Alternating current insulation circuit and alternating current power supply circuit using same

Abstract

An AC insulated circuit (1) is provided with: an insulated DC-DC converter (21) provided with an input positive electrode connected to a positive input terminal (P1), an input negative electrode connected to a negative input terminal (P2), an output positive electrode connected to a first output terminal (S1), and an output negative electrode connected to a second output terminal (S2); a first capacitor Cb1 connected between the positive input terminal P1 and the input positive electrode; a first DC power source (11) connected in parallel to the first capacitor (Cb1) and outputting a first DC voltage (Vcb1) for charging the first capacitor (Cb1); a second capacitor Cb2 connected between the first output terminal S1 and the output positive electrode; and a second DC power source (12) connected in parallel to the second capacitor (Cb2) and outputting a second DC voltage (Vcb2) for charging the second capacitor (Cb2).

Description

Technical Field

[0001] The present invention relates to an AC insulation circuit and an AC power supply circuit using the AC insulation circuit. Background Art

[0002] As an AC isolation circuit, usually use Figure 17 Schematic diagram of an insulating transformer for commercial voltage. Figure 17 Commercial voltage isolation transformers are designed for commercial voltage frequency f, for example, 50 [Hz]. Generally, the core of the transformer must be used below the saturation magnetic flux density.

[0003] Figure 18 This shows the relationship between the applied commercial voltage V, the magnetic flux density B in the core of the commercial voltage isolation transformer, and the phase θ=ωt (ω is the angular frequency of the commercial voltage V, ω=2πf, and t is time). Since the magnetic flux density changes from -B to +B (-B to +B) in response to the applied voltage on the positive side, the maximum magnetic flux density is calculated by integrating over a quarter period (π / 2). The maximum magnetic flux density Bm is calculated using (Equation 1).

[0004] [Mathematical formula 1]

[0005] …(Equation 1)

[0006] Here, E is the effective value voltage of the commercial voltage V, N is the number of turns of the primary winding of the transformer, and S is the cross-sectional area of ​​the core of the transformer.

[0007] Figure 19 This diagram schematically illustrates a conventional circuit diagram of a commercial voltage isolation transformer used to convert a single-phase, two-wire commercial voltage into a single-phase, three-wire AC voltage. For example, if an AC voltage of 100V RMS and a frequency of 50Hz is input to the primary winding Lp as the commercial voltage AC, an AC voltage of 100V RMS and a frequency of 50Hz is output between the red and white terminals (Vo1) of the first secondary winding Ls1 and between the white and black terminals (Vo2) of the second secondary winding Ls2. An AC voltage of 200V RMS and a frequency of 50Hz is output between the red and black terminals (Vo1 + Vo2).

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-129922

[0011] Patent Document 2: Japanese Patent No. 6564102 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] In commercial voltage isolation transformers, the commercial voltage V used has a relatively low frequency of 50 Hz. Therefore, as can be seen from Equation 1, the magnetic flux density B becomes very high. To address this, commercial voltage isolation transformers typically use silicon steel sheets with high saturation magnetic flux density as their core. Consequently, commercial voltage isolation transformers become very large and heavy.

[0014] An object of the present invention is to provide a small and lightweight AC isolation circuit and an AC power supply circuit using the AC isolation circuit.

[0015] Means for solving problems

[0016] An AC isolation circuit according to one embodiment of the present invention comprises: a positive input terminal and a negative input terminal, to which a first AC voltage having a first frequency is input; a first output terminal and a second output terminal; and an isolated DC-DC converter controlled by a second frequency higher than the first frequency, comprising an input positive electrode connected to the positive input terminal, an input negative electrode connected to the negative input terminal, an output positive electrode connected to the first output terminal, and an output negative electrode connected to the second output terminal, wherein the input positive electrode and the input negative electrode, and the output positive electrode and the output negative electrode are connected to each other. The electrodes are insulated; a first capacitor is connected to at least one of between the positive input terminal and the input positive electrode and between the negative input terminal and the input negative electrode; a first DC power supply is connected in parallel with the first capacitor and outputs a first DC voltage for charging the first capacitor; a second capacitor is connected to at least one of between the first output terminal and the output positive electrode and between the second output terminal and the output negative electrode; and a second DC power supply is connected in parallel with the second capacitor and outputs a second DC voltage for charging the second capacitor.

[0017] Effects of the Invention

[0018] According to the present invention, a small and lightweight AC insulation circuit and an AC power supply circuit using the AC insulation circuit can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a circuit diagram of the AC insulation circuit according to the first embodiment.

[0020] Figure 2 This is a timing chart showing the waveforms of various parts of the AC insulation circuit.

[0021] Figure 3 This is a circuit diagram of an isolated DC-DC converter used in an AC isolation circuit.

[0022] Figure 4A It means in Figure 3 This is a timing diagram of the waveforms of various components in an isolated DC-DC converter when the input voltage Vi = E and a load is present at the output end.

[0023] Figure 4B It means in Figure 3 This is a timing diagram of the waveforms of various components in an isolated DC-DC converter when the input voltage Vi = E and there is no load at the output end.

[0024] Figure 4C It means in Figure 3 This is a timing diagram of the waveforms of various components in an isolated DC-DC converter when the input voltage Vi = E / 2 and a load is present at the output.

[0025] Figure 4D It means in Figure 3 This is a timing diagram of the waveforms of various components in an isolated DC-DC converter when the input voltage Vi = E / 2 and there is no load at the output end.

[0026] Figure 5 This is a circuit diagram showing an isolated DC-DC converter according to a first modification.

[0027] Figure 6 This is a circuit diagram showing an isolated DC-DC converter according to a second modification.

[0028] Figure 7 This is a circuit diagram showing an isolated DC-DC converter according to a third modification.

[0029] Figure 8 This is a circuit diagram showing an isolated DC-DC converter according to a fourth modification.

[0030] Figure 9 This is a circuit diagram showing an isolated DC-DC converter according to a fifth modification.

[0031] Figure 10 This is a circuit diagram of an AC insulation circuit according to a second embodiment.

[0032] Figure 11 It is a timing chart showing waveforms of various parts of the AC insulation circuit according to the second embodiment.

[0033] Figure 12 This is a circuit diagram of an AC insulation circuit according to a modification of the second embodiment.

[0034] Figure 13It is a timing chart showing waveforms of various parts of the AC insulation circuit according to the modification of the second embodiment.

[0035] Figure 14 This is a circuit diagram of a single-phase three-wire AC power supply circuit according to the third embodiment.

[0036] Figure 15 This is a timing chart showing waveforms of various components of the single-phase three-wire AC power supply circuit according to the third embodiment.

[0037] Figure 16 This is a circuit diagram of a single-phase three-wire AC power supply circuit according to a modification of the third embodiment.

[0038] Figure 17 This is a schematic diagram showing the structure of a conventional AC insulation circuit (commercial voltage insulation transformer).

[0039] Figure 18 This is a graph showing the relationship between the phase of the commercial voltage applied to the commercial voltage isolation transformer and the magnetic flux density and phase of the core of the commercial voltage isolation transformer.

[0040] Figure 19 This is a diagram schematically showing a conventional example of a circuit of a commercial voltage insulating transformer for converting a single-phase two-wire commercial voltage into a single-phase three-wire AC voltage. DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Elements having the same functions are denoted by the same reference numerals, and repeated descriptions are omitted. The present invention is not limited to the embodiments described below.

[0042] (First embodiment)

[0043] Figure 1 This is a circuit diagram of an AC isolation circuit 1 according to a first embodiment. The AC isolation circuit 1 converts an AC voltage Vaci of a commercial AC power source AC, which is an input first AC voltage, into an AC output voltage Vaco, which is a second AC voltage isolated from the commercial AC power source AC, and outputs the converted voltage.

[0044] As the AC voltage Vaci of the commercial AC power source AC, for example, an AC voltage having a first frequency of f = 50 Hz and an effective voltage of 100 V supplied from a power company is used. The AC isolation circuit 1 converts the AC voltage Vaci of the commercial AC power source AC into an AC output voltage Vaco having a frequency of f = 50 Hz and an effective voltage of 100 V, which is isolated from the commercial AC power source AC and has the same specifications as the commercial AC power source AC. The AC isolation circuit 1 can also set the effective voltage of the AC voltage Vaci of the commercial AC power source AC and the effective voltage of the AC output voltage Vaco to different values.

[0045] AC isolation circuit 1 includes a positive input terminal P1, a negative input terminal P2, a first capacitor Cb1, a first DC power supply 11, an isolated DC-DC converter 21, a second capacitor Cb2, a second DC power supply 12, a first output terminal S1, and a second output terminal S2. The positive and negative electrodes of a commercial AC power supply AC are connected to the positive and negative input terminals P1 and P2.

[0046] The isolated DC-DC converter 21 is a high-frequency switching bidirectional DC-DC converter with a substantially constant conversion ratio between input voltage and output voltage. The input and output sides are insulated. Specifically, the isolated DC-DC converter 21 has a predetermined conversion ratio, converting the input voltage at that predetermined conversion ratio and outputting the converted voltage. While the conversion ratio between the input voltage and output voltage of the isolated DC-DC converter 21 is set to 1, the conversion ratio can be set to any value other than 1.

[0047] Positive input terminal P1 is connected to the positive input terminal of isolated DC-DC converter 21 via first capacitor Cb1. First DC power supply 11 is connected in parallel with first capacitor Cb1. Negative input terminal P2 is connected to the negative input terminal of isolated DC-DC converter 21. Input capacitor Ci is connected between the positive and negative input terminals of isolated DC-DC converter 21. First DC power supply 11 is insulated from commercial AC power supply AC.

[0048] Furthermore, the first capacitor Cb1 is not limited to being connected between the positive input terminal P1 and the positive input electrode of the isolated DC-DC converter 21. Instead, it may be connected between the negative input terminal P2 and the negative input electrode of the isolated DC-DC converter 21. Furthermore, the first capacitor Cb1 may be connected both between the positive input terminal P1 and the positive input electrode of the isolated DC-DC converter 21 and between the negative input terminal P2 and the negative input electrode of the isolated DC-DC converter 21. In either case, the first DC power supply 11 is connected in parallel with the first capacitor Cb1.

[0049] The first capacitor Cb1 is charged to a predetermined first DC voltage Vcb1 by the first DC power supply 11. For example, the first DC voltage Vcb1 is set to a voltage sufficient to reliably level-shift the peak voltage on the negative side of the commercial AC power supply AC toward the positive side in all phases. Specifically, the first DC voltage Vcb1 is set to a value obtained by multiplying the effective value of the AC voltage Vaci of the commercial AC power supply AC by √2 and then adding an additional DC voltage α (α > 0) (effective value of Vaci × √2 + α).

[0050] A first positive voltage Vi, a voltage obtained by adding a first DC voltage Vcb1 to an AC voltage Vaci, is input between the negative and positive input terminals of the isolated DC-DC converter 21. The isolated DC-DC converter 21 converts the input first positive voltage Vi into a second positive voltage Vo that has a voltage conversion ratio of 1 with respect to the first positive voltage Vi and is insulated from the first positive voltage Vi, and outputs the second positive voltage Vo between the negative and positive output terminals.

[0051] The positive output electrode of the isolated DC-DC converter 21 is connected to the first output terminal S1 via the second capacitor Cb2. The second DC power supply 12 is connected in parallel to the second capacitor Cb2. The negative output electrode of the isolated DC-DC converter 21 is connected to the second output terminal S2. The second DC power supply 12 is insulated from the commercial AC power supply AC and the first DC power supply 11.

[0052] Furthermore, the second capacitor Cb2 is not limited to being connected between the positive output electrode of the isolated DC-DC converter 21 and the first output terminal S1. Instead, it may be connected between the negative output electrode of the isolated DC-DC converter 21 and the second output terminal S2. Furthermore, the second capacitor Cb2 may be connected between the positive output electrode of the isolated DC-DC converter 21 and the first output terminal S1, and between the negative output electrode of the isolated DC-DC converter 21 and the second output terminal S2. In either case, the second DC power supply 12 is connected in parallel with the second capacitor Cb2.

[0053] The second capacitor Cb2 is charged to a predetermined second DC voltage Vcb2 by the second DC power supply 12. The second DC voltage Vcb2 is set to a voltage obtained by subtracting a predetermined DC voltage component from the second positive voltage Vo. For example, if the voltage conversion ratio of the isolated DC-DC converter 21 is 1, the second DC voltage Vcb2 can be set to a value obtained by subtracting a voltage having an absolute value equal to the first DC voltage Vcb1 from the second positive voltage Vo. Alternatively, the second DC voltage Vcb2 can be set to a value obtained by subtracting the average potential of the second positive voltage Vo or a potential close thereto from the average potential of the second positive voltage Vo.

[0054] An AC output voltage Vaco, obtained by subtracting the second DC voltage Vcb2 from the second positive voltage Vo, is output between the first output terminal S1 and the second output terminal S2. When the conversion ratio of the isolated DC-DC converter 21 is 1, the AC output voltage Vaco is isolated from the AC voltage Vaci of the commercial AC power supply AC and has the same frequency and amplitude.

[0055] For example, a general DC constant voltage source can be used as the first DC power supply 11 and the second DC power supply 12. Alternatively, the first DC power supply 11 and the second DC power supply 12 may be configured to apply a DC voltage obtained by rectifying the AC voltage Vaci of the commercial AC power supply AC and then converting it through an isolated DC-DC converter such as a flyback converter.

[0056] Next, use Figure 2 The waveforms of the various parts of the AC insulation circuit 1 are explained with reference to the timing diagram of FIG.

[0057] Figure 2 (1) is the waveform of the AC voltage Vaci of the commercial AC power supply AC input to the AC isolation circuit 1. If the effective value voltage Vaci of the commercial AC power supply AC input to the AC isolation circuit 1 is 100 [V] and the frequency is 50 [Hz], then the peak voltage on the positive side of the sine wave is √2 times the effective value voltage +141 [V], and the peak voltage on the negative side is -141 [V], and one period of the sine wave is 20 [ms].

[0058] Figure 2 (2) represents the first DC voltage Vcb1 applied to both ends of the first capacitor Cb1 by the first DC power supply 11. The first DC voltage Vcb1 is a positive DC voltage having a value greater than or equal to the absolute value of the negative peak value of the AC voltage Vaci. More preferably, the first DC voltage Vcb1 is a positive DC voltage having a value obtained by adding the absolute value of the negative peak value of the AC voltage Vaci to an additional DC voltage α [V] (α>0). In other words, if the AC voltage Vaci is a sine wave with an effective voltage of 100 [V] and a frequency of 50 [Hz], the first DC voltage Vcb1 can be set to ≥ 141 [V]. More preferably, the first DC voltage Vcb1 can be set to 141 + α [V].

[0059] So, if Figure 2 As shown in (3), the first positive voltage Vi applied between the input negative electrode and the input positive electrode of the isolated DC-DC converter 21 is shifted to the positive side by adding the first DC voltage Vcb1 to the AC voltage Vaci, and the negative side component disappears, leaving only the positive side component.

[0060] Since the first positive voltage Vi does not include a negative component, the first positive voltage Vi is converted into a positive voltage by the isolated DC-DC converter 21. Figure 2 As shown in (4), a second positive voltage Vo of the same waveform as the first positive voltage Vi is insulated.

[0061] By subtracting the second positive voltage Vo from Figure 2 The second DC voltage Vcb2, whose absolute value is equal to the first DC voltage Vcb1, is generated as shown in (5). Figure 2 The AC output voltage Vaco is as shown in (6).

[0062] In this way, the AC insulation circuit 1 can Figure 2 (1) The AC voltage Vaci of the commercial AC power source AC is input as Figure 2 The AC output voltage Vaco as in (6) is output as an insulated voltage with a constant voltage conversion ratio.

[0063] Next, the isolated DC-DC converter 21 will be described.

[0064] Figure 3 1 is a circuit diagram of an isolated DC-DC converter 21 used in the AC isolation circuit 1 . Figure 4A : is the waveform of each part of the isolated DC-DC converter 21 when the input voltage (first positive voltage) Vi=E and the load RL is present. Figure 4B : is the waveform of each part of the isolated DC-DC converter 21 when the input voltage Vi=E and there is no load RL. Figure 4C : is the waveform of each part of the isolated DC-DC converter 21 when the input voltage Vi=E / 2 and the load RL is present. Figure 4D 1 and 2 are waveforms of various parts of the isolated DC-DC converter 21 when the input voltage Vi=E / 2 and the load RL is not present.

[0065] like Figure 3 As shown, the isolated DC-DC converter 21 includes: a high-frequency transformer T having a core for high-frequency voltage, a primary winding Lp, a first secondary winding Ls1, and a second secondary winding Ls2; a half-bridge circuit as a primary-side circuit connected to the primary winding Lp of the high-frequency transformer T; and a double-wave rectification type synchronous rectification circuit as a secondary-side circuit connected to the first secondary winding and the second secondary winding of the high-frequency transformer T.

[0066] The high-frequency transformer T includes a core, a primary winding Lp, and a first and second secondary windings Ls1 and Ls2 coupled to the primary winding Lp via the core. It is designed for high-frequency AC voltages ranging from several kHz to several hundred kHz. The primary winding Lp of the high-frequency transformer T is insulated from the first and second secondary windings Ls1 and Ls2.

[0067] The primary-side circuit of the isolated DC-DC converter 21 is a half-bridge circuit in which a series circuit consisting of a first primary-side switching element Q11 and a second primary-side switching element Q12, and a series circuit (current resonating capacitor) consisting of a first current resonating capacitor C11 and a second current resonating capacitor C12 are connected in parallel with respect to the input voltage Vi.

[0068] The primary-side first switching element Q11 and the primary-side second switching element Q12 are formed of semiconductor switching elements and have regenerative diodes. In the first embodiment, the primary-side first switching element Q11 and the primary-side second switching element Q12 are formed of N-channel MOSFETs.

[0069] In the series circuit of the first primary-side switching element Q11 and the second primary-side switching element Q12, the drain of the first primary-side switching element Q11 is connected to the positive side of the input voltage Vi. Furthermore, the source of the first primary-side switching element Q11 is connected to the drain of the second primary-side switching element Q12, and the source of the second primary-side switching element Q12 is connected to the negative side of the input voltage Vi.

[0070] A first voltage quasi-resonant capacitor Cv11 is connected in parallel to the first primary-side switching element Q11 , and a second voltage quasi-resonant capacitor Cv12 is connected in parallel to the second primary-side switching element Q12 .

[0071] A series circuit of a primary winding Lp of a high-frequency transformer T and a current resonance inductor Lr is connected between a connection point between the primary-side first switching element Q11 and the primary-side second switching element Q12 and a connection point between the first current resonance capacitor C11 and the second current resonance capacitor C12.

[0072] A primary-side control circuit CT10 is connected between the gate and source of the first primary-side switching element Q11 and the gate and source of the second primary-side switching element Q12. This primary-side control circuit CT10 can output a gate signal Vg11 for turning on the first primary-side switching element Q11 and a gate signal Vg12 for turning on the second primary-side switching element Q12.

[0073] A first secondary winding Ls1 and a second secondary winding Ls2 are connected in series on the secondary side of the high-frequency transformer T. The secondary-side circuit of the isolated DC-DC converter 21 includes a dual-wave rectification type synchronous rectification circuit, which is composed of a series circuit of a first secondary-side switching element Q21 and a second secondary-side switching element Q22 connected to both ends of the series circuit of the first secondary winding Ls1 and the second secondary winding Ls2.

[0074] The first secondary-side switching element Q21 and the second secondary-side switching element Q22 are semiconductor switching elements and include regenerative diodes. In the first embodiment, the first secondary-side switching element Q21 and the second secondary-side switching element Q22 are each comprised of an N-channel MOSFET. Snubber capacitors C21 and C22 are connected in parallel with the first secondary-side switching element Q21 and the second secondary-side switching element Q22, respectively, to suppress inrush current when the switches are turned off.

[0075] The source of the first secondary-side switching element Q21 is connected to the first secondary winding Ls1 side of the series circuit of the first secondary winding Ls1 and the second secondary winding Ls2. The source of the second secondary-side switching element Q22 is connected to the second secondary winding Ls2 side of the series circuit of the first secondary winding Ls1 and the second secondary winding Ls2.

[0076] The drain of the secondary-side first switching element Q21 and the drain of the secondary-side second switching element Q22 are connected to the positive-side output terminal of the isolated DC-DC converter 21 via one end of the output smoothing capacitor Co.

[0077] A connection point between the first secondary winding Ls1 and the second secondary winding Ls2 is connected to the negative output terminal via the other end of the output smoothing capacitor Co.

[0078] A secondary-side first control circuit CT21 capable of outputting a gate signal Vg21 for turning on the secondary-side first switching element Q21 is connected between the gate and the source of the secondary-side first switching element Q21 .

[0079] A secondary-side second control circuit CT22 capable of outputting a gate signal Vg22 for turning on the secondary-side second switching element Q22 is connected between the gate and the source of the secondary-side second switching element Q22 .

[0080] Next, the operation of the isolated DC-DC converter 21 will be described in detail.

[0081] The primary-side first switching element Q11 and the primary-side second switching element Q12 are alternately switched at a second frequency fs of several hundred kHz (e.g., 100 kHz) by gate signals Vg11 and Vg12 generated by the primary-side control circuit CT10. Figures 4A-4D (5)) and Vg12 ( Figures 4A-4D (6)) has a small dead time period during which the primary side first switching element Q11 and the primary side second switching element Q12 are necessarily turned off at the same time (see the following Figures 4A-4D The waveforms after t21, t22, and t23 of (5) and (6).

[0082] The gate signal Vg21 ( Figures 4A-4D (5)) is a signal having the same timing as the gate signal Vg11 of the primary-side first switching element Q11.

[0083] The gate signal Vg22 ( Figures 4A-4D (6)) is a signal having the same timing as the gate signal Vg12 of the primary-side second switching element Q12.

[0084] When input voltage Vi is applied to the isolated DC-DC converter 21, the first and second current resonant capacitors C11 and C12 are charged, each reaching a potential difference of 1 / 2Vi. The first and second primary-side switching elements Q11 and Q12 are alternately turned on and off, alternating voltages of +1 / 2Vi and -1 / 2Vi are applied to the primary winding Lp of the high-frequency transformer T. In other words, an AC voltage with a switching frequency fs that fluctuates between +1 / 2Vi and -1 / 2Vi is applied to the primary winding Lp of the high-frequency transformer T.

[0085] When the load RL is not connected to the output terminal of the isolated DC-DC converter 21 (the output side is open), the primary side first switching element Q11 is turned on by the gate signal Vg11 after the dead time period (immediately after Figure 4B After t21 in (5), the current flows through the paths Vi→Q11→Lr→Lp→C12→Vi and C11→Q11→Lr→Lp→C11. The resonant frequency fr of the primary circuit at this time is as shown in (Equation 2).

[0086] [Mathematical formula 2]

[0087] …(Equation 2)

[0088] Here, if the value of the inductor is set such that the primary winding Lp >> the inductor Lr for current resonance, then when the switching frequencies of all the switching elements Q11, Q12, Q21, and Q22 are set to fs, fr << fs. When the primary side first switching element Q11 is turned on, the waveform of the drain current Id(Q11) becomes the resonance frequency fr. However, for the waveform of this drain current Id(Q11), the resonance frequency fr is a frequency much lower than the switching frequency fs, so a part of the sine wave of the resonance frequency fr appears as a linearly rising waveform to the right ( Figure 4B of (2) between t21 - t22 of Id(Q11)). In addition, this current waveform is also the waveform of the exciting current of the high-frequency transformer T.

[0089] Through the switching current (drain current) Id(Q11) when the primary side first switching element Q11 is turned off, the energy ε stored in the primary winding Lp and the inductor Lr for current resonance is as shown in (Equation 3).

[0090] [Equation 3]

[0091] … (Equation 3)

[0092] The energy ε stored in the primary winding Lp and the inductor Lr for current resonance is released to the voltage quasi-resonance capacitor circuit of the first voltage quasi-resonance capacitor Cv11 and the second voltage quasi-resonance capacitor Cv12 during the dead time between the primary side first switching element Q11 and the primary side second switching element Q12. The relationship with the energy ε at this time is as shown in (Equation 4).

[0093] [Equation 4]

[0094] … (Equation 4)

[0095] The capacitance value of Cv11 + Cv12 and the inductance value of Lp + Lr are determined such that the voltage V in (Equation 4) becomes equal to or higher than the input voltage Vi. And 1 / 4 of the period of the voltage quasi-resonance frequency fv is set to be less than or equal to the dead time between the primary side first switching element Q11 and the primary side second switching element Q12 so that voltage quasi-resonance can be achieved during the dead time. Here, the voltage quasi-resonance frequency fv is as shown in (Equation 5).

[0096] [Equation 5]

[0097] … (Equation 5)

[0098] When the load RL is connected to the output terminal of the isolated DC-DC converter 21, the primary-side first switching element Q11 is turned on by the gate signal Vg11 after the dead time period (immediately after the dead time period). Figure 4A (After t21 in (5)). Thus, in the primary circuit, current flows along the paths Vi → Q11 → Lr → Lp → C12 → Vi and C11 → Q11 → Lr → Lp → C11. Simultaneously, the first secondary-side switching element Q21 is turned on by gate signal Vg21, so current flows through the paths Ls1 → Q21 → RL → Ls1 in the secondary circuit via high-frequency transformer T. The resonant frequency fr at this time is as shown in (Equation 6).

[0099] [Formula 6]

[0100] …(Equation 6)

[0101] The values ​​of the current resonant inductor Lr, the first current resonant capacitor C11, and the second current resonant capacitor C12 are set so that the resonant frequency fr of (Equation 6) is approximately equal to the switching frequency fs. Thus, while the primary-side first switching element Q11 is on, the sinusoidal current of the half cycle of the switching frequency fs becomes a drain current Id(Q11) ( ) which is superimposed on the rightward-rising straight line waveform when the load RL is not connected to the output terminal of the isolated DC-DC converter 21. Figure 4A (2) between t21 and t22).

[0102] In addition, when the output terminal of the isolated DC-DC converter 21 is not connected to the output side of the load RL and is open, after the dead time period, the primary side second switching element Q12 is turned on by the gate signal Vg12. Figure 4B After t22 in (6), current flows through the paths of C12 → Lp → Lr → Q12 → C12 and Vi → C11 → Lp → Lr → Q12 → Vi. The resonant frequency fr of the primary circuit at this time is as shown in (Equation 7).

[0103] [Formula 7]

[0104] …(Equation 7)

[0105] Here, if the value of the inductor is set such that the primary winding Lp >> the inductor Lr for current resonance, then when the switching frequencies of all the switching elements Q11, Q12, Q21, and Q22 are set to fs, fr << fs. When the primary-side second switching element Q12 is turned on, the waveform of the drain current Id(Q12) becomes the resonance frequency fr. However, for the waveform of this drain current Id(Q12), the resonance frequency fr is a frequency much lower than the switching frequency fs, so a part of the sine wave of the resonance frequency fr appears as a linearly rising waveform to the right ( Figure 4B during t22 - t23 in (4) of

[0106] ). Also, the waveform of this drain current Id(Q12) is also the waveform of the excitation current of the high-frequency transformer T.

[0107] [Equation 8]

[0108] … (Equation 8)

[0109] The energy ε stored in the primary winding Lp and the inductor Lr for current resonance is released to the first voltage quasi-resonance capacitor Cv11 and the second voltage quasi-resonance capacitor Cv12 (voltage quasi-resonance capacitor circuit) during the dead time of the primary-side first switching element Q11 and the primary-side second switching element Q12. The relationship with the energy ε at this time is as in (Equation 9).

[0110] [Equation 9]

[0111] … (Equation 9)

[0112] The values of the capacitance of Cv11 + Cv12 and the inductance of Lp + Lr are determined such that the voltage V in Equation 9 becomes equal to or higher than the input voltage Vi. And the 1 / 4 period of the voltage quasi-resonance frequency fv is set to be less than or equal to the dead time of the primary-side first switching element Q11 and the primary-side second switching element Q12, so as to achieve voltage quasi-resonance during the dead time of the primary-side first switching element Q11 and the primary-side second switching element Q12. The voltage quasi-resonance frequency fv is as in (Equation 10).

[0113] [Equation 10]

[0114] … (Equation 10)

[0115] Furthermore, when load RL is connected to the output terminals of isolated DC-DC converter 21, the second primary-side switching element Q12 is turned on by gate signal Vg12 after the dead time period. Consequently, current flows in the primary-side circuit along the paths C12 → Lp → Lr → Q12 → C12 and Vi → C11 → Lp → Lr → Q12 → Vi. Simultaneously, the second secondary-side switching element Q22 is turned on by gate signal Vg22, causing current to flow in the secondary-side circuit along the paths Ls2 → Q22 → RL → Ls2 via high-frequency transformer T. The resonant frequency fr at this time is as shown in (Equation 11).

[0116] [Mathematical formula 11]

[0117] …(Equation 11)

[0118] The values ​​of the current resonance inductor Lr, the first current resonance capacitor C11, and the second current resonance capacitor C12 are set so that the resonant frequency fr of (Equation 11) is approximately equal to the switching frequency fs. Thus, while the primary-side second switching element Q12 is on, the sinusoidal current of the half cycle of the switching frequency fs becomes a drain current Id(Q12) ( ) which is superimposed on the rightward-rising straight line waveform when the load RL is not connected to the output terminal of the isolated DC-DC converter 21. Figure 4A (4) between t22 and t23).

[0119] Next, use Figures 4A-4D The waveforms of each portion when a load RL is present at the output terminal of the isolated DC-DC converter 21 and when no load RL is present will be described.

[0120] Figures 4A-4D(1) represents the waveform of the drain-source voltage Vds(Q11) of the primary-side first switching element Q11, and (2) represents the waveform of the drain current Id(Q11) of the primary-side first switching element Q11. In addition, (3) represents the waveform of the drain-source voltage Vds(Q12) of the primary-side second switching element Q12, and (4) represents the waveform of the drain current Id(Q12) of the primary-side second switching element Q12. Furthermore, (5) represents the waveform of the gate signal Vg11 of the primary-side first switching element Q11 and the gate signal Vg21 of the secondary-side first switching element Q21, and (6) represents the waveform of the gate signal Vg12 of the primary-side second switching element Q12 and the gate signal Vg22 of the secondary-side second switching element Q22. Similarly, (7) shows the waveform of the drain current Id(Q21) of the secondary-side first switching element Q21, (8) shows the waveform of the drain current Id(Q22) of the secondary-side second switching element Q22, and (9) shows the waveform of the output voltage (second positive voltage) Vo of the isolated DC-DC converter 21.

[0121] Depend on Figures 4A-4D It can be seen that the presence or absence of the load RL can be detected between t21 and t22 of (2) Id (Q11) and (7) Id (Q21), and between t22 and t23 of (4) Id (Q12) and (8) Id (Q22), which are the drain currents of the switching elements.

[0122] Depending on the magnitude of the input voltage Vi, the drain-source voltage Vds(Q11) of the first primary-side switching element Q11 and the drain-source voltage Vds(Q12) of the second primary-side switching element Q12 vary. Furthermore, the drain current Id(Q11) of the first primary-side switching element Q11 and the drain current Id(Q12) of the second primary-side switching element Q12, which serve as the excitation current for the high-frequency transformer T, also vary, and the output voltage Vo also varies. In other words, as the input voltage Vi changes, a corresponding output voltage Vo is generated. This voltage conversion ratio is determined by the turns ratio of the high-frequency transformer T's primary winding Lp to the first and second secondary windings Ls1 and Ls2. Furthermore, in the isolated DC-DC converter 21, the drain current Id(Q21) of the secondary-side first switching element Q21 and the drain current Id(Q22) of the secondary-side second switching element Q22, which serve as output current, form a sinusoidal resonant current whose amplitude varies according to the output current. The starting and ending points of this sinusoidal resonant current remain substantially constant regardless of the output current. Specifically, the starting and ending points of the current remain the same when the primary-side first switching element Q11 or the primary-side second switching element Q12 is off, regardless of the output current, maintaining voltage quasi-resonance. Furthermore, the drain currents Id(Q11) and Id(Q12), which serve as the excitation current of the high-frequency transformer T, also vary in magnitude with the input voltage Vi, maintaining voltage quasi-resonance. Furthermore, the isolated DC-DC converter 21 is a synchronous rectification circuit in which the secondary-side switching element and the primary-side switching element are turned on and off at exactly the same timing, enabling bidirectional operation. The isolated DC-DC converter 21 similarly maintains the resonant operation even when operating in the reverse direction.

[0123] That is, the isolated DC-DC converter 21 can constitute an isolated bidirectional DC-DC converter having a substantially constant voltage conversion ratio.

[0124] The current resonance inductor Lr can utilize the leakage inductance of the high-frequency transformer T. A voltage quasi-resonance capacitor can also be connected in parallel with the switching elements Q21 and Q22 of the secondary-side circuit.

[0125] In the AC isolation circuit 1 involved in the first embodiment, the AC voltage Vaci of the commercial AC power source AC applied to the input terminal is insulated, and is output to the output terminal as an AC output voltage Vaco at a certain voltage ratio. The AC voltage Vaci of the input commercial AC power source AC is added to the first DC voltage Vcb1 to become the first positive voltage Vi. The first positive voltage Vi is converted into an isolated second positive voltage Vo by the insulating DC-DC converter 21. The second positive voltage Vo becomes an AC output voltage Vaco with zero DC voltage component by subtracting the second DC voltage Vcb2. Moreover, they can act in both directions and can flow from a high voltage place to a low voltage place in response to phase delays, advances, etc. that are unique to AC circuits. That is, they can be used in conjunction with Figure 17 The operation is similar to that of the conventional commercial frequency transformer shown in FIG. Furthermore, the isolated DC-DC converter 21 used in the AC isolation circuit 1 can achieve a switching frequency of several hundred kHz, thereby significantly reducing the size of the transformer (high-frequency transformer) that performs voltage conversion with isolation. Furthermore, the isolated DC-DC converter 21 can operate in resonance under almost all input and output conditions, and because of so-called soft switching, it reduces switching noise and achieves high efficiency.

[0126] Therefore, in order to cope with 50 / 60 [Hz], Figure 17 Unlike a voltage conversion transformer made of silicon steel sheets, which is large and heavy, a compact and lightweight high-frequency transformer can be used in the AC isolation circuit 1 by performing high-frequency switching of several hundred kHz. Furthermore, by adopting a resonant switching power supply structure with minimal switching loss and the effects of switching noise, a high-frequency modulation commercial frequency transformer with low noise, high efficiency, and a compact and lightweight design can be provided, which can be mounted on a single (or a small number of) substrates.

[0127] (First Modification)

[0128] Figure 5 This is a circuit diagram showing the configuration of an insulating DC-DC converter 21A according to a first modification. Figure 3 The difference of the isolated DC-DC converter 21 is that the secondary side circuit is a full-bridge synchronous rectification, and the primary side circuit is composed of Figure 3 The insulating DC-DC converter 21 has the same half-bridge circuit configuration as the insulating DC-DC converter 21. Therefore, only the configuration of the secondary side circuit will be described, and the configuration of the primary side circuit will be omitted.

[0129] In the isolated DC-DC converter 21A of the first modified example, one secondary winding Ls is connected to the secondary side of the high-frequency transformer T.

[0130] Specifically, a high-frequency transformer T includes a core, a primary winding Lp, and a secondary winding Ls coupled to the core. It is designed for high-frequency AC voltages ranging from several kHz to several hundred kHz. Furthermore, the primary winding Lp and secondary winding Ls of the high-frequency transformer T are insulated.

[0131] At both ends of the secondary winding Ls, a series circuit of a secondary-side first switching element Q21 and a secondary-side second switching element Q22, and a series circuit of a secondary-side third switching element Q23 and a secondary-side fourth switching element Q24 are connected in parallel as a synchronous rectification circuit of the isolated DC-DC converter 21A.

[0132] Each of the secondary-side circuit's switching elements Q21, Q22, Q23, and Q24 is comprised of a semiconductor switching element and includes a regenerative diode. In the first modified example, each of the secondary-side circuit's switching elements Q21, Q22, Q23, and Q24 is comprised of an N-channel MOSFET. Snubber capacitors C21, C22, C23, and C24 are connected in parallel to each of the secondary-side circuit's switching elements Q21, Q22, Q23, and Q24 to suppress inrush current during switch-off.

[0133] The source of the secondary-side first switching element Q21 is connected to the positive side of the secondary winding Ls, the source of the secondary-side second switching element Q22 is connected to the negative side of the secondary winding Ls, and the drain of the secondary-side first switching element Q21 is connected to the drain of the secondary-side second switching element Q22.

[0134] The drain of the secondary side third switching element Q23 is connected to the positive side of the secondary winding Ls, the drain of the secondary side fourth switching element Q24 is connected to the negative side of the secondary winding Ls, and the source of the secondary side third switching element Q23 is connected to the source of the secondary side fourth switching element Q24.

[0135] A connection point between the secondary-side first switching element Q21 and the secondary-side second switching element Q22 is connected to the positive-side output terminal of the isolated DC-DC converter 21A via one end of the output smoothing capacitor Co.

[0136] A connection point between the third secondary-side switching element Q23 and the fourth secondary-side switching element Q24 is connected to the negative-side output terminal of the isolated DC-DC converter 21A via the other end of the output smoothing capacitor Co.

[0137] A secondary-side first control circuit CT21 capable of outputting a gate signal Vg21 for turning on the secondary-side first switching element Q21 is connected between the gate and the source of the secondary-side first switching element Q21 .

[0138] A secondary-side second control circuit CT22 capable of outputting a gate signal Vg22 for turning on the secondary-side second switching element Q22 is connected between the gate and the source of the secondary-side second switching element Q22 .

[0139] A secondary-side third control circuit CT23 capable of outputting a gate signal Vg23 for turning on the secondary-side third switching element Q23 is connected between the gate and the source of the secondary-side third switching element Q23 .

[0140] A secondary-side fourth control circuit CT24 capable of outputting a gate signal Vg24 for turning on the secondary-side fourth switching element Q24 is connected between the gate and the source of the secondary-side fourth switching element Q24 .

[0141] The gate signal Vg21 of the secondary-side first switching element Q21 generated by the secondary-side first control circuit CT21 and the gate signal Vg24 of the secondary-side fourth switching element Q24 generated by the secondary-side fourth control circuit CT24 are signals with the same timing as the gate signal Vg11 of the primary-side first switching element Q11. Figures 4A-4D The waveform of (5) is the same.

[0142] The gate signal Vg22 of the secondary-side second switching element Q22 generated by the secondary-side second control circuit CT22 and the gate signal Vg23 of the secondary-side third switching element Q23 generated by the secondary-side third control circuit CT23 are signals with the same timing as the gate signal Vg12 of the primary-side second switching element Q12. Figures 4A-4D The waveform of (6) is the same.

[0143] In the isolated DC-DC converter 21A of the first modified example configured in this manner, when the first primary-side switching element Q11 is turned on, current flows on the primary side via two paths: Vi → Q11 → Lr → Lp → C12 → Vi, and C11 → Q11 → Lr → Lp → C11. In the secondary-side circuit, current flows via Ls → Q21 → RL → Q24 → Ls. Furthermore, when the second primary-side switching element Q12 is turned on, current flows on the primary side via two paths: Vi → C11 → Lp → Lr → Q12 → Vi, and C12 → Lp → Lr → Q12 → C12. In the secondary-side circuit, current flows via Ls → Q22 → RL → Q23 → Ls.

[0144] Even when the insulating DC-DC converter 21A of the first modification is used, it is possible to perform the same Figure 3 The insulating DC-DC converter 21 operates in the same manner as above.

[0145] exist Figure 3In the isolated DC-DC converter 21 of the first modification, the number of switching elements in the secondary side circuit is two. In contrast, in the isolated DC-DC converter 21A of the first modification, the number of switching elements in the secondary side circuit is four. Figure 3 The isolated DC-DC converter 21 of the first modification requires two secondary windings Ls1 and Ls2 , but the isolated DC-DC converter 21A of the first modification only requires one secondary winding Ls, thereby reducing the number of secondary windings.

[0146] (Second Modification)

[0147] Figure 6 This is a circuit diagram showing the configuration of an insulating DC-DC converter 21B according to a second modification. Figure 3 The difference of the isolated DC-DC converter 21 is that the primary side circuit is a full-bridge circuit and the secondary side circuit is Figure 3 The insulating DC-DC converter 21 is the same as the double-wave rectification type synchronous rectification circuit. Therefore, only the structure of the primary side circuit is described, and the description of the structure of the secondary side circuit is omitted.

[0148] The high-frequency transformer T includes a core, a primary winding Lp, and a first secondary winding Ls1 and a second secondary winding Ls2 coupled to the primary winding Lp via the core. It is designed for high-frequency AC voltages ranging from several kHz to several hundred kHz. The primary winding Lp of the high-frequency transformer T is insulated from the first secondary winding Ls1 and the second secondary winding Ls2.

[0149] In the isolated DC-DC converter 21B of the second modification, a series circuit of a first primary-side switching element Q11 and a second primary-side switching element Q12 and a series circuit of a third primary-side switching element Q13 and a fourth primary-side switching element Q14 are connected in parallel with respect to the input voltage Vi.

[0150] Each of the primary-side switching elements Q11, Q12, Q13, and Q14 is composed of a semiconductor switching element and has a regenerative diode. In the second modification, each of the primary-side switching elements Q11, Q12, Q13, and Q14 is composed of an N-channel MOSFET.

[0151] In the series circuit of the first primary-side switching element Q11 and the second primary-side switching element Q12, the drain of the first primary-side switching element Q11 is connected to the positive side of the input voltage Vi. Furthermore, the source of the first primary-side switching element Q11 is connected to the drain of the second primary-side switching element Q12, and the source of the second primary-side switching element Q12 is connected to the negative side of the input voltage Vi.

[0152] In the series circuit of the third primary-side switching element Q13 and the fourth primary-side switching element Q14, the drain of the third primary-side switching element Q13 is connected to the positive electrode of the input voltage Vi. Furthermore, the source of the third primary-side switching element Q13 is connected to the drain of the fourth primary-side switching element Q14, and the source of the fourth primary-side switching element Q14 is connected to the negative electrode of the input voltage Vi.

[0153] A first voltage quasi-resonant capacitor Cv11 is connected in parallel to the first primary-side switching element Q11. A second voltage quasi-resonant capacitor Cv12 is connected in parallel to the second primary-side switching element Q12. A third voltage quasi-resonant capacitor Cv13 is connected in parallel to the third primary-side switching element Q13. A fourth voltage quasi-resonant capacitor Cv14 is connected in parallel to the fourth primary-side switching element Q14.

[0154] A series circuit of the primary winding Lp of the high-frequency transformer T, the current resonance inductor Lr, and the current resonance capacitor C12 is connected between the connection point of the primary-side first switching element Q11 and the primary-side second switching element Q12 and the connection point of the primary-side third switching element Q13 and the primary-side fourth switching element Q14. Figure 3 The first current resonance capacitor C11 and the second current resonance capacitor C12 of the primary side circuit of the isolated DC-DC converter 21 are combined.

[0155] A primary-side control circuit CT10 is connected between the gate and source of the first primary-side switching element Q11, the gate and source of the second primary-side switching element Q12, the gate and source of the third primary-side switching element Q13, and the gate and source of the fourth primary-side switching element Q14. The primary-side control circuit CT10 can output a gate signal Vg11 for turning on the first primary-side switching element Q11, a gate signal Vg12 for turning on the second primary-side switching element Q12, a gate signal Vg13 for turning on the third primary-side switching element Q13, and a gate signal Vg14 for turning on the fourth primary-side switching element Q14.

[0156] The gate signal Vg11 of the primary-side first switching element Q11 and the gate signal Vg14 of the primary-side fourth switching element Q14 generated by the primary-side control circuit CT10 are signals with the same timing. Figures 4A-4D The waveform of (5) is the same.

[0157] The gate signal Vg12 of the primary-side second switching element Q12 and the gate signal Vg13 of the primary-side third switching element Q13 generated by the primary-side control circuit CT10 are signals with the same timing. Figures 4A-4D The waveform of (6) is the same.

[0158] Next, the operation of the isolated DC-DC converter 21B will be described.

[0159] The first primary-side switching element Q11, the second primary-side switching element Q12, the third primary-side switching element Q13, and the fourth primary-side switching element Q14 are switched at a high frequency of several hundred kHz (e.g., 100 kHz) by gate signals Vg11, Vg12, Vg13, and Vg14 generated by the primary-side control circuit CT10. Here, the first primary-side switching element Q11 and the fourth primary-side switching element Q14 are controlled to be turned on and off simultaneously (see Figures 4A-4D (5) waveform), the primary side second switching element Q12 and the primary side third switching element Q13 are turned on and off at the same time (refer to Figures 4A-4D (6)). In addition, the gate signals Vg11, Vg12, Vg13, and Vg14 have a small dead time period during which the first primary-side switching element Q11, the second primary-side switching element Q12, the third primary-side switching element Q13, and the fourth primary-side switching element Q14 are necessarily turned off at the same time (see the following). Figures 4A-4D The waveforms after t21, t22, and t23 of (5) and (6).

[0160] The gate signal Vg21 of the secondary-side first switching element Q21 generated by the secondary-side first control circuit CT21 is a signal of the same timing as the gate signal Vg11 of the primary-side first switching element Q11 (see Figures 4A-4D The waveform of (5)).

[0161] The gate signal Vg22 of the secondary-side second switching element Q22 generated by the secondary-side second control circuit CT22 is a signal with the same timing as the gate signal Vg12 of the primary-side second switching element Q12 (see Figures 4A-4D The waveform of (6)).

[0162] When load RL is not connected to the output terminals of isolated DC-DC converter 21B (the output side is open), after the dead time period, the first primary-side switching element Q11 and the fourth primary-side switching element Q14 are turned on by gate signals Vg11 and Vg14. This causes current to flow along the path Vi → Q11 → Lr → Lp → C12 → Q14 → Vi. The resonant frequency fr of the primary-side circuit at this time is expressed as (Equation 12).

[0163] [Mathematical formula 12]

[0164] …(Equation 12)

[0165] Here, if the value of the inductor is set such that the primary winding Lp >> the inductor Lr for current resonance, then when the switching frequencies of all the switching elements Q11, Q12, Q13, Q14, Q21, Q22 are set to fs, fr << fs. When the primary side first switching element Q11 and the primary side fourth switching element Q14 are conducting, the waveform of the drain current Id(Q11) becomes the resonance frequency fr. However, for the waveform of this drain current Id(Q11), the resonance frequency fr is a frequency much lower than the switching frequency fs, so a part of the sine wave of the resonance frequency fr appears as a linearly rising waveform to the right ( Figure 4B during t21 - t22 of (2)). In addition, this current waveform is also the waveform of the magnetizing current of the high-frequency transformer T.

[0166] Through the switching current (drain current) Id(Q11) when the primary side first switching element Q11 and the primary side fourth switching element Q14 are turned off, the energy ε stored in the primary winding Lp and the inductor Lr for current resonance is as in (Equation 13).

[0167] [Equation 13]

[0168] … (Equation 13)

[0169] The energy ε stored in the primary winding Lp and the inductor Lr for current resonance is released to each of the voltage quasi-resonance capacitors Cv11, Cv12, Cv13, Cv14 during the dead time when the primary side first switching element Q11 and the primary side fourth switching element Q14 are turned off. The relationship with the energy ε at this time is as in (Equation 14).

[0170] [Equation 14]

[0171] … (Equation 14)

[0172] The capacitance values of each of the voltage quasi-resonance capacitors Cv11, Cv12, Cv13, Cv14 and the inductance value of Lp + Lr are determined such that the voltage V in (Equation 14) becomes above the input voltage Vi. And, 1 / 4 of the period of the voltage quasi-resonance frequency fv is set to be below the dead time period so that voltage quasi-resonance can be achieved during the dead time when the primary side first switching element Q11 and the primary side fourth switching element Q14 are turned off. Here, the voltage quasi-resonance frequency fv is as in (Equation 15).

[0173] [Equation 15]

[0174] … (Equation 15)

[0175] Furthermore, when load RL is connected to the output terminals of isolated DC-DC converter 21B, after the dead time period, the first primary-side switching element Q11 and the fourth primary-side switching element Q14 are turned on by gate signals Vg11 and Vg14. Consequently, in the primary-side circuit, current flows along the path Vi → Q11 → Lr → Lp → C12 → Q14 → Vi. Simultaneously, the first secondary-side switching element Q21 is turned on by gate signal Vg21, and in the secondary-side circuit, current flows along the path Ls1 → Q21 → RL → Ls1 via high-frequency transformer T. The resonant frequency fr at this time is as shown in (Equation 16).

[0176] [Mathematical formula 16]

[0177] …(Equation 16)

[0178] The values ​​of the current resonance inductor Lr and the current resonance capacitor C12 are set so that the resonant frequency fr of (Equation 16) is approximately equal to the switching frequency fs. Thus, while the primary-side first switching element Q11 and the primary-side fourth switching element Q14 are on, the sinusoidal current of the half cycle of the switching frequency fs becomes a drain current Id(Q11) ( ) which is superimposed on the rightward-rising straight line waveform when the load RL is not connected to the output terminal of the isolated DC-DC converter 21. Figure 4A (2) between t21 and t22).

[0179] After the dead time period, when the output terminals of isolated DC-DC converter 21 are disconnected from load RL (the output side is open), the second and third primary-side switching elements Q12 and Q13 are turned on by gate signals Vg12 and Vg13, respectively. Current then flows along the path Vi, Q13, C12, Lp, Lr, Q12, and Vi. The resonant frequency fr of the primary-side circuit at this time is expressed as (Equation 17).

[0180] [Mathematical formula 17]

[0181] …(Equation 17)

[0182] Here, if the value of the inductor is set such that the primary winding Lp >> the inductor Lr for current resonance, then when the switching frequencies of all the switching elements Q11, Q12, Q13, Q14, Q21, Q22 are set to fs, fr << fs. When the primary-side second switching element Q12 and the primary-side third switching element Q13 are conducting, the waveform of the drain current Id(Q12) becomes the resonance frequency fr. However, for the waveform of this drain current Id(Q12), the resonance frequency fr is a frequency much lower than the switching frequency fs, so a part of the sine wave of the resonance frequency fr appears as a linearly rising waveform to the right ( Figure 4B during t22 - t23 of (4)). Also, the waveform of this drain current Id(Q12) is also the waveform of the exciting current of the high-frequency transformer T.

[0183] The energy ε stored in the primary winding Lp and the inductor Lr for current resonance by the switching current (drain current) Id(Q12) when the primary-side second switching element Q12 is turned off is as shown in (Equation 18).

[0184] [Equation 18]

[0185] … (Equation 18)

[0186] The energy ε stored in the primary winding Lp and the inductor Lr for current resonance is released to each voltage quasi-resonance capacitor Cv11, Cv12, Cv13, Cv14 during the dead time. The relationship with the energy ε at this time is as shown in (Equation 19).

[0187] [Equation 19]

[0188] … (Equation 19)

[0189] The capacitance values of each voltage quasi-resonance capacitor Cv11, Cv12, Cv13, Cv14 and the inductance value of Lp + Lr are determined such that the voltage V in Equation 19 becomes equal to or higher than the input voltage Vi. Also, 1 / 4 of the period of the voltage quasi-resonance frequency fv is set to be less than the dead time, so that voltage quasi-resonance can be achieved during the dead time when the primary-side second switching element Q12 and the primary-side third switching element Q13 are turned off. The voltage quasi-resonance frequency fv at this time is as shown in (Equation 20).

[0190] [Equation 20]

[0191] … (Equation 20)

[0192] Furthermore, when load RL is connected to the output terminals of isolated DC-DC converter 21B, after the dead time period, the second and third primary-side switching elements Q12 and Q13 are turned on by gate signals Vg12 and Vg13, respectively. Consequently, in the primary-side circuit, current flows along the path Vi → Q13 → C12 → Lp → Lr → Q12 → Vi. Simultaneously, the second secondary-side switching element Q22 is turned on by gate signal Vg22, and in the secondary-side circuit, current flows along the path Ls2 → Q22 → RL → Ls2 via high-frequency transformer T. The resonant frequency fr at this time is as shown in (Equation 21).

[0193] [Mathematical formula 21]

[0194] …(Equation 21)

[0195] The values ​​of the current resonance inductor Lr and the current resonance capacitor C12 are set so that the resonant frequency fr of (Equation 21) is approximately equal to the switching frequency fs. Thus, while the second primary-side switching element Q12 and the third primary-side switching element Q13 are on, the sinusoidal current of the half cycle of the switching frequency fs becomes a drain current Id(Q12) ( ) which is superimposed on the rightward-rising straight line waveform when the load RL is not connected to the output terminal of the isolated DC-DC converter 21B. Figure 4A (4) between t22 and t23).

[0196] Even when the insulating DC-DC converter 21B of the second modified example is used, it is possible to perform the same Figure 3 The insulating DC-DC converter 21 operates in the same manner as above.

[0197] exist Figure 3 In the isolated DC-DC converter 21 of the second modified example, the number of switching elements in the primary side circuit is two. In contrast, in the isolated DC-DC converter 21B of the second modified example, the number of switching elements in the primary side circuit is four. Figure 3 The average voltage Vi of the current resonant capacitors C11 and C12 of the isolated DC-DC converter 21 of the second modification is 1 / 2Vi. The average voltage of the current resonant capacitor C12 of the isolated DC-DC converter 21B of the second modification is zero. Therefore, the current resonant capacitor C12 of the isolated DC-DC converter 21B of the second modification can reduce the withstand voltage.

[0198] (Third Modification)

[0199] Figure 7This is a circuit diagram showing the configuration of an isolated DC-DC converter 21C according to a third modification. The isolated DC-DC converter 21C according to the third modification differs from the isolated DC-DC converter 21B according to the second modification in that the secondary-side circuit employs a full-bridge synchronous rectification circuit similar to that of the first modification, and the primary-side circuit employs a full-bridge circuit similar to that of the second modification.

[0200] The high-frequency transformer T includes a core, a primary winding Lp, and a secondary winding Ls coupled to the core. It is designed for high-frequency AC voltages ranging from several kHz to several hundred kHz. The primary winding Lp and secondary winding Ls of the high-frequency transformer T are insulated.

[0201] Even when the insulating DC-DC converter 21C of the third modified example is used as described above, it is possible to perform the same operation as described above. Figure 3 The insulating DC-DC converter 21 operates in the same manner as above.

[0202] (Fourth Modification)

[0203] Figure 8 This is a circuit diagram showing the configuration of an insulating DC-DC converter 21D according to a fourth modified example. Figure 3 The difference of the isolated DC-DC converter 21 is that the primary side circuit is a half-bridge circuit in which the first current resonance capacitor C11 and the first voltage quasi-resonance capacitor Cv11 are omitted. Figure 3 The same double-wave rectification type synchronous rectification circuit as the isolated DC-DC converter 21 of the fourth modification is used. Figure 3 The first current resonance capacitor C11 is omitted in the isolated DC-DC converter 21, but the second current resonance capacitor C12 may be omitted instead. Figure 3 In the isolated DC-DC converter 21, the first voltage quasi-resonant capacitor Cv11 is omitted, but the second voltage quasi-resonant capacitor Cv12 may be omitted instead.

[0204] The high-frequency transformer T includes a core, a primary winding Lp, and a first secondary winding Ls1 and a second secondary winding Ls2 coupled to the primary winding Lp via the core. It is designed for high-frequency AC voltages ranging from several kHz to several hundred kHz. The primary winding Lp of the high-frequency transformer T is insulated from the first secondary winding Ls1 and the second secondary winding Ls2.

[0205] In the fourth modified example, an isolated DC-DC converter 21D is integrated with the second current resonance capacitor C12. Figure 3 The first current resonance capacitor C11 of the isolated DC-DC converter 21 is integrated with the second voltage quasi-resonance capacitor Cv12. Figure 3 The first voltage quasi-resonance capacitor Cv11 of the isolated DC-DC converter 21 is provided.

[0206] In the insulated DC-DC converter 21D of the fourth modified example configured in this manner, when the first primary-side switching element Q11 is on, current flows along the path Vi→Q11→Lr→Lp→C12→Vi in the primary-side circuit, and along the path Ls1→Q21→RL→Ls1 in the secondary-side circuit. Furthermore, when the second primary-side switching element Q12 is on, current flows along the path C12→Lp→Lr→Q12→C12 in the primary-side circuit, and along the path Ls2→Q22→RL→Ls2 in the secondary-side circuit.

[0207] Even when the insulating DC-DC converter 21D of the fourth modification is used, it is possible to perform the same Figure 3 The insulating DC-DC converter 21 operates in the same manner as above.

[0208] (Fifth Modification)

[0209] Figure 9 This is a circuit diagram showing the structure of an isolated DC-DC converter 21E according to a fifth modification. The isolated DC-DC converter 21E according to the fifth modification differs from the isolated DC-DC converter 21D according to the fourth modification in that the secondary-side circuit employs a full-bridge synchronous rectification circuit, similar to the isolated DC-DC converter 21A according to the first modification. Furthermore, the primary-side circuit employs a half-bridge circuit, similar to the isolated DC-DC converter 21D according to the fourth modification, but without the first current resonant capacitor C11 and the first voltage quasi-resonant capacitor Cv11.

[0210] The high-frequency transformer T includes a core, a primary winding Lp, and a secondary winding Ls coupled to the primary winding Lp via the core. It is designed for high-frequency AC voltages ranging from several kHz to several hundred kHz. The primary winding Lp and secondary winding Ls of the high-frequency transformer T are insulated.

[0211] Even when the insulating DC-DC converter 21E of the fifth modified example is used as described above, it is possible to perform the same operation as described above. Figure 3 The insulating DC-DC converter 21 operates in the same manner as above.

[0212] (Second embodiment)

[0213] Figure 10 1A is a circuit diagram of an AC insulation circuit according to a second embodiment. Figure 11 Yes Figure 10 1A and 1B are timing charts of waveforms of various parts of an AC isolation circuit 1A according to a second embodiment. The AC isolation circuit 1A according to the second embodiment constitutes a single-phase three-wire AC power supply circuit.

[0214] In the past, Figure 19 As shown, by configuring a single-phase three-wire commercial AC power supply from a single-phase two-wire commercial AC power supply using a commercial frequency transformer as in the AC insulation circuit 1A of the second embodiment, a single-phase three-wire AC power supply circuit can be realized.

[0215] In the AC isolation circuit 1A according to the second embodiment, another circuit set similar to the AC isolation circuit 1 according to the first embodiment is prepared. Specifically, the AC isolation circuit 1A according to the second embodiment includes a circuit set consisting of a first capacitor Cb1, a first DC power supply 11, a first input capacitor Ci1, a first isolated DC-DC converter 21, a second capacitor Cb2, and a second DC power supply 12; and a circuit set consisting of a third capacitor Cb3, a third DC power supply 13, a second input capacitor Ci2, a second isolated DC-DC converter 22, a fourth capacitor Cb4, and a fourth DC power supply 14. Furthermore, the AC isolation circuit 1A includes a positive input terminal P1 and a negative input terminal P2 for connecting to the positive and negative electrodes of a commercial AC power supply AC.

[0216] Positive input terminal P1 is connected to the positive input electrode of first isolated DC-DC converter 21 via first capacitor Cb1, and to the positive input electrode of second isolated DC-DC converter 22 via third capacitor Cb3. Negative input terminal P2 is connected to the negative input electrode of first isolated DC-DC converter 21 and to the negative input electrode of second isolated DC-DC converter 22. First DC power supply 11 is connected in parallel with first capacitor Cb1. Third DC power supply 13 is connected in parallel with third capacitor Cb3. First input capacitor Ci1 is connected between the positive and negative input electrodes of first isolated DC-DC converter 21. Second input capacitor Ci2 is connected between the positive and negative input electrodes of second isolated DC-DC converter 22.

[0217] The positive output electrode of the first isolated DC-DC converter 21 is connected to the red output terminal, serving as the first output terminal, via the second capacitor Cb2. The negative output electrode of the first isolated DC-DC converter 21 is connected to the white output terminal, serving as the second output terminal. Furthermore, the positive output electrode of the second isolated DC-DC converter 22 is connected to the white output terminal, via the fourth capacitor Cb4. The negative output electrode of the second isolated DC-DC converter 22 is connected to the black output terminal, serving as the third output terminal. The second DC power supply 12 is connected in parallel with the second capacitor Cb2. The fourth DC power supply 14 is connected in parallel with the fourth capacitor Cb4.

[0218] The combination of the third capacitor Cb3 and the third DC power supply 13 is configured similarly to the combination of the first capacitor Cb1 and the first DC power supply 11 in the first embodiment. The second isolated DC-DC converter 22 is configured similarly to the isolated DC-DC converter 21 in the first embodiment. The combination of the fourth capacitor Cb4 and the fourth DC power supply 14 is configured similarly to the combination of the second capacitor Cb2 and the second DC power supply 12 in the first embodiment.

[0219] Next, use Figure 11 The operation of the AC insulation circuit 1A according to the second embodiment is described with reference to the timing chart of FIG.

[0220] Figure 11 (1) is the waveform of the AC voltage Vaci of the commercial AC power supply AC input to the AC isolation circuit 1A. If the effective value voltage Vaci of the commercial AC power supply AC input to the AC isolation circuit 1A is 100 [V] and the frequency is 50 [Hz], then the peak voltage on the positive side of the sine wave is √2 times the effective value voltage +141 [V], and the peak voltage on the negative side is -141 [V]. One cycle of the sine wave is 20 [ms].

[0221] Figure 11 (2) represents the first DC voltage Vcb1 applied to both ends of the first capacitor Cb1 by the first DC power supply 11, and the third DC voltage Vcb3 applied to both ends of the third capacitor Cb3 by the third DC power supply 13. The first DC voltage Vcb1 and the third DC voltage Vcb3 are positive DC voltages with a value greater than or equal to the absolute value of the peak value on the negative side of the AC voltage Vaci. More preferably, the first DC voltage Vcb1 and the third DC voltage Vcb3 are positive DC voltages with a value obtained by adding the absolute value of the peak value on the negative side of the AC voltage Vaci to an additional DC voltage α [V] (α>0). In other words, if the AC voltage Vaci is a sine wave with an effective value voltage of 100 [V] and a frequency of 50 [Hz], the first DC voltage Vcb1 can be set to ≥ 141 [V]. More preferably, the first DC voltage Vcb1 can be set to 141 + α [V].

[0222] So, if Figure 11 As shown in (3), the first input voltage Vi1, which is the first positive voltage applied between the negative input electrode and the positive input electrode of the first isolated DC-DC converter 21, is shifted toward the positive side by adding the first DC voltage Vcb1 to the AC voltage Vaci, and the negative component disappears, leaving only the positive component. Similarly, the second input voltage Vi2, which is the first positive voltage applied between the negative input electrode and the positive input electrode of the second isolated DC-DC converter 22, is shifted toward the positive side by adding the third DC voltage Vcb3 to the AC voltage Vaci, and the negative component disappears, leaving only the positive component.

[0223] Since the first input voltage Vi1 does not include a negative component, the first input voltage Vi1 is converted by the first insulating DC-DC converter 21 into the following Figure 11 As shown in (4), the first output voltage (second positive voltage) Vo1 of the same waveform as the first input voltage Vi1 is insulated. Similarly, since the second input voltage Vi2 does not contain a negative component, the second input voltage Vi2 is converted into the first output voltage (second positive voltage) Vo1 by the second insulating DC-DC converter 22. Figure 11 As shown in (4), the second output voltage (second positive voltage) Vo2 of the same waveform is insulated from the second input voltage Vi2.

[0224] By subtracting the first output voltage Vo1 Figure 11 The second DC voltage Vcb2, whose absolute value is equal to the first DC voltage Vcb1, is generated as shown in (5). Figure 11 The first AC output voltage Vaco1 is as shown in (6). Similarly, by subtracting the second output voltage Vo2 Figure 11 The fourth DC voltage Vcb4, whose absolute value is equal to the third DC voltage Vcb3, is generated as shown in (5). Figure 11 The second AC output voltage Vaco2 as shown in (6).

[0225] In this way, the AC insulation circuit 1A can Figure 11 (1) The AC voltage Vaci of the input commercial AC power supply is as Figure 11 The first AC output voltage Vaco1 as shown in (6) is output between the red output terminal and the white output terminal. Figure 11 (1) The AC voltage Vaci of the input commercial AC power supply is as Figure 11 The second AC output voltage Vaco2 as shown in (6) is output between the white output terminal and the black output terminal. Figure 11(1) The AC voltage Vaci of the input commercial AC power supply is as Figure 11 The sum of the first AC output voltage Vaco1 and the second AC output voltage Vaco2 as shown in (7) (indicated by a dotted line) is output between the red output terminal and the black output terminal. If the voltage conversion ratio of the isolated DC-DC converters 21 and 22 is 1:1, when a single-phase 100 [V], 50 [Hz] AC voltage Vaci is input from the commercial AC power supply AC, single-phase 100 [V], 50 [Hz] AC output voltages Vaco1 and Vaco2, which are insulated from the commercial AC power supply AC, can be taken out between the red and white terminals, and between the white and black terminals, respectively. In addition, a single-phase 200 [V], 50 [Hz] AC output voltage Vaco1 + Vaco2, which is insulated from the commercial AC power supply AC, can be taken out between the red and black terminals.

[0226] In the second embodiment, the combination of the first capacitor Cb1 and the first DC power supply 11 and the combination of the third capacitor Cb3 and the third DC power supply 13 may be shared by a single combination of the first capacitor Cb1 and the first DC power supply 11 (see a modified example of the second embodiment).

[0227] By setting the structure to be the AC isolation circuit 1A involved in the second embodiment, it is possible to replace the previous large and heavy single-phase three-wire commercial isolation frequency transformer and provide a small and lightweight isolation type single-phase three-wire AC power supply circuit that can be installed on one (or a few) substrates.

[0228] As with the AC isolation circuit 1A according to the second embodiment, it is also possible to convert from a single-phase two-wire system to a single-phase three-wire system by combining several AC isolation circuits 1 according to the first embodiment. Furthermore, the AC isolation circuit 1 according to the first embodiment can also handle three-phase AC by, for example, preparing three sets of identical AC isolation circuits and implementing delta or Y connections. This makes it possible to replace large and heavy commercial three-phase isolation frequency transformers with a compact and lightweight three-phase AC isolation circuit that can be mounted on, for example, a single substrate (or a small number of substrates).

[0229] The AC isolation circuit 1A according to the second embodiment includes two sets of the AC isolation circuits 1 according to the first embodiment, and has the same operational effects as those of the AC isolation circuit 1 according to the first embodiment.

[0230] (Modification of the Second Embodiment)

[0231] Figure 12 This is a circuit diagram of a single-phase three-wire AC isolation circuit 1B according to a modified example of the second embodiment. Figure 10The AC insulation circuit 1A according to the second embodiment shown is different in that it does not include a set of a third capacitor Cb3 and a third DC power supply 13 .

[0232] Specifically, the AC isolation circuit 1B according to the second embodiment includes a circuit group consisting of a first capacitor Cb1, a first DC power supply 11, a first input capacitor Ci1, a first isolated DC-DC converter 21, a second capacitor Cb2, and a second DC power supply 12; and a circuit group consisting of a second input capacitor Ci2, a second isolated DC-DC converter 22, a fourth capacitor Cb4, and a fourth DC power supply 14. The AC isolation circuit 1B includes a positive input terminal P1 and a negative input terminal P2 connected to the positive and negative electrodes of a commercial AC power supply AC.

[0233] Positive input terminal P1 is connected to the positive input electrode of first isolated DC-DC converter 21 and the positive input electrode of second isolated DC-DC converter 22 via first capacitor Cb1. Negative input terminal P2 is connected to the negative input electrode of first isolated DC-DC converter 21 and to the negative input electrode of second isolated DC-DC converter 22. First DC power supply 11 is connected in parallel with first capacitor Cb1. First input capacitor Ci1 is connected between the positive and negative input electrodes of first isolated DC-DC converter 21. Second input capacitor Ci2 is connected between the positive and negative input electrodes of second isolated DC-DC converter 22.

[0234] The positive output electrode of the first insulated DC-DC converter 21 is connected to the red output terminal, serving as the first output terminal, via the second capacitor Cb2. The negative output electrode of the first insulated DC-DC converter 21 is connected to the white output terminal, serving as the second output terminal. Furthermore, the positive output electrode of the second insulated DC-DC converter 22 is connected to the white output terminal. The negative output electrode of the second insulated DC-DC converter 22 is connected to the black output terminal, serving as the third output terminal, via the fourth capacitor Cb4. Furthermore, the positive output electrode of the second insulated DC-DC converter 22 may be connected to the white output terminal via the fourth capacitor Cb4, and the negative output electrode of the second insulated DC-DC converter 22 may be connected to the black output terminal. A second DC power supply 12 is connected in parallel with the second capacitor Cb2. A fourth DC power supply 14 is connected in parallel with the fourth capacitor Cb4.

[0235] The second isolated DC-DC converter 22 is configured similarly to the isolated DC-DC converter 21 of the first embodiment. The fourth capacitor Cb4 and the fourth DC power supply 14 are configured similarly to the second capacitor Cb2 and the second DC power supply 12 of the first embodiment.

[0236] Next, use Figure 13The operation of the AC insulation circuit 1B according to the modification of the second embodiment is described with reference to the timing chart.

[0237] Figure 13 (1) is the waveform of the AC voltage Vaci of the commercial AC power supply AC input to the AC isolation circuit 1B. If the AC voltage Vaci of the commercial AC power supply AC input to the AC isolation circuit 1B has an effective value of 100 [V] and a frequency of 50 [Hz], the peak voltage on the positive side of the sine wave is √2 times the effective value voltage +141 [V], and the peak voltage on the negative side is -141 [V]. One cycle of the sine wave is 20 [ms].

[0238] Figure 13 (2) represents the first DC voltage Vcb1 applied to both ends of the first capacitor Cb1 by the first DC power supply 11. The first DC voltage Vcb1 is a positive DC voltage having a value greater than or equal to the absolute value of the peak value on the negative side of the AC voltage Vaci. More preferably, the first DC voltage Vcb1 is a positive DC voltage having a value obtained by adding the absolute value of the peak value on the negative side of the AC voltage Vaci to an additional DC voltage α [V] (α>0). In other words, if the AC voltage Vaci is a sine wave with an effective value voltage of 100 [V] and a frequency of 50 [Hz], the first DC voltage Vcb1 can be set to ≥ 141 [V]. More preferably, the first DC voltage Vcb1 can be set to 141 + α [V].

[0239] So, if Figure 13 As shown in (3), the first positive voltage Vi applied between the input negative electrode and the input positive electrode of the first insulating type DC-DC converter 21 and between the input negative electrode and the input positive electrode of the second insulating type DC-DC converter 22 is shifted to the positive side by adding the first DC voltage Vcb1 to the AC voltage Vaci, and the negative side component disappears, leaving only the positive side component.

[0240] Since the first positive voltage Vi does not include a negative component, the first positive voltage Vi is converted by the first insulating DC-DC converter 21 into the following: Figure 13 As shown in (4), the first output voltage Vo1 of the same waveform as the first positive voltage Vi1 is insulated. Similarly, since the first positive voltage Vi does not contain a negative component, the first positive voltage Vi is converted into the first positive voltage Vi through the second insulating DC-DC converter 22. Figure 13 As shown in (4), the second output voltage Vo2 has the same waveform as the first positive voltage Vi and is insulated.

[0241] By subtracting the first output voltage Vo1 Figure 13 The second DC voltage Vcb2, whose absolute value is equal to the first output voltage Vo1, is generated as shown in (5). Figure 13 The first AC output voltage Vaco1 is as shown in (6). Similarly, by subtracting the second output voltage Vo2 Figure 11 The fourth DC voltage Vcb4, whose absolute value is equal to the first output voltage Vo1, is generated as shown in (5). Figure 13 The second AC output voltage Vaco2 as shown in (6).

[0242] In this way, the AC insulation circuit 1B can Figure 13 (1) The AC voltage Vaci of the input commercial AC power supply AC is as Figure 13 The first AC output voltage Vaco1 as shown in (6) is output between the red output terminal and the white output terminal. Similarly, the AC insulation circuit 1B can Figure 13 (1) The AC voltage Vaci of the input commercial AC power supply AC is as Figure 13 The second AC output voltage Vaco2 as shown in (6) is output between the white output terminal and the black output terminal. Figure 13 (1) The AC voltage Vaci of the input commercial AC power supply AC is as Figure 13 The sum of the first AC output voltage Vaco1 and the second AC output voltage Vaco2 as shown in (7) (indicated by a dotted line) is output between the red output terminal and the black output terminal. If the voltage conversion ratio of the isolated DC-DC converters 21 and 22 is 1:1, when a single-phase 100 [V], 50 [Hz] AC voltage Vaci is input from the commercial AC power supply AC, single-phase 100 [V], 50 [Hz] AC output voltages Vaco1 and Vaco2, which are insulated from the commercial AC power supply AC, can be taken out between the red and white terminals, and between the white and black terminals, respectively. In addition, a single-phase 200 [V], 50 [Hz] AC output voltage Vaco1 + Vaco2, which is insulated from the commercial AC power supply AC, can be taken out between the red and black terminals.

[0243] In the AC isolation circuit 1B according to the modification of the second embodiment, the combination of the third capacitor Cb3 and the third DC power supply 13 is omitted from the AC isolation circuit 1A according to the second embodiment, and thus can be configured with fewer components.

[0244] Even with a structure like the AC isolation circuit 1B involved in a modified example of the second embodiment, it is possible to replace the conventional large and heavy single-phase three-wire commercial isolation frequency transformer and provide a small and lightweight isolated single-phase three-wire AC power supply circuit that can be mounted on, for example, one (or a small number of) substrates.

[0245] (Third embodiment)

[0246] Figure 14 1C is a circuit diagram of a single-phase three-wire AC power supply circuit 1C according to the third embodiment. Figure 1 The AC isolation circuit 1 according to the first embodiment shown constitutes a non-insulated single-phase three-wire AC power supply circuit. Specifically, the single-phase three-wire AC power supply circuit 1C, like the first embodiment, includes a first capacitor Cb1, a first DC power supply 11, an input capacitor Ci, an isolated DC-DC converter 21, a second capacitor Cb2, and a second DC power supply 12. The single-phase three-wire AC power supply circuit 1C according to the third embodiment includes a red output terminal as a first output terminal connected to the positive electrode of the first AC output voltage Vaco1, a white output terminal as a second output terminal connected to the negative electrode, and a black output terminal as a third output terminal. Furthermore, a power line connected to the positive input terminal of the commercial AC power supply AC and a line connected to the white output terminal are connected via a first electric wire 41. Furthermore, a power line connected to the negative electrode of the commercial AC power supply AC and the black output terminal are connected via a second electric wire 42. In the single-phase three-wire AC power supply circuit 1C, the AC voltage Vaci of the commercial AC power supply AC is directly output as the second AC output voltage Vaco2 between the white output terminal and the black output terminal. The remaining structure of the single-phase three-wire AC power supply circuit 1C is the same as that of the AC isolation circuit 1 according to the first embodiment, and therefore its description is omitted.

[0247] Next, use Figure 15 The timing chart of FIG. 1 illustrates the operation of the single-phase three-wire AC power supply circuit 1C according to the third embodiment.

[0248] Figure 15 (1) is the waveform of the AC voltage Vaci of the commercial AC power supply AC input to the single-phase three-wire AC power supply circuit 1C. If the AC voltage Vaci of the commercial AC power supply AC input to the single-phase three-wire AC power supply circuit 1C has an effective value of 100 [V] and a frequency of 50 [Hz], then the peak voltage on the positive side of the sine wave is √2 times the effective value voltage +141 [V], and the peak voltage on the negative side is -141 [V]. One cycle of the sine wave is 20 [ms].

[0249] Figure 15(2) represents the first DC voltage Vcb1 applied to both ends of the first capacitor Cb1 by the first DC power supply 11. The first DC voltage Vcb1 is a positive DC voltage having a value greater than or equal to the absolute value of the peak value on the negative side of the AC voltage Vaci. More preferably, the first DC voltage Vcb1 is a positive DC voltage having a value obtained by adding the absolute value of the peak value on the negative side of the AC voltage Vaci to an additional DC voltage α [V] (α>0). In other words, if the AC voltage Vaci is a sine wave with an effective value voltage of 100 [V] and a frequency of 50 [Hz], the first DC voltage Vcb1 can be set to ≥ 141 [V]. More preferably, the first DC voltage Vcb1 can be set to 141 + α [V].

[0250] So, if Figure 15 As shown in (3), the first positive voltage Vi applied between the input negative electrode and the input positive electrode of the isolated DC-DC converter 21 is shifted to the positive side by adding the first DC voltage Vcb1 to the AC voltage Vaci, and the negative side component disappears, leaving only the positive side component.

[0251] Since the first positive voltage Vi does not include a negative component, the first positive voltage Vi is converted by the insulating DC-DC converter 21 into the following: Figure 15 (4) shows a second positive voltage Vo of the same waveform as the first positive voltage Vi and insulated therefrom.

[0252] By subtracting the second positive voltage Vo from Figure 15 The second DC voltage Vcb2, whose absolute value is equal to the first output voltage Vo1, is generated as shown in (5). Figure 15 In the single-phase three-wire AC power supply circuit 1C, the AC voltage Vaci of the commercial AC power supply AC is directly output as the second AC output voltage Vaco2.

[0253] In the single-phase three-wire AC power supply circuit 1C, if Figure 14 As shown, the connection point of the negative terminal of the first AC output voltage Vaco1 and the positive terminal of the second AC output voltage Vaco2 is set as the white output terminal, the positive terminal of the first AC output voltage Vaco1 is set as the red output terminal, and the negative terminal of the second AC output voltage Vaco2 is set as the black output terminal. Thus, if the voltage conversion ratio of the isolated DC-DC converter 21 is 1:1, when a single-phase 100 [V] voltage is input as the voltage of the commercial AC power supply AC, a single-phase 100 [V] AC voltage can be extracted from the red and white, and white and black output terminals, respectively ( Figure 15 (6)). In addition, a single-phase 200[V] AC voltage can be taken out between the red and black terminals ( Figure 15(7) (indicated by the dotted line).

[0254] The single-phase three-wire AC power supply circuit 1C of the third embodiment directly outputs the AC voltage Vaci of the commercial AC power supply AC as the second AC output voltage Vaco2. Therefore, the commercial AC power supply AC is not insulated from the output terminals of the single-phase three-wire AC power supply circuit 1C. However, the single-phase three-wire AC power supply circuit 1C according to the third embodiment can be constructed simply by adding the first electric wire 41 and the second electric wire 42 to the AC isolation circuit 1 according to the first embodiment. Therefore, the single-phase three-wire AC power supply circuit can be constructed more simply than the AC isolation circuit 1A according to the second embodiment.

[0255] By setting the structure to be the single-phase three-wire AC power supply circuit 1C involved in the third embodiment, it is possible to replace the previous large and heavy single-phase three-wire commercial insulating frequency transformer and provide a small and lightweight single-phase three-wire AC power supply circuit that can be installed on one (or a few) substrates.

[0256] (Modification of the third embodiment)

[0257] Figure 16 This is a circuit diagram of a single-phase three-wire AC power supply circuit 1D according to a modified example of the third embodiment. The single-phase three-wire AC power supply circuit 1D uses Figure 1The AC isolation circuit 1 according to the first embodiment shown constitutes a non-insulated single-phase three-wire AC power supply circuit. Specifically, the single-phase three-wire AC power supply circuit 1D, similar to the first embodiment, includes a first capacitor Cb1, a first DC power supply 11, an input capacitor Ci, an isolated DC-DC converter 21, a second capacitor Cb2, and a second DC power supply 12. The single-phase three-wire AC power supply circuit 1D, unlike the AC isolation circuit 1 according to the first embodiment, includes a white output terminal (first output terminal) connected to the positive electrode of a first AC output voltage Vaco1 corresponding to the AC output voltage Vaco of the AC isolation circuit 1, a black output terminal (second output terminal) connected to the negative electrode, and a red output terminal (third output terminal). Furthermore, a power line connected to the negative electrode of a commercial AC power source AC (corresponding to the negative input of the AC isolation circuit 1 according to the first embodiment) is connected to the positive electrode of the first AC output voltage Vaco1 (corresponding to the positive output of the AC isolation circuit 1 according to the first embodiment) via a first electric wire 41A. Furthermore, a power line connected to the positive electrode of the commercial AC power source AC is connected to the red output terminal via a second electric wire 42A. In the single-phase three-wire AC power supply circuit 1D, the AC voltage Vaci of the commercial AC power source AC is directly output as a second AC output voltage Vaco2 between the red and white output terminals. The remaining configuration of the single-phase three-wire AC power supply circuit 1C according to the third embodiment is the same as that of the AC isolation circuit 1 according to the first embodiment, and therefore, its description is omitted.

[0258] In the single-phase three-wire AC power supply circuit 1D according to the modification of the third embodiment, it is also possible to provide a circuit for using the single-phase three-wire AC power supply circuit 1C according to the third embodiment. Figure 15 The timing diagram illustrates the operation of the same operation as that of a single-phase three-wire AC power supply circuit.

[0259] Even with a structure like the single-phase three-wire AC power supply circuit 1D involved in a modified example of the third embodiment, it is possible to replace the conventional large and heavy single-phase three-wire commercial insulating frequency transformer and provide a small and lightweight single-phase three-wire AC power supply circuit that can be mounted on, for example, one (or a small number of) substrates.

[0260] In addition, the first embodiment Figures 5 to 8 The isolated DC-DC converters 21A to 21E of the first to fifth modified examples shown above are also applicable to the second embodiment, the third embodiment, and their modified examples.

[0261] Description of Reference Numerals

[0262] 1, 1A, 1B AC isolation circuit; 1C, 1D single-phase three-wire AC power supply circuit; 11 First DC power supply; 12 Second DC power supply; 13 Third DC power supply; 14 Fourth DC power supply; 21 Isolated DC-DC converter (First isolated DC-DC converter); 22 Second isolated DC-DC converter; 41 First wire; 42 Second wire; AC Commercial AC power supply; C11 First current resonance capacitor; C12 Second current resonance capacitor; Ci Input capacitor; Co Output smoothing capacitor; Cb1 First capacitor; Cb2 Second capacitor; Cb3 Third capacitor; Cb4 Fourth capacitor; Cv11 First voltage quasi-resonant capacitor; Cv12 Second voltage quasi-resonant capacitor; f Commercial AC power supply frequency (First frequency); fr Resonant frequency; fs Switching frequency (Second frequency); fv Voltage quasi-resonant frequency; P1 Positive input terminal; P2 Negative input terminal; S1 First output terminal; S2 Second output terminal; T high-frequency transformer; Vaci AC voltage (first AC voltage); Vaco AC output voltage (second AC voltage); Vcb1 first DC voltage; Vcb2 second DC voltage; Vcb3 third DC voltage; Vcb4 fourth DC voltage; Vi first positive voltage; Vo second positive voltage.

Claims

1. An AC insulation circuit comprising: The positive input terminal and the negative input terminal are input with a first AC voltage having a first frequency; A first output terminal and a second output terminal; an isolated DC-DC converter controlled by a second frequency higher than the first frequency, comprising an input positive electrode connected to the positive input terminal, an input negative electrode connected to the negative input terminal, an output positive electrode connected to the first output terminal, and an output negative electrode connected to the second output terminal, the input positive electrode and the input negative electrode being insulated from the output positive electrode and the output negative electrode; a first capacitor connected to at least one of between the positive input terminal and the positive input electrode and between the negative input terminal and the negative input electrode; a first DC power supply connected in parallel with the first capacitor and outputting a first DC voltage for charging the first capacitor; a second capacitor connected to at least one of between the first output terminal and the output positive electrode and between the second output terminal and the output negative electrode; and The second DC power supply is connected in parallel with the second capacitor and outputs a second DC voltage for charging the second capacitor.

2. The AC insulation circuit according to claim 1, wherein: The first DC voltage is set to a value such that, when added to the first AC voltage, the first AC voltage becomes a first positive voltage shifted toward the positive side across all phases. The isolated DC-DC converter converts the input first positive voltage into a second positive voltage insulated from the first positive voltage at a predetermined voltage conversion ratio and outputs the second positive voltage. The second DC voltage is set to a value obtained by subtracting a predetermined DC voltage component from the second positive voltage to obtain a second AC voltage. The second AC voltage is output between the first output terminal and the second output terminal.

3. The AC insulation circuit according to claim 2, wherein: The isolated DC-DC converter comprises: a high-frequency transformer comprising a core, a primary winding, and a secondary winding coupled to the primary winding via the core, the primary winding and the secondary winding being insulated from each other and operable at the second frequency; a primary-side circuit connected between the input positive electrode, the input negative electrode and the primary winding; and A secondary side circuit, connected with the secondary winding, The primary side circuit is controlled by the second frequency, converts the first positive voltage into a third AC voltage having the second frequency and applies the third AC voltage to the primary winding. The secondary winding outputs a fourth AC voltage having the second frequency based on the third AC voltage applied to the primary winding. The secondary side circuit is controlled by the second frequency, rectifies the fourth AC voltage, and outputs the second positive voltage.

4. The AC insulation circuit according to claim 3, wherein: The primary side circuit comprises: a first series circuit including a primary-side first switching element and a primary-side second switching element connected in parallel with the input positive electrode and the input negative electrode; a current resonating capacitor connected in parallel with the first series circuit relative to the positive input electrode and the negative input electrode, the capacitor being composed of a first current resonating capacitor and a second current resonating capacitor connected in series; a voltage quasi-resonance capacitor circuit, which is a series circuit of a first voltage quasi-resonance capacitor connected in parallel with the primary-side first switching element and a second voltage quasi-resonance capacitor connected in parallel with the primary-side second switching element; as well as Current resonance with an inductor, connected in series with the primary winding, In the primary-side circuit, a series circuit of the primary winding and the current-resonating inductor is connected between a connection point between the primary-side first switching element and the primary-side second switching element and a connection point between the first current-resonating capacitor and the second current-resonating capacitor. The primary-side first switching element and the primary-side second switching element are turned on and off in synchronization with the second frequency.

5. The AC insulation circuit according to claim 3, wherein: The primary side circuit comprises: a series circuit including a primary-side first switching element and a primary-side second switching element connected in parallel with the input positive electrode and the input negative electrode; a voltage quasi-resonance capacitor circuit comprising a voltage quasi-resonance capacitor connected in parallel to one of the primary-side first switching element and the primary-side second switching element; as well as A current resonance inductor and a current resonance capacitor are connected in series with the primary winding. In the primary-side circuit, a series circuit of the primary winding, the current-resonant inductor, and the current-resonant capacitor is connected in parallel with one of the primary-side first switching element and the primary-side second switching element. The primary-side first switching element and the primary-side second switching element are turned on and off in synchronization with the second frequency.

6. The AC insulation circuit according to claim 3, wherein: The primary side circuit comprises: a first series circuit and a second series circuit, wherein the first series circuit is a series circuit of a first primary-side switching element and a second primary-side switching element connected in parallel with the positive input electrode and the negative input electrode, and the second series circuit is a series circuit of a third primary-side switching element and a fourth primary-side switching element connected in parallel with the positive input electrode and the negative input electrode; a first voltage quasi-resonance capacitor connected in parallel with the first primary-side switching element; a second voltage quasi-resonance capacitor connected in parallel with the primary-side second switching element; a third voltage quasi-resonance capacitor connected in parallel with the third primary-side switching element; a fourth voltage quasi-resonant capacitor connected in parallel with the fourth primary-side switching element; as well as A current resonance inductor and a current resonance capacitor are connected in series with the primary winding. In the primary-side circuit, a series circuit of the primary winding, the current-resonating inductor, and the current-resonating capacitor is connected between a connection point between the primary-side first switching element and the primary-side second switching element and a connection point between the primary-side third switching element and the primary-side fourth switching element. The first primary-side switching element, the second primary-side switching element, the third primary-side switching element, and the fourth primary-side switching element are turned on and off in synchronization with the second frequency.

7. The AC insulation circuit according to any one of claims 4 to 6, wherein: The secondary side circuit includes a series circuit of a secondary side first switching element and a secondary side second switching element connected in parallel to a series circuit of a first secondary winding and a second secondary winding as the secondary winding. A connection point between the secondary-side first switching element and the secondary-side second switching element is connected to an output terminal of the secondary-side circuit via one end of an output smoothing capacitor. A connection point between the first secondary winding and the second secondary winding is connected to the other output terminal of the secondary side circuit via the other end of the output smoothing capacitor. The secondary-side first switching element and the secondary-side second switching element are turned on and off in synchronization with the respective switching elements of the primary-side circuit by the second frequency.

8. The AC insulation circuit according to any one of claims 4 to 6, wherein: The secondary side circuit includes a series circuit of a secondary side first switching element and a secondary side second switching element and a series circuit of a secondary side third switching element and a secondary side fourth switching element, which are connected in parallel with the secondary winding. A connection point between the secondary-side first switching element and the secondary-side second switching element is connected to an output terminal of the secondary-side circuit via one end of an output smoothing capacitor. The connection point between the secondary-side third switching element and the secondary-side fourth switching element is connected to the other output terminal of the secondary-side circuit via the other end of the output smoothing capacitor. The secondary-side first switching element, the secondary-side second switching element, the secondary-side third switching element, and the secondary-side fourth switching element are turned on and off in synchronization with the respective switching elements of the primary-side circuit by the second frequency.

9. The AC insulation circuit according to claim 4 or claim 5, wherein: The isolated DC-DC converter includes a primary-side control circuit that controls the first primary-side switching element and the second primary-side switching element so that they are alternately turned on and off at the second frequency with substantially the same conduction width, a dead time during which the first primary-side switching element and the second primary-side switching element are simultaneously turned off.

10. The AC insulation circuit according to claim 9, wherein: Voltage quasi-resonance is performed during the dead time at the resonant frequency of the inductance of the primary winding and the capacitor circuit for voltage quasi-resonance.

11. The AC insulation circuit according to claim 4 or claim 5, wherein: The capacitance value of the current resonant capacitor and the value of the current resonant inductor are set so that the resonant frequencies of the current resonant capacitor and the current resonant inductor are substantially equal to the second frequency.

12. The AC insulation circuit according to claim 6, wherein: The isolated DC-DC converter includes a primary-side control circuit that controls the first, second, third, and fourth primary-side switching elements to be alternately turned on and off at the second frequency with substantially the same conduction width, a dead time during which the first, second, third, and fourth primary-side switching elements are simultaneously turned off. The first and fourth primary-side switching elements are simultaneously turned on and off, and the second and third primary-side switching elements are simultaneously turned on and off.

13. The AC insulation circuit according to claim 12, wherein: Voltage quasi-resonance is performed during the dead time at a resonant frequency of the inductance of the primary winding, the combined capacitance of the series circuit of the first voltage quasi-resonance capacitor and the third voltage quasi-resonance capacitor, and the series circuit of the second voltage quasi-resonance capacitor and the fourth voltage quasi-resonance capacitor.

14. The AC insulation circuit according to claim 6, wherein: The capacitance value of the current resonant capacitor and the value of the current resonant inductor are set so that the resonant frequencies of the current resonant capacitor and the current resonant inductor are substantially equal to the second frequency.

15. The AC insulation circuit according to claim 1 or claim 2, wherein: The first frequency is equal to the frequency of the commercial AC power supply.

16. The AC insulation circuit according to claim 2, wherein: The second AC voltage has a frequency equal to the first frequency.

17. An AC insulation circuit, A first AC insulation circuit and a second AC insulation circuit, each of which is the AC insulation circuit according to claim 1 or claim 2, The positive input terminal of the first AC isolation circuit is connected to the positive input terminal of the second AC isolation circuit, the negative input terminal of the first AC isolation circuit is connected to the negative input terminal of the second AC isolation circuit, and the second output terminal of the first AC isolation circuit is connected to the first output terminal of the second AC isolation circuit.

18. An AC insulation circuit comprising: The AC insulation circuit according to claim 1 or claim 2; 3rd output terminal; a second insulating DC-DC converter controlled by the second frequency, comprising a second positive input electrode connected to the positive input electrode of the insulating DC-DC converter, a second negative input electrode connected to the negative input electrode of the insulating DC-DC converter, a second positive output electrode connected to the second output terminal, and a second negative output electrode connected to the third output terminal, wherein the second positive input electrode and the second negative input electrode are insulated from the second positive output electrode and the second negative output electrode; a third capacitor connected to one of between the second output terminal and the second output positive electrode and between the third output terminal and the second output negative electrode; and The third DC power supply is connected in parallel with the third capacitor and outputs a third DC voltage for charging the third capacitor.

19. An AC power circuit comprising: The AC insulation circuit according to claim 1 or claim 2; and The third output terminal is connected to the negative input terminal. The positive input terminal is connected to the second output terminal.

20. An AC power circuit comprising: The AC insulation circuit according to claim 1 or claim 2; and The third output terminal is connected to the positive input terminal. The negative input terminal is connected to the first output terminal.

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