Insulated DCDC Converter

Abstract

An isolated DC-DC converter (100) comprises a transformer (10), a full-bridge switch circuit (20), a protection circuit (21), a control unit (40), an inductor (13), and an output circuit (30). The isolated DC-DC converter (100) comprises a first voltage detection unit (40A) for detecting a voltage value between a first conductive path (1) and a second conductive path (2), and a first current detection unit (40C) for detecting a current value of the inductor (13). The control unit (40) determines at least one of a first dead time and a second dead time based on a voltage value detected by the first voltage detection unit (40A) and a current value detected by the first current detection unit (40C), such that the larger the voltage value, the larger the dead time, and the larger the current value, the smaller the dead time.

Description

Technical Field

[0001] The present disclosure relates to an isolation type DCDC converter. Background Art

[0002] The isolated DCDC converter seeks to adapt to a wide range of input voltage and output load while maintaining high efficiency. As a method of achieving high efficiency, a method is known in which a full-bridge circuit is provided on the primary side of a transformer and a rectifier circuit is provided on the secondary side, and the drain-source voltage of a switching element is reduced to 0 V during the dead time of the full-bridge circuit before the next switching element is turned on (soft switching).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2004-140913

[0006] Patent Document 2: Japanese Patent Application Publication No. 2016-111805

[0007] Patent Document 3: Japanese Patent Application Publication No. 2013-132112 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The time when the voltage between the terminals of the switching element reaches the minimum can be changed according to the current flowing in the resonant inductor, so it is preferable to change the dead time according to the current of the inductor. However, in the cited documents, it is not realized to dynamically obtain the dead time according to the current flowing in the resonant inductor.

[0010] The present disclosure provides an isolated DC-DC converter that can achieve high efficiency more simply.

[0011] Solutions to Solve Problems

[0012] As one of the insulating DCDC converters disclosed herein, the insulating DCDC converter of the phase shift type comprises: a transformer having a primary coil and a secondary coil; a full-bridge switching circuit having a first switching element, a second switching element, a third switching element and a fourth switching element; a protection circuit having a first diode and a second diode; a control unit for controlling the operation of the switching circuit; an inductor; and an output circuit connected to the secondary coil, wherein the first switching element and the second switching element are connected in series between a first conductive circuit and a second conductive circuit, the third switching element and the fourth switching element are connected in series between the first conductive circuit and the second conductive circuit, one end of the inductor is electrically connected to a first connection point between the first switching element and the second switching element, the other end of the inductor is electrically connected to one end of the primary coil, the anode of the first diode, and the cathode of the second diode, and the The other end of the primary side coil is electrically connected to a second connection point between the third switching element and the fourth switching element, the cathode of the first diode is electrically connected to the first conducting circuit, and the anode of the second diode is electrically connected to the second conducting circuit. The isolated DCDC converter comprises: a voltage detection unit for detecting a voltage value between the first conducting circuit and the second conducting circuit; and a current detection unit for detecting a current value of the inductor. The control unit determines at least one of a first dead time and a second dead time based on the voltage value detected by the voltage detection unit and the current value detected by the current detection unit in such a manner that the larger the voltage value, the larger the dead time, and the larger the current value, the smaller the dead time. The first dead time is a time when both the first switching element and the second switching element are turned off, and the second dead time is a time when both the third switching element and the fourth switching element are turned off.

[0013] Effects of the Invention

[0014] According to the present disclosure, a simple and highly efficient isolated DCDC converter can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 1 is a circuit diagram showing an isolated DCDC converter according to the first embodiment.

[0016] Figure 2 This is a circuit diagram showing the path of current flowing through the primary side and the secondary side of a transformer when the first switching element and the fourth switching element are in the on state in a basic isolation type DCDC converter.

[0017] Figure 3This is a circuit diagram showing a path of a current flowing on the secondary side of a transformer when a first switching element, a second switching element, a third switching element, and a fourth switching element are in an off state in a basic isolation type DCDC converter.

[0018] Figure 4 This is a circuit diagram showing the path of current flowing through the primary side and the secondary side of a transformer when the second switching element and the third switching element are in the on state in a basic isolation type DCDC converter.

[0019] Figure 5 This is a timing chart showing the timing at which each of the first switching element, the second switching element, the third switching element, and the fourth switching element is switched on and off in the isolated DCDC converter according to the first embodiment.

[0020] Figure 6 Shown on the upper side Figure 5 The enlarged view of the timing chart of the first switching element and the second switching element at time T2 in FIG. 1 is a diagram showing changes in the voltage applied between the drain and the source of the second switching element at time T2 at the lower side.

[0021] Figure 7 : is a graph showing the relationship between the current IL flowing through the inductor and the current Iout flowing through the choke coil.

[0022] Figure 8 This is a circuit diagram showing an isolated DCDC converter according to the second embodiment. DETAILED DESCRIPTION

[0023] [Description of Embodiments of the Present Disclosure]

[0024] First, embodiments of the present disclosure will be described by way of examples.

[0025] [1] An insulating type DCDC converter disclosed in the present invention comprises a transformer, a full-bridge type switching circuit, a protection circuit, a control unit, an inductor and an output circuit. The transformer comprises a primary side coil and a secondary side coil. The full-bridge type switching circuit comprises a first switching element, a second switching element, a third switching element and a fourth switching element. The protection circuit comprises a first diode and a second diode. The control unit controls the operation of the switching circuit. The output circuit is connected to the secondary side coil. The first switching element and the second switching element are connected in series between the first conductive circuit and the second conductive circuit. The third switching element and the fourth switching element are connected in series between the first conductive circuit and the second conductive circuit. One end of the inductor is electrically connected to a first connection point between the first switching element and the second switching element. The other end of the inductor is electrically connected to one end of the primary side coil, the anode of the first diode and the cathode of the second diode. The other end of the primary side coil is electrically connected to a second connection point between the third switching element and the fourth switching element. The cathode of the first diode is electrically connected to the first conductive circuit. The insulating type DCDC converter disclosed in the present invention is an insulating type DCDC converter of a phase shift type in which the anode of the second diode is electrically connected to the second conductive circuit. The insulated DCDC converter of the present disclosure includes a voltage detection unit for detecting a voltage value between a first conductive path and a second conductive path and a current detection unit for detecting a current value of an inductor. The control unit determines at least one of a first dead time and a second dead time based on the voltage value detected by the voltage detection unit and the current value detected by the current detection unit, such that the larger the voltage value, the larger the dead time, and the larger the current value, the smaller the dead time.

[0026] In the isolated DCDC converter of [1], the first dead time is the time when the first switching element and the second switching element are both turned off. The second dead time is the time when the third switching element and the fourth switching element are both turned off. Therefore, the isolated DCDC converter can absorb the recovery surge generated in the secondary side coil of the transformer through the protection circuit. At the same time, the isolated DCDC converter calculates the first dead time and the second dead time based on the current value of the current flowing in the inductor detected by the current detection unit. Therefore, the isolated DCDC converter can dynamically obtain the dead time based on the value corresponding to the current flowing in the inductor.

[0027] [2] In the isolated DCDC converter of [1] above, the control unit determines whether to reflect the magnetizing inductance of the transformer when determining at least one of the first dead time and the second dead time based on an increase state of the current value.

[0028] The isolated DCDC converter of [2] can regard the increase of the current value as the state of the load current. Therefore, it is determined whether to reflect the excitation inductance according to the state of the load current, and the first dead time and the second dead time are calculated and calculated, so that the dead time can be obtained more finely.

[0029] [3] In the isolated DCDC converter of [2] above, the control unit may reflect the magnetizing inductance and determine at least one of the first dead time and the second dead time when the rate of increase of the current value is less than a threshold value. Alternatively, the control unit may determine at least one of the first dead time and the second dead time without reflecting the magnetizing inductance when the rate of increase of the current value exceeds the threshold value.

[0030] In the above-mentioned insulating type DCDC converter [3], when the excitation inductance is reflected when the rate of increase of the current value is below the threshold value, the dead time of the state in which the load current is small but the magnitude of the excitation current flowing in the primary side coil cannot be ignored is calculated. On the other hand, when the rate of increase of the current value exceeds the threshold value, when the excitation inductance is not reflected, the dead time of the state in which the load current is large but the magnitude of the excitation current flowing in the primary side coil can be ignored is calculated. Therefore, by reflecting the state of the excitation current flowing in the primary side coil according to the magnitude of the load current, a more accurate dead time can be obtained.

[0031] [4] In the isolated DCDC converter of any one of [1] to [3] above, the voltage detection unit includes a secondary side voltage measuring unit for measuring the secondary side voltage applied from the secondary side coil of the transformer, and detects the voltage value between the first conductive path and the second conductive path based on the secondary side voltage measured by the secondary side voltage measuring unit.

[0032] The above-mentioned insulating type DCDC converter of [4] can detect the voltage value between the first conductive path and the second conductive path based on the secondary side voltage measured by the secondary side voltage measuring unit. Therefore, the insulating type DCDC converter is advantageous in a case where it is difficult to directly measure the voltage value between the first conductive path and the second conductive path or in a case where it is more preferable to estimate the voltage value by measuring the secondary side voltage rather than directly measuring it.

[0033] [5] In the isolated DCDC converter of [4] above, the voltage detection unit obtains a voltage value between the first conductive path and the second conductive path based on the secondary side voltage and the turns ratio of the primary side coil to the secondary side coil.

[0034] The above-mentioned insulating type DCDC converter of [5] can more simply realize a structure that can more accurately determine the voltage value between the first conductive path and the second conductive path based on the secondary side voltage.

[0035] [6] In the isolated DCDC converter of any one of [4] or [5] above, the isolated DCDC converter is a step-down DCDC converter that steps down an input voltage applied between the first conductive path and the second conductive path and outputs an output voltage.

[0036] The above-mentioned insulating type DCDC converter of [6] can measure an output voltage which is a relatively low value compared to the voltage value between the first conductive path and the second conductive path and derive the voltage value between the first conductive path and the second conductive path based on the output voltage. Therefore, the insulating type DCDC converter can omit or simplify the structure required for detecting a higher voltage, and can further miniaturize the structure capable of detecting the voltage value between the first conductive path and the second conductive path.

[0037] [7] In the isolated DCDC converter of any one of [4] to [6] above, the first conductive circuit and the second conductive circuit are insulated from the output circuit and the control unit, and the fourth conductive circuit in a pair of third conductive circuits and fourth conductive circuits for applying an output voltage in the output circuit is electrically connected to a reference conductive circuit of the control unit.

[0038] [Details of the embodiments of the present disclosure]

[0039] <Implementation method 1>

[0040] [Overview of isolated DCDC converter]

[0041] The insulated DCDC converter 100 of the first embodiment (hereinafter, also referred to as the converter 100) is used as a power source for outputting electric power for driving an electric drive device (motor, etc.) in a vehicle such as a hybrid vehicle or an electric vehicle (EV (Electric Vehicle)). The converter 100 transforms the input voltage Vin supplied between the first conductive path 1 and the second conductive path 2 to generate an output voltage Vout, and applies the output voltage Vout between the third conductive path 3 and the fourth conductive path 4. Figure 1 As shown, the converter 100 includes a transformer 10, a switch circuit 20 provided between the first conductive path 1 and the transformer 10, an output circuit 30 connected between the transformer 10 and the third conductive path 3, and a control unit 40 for controlling the operation of the switch circuit 20. In actual use, a DC power supply (not shown) is connected between the first conductive path 1 and the second conductive path 2, and a load 6 is connected between the third conductive path 3 and the fourth conductive path 4. In addition, an input capacitor 7 for stabilizing the input voltage Vin is connected between the first conductive path 1 and the second conductive path 2.

[0042] The transformer 10 includes a primary coil 11 and secondary coils 12A and 12B. The number of turns of the primary coil 11 is N1. The number of turns of the secondary coils 12A and 12B is N2. The secondary coils 12A and 12B are electrically connected in series with each other at a third connection point P3. The turns ratio N of the transformer 10 is represented by N2 / N1. In the transformer 10, an excitation inductance 14 is formed in parallel with the primary coil 11.

[0043] The switch circuit 20 converts the DC voltage supplied to the first conductive path 1 and the second conductive path 2, that is, the input voltage Vin, into AC, and supplies it to the primary side coil 11 of the transformer 10. The switch circuit 20 has a structure in which a first switch element 20A, a second switch element 20B, a third switch element 20C, and a fourth switch element 20D (hereinafter, also referred to as switch elements 20A, 20B, 20C, 20D) are connected in a full bridge.

[0044] The switch circuit 20 includes switch elements 20A, 20B, 20C, 20D, a first diode 20E, a second diode 20F, and an inductor 13. The switch elements 20A, 20B, 20C, 20D may be various known switch elements, but MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is preferably used.

[0045] The switching elements 20A, 20B, 20C, and 20D are each provided with a parasitic diode 20G, 20H, 20J, and 20K as a parasitic component. Specifically, in each of the switching elements 20A, 20B, 20C, and 20D, the cathode of each of the parasitic diodes 20G, 20H, 20J, and 20K is electrically connected to the drain side, and the anode is electrically connected to the source side. In addition to the parasitic diodes 20G, 20H, 20J, and 20K, another diode may be added as another element.

[0046] The switch elements 20A, 20B, 20C, and 20D are each electrically connected in parallel with a capacitor 20L, 20M, 20N, and 20P as a capacitance component. Specifically, the drain of each of the switch elements 20A, 20B, 20C, and 20D is electrically connected to one terminal of each capacitor 20L, 20M, 20N, and 20P, and the source is electrically connected to the other terminal of each capacitor 20L, 20M, 20N, and 20P. In addition, when MOSFET is used as the switch element 20A, 20B, 20C, and 20D, a parasitic capacitance component is formed in each of the switch elements 20A, 20B, 20C, and 20D in a parasitic manner of the capacitance component. Therefore, it is also possible to configure the parasitic capacitance component without providing the capacitors 20L, 20M, 20N, and 20P.

[0047] The first switch element 20A and the second switch element 20B are connected in series between the first conductive path 1 and the second conductive path 2 to which the input voltage is input to the switch circuit 20, and are electrically connected to each other at a first connection point P1. The third switch element 20C and the fourth switch element 20D are connected in series between the first conductive path 1 and the second conductive path 2, and are electrically connected to each other at a second connection point P2.

[0048] The cathode of the first diode 20E is electrically connected to the first conductive path 1 (conductive path on the high potential side), and the anode terminal of the second diode 20F is electrically connected to the second conductive path 2 (conductive path on the low potential side). The anode terminal of the first diode 20E is electrically connected to the cathode terminal of the second diode 20F. The first diode 20E and the second diode 20F constitute a protection circuit 21 that absorbs surge voltage generated in the fifth switching element 30A and the sixth switching element 30B on the secondary side of the transformer 10 through the inductor 13.

[0049] One end of the inductor 13 is electrically connected to the first connection point P1. The other end of the inductor 13 is electrically connected to the anode terminal of the first diode 20E, the cathode terminal of the second diode 20F, and one end of the primary side coil 11 of the transformer 10. The second connection point P2 is electrically connected to the other end of the primary side coil 11. The inductor 13 is provided for the purpose of LC resonance with the capacitors 20L, 20M, 20N, and 20P in order to reduce the switching loss generated in the switching circuit 20. The inductance value of the inductor 13 is preferably set to a value sufficiently larger than the leakage inductance (not shown) of the transformer 10.

[0050] The output circuit 30 rectifies and smoothes the AC voltage appearing in the secondary coils 12A and 12B of the transformer 10 to generate an output voltage Vout which is a DC voltage, and applies the output voltage Vout between the third conductive path 3 and the fourth conductive path 4. The output circuit 30 includes a fifth switching element 30A, a sixth switching element 30B, a rectified output path 30C, a choke coil 33, and an output capacitor 34. The fifth switching element 30A is connected between one end of the secondary coil 12A of the transformer 10 and the ground path G. The sixth switching element 30B is connected between one end of the secondary coil 12B of the transformer 10 and the ground path G. One end of the rectified output path 30C is electrically connected to a third connection point P3 to which the other end of the secondary coil 12A and the other end of the secondary coil 12B are electrically connected. One end of the choke coil 33 is electrically connected to the other end of the rectified output path 30C. The other end of the choke coil 33 (i.e., the end on the side away from the third connection point P3) is electrically connected to the third conductive path 3, and is electrically connected to the fourth conductive path 4 via the output capacitor 34. That is, the choke coil 33 is interposed between the third connection point P3 and the third conductive path 3. The output capacitor 34 is electrically connected between the third conductive path 3 and the fourth conductive path 4. The fourth conductive path 4 is electrically connected to the ground path G.

[0051] The fifth switch element 30A and the sixth switch element 30B can use various known switch elements, but MOSFET is preferably used. The drain of the fifth switch element 30A is electrically connected to one end of the secondary side coil 12A, and the source is electrically connected to the ground path G. The drain of the sixth switch element 30B is electrically connected to one end of the secondary side coil 12B, and the source is electrically connected to the ground path G. The fifth switch element 30A and the sixth switch element 30B are each configured to have a parasitic diode as a parasitic component. Specifically, in each of the fifth switch element 30A and the sixth switch element 30B, the cathode of the parasitic diode is electrically connected to the drain side, and the anode is electrically connected to the source side.

[0052] In the output circuit 30 having such a configuration, the fifth switching element 30A and the sixth switching element 30B constitute a rectifying circuit that rectifies the AC voltage appearing in the secondary coils 12A and 12B of the transformer 10. The choke coil 33 and the output capacitor 34 smooth the rectified output appearing in the rectified output path 30C.

[0053] The control unit 40 is mainly composed of, for example, a microcomputer, and has a computing device such as a CPU (Central Processing Unit), a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), an A / D converter, etc. The control unit 40 is configured to grasp the voltage value of the first conductive circuit 1 through the first voltage detection unit 40A. The control unit 40 is configured to grasp the voltage value of the third conductive circuit 3 through the second voltage detection unit 40B. The first voltage detection unit 40A and the second voltage detection unit 40B are configured as a known voltage detection circuit. The control unit 40 is configured to grasp the current value flowing in the first conductive circuit 1 through the first current detection unit 40C. The control unit 40 is configured to grasp the current value flowing in the third conductive circuit 3 through the second current detection unit 40D. The first current detection unit 40C and the second current detection unit 40D are configured as a known current detection circuit such as a current transformer.

[0054] The control unit 40 outputs a PWM signal to each gate of the switching elements 20A, 20B, 20C, and 20D by a phase shift method based on the values ​​input from the first voltage detection unit 40A, the second voltage detection unit 40B, the first current detection unit 40C, and the second current detection unit 40D. Thus, the switching elements 20A, 20B, 20C, and 20D perform switching operations by a phase shift method. In addition, the control unit 40 is configured to output a switching signal at a predetermined time to each gate of the fifth switching element 30A and the sixth switching element 30B based on the values ​​input from the first voltage detection unit 40A, the second voltage detection unit 40B, the first current detection unit 40C, and the second current detection unit 40D.

[0055] [Operation of isolated DCDC converter]

[0056] Next, the operation of the converter 100 will be described. In a vehicle equipped with the converter 100, for example, the ignition switch is switched from the OFF state to the ON state. Then, the control unit 40 outputs a PWM signal to each of the switching elements 20A, 20B, 20C, and 20D, and outputs a switching signal at a predetermined timing to each of the fifth switching element 30A and the sixth switching element 30B.

[0057] Basically, if Figure 2 to Figure 4As shown, in the insulated DCDC converter having a full-bridge connected switching circuit, the first switching element 120A and the fourth switching element 120D of the switching circuit 120 are alternately turned on and off repeatedly with the second switching element 120B and the third switching element 120C. As a result, it is possible to operate in a manner that an AC voltage is applied from a DC power supply to the primary side coil 111 of the transformer 110, and an output voltage is generated on the output circuit 130 side. Specifically, when the first switching element 120A and the fourth switching element 120D are turned on, a current flows through the path indicated by the arrow C1 on the switching circuit 120 side (the primary side of the transformer 110). The path indicated by the arrow C1 is the path of the first conductive path 101 → the first switching element 120A → the primary side coil 111 → the fourth switching element 120D → the second conductive path 102. Correspondingly, a current flows through the path indicated by the arrow C2 on the output circuit 130 side (the secondary side of the transformer 110). The path indicated by arrow C2 is the path of the fourth conductive path 104 → the sixth switching element 130B → the secondary coil 112B → the rectifier output path 130C → the choke coil 133 → the third conductive path 103 (see Figure 2 . ).

[0058] Next, the first switch element 120A and the fourth switch element 120D are switched from on to off, and the first switch element 120A, the second switch element 120B, the third switch element 120C and the fourth switch element 120D are all turned off. In this way, current no longer flows on the switch circuit 120 side (the primary side of the transformer 110). On the output circuit 130 side (the secondary side of the transformer 110), current flows through the path of arrow C3 or arrow C4 through the energy accumulated in the choke coil 133. The path indicated by arrow C3 is the path of the fourth conductive circuit 104→the sixth switch element 130B→the secondary side coil 112B→the rectifier output path 130C→the choke coil 133→the third conductive circuit 103. The path indicated by arrow C4 is the path of the fourth conductive circuit 104→the fifth switch element 130A→the secondary side coil 112A→the rectifier output path 130C→the choke coil 133→the third conductive circuit 103 (refer to Figure 3 . ).

[0059] Next, the second switch element 120B and the third switch element 120C are switched from off to on. In this way, current flows through the path indicated by arrow C5 on the switching circuit 120 side (primary side of the transformer 110). The path indicated by arrow C5 is the path of the first conductive path 101 → the third switch element 120C → the primary side coil 111 → the second switch element 120B → the second conductive path 102. Correspondingly, current flows through the path indicated by arrow C6 on the output circuit 130 side (secondary side of the transformer 110). The path indicated by arrow C6 is the path of the fourth conductive path 104 → the fifth switch element 130A → the secondary side coil 112A → the rectifier output path 130C → the choke coil 133 → the third conductive path 103 (refer to Figure 4 . ).

[0060] Next, the second switch element 120B and the third switch element 120C are switched from on to off, and the first switch element 120A, the second switch element 120B, the third switch element 120C and the fourth switch element 120D are all turned off. In this way, current no longer flows on the switch circuit 120 side (the primary side of the transformer 110). On the output circuit 130 side (the secondary side of the transformer 110), current flows through the path of arrow C3 or arrow C4 through the energy accumulated in the choke coil 133. The path indicated by arrow C3 is the path of the fourth conductive circuit 104 → the sixth switch element 130B → the secondary side coil 112B → the rectifier output path 130C → the choke coil 133 → the third conductive circuit 103. The path indicated by arrow C4 is the path of the fourth conductive circuit 104 → the fifth switch element 130A → the secondary side coil 112A → the rectifier output path 130C → the choke coil 133 → the third conductive circuit 103 (refer to Figure 3 . ).

[0061] In this regard, the converter 100 of the present disclosure performs switching operation by phase shifting. Figure 5As shown, the phase shift method is a method of controlling in the following manner: the timing of the on-off action between the first switch element 20A and the fourth switch element 20D is staggered, the timing of the on-off action between the second switch element 20B and the third switch element 20C is staggered, and further, the timing of the on-off action of the switch elements 20A, 20B, 20C, and 20D is staggered. As a result, ZVS (Zero Voltage Switching) is achieved when the switch elements 20A, 20B, 20C, and 20D are switched from off to on, and the converter 100 can operate more efficiently. In the phase shift method, the first switch element 20A and the second switch element 20B are treated as a group (hereinafter also referred to as the first branch) and the third switch element 20C and the fourth switch element 20D are treated as a group (hereinafter also referred to as the second branch). In the first branch, the time when the first switch element 20A and the second switch element 20B are both off ( Figure 5 In the second branch, the time when the third switch element 20C and the fourth switch element 20D are both turned off ( Figure 5 T1, T3, T5, T7) is the second dead time.

[0062] Here, focusing on the time T2, the case where the second switching element 20B is switched from off to on during the first dead time is described. Figure 6 As shown, before time T2S (ie, the first switch element 20A is turned on), a DC input voltage Vin is applied between the drain and source of the second switch element 20B (see Figure 6 ). At this time, the capacitor 20M connected in parallel with the second switch element 20B is also in a state where the DC input voltage Vin is applied. Then, when the first switch element 20A is switched from on to off at time T2S, no current flows through the first switch element 20A. At this time, LC resonance starts between the capacitor 20M connected in parallel to the second switch element 20B and the inductor 13, and the voltage between the drain and source of the second switch element 20B is close to half the size of the DC input voltage Vin. The voltage between the drain and source of the second switch element 20B is closest to 0V at time T2E when the voltage first decreases after the start of LC resonance (refer to Figure 6 Therefore, by setting the time when the second switching element 20B switches from off to on as T2E, ZVS of the second switching element 20B can be achieved. In addition, the time when the second switching element 20B switches from off to on can be switched to a time slightly earlier than T2E.

[0063] Although the description has been made with focus on the case where the second switching element 20B switches from off to on during the first dead time at time T2, Figure 5 The same applies to other times T1, T3, T4, T5, T6, T7, T8 and the cases where the other switching elements 20A, 20C, and 20D are switched from off to on.

[0064] Here, the first dead time (tdead_a) in the first branch can be obtained by the equation shown in Formula 1.

[0065] [Number 1]

[0066]

[0067]

[0068] In addition, the second dead time (tdead_b) in the second branch can be obtained by the equation shown in Formula 2.

[0069] [Number 2]

[0070]

[0071]

[0072] Here, Vin is the input voltage of the DC power supply. N is the turns ratio between the number of turns N1 of the primary side coil 11 and the number of turns N2 of the secondary side coil 12A or 12B. Vout is the voltage applied between the third conductive path 3 and the fourth conductive path 4. IL is the current flowing in the inductor 13. Ca1 is the electrostatic capacitance of the capacitor 20L. Ca2 is the electrostatic capacitance of the capacitor 20M. Cb1 is the electrostatic capacitance of the capacitor 20N. Cb2 is the electrostatic capacitance of the capacitor 20P. L is the inductance of the inductor 13. Lchoke is the inductance of the choke coil 33.

[0073] The right side of each of tdead_a and tdead_b in the mathematical formulas shown in equations 1 and 2 is the time from the moment when one switching element is switched off and both switching elements are off in the first branch and the second branch to the moment when the voltage between the drain and the source of the other switching element becomes minimum for the first time due to LC resonance. That is, this time is referred to as the first dead time (tdead_a) and the second dead time (tdead_b).

[0074] The control unit 40 detects Vin through the first voltage detection unit 40A and detects Vout through the second voltage detection unit 40B. IL is detected by the first current detection unit 40C. In this way, the control unit 40 can obtain Vin, IL, and Vout and calculate and dynamically calculate the first dead time (tdead_a) and the second dead time (tdead_b) based on the mathematical formulas shown in Figures 1 and 2. And, the PWM signal is output to each switching element 20A, 20B, 20C, and 20D in a manner that becomes the calculated first dead time (tdead_a) and the second dead time (tdead_b). As a result, ZVS can be achieved in the switching elements 20A, 20B, 20C, and 20D.

[0075] According to the equations shown in equation 1 and equation 2, the larger the value of the input voltage Vin of the DC power supply (i.e., the voltage value detected by the first voltage detection unit 40A), the larger the dead time is, and the larger the value of the current IL flowing through the inductor 13 (i.e., the current value detected by the first current detection unit 40C), the smaller the dead time is. In addition, the larger the value of the output voltage Vout applied between the third conductive path 3 and the fourth conductive path 4 (i.e., the voltage value detected by the second voltage detection unit 40B), the larger the dead time is.

[0076] Next, the case where the current in the choke coil 33 is in a discontinuous mode is described. There is a difference between the current IL flowing in the inductor 13 and the current Iout flowing in the load 6 (that is, the current flowing in the choke coil 33). Figure 7 The coordinate diagram shows such a relationship. Figure 7 In the case where Iout is larger than Ic, the current in the choke coil 33 is in continuous mode, and when Iout is less than Ic, the current in the choke coil 33 is in discontinuous mode. When the magnitude of the current of Iout is larger than Ic (i.e., in the case of continuous mode), Iout and IL are in a positive proportional relationship represented by IL=Iout / N. N is the turns ratio between the number of turns N1 of the primary side coil 11 and the number of turns N2 of the secondary side coil 12A or 12B. In the case of continuous mode, the first dead time (tdead_a) and the second dead time (tdead_b) are calculated and dynamically calculated based on the mathematical formulas shown in Figures 1 and 2.

[0077] On the other hand, when the excitation current flows from the secondary coils 12A and 12B to the primary coil 11, the dead time can be calculated using a different mathematical expression from that of equation 1 or 2. The excitation current has the property of flowing through the secondary coils 12A and 12B when the load current is relatively large and flowing through the primary coil 11 when the load current is relatively small. Therefore, when the magnitude of Iout is less than Ic, a positive proportional relationship having a smaller slope (i.e., a slope smaller than 1 / N) than the straight line IL=Iout / N holds. This is a result reflecting the property that the excitation current flowing through the primary coil 11 increases when the magnitude of Iout is less than Ic and the excitation current flowing through the primary coil 11 becomes larger as Iout approaches 0. Therefore, the rate of increase (i.e., slope) of the current in the interval where the magnitude of Iout is 0 to Ic is smaller than the rate of increase (i.e., slope) in the interval where the magnitude of Iout is greater than Ic. Since the rate of increase in the interval where the magnitude of Iout is 0 to Ic is reflected in the current IL flowing in the excitation current in the inductor 13, it is smaller than the rate of increase (i.e., the slope 1 / N) in the interval where the magnitude of Iout is greater than Ic. For example, a method is considered in which the rate of increase of Iout or IL is monitored in the control unit 40, and Ic is detected by comparing the rate of increase with a predetermined threshold value pre-stored in the control unit 40.

[0078] Here, when the excitation current flows through the primary coil 11 (ie, Figure 7 In the case where the magnitude of Iout in the first branch is in the range of 0 to Ic), the first dead time (tdead_a) in the first branch can be obtained by the equation shown in Formula 3.

[0079] [Number 3]

[0080]

[0081]

[0082] When the current flowing through the choke coil 33 is in a discontinuous mode, the second dead time (tdead_b) in the second branch can be obtained by the equation shown in Formula 4.

[0083] [Number 4]

[0084]

[0085]

[0086] Here, Lmag is the value of the excitation inductance 14. The right sides of tdead_a and tdead_b in the mathematical formulas shown in equations 3 and 4 are the time from the moment when one switching element is switched off and both switching elements are off in the first branch and the second branch to the moment when the voltage between the drain and the source of the other switching element becomes minimum for the first time due to LC resonance. That is, this time is set as the first dead time (tdead_a) and the second dead time (tdead_b) in the discontinuous mode.

[0087] Therefore, when the current flowing in the choke coil 33 is in a discontinuous mode (i.e., when it is less than Ic), the control unit 40 can reflect the value of the excitation inductance 14 based on the mathematical formulas shown in Formulas 3 and 4 to calculate and dynamically calculate the first dead time (tdead_a) and the second dead time (tdead_b). And, the PWM signal is output to each switching element 20A, 20B, 20C, and 20D in a manner that becomes the calculated first dead time (tdead_a) and the second dead time (tdead_b). As a result, ZVS can be achieved in the switching elements 20A, 20B, 20C, and 20D even when the excitation current flows through the primary side coil 11. That is, the control unit 40 determines whether to reflect the excitation inductance 14 of the transformer 10 when determining the first dead time and the second dead time based on the increase state of the current Iout flowing in the choke coil 33 (i.e., the current IL flowing in the inductor 13).

[0088] According to the equations shown in equation 3 and equation 4, the larger the value of the input voltage Vin of the DC power supply (i.e., the voltage value detected by the first voltage detection unit 40A), the larger the dead time is, and the larger the value of the current IL flowing through the inductor 13 (i.e., the current value detected by the first current detection unit 40C), the smaller the dead time is. In addition, the larger the value of the output voltage Vout applied between the third conductive path 3 and the fourth conductive path 4 (i.e., the voltage value detected by the second voltage detection unit 40B), the larger the dead time is.

[0089] Next, the effects of this structure are exemplified.

[0090] The insulated DCDC converter 100 disclosed in the present invention includes a transformer 10, a full-bridge switching circuit 20, a protection circuit 21, a control unit 40, an inductor 13, and an output circuit 30. The transformer 10 includes a primary coil 11 and secondary coils 12A and 12B. The full-bridge switching circuit 20 includes switching elements 20A, 20B, 20C, and 20D. The protection circuit 21 includes a first diode 20E and a second diode 20F. The control unit 40 controls the operation of the switching circuit 20. The output circuit 30 is connected to the secondary coils 12A and 12B. The first switching element 20A and the second switching element 20B are connected in series between the first conductive path 1 and the second conductive path 2. The third switching element 20C and the fourth switching element 20D are connected in series between the first conductive path 1 and the second conductive path 2. One end of the inductor 13 is electrically connected to the first connection point P1 between the first switching element 20A and the second switching element 20B. The other end of the inductor 13 is electrically connected to one end of the primary coil 11, the anode of the first diode 20E, and the cathode of the second diode 20F. The other end of the primary coil 11 is electrically connected to the second connection point P2 between the third switching element 20C and the fourth switching element 20D. The cathode of the first diode 20E is electrically connected to the first conductive path 1. The insulating DCDC converter 100 of the present disclosure is a phase-shift insulating DCDC converter in which the anode of the second diode 20F is electrically connected to the second conductive path 2. The insulating DCDC converter 100 of the present disclosure includes a first voltage detection unit 40A for detecting a voltage value between the first conductive path 1 and the second conductive path 2, and a first current detection unit 40C for detecting a current value of the inductor 13. The control unit 40 determines at least one of the first dead time and the second dead time in such a manner that the larger the voltage value, the larger the dead time, and the larger the current value, the smaller the dead time. The first dead time is a time when the first switching element 20A and the second switching element 20B are both turned off. The second dead time is a time when the third switching element 20C and the fourth switching element 20D are both turned off.

[0091] Therefore, the isolated DCDC converter 100 can absorb the recovery surge generated on the secondary side of the transformer 10 through the protection circuit 21. At the same time, the isolated DCDC converter 100 calculates the first dead time and the second dead time based on the current value of the current IL flowing in the inductor 13 detected by the first current detection unit 40C. Therefore, the isolated DCDC converter 100 can dynamically obtain the dead time based on the value corresponding to the current flowing in the inductor 13.

[0092] The control unit 40 of the isolated DCDC converter 100 of the present disclosure determines whether to reflect the magnetizing inductance 14 of the transformer 10 when determining the first dead time and the second dead time based on the increase state of the current value.

[0093] With this configuration, the increase state of the current value can be regarded as the state of the load current. Therefore, whether to reflect the exciting inductance 14 is determined according to the state of the load current, and the first dead time and the second dead time are calculated and calculated, so that the dead time can be obtained more finely.

[0094] The control unit 40 of the isolated DCDC converter 100 of the present disclosure determines at least one of the first dead time and the second dead time by reflecting the magnetizing inductance 14 when the increase rate of the current value is less than a threshold value. The control unit 40 determines the first dead time and the second dead time without reflecting the magnetizing inductance 14 when the increase rate of the current value exceeds the threshold value.

[0095] According to this configuration, when the rate of increase of the current value is less than the threshold value, the excitation inductance 14 is reflected, and the dead time of the state in which the load current is small and the magnitude of the excitation current flowing in the primary side coil 11 cannot be ignored is obtained. On the other hand, when the rate of increase of the current value exceeds the threshold value, the excitation inductance 14 is not reflected, and the dead time of the state in which the load current is large and the magnitude of the excitation current flowing in the primary side coil 11 can be ignored is obtained. Therefore, by reflecting the state of the excitation current flowing in the primary side coil according to the magnitude of the load current, a more accurate dead time can be obtained.

[0096] <Implementation method 2>

[0097] The following description involves Figure 8 An isolated DCDC converter 200 according to the second embodiment is shown.

[0098] The insulating type DCDC converter 200 of the second embodiment is different from the insulating type DCDC converter 100 of the first embodiment in that the first voltage detection unit 40A is omitted (the first difference). Furthermore, the insulating type DCDC converter 200 of the second embodiment is different from the insulating type DCDC converter 100 of the first embodiment in that the secondary side voltage detection unit 40E is provided (the second difference). Furthermore, the insulating type DCDC converter 200 of the second embodiment is different from the insulating type DCDC converter 100 of the first embodiment in that the "voltage value between the first conductive path 1 and the second conductive path 2" is detected by a method different from that of the first embodiment (the third difference). On the other hand, except for the first difference, the second difference, and the third difference, the structure, operation, etc. of the insulating type DCDC converter 200 of the second embodiment are all the same as those of the insulating type DCDC converter 100 of the first embodiment.

[0099] The isolated DC-DC converter 200 of the second embodiment is also a step-down DC-DC converter that steps down the input voltage Vin applied between the first conductive path 1 and the second conductive path 2 and outputs the output voltage Vout which is a DC voltage lower than the input voltage Vin.

[0100] In the isolated DCDC converter 200 , the secondary side voltage detection unit 40E and the control unit 40 correspond to an example of a voltage detection unit.

[0101] The secondary side voltage detection unit 40E measures the secondary side voltage Vtr2 applied from the secondary side coils 12A and 12B of the transformer 10. The secondary side voltage Vtr2 is the potential difference between the rectifier output path 30C (fifth conductive path) electrically connected to the transformer 10 and the fourth conductive path 4 electrically connected to the ground. The rectifier output path 30C is a conductive path between the middle position (center tap) of the secondary side coils 12A and 12B in the transformer 10 and the choke coil 33. That is, the secondary side voltage Vtr2 is the voltage of the rectifier output path 30C (fifth conductive path) based on the potential (ground potential) of the fourth conductive path 4. The secondary side voltage Vtr2 is a value representing the voltage across the secondary side coils 12A and 12B before being smoothed by the filter circuit composed of the choke coil 33 and the output capacitor 34. In addition, the value indicated by the second voltage detection unit 40B is the potential difference between the third conductive path 3 and the fourth conductive path 4, and the voltage across the two ends is the value of the DC voltage after being smoothed by the filter circuit. The secondary side voltage detection unit 40E inputs a signal indicating the value of the secondary side voltage Vtr2 to the control unit 40. The signal indicating the value of the secondary side voltage Vtr2 may be any signal that can determine the value of the secondary side voltage Vtr2, and may be a signal indicating the value of the secondary side voltage Vtr2 itself, or a signal indicating a value obtained by dividing the secondary side voltage Vtr2 at a predetermined voltage division ratio.

[0102] The control unit 40 detects the voltage value between the first conductive path 1 and the second conductive path 2 based on the secondary voltage Vtr2 measured by the secondary voltage detection unit 40E. The voltage value between the first conductive path 1 and the second conductive path 2 is the value of the input voltage Vin and is the potential difference between the first conductive path 1 and the second conductive path 2.

[0103] The control unit 40 sets the value of the secondary side voltage to Vtr2, sets the turn ratio of the primary side coil 11 and the secondary side coil 12A and the turn ratio of the primary side coil 11 and the secondary side coil 12B to N, and sets the voltage value (the value of the input voltage) between the first conductive path 1 and the second conductive path 2 to Vin. The number of turns of the primary side coil 11 is N1, and the number of turns of the secondary side coils 12A and 12B are both N2. The turn ratio N is N=N1 / N2. And, based on this, the control unit 40 calculates Vin by the formula of Vin=Vtr2×N. In addition, in the isolated DCDC converter 200, the control using Vin is the same as that in embodiment 1, and the control other than that is also the same as that in embodiment 1.

[0104] In this way, the isolated DCDC converter 200 of the second embodiment can detect the voltage value (the value of the input voltage Vin) between the first conductive path 1 and the second conductive path 2 based on the secondary side voltage Vtr2 measured by the secondary side voltage measuring unit. Therefore, the isolated DCDC converter is advantageous in the case where it is difficult to directly measure the voltage value (the value of the input voltage Vin) between the first conductive path 1 and the second conductive path 2 or in the case where it is more preferable to estimate the voltage value by measuring the secondary side voltage Vtr2 rather than directly measuring it.

[0105] The isolated DCDC converter 200 can more simply realize a structure that can more accurately obtain the voltage value (the value of the input voltage Vin) between the first conductive path 1 and the second conductive path 2 based on the secondary side voltage Vtr2 based on the turns ratio N. In addition, the above-mentioned calculation method (Vin=Vtr2×N) is only an example, and other calculation methods can also be used as long as they are methods that can calculate the input voltage Vin based on the secondary side voltage Vtr2 and the turns ratio of the transformer.

[0106] The isolated DCDC converter 200 can measure the secondary side voltage Vtr2 which is a relatively low value compared to the voltage value between the first conductive path 1 and the second conductive path 2 (the value of the input voltage Vin), and derive the voltage value between the first conductive path 1 and the second conductive path 2 based on the secondary side voltage Vtr2. Therefore, the isolated DCDC converter 200 can omit or simplify the structure required for detecting a higher voltage, and can further miniaturize the structure that can detect the voltage value between the first conductive path 1 and the second conductive path 2. For example, in the case where the value of the input voltage Vin is directly measured and the measured value is input to the control unit 40, when the value of the input voltage Vin increases, an insulating part such as an insulating amplifier is required between the input side and the control unit 40, but such a component can be omitted according to the method of the second embodiment.

[0107] In particular, in this structure, the secondary side coils 12A, 12B, and the rectifier output path 30C are insulated from both the first conductive path 1 and the second conductive path 2, and the fourth conductive path 4 is insulated from both the first conductive path 1 and the second conductive path 2. Moreover, the fourth conductive path 4 is electrically connected to a reference conductive path (not shown) in the control unit 40, and the fourth conductive path 4 has the same potential as the reference conductive path of the control unit 40. Therefore, the measurement result of the secondary side voltage Vtr2 can be well input to the control unit 40 without insulation, and on the other hand, the "secondary side voltage Vtr2 measurement path and the control unit 40" and the "first conductive path 1 and the second conductive path 2 on the input side" can be reliably insulated from each other.

[0108] <Other embodiments>

[0109] This structure is not limited to the embodiment described in the above description and drawings, and for example, the following embodiment is also included in the technical scope of the present invention.

[0110] In embodiments 1 and 2, the first dead time (tdead_a) and the second dead time (tdead_b) are calculated and computed in the control unit 40, but it may also be that the control unit stores a data table storing the first dead time and the second dead time corresponding to the input voltage, the current flowing in the inductor, and the output voltage, and each switching element is switched from off to on based on the first dead time and the second dead time corresponding to the input voltage, the current flowing in the inductor, and the output voltage obtained by calculation according to the data table.

[0111] In the first and second embodiments, MOSFETs are used for the fifth switching element 30A and the sixth switching element 30B, but they may be configured to use diodes.

[0112] In the first and second embodiments, the control unit 40 is mainly composed of a microcomputer, but may be realized by a plurality of hardware circuits other than a microcomputer.

[0113] In the first and second embodiments, both the first dead time and the second dead time are obtained, but at least one of the first dead time and the second dead time may be obtained.

[0114] In the first embodiment, the voltage value of the input voltage Vin is detected by the first voltage detection unit 40A, but the input voltage Vin may be calculated by operation based on the voltage value of the output voltage Vout detected by the second voltage detection unit, the turns ratio of the transformer, and the duty cycle of the PWM signal. Alternatively, the value of the input voltage Vin may be detected in the structure of the first embodiment as in the second embodiment.

[0115] In the first and second embodiments, the current IL flowing through the inductor 13 is detected by the first current detection unit 40C provided in the first conductive path 1 , but the position and structure of the current detection unit may be any as long as the current flowing through the inductor can be detected.

[0116] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed this time, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0117] Description of Reference Numerals

[0118] 1…First conductive circuit

[0119] 2…Second conductive circuit

[0120] 3…Third Conductive Circuit

[0121] 4…Fourth conductive circuit

[0122] 6…Load

[0123] 7…Input capacitor

[0124] 10…Transformer

[0125] 11…Primary coil

[0126] 12A, 12B…Secondary coil

[0127] 13…Inductor

[0128] 14…Magnetic inductance

[0129] 20…Switch circuit

[0130] 20A…First switching element

[0131] 20B...second switching element

[0132] 20C…Third switching element

[0133] 20D ... fourth switching element

[0134] 20E…First diode

[0135] 20F…Second diode

[0136] 20G, 20H, 20J, 20K…parasitic diode

[0137] 20L, 20M, 20N, 20P...capacitors

[0138] 21…Protection circuit

[0139] 30…Output circuit

[0140] 30A...Fifth switch element

[0141] 30B...sixth switching element

[0142] 30C... Rectification output path

[0143] 33… Choke Coil

[0144] 34…Output capacitor

[0145] 40…Control unit (voltage detection unit)

[0146] 40A...First voltage detection unit (voltage detection unit)

[0147] 40B...second voltage detection unit (voltage detection unit)

[0148] 40C ... first current detection unit (current detection unit)

[0149] 40D ... second current detection unit

[0150] 40E…Secondary side voltage detection unit (voltage detection unit)

[0151] 100, 200…Isolated DCDC converter

[0152] 101…First conductive circuit

[0153] 102…Second conductive circuit

[0154] 103…Third conductive circuit

[0155] 104…Fourth conductive circuit

[0156] 110…Transformer

[0157] 111…Primary coil

[0158] 112A, 112B…Secondary coil

[0159] 120…Switching circuit

[0160] 120A…First switch element

[0161] 120B…Second switch element

[0162] 120C…Third switch element

[0163] 120D ... fourth switching element

[0164] 130…Output circuit

[0165] 130A...Fifth switch element

[0166] 130B...sixth switch element

[0167] 130C… Rectification output path

[0168] 133… Choke Coil

[0169] G…ground path

[0170] P1…First connection point

[0171] P2…Second connection point

[0172] P3…Third connection point

[0173] Vin…Input voltage

[0174] Vout…output voltage

[0175] Vtr2…Secondary side voltage.

Claims

1. An isolated DC-DC converter is a phase-shifted isolated DC-DC converter having: A transformer having a primary coil and a secondary coil; A full-bridge switching circuit comprising a first switching element, a second switching element, a third switching element and a fourth switching element; A protection circuit having a first diode and a second diode; A control unit, which controls the operation of the switch circuit; Inductors; and An output circuit connected to the secondary coil, The first switch element and the second switch element are connected in series between the first conductive path and the second conductive path, The third switch element and the fourth switch element are connected in series between the first conductive circuit and the second conductive circuit. One end of the inductor is electrically connected to a first connection point between the first switching element and the second switching element, The other end of the inductor is electrically connected to one end of the primary coil, the anode of the first diode, and the cathode of the second diode. The other end of the primary side coil is electrically connected to a second connection point between the third switching element and the fourth switching element. The cathode of the first diode is electrically connected to the first conductive circuit, The anode of the second diode is electrically connected to the second conductive circuit. The isolated DCDC converter comprises: a voltage detection unit, configured to detect a voltage value between the first conductive circuit and the second conductive circuit; and a current detection unit for detecting a current value of the inductor; The control unit determines at least one of a first dead time and a second dead time based on the voltage value detected by the voltage detection unit and the current value detected by the current detection unit, such that the larger the voltage value is, the longer the dead time is, and the larger the current value is, the shorter the dead time is, the first dead time is a time when both the first switching element and the second switching element are turned off, and the second dead time is a time when both the third switching element and the fourth switching element are turned off, The control unit determines whether to reflect the magnetizing inductance of the transformer when determining at least one of the first dead time and the second dead time based on the increase state of the current value.

2. The isolated DCDC converter according to claim 1, wherein: The control unit determines at least one of the first dead time and the second dead time by reflecting the excitation inductance when the rate of increase of the current value is below a threshold value, and determines at least one of the first dead time and the second dead time without reflecting the excitation inductance when the rate of increase of the current value exceeds the threshold value.

3. The isolated DCDC converter according to claim 1 or 2, wherein: The voltage detection unit includes a secondary-side voltage measurement unit that measures a secondary-side voltage applied from the secondary-side coil of the transformer, and detects the voltage value based on the secondary-side voltage measured by the secondary-side voltage measurement unit.

4. The isolated DCDC converter according to claim 3, wherein: The voltage detection unit obtains the voltage value based on the secondary side voltage and a turns ratio between the primary side coil and the secondary side coil.

5. The isolated DCDC converter according to claim 3, wherein: The insulating type DCDC converter is a step-down type DCDC converter that steps down an input voltage applied between the first conductive circuit and the second conductive circuit and outputs an output voltage.

6. The isolated DCDC converter according to claim 4, wherein: The insulating type DCDC converter is a step-down type DCDC converter that steps down an input voltage applied between the first conductive circuit and the second conductive circuit and outputs an output voltage.

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