JP2018082506A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter which can inhibit switching loss while avoiding complication of control and use of a large-sized structure.SOLUTION: A DC-DC converter 1 comprises a parallel circuit part 10 in which plural switching circuit parts 11 and 12 are connected in parallel and a main inductor La. The switching circuit part 11 includes a high side first switching element H1, a low side second switching element L1, and an auxiliary inductor Lb1 with an end electrically connected with a connection 11A connecting the first switching element H1 with the second switching element L1. The switching circuit part 12 also is structured to be the same as the switching circuit part 11. The main inductor La is arranged between the other end of each of auxiliary inductors Lb1 and Lb2 in the plural switching circuit parts 11 and 12 and a second conducting path 22.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a DCDC converter.

  In the DCDC converter, since switching loss occurs during the on / off operation of the switching element, it is required to suppress these losses. As a method for suppressing the switching loss, a method as in Patent Document 1 has been proposed. Patent Document 1 discloses a technique related to a soft switching method in which a switching element is operated at zero current or zero voltage. Specifically, a resonant capacitor and an inductor are provided in a buck-boost circuit unit to use a resonance phenomenon. Thus, the soft switching operation is performed.

JP 2014-236620 A

  However, when the soft switching operation is performed using the resonance phenomenon like the DCDC converter disclosed in Patent Document 1, there are problems of high breakdown voltage and complicated control system due to the use of the resonance phenomenon. Prone to occur. For example, in the method of Patent Document 1, since it is necessary to cope with an excessive resonance voltage or resonance current that occurs instantaneously, the size of the element and the number of parallel devices are likely to increase. Further, since it is necessary to control the resonance voltage or the resonance current, a complicated control system is required, and this tends to increase the number of elements.

  The present invention has been made based on the above-described circumstances, and it is an object of the present invention to realize a DCDC converter capable of suppressing switching loss while suppressing the complexity of control and the increase in size of the structure. is there.

The DCDC converter of the first invention is
The first switching element between the first switching element electrically connected to the first conduction path and the reference conduction path maintained at a lower potential than the first switching element and the first conduction path. A low-side second switching element connected in series with the switching element; and an auxiliary inductor having one end electrically connected to a connection portion connecting the first switching element and the second switching element. A parallel circuit unit in which a plurality of switching circuit units are connected in parallel;
A main inductor disposed between the other end of each of the auxiliary inductors and a second conductive path in the plurality of switching circuit units;
A PWM signal is output to each of the first switching element and the second switching element in the plurality of switching circuit units, and an ON signal is output to the first switching element for each of the switching circuit units. A drive unit that periodically performs a switching operation to output an ON signal to the second switching element later;
Have

The DCDC converter of the second invention is
The first switching element between the first switching element electrically connected to the first conduction path and the reference conduction path maintained at a lower potential than the first switching element and the first conduction path. A low-side second switching element connected in series with the switching element; and an auxiliary inductor having one end electrically connected to a connection portion connecting the first switching element and the second switching element. A parallel circuit unit in which a plurality of switching circuit units are connected in parallel;
A main inductor disposed between the other end of each of the auxiliary inductors and a second conductive path in the plurality of switching circuit units;
A PWM signal is output to each of the first switching element and the second switching element in the plurality of switching circuit units, and an ON signal is output to the second switching element for each of the switching circuit units. A drive unit that periodically performs a switching operation to output an ON signal to the first switching element later;
Have

  A DCDC converter according to a first aspect of the present invention includes a parallel circuit unit in which a plurality of switching circuit units are connected in parallel. In each switching circuit unit, a first switching element on a high side and a second switching element on a low side are provided. An auxiliary inductor is disposed between the path from the connecting portion to the main inductor. In such a configuration, when a switching operation for outputting an on signal to the second switching element after outputting an on signal to the first switching element is periodically performed for each switching circuit unit, the switching circuit unit is applied to the first conductive path. In this step-down operation, the current flowing through the first switching element when the first switching element is switched from the off state to the on state can be performed. Can be delayed. Therefore, the current immediately after the first switching element is turned on can be reliably reduced, and the switching loss can be effectively suppressed.

  The DCDC converter according to a second aspect of the present invention includes a parallel circuit unit in which a plurality of switching circuit units are connected in parallel. In each switching circuit unit, a first switching element on the high side and a second switching element on the low side are provided. An auxiliary inductor is disposed between the path from the connecting portion to the main inductor. In such a configuration, when a switching operation for outputting an ON signal to the first switching element after outputting an ON signal to the second switching element is periodically performed for each switching circuit unit, the switching circuit portion is applied to the second conductive path. In this step-up operation, when the second switching element is switched from the off state to the on-state, an energization current flowing through the second switching element can be increased. Can be delayed. Therefore, the current immediately after the second switching element is turned on can be reliably reduced, and the switching loss can be effectively suppressed.

FIG. 1 is a circuit diagram schematically illustrating an in-vehicle power supply system including the DCDC converter according to the first embodiment. FIG. 2 illustrates a gate signal applied to the first switching element and the second switching element of each switching circuit unit, a current flowing through each auxiliary inductor, and a main inductor when the DCDC converter according to the first embodiment performs a step-down operation. It is a timing chart which shows the relationship with an electric current. FIG. 3 shows the drain-source voltage of the first switching element, the energization current flowing through the first switching element, and the loss (switching loss) generated in the first switching element when the DCDC converter of Example 1 performs the step-down operation. It is a timing chart which shows the relationship. FIG. 4 shows the gate signals given to the first switching element and the second switching element of each switching circuit unit, the current flowing through each auxiliary inductor, and the main inductor when the DCDC converter according to the first embodiment performs a step-up operation. It is a timing chart which shows the relationship with an electric current.

Here, a desirable example of the invention will be shown.
In the first invention, the drive unit outputs a PWM signal with a phase shifted with respect to each of the first switching elements of the plurality of switching circuit units, and an on signal to the first switching element for each of the switching circuit units. The ON signal is output to the second switching element after the end of the signal, and the ON signal is output to the first switching element of the switching circuit unit that operates next after the ON signal to the second switching element ends. May function.

  In the DCDC converter having such a configuration, when the body diode energization starts in the second switching element when the synchronous rectification by the second switching element is finished in each switching circuit part, By turning on one switching element, reflux in the second switching element can be suppressed.

  In the second invention, the drive unit outputs a PWM signal with a phase shifted with respect to each of the second switching elements of the plurality of switching circuit units, and an on signal to the second switching element for each of the switching circuit units. The ON signal is output to the first switching element after the end of the signal, and the ON signal is output to the second switching element of the switching circuit unit that operates next after the ON signal to the first switching element ends. May function.

  In the DCDC converter having such a configuration, when the body diode energization starts in the first switching element when the synchronous rectification by the first switching element is finished in each switching circuit section, By turning on the two switching elements, the reflux in the first switching element can be suppressed.

  In both the first and second inventions, the inductances of the plurality of auxiliary inductors may be smaller than the inductance of the main inductor.

  According to this configuration, a DCDC converter that can reduce the switching loss by delaying the energization current immediately after turn-on can be realized while suppressing the increase in size of the auxiliary inductor.

<Example 1>
Hereinafter, a more specific example of the present invention will be described.
The DCDC converter 1 shown in FIG. 1 is configured as, for example, an in-vehicle DCDC converter that is mounted on a vehicle and performs voltage conversion, and forms part of the in-vehicle power supply system 100 shown in FIG. The in-vehicle power supply system 100 includes a first power supply unit 91, a second power supply unit 92, and the DCDC converter 1, and is configured as a system that can supply power to various electrical components mounted on the vehicle.

  The first power supply unit 91 is configured by power storage means such as a lithium ion battery or an electric double layer capacitor, for example, and generates a first predetermined voltage during vehicle operation. For example, during vehicle operation, the high potential side terminal of the first power supply unit 91 is kept at 48V, and the low potential side terminal is kept at the ground potential (0V).

  The wiring part 81 electrically connected to the terminal on the high potential side of the first power supply part 91 is a conductive path electrically connected to the first conductive path 21 described later, and when the operation of the DCDC converter 1 is stopped. The output voltage (for example, 48V) of the 1st power supply part 91 is applied at the time of the pressure | voltage fall operation mentioned later. In addition, an output voltage from the voltage converter 3 is applied during a boosting operation described later.

  For example, the second power supply unit 92 is configured by power storage means such as a lead storage battery and generates a second predetermined voltage lower than the first predetermined voltage generated by the first power supply unit 91. For example, the terminal on the high potential side of the second power supply unit 92 is kept at 12V, and the terminal on the low potential side is kept at the ground potential (0V).

  The wiring part 82 electrically connected to the high potential side terminal of the second power supply part 92 is a conductive path electrically connected to the second conductive path 22 described later, and when the operation of the DCDC converter 1 is stopped. The output voltage (for example, 12 V) of the second power supply unit 92 is applied during the boosting operation described later. In addition, an output voltage from the voltage converter 3 is applied during a step-down operation described later.

  The DCDC converter 1 steps down the direct current voltage applied to the first conductive path 21 and applies a desired output voltage to the second conductive path 22, and boosts the direct current voltage applied to the second conductive path 22. In addition, it is configured as a bidirectional buck-boost converter capable of performing a boosting operation for applying a desired output voltage to the first conductive path 21.

  In the DCDC converter 1, the first conductive path 21 connected to the above-described wiring portion 81, the second conductive path 22 connected to the above-described wiring portion 82, the first conductive path 21 and the second conductive path 22. And a reference conductive path 23 that is maintained at a constant reference potential lower than the potential of. Further, the DCDC converter 1 is provided with a voltage conversion unit 3, a drive unit 5, a current detection unit and a voltage detection unit (not shown), and the like.

  The first conductive path 21 is configured as a high-voltage power supply line to which a relatively high voltage is applied. The first conductive path 21 is electrically connected to a high potential side terminal of the first power supply unit 91 and is configured to be applied with a predetermined DC voltage from the first power supply unit 91. When the voltage conversion unit 3 performs a step-down operation described later, the first conductive path 21 serves as an input side conductive path. When the voltage conversion unit 3 performs a step-up operation described later, the first conductive path 21 outputs It becomes a conductive path on the side.

  The second conductive path 22 is configured as a low-voltage power line to which a relatively low voltage is applied. For example, the second conductive path 22 is electrically connected to a terminal on the high potential side of the second power supply unit 92, and a DC voltage smaller than the output voltage of the first power supply unit 91 is applied from the second power supply unit 92. Make. When the voltage conversion unit 3 performs a step-down operation, which will be described later, the second conductive path 22 becomes an output-side conductive path, and when the voltage conversion unit 3 performs a step-up operation, which will be described later, the second conductive path 22 is input. It becomes a conductive path on the side.

  The reference conductive path 23 is electrically connected to a ground portion (not shown) provided outside the DCDC converter 1. The ground portion is maintained at a ground potential of 0 V, and the reference conductive path 23 functions as a ground path maintained at this ground potential.

  The voltage conversion unit 3 includes a parallel circuit unit 10 and a main inductor La, and further includes a capacitor (not shown) connected between the first conductive path 21 and the ground, or the second conductive path 22 and the ground. And a capacitor (not shown) disposed between the two.

  The parallel circuit unit 10 has a configuration in which two switching circuit units 11 and 12 are connected in parallel. The switching circuit unit 11 and the switching circuit unit 12 have, for example, the same equivalent circuit configuration.

  The switching circuit unit 11 includes a first switching element H1 on the high side that is electrically connected to the first conductive path 21, and a reference conductivity that is maintained at a lower potential than the first switching element H1 and the first conductive path 21. A low-side second switching element L1 connected in series with the first switching element H1 between the path 23 and the connection portion 11A which is a conductive path connecting the first switching element H1 and the second switching element L1. And an auxiliary inductor Lb1 whose one end is electrically connected.

  The first switching element H1 on the high side is configured as, for example, an N-channel MOSFET, the drain is electrically connected to the first conductive path 21, and the source is one end of the auxiliary inductor Lb1 and the second switching element L1. It is configured to be electrically connected to the drain. The second switching element L1 on the low side is configured as, for example, an N-channel MOSFET, the drain is electrically connected to the source of the first switching element H1 and one end of the auxiliary inductor Lb1, and the source is the reference conductive path 23. It is configured to be electrically connected to. The connecting portion 11A is a conductive path that electrically connects the source of the first switching element H1 and the drain of the second switching element L1. The auxiliary inductor Lb1 has one end electrically connected to the source of the first switching element H1 and the drain of the second switching element L1, and the other end electrically connected to one end of the main inductor La and the other end of the auxiliary inductor Lb2. Connected. The auxiliary inductor Lb1 is configured as a coil having an inductance smaller than that of a main inductor La described later, and functions as an auxiliary coil that delays an energization current during a switching operation.

  The switching circuit unit 12 is in series with the first switching element H2 between the first switching element H2 on the high side electrically connected to the first conductive path 21, and between the first switching element H2 and the reference conductive path 23. A low-side second switching element L2 connected to the first switching element H2, and an auxiliary inductor Lb2 whose one end is electrically connected to a connection part 12A that is a conductive path connecting the first switching element H2 and the second switching element L2. Is provided.

  The first switching element H2 on the high side is configured as, for example, an N-channel MOSFET, the drain is electrically connected to the first conductive path 21, and the source is one end of the auxiliary inductor Lb2 and the second switching element L2. It is configured to be electrically connected to the drain. The second switching element L2 on the low side is configured as, for example, an N-channel MOSFET, the drain is electrically connected to the source of the first switching element H2 and one end of the auxiliary inductor Lb2, and the source is the reference conductive path 23. It is configured to be electrically connected to. The connecting portion 12A is a conductive path that electrically connects the source of the first switching element H2 and the drain of the second switching element L2. The auxiliary inductor Lb2 has one end electrically connected to the source of the first switching element H2 and the drain of the second switching element L2, and the other end electrically connected to one end of the main inductor La and the other end of the auxiliary inductor Lb1. Connected. The auxiliary inductor Lb2 is configured as a coil having an inductance smaller than that of a main inductor La described later, and functions as an auxiliary coil that delays an energization current during a switching operation. The inductances of both auxiliary inductors Lb1 and Lb2 are approximately the same, and are approximately 1/10 of the inductance of the main inductor La.

  The main inductor La is configured as a choke coil disposed between the other end portions of the auxiliary inductors Lb1 and Lb2 in the plurality of switching circuit portions 11 and 12 and the second conductive path 22. One end portion of the main inductor La is electrically connected to the other end portions of the auxiliary inductors Lb1 and Lb2 of the switching circuit portions 11 and 12, respectively, and the other end portion of the main inductor La is electrically connected to the second conductive path 22. It is connected. The inductance of the main inductor La is larger than the inductances of both auxiliary inductors Lb1 and Lb2.

  The drive unit 5 includes, for example, a control circuit 5B (a microcomputer or the like) having a CPU, ROM, RAM, AD converter, and the like, and gate signals given to the gates of the first switching elements H1 and H2 and the second switching elements L1 and L2. And a drive circuit 5A for generating

  The DCDC converter 1 includes a first voltage detection circuit (not shown) that detects the voltage of the first conductive path 21. The first voltage detection circuit may be configured to be able to input a value indicating the voltage of the first conductive path 21 to the drive unit 5, and the value (analog voltage value) of the voltage applied to the first conductive path 21 is directly set. It may be a circuit that inputs to the drive unit 5, such as a circuit that divides the voltage applied to the first conductive path 21 by a voltage dividing circuit and inputs the divided analog voltage value to the drive unit 5. Also good. The DCDC converter 1 includes a first current detection circuit that detects a current flowing through the first conductive path 21. The first current detection circuit is configured as a known current detection circuit, and has, for example, a resistor and a differential amplifier that are interposed in the first conductive path 21, and a voltage drop generated in the resistor is amplified by the differential amplifier. Thus, a circuit that inputs the analog voltage value to the driving unit 5 can be used.

  The DCDC converter 1 includes a second voltage detection circuit (not shown) that detects the voltage of the second conductive path 22. The second voltage detection circuit only needs to be configured to be able to input a value indicating the voltage of the second conductive path 22 to the drive unit 5, and the value of the voltage (analog voltage value) applied to the second conductive path 22 is directly set. It may be a circuit that inputs to the drive unit 5, such as a circuit that divides the voltage applied to the second conductive path 22 by a voltage dividing circuit and inputs the divided analog voltage value to the drive unit 5. Also good. Further, the DCDC converter 1 includes a second current detection circuit that detects a current flowing through the second conductive path 22. The second current detection circuit is configured as a known current detection circuit, and has, for example, a resistor and a differential amplifier interposed in the second conductive path 22, and a voltage drop generated in the resistor is amplified by the differential amplifier. Thus, a circuit that inputs the analog voltage value to the driving unit 5 can be used.

Next, the step-down operation performed by the DCDC converter 1 will be described.
The drive unit 5 starts a drive operation in which the voltage applied to the first conductive path 21 is stepped down and applied to the second conductive path 22 when a predetermined step-down operation start condition is satisfied. “When a predetermined step-down operation start condition is satisfied” is not particularly limited. For example, it may be when the ignition switch is switched from an off state to an on state, or when a step-down command is given to the DCDC converter 1 from an external device of the DCDC converter 1.

  When the predetermined step-down operation start condition described above is satisfied, the drive unit operates in the first mode (step-down mode). When the driving unit 5 operates in the first mode (step-down mode), the driving unit 5 outputs a PWM signal to each of the first switching element and the second switching element in the plurality of switching circuit units 11 and 12, and the switching circuit unit. For each of 11 and 12, a switching operation of outputting an ON signal to the second switching element after outputting an ON signal to the first switching element is periodically performed. Specifically, a PWM signal is output to the gate of the first switching element H1 as in the gate signal (H1) shown in FIG. 2, and the gate of the second switching element L1 is output as in the gate signal (L1). On the other hand, a PWM signal for performing synchronous rectification is complementarily output with the PWM signal for the first switching element H1. Further, a PWM signal is output to the gate of the first switching element H2 as in the gate signal (H2) shown in FIG. 2, and is synchronized with the gate of the second switching element L2 as in the gate signal (L2). A PWM signal for rectification is complementarily output with the PWM signal for the first switching element H2. The duty of the PWM signal output to the gates of the first switching elements H1 and H2 by the drive unit 5 is the same. Specifically, the voltage (output voltage) applied to the second conductive path 22 is set as a desired target voltage. Thus, the duty of the PWM signal is adjusted by feedback control. In this configuration, the control circuit 5B performs the feedback calculation for determining the duty at short time intervals. Each time the duty is updated, the drive circuit 5A outputs a PWM signal corresponding to the updated duty to the gates of the first switching elements H1 and H2, and with respect to the gates of the second switching elements L1 and L2. Outputs a PWM signal for performing synchronous rectification.

  When there are N switching circuit units and the period of the PWM signal applied to the first switching element and the second switching element is T, the driving unit 5 performs the following operation on each first switching element of the plurality of switching circuit units. PWM signals are output at different phases by shifting the time of T / N. For example, when there are two switching circuit units 11 and 12 as shown in FIG. 1, that is, when N = 2, the driving unit 5 operates in the first mode (step-down mode) as shown in FIG. As described above, the PWM signals are output at different phases by shifting the time by T / 2 with respect to the first switching elements of the two switching circuit units 11 and 12. Specifically, an on signal to the second switching element is output to the respective switching circuit units 11 and 12 after the on signal to the first switching element is finished, and after the on signal to the second switching element is finished. Then, an ON signal is output to the first switching element of the switching circuit unit that operates next.

  For example, as shown in FIG. 2, an on signal to the second switching element L1 is output to the switching circuit unit 11 with a start timing T2 that arrives after the end timing T1 of the on signal to the first switching element H1 as a start time. As described above, a PWM signal is output to each switching element while setting a dead time between the end timing T1 and the start timing T2. Then, an on signal is output to the first switching element H2 of the switching circuit unit 12 that operates next with a start timing T4 after the end timing T3 of the on signal to the second switching element L1 as a start time point. PWM is output to the first switching element H2 while setting a dead time between the end timing T3 and the start timing T4. Similarly, the switching circuit unit 12 ends so as to output the ON signal to the second switching element L2 with the start timing T6 coming after the end timing T5 of the ON signal to the first switching element H2 as the starting time. A PWM signal is output to each switching element while setting a dead time between timing T5 and start timing T6. Then, an on signal is output to the first switching element H1 of the switching circuit unit 11 that operates next with a start timing T8 after the end timing T7 of the on signal to the second switching element L2 as a start time point. PWM is output to the first switching element H1 while setting a dead time between the end timing T7 and the start timing T8.

  FIG. 3 shows changes over time in the drain-source voltage of the first switching element, the energization current flowing through the first switching element, and the switching loss (switching loss) generated in the first switching element when the first switching element is turned on. It is a chart shown in. The relationship as shown in FIG. 3 occurs in both the first switching elements H1 and H2.

  When the drive unit 5 operates in the first mode (step-down mode), the first switching element H1 is turned on in response to the gate signal for the first switching element H1 being switched to the on signal as shown in FIG. Current supply to the main inductor La (choke coil) is started through Lb1 (auxiliary coil). At the time of this ON operation, as shown in FIG. 3, the current flowing through the first switching element H1 is delayed due to the presence of the auxiliary inductor Lb1, and the rapid increase is suppressed. For example, the drain-source voltage of the first switching element H1 is 0V. The current rises in the state of being close. Therefore, the switching loss at the time when the first switching element H1 is switched to the on state is reliably suppressed. Such an effect similarly occurs when the first switching element H2 is turned on.

  Note that, when the first switching element H1 is turned on, an inrush current due to parasitic capacitance or the like actually occurs, so that a slight switching loss occurs. This switching loss is a general synchronous rectification method in which the auxiliary inductor Lb1 does not exist. Compared with switching at, it is sufficiently small. When the first switching element H1 is turned off, a loss similar to that of general hard switching occurs.

  In the DCDC converter 1 in FIG. 1, when the gate signal (L1) for the second switching element L1 for synchronous rectification is switched from the on signal to the off signal at time T3 as shown in FIG. 2, the second switching is performed accordingly. The element L1 is turned off, and current circulation through the body diode of the second switching element L1 starts. However, since the next on-operation of the first switching element H2 starts at time T4 after time T3, it is possible to suppress or stop the return of current through the body diode of the second switching element L1. Such an effect similarly occurs when the first switching element H1 is turned on after the second switching element L2 is turned off.

Next, the boosting operation performed by the DCDC converter 1 will be described.
The drive unit 5 starts a driving operation in which the voltage applied to the second conductive path is boosted and applied to the first conductive path when a predetermined boosting operation start condition is satisfied. “When a predetermined step-up operation start condition is satisfied” is not particularly limited. For example, it may be when the ignition switch is switched from the off state to the on state, or when a boost command is given to the DCDC converter 1 from an external device of the DCDC converter 1.

  When the predetermined boost operation start condition is satisfied, the drive unit 5 operates in the second mode (boost mode). When the drive unit 5 operates in the second mode (boost mode), the drive unit 5 outputs a PWM signal to each of the first switching element and the second switching element in the plurality of switching circuit units 11 and 12, and the switching circuit unit. For each of 11 and 12, a switching operation of outputting an ON signal to the first switching element after outputting an ON signal to the second switching element is periodically performed. Specifically, a PWM signal is output to the gate of the second switching element L1 as in the gate signal (L1) shown in FIG. 4, and the gate of the first switching element H1 is output as in the gate signal (H1). On the other hand, a PWM signal for performing synchronous rectification is complementarily output with the PWM signal for the second switching element L1. Further, a PWM signal is output to the gate of the second switching element L2 as in the gate signal (L2) shown in FIG. 4, and is synchronized with the gate of the first switching element H2 as in the gate signal (H2). The PWM signal for rectification is complementarily output with the PWM signal for the second switching element L2. The duty of the PWM signal output to the gates of the second switching elements L1 and L2 by the drive unit 5 is the same. Specifically, the voltage (output voltage) applied to the first conductive path 21 is set as a desired target voltage. Thus, the duty of the PWM signal is adjusted by feedback control. In this configuration, the control circuit 5B performs the feedback calculation for determining the duty at short time intervals. Each time the duty is updated, the drive circuit 5A outputs a PWM signal corresponding to the updated duty to the gates of the second switching elements L1 and L2, and with respect to the gates of the first switching elements H1 and H2. Outputs a PWM signal for performing synchronous rectification.

  When there are N switching circuit units and the period of the PWM signal applied to the first switching element and the second switching element is T, the driving unit 5 performs the following operation on each first switching element of the plurality of switching circuit units. PWM signals are output at different phases by shifting the time of T / N. For example, when there are two switching circuit units 11 and 12 as shown in FIG. 1, that is, when N = 2, the driving unit 5 operates in the second mode (boost mode) as shown in FIG. As described above, the PWM signals are output at different phases by shifting the time by T / 2 with respect to the second switching elements of the two switching circuit units 11 and 12. Specifically, an ON signal to the first switching element is output to each of the switching circuit units 11 and 12 after the ON signal to the second switching element ends, and after the ON signal to the first switching element ends. Then, an ON signal is output to the second switching element of the switching circuit unit that operates next.

  For example, as shown in FIG. 4, an on signal to the first switching element H1 is output to the switching circuit unit 11 with the start timing T12 coming after the end timing T11 of the on signal to the second switching element L1 as the start time. As described above, a PWM signal is output to each switching element while setting a dead time between the end timing T11 and the start timing T12. Then, an on signal is output to the second switching element L2 of the switching circuit unit 12 that operates next, with the start timing T14 after the end timing T13 of the on signal to the first switching element H1 as the start time. PWM is output to the second switching element L2 while setting a dead time between the end timing T13 and the start timing T14. Similarly, the switching circuit unit 12 ends so as to output the ON signal to the first switching element H2 with the start timing T16 coming after the end timing T15 of the ON signal to the second switching element L2 as the start time. A PWM signal is output to each switching element while setting a dead time between timing T15 and start timing T16. Then, an on signal is output to the second switching element L1 of the switching circuit unit 11 that operates next, with the start timing T18 after the end timing T17 of the on signal to the first switching element H2 as a start time. PWM is output to the second switching element L1 while setting a dead time between the end timing T17 and the start timing T18.

  When the driving unit 5 operates in the second mode (boost mode) as described above, the second switching is performed in response to the gate signal (L1) for the second switching element L1 being switched from the off signal to the on signal as illustrated in FIG. The element L1 is turned on, and a current flows through the main inductor La (choke coil) and the auxiliary inductor Lb1 (auxiliary coil). At the time of this on operation, the current flowing through the second switching element L1 is delayed due to the presence of the auxiliary inductor Lb1, and the rapid increase is suppressed. For example, the drain-source voltage of the second switching element L1 is close to 0V. The current will rise. Therefore, the switching loss when the second switching element L1 is switched to the on state is reliably suppressed. Such an effect similarly occurs when the second switching element L2 is turned on.

  Further, in the DCDC converter 1 of FIG. 1, when the step-up operation is performed, if the gate signal (H1) for the first switching element H1 for synchronous rectification is switched from the on signal to the off signal at time T13 as shown in FIG. Accordingly, the first switching element H1 is turned off, and current circulation through the body diode of the first switching element H1 starts. However, after the time T13, the next on-operation of the second switching element L2 starts at the time T14, so that the current circulation through the body diode of the first switching element H1 can be suppressed or stopped. Such an effect also occurs when the second switching element L1 is turned on after the first switching element H2 is turned off.

Next, the effect of the DCDC converter 1 of this structure is illustrated.
The DCDC converter 1 includes a parallel circuit unit 10 in which a plurality of switching circuit units 11 and 12 are connected in parallel. In the switching circuit unit 11, the auxiliary inductor Lb1 is disposed in a path from the connection unit 11A between the first switching element H1 on the high side and the second switching element L1 on the low side to the main inductor La. In the switching circuit unit 12, the auxiliary inductor Lb2 is disposed between the path from the connection unit 12A between the high-side first switching element H2 and the low-side second switching element L2 to the main inductor La.

  In such a configuration, when the switching operation of outputting the ON signal to the second switching element after the ON signal is output to the first switching element for each of the switching circuit units 11 and 12, the first conductive is performed. A step-down operation can be performed in which the voltage applied to the path 21 is stepped down and applied to the second conductive path 22, and in this step-down operation, the first switching element of each switching circuit unit is switched from the off state to the on state. The energization current flowing through the first switching element can be delayed. Therefore, the current immediately after the first switching element is turned on can be reliably reduced, and the switching loss can be effectively suppressed during the step-down operation.

  Further, when the switching operation of outputting the ON signal to the first switching element after the ON signal is output to the second switching element for each of the switching circuit units 11 and 12 is applied to the second conductive path 22. The boosted voltage can be boosted and applied to the first conductive path 21. In this boosting operation, the energization current that flows through the second switching element when the second switching element is switched from the off state to the on state. Can be delayed. Therefore, the current immediately after the second switching element is turned on can be reliably reduced, and the switching loss can be effectively suppressed even during the boosting operation.

  When performing the step-down operation, the drive unit 5 outputs a PWM signal with a phase shifted with respect to each of the first switching elements of the plurality of switching circuit units 11 and 12, and for each of the switching circuit units 11 and 12, An on signal to the second switching element is output after the end of the on signal to the first switching element, and the first switching element of the switching circuit unit that operates next after the on signal to the second switching element ends. Output an ON signal. For example, the PWM signal to each switching element is output to the switching circuit unit 11 so that the ON signal to the second switching element L1 is output after the end of the ON signal to the first switching element H1, and the second switching element After the end of the ON signal to L1, PWM is output to the first switching element H2 so that the ON signal is output to the first switching element H2 of the switching circuit unit 12 that operates next. Similarly, a PWM signal to each switching element is output to the switching circuit unit 12 so that an ON signal is output to the second switching element L2 after the ON signal to the first switching element H2 is completed, and the second switching element After the end of the ON signal to L2, the PWM signal for the first switching element H1 is output so as to output the ON signal to the first switching element H1 of the switching circuit unit 11 that operates next.

  The DCDC converter 1 configured in this manner operates next when body diode energization starts in the second switching element when the synchronous rectification by the second switching element is finished in each of the switching circuit units 11 and 12. By turning on the first switching element of the switching circuit section to be turned on, reflux in the second switching element can be suppressed. As a result, the surge voltage can be suppressed, and as a result, the breakdown voltage of the switching element can be reduced. For example, when energization is started in the body diode of the second switching element L1 when the synchronous rectification by the second switching element L1 is completed in the switching circuit unit 11, the first switching element of the switching circuit unit 12 that operates next By turning H2 on, reflux in the second switching element L1 can be suppressed. Similarly, when energization is started in the body diode of the second switching element L2 when the synchronous rectification by the second switching element L2 is completed in the switching circuit unit 12, the first switching of the switching circuit unit 11 that operates next is performed. By turning on the element H1, the reflux in the second switching element L2 can be suppressed.

  The same applies to the step-up operation, and when performing the step-up operation, the drive unit 5 outputs a PWM signal with a phase shifted with respect to the second switching elements L1 and L2 of the plurality of switching circuit units 11 and 12, An ON signal to the first switching element is output after the end of the ON signal to the second switching element to each of the switching circuit units 11 and 12, and the next operation is performed after the ON signal to the first switching element is ended. An ON signal is output to the second switching element of the switching circuit unit.

  The DCDC converter 1 having such a configuration is the switching that operates next when body diode energization starts in the first switching element when the synchronous rectification by the first switching element is finished in each of the switching circuit units 11 and 12. By turning on the second switching element of the circuit unit, reflux in the first switching element can be suppressed.

  Further, in this configuration, the frequency of the energizing current flowing through the main inductor La is N times the driving frequency f (1 / T) (N = 2 in the example of FIG. 1). Can be planned.

  Further, in the DCDC converter 1, the inductances of the plurality of auxiliary inductors Lb1 and Lb2 are all smaller than the inductance of the main inductor La, and a smaller component can be used compared with the main inductor La. Yes.

  According to this configuration, it is possible to realize the DCDC converter 1 that can reduce the switching loss by delaying the energization current immediately after the turn-on while suppressing the increase in size of the auxiliary inductors Lb1 and Lb2.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention. In addition, the embodiments described above and the embodiments described later can be combined within a consistent range.

  The DCDC converter 1 according to the first embodiment may be configured to perform only a step-down operation. That is, the driving unit 5 may perform the first mode (step-down mode) operation and may not perform the second mode (step-up mode) operation.

  The DCDC converter 1 according to the first embodiment may be configured to perform only the boosting operation. That is, the drive unit 5 may perform the second mode (boost mode) operation and may not perform the first mode (step-down mode) operation.

  In the first embodiment, the parallel circuit unit 10 is configured with a configuration in which two switching circuit units 11 and 12 are connected in parallel. However, N units (N is the same as the switching circuit units 11 and 12). The parallel circuit unit 10 may be configured such that three or more switching circuit units are connected in parallel. In this case, when the driving unit operates in the first mode (step-down mode), T / N (T is the period of the PWM signal) is shifted in time by different phases with respect to the first switching element of each switching circuit unit. The PWM signal may be output, and the second switching element of each switching circuit unit may perform synchronous rectification so that the OFF operation is completed before the ON operation of the first switching element of the switching circuit unit that operates next. When the driving unit operates in the second mode (boost mode), PWM is performed at different phases by shifting the time by T / N (T is the period of the PWM signal) with respect to the second switching element of each switching circuit unit. A signal is output, and the first switching element of each switching circuit unit may perform synchronous rectification so that the OFF operation is completed before the second switching element of the switching circuit unit that operates next is turned ON.

  In the first embodiment, the DCDC converter 1 having only one voltage conversion unit 3 is illustrated, but a plurality of voltage conversion units 3 connected in parallel between the first conductive path 21 and the second conductive path 22 are illustrated. A phase DCDC converter may be used.

DESCRIPTION OF SYMBOLS 1 ... DCDC converter 5 ... Drive part 10 ... Parallel circuit part 11, 12 ... Switching circuit part 11A, 12A ... Connection part 21 ... 1st conductive path 22 ... 2nd conductive path 23 ... Reference | standard conductive path H1, H2 ... 1st switching Element L1, L2 ... 2nd switching element La ... Main inductor Lb1, Lb2 ... Auxiliary inductor

Claims (5)

The first switching element between the first switching element electrically connected to the first conduction path and the reference conduction path maintained at a lower potential than the first switching element and the first conduction path. A low-side second switching element connected in series with the switching element; and an auxiliary inductor having one end electrically connected to a connection portion connecting the first switching element and the second switching element. A parallel circuit unit in which a plurality of switching circuit units are connected in parallel;
A main inductor disposed between the other end of each of the auxiliary inductors and a second conductive path in the plurality of switching circuit units;
A PWM signal is output to each of the first switching element and the second switching element in the plurality of switching circuit units, and an ON signal is output to the first switching element for each of the switching circuit units. A drive unit that periodically performs a switching operation to output an ON signal to the second switching element later;
DCDC converter having   The drive unit outputs a PWM signal with a phase shifted with respect to each of the first switching elements of each of the plurality of switching circuit units, and outputs an ON signal to the first switching element to each of the switching circuit units. After the end, an ON signal is output to the second switching element, and after the ON signal to the second switching element ends, an ON signal is output to the first switching element of the switching circuit unit that operates next. The DCDC converter according to claim 1. The first switching element between the first switching element electrically connected to the first conduction path and the reference conduction path maintained at a lower potential than the first switching element and the first conduction path. A low-side second switching element connected in series with the switching element; and an auxiliary inductor having one end electrically connected to a connection portion connecting the first switching element and the second switching element. A parallel circuit unit in which a plurality of switching circuit units are connected in parallel;
A main inductor disposed between the other end of each of the auxiliary inductors and a second conductive path in the plurality of switching circuit units;
A PWM signal is output to each of the first switching element and the second switching element in the plurality of switching circuit units, and an ON signal is output to the second switching element for each of the switching circuit units. A drive unit that periodically performs a switching operation to output an ON signal to the first switching element later;
DCDC converter having   The driving unit outputs a PWM signal with a phase shifted with respect to the second switching element of each of the plurality of switching circuit units, and an ON signal to the second switching element is output to each of the switching circuit units. An ON signal is output to the first switching element after the completion, and an ON signal is output to the second switching element of the switching circuit unit that operates next after the ON signal to the first switching element is completed. The DCDC converter according to claim 3.   5. The DCDC converter according to claim 1, wherein inductances of the plurality of auxiliary inductors are all smaller than inductances of the main inductor. 6.

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