JP2022108786A - Insulation type dcdc converter - Google Patents

Abstract

To provide an insulation type DCDC converter that favorably calculates primary side voltage of a transformer on the basis of secondary side voltage of the transformer.SOLUTION: An insulation type DCDC converter 100 includes: a choke coil 33 that lies on a path between a second conducting path 2 and second coil parts 12A, 12B; and a control unit 40 for controlling a first switching circuit 20 and a second switching circuit 30. The control unit 40 performs first control of making the second switching circuit 30 perform rectification operation in a synchronous rectification mode and second control of making the second switching circuit perform rectification operation in a diode rectification mode. At the time of the first control, the control unit 40 calculates input voltage using a first determination method on the basis of a voltage Vtr2 on the side of the second coil parts 12A, 12B of the choke coil 33 taking electric potential of a ground path G as its reference. At the time of the second control, the control unit calculates input voltage using a second determination method on the basis of a voltage Vtr2 on the side of the second coil parts 12A, 12B of the choke coil 33 taking electric potential of the ground path G as its reference.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to isolated DCDC converters.

Patent Literature 1 discloses a technique of obtaining a voltage value on the primary side of a transformer based on a voltage value on the secondary side of the transformer. According to Patent Document 1, soft switching between the main switching element and the reset switching element can be performed based on the voltage value on the primary side of the transformer thus obtained.

JP 2012-34549 A

In Patent Document 1, a rectifier circuit using a diode is provided on the secondary side of the transformer. It is well known that rectification can be achieved by replacing the diode of this rectifier circuit with an FET (Field Effect Transistor). When a rectifier circuit is configured using FETs, if the current flowing through the load (output current from the secondary side) is greater than a predetermined magnitude, the FETs are turned on and off to rectify (this is called a synchronous rectification mode). ), when the current flowing through the load is smaller than a predetermined magnitude, the on/off operation of the FET is stopped and the body diode of the FET is used for rectification (this is called a diode rectification mode). The magnitude of the voltage drop across the drain-source of the FET in diode rectification mode is the forward voltage of the body diode. On the other hand, the drain-source voltage drop in the synchronous rectification mode is much smaller than the forward voltage. Therefore, in each of the diode rectification mode and the synchronous rectification mode in this configuration (configuration of a rectifier circuit using FETs), when obtaining the voltage value on the primary side of the transformer based on the voltage value on the secondary side of the transformer, There is concern about the influence of FET characteristics on the obtained voltage value on the primary side of the transformer.

An object of the present disclosure is to provide a DCDC converter that can satisfactorily determine the voltage on the primary side of a transformer based on the voltage on the secondary side of the transformer.

The isolated DCDC converter of the present disclosure is
An insulated DCDC that includes a first switching circuit, a second switching circuit, and a transformer that includes a first coil section and a second coil section, and performs voltage conversion between the first conductive path and the second conductive path. a converter,
a choke coil interposed in a path between the second coil portion and the second conductive path;
a control unit that controls the first switching circuit and the second switching circuit;
The first switching circuit performs a conversion operation of applying an AC voltage to the first coil portion with the voltage applied to the first conductive path as an input voltage,
The second switching circuit includes an FET having a body diode, is electrically connected to a reference conductive path, and controls the voltage generated in the second coil section in response to the conversion operation performed by the first switching circuit. performing a rectifying operation of rectifying and applying an output voltage to the second conduction path;
The control unit performs a first control that causes the second switching circuit to perform a rectification operation in a synchronous rectification mode, and a second control that causes the second switching circuit to perform a rectification operation in a diode rectification mode. do,
The control unit obtains the input voltage by a first determination method based on the voltage on the second coil unit side of the choke coil based on the potential of the reference conductive path during the first control, and During the second control, the input voltage is obtained by a second determination method based on the voltage of the second coil portion of the choke coil with reference to the potential of the reference conductive path.

According to the present disclosure, the voltage on the primary side of the transformer can be obtained satisfactorily based on the voltage on the secondary side of the transformer.

FIG. 1 is a circuit diagram showing an insulated DCDC converter of Embodiment 1. FIG. FIG. 2 is a circuit diagram showing paths of currents flowing to the primary side and secondary side of the transformer when the first switch element and the fourth switch element are in the ON state in a basic insulated DCDC converter. FIG. 3 shows the path of the current flowing on the secondary side of the transformer when the first, second, third, and fourth switching elements are off in a basic isolated DCDC converter. It is a circuit diagram showing. FIG. 4 is a circuit diagram showing paths of currents flowing to the primary side and secondary side of the transformer when the second switch element and the third switch element are in the ON state in a basic insulated DCDC converter. FIG. 5 is a timing chart showing the timing of turning on and off each of the first switch element, the second switch element, the third switch element, and the fourth switch element in the isolated DCDC converter of the first embodiment. . FIG. 6 shows an enlarged view of the timing chart of the first switch element and the second switch element at time T2 in FIG. A graph showing the changes is shown below. FIG. 7 is an example of table data showing on-resistance corresponding to ambient temperature. FIG. 8 is an example of table data showing forward voltages corresponding to ambient temperatures and output currents. FIG. 9 is a circuit diagram showing an insulated DCDC converter of Embodiment 2. FIG.

[Description of Embodiments of the Present Disclosure]
First, the embodiments of the present disclosure are listed and described.

[1] An isolated DCDC converter according to the present disclosure includes a first switching circuit, a second switching circuit, and a transformer including a first coil section and a second coil section, and a first conducting path and a second conducting path. It is an insulated DCDC converter that converts voltage between circuits. An isolated DCDC converter of the present disclosure includes a choke coil interposed in a path between a second coil section and a second conductive path, and a control section that controls the first switching circuit and the second switching circuit. there is The first switching circuit performs a conversion operation of applying an AC voltage to the first coil section using the voltage applied to the first conducting path as an input voltage. The second switching circuit includes an FET with a body diode, is electrically connected to the reference conductive path, and rectifies the voltage developed in the second coil section in response to the conversion operation of the first switching circuit to produce a second coil. A rectifying operation is performed by applying an output voltage to the two conducting paths. The control unit performs first control for causing the second switching circuit to perform rectification operation in the synchronous rectification mode and second control for causing the second switching circuit to perform the rectification operation in the diode rectification mode. The control unit obtains the input voltage by the first determination method based on the voltage of the second coil unit side of the choke coil with reference to the potential of the reference conductive path during the first control. The control section obtains the input voltage by a second determination method based on the voltage of the second coil section side of the choke coil based on the potential of the reference conductive path during the second control.

The isolated DCDC converter of [1] can determine the input voltage in each of the synchronous rectification mode and the diode rectification mode by individual determination methods.

[2] In the isolated DCDC converter of [1] above, the control unit executes the second control when the value indicating the output current output from the second conductive path is smaller than a predetermined threshold, and indicates the output current. A first control may be performed if the value is greater than or equal to a predetermined threshold.

The insulated DCDC converter [2] can obtain the input voltage individually according to the magnitude of the value indicating the output current.

[3] In the insulated DCDC converter of [1] or [2] above, N is the turns ratio between the number of turns of the first coil section and the number of turns of the second coil section. The input voltage is obtained by multiplying the sum of the voltage Vtr2 on the side of the second coil portion of the choke coil based on the potential of the reference conduction path and the voltage Vdrop between the drain and source of the FET by the turns ratio N. 1 is Vin. When in synchronous rectification mode, the voltage Vdrop is the voltage Vds between the drain and source of the FET in Equation 2. When in diode rectification mode, the voltage Vdrop can be the forward voltage Vf of the body diode in Equation 3.
Vin=N×(Vtr2+Vdrop) Equation 1
Vdrop=Vds Equation 2
Vdrop=Vf Equation 3

The isolated DCDC converter of [3] above can determine the input voltage in the diode rectification mode in consideration of the forward voltage of the body diode, so the input voltage in the diode rectification mode can be determined more accurately.

[4] In the isolated DCDC converter of [3] above, the controller controls the forward voltage Vf based on at least one of the ambient temperature and the magnitude of the value indicating the output current output from the second conductive path. can decide.

The isolated DCDC converter of [4] above can obtain a more accurate input voltage.
[Details of the embodiment of the present disclosure]

<Embodiment 1>
[Overview of isolated DCDC converter]
An insulated DCDC converter 100 (hereinafter also simply referred to as converter 100) of Embodiment 1 supplies 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)). It is used as an output power supply. The converter 100 transforms the input voltage Vin applied between the first high potential side conductive path 1A as the first conductive path 1 and the first low potential side conductive path 1B as the first conductive path 1 to convert the input voltage It generates an output voltage Vout which is a DC voltage lower than Vin. Then, the converter 100 applies the output voltage Vout between the second conductive path 2, which is the second high potential side conductive path 2A, and the second conductive path 2, which is the second low potential side conductive path 2B. That is, the converter 100 is a step-down DCDC converter that performs voltage conversion between the first conducting path 1 and the second conducting path 2 .

The converter 100 includes a transformer 10, a first switching circuit 20, a second switching circuit 30, and a control section 40, as shown in FIG. A first switching circuit 20 is provided between the first conducting path 1 and the transformer 10 . A second switching circuit 30 is provided between the transformer 10 and the second conducting path 2 . The control unit 40 controls operations of the first switching circuit 20 and the second switching circuit 30 . In actual use, a DC power supply (not shown) is connected between the first high potential side conducting path 1A and the first low potential side conducting path 1B, and the second high potential side conducting path 2A and the second high potential side conducting path 2A are connected to each other. A load 6 is connected between it and the low potential side conductive path 2B. An input capacitor 7 for stabilizing the input voltage Vin is connected between the first high potential side conductive path 1A and the first low potential side conductive path 1B.

The transformer 10 includes a first coil section 11 and second coil sections 12A and 12B. The number of turns of the first coil portion 11 is N1. The number of turns of the second coil portions 12A and 12B is both N2. The second coil portions 12A and 12B are electrically connected in series with each other at a third connection point P3. The third connection point P3 corresponds to a center tap. That is, center taps are provided in the second coil portions 12A and 12B. A turn ratio N of the transformer 10 is represented by N=N2/N1.

In the present disclosure, “electrically connected” preferably means a configuration in which the objects are connected in a conductive state (a state in which current can flow) so that the potentials of both of the objects to be connected are equal. However, it is not limited to this configuration. For example, "electrically connected" may be a configuration in which both connection objects are connected in a state in which an electric component is interposed between them and both connection objects are electrically connected.

The first switching circuit 20 converts the input voltage Vin, which is a DC voltage applied to the first high-potential side conductive path 1A and the first low-potential side conductive path 1B, into an AC voltage, and converts the input voltage Vin into an AC voltage. 11 performs a conversion operation to apply this AC voltage. In the first switching circuit 20, 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, and 20D) are connected in a full bridge. It has a configured configuration.

The first switching circuit 20 has switch elements 20A, 20B, 20C, and 20D and an inductor 13 . Various known switch elements can be used for the switch elements 20A, 20B, 20C, and 20D, but MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), which are FETs, are preferably used.

Body diodes 20G, 20H, 20J and 20K, which are parasitic components, are provided in the switch elements 20A, 20B, 20C and 20D, respectively. Specifically, in each of the switch elements 20A, 20B, 20C, and 20D, the cathode of each body diode 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 body diodes 20G, 20H, 20J and 20K, diodes may be added as separate elements.

Capacitors 20L, 20M, 20N and 20P are electrically connected in parallel to the switch elements 20A, 20B, 20C and 20D, respectively. Specifically, one terminal of each capacitor 20L, 20M, 20N, 20P is electrically connected to the drain of each of the switch elements 20A, 20B, 20C, 20D, and the source of each of the capacitors 20L, 20M, 20N, 20P is connected. is electrically connected to the other terminal of Also, when MOSFETs are used for the switch elements 20A, 20B, 20C, and 20D, parasitic capacitance components are formed so as to parasitize the respective switch elements 20A, 20B, 20C, and 20D. Therefore, a configuration using parasitic capacitance components may be employed without providing the capacitors 20L, 20M, 20N, and 20P.

The first switch element 20A and the second switch element 20B are connected in series between the first high potential side conducting path 1A and the first low potential side conducting path 1B for inputting the input voltage Vin to the first switching circuit 20. , 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 high potential side conductive path 1A and the first low potential side conductive path 1B, and are electrically connected to each other at the second connection point P2. Connected.

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 one end of the first coil section 11 of the transformer 10 . The second connection point P2 is electrically connected to the other end of the first coil portion 11 . The inductor 13 is provided for the purpose of LC resonance with the capacitors 20L, 20M, 20N, 20P in order to reduce the switching loss that occurs in the first switching circuit 20. FIG. The inductance value of inductor 13 is preferably set to a value sufficiently larger than the leakage inductance (not shown) of transformer 10 .

The second switching circuit 30 rectifies and smoothes the AC voltage generated in the second coil units 12A and 12B of the transformer 10 in response to the conversion operation of the first switching circuit 20 to generate an output voltage Vout which is a DC voltage. do. Then, the second switching circuit 30 applies the output voltage Vout between the second high potential side conductive path 2A and the second low potential side conductive path 2B. Thus, the second switching circuit 30 performs rectifying operation. The second switching circuit 30 includes a fifth switch element 30A, a sixth switch element 30B, a rectification output path 30C, a choke coil 33, and an output capacitor . The fifth switch element 30A is connected between one end of the second coil portion 12A of the transformer 10 and the ground path G, which is a reference conductive path. The sixth switch element 30B is connected between one end of the second coil portion 12B of the transformer 10 and the ground path G. That is, the second switching circuit 30 is electrically connected to the ground path G (reference conductive path).

One end of the rectification output path 30C is electrically connected to a third connection point P3 (center tap) where the other end of the second coil portion 12A and the other end of the second coil portion 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 (that is, the end on the side away from the third connection point P3) is electrically connected to the second high potential side conductive path 2A and is connected to the second low potential side conductive path 2A via the output capacitor . It is electrically connected to the potential side conducting path 2B. That is, the choke coil 33 is interposed in the path between the second coil portions 12A, 12B and the second conductive path 2 between the third connection point P3 and the second high potential side conductive path 2A. The output capacitor 34 is electrically connected between the second high potential side conductive path 2A and the second low potential side conductive path 2B. The second low potential side conductive path 2B is electrically connected to the ground path G.

Various known switch elements can be used for the fifth switch element 30A and the sixth switch element 30B, but MOSFETs, which are FETs, are preferably used. The drain of the fifth switch element 30A is electrically connected to one end of the second coil section 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 second coil section 12B, and the source is electrically connected to the ground path G. Body diodes 30D and 30E, which are parasitic components, are provided in the fifth switch element 30A and the sixth switch element 30B, respectively. Specifically, in each of the fifth switch element 30A and the sixth switch element 30B, the cathodes of the body diodes 30D and 30E are electrically connected to the drain side, and the anodes are electrically connected to the source side. That is, the fifth switch element 30A and the sixth switch element 30B have body diodes 30D and 30E.

In the second switching 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 generated in the second coil portions 12A and 12B of the transformer 10. Choke coil 33 and output capacitor 34 smooth the rectified output appearing on rectified output path 30C.

The control unit 40 is mainly composed of, for example, a microcomputer, and includes an arithmetic unit 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, and the like. have. The control section 40 is configured to detect the voltage value of the first high potential side conductive path 1A by means of the secondary side voltage detection section 40E. The control unit 40 is configured to detect the voltage value of the second high potential side conductive path 2A by the second voltage detection unit 40B. The secondary side voltage detection section 40E and the second voltage detection section 40B are configured as voltage detection circuits. The controller 40 is configured to detect the value of the current flowing through the first high-potential-side conductive path 1A by means of the first current detector 40C. The control unit 40 is configured to detect the value of the current flowing through the second high-potential-side conductive path 2A using the second current detection unit 40D. The first current detection section 40C and the second current detection section 40D are configured as current detection circuits such as current transformers.

The control unit 40 switches the switch elements 20A, 20A, 20B, 20A, 20B, 20D, 20D, 20D, 20D, 20D, 20D, 20E, 20D, 20A, 20B, 20A, 20B, 20A, 20B, 20A, 20B, 20A, 20B, 20A, 20B, 20A, 20B, 20A, 20B, and 40D. A PWM signal is output toward each gate of 20B, 20C, and 20D. As a result, the switching elements 20A, 20B, 20C, and 20D perform switching operations by the phase shift method.

Based on the value input from the second current detection unit 40D, the control unit 40 outputs a switching signal at a predetermined timing to each gate of the fifth switching element 30A and the sixth switching element 30B, or outputs a switching signal. stop the output of Specifically, the control unit 40 executes the first control when the value indicating the output current Iout output from the second high potential side conductive path 2A detected by the second current detection unit 40D is equal to or greater than a predetermined threshold value. . The first control is a control for outputting a switching signal with a predetermined timing to the gate of each of the fifth switch element 30A and the sixth switch element 30B of the second switching circuit 30 to perform rectification operation in the synchronous rectification mode. . The predetermined threshold value is stored in the ROM of the control unit 40 or the like.

Then, when the value indicating the output current Iout output from the second high-potential-side conductive path 2A detected by the second current detection section 40D is smaller than a predetermined threshold value, the control section 40 executes the second control. The second control stops outputting switching signals to the gates of the fifth switch element 30A and the sixth switch element 30B of the second switching circuit 30, and rectifies the second switching circuit 30 in the diode rectification mode. It is a control that causes the The diode rectification mode is a mode in which rectification is performed using body diodes 30D and 30E provided in the fifth switch element 30A and the sixth switch element 30B.

Converter 100 is provided with temperature detection unit 50 . The temperature detection unit 50 is configured as a temperature sensor such as a thermistor, for example. The temperature detection unit 50 is configured to output to the control unit 40 a voltage value indicating the temperature of the position where the temperature detection unit 50 is located. Temperature detection unit 50 is fixed, for example, in contact with the surface of an electric board (not shown) on which converter 100 is mounted, and detects a voltage value indicating the surface temperature (external surface temperature) of the electric board. output as Note that the temperature detection unit 50 may be arranged at a position where it can detect temperature changes in the first switching circuit 20, the transformer 10, the second switching circuit 30, etc., and does not have to be in contact with the electric substrate. For example, the temperature detection unit 50 may be located in the vicinity of any one of the first switching circuit 20, the transformer 10, and the second switching circuit 30 on the electric board on which the first switching circuit 20, the transformer 10, and the second switching circuit 30 are mounted. It may be fixed in the form of being implemented in

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

Basically, an isolated DCDC converter having switching circuits connected in a full bridge operates as shown in FIGS. 2 to 4. FIG. Specifically, in this isolated DCDC converter, the first switching element 120A and the fourth switching element 120D and the second switching element 120B and the third switching element 120C of the first switching circuit 120 are alternately turned on and off. and repeat. As a result, an AC voltage is applied from the DC power supply to the first coil portion 111 of the transformer 110, and a voltage can be generated on the second switching circuit 130 side. Specifically, when the first switch element 120A and the fourth switch element 120D are turned on, current flows through the first switching circuit 120 side (the primary side of the transformer 110) along the path indicated by the arrow C1. The path indicated by arrow C1 is the first high potential side conductive path 101A→first switch element 120A→first coil portion 111→fourth switch element 120D→first low potential side conductive path 101B. Correspondingly, a current flows to the second switching circuit 130 side (the secondary side of the transformer 110) along the path indicated by the arrow C2. The path indicated by arrow C2 is the second low potential side conductive path 102B→sixth switch element 130B→second coil section 112B→rectification output path 130C→choke coil 133→second high potential side conductive path 102A ( See Figure 2).

Next, the first switch element 120A and the fourth switch element 120D are switched from ON to OFF, and all of the first switch element 120A, the second switch element 120B, the third switch element 120C, and the fourth switch element 120D are turned off. become a state. Then, no current flows to the first switching circuit 120 side (the primary side of the transformer 110). On the side of the second switching circuit 130 (secondary side of the transformer 110), the energy stored in the choke coil 133 causes current to flow along the path of arrow C3 or arrow C4. The path indicated by arrow C3 is the second low potential side conductive path 102B→sixth switch element 130B→second coil section 112B→rectification output path 130C→choke coil 133→second high potential side conductive path 102A. The path indicated by arrow C4 is the second low potential side conductive path 102B→fifth switch element 130A→second coil section 112A→rectification output path 130C→choke coil 133→second high potential side conductive path 102A ( See Figure 3).

Next, the second switch element 120B and the third switch element 120C are switched from off to on. Then, current flows to the first switching circuit 120 side (the primary side of the transformer 110) along the path indicated by the arrow C5. A route indicated by an arrow C5 is a route of first high potential side conductive path 101A→third switch element 120C→first coil section 111→second switch element 120B→first low potential side conductive path 101B. Correspondingly, a current flows to the second switching circuit 130 side (the secondary side of the transformer 110) through the path indicated by the arrow C6. The path indicated by arrow C6 is the second low potential side conductive path 102B→fifth switch element 130A→second coil section 112A→rectification output path 130C→choke coil 133→second high potential side conductive path 102A ( See Figure 4).

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. become a state. Then, no current flows to the first switching circuit 120 side (the primary side of the transformer 110). On the side of the second switching circuit 130 (secondary side of the transformer 110), the energy stored in the choke coil 133 causes current to flow along the path of arrow C3 or arrow C4. The path indicated by arrow C3 is the second low potential side conductive path 102B→sixth switch element 130B→second coil section 112B→rectification output path 130C→choke coil 133→second high potential side conductive path 102A. The path indicated by the arrow C4 is the second low potential side conductive path 102B→fifth switch element 130A→second coil section 112A→rectification output path 130C→choke coil 133→second high potential side conductive path 102A ( See Figure 3).

On the other hand, the converter 100 of the present disclosure performs switching operation using a phase shift method. In the phase shift method, as shown in FIG. 5, the first switch element 20A and the fourth switch element 20D shift the on/off timings of each other, and the second switch element 20B and the third switch element 20C shift the on/off timings of each other. Change the timing of action. Along with this, the phase shift method controls the switching elements 20A, 20B, 20C, and 20D so as to shift the timings of their ON/OFF operations. Thereby, ZVS (Zero Voltage Switching) can be achieved when switch elements 20A, 20B, 20C, and 20D are switched from OFF to ON, and converter 100 can be operated with higher efficiency. In the phase shift method, the first switch element 20A and the second switch element 20B are set as one set (hereinafter also referred to as the first leg), and the third switch element 20C and the fourth switch element 20D are set as one set (hereinafter referred to as the first leg). 2 legs). In the first leg, the times (T2, T4, T6, and T8 in FIG. 5) during which both the first switch element 20A and the second switch element 20B are turned off are first dead times. In the second leg, the times (T1, T3, T5 and T7 in FIG. 5) during which both the third switch element 20C and the fourth switch element 20D are turned off are second dead times.

Here, focusing on the time T2, the case where the second switch element 20B is switched from OFF to ON during the first dead time will be described. As shown in FIG. 6, before time T2S (that is, 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 bottom of FIG. 6). At this time, the DC input voltage Vin is also applied to the capacitor 20M connected in parallel with the second switch element 20B. Then, at time T2S, when the first switching element 20A is switched from ON to OFF, current stops flowing through the first switching 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 becomes the DC input voltage Vin. Approaching half size. The voltage between the drain and the source of the second switch element 20B becomes closest to 0V at time T2E when the LC resonance starts and the voltage drops for the first time (see the lower side of FIG. 6). Therefore, by setting the time at which the second switch element 20B is switched from off to on to be T2E, ZVS in the second switch element 20B can be achieved. Note that the time for switching the second switch element 20B from off to on may be switched to a time slightly earlier than T2E.

Focusing on the time T2, the case where the second switch element 20B is switched from OFF to ON during the first dead time has been described. This is not limited to this, and the same applies to other times T1, T3, T4, T5, T6, T7, T8 in FIG. 5 and other switch elements 20A, 20C, 20D that are switched from off to on.

[How to find the input voltage]
The secondary side voltage detection section 40E detects a voltage Vtr2 generated between one end of the second coil section 12B of the transformer 10 and the third connection point P3 (that is, the voltage on the secondary side of the transformer 10, A voltage generated in the coil portion 12B) is detected. The voltage Vtr2 is the potential difference between the rectified output path 30C (fifth conductive path) electrically connected to the transformer 10 and the second low potential side conductive path 2B electrically connected to ground (Fig. 1). The rectified output path 30C is a conductive path between the choke coil 33 and the third connection point P3 (center tap), which is an intermediate position between the second coil portions 12A and 12B in the transformer 10. FIG. That is, the voltage Vtr2 is the voltage of the rectified output path 30C (fifth conductive path) with reference to the potential (ground potential) of the second low potential side conductive path 2B, and is the voltage generated in the second switching circuit 30.

The voltage Vtr2 is the sum of the voltage across the second coil section 12B and the voltage Vdrop between the drain and source of the sixth switch element 30B. This value is the value before being smoothed by the filter circuit having the choke coil 33 and the output capacitor 34 . The value indicated by the second voltage detection section 40B is the potential difference between the second high-potential-side conductive path 2A and the second low-potential-side conductive path 2B. is the DC voltage value of The secondary side voltage detector 40E inputs a signal indicating the value of the voltage Vtr2 to the controller 40 . The signal indicating the value of the voltage Vtr2 may be a signal capable of specifying the value of the voltage Vtr2, or may be a signal indicating the value of the voltage Vtr2 itself. It may be a signal indicating

The control unit 40 obtains the voltage value between the first high-potential conductive path 1A and the first low-potential conductive path 1B based on the voltage Vtr2 detected by the secondary voltage detection unit 40E. A voltage value between the first high-potential-side conductive path 1A and the first low-potential-side conductive path 1B is a value indicating the input voltage Vin, and the first high-potential-side conductive path 1A and the first low-potential-side conductive path 1B.

A voltage value (input voltage Vin) between the first high-potential-side conductive path 1A and the first low-potential-side conductive path 1B can be obtained by the formula shown in Equation (1).

Here, Vtr2 is the voltage value (produced in the second coil portion 12B) on the second coil portion 12B side of the choke coil 33 with reference to the potential of the ground path G, and N is the number of turns of the first coil portion 11 and the second coil. Vdrop is the voltage between the drain and the source of the sixth switch element 30B (hereinafter simply referred to as the voltage Vdrop), which is the turn ratio to the number of turns of the portion 12B (12A) (hereinafter also simply referred to as the turns ratio N). That is, the formula shown in Equation 1 indicates that the input voltage Vin can be obtained by multiplying the sum of the voltage Vtr2 and the voltage Vdrop by the turn ratio N.

When the control unit 40 executes the first control for causing the second switching circuit 30 to perform rectification operation in the synchronous rectification mode, the voltage Vdrop is the voltage between the drain and source of the FET (sixth switch element 30B). Vds (hereinafter also simply referred to as voltage Vds). That is, when in synchronous rectification mode, the voltage Vdrop is Vdrop=Vds. On the other hand, when the control unit 40 executes the second control for causing the second switching circuit 30 to perform the rectification operation in the diode rectification mode, the voltage Vdrop is the forward voltage Vf of the body diode 30E (hereinafter simply referred to as (also called forward voltage Vf). That is, when in diode rectification mode, the voltage Vdrop is Vdrop=Vf.

[Method for determining input voltage in first determination method in synchronous rectification mode]
During the first control that causes the second switching circuit 30 to perform rectification operation in the synchronous rectification mode, the control unit 40 controls the (second A method for obtaining the input voltage Vin by the first determination method based on the voltage Vtr2 (produced in the two-coil section 12B) will be described.

The value of the voltage Vds is determined by the output current Iout flowing through the rectified output path 30C (the value detected by the second current detection section 40D) and the ON resistance Rds of the FET (sixth switch element 30B) (hereinafter also simply referred to as the ON resistance Rds). can be obtained by multiplying That is, the voltage Vds is Vds=Iout×Rds. The on-resistance Rds has the property of changing according to the ambient temperature T. In order to determine the input voltage Vin in consideration of this property, the ROM or the like of the control unit 40 stores table data D1 shown in FIG. In the table data D1, for example, a plurality of on-resistance Rds values of the FET (sixth switch element 30B) corresponding to the ambient temperature T are arranged.

In the synchronous rectification mode, the control unit 40 determines the on-resistance Rds based on the voltage value indicating the ambient temperature T acquired from the temperature detection unit 50 using the table data D1. For example, when the voltage value indicating the ambient temperature T obtained from the temperature detection unit 50 indicates 10° C. or more and less than 20° C. (that is, 10° C.≦T<20° C.), the control unit 40 turns on Rds3 in FIG. Used as resistor Rds. Then, the control unit 40 obtains the voltage Vds by multiplying the value (output current Iout) detected by the second current detection unit 40D at this time by Rds3. Then, the control unit 40 obtains the input voltage Vin based on the voltage Vds thus obtained and the voltage Vtr2 detected by the secondary voltage detection unit 40E. The control unit 40 can obtain the voltage Vds by selecting the on-resistance Rds corresponding to the voltage value indicating the ambient temperature T obtained from the temperature detection unit 50 at predetermined time intervals (periodically) from the table data D1. It is Accordingly, the control unit 40 can dynamically obtain the input voltage Vin using the voltage Vds and the voltage Vtr2 thus obtained.

[How to find the input voltage in the second determination method in the diode rectification mode]
Next, during the second control for causing the second switching circuit 30 to perform the rectification operation in the diode rectification mode, the control section 40 controls the second coil section 12A and the second coil section 12A of the choke coil 33 with the potential of the ground path G as a reference. A method for obtaining the input voltage Vin by the second determination method based on the voltage Vtr2 (produced in the second coil section 12B) on the 12B side will be described.

The forward voltage Vf is described, for example, in the data sheet of the FET used for the sixth switch element 30B. The voltage Vds in synchronous rectification mode is smaller than the forward voltage Vf. Here, the forward voltage Vf has the property of changing according to the ambient temperature T and the output current Iout flowing through the rectified output path 30C (the value detected by the second current detection section 40D). In order to determine the input voltage Vin in consideration of this property, the ROM of the control unit 40 or the like stores table data D2 shown in FIG.

In table data D2, for example, a plurality of values of forward voltage Vf of body diode 30E corresponding to two values of ambient temperature T and output current Iout are arranged. In the diode rectification mode, the control unit 40 uses the table data D2 to determine the forward voltage Vf based on the ambient temperature T and the magnitude of the value indicating the output current Iout. For example, when the voltage value indicating the ambient temperature T obtained from the temperature detection unit 50 indicates 30° C. or more and less than 40° C. (that is, 30° C.≦T<40° C.), the control unit 40 controls Vf41, Vf42 . A value corresponding to the value indicating the output current Iout is selected as the forward voltage Vf from Vf4m. At this time, for example, when the value (output current Iout) detected by the second current detection unit 40D indicates 10A or more and less than 20A (that is, 10A≤Iout<20A), the control unit 40 sets Vf42 as the forward voltage Vf. select.

The control unit 40 obtains the input voltage Vin based on the forward voltage Vf and the voltage Vtr2 thus selected. The control unit 40 detects the voltage value indicating the ambient temperature T acquired from the temperature detection unit 50 at predetermined time intervals (periodically) and the value (output current Iout) detected by the second current detection unit 40D. The forward voltage Vf can be obtained by selecting the direction voltage Vf from the table data D2. Thereby, the control unit 40 can dynamically obtain the input voltage Vin using the forward voltage Vf and the voltage Vtr2 thus obtained.

In this manner, the control unit 40 controls the first high potential side conductive path 1A and the first low potential side conductive path based on the voltage Vtr2, the voltage Vds, and the forward voltage Vf detected by the secondary side voltage detection unit 40E. A voltage value (input voltage Vin) between 1B and 1B can be obtained. Therefore, the converter 100 cannot directly detect the voltage value (input voltage Vin) between the first high potential side conductive path 1A and the first low potential side conductive path 1B, or the voltage Vtr2 rather than directly detecting it. This is advantageous when there are circumstances in which it is desirable to detect and estimate the voltage value.

The converter 100 detects a voltage Vtr2 that is relatively lower than the voltage value (input voltage Vin) between the first high potential side conductive path 1A and the first low potential side conductive path 1B. Then, the converter 100 can obtain the voltage value between the first high potential side conductive path 1A and the first low potential side conductive path 1B from this voltage Vtr2. Therefore, the converter 100 can omit or simplify the essential configuration for detecting high voltage, and the voltage value between the first high-potential-side conductive path 1A and the first low-potential-side conductive path 1B can be A more compact configuration that can be detected can be realized. For example, when directly detecting the value of the input voltage Vin and inputting the detected value to the control unit 40, if the value of the input voltage Vin increases, an insulating unit such as an insulation amplifier is required between the input side and the control unit 40. However, according to the present disclosure, such components can be omitted.

Next, the effect of this configuration will be illustrated.
The isolated DCDC converter 100 of the present disclosure includes a first switching circuit 20, a second switching circuit 30, and a transformer 10 including a first coil section 11 and second coil sections 12A and 12B. The isolated DCDC converter 100 of the present disclosure performs voltage conversion between the first conducting path 1 and the second conducting path 2 . The isolated DCDC converter 100 of the present disclosure controls the choke coil 33 interposed in the path between the second coil units 12A and 12B and the second conductive path 2, the first switching circuit 20 and the second switching circuit 30. and a control unit 40 . The first switching circuit 20 performs a conversion operation of applying an AC voltage to the first coil section 11 using the voltage applied to the first conductive path 1 as the input voltage Vin. The second switching circuit 30 includes a fifth switch element 30A and a sixth switch element 30B each having body diodes 30D and 30E. The second switching circuit 30 is electrically connected to the ground path G. The second switching circuit 30 rectifies the voltage Vtr2 generated in the second coil section 12B in response to the conversion operation of the first switching circuit 20 and applies the output voltage Vout to the second conducting path 2. . The control unit 40 performs first control that causes the second switching circuit 30 to perform rectification operation in the synchronous rectification mode and second control that causes the second switching circuit 30 to perform rectification operation in the diode rectification mode. conduct. The control unit 40 obtains the input voltage Vin by the first determination method based on the voltage Vtr2 of the second coil units 12A and 12B of the choke coil 33 based on the potential of the ground path G during the first control. In the second control, the control section 40 obtains the input voltage Vin by the second determination method based on the voltage Vtr2 on the second coil section 12A, 12B side of the choke coil 33 based on the potential of the ground path. According to this configuration, the input voltage Vin in each of the synchronous rectification mode and the diode rectification mode can be obtained by separate determination methods.

In the isolated DCDC converter 100 of the present disclosure, the control unit 40 performs the second control when the value indicating the output current Iout output from the second conduction path 2 is smaller than a predetermined threshold, and indicates the output current Iout. The first control is executed when the value is greater than or equal to a predetermined threshold. According to this configuration, the isolated DCDC converter 100 can individually obtain the input voltage Vin according to the magnitude of the value indicating the output current Iout.

In the isolated DCDC converter 100 of the present disclosure, the second coil portions 12A and 12B are provided with a third connection point P3, and the turns ratio between the number of turns of the first coil portion 11 and the number of turns of the second coil portion 12B is N is. The input voltage Vin is the voltage Vtr2 on the side of the second coil portions 12A and 12B of the choke coil 33, which is based on the potential of the ground path G, and the voltage Vdrop between the drain and source of the FET (sixth switch element 30B). is added and multiplied by the turn ratio N to obtain Vin in Equation 1. When in synchronous rectification mode, the voltage Vdrop is the voltage Vds between the drain and source of the FET in Equation 2. Voltage Vdrop is the forward voltage Vf of body diode 30E in Equation 3 when in diode rectification mode.
Vin=N×(Vtr2+Vdrop) Equation 1
Vdrop=Vds Equation 2
Vdrop=Vf Equation 3
According to this configuration, the isolated DCDC converter 100 can determine the input voltage Vin in consideration of the forward voltage Vf of the body diode 30E in the diode rectification mode. Therefore, the isolated DCDC converter 100 can more accurately obtain the input voltage Vin in the diode rectification mode.

In the isolated DCDC converter 100 of the present disclosure, the controller 40 determines the forward voltage Vf based on the ambient temperature T and the magnitude of the value indicating the output current Iout output from the second conducting path 2 . With this configuration, the isolated DCDC converter 100 can obtain a more accurate input voltage Vin.

<Embodiment 2>
An insulated DCDC converter 200 according to Embodiment 2 of the present disclosure will be described with reference to FIG. The isolated DCDC converter 200 according to the second embodiment differs from the first embodiment in the configuration of the transformer 210 and the second switching circuit 230 being a so-called full-wave rectifier circuit using four switching elements. The same reference numerals are assigned to the same configurations as those of the first embodiment, and descriptions of the structures, functions and effects are omitted.

The transformer 210 has a first coil section 211 and a second coil section 212 . The number of turns of the first coil portion 211 is N1. The number of turns of the second coil portion 212 is N2. A turns ratio N of the transformer 210 is represented by N=N2/N1.

The second switching circuit 230 is a so-called full-wave rectifier circuit, which rectifies and smoothes the AC voltage generated in the second coil section 212 of the transformer 210 in accordance with the conversion operation of the first switching circuit 20 to generate a DC voltage. produces an output voltage Vout that is Then, the second switching circuit 230 applies this output voltage Vout between the second high potential side conductive path 2A and the second low potential side conductive path 2B. Thus, the second switching circuit 230 performs rectifying operation. The second switching circuit 230 includes a fifth switch element 230A, a sixth switch element 230B, a seventh switch element 230C, an eighth switch element 230D, a rectification output path 230J, a choke coil 33, and an output capacitor .

The fifth switch element 230A is connected between one end of the second coil section 212 of the transformer 210 and the rectified output path 230J. The sixth switch element 230B is connected between one end of the second coil section 212 and the ground path G, which is the reference conductive path. The seventh switch element 230C is connected between the other end of the second coil section 212 and the rectification output path 130J. The eighth switch element 230D is connected between the other end of the second coil section 212 and the ground path G. That is, the second switching circuit 230 is electrically connected to the reference conductive path.

A choke coil 33 is interposed between the rectified output path 230J and the second high-potential-side conductive path 2A (second conductive path 2). The choke coil 33 is electrically connected to the second high potential side conductive path 2A and is also electrically connected via the output capacitor 34 to the second low potential side conductive path 2B. The choke coil 33 is interposed in the path between the second coil portion 212 and the second conductive path 2 . The output capacitor 34 is electrically connected between the second high potential side conductive path 2A and the second low potential side conductive path 2B. The second low potential side conductive path 2B is electrically connected to the ground path G.

Various known switch elements can be used for the fifth switch element 230A, the sixth switch element 230B, the seventh switch element 230C, and the eighth switch element 230D, but it is preferable to use a MOSFET which is an FET. . The source of the fifth switch element 230A is electrically connected to one end of the second coil section 212, and the drain is electrically connected to the rectification output path 230J. The drain of the sixth switch element 230B is electrically connected to one end of the second coil section 212, and the source is electrically connected to the ground path G. The source of the seventh switch element 230C is electrically connected to the other end of the second coil section 212, and the drain is electrically connected to the rectification output path 230J. The drain of the eighth switch element 230D is electrically connected to the other end of the second coil section 212, and the source is electrically connected to the ground path G.

Body diodes 230E, 230F, 230G, and 230H, which are parasitic components, are provided in the fifth switch element 230A, the sixth switch element 230B, the seventh switch element 230C, and the eighth switch element 230D, respectively. there is Specifically, in each of the fifth switching element 230A, the sixth switching element 230B, the seventh switching element 230C, and the eighth switching element 230D, the cathodes of the body diodes 230E, 230F, 230G, and 230H are on the drain side, and the anodes are on the drain side. It is configured to be electrically connected to the source side. That is, the fifth switch element 230A, the sixth switch element 230B, the seventh switch element 230C, and the eighth switch element 230D have body diodes 230E, 230F, 230G, and 230H.

In the second switching circuit 230 having such a configuration, the fifth switching element 230A, the sixth switching element 230B, the seventh switching element 230C, and the eighth switching element 230D switch the AC voltage generated in the second coil section 212 to Configure a rectifying circuit that rectifies. Choke coil 33 and output capacitor 34 smooth the rectified output appearing on rectified output path 130J.

Based on the value input from the second current detection unit 40D, the control unit 40 outputs a It outputs a switching signal at a predetermined timing or stops outputting the switching signal. Specifically, the control unit 40 executes the first control when the value indicating the output current Iout output from the second high potential side conductive path 2A detected by the second current detection unit 40D is equal to or greater than a predetermined threshold value. . The first control outputs a switching signal with a predetermined timing to each gate of the fifth switch element 230A, the sixth switch element 230B, the seventh switch element 230C, and the eighth switch element 230D of the second switching circuit 230. This is the control to perform the rectification operation in the synchronous rectification mode.

Then, when the value indicating the output current Iout output from the second high-potential-side conductive path 2A detected by the second current detection section 40D is smaller than a predetermined threshold value, the control section 40 executes the second control. The second control stops outputting switching signals to gates of the fifth switch element 230A, the sixth switch element 230B, the seventh switch element 230C, and the eighth switch element 230D of the second switching circuit 230, 2 switching circuit 230 to perform the rectification operation in the diode rectification mode. In the diode rectification mode, rectification is performed using body diodes 230E, 230F, 230G, and 230H provided in the fifth switch element 230A, the sixth switch element 230B, the seventh switch element 230C, and the eighth switch element 230D. mode.

[How to find the input voltage]
The secondary-side voltage detection unit 40E detects the voltage Vtr2 generated between the rectified output path 130J and the ground path G, which is the reference conductive path (that is, the voltage on the secondary side of the transformer 210 and generated in the second coil unit 212). voltage). The voltage Vtr2 is the potential difference between the rectified output path 230J and the second low-potential side conductive path 2B electrically connected to the ground path G, and is the potential difference of the choke coil 33 with the potential of the ground path G as a reference. This is the voltage on the side of the second coil section 212 (see FIG. 9). That is, the voltage Vtr2 is the voltage of the rectified output path 230J based on the potential (ground potential) of the second low potential side conductive path 2B, and is the voltage generated in the second switching circuit 230. FIG.

The voltage Vtr2 is the sum of the voltage across the second coil section 212, the voltage Vdrop between the drain and source of the fifth switch element 230A, and the voltage Vdrop between the drain and source of the eighth switch element 230D. value. Alternatively, the voltage Vtr2 is the voltage across the second coil section 212, the voltage Vdrop between the drain and source of the sixth switch element 230B, the voltage Vdrop between the drain and source of the seventh switch element 230C, is the sum of This value is the value before being smoothed by the filter circuit having the choke coil 33 and the output capacitor 34 . The secondary side voltage detector 40E inputs a signal indicating the value of the voltage Vtr2 to the controller 40 .

The control unit 40 obtains the voltage value between the first high potential side conducting path 1A and the first low potential side conducting path 1B based on the voltage Vtr2 detected by the secondary side voltage detecting part 40E. A voltage value (input voltage Vin) between the first high-potential-side conductive path 1A and the first low-potential-side conductive path 1B can be obtained by the formula shown in Equation (1). Here, Vdrop in Equation 1 is the sum of the voltage Vdrop between the drain and source of the fifth switch element 230A and the voltage Vdrop between the drain and source of the eighth switch element 230D (or The sum of the voltage Vdrop between the drain and source of the sixth switch element 230B and the voltage Vdrop between the drain and source of the seventh switch element 230C) is applied.

Here, in Embodiment 1, the voltage between the drain and source of one sixth switch element 30B is applied to Vdrop. That is, even if the number of switch elements to be considered is changed according to the circuit configuration of the second switching circuit, the voltage between the drain and the source corresponding to the number of switch elements is applied to Vdrop in the formula shown in Equation 1. By doing so, the input voltage Vin can be obtained.

When the control unit 40 executes the first control, the voltage Vdrop is the voltage between the drain and source of the fifth switching element 230A, which is an FET, and the voltage between the drain and source of the eighth switching element 230D, which is an FET. or the sum of the voltage between the drain and source of the sixth switch element 230B, which is an FET, and the voltage between the drain and source of the seventh switch element 230C, which is an FET voltage Vds. That is, when in synchronous rectification mode, the voltage Vdrop is Vdrop=Vds.

On the other hand, when the control unit 40 executes the second control, the voltage Vdrop is the total voltage Vf of the forward voltages of the body diodes 230E and 230H, or the total forward voltage Vf of the body diodes 230F and 230G. is the total voltage Vf with the forward voltage of each of . That is, when in diode rectification mode, the voltage Vdrop is Vdrop=Vf.

During the first control, the control unit 40 performs the first determination method based on the voltage Vtr2 on the side of the second coil unit 212 of the choke coil 33 (generated in the second coil unit 212) with the potential of the ground path G as a reference. is the same as that disclosed in the first embodiment. Further, during the second control, the control unit 40 performs the second control based on the voltage Vtr2 (produced in the second coil unit 212) on the second coil unit 212 side of the choke coil 33 based on the potential of the ground path G. The determination method for determining the input voltage Vin is the same as disclosed in the first embodiment.

<Other embodiments>
The present configuration is not limited to the embodiments explained by the above description and drawings, and for example, the following embodiments are also included in the technical scope of the present invention.

In the first embodiment, the control unit 40 is mainly composed of a microcomputer, but may be realized by a plurality of hardware circuits other than the microcomputer.

In the first embodiment, the control unit 40 obtains the voltage Vds using the table data D1 that defines the on-resistance Rds corresponding to the ambient temperature T. However, it is not limited to this example, and the voltage Vds may be obtained with the on-resistance Rds as a fixed value. Furthermore, the voltage Vds may be determined by an arithmetic expression for obtaining Vds using the voltage value indicating the ambient temperature T detected by the temperature detection unit 50 and the output current Iout as variables.

In the first embodiment, the control unit 40 obtains the forward voltage Vf using the table data D2 that defines the forward voltage Vf corresponding to two values of the ambient temperature T and the output current Iout. However, it is not limited to this example, and the forward voltage Vf may be a fixed value. Furthermore, Vf may be determined by an arithmetic expression for obtaining the forward voltage Vf using the voltage value indicating the ambient temperature T detected by the temperature detection unit 50 and the output current Iout as variables. Furthermore, the forward voltage Vf may be obtained using table data that defines the forward voltage Vf corresponding only to either the ambient temperature T or the value of the output current Iout. That is, the forward voltage Vf may be determined based on either the ambient temperature T or the magnitude of the output current Iout.

In Embodiment 1, the second switching circuit 30 is provided with two FETs (the fifth switching element 30A and the sixth switching element 30B). However, the configuration is not limited to this, and one or three or more FETs may be provided in the second switching circuit.

Embodiment 1 exemplified the step-down DCDC converter. However, the present invention is not limited to this, and may be a step-up DCDC converter that steps up the voltage applied to the first conductive path and applies the voltage to the second conductive path, or a step-up/step-down DCDC converter. Also, a voltage conversion operation in which the voltage applied to the first conductive path is stepped up or stepped down and applied to the second conductive path, and the voltage applied to the second conductive path is stepped up or stepped down and applied to the first conductive path. It may be a bi-directional DCDC converter capable of performing a voltage conversion operation.

In Embodiment 1, the secondary side voltage detection section 40E detects the voltage generated in the second coil section 12B of the transformer 10 . However, not limited to this, the secondary side voltage detection section 40E may detect the voltage generated in the second coil section 12A of the transformer 10 . In this case, the on-resistance Rds, the voltage Vdrop, the voltage Vds, and the forward voltage Vf of the fifth switch element may be used.

It should be considered that the embodiments disclosed this time are illustrative in all respects 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 includes all modifications within the meaning and scope of claims equivalent to the claims. intended.

Reference Signs List 1 First conductive paths 1A, 101A First high potential side conductive paths 1B, 101B First low potential side conductive paths 2 Second conductive paths 2A, 102A Second high potential side conductive paths 2B, 102B Second 2 Low potential side conducting path 6 Load 7 Input capacitor 10, 110, 210 Transformer 11, 111, 211 First coil section 12A, 12B, 112A, 112B, 212 Second coil section 13 Inductor 20, 120 First switching circuits 20A, 120A First switching elements 20B, 120B Second switching elements 20C, 120C Third switching elements 20D, 120D Fourth switching elements 20L, 20M, 20N, 20P Capacitors 30, 130, 230 Second switching circuits 30A, 130A, 230A Fifth switch elements 30B, 130B, 230B Sixth switch element 230C Seventh switch element 230D Eighth switch element 30C, 130C, 230J Rectification output paths 30D, 30E , 230E, 230F, 230G, 230H body diodes 33, 133 choke coil 34 output capacitor 40 control section 40B second voltage detection section 40C first current detection section 40D second current detection section 40E secondary Side voltage detection unit 50 Temperature detection unit 100 Insulated DCDC converters C1, C2, C3, C4, C5, C6 Arrows D1, D2 Table data G Ground path (reference conductive path)
Iout ... Output current N ... Turns ratio (turns ratio between the number of turns of the first coil portion and the number of turns of the second coil portion)
N1 Number of turns of the first coil portion N2 Number of turns of the second coil portion P1 First connection point P2 Second connection point P3 Third connection point (center tap)
Rds: On-resistance of FET (sixth switch element) T: Ambient temperature Vdrop: Voltage between drain and source of FET Vds: Voltage between drain and source of FET Vf: Forward voltage of body diode Vin ... input voltage Vout ... output voltage Vtr2 ... voltage (voltage on the second coil section side of the choke coil based on the potential of the ground path) (voltage generated between one end of the second coil section and the center tap)

Claims (4)

An insulated DCDC that includes a first switching circuit, a second switching circuit, and a transformer that includes a first coil section and a second coil section, and performs voltage conversion between the first conductive path and the second conductive path. a converter,
a choke coil interposed in a path between the second coil portion and the second conductive path;
a control unit that controls the first switching circuit and the second switching circuit;
The first switching circuit performs a conversion operation of applying an AC voltage to the first coil portion with the voltage applied to the first conductive path as an input voltage,
The second switching circuit includes an FET having a body diode, is electrically connected to a reference conductive path, and controls the voltage generated in the second coil section in response to the conversion operation performed by the first switching circuit. performing a rectification operation of rectifying and applying an output voltage to the second conduction path;
The control unit performs a first control that causes the second switching circuit to perform a rectification operation in a synchronous rectification mode, and a second control that causes the second switching circuit to perform a rectification operation in a diode rectification mode. do,
The control section obtains the input voltage by a first determination method based on the voltage of the second coil section side of the choke coil based on the potential of the reference conductive path during the first control, and The isolated DCDC converter obtains the input voltage by a second determination method based on the voltage on the second coil portion side of the choke coil with reference to the potential of the reference conductive path during the second control. The control unit
executing the second control when a value indicating the output current output from the second conductive path is smaller than a predetermined threshold;
2. The isolated DCDC converter according to claim 1, wherein said first control is executed when the value indicating said output current is equal to or greater than said predetermined threshold. A turns ratio between the number of turns of the first coil portion and the number of turns of the second coil portion is N,
The input voltage is obtained by adding the voltage Vtr2 on the side of the second coil portion of the choke coil with reference to the potential of the reference conductive path and the voltage Vdrop between the drain and the source of the FET and the number of turns. is Vin in Equation 1 multiplied by the ratio N,
when in the synchronous rectification mode, the voltage Vdrop is the voltage Vds between the drain and source of the FET in Equation 2;
3. The isolated DCDC converter according to claim 1 or 2, wherein in the diode rectification mode, the voltage Vdrop is the forward voltage Vf of the body diode in equation (3).
Vin=N×(Vtr2+Vdrop) Equation 1
Vdrop=Vds Equation 2
Vdrop=Vf Equation 3 4. The insulated DCDC according to claim 3, wherein said controller determines said forward voltage Vf based on at least one of ambient temperature and magnitude of a value indicating output current output from said second conductive path. converter.

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