CN107124104B

CN107124104B - DC/DC converter

Info

Publication number: CN107124104B
Application number: CN201610104203.4A
Authority: CN
Inventors: 代佳乐; 曹宇; 王可志
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2016-02-25
Filing date: 2016-02-25
Publication date: 2020-04-21
Anticipated expiration: 2036-02-25
Also published as: CN107124104A

Abstract

The present invention provides a DCDC conversion device, including: a voltage conversion circuit that converts a direct-current power supply voltage into a direct-current output, including a resonance circuit and a plurality of power switching elements that apply the power supply voltage to the resonance circuit in different directions to generate the direct-current output; a switching control drive unit that outputs a control signal to the plurality of power switching elements and controls the plurality of power switching elements to be turned on or off to generate a direct current output; and a conversion part connected with the switch control driving part and connected with a power voltage through a voltage conversion circuit, wherein the conversion part supplies power to the switch control driving part by using the power voltage in an initial starting stage, and supplies power to the switch control driving part by using the direct current output in a normal working stage. The DCDC conversion device of the invention can improve the overall power efficiency of the DCDC converter, reduce the manufacturing cost and simplify the circuit structure.

Description

DC/DC converter

Technical Field

The present invention relates to a DC/DC converter, and more particularly, to a DC/DC converter capable of supplying an operating voltage to a switch drive control unit using a DC power supply voltage at an initial start-up stage.

Background

In the prior art, a switching power supply is a power supply which utilizes modern power electronics technology to control the time ratio of the switch on and off and maintain a stable output voltage, wherein a DC/DC conversion device, i.e. a DC-DC conversion circuit, is a voltage converter which effectively converts a DC input voltage into a fixed DC output voltage. Generally, DC/DC conversion devices are classified into three categories: the boost type DC/DC converter, the buck type DC/DC converter and the boost type DC/DC converter can adopt three types of control according to requirements. Specifically, the high-frequency switching operation is performed by a controllable switch (such as a MOSFET) using the energy storage characteristics of a capacitor and an inductor, and the input electric energy is stored in the capacitor or the inductor and is released to the load to supply energy when the switch is turned off. The power or voltage it outputs is related to the duty cycle, i.e. the ratio of the switch on time to the period of the whole switch.

However, with the rapid development of power electronics technology, switching power supplies are required to have higher frequencies, higher conversion efficiency, higher power density, smaller size, lower noise, and the like.

Fig. 5 shows a conventional DC/DC conversion apparatus using an LLC full-bridge conversion circuit. As shown in fig. 3, the DC/DC conversion device has an LC resonance circuit composed of an inductor Lr and a capacitor Cr, and a transformer composed of inductors Tr1 and Tr 2. The DC/DC converter further includes 4 switching elements Q1 to Q4 constituting an LLC full-bridge converter circuit, and by controlling the on and off of the switching elements Q1 to Q4, the energy transmitted from the primary inductor Tr1 to the secondary inductor Tr2 of the transformer can be controlled.

In the DC/DC conversion device shown in fig. 5, the on and off of the switching elements Q1 to Q4 are controlled by a switch driving unit (connections between the switch driving unit and the gates of the switching elements Q2 to Q4 are omitted in the figure). The switch driving unit switches on/off at proper time by controlling the switching elements Q1-Q4 to change the direction of the power supply voltage loaded on the LC resonant tank, thereby realizing dc/dc voltage conversion. As an example, here, a case where all of the switching elements Q1 to Q4 use N-channel MOS transistors is shown. In this case, the switch driving unit turns on the switch by giving a high level signal to the G pole of the MOS transistor.

As shown in fig. 6, a similar LLC converter is proposed in patent document 1, in which a high-side driver Z1 controls switching elements Q1 and Q2 to be turned on and off, thereby converting a direct-current voltage E into a desired direct-current output Vout.

However, as shown in fig. 5 and 6, the DC/DC converter generally uses an additional external power source to power the switch driving unit. For example, the switch drive unit of FIG. 5 is powered by an additional external power supply, and the high-side driver Z1 of FIG. 6 is powered by an additional power supply Vcc 1.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2015-216720

Disclosure of Invention

Problems to be solved by the invention

However, in the above case, the efficiency of the external power supply is generally not as high as that of the DC/DC converter itself, and the use of the external power supply certainly causes a part of the loss. On the other hand, the provision of an external power supply also causes problems such as increased cost and complicated circuit structure.

Means for solving the problems

The present invention has been made to solve the above problems, and an object of the present invention is to provide a DC/DC converter device which can improve the power efficiency of the entire DC/DC converter, reduce the manufacturing cost, and simplify the circuit configuration by avoiding the use of an external power source.

A DC/DC converter according to a first aspect of the present invention includes: a voltage conversion circuit that converts a direct-current power supply voltage into a direct-current output, including a resonance circuit and a plurality of power switching elements that cause the power supply voltage to be applied to the resonance circuit in different directions to generate the direct-current output; and a switching control drive unit that outputs a control signal to the plurality of power switching elements and controls on/off of the plurality of power switching elements to generate the direct current output, the DC/DC converter further comprising: and a conversion unit connected to the switching control drive unit and connected to the power supply voltage via the voltage conversion circuit, the conversion unit supplying power to the switching control drive unit by the power supply voltage at an initial start-up stage of the DC/DC conversion device, and supplying power to the switching control drive unit by the DC output at a normal operation stage of the DC/DC conversion device.

In the DC/DC converter according to the second aspect of the present invention, the resonant circuit includes a resonant inductor, the converter includes a power supply inductor, and the converter supplies power to the switching control driver by the power supply voltage through electromagnetic coupling between the resonant inductor and the power supply inductor.

In the DC/DC converter according to the third aspect of the present invention, the voltage conversion circuit further includes: a transformer connected in series with the resonant circuit; and a switching circuit connected between a connection point of the resonance circuit and a transformer (Tr) and a ground, the converting section including: an input side circuit that controls on or off of at least one of the plurality of power switching elements and the switching circuit; an output side circuit including a power supply inductance electromagnetically coupled with a resonance inductance in the resonance circuit, thereby supplying power to the switch control drive section with the power supply voltage.

In the DC/DC converter according to the fourth aspect of the present invention, the input-side circuit includes an oscillator that receives power supply from the power supply voltage, and in the initial start-up phase, the oscillator repeatedly turns on and off the at least one power switching element at a predetermined frequency and turns on the switching circuit, and in the normal operation phase, the oscillator does not control the at least one power switching element and turns off the switching circuit.

In the DC/DC converter according to the fifth aspect of the present invention, the oscillator may further turn on another power switching element other than the at least one power switching element among the plurality of power switching elements in the initial start-up stage.

In the DC/DC converter according to the sixth aspect of the present invention, a power switch is provided between the oscillator and the power supply voltage, and the power switch is turned on in the initial startup phase and turned off in the normal operation phase.

In the DC/DC converter according to the seventh aspect of the present invention, the output side circuit further includes a capacitor and a diode, a series circuit of the feed inductance and the diode is connected in parallel with the capacitor between the DC output and the ground, a cathode side of the diode is connected to the DC output side, and an anode side of the diode is connected to the ground.

In the DC/DC converter according to the eighth aspect of the present invention, the output side circuit further includes a voltage detection device that detects a voltage level of the DC output, and the normal operation stage is entered from the initial start stage when the voltage level detected by the voltage detection device exceeds a predetermined threshold.

In the DC/DC converter according to a ninth aspect of the present invention, the switching circuit includes a series circuit of a switching element and a diode, wherein a source of the switching element is connected to a connection point between the resonance circuit and the transformer, an anode of the diode is connected to a drain of the switching element, and a cathode of the diode is connected to ground.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, since the output of the DC/DC converter itself is directly used to supply power to the switch driving unit in the normal operation stage, the power efficiency of the DC/DC converter as a whole can be improved, the manufacturing cost can be reduced, and the circuit configuration can be simplified.

Drawings

Fig. 1 is a schematic block diagram showing the overall configuration of a DC/DC converter according to an embodiment of the present invention.

Fig. 2 is a schematic block diagram showing an overall configuration of a DC/DC converter according to another embodiment of the present invention.

Fig. 3 is a diagram showing a specific circuit configuration example of the DC/DC converter of fig. 2.

Fig. 4 is a diagram showing another specific circuit configuration example of the DC/DC converter of fig. 2.

Fig. 5 is a schematic diagram of a prior art DC/DC conversion device.

Fig. 6 is a schematic diagram of a DC/DC conversion device of the related art.

Detailed Description

A DC/DC converter according to an embodiment of the present invention will be described with reference to fig. 1.

Fig. 1 is a schematic block diagram showing an overall configuration of a DC/DC converter according to an embodiment of the present invention. As shown in fig. 1, according to one embodiment of the present invention, a DC/DC conversion device has a voltage conversion circuit 1, and the voltage conversion circuit 1 converts a direct-current power supply voltage into a direct-current output Vout of a different voltage. The voltage conversion circuit 1 may be generally configured by a voltage conversion circuit including a resonance circuit, such as an LLC full-bridge conversion circuit or an LLC half-bridge conversion circuit. The voltage conversion circuit 1 typically further comprises a plurality of power switching elements for applying a supply voltage Vdd to the resonant circuit in different directions to generate a dc output Vout. As to the specific circuit structure of the voltage conversion circuit 1, it will be described in further detail later.

The DC/DC conversion device according to the present invention further includes a switching control drive section 2. The switching control drive unit 2 outputs control signals to the plurality of power switching elements in the voltage conversion circuit 1, and controls on and off of the power switching elements to generate the dc output Vout.

As an important component of the present invention different from the prior art, the present invention further provides a switching part 3, and the switching part 3 is connected with the switch control driving part 2 to supply power to the switch control driving part. Meanwhile, the converter 3 is also connected to the power supply voltage Vdd via the voltage conversion circuit 1.

In an initial start-up stage of the DC/DC conversion device, the conversion section 3 supplies power Vin to the switch control drive section 2 by using the power supply voltage Vdd. After the DC/DC converter finishes the initial start-up stage, when the DC/DC converter enters the normal operation stage, the DC output Vout of the DC/DC converter is used to supply the power Vin to the switching control driving unit 2.

In the above, the initial start-up phase of the DC/DC conversion device refers to a phase just before the power supply voltage Vdd is applied to the voltage conversion circuit 1 and the DC output Vout thereof has not reached a level that satisfies the operation requirement of the switching control drive section 2. At this stage, since the dc output Vout cannot normally operate the switching control drive unit 2, the switching control drive unit 2 needs to be designed so that the converter 3 can supply power to the switching control drive unit 2 by the power supply voltage Vdd.

Once the dc output Vout reaches a level that satisfies the operation requirement of the switching control driving unit 2, i.e., enters a normal operation stage, the converting unit 3 switches the power supply of the switching control driving unit 2 from the power supply voltage Vdd to the dc output Vout. Therefore, compared with the prior art (fig. 5-6), the switch control driving part 2 does not need an additional external power supply. In the normal working phase, the power supply source of the switch control driving part 2 is the DC output Vout of the DC/DC conversion device itself, and the efficiency thereof is much higher than that of the external power supply, so that the design of the present embodiment has less loss and higher overall efficiency.

In the initial start-up stage, the converter 3 may directly supply the power supply voltage Vdd to the switch control driver 2 as shown in fig. 1, but it is preferable to adopt the scheme shown in fig. 2 because voltage matching, electrical isolation, or the like needs to be taken into consideration. That is, the power supply voltage Vdd is indirectly supplied to the switching control drive unit 2 via the components in the voltage conversion circuit 1. Thus, the overall stability of the DC/DC converter of the present embodiment is higher due to the above-mentioned electrical isolation.

Next, a specific circuit configuration example of the DC/DC converter shown in fig. 2 will be described with reference to fig. 3. It will be readily understood by those skilled in the art that the specific circuit configuration example shown here is not limitative, and other circuit configurations are also applicable to the present invention as long as power can be supplied to the switch control driving unit 2 by the power supply voltage Vdd.

As shown in fig. 3, the LLC full-bridge converter circuit corresponding to the voltage converter circuit 1 in fig. 1 includes a series resonant circuit including a resonant inductor Lr and a resonant capacitor Cr, and a plurality of switching elements Q1 to Q4. The series resonant circuit is electrically connected to a power supply voltage Vdd via a plurality of switching elements Q1 to Q4. By switching the plurality of switching elements Q1 to Q4 on and off, the power supply voltage Vdd and the series resonant circuit can be electrically connected or disconnected, and the direction of the power supply voltage applied to the series resonant circuit can be switched between different directions. A primary inductor Tr1 of the transformer is also connected in series to the series resonant circuit formed by the inductor Lr and the capacitor Cr. The transformer secondary inductor Tr2 constitutes an output unit of the LLC full-bridge converter circuit together with the rectifier diodes P1 and P2, the output capacitor Co, and the like. The output part is connected to the load R_LAnd outputting the direct current output Vout. The switch control drive unit 2 outputs gate drive signals S1 to S4 to the gates of the switching elements Q1 to Q4, respectively, to control on/off of the switching elements Q1 to Q4.

The above specific circuit configuration of the LLC full-bridge conversion circuit is not different from the prior art (fig. 5) in the present invention, and is not described herein again.

As an important point of the present invention, the present invention further provides a switching circuit 15 in the LLC full-bridge conversion circuit. The switching circuit 15 includes a series circuit of a switching element Q5 and a diode D5, in which a source of the switching element Q5 is connected to a connection point of a resonant circuit constituted by a resonant inductor Lr and a resonant capacitor Cr and a transformer (Tr), and an anode of the diode D5 is connected to a drain of the switching element Q5, and a cathode is connected to ground. That is, the diode D5 has the opposite polarity to the body diode of the switching element Q5. Thereby, a reverse current can be prevented from flowing through the switching element Q5. Of course, the present invention is not limited to this, and the diode D5 may be replaced by a switching element having a channel type opposite to that of the switching element Q5, for example, if the switching element Q5 in this embodiment is an N-channel MOSFET, the diode D5 may be replaced by a P-channel MOSFET. Other circuit configurations are also applicable to the switching circuit 15 of the present invention as long as they can function as an on/off circuit.

In the present invention, a converter 3 including an input side circuit 31 and an output side circuit 32 is provided to supply power to the switching control drive unit 2. The input side circuit 31 is used to control the on/off of the switching element Q1 and the switching circuit 15 in the LLC full-bridge conversion circuit. The output side circuit 32 includes a supply inductance Lraux electromagnetically coupled to a resonance inductance Lr in the resonance circuit, thereby supplying the power Vin to the switch control drive section 2 with the power supply voltage Vdd at the initial start-up stage. The output side circuit 32 is also connected to a dc output Vout of the LLC full-bridge converter circuit via a diode D7, and thereby supplies power Vin to the switch control drive unit 2 via a Pol circuit by using the dc output Vout. The Pol circuit is a voltage conversion device or circuit for converting Vout into a voltage required for the switching control drive section 2. That is, in the initial startup phase, the input-side circuit 31 controls the operations of the switching element Q1 and the switching element Q5, so that the current in the inductor Lr changes, and the current is transmitted to the power supply inductor Lraux by electromagnetic induction, so that the power source Vin can indirectly and temporarily supply power to the switching control drive unit 2.

In addition, if the power supply voltage Vdd is directly used as the operating voltage source of the switching elements Q1-4, the method needs to change the states of the four switching elements Q1-4 at the same time, and due to various reasons such as electrical environment, certain noise is generated, which affects the control of the switching elements Q1-4.

In this embodiment, the switching circuit 15 is provided to supply power to the current transfer switch control driving unit 2 by using the inductor Lr, and the input side circuit 31 only needs to constantly switch the state of the switching element Q1, and at this time, the states of the switching elements Q5 and Q2 to Q4 are not changed at the initial start-up stage, and are less affected by noise.

Of course, the input-side circuit 31 may control the switching elements Q1, Q5 in various ways, for example, by controlling the switching element Q5 to be turned on and off at a certain frequency while controlling the switching element Q1 to be always on, or by controlling the switching element Q1 to be turned off after being turned on once while controlling the switching element Q5 to be always on, or by controlling the switching elements Q1, Q5 to be turned on and off at a certain frequency. Any method may be used as long as the current on the inductor Lr can be changed.

More specifically, the input-side circuit 31 includes a resonator 10, and the resonator 10 is connected to a power supply voltage Vdd to obtain an operating voltage obtained by dividing the power supply voltage Vdd by resistors R1 and R2. Specifically, the oscillator 10 outputs gate drive signals G1 and G5 for controlling the gates of the switching elements Q1 and Q5. The input-side circuit 31 further includes a zener diode D6 and a storage capacitor C1 connected in parallel to the resistor R2 to stabilize the power supply of the oscillator 10. Here, in order to reduce the cost, the efficiency of the power supply itself to the oscillator 10 and the switching elements Q1 and Q5 due to the elements such as the resistors R1 and R2 in the input side circuit 31 acting in cooperation with the power supply voltage Vdd is general, but since the power supply is present only in the initial start-up stage, the influence on the efficiency of the entire DC/DC conversion device is small.

In addition, the oscillator 10 can provide a level signal output from a chip-type oscillator (e.g., 555 oscillator), a free-running resonant circuit (e.g., LC tank circuit, etc.), and is low in cost, and as described above, since it is only necessary to repeatedly change the state of one switching element (e.g., the switching element Q1) by the level signal, the noise immunity of the DC/DC conversion device can be improved. The output side circuit 32 includes a capacitor C2 and a diode D8 in addition to the power supply inductance Lraux, and a series circuit of the power supply inductance Lraux and the diode D8 is connected between the dc output Vout and the ground in parallel with the capacitor C2. The diode D8 has a cathode connected to the dc output Vout side and an anode connected to the ground via the supply inductor Lraux. Since the switching control drive unit 2 is supplied with power from the dc output Vout during the normal operation, the diode D8 is provided as described above, and the current of the dc output Vout can be prevented from flowing back to the resonant inductor Lr via the supply inductor Lraux.

The operation of the DC/DC converter of the present invention will be explained.

Immediately after the DC/DC converter is started (initial start-up stage), the power supply voltage Vdd is applied to the voltage conversion circuit 1 (LLC full-bridge conversion circuit in fig. 3), and at this time, since the switching elements Q1 to Q4 are not yet operated, the DC output Vout of the output unit is 0, and power cannot be supplied to the switch control drive unit 2.

At this time, the power supply voltage Vdd is divided by the resistors R1 and R2, and then supplies power to the oscillator 10. The oscillator 10 then outputs a gate driving signal G1 to the gate of the switching device Q1 at a set frequency, and repeatedly turns on/off the switching device Q1 at the set frequency. At the same time, the oscillator 10 outputs a gate drive signal G5 to the gate of the switching element Q5, and turns on the switching element Q5. On the other hand, the switching elements Q2 to Q4 are in an off state because the switching control drive unit 2 is not supplied with power and the gate drive signals S2 to S4 cannot be supplied to their gates.

Thus, a loop is formed from the power supply voltage to the ground via the switching element Q1 and the switching element Q5, and the current fluctuates in the loop according to the set frequency.

The current flowing through the resonant inductor Lr changes and is transmitted to the power supply inductor Lraux side in the output side circuit 32 of the converter 3. The induced electromotive force generated by the supply inductor Lraux is used to supply the supply voltage Vin to the switching control drive section 2. An energy storage inductor C2 in parallel with the supply inductor Lraux is used to stabilize the supply voltage Vin. Naturally, the energy storage inductor C2 is not necessary in the case where the switching control drive unit 2 is not sensitive to fluctuations in the supply voltage Vin. In addition, the diode D8 in the output side circuit 32 is used to prevent the output terminal current (the current generated by Vout) from flowing backward to the resonant inductor Lr via the supply inductor Lraux, thereby affecting the operation of the resonant circuit.

After the switching control drive unit 2 receives the power supply, it starts to control the switching elements Q1 to Q4 to turn on or off in accordance with a predetermined operation. At this time, the dc output Vout of the output part of the voltage conversion circuit 1 generates an output voltage, and gradually increases to a level at which the switching control drive part 2 can normally supply power.

When the dc output Vout is higher than a predetermined threshold, i.e. when the initial startup phase shifts to the normal operation phase, the switching control driving unit 2 is powered by the dc output voltage Vout. At this time, the oscillator 10 does not continue to control the power switching element Q1, and the switching circuit (15) is turned off. That is, the control right of the power switching elements Q1 to Q4 is given to the switching control drive unit 2. The voltage conversion circuit 1 and the switch control drive section 2 will start to normally perform the voltage conversion action as in the related art (fig. 5).

After the initial starting stage is shifted to the normal working stage, the operation of the oscillator 10 can also be stopped, so as to save unnecessary power consumption. Here, as an example, a switch K1 is provided on a path through which the power supply voltage Vdd is supplied to the oscillator 10, and the operation of the oscillator 10 is stopped by disconnecting the electrical connection when necessary. The signal for turning off the switch K1 may be sent by the switch control drive unit 2.

Of course, the present invention is not limited to this, and the operation may be stopped by sending a signal to stop the operation to the oscillator 10.

As described above, the threshold value should be equal to or larger than a value that can ensure the normal operation of the switching control drive section 2. May be set in advance according to the specification of the switching control driving unit 2 to be used. As shown in fig. 3, a voltage detector 12 may be provided to determine whether the dc output Vout exceeds the threshold. This determination may be made by the switching control drive unit 2 itself.

In addition, in the above description, the oscillator 10 sends out the gate driving signals G1 and G5 only to the switching elements Q1 and Q5, however, the oscillator 10 of the present invention is preferably further connected to Q4 and sends out the gate driving signal G4 to the gate thereof at the initial start-up stage to be always turned on. Thus, the transformer Tr is short-circuited, and thus no energy is transmitted to the secondary output through the transformer Tr.

In the embodiment of fig. 2 to 4, power is supplied to the switching control drive unit 2 by electromagnetic coupling of Lr and Lraux at the initial start-up stage, and thus electric energy is transmitted by coupling via the coil, which meets the requirement of electrical isolation, as compared with the method of directly supplying Vdd of fig. 1. That is, since there is no direct electrical connection between the power consumption circuit of the switching control drive unit 2 and the power generation circuit of the voltage conversion circuit 2, the mutual interference between these two circuits can be reduced. For example, if a fault such as ground occurs on the power supply circuit side of the switching control drive unit 2 and if the power supply circuit is directly connected to the power supply Vdd without electrical isolation, the power generation circuit of the voltage conversion circuit 2 may be affected by the fault and may not operate normally.

Although fig. 3 illustrates an example in which the voltage conversion circuit 1 of the present invention is an LLC full-bridge conversion circuit, the present invention is not limited to this. As can be understood by those skilled in the art from the above description, any rectifier circuit that performs voltage conversion and rectification by periodic change of current, including a resonant circuit such as the series resonant circuit composed of Lr and Cr mentioned in the present invention, can be applied to the present invention. For example, the present invention is also applicable to the LLC half-bridge converter circuit shown in fig. 4, which is formed by omitting Q3 and Q4 in fig. 3.

The present invention is susceptible to various embodiments and modifications without departing from the broad spirit and scope of the present invention. The above embodiments are merely illustrative of the present invention, and do not limit the scope of the present invention. That is, the scope of the present invention is shown by the scope of claims, not by the above embodiments. Various modifications made within the scope of the claims and within the scope of the equivalent meaning to the claims are also considered to be within the scope of the present invention.

Description of the reference symbols

1 voltage conversion circuit

2 switch control drive part

3 converting part

10 vibration generator

12 voltage detector

15 switching circuit

31 input side circuit

32 output side circuit

Cr resonant capacitor

C1, C2 energy storage capacitor

D5, D7, D8, P1 and P2 diodes

D6 zener diode

G1, G4, G5, S1-S4 gate drive signals

K1 switch

Lr resonance inductor

Lraux power supply inductor

Q1-Q4 switching element

R1, R2 divider resistance

R_LLoad(s)

Tr1 transformer primary side inductance

Tr2 secondary inductor of transformer

Vdd power supply voltage

Vout DC output

Vin supply voltage.

Claims

1. A DC/DC conversion apparatus comprising:

a voltage conversion circuit that converts a direct-current power supply voltage into a direct-current output, including a resonance circuit and a plurality of power switching elements that cause the power supply voltage to be applied to the resonance circuit in different directions to generate the direct-current output; and

a switch control drive unit that outputs a control signal to the plurality of power switching elements and controls on/off of the plurality of power switching elements to generate the direct current output,

the DC/DC conversion device is characterized by further comprising:

a conversion section connected to the switch control drive section and connected to the power supply voltage via the voltage conversion circuit,

the conversion part supplies power to the switch control driving part by using the power supply voltage at an initial start-up stage of the DC/DC conversion device, and supplies power to the switch control driving part by using the DC output at a normal operation stage of the DC/DC conversion device,

the resonance circuit comprises a resonance inductor, the conversion part comprises a power supply inductor, and the conversion part supplies power to the switch control driving part by using the power supply voltage through electromagnetic coupling between the resonance inductor and the power supply inductor.

2. The DC/DC conversion device according to claim 1, wherein the voltage conversion circuit further comprises:

a transformer connected in series with the resonant circuit; and

a switching circuit connected between a connection point of the resonance circuit and the transformer and a ground,

the conversion section includes:

an input side circuit that controls on or off of at least one of the plurality of power switching elements and the switching circuit;

an output side circuit including a power supply inductance electromagnetically coupled with a resonance inductance in the resonance circuit, thereby supplying power to the switch control drive section with the power supply voltage.

3. The DC/DC conversion device according to claim 2, wherein the input side circuit includes an oscillator that receives power supply from the power supply voltage,

in the initial starting stage, the oscillator repeatedly turns on or off the at least one power switching element at a set frequency and turns on the switching circuit,

in the normal operation phase, the oscillator does not control the at least one power switching element and opens the switching circuit.

4. A DC/DC conversion apparatus according to claim 3, wherein the oscillator further turns on another power switching element other than the at least one power switching element among the plurality of power switching elements in the initial starting stage.

5. A DC/DC conversion device according to claim 3, wherein a power switch is provided between said oscillator and said power supply voltage, said power switch being closed during said initial start-up phase and being open during said normal operation phase.

6. The DC/DC conversion apparatus according to claim 2, wherein the output side circuit further includes a capacitor and a diode,

a series circuit of the supply inductance and the diode is connected in parallel with the capacitance between the dc output and ground,

the cathode side of the diode is connected to the dc output side, and the anode side of the diode is connected to the ground side.

7. The DC/DC conversion apparatus according to claim 2, wherein the output side circuit further includes a voltage detection means for detecting a voltage level of the DC output, and the normal operation stage is entered from the initial start-up stage when the voltage level detected by the voltage detection means exceeds a predetermined threshold.

8. The DC/DC conversion apparatus according to claim 2, wherein the switching circuit comprises a series circuit of a switching element and a diode, wherein a source of the switching element is connected to a connection point of the resonance circuit and the transformer, and an anode of the diode is connected to a drain of the switching element, and a cathode is connected to ground.