Isolated ac / DC converter

Abstract

The purpose of the present disclosure is to improve the power factor. This isolated AC / DC converter (1) is provided with a first series circuit (2) in which first through fourth semiconductor switches (S1 to S4) are connected in series. A second end (a2) of an alternating current power source (PS1) is connected to a first connection point (P1) of the second and third semiconductor switches (S2, S3). A second series circuit (3) of first and second capacitors (C1, C2) is connected in parallel to the first series circuit (2). A third diode (D3) is connected between a connection point (P3) of the first and second semiconductor switches (S1, S2) and a second connection point (P2) of the first and second capacitors (C1, C2), and a fourth diode (D4) is connected between a connection point (P4) of the third and fourth semiconductor switches (S3, S4) and the second connection point (P2). An inductor (L1) is connected between at least one of a first rectifier circuit (4) and the first series circuit (2) and the alternating current power source (PS1). A primary winding (11) of a transformer (10) is connected between the first connection point (P1) and the second connection point (P2).

Description

Isolated AC / DC converter

[0001] The present disclosure relates to an isolated AC / DC converter, and more particularly to an isolated AC / DC converter having a multilevel converter circuit.

[0002] Patent Document 1 discloses a three-level power conversion device that performs voltage conversion of a DC voltage input from a DC power supply. The three-level power conversion device described in Patent Document 1 includes a capacitor circuit including a series circuit of a plurality of capacitors connected in parallel to the DC power supply, and a switching circuit including a series circuit of first to fourth semiconductor switching elements connected in parallel to the capacitor circuit.

[0003] JP 2019-97300 A

[0004] An object of the present disclosure is to provide an isolated AC / DC converter that can improve the power factor with simple control.

[0005] An isolated AC / DC converter according to one aspect of the present disclosure includes a first rectifier circuit, a first series circuit, a second series circuit, a third diode, a fourth diode, an inductor, a transformer, a second rectifier circuit, and a control circuit. The first rectifier circuit includes a series circuit of a first diode and a second diode, the cathode of which is connected to the anode of the first diode. A first end of an AC power supply is connected to a connection point between the first diode and the second diode. The first series circuit includes a first semiconductor switch, a second semiconductor switch, a third semiconductor switch, and a fourth semiconductor switch connected in series between the cathode of the first diode and the anode of the second diode. A second end of the AC power supply is connected to a connection point between the second semiconductor switch and the third semiconductor switch. The second series circuit includes a series circuit of a first capacitor and a second capacitor and is connected in parallel with the first series circuit. The third diode has a cathode connected to the connection point between the first semiconductor switch and the second semiconductor switch and an anode connected to the connection point between the first capacitor and the second capacitor. The fourth diode has an anode connected to the connection point of the third semiconductor switch and the fourth semiconductor switch and a cathode connected to the connection point of the first capacitor and the second capacitor. The inductor is connected between the AC power supply and at least one of the first rectifier circuit and the first series circuit. The transformer has a primary winding connected between the connection point of the second semiconductor switch and the third semiconductor switch and the connection point of the first capacitor and the second capacitor. The second rectifier circuit is connected to the secondary winding of the transformer and rectifies the current flowing through the secondary winding and outputs the rectified current to a load. The control circuit controls each of the first semiconductor switch, the second semiconductor switch, the third semiconductor switch, and the fourth semiconductor switch to an on state or an off state.

[0006] Fig. 1 is a schematic circuit diagram of an isolated AC / DC converter according to an embodiment of the present disclosure. Fig. 2 is a waveform diagram of an input current of the isolated AC / DC converter and a voltage generated in a primary winding of a transformer. Fig. 3 is a schematic circuit diagram illustrating a current path in a first operation mode of the isolated AC / DC converter. Fig. 4 is a schematic circuit diagram illustrating a current path in a second operation mode of the isolated AC / DC converter. Fig. 5 is a schematic circuit diagram illustrating a current path in a third operation mode of the isolated AC / DC converter.

[0007] Hereinafter, isolated AC / DC converters according to embodiments will be described in detail with reference to the drawings. The configurations described in the following embodiments are merely examples of the present disclosure. The present disclosure is not limited to the following embodiments, and various modifications are possible depending on the design, etc., as long as the effects of the present disclosure can be achieved.

[0008] (Embodiment) (1) Overview As shown in FIG. 1 , an isolated AC / DC converter 1 of this embodiment includes a first rectifier circuit 4, a first series circuit 2, a second series circuit 3, a third diode D3, a fourth diode D4, an inductor L1, a transformer 10, a second rectifier circuit 30, and a control circuit 20.

[0009] The first rectifier circuit 4 includes a series circuit of a first diode D1 and a second diode D2 whose cathode is connected to the anode of the first diode D1. A first terminal a1 of the AC power supply PS1 is connected to a connection point P5 between the first diode D1 and the second diode D2.

[0010] The first series circuit 2 includes a first semiconductor switch S1, a second semiconductor switch S2, a third semiconductor switch S3, and a fourth semiconductor switch S4 connected in series between the cathode of the first diode D1 and the anode of the second diode D2. In the first series circuit 2, a second end a2 of the AC power supply PS1 is connected to a connection point P1 between the second semiconductor switch S2 and the third semiconductor switch S3.

[0011] The second series circuit 3 includes a series circuit of a first capacitor C1 and a second capacitor C2, and is connected in parallel with the first series circuit 2.

[0012] The third diode D3 has a cathode connected to a connection point P3 between the first semiconductor switch S1 and the second semiconductor switch S2, and an anode connected to a connection point P2 between the first capacitor C1 and the second capacitor C2.

[0013] The fourth diode D4 has an anode connected to a connection point P4 between the third semiconductor switch S3 and the fourth semiconductor switch S4, and a cathode connected to a connection point P2 between the first capacitor C1 and the second capacitor C2.

[0014] The inductor L1 is connected between the AC power supply PS1 and at least one of the first rectifier circuit 4 and the first series circuit 2. In the circuit shown in Fig. 1, the inductor L1 is connected between the first series circuit 2 and the AC power supply PS1.

[0015] The transformer 10 has a primary winding 11 connected between a connection point P1 between the second semiconductor switch S2 and the third semiconductor switch S3 and a connection point P2 between the first capacitor C1 and the second capacitor C2.

[0016] The second rectifier circuit 30 is connected to the secondary winding 12 of the transformer 10 , rectifies the current flowing through the secondary winding 12 , and outputs the rectified current to a load 40 .

[0017] The control circuit 20 controls each of the first semiconductor switch S1, the second semiconductor switch S2, the third semiconductor switch S3, and the fourth semiconductor switch S4 to an on state or an off state.

[0018] Here, "two circuit elements being connected" refers to a state in which the two circuit elements are electrically connected, and is not limited to a state in which the two circuit elements are directly connected, but may also include a state in which the two circuit elements are indirectly connected via another circuit element. In the following description, the isolated AC / DC converter 1 will be abbreviated as "converter 1," and the first to fourth semiconductor switches S1 to S4 will also be abbreviated as "first to fourth switches S1 to S4," respectively. In FIG. 1 and other figures, the second rectifier circuit 30 will also be abbreviated as "rectifier circuit." The connection point P1 will also be referred to as the first connection point, and the connection point P2 will also be referred to as the second connection point.

[0019] In the converter 1 of this embodiment, the control circuit 20 controls the first to fourth switches S1 to S4 to an on or off state, thereby controlling the charging voltages of the first capacitor C1 and the second capacitor C2. Because a voltage higher than the charging voltages of the first capacitor C1 and the second capacitor C2 is not applied to the first to fourth switches S1 to S4, controlling the charging voltages of the first capacitor C1 and the second capacitor C2 can suppress the voltages applied to the first to fourth switches S1 to S4, allowing semiconductor switches with low voltage resistance to be used as the first to fourth switches S1 to S4.

[0020] In the converter 1 of this embodiment, a current flows through the primary winding 11 of the transformer 10, and power is supplied to the load 40 connected to the secondary winding 12 of the transformer 10 in two operation modes: one in which the first switch S1 and the second switch S2 are on and the third switch S3 and the fourth switch S4 are off (a first operation mode described below), and the other in which the third switch S3 and the fourth switch S4 are on and the first switch S1 and the second switch S2 are off (a third operation mode described below). Here, a current roughly proportional to the input voltage Vin from the AC power supply PS1 flows through the inductor L1, enabling the power factor to be improved with simple control without requiring the control circuit 20 to perform complex control. The control circuit 20 can adjust the proportion of the first operation mode and the third operation mode within one switching period in which the first to fourth switches S1 to S4 are switched, thereby adjusting the power supplied to the load 40.

[0021] (2) Details The isolated AC / DC converter (converter) 1 according to this embodiment will be described in detail below with reference to the drawings.

[0022] (2.1) Configuration FIG. 1 is a schematic circuit diagram of a converter 1.

[0023] The converter 1 is an isolated AC / DC converter that converts an AC voltage input from an AC power supply PS1 such as a commercial AC power supply into a DC voltage and supplies the DC voltage to a load 40 .

[0024] As described above, the converter 1 includes the first rectifier circuit 4, the first series circuit 2, the second series circuit 3, the third diode D3, the fourth diode D4, the inductor L1, the transformer 10, the second rectifier circuit 30, and the control circuit 20. The converter 1 also includes a filter circuit F1. Note that the first rectifier circuit 4, the third diode D3, the fourth diode D4, and the transformer 10 are as described in "(1) Overview," and therefore will not be described here.

[0025] As described above, the first series circuit 2 includes first to fourth switches S1 to S4 connected in series between the cathode of the first diode D1 and the anode of the second diode D2. The first to fourth switches S1 to S4 are connected between the cathode of the first diode D1 and the anode of the second diode D2 in the order of the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4. The first to fourth switches S1 to S4 are, for example, N-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). Each of the first to fourth switches S1 to S4 is controlled to an on or off state by a control signal input from the control circuit 20 to its gate electrode.

[0026] The second series circuit 3 includes a series circuit of a first capacitor C1 and a second capacitor C2 and is connected in parallel with the first series circuit 2. Here, the capacitance of the first capacitor C1 and the capacitance of the second capacitor C2 are the same. Note that the fact that the circuit constants (e.g., capacitances) of two circuit elements are the same does not necessarily mean that the circuit constants of the two circuit elements are completely identical, but may also include cases where the difference in the circuit constants of the two circuit elements is small enough to be considered a manufacturing error. Because the capacitances of the first capacitor C1 and the second capacitor C2 are set to the same value, the voltage at the connection point P2 between the first capacitor C1 and the second capacitor C2 is half the voltage Vbus across the second series circuit 3.

[0027] The control circuit 20 mainly comprises, for example, a computer system having one or more processors and a memory. The functions of the control circuit 20 are realized by the processor of the computer system executing a program stored in the memory of the computer system. The program may be stored in the memory, or may be provided via a telecommunications line such as the Internet, or may be provided by being recorded on a non-transitory recording medium such as a memory card.

[0028] The control circuit 20 receives, as feedback, for example, a voltage Vbus across a second series circuit 3 including a series circuit of a first capacitor C1 and a second capacitor C2, and a voltage V1 across a primary winding 11 of a transformer 10. The control circuit 20 controls the power supplied to the load 40 by controlling each of the first to fourth switches S1 to S4 to an on or off state based on the feedback values ​​of the voltage Vbus and the voltage V1, etc.

[0029] The filter circuit F1 is an LC filter including a coil L2 having a first end connected to the second end a2 of the AC power supply PS1, and a capacitor C3 connected between the first end a1 of the AC power supply PS1 and the second end of the coil L2.

[0030] The inductor L1 is connected between a connection point P1 between the second switch S2 and the third switch S3 and the second end a2 of the AC power supply PS1. More specifically, the inductor L1 is connected between the connection point P1 between the second switch S2 and the third switch S3 and the coil L2.

[0031] A pair of input terminals of the second rectifier circuit 30 are connected to both ends of the secondary winding 12 of the transformer 10. The second rectifier circuit 30 includes, for example, a diode bridge circuit in which a plurality of diodes are bridge-connected. A pair of input terminals of the diode bridge circuit are connected to the secondary winding 12 of the transformer 10. Here, the converter 1 preferably further includes, in a stage subsequent to the second rectifier circuit 30, a smoothing circuit that smooths the pulsating voltage output from the second rectifier circuit 30. The DC voltage rectified by the second rectifier circuit 30 and smoothed by the smoothing circuit is supplied to the load 40.

[0032] (2.2) Description of Operation The operation of the converter 1 of this embodiment will be described with reference to FIGS.

[0033] The control circuit 20 controls each of the first to fourth switches S1 to S4 to an on or off state by outputting a control signal to the gate electrodes of the first to fourth switches S1 to S4.

[0034] More specifically, the control circuit 20 controls each of the first to fourth switches S1 to S4 to an on or off state so as to cyclically repeat a first operation mode, a second operation mode, a third operation mode, and a fourth operation mode. In the first operation mode, the first switch S1 and the second switch S2 are on, and the third switch S3 and the fourth switch S4 are off. In the second and fourth operation modes, the second switch S2 and the third switch S3 are on, and the first switch S1 and the fourth switch S4 are off. In the third operation mode, the third switch S3 and the fourth switch S4 are on, and the first switch S1 and the second switch S2 are off.

[0035] The control circuit 20 controls the time lengths of the first, second, third and fourth operation modes so as to operate in a discontinuous mode in which the current I1 flowing through the inductor L1 is discontinuous.

[0036] The control circuit 20 controls the time length of the first operation mode and the time length of the third operation mode to be the same. The control circuit 20 controls the time lengths of the first, second, third, and fourth operation modes so that the voltage Vbus across the second series circuit 3 is at least twice the peak value of the input voltage Vin input from the AC power supply PS1. Note that the time lengths of the two operation modes being the same does not necessarily mean that the time lengths of the two operation modes are exactly the same, but may also include a state in which the difference in time length between the two operation modes is within ±several percent (e.g., ±10%) of either time length.

[0037] The operation of the converter 1 in the first to fourth operation modes will now be described with reference to Figures 2 to 5. Figures 2 to 5 describe the current path when the input voltage Vin from the AC power supply PS1 is in a positive half cycle in which the first terminal a1 has a higher potential than the second terminal a2.

[0038] 2 is a waveform diagram of the current I1 flowing through the inductor L1 and the voltage V1 generated in the primary winding 11 of the transformer 10. In FIG. 2, periods t1 to t4 indicate periods during which the device operates in the first to fourth operating modes, respectively. Furthermore, period T1 indicates the duration of one switching cycle of the first to fourth switches S1 to S4, and the switching frequency of the first to fourth switches S1 to S4 is, for example, approximately 100 kHz. Note that FIG. 2 shows the waveforms of the current I1 and voltage V1 for one switching cycle.

[0039] 3 to 5 are schematic circuit diagrams showing paths through which current flows in the first, second, and third operation modes, respectively. In these diagrams, the on / off states of the first to fourth switches S1 to S4 are shown schematically, and the control circuit 20 is not shown. The dotted arrows A1 to A5 in these diagrams indicate paths through which current flows.

[0040] When the period t1 of the first operating mode begins, the control circuit 20 controls the first switch S1 and the second switch S2 to an ON state and the third switch S3 and the fourth switch S4 to an OFF state, as shown in FIG. 3 . During the period t1 of the first operating mode, the voltage at the connection point P1 between the second switch S2 and the third switch S3 becomes equal to the voltage Vbus. In the first operating mode, current flows through the path indicated by the arrow A1: AC power supply PS1 → first diode D1 → first switch S1 → second switch S2 → inductor L1 → coil L2 → AC power supply PS1. As a result of the current flowing through the path indicated by the arrow A1, the current I1 flowing through the inductor L1 gradually increases during the period t1 of the first operating mode (see FIG. 2 ), and energy is stored in the inductor L1. Here, if the inductance of the inductor L1 is L, the current I1 gradually increases at a slope of Vin / L.

[0041] In the first operating mode, the first capacitor C1 is connected in parallel with the primary winding 11 of the transformer 10, so that the voltage V1 across the primary winding 11 of the transformer 10 is equal to the charging voltage (Vbus / 2) of the first capacitor C1 (see FIG. 2). At this time, a current flows through the path (indicated by the arrow A2) of the first capacitor C1 → first switch S1 → second switch S2 → primary winding 11 → first capacitor C1, and power is supplied to the secondary side of the transformer 10.

[0042] A second rectifier circuit 30 is connected to the secondary winding 12 of the transformer 10. The second rectifier circuit 30 rectifies the current generated in the secondary winding 12 of the transformer 10, and the smoothing circuit smooths the rectified current to generate a DC voltage of a predetermined voltage value, and DC power is supplied to the load 40.

[0043] When the period t1 of the first operation mode ends, the control circuit 20 switches the operation mode of the converter 1 from the first operation mode to the second operation mode. During the period t2 of the second operation mode, the control circuit 20 controls the second switch S2 and the third switch S3 to an ON state and the first switch S1 and the fourth switch S4 to an OFF state, as shown in FIG. 4 . In the second operation mode, the voltage at the connection point P1 between the second switch S2 and the third switch S3 is (Vbus / 2). In the second operation mode, current flows along the path indicated by the arrow A3: AC power supply PS1 → first diode D1 → first capacitor C1 → third diode D3 → second switch S2 → inductor L1 → coil L2 → AC power supply PS1. The inductor L1 releases the energy stored in the first operation mode to charge the first capacitor C1. In the second operating mode, the voltage applied to inductor L1 is (Vin-Vbus / 2), and because voltage Vbus is charged to a voltage greater than twice the maximum value of input voltage Vin, (Vin-Vbus / 2)<0. Therefore, current I1 flowing through inductor L1 gradually decreases at a slope of (Vin-Vbus / 2) / L.

[0044] In addition, in the second operating mode, both ends of the primary winding 11 of the transformer 10 are short-circuited in both directions via the series circuit of the second switch S2 and the third diode D3 and the series circuit of the third switch S3 and the fourth diode D4, so that no current flows through the primary winding 11 and no power is supplied to the secondary side of the transformer 10.

[0045] When the period t2 of the second operation mode ends, the control circuit 20 switches the operation mode of the converter 1 from the second operation mode to the third operation mode. During the period t3 of the third operation mode, the control circuit 20 controls the third switch S3 and the fourth switch S4 to an on state and the first switch S1 and the second switch S2 to an off state, as shown in FIG. 5 . In the third operation mode, the voltage at the connection point P1 of the second switch S2 and the third switch S3 becomes zero. In the third operation mode, a current flows through the path (indicated by arrow A4) of the AC power supply PS1 → first diode D1 → first capacitor C1 → second capacitor C2 → fourth switch S4 → third switch S3 → inductor L1 → coil L2 → AC power supply PS1, causing the inductor L1 to release energy and charge the first capacitor C1 and the second capacitor C2. Here, the voltage applied to inductor L1 is (Vin - Vbus), and because Vbus is charged to a voltage greater than twice the maximum value of input voltage Vin, (Vin - Vbus) < 0. Therefore, current I1 flowing through inductor L1 gradually decreases at a slope of (Vin - Vbus) / L (see FIG. 2). Because control circuit 20 controls the duration of the first operating mode (period t1) and the duration of the third operating mode (period t3) to be the same, current I1 always decreases to zero in the second operating mode or the third operating mode, and does not flow again until the operating mode is switched back to the first operating mode.

[0046] In the third operating mode, the second capacitor C2 is connected in parallel with the primary winding 11 of the transformer 10, and the voltage V1 across the primary winding 11 of the transformer 10 is equal to (−Vbus / 2) (see FIG. 2). At this time, a current flows through the path (indicated by the arrow A5) of the second capacitor C2 → primary winding 11 → third switch S3 → fourth switch S4 → second capacitor C2, and power is supplied to the secondary side of the transformer 10.

[0047] When the period t3 of the third operation mode ends, the control circuit 20 switches the operation mode of the converter 1 from the third operation mode to the fourth operation mode. During the period t4 of the fourth operation mode, the control circuit 20 controls the second switch S2 and the third switch S3 to an on state and the first switch S1 and the fourth switch S4 to an off state. The states of the first to fourth switches S1 to S4 in the fourth operation mode are the same as those of the first to fourth switches S1 to S4 in the second operation mode. Even in the fourth operation mode, both ends of the primary winding 11 of the transformer 10 are short-circuited in both directions via the series circuit of the second switch S2 and the third diode D3 and the series circuit of the third switch S3 and the fourth diode D4. Therefore, no current flows through the primary winding 11, and no power is supplied to the secondary side of the transformer 10. Furthermore, since the discharge of the inductor L1 has finished and the current I1 has become zero in the third operation mode, the current I1 also does not flow in the fourth operation mode.

[0048] After that, when the period t4 of the fourth operation mode ends, the control circuit 20 switches the operation mode of the converter 1 from the fourth operation mode to the first operation mode. The operation of the first operation mode is as described above. Here, the current I1 is zero from the middle of the third operation mode to the start of the first operation mode, so the first switch S1 can be switched from the OFF state to the ON state while the current I1 is zero. Because the first switch S1 switches from the OFF state to the ON state while the current is zero, zero current switching (ZCS) can be performed, thereby reducing switching loss.

[0049] In this embodiment, the control circuit 20 controls the first to fourth switches S1 to S4 so that the first, second, third, and fourth operation modes are periodically repeated in this order, thereby controlling the voltage Vbus across the second series circuit 3 and the voltage V1 applied to the primary winding 11 of the transformer 10. The converter 1 of this embodiment is a multilevel converter circuit in which the voltage at the connection point between the second switch S2 and the third switch S3 changes between three levels: Vbus, (Vbus / 2), and 0. The control circuit 20 controls the time lengths of the first, second, third, and fourth operation modes so that the time lengths of the first and third operation modes are the same and the voltage Vbus across the second series circuit 3 is at least twice the peak value of the input voltage Vin input from the AC power supply PS1. By performing such control by the control circuit 20, the current I1 becomes zero during operation in the third operation mode, and switching operation can be performed in a discontinuous mode in which the current I1 is discontinuous. In addition, since the current I1 flows in a manner roughly proportional to the input voltage Vin from the AC power supply PS1, there is an advantage that the power factor can be improved with simple control.

[0050] Note that, even during a negative half cycle of the input voltage Vin from the AC power supply PS1, the control circuit 20 controls the first to fourth switches S1 to S4 to cyclically repeat the first, second, third, and fourth operation modes in this order. During a negative half cycle of the input voltage Vin from the AC power supply PS1, energy is stored in the inductor L1 in the third operation mode, and the energy stored in the inductor L1 is released in the fourth operation mode and the first operation mode, which follow the third operation mode. Note that, although a description of the operation of the converter 1 during the negative half cycle of the input voltage Vin will be omitted, during the negative half cycle of the input voltage Vin, energy is stored in the inductor L1 during a third period t3, and the energy stored in the inductor L1 is released during a fourth period t4 following the third period t3 and during the first period t1.

[0051] The converter 1 supplies power to the secondary side of the transformer 10 in the first and third operation modes and stops power supply to the secondary side of the transformer 10 in the second and fourth operation modes. The control circuit 20 controls the duration of the first and third operation modes to be the same, and adjusts the ratio between the total duration of the first and third operation modes and the total duration of the second and fourth operation modes, thereby controlling the power supplied to the load 40. The greater the ratio of the duration of the first and third operation modes in one cycle T1 of the switching period, the greater the power supplied to the load 40. Therefore, the control circuit 20 can adjust the period during which power is supplied to the secondary side of the transformer 10 by adjusting the ratio between the total duration of the first and third operation modes and the total duration of the second and fourth operation modes. Therefore, the control circuit 20 can adjust the power supplied to the load 40 without changing the switching frequencies of the first to fourth switches S1 to S4.

[0052] (3) Modifications The above embodiment is merely one of various embodiments of the present disclosure. The above embodiment can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0053] Modifications of the above embodiment are listed below. The modifications described below can be applied in appropriate combinations. Hereinafter, the above embodiment may also be referred to as the basic configuration.

[0054] The converter 1 of the present disclosure includes a computer system. The computer system is primarily composed of a processor and memory as hardware. The processor executes a program stored in the memory of the computer system to realize the functions of the control circuit 20 of the converter 1 of the present disclosure. The program may be pre-stored in the memory of the computer system, provided via a telecommunications line, or provided on a non-transitory recording medium readable by the computer system, such as a memory card, optical disk, or hard disk drive. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). The integrated circuits, such as ICs and LSIs, are referred to by different names depending on the degree of integration, and include integrated circuits called system LSIs, very large-scale integrations (VLSIs), or ultra-large-scale integrations (ULSIs). Furthermore, field-programmable gate arrays (FPGAs), which are programmed after the LSI is manufactured, or logic devices capable of reconfiguring the connections within the LSI or the circuit partitions within the LSI, can also be used as processors. The electronic circuits may be integrated into one chip or distributed across multiple chips. The chips may be integrated into one device or distributed across multiple devices. The computer system referred to here includes a microcontroller having one or more processors and one or more memories. Therefore, the microcontroller is also composed of one or more electronic circuits including a semiconductor integrated circuit or a large-scale integrated circuit.

[0055] In the above embodiment, the control circuit 20 controls the AC power supply PS1 to periodically repeat the first, second, third, and fourth operation modes. However, the operation modes in which the current flowing through the inductor L1 is zero and no power is supplied to the secondary side of the transformer 10 can be omitted as appropriate. For example, the control circuit 20 may control the AC power supply PS1 to periodically repeat the first, second, and third operation modes by setting the period of the fourth operation mode to zero during a positive half cycle in which the first terminal a1 of the AC power supply PS1 is at a higher potential than the second terminal a2. Furthermore, the control circuit 20 may control the AC power supply PS1 to periodically repeat the first, third, and fourth operation modes by setting the period of the second operation mode to zero during a negative half cycle in which the first terminal a1 of the AC power supply PS1 is at a lower potential than the second terminal a2. In this way, omitting the fourth operation mode or the second operation mode and controlling the AC power supply PS1 to periodically repeat the remaining three operation modes has the advantage of shortening the switching period.

[0056] In the above embodiment, the first to fourth semiconductor switches S1 to S4 are N-channel MOSFETs, but the first to fourth semiconductor switches S1 to S4 may also be semiconductor switches such as bipolar transistors or IGBTs (Insulated Gate Bipolar Transistors).

[0057] In the above embodiment, the inductor L1 is connected between the first series circuit 2 and the AC power supply PS1, but the inductor L1 may be connected between the first rectifier circuit 4 and the AC power supply PS1, that is, between the connection point P5 of the first diode D1 and the second diode D2 and the first end a1 of the AC power supply PS1. Furthermore, the inductor L1 may be connected between the first series circuit 2 and the AC power supply PS1, and between the first rectifier circuit 4 and the AC power supply PS1.

[0058] In the above embodiment, the converter 1 includes a filter circuit F1 such as an LC filter, but the circuit configuration of the filter circuit F1 can be changed as appropriate. The filter circuit F1 is not an essential component of the converter 1 and can be omitted as appropriate.

[0059] Furthermore, in the above embodiment, the second rectifier circuit 30 including a diode bridge circuit is connected to the secondary side of the transformer 10, but the configuration of the second rectifier circuit 30 can be changed as appropriate, and it may also be a full-bridge type synchronous rectifier circuit configured with semiconductor switches, or the like.

[0060] (Summary) The above-described embodiments and the like disclose the following aspects.

[0061] An isolated AC / DC converter (1) of a first aspect includes a first rectifier circuit (4), a first series circuit (2), a second series circuit (3), a third diode (D3), a fourth diode (D4), an inductor (L1), a transformer (10), a second rectifier circuit (30), and a control circuit (20). The first rectifier circuit (4) includes a series circuit of a first diode (D1) and a second diode (D2) having a cathode connected to the anode of the first diode (D1), and a first end (a1) of an AC power supply (PS1) is connected to a connection point between the first diode (D1) and the second diode (D2). The first series circuit (2) includes a first semiconductor switch (S1), a second semiconductor switch (S2), a third semiconductor switch (S3), and a fourth semiconductor switch (S4) connected in series between the cathode of the first diode (D1) and the anode of the second diode (D2), and a second end (a2) of the AC power supply (PS1) is connected to a connection point between the second semiconductor switch (S2) and the third semiconductor switch (S3). The second series circuit (3) includes a series circuit of a first capacitor (C1) and a second capacitor (C2) and is connected in parallel with the first series circuit (2). The third diode (D3) has a cathode connected to the connection point between the first semiconductor switch (S1) and the second semiconductor switch (S2) and an anode connected to the connection point between the first capacitor (C1) and the second capacitor (C2). The fourth diode (D4) has an anode connected to the connection point between the third semiconductor switch (S3) and the fourth semiconductor switch (S4) and a cathode connected to the connection point between the first capacitor (C1) and the second capacitor (C2). The inductor (L1) is connected between the AC power supply (PS1) and at least one of the first rectifier circuit (4) and the first series circuit (2). The transformer (10) has a primary winding (11) connected between the connection point between the second semiconductor switch (S2) and the third semiconductor switch (S3) and the connection point between the first capacitor (C1) and the second capacitor (C2). The second rectifier circuit (30) is connected to the secondary winding (12) of the transformer (10) and rectifies the current flowing through the secondary winding (12) and outputs the rectified current to the load (40). The control circuit (20) controls each of the first semiconductor switch (S1), the second semiconductor switch (S2), the third semiconductor switch (S3), and the fourth semiconductor switch (S4) to an on state or an off state.

[0062] According to this aspect, in a first operating mode in which the first semiconductor switch (S1) and the second semiconductor switch (S2) are turned on and the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are turned off, a current flows through the primary winding (11) of the transformer (10), and power is supplied to a load (40) connected to the secondary winding (12) of the transformer (10). Also, in a third operating mode in which the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are turned on and the first semiconductor switch (S1) and the second semiconductor switch (S2) are turned off, a current flows through the primary winding (11) of the transformer (10), and power is supplied to a load (40) connected to the secondary winding (12) of the transformer (10). Therefore, the control circuit (20) can adjust the proportion of the first operating mode and the third operating mode within one switching period in which the first to fourth semiconductor switches (S1 to S4) are switched, thereby adjusting the power supplied to the load (40). Furthermore, since a current roughly proportional to the input voltage from the AC power supply (PS1) flows through the inductor (L1), an isolated AC / DC converter (1) capable of improving the power factor can be realized with simple control.

[0063] In the isolated AC / DC converter (1) of the second aspect, the capacitance of the first capacitor (C1) and the capacitance of the second capacitor (C2) are the same as in the first aspect.

[0064] According to this aspect, the voltage at the connection point between the first capacitor (C1) and the second capacitor (C2) can be set to half the voltage (Vbus) across the second series circuit (3).

[0065] In the isolated AC / DC converter (1) of the third aspect, in the first or second aspect, the control circuit (20) controls the converter (1) to periodically repeat a first operation mode, a second operation mode, a third operation mode, and a fourth operation mode. In the first operation mode, the first semiconductor switch (S1) and the second semiconductor switch (S2) are in an ON state, and the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are in an OFF state. In the second operation mode and the fourth operation mode, the second semiconductor switch (S2) and the third semiconductor switch (S3) are in an ON state, and the first semiconductor switch (S1) and the fourth semiconductor switch (S4) are in an OFF state. In the third operation mode, the third semiconductor switch (S3) and the fourth semiconductor switch (S4) are in an ON state, and the first semiconductor switch (S1) and the second semiconductor switch (S2) are in an OFF state.

[0066] According to this aspect, by periodically repeating the first to fourth operation modes, it is possible to convert the input voltage (Vin) from the AC power supply (PS1) into a DC voltage and supply it to the load (40).

[0067] In the isolated AC / DC converter (1) of the fourth aspect, in the third aspect, the control circuit (20) controls the time lengths of the first, second, third, and fourth operation modes so as to operate in a discontinuous mode in which the current flowing through the inductor (L1) is discontinuous.

[0068] According to this aspect, the zero current switching can be performed to reduce switching loss.

[0069] In the isolated AC / DC converter (1) of the fifth aspect, in the fourth aspect, the control circuit (20) controls the time length of the first operation mode and the time length of the third operation mode to be the same time length, and controls the time lengths of the first operation mode, the second operation mode, the third operation mode, and the fourth operation mode so that the voltage (Vbus) between both ends of the second series circuit (3) is at least twice the peak value of the input voltage (Vin) input from the AC power supply (PS1).

[0070] According to this embodiment, it is possible to operate in discontinuous mode.

[0071] In the isolated AC / DC converter (1) of a sixth aspect, in any one of the third to fifth aspects, the control circuit (20) controls the time length of the first operation mode and the time length of the third operation mode to be the same time length. The control circuit (20) controls the power supply to the load (40) by adjusting the ratio between the total time length of the first operation mode and the third operation mode and the total time length of the second operation mode and the fourth operation mode.

[0072] According to this aspect, power is supplied to the load (40) in the first and third operating modes, and power supply to the load (40) is stopped in the second and fourth operating modes, so that the power supply to the load (40) can be controlled by adjusting the ratio between the time length of the first operating mode (or the time length of the second operating mode) and the time length of the second operating mode (or the time length of the fourth operating mode).

[0073] In the isolated AC / DC converter (1) of a seventh aspect, in any of the third to sixth aspects, the control circuit (20) controls the first, second, and third operation modes to be periodically repeated by setting the period of the fourth operation mode to zero during a positive half cycle in which the first terminal (a1) of the AC power supply (PS1) is at a higher potential than the second terminal (a2).The control circuit (20) controls the first, second, and fourth operation modes to be periodically repeated by setting the period of the second operation mode to zero during a negative half cycle in which the first terminal (a1) of the AC power supply (PS1) is at a lower potential than the second terminal (a2).

[0074] According to this aspect, the switching period can be shortened.

[0075] In the isolated AC / DC converter (1) of an eighth aspect, in any one of the first to seventh aspects, the second rectifier circuit (30) includes a diode bridge circuit.

[0076] According to this aspect, the second rectifier circuit (30) is configured as a diode bridge circuit that does not require control, so that the configuration of the control circuit (20) can be simplified.

[0077] The configurations according to the second to eighth aspects are not essential for the isolated AC / DC converter (1) and can be omitted as appropriate.

[0078] REFERENCE SIGNS LIST 1 Isolated AC / DC converter 2 First series circuit 3 Second series circuit 4 Rectifier circuit (first rectifier circuit) 10 Transformer 11 Primary winding 12 Secondary winding 20 Control circuit 30 Rectifier circuit (second rectifier circuit) 40 Load a1 First terminal a2 Second terminal C1 First capacitor C2 Second capacitor D1 First diode D2 Second diode D3 Third diode D4 Fourth diode L1 Inductor PS1 AC power supply S1 First semiconductor switch S2 Second semiconductor switch S3 Third semiconductor switch S4 Fourth semiconductor switch

Claims

1. A first rectifier circuit including a series circuit of a first diode and a second diode, the cathode of which is connected to the anode of the first diode, and a first end of an AC power supply is connected to a connection point of the first diode and the second diode; a first series circuit including a first semiconductor switch, a second semiconductor switch, a third semiconductor switch, and a fourth semiconductor switch connected in series between the cathode of the first diode and the anode of the second diode, and a second end of the AC power supply is connected to a connection point of the second semiconductor switch and the third semiconductor switch; a second series circuit including a series circuit of a first capacitor and a second capacitor, and connected in parallel with the first series circuit; a third diode, the cathode of which is connected to the connection point of the first semiconductor switch and the second semiconductor switch, and the anode of which is connected to the connection point of the first capacitor and the second capacitor; and a fourth diode, the anode of which is connected to the connection point of the third semiconductor switch and the fourth semiconductor switch, and the cathode of which is connected to the connection point of the first capacitor and the second capacitor. an inductor connected between at least one of the first rectifier circuit and the first series circuit and the AC power supply; a transformer having a primary winding connected between a connection point of the second semiconductor switch and the third semiconductor switch and a connection point of the first capacitor and the second capacitor; a second rectifier circuit connected to a secondary winding of the transformer, rectifying a current flowing through the secondary winding and outputting the current to a load; and a control circuit controlling each of the first semiconductor switch, the second semiconductor switch, the third semiconductor switch, and the fourth semiconductor switch to an on state or an off state.

2. The isolated AC / DC converter according to claim 1, wherein the capacitance of the first capacitor and the capacitance of the second capacitor are the same.

3. The isolated AC / DC converter according to claim 1 or 2, wherein the control circuit performs control to cyclically repeat a first operation mode, a second operation mode, a third operation mode, and a fourth operation mode, wherein in the first operation mode, the first semiconductor switch and the second semiconductor switch are in an on state, and the third semiconductor switch and the fourth semiconductor switch are in an off state, wherein in the second operation mode and the fourth operation mode, the second semiconductor switch and the third semiconductor switch are in an on state, and the first semiconductor switch and the fourth semiconductor switch are in an off state, and wherein in the third operation mode, the third semiconductor switch and the fourth semiconductor switch are in an on state, and the first semiconductor switch and the second semiconductor switch are in an off state.

4. The isolated AC / DC converter according to claim 3, wherein the control circuit controls the time lengths of the first operation mode, the second operation mode, the third operation mode, and the fourth operation mode so as to operate in a discontinuous mode in which the current flowing through the inductor is discontinuous.

5. The isolated AC / DC converter according to claim 4, wherein the control circuit controls the time length of the first operation mode and the time length of the third operation mode to be the same, and controls the time lengths of the first operation mode, the second operation mode, the third operation mode and the fourth operation mode so that the voltage between both ends of the second series circuit is at least twice the peak value of the input voltage input from the AC power supply.

6. The isolated AC / DC converter according to any one of claims 3 to 5, wherein the control circuit controls the time length of the first operation mode and the time length of the third operation mode to be the same time length, and controls the power supplied to the load by adjusting a ratio between a total time length of the first operation mode and a total time length of the third operation mode and a total time length of the second operation mode and a total time length of the fourth operation mode.

7. The isolated AC / DC converter according to any one of claims 3 to 6, wherein the control circuit controls the first, second, and third operation modes to be repeated cyclically, with a period of the fourth operation mode set to zero in a positive half cycle in which the first end of the AC power supply is at a higher potential than the second end, and controls the first, second, and fourth operation modes to be repeated cyclically, with a period of the second operation mode set to zero in a negative half cycle in which the first end of the AC power supply is at a lower potential than the second end.

8. The isolated AC / DC converter according to any one of claims 1 to 7, wherein the second rectifier circuit includes a diode bridge circuit.

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