rectifier bridge circuit includes a first thyristor coupled between a first input node and a first output node, a second thyristor coupled between a second input node and the first output node, a first diode coupled between the first input node and a second output node, and a second diode coupled between the second input node and the second output node, wherein the first input node and the second input node are coupled to receive an AC voltage; An AC capacitor having a first electrode and a second electrode coupled to the first input node and the second input node, respectively; and A control circuit configured to detect an interruption in the received AC voltage at the first electrode and the second electrode of the AC capacitor and, in response to detecting the interruption, simultaneously apply the same gate current to the first thyristor and the second thyristor to provide a circuit path for discharging the voltage across the AC capacitor, and wherein, in the presence of the AC voltage, the first thyristor and the second thyristor are also controlled with pulses to rectify the AC voltage.

26. The circuit according to claim 25, wherein one of the first thyristor and the second thyristor conducts in the reverse direction in response to the simultaneous application of the gate current.

27. The circuit according to claim 25, wherein the gate current is applied continuously.

28. The circuit according to claim 25, wherein the gate current is applied in pulses.

29. The circuit according to claim 25, wherein the first thyristor and the second thyristor are cathode-gate thyristors.

30. The circuit according to claim 25, wherein the first thyristor and the second thyristor are anode-gate thyristors.

31. The circuit according to claim 25, wherein the control circuit detects an interruption in the received AC voltage if the interrupted reception of the AC voltage lasts longer than a first threshold period, wherein the first threshold is at least one half-cycle of the AC voltage.

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