JP2016052222A - Dc-dc converter apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter apparatus which suppresses a surge voltage generated on a secondary side of a transformer, and also reduces a loss when a variable range of output voltage is increased.SOLUTION: In a DC-DC converter apparatus, a snubber circuit 22 having a first series circuit including a diode 224, a switching element 225 and a capacitor 226, a second series circuit including a diode 228 and a capacitor 229, diodes 221, 222 whose anodes are connected to each end of a secondary winding 202, and resistors 223, 227 is connected between a rectifier circuit 21 and an LC filter circuit 23. Energy of spike-like voltage exceeding a charge voltage of a capacitor 226, as a constant voltage source, is temporality absorbed in the capacitor 229 and then charged to the capacitor 226 through the resistor 227. Consequently, an output voltage is clamped at the charge voltage level of the capacitor 226, thus a surge voltage is suppressed. When the switching element 225 is turned on for a predetermined time, the energy of the spike-like voltage stored in the capacitor 226 is discharged and regenerated to a load 26.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a DC-DC converter device in which a primary side circuit and a secondary side circuit are electrically insulated by a transformer, and more specifically, a snubber circuit that suppresses a surge voltage generated during switching is used as a secondary side circuit. The present invention relates to a provided DC-DC converter device.

  The DC-DC converter device is characterized by being highly efficient while being small and light, and has recently been widely used as a power source for various electronic devices and devices.

  A general DC-DC converter device has a configuration in which a primary side circuit and a secondary side circuit are electrically insulated using a transformer, and the primary side circuit has a direct current supplied from a direct current power source. A switching circuit for switching power is provided. By the switching operation in the switching circuit, a current is supplied to the primary winding of the transformer so as to intermittently reverse its direction. Due to this alternating current flowing in the primary winding, a square wave voltage corresponding to the turns ratio of the transformer is induced in the secondary winding. Then, the current flowing by the voltage is rectified by a rectifier circuit such as a diode bridge, smoothed by a filter circuit, and supplied to a load as DC power.

  In the switching circuit, a switching element such as a power MOSFET is used. In many cases, a surge voltage is generated when the switching element is turned on and off. FIG. 3A shows an actually measured waveform of the anode-cathode voltage of the diode included in the rectifier circuit of the secondary side circuit. It can be seen that immediately after the rising of the square wave voltage, a large surge voltage is generated due to the leakage inductance of the transformer and the reverse recovery time of the secondary rectifier diode. If such a surge voltage exceeds the withstand voltage of the diode, the diode may be damaged. Therefore, if the surge voltage is large, it is necessary to use a diode having a large withstand voltage for the rectifier circuit, which increases the cost.

For this reason, a DC-DC converter device in which a snubber circuit is provided in a secondary circuit in order to suppress a surge voltage is conventionally known.
FIG. 4 is a configuration diagram of a secondary circuit in the DC-DC converter device described in Patent Document 1. The primary winding 201 of the transformer 20 is connected to a primary side circuit (not shown), the secondary winding 202 is connected to a rectifier circuit 41 having a diode bridge configuration included in the secondary side circuit, An LC filter composed of 43 and a capacitor 44 is connected. Both ends of the capacitor 44 are output ends, and a load 45 is connected to the output end.

  The snubber circuit 42 includes diodes 421 and 422 each having an anode connected to both ends of the secondary winding 202 of the transformer 20, and a common cathode between the diodes 421 and 422 and a high voltage side output of the rectifier circuit 41. A connected diode 423, a capacitor 424 connected between the common cathode and the low voltage side output of the rectifier circuit 41, and a resistor connected between the common cathode and the output side end of the reactor 43 425 and a capacitor 426 connected between the resistor 425 and the low voltage side output.

  When the DC-DC converter device operates, a square wave voltage appears at both ends of the secondary winding 202 of the transformer 20 as described above. In the snubber circuit 42, the anodes of the diodes 421 and 422 are respectively connected to both ends of the secondary winding 202, and when the voltage across the capacitor 424 becomes lower than the secondary side voltage of the transformer, the capacitor 424 passes through the diode 421 or 422. The current flows into the battery and is charged. For this reason, the voltage across the capacitor 424 is substantially fixed to the voltage generated across the secondary winding 202. That is, the capacitor 424 basically functions as a constant voltage source.

  When a surge voltage is generated in the secondary side voltage of the transformer 20, a surge current flows into the capacitor 424 from the secondary winding 202 through the diode 421 or 422. Further, when a surge voltage is generated in the high voltage side line of the rectifier circuit 41, a surge current flows into the capacitor 424 through the diode 423. Therefore, in both cases, the surge voltage is clamped to the charging voltage of the capacitor 424, and the surge current is charged to the capacitor 424. When the voltage of the capacitor 424 rises due to the charging of the surge current, the energy is released to the smoothing capacitor 44 through the resistor 425. As a result, the snubber circuit 42 can suppress the surge voltage. The diode 423 blocks the discharge of the capacitor 424 and operates as a discharge blocking snubber.

  The DC-DC converter device is a useful circuit when the output terminal voltage is constant, for example, the load 45 is a battery. However, this is not suitable when the output voltage needs to be varied greatly. This is because the capacitor 424 functions as a constant voltage source, so that when the output voltage is lowered to near 0 V, the potential difference between both ends of the resistor 425 increases, and heat generation at the resistor 425 becomes a problem.

  On the other hand, Patent Document 2 discloses a DC-DC converter device that can widen the variable width of the output voltage. FIG. 5 is a configuration diagram of a secondary circuit in the DC-DC converter device. In this configuration, a snubber circuit 52 provided between a rectifier circuit 51 having a diode bridge configuration and an LC filter including a reactor 53 and a capacitor 54 includes a series circuit of a diode 521 and a capacitor 522 for preventing discharge, A switching element 523 for regeneration connected in parallel with the diode 521. The switching element 523 is driven to turn on when all of the switching elements included in the switching circuit of the primary circuit (not shown) are in an off state, that is, during a period of dead time.

  In this DC-DC converter device, similarly to the circuit shown in FIG. 4, when a surge voltage is generated on the high voltage side line of the rectifier circuit 51, a surge current flows into the capacitor 522 through the diode 521, and the capacitor 522 is charged. The On the other hand, the charged capacitor 522 is discharged through the switching element 523 for regeneration. That is, when the switching element 523 is turned on while the rectifier circuit 51 is in the recirculation operation period, the energy stored in the capacitor 522 due to the constant current action of the reactor 53 is released through the switching element 523. Since the on-resistance of the switching element 523 is very small, there is almost no loss due to heat generation of the resistance.

  However, in the DC-DC converter device shown in FIG. 5, since the capacity of the capacitor 522 must be reduced, the charge / discharge energy is also small. Therefore, the ON period of the switching element 523 that determines the discharge time of the capacitor 522 cannot be extended, and adjustment is quite difficult.

JP 2013-74767 A International Publication No. 2010/067629

  The present invention has been made to solve the above-mentioned problems, and its object is to absorb only the spike-like voltage portion when a surge voltage occurs while supporting a wide variable output voltage. An object of the present invention is to provide a DC-DC converter device capable of suppressing a surge voltage with less energy loss.

The present invention, which has been made to solve the above problems, includes a DC power supply, a transformer having a primary winding and a secondary winding, and a plurality of main switching elements, and switches a DC current supplied from the DC power supply. And a switching circuit for supplying alternating current to the primary winding of the transformer, and the alternating current power induced in the secondary winding by the current flowing through the primary winding of the transformer is converted into a direct current to a load. In the supplied DC-DC converter device,
a) a rectifying circuit including a plurality of rectifying diodes connected to the secondary winding of the transformer;
b) a smoothing circuit including a reactor and a capacitor connected to the output terminal of the rectifier circuit;
c) a snubber circuit interposed between the rectifier circuit and the smoothing circuit and connected in parallel to the rectifier circuit;
d) A drive control unit that turns on and off the main switching element and a snubber switching element described later, converts the AC power induced in the secondary winding of the transformer into a DC by the rectifier circuit, and supplies the AC power to the load When,
With
The snubber circuit includes a first series circuit in which a third diode connected in the reverse direction, a snubber switching element and a first capacitor are connected in series, and a forward connection connected in parallel to the rectifier circuit. A second series circuit in which a fourth diode and a second capacitor are connected in series; a connection point A between the first capacitor in the first series circuit and the snubber switching element; A first resistor connected between a second capacitor in the series circuit of 2 and a connection point B of the fourth diode, an anode connected to both ends of the secondary winding, and a cathode Each including a first and a second diode connected to the connection point A via a common second resistor,
The drive control unit charges the first capacitor through the first resistor by charging energy of the second capacitor after charging the second capacitor through the fourth diode, The charging energy stored in the capacitor is controlled such that when the plurality of main switching elements are in an off state, the snubber switching element is turned on for a predetermined period and discharged to the load through the third diode. It is characterized by.

  In the DC-DC converter device according to the present invention, the configuration of the primary side circuit connected to the primary winding of the transformer is not particularly limited. For example, the switching circuit may be a full bridge circuit using four main switching elements. A half bridge circuit using a single main switching element or a push-pull circuit may be used.

  In the DC-DC converter device according to the present invention, the first and second diodes and the first capacitor function as a constant voltage source using a voltage generated at both ends of the secondary winding of the transformer. Therefore, it can be considered that the voltage across the first capacitor is almost constant. Since the connection point A and the connection point B are connected via the first resistor, the current flows through the fourth diode so that the voltage across the second capacitor is equal to the voltage across the first capacitor. Flowing. That is, when a spike-like surge voltage appears at the output terminal of the rectifier circuit, the voltage exceeding the voltage across the first capacitor (charging voltage) flows into the second capacitor through the fourth diode, The capacitor is charged.

  When the charging voltage of the second capacitor rises due to absorption of the spike voltage, a potential difference is generated across the first resistor, so that a current flows from the second capacitor to the first capacitor through the first resistor, and the second capacitor 1 capacitor is charged. Normally, the energy due to the spike voltage is not so large, and the capacitance of the first capacitor is set to be somewhat large in order to constitute a constant voltage source, so that the first current due to the current flowing from the second capacitor is set. The voltage rise of the capacitor 1 is small. In this way, the voltage appearing at the output terminal of the rectifier circuit is clamped at the level of the voltage across the first capacitor, and the spike voltage is suppressed.

  The drive control unit drives the main switching element on and off in order to flow current alternately to the primary winding of the transformer, but only during a dead time during which the plurality of main switching elements are all off, The snubber switching element is turned on. When the snubber switching element is turned on, energy derived from the spike voltage charged in the first capacitor is released through the third diode and regenerated to the load.

  In order to keep the voltage across the first capacitor substantially constant, the snubber switching element is turned on for a predetermined period of time so that the energy stored in the first capacitor can be released by the spike voltage. Although it is necessary to determine the length in advance, if the capacitance of the first capacitor is increased, the length of the predetermined time may not be so strict.

  In addition, the drive control unit does not need to turn on the snubber switching element every dead time, and may turn on the snubber switching element only once every predetermined number of dead times, for example. For example, if the snubber switching element is turned on every dead time, the on-time (predetermined time) may need to be considerably shortened, but the snubber switching element once every plural dead times. If ON is turned on, one ON time can be lengthened to some extent, thereby facilitating control.

  According to the DC-DC converter device of the present invention, a spike voltage exceeding the voltage across the first capacitor can be reliably ensured while avoiding clamping of the voltage not exceeding the voltage across the first capacitor. By removing it, the surge voltage can be suppressed. Moreover, since the energy derived from the surge voltage stored in the first capacitor is regenerated to the load, the energy can be used effectively. Further, even when the output voltage needs to be lowered to around 0 V corresponding to the load, loss due to the difference between the voltage across the first capacitor and the output voltage does not occur, so the variable width of the output voltage seems to be large. It can cope with various loads.

The block diagram of the DC-DC converter apparatus which is one Example of this invention. The operation | movement timing and waveform diagram in the DC-DC converter apparatus of a present Example. The figure which shows the measured waveform of the voltage between the both ends of the rectifier diode of the secondary side circuit when not using the snubber circuit by a present Example. The block diagram of an example of the conventional DC-DC converter apparatus. The block diagram of an example of the conventional DC-DC converter apparatus.

A DC-DC converter device according to an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a configuration diagram of the DC-DC converter device of the present embodiment, and FIG. 2 is an operation timing and waveform diagram of the DC-DC converter device of the present embodiment.

  The primary circuit 1 connected to the primary winding 201 of the insulated transformer 20 includes a DC power supply 10 and first to fourth main switching elements 111, 121, 131 such as a plurality (four) of power MOSFETs. , 141 and a switching circuit having a full bridge configuration, and clamp diodes 112, 122, 132, 142 are connected in antiparallel to the first to fourth main switching elements 111, 121, 131, 141, respectively. Has been. The primary winding 201 of the transformer 20 includes a connection point between the first main switching element 111 and the second main switching element 121, and a connection point between the third main switching element 131 and the fourth main switching element 141. , Connected between. The first to fourth main switching elements 111 to 141 are on / off controlled by a drive signal generated by the main switching element drive unit 31 based on a control signal from the drive control unit 30.

  The secondary circuit 2 connected to the secondary winding 202 of the transformer 20 includes a rectifier circuit 21, a snubber circuit 22, and an LC filter circuit 23. That is, both ends of the secondary winding 202 of the transformer 20 are connected to a rectifier circuit 21 in which four diodes 211, 212, 213, and 214 are configured as a full bridge, and the output voltage rectified by the rectifier circuit 21 is The LC filter circuit 23, which is a smoothing circuit including the reactor 24 and the capacitor 25, is smoothed by the LC filter circuit 23 and output to the load 26. A snubber circuit 22 that suppresses a surge voltage generated on the secondary side of the transformer 20 is provided between the rectifier circuit 21 and the LC filter circuit 23.

  The snubber circuit 22 includes a first series circuit in which a third diode 224, a snubber switching element 225, and a first capacitor 226 are connected in series, and a fourth diode 228 and a second capacitor 229 in series. The connected second series circuit, the connection point A between the snubber switching element 225 and the first capacitor 226 in the first series circuit, the fourth diode 228 in the second series circuit, and the second A first resistor 227 connected between the connection point B and the capacitor 229; first and second diodes 221 and 222 having anodes connected to both ends of the secondary winding 202 of the transformer 20; And a second resistor 223 connected between the common cathode of the diodes 221 and 222 and the connection point A in the first series circuit. The snubber switching element 225 is on / off controlled by a drive signal generated by the snubber switching element drive unit 32 based on a control signal from the drive control unit 30.

  The drive control unit 30 can include a CPU (for example, a flash ROM) in which a control program is stored in order to perform characteristic operations described later.

Next, the power conversion operation in the DC-DC converter device of the present embodiment will be described with reference to FIG.
In FIG. 2, the main switching elements 111, 121, 131, 141, and the snubber switching element 225 are referred to as SW1, SW2, SW3, SW4, SW5, respectively, and the diodes 211, 212, 213, 214 are referred to as D1, D2, These are referred to as D3 and D4.

  Based on an instruction from the drive control unit 30, the main switching element drive unit 31 gives the drive signals shown in FIG. 2A to the gate terminals of the two main switching elements 111 and 141 included in different arms of the full bridge circuit. Similarly, the drive signals shown in FIG. 2B are given to the gate terminals of the two main switching elements 121 and 131 included in different arms. Here, one cycle of the switching control is 80 kHz, and the drive signals given to the second and third main switching elements 121 and 131 are the drive signals given to the first and fourth main switching elements 111 and 141. In contrast, the phase is delayed by 180 °. When these drive signals are at a high level, the first to fourth main switching elements 111 to 141 are turned on. That is, the set of the first and fourth main switching elements 111 and 141 and the set of the second and third main switching elements 121 and 131 are alternately arranged with a predetermined dead time in which both of them are off. Turns on. Of course, the frequency of one cycle is not limited to this.

  2C shows the drain-source voltage of the first and fourth main switching elements 111 and 141, FIG. 2D shows the current flowing through the primary winding 201 of the transformer 20, and FIG. 2E shows driving of the snubber switching element. (F) is a current applied to the diodes 211 and 214 of the rectifier circuit 21, (g) is a current applied to the diodes 212 and 213 of the rectifier circuit 21, h) is the voltage between the anodes and cathodes of the diodes 211 and 214, (i) is the charging current of the second capacitor 229, and (j) is the discharging current discharged from the first capacitor 226 through the snubber switching element 225. The waveforms are shown respectively.

Immediately before time t ₀ , the first to fourth main switching elements 111 to 141 are all in an off state. At this time, each of the rectifier circuits 21 is based on the energy accumulated in the reactor 24 before that time. The diodes 211 to 214 each have a current substantially half of the output current I ₀ (see FIGS. 2F and 2G).

When the drive signal applied to the gate terminals of the first and fourth main switching elements 111 and 141 rises at time t _{0 and both} the main switching elements 111 and 141 are turned on, the primary winding 201 of the transformer 20 has a predetermined value. Current begins to flow in the direction (from top to bottom in FIG. 1). FIG. 2D shows the direction of current at this time in positive polarity. This primary current, at both ends of the secondary winding 202 of the transformer 20 is induced voltage corresponding to the turns ratio, as shown in FIG. 2 (f), the current flowing through the diode 211, 214 from I _0/2 Start to increase. On the contrary, as shown in FIG. 2 (g), the current flowing through the diode 212 and 213 begins to decrease from I _0/2. At time t ₁ , currents flowing through the diodes 211 and 214 reach I ₀ , while currents flowing through the diodes 212 and 213 become zero, and the diodes 212 and 213 are cut off.

However, since the recovery time exists in principle for the diodes 212 and 213 to be turned off, the current flowing through the diodes 211 and 214 continues to increase for a while (until time t ₂ ). The current flowing through 213 continues to decrease below zero. That the currents of the diodes 212 and 213 become zero or less means that the current flows backward from the cathode toward the anode. Therefore, a short-circuit current flows through the diodes 211 to 214, and thereby energy is accumulated in the leakage inductance of the secondary winding 202 of the transformer 20.

  When the snubber circuit 22 is not provided, a spike-like induced voltage, that is, a surge voltage is generated when the diodes 212 and 213 begin to recover the reverse current blocking capability during the period from time t2 to time t3. On the other hand, in the DC-DC converter device according to the present embodiment, when a surge voltage is generated, the second capacitor 229 absorbs the spike voltage portion.

The snubber circuit 22 operates as follows.
In the snubber circuit 22, the first and second diodes 221, 222, the second resistor 223, and the first capacitor 226 function as a constant voltage source. That is, when the voltage across the secondary winding 202 of the transformer 20 becomes higher than the charging voltage of the first capacitor 226, the secondary winding passes through the first diode 221 or the second diode 222 and the second resistor 223. Current flows from line 202 to first capacitor 226, charging first capacitor 226. Therefore, the voltage across the first capacitor 226, that is, the potential at the connection point A, is kept substantially constant by the voltage across the secondary winding 202. Note that the second resistor 223 suppresses an inrush current to the first capacitor 226.

When the snubber switching element 225 is in the OFF state, the charging voltage of the first capacitor 226 and the charging voltage of the second capacitor 229 are substantially equal. This is because if there is a difference between the charging voltages, a current flows through the first resistor 227, thereby making both charging voltages substantially equal. Therefore, the potential of the anode of the fourth diode 228 is approximately clamped to the charging voltage of the first capacitor 226. Therefore, when a surge voltage is generated in the secondary winding 202 of the transformer 20 and a spike voltage appears at the output terminal of the rectifier circuit 21, the spike voltage portion exceeding the charging voltage of the first capacitor 226 is the fourth voltage. It flows into the 2nd capacitor | condenser 229 through the diode 228, and the 2nd capacitor | condenser 229 is once charged (refer FIG.2 (i)). As a result, the charging voltage of the second capacitor 229 once rises, but current flows into the first capacitor 226 through the first resistor 227 and charges the first capacitor 226.
That is, the second capacitor 229 has a function of instantaneously and temporarily absorbing energy caused by the spike-like voltage, and the first capacitor 226 has a function of holding energy caused by the spike-like voltage for a longer time.

  As described above, since the spike-like voltage portion of the surge voltage generated due to commutation is removed, the voltage across the diodes 211 and 214 of the rectifier circuit 21 is flat immediately after the rise as shown in FIG. become.

  Note that although the charging voltage of the first capacitor 226 increases, the capacitance of the first capacitor 226 is usually much larger than the capacitance of the second capacitor 229. For example, the former is 10 to 100 times the latter. Further, even when the spike voltage is large, since it is a very short time, the energy by the spike voltage is small. Therefore, even if the charging voltage of the first capacitor 226 increases, the increase is slight.

  The snubber switching element is driven by the drive signal from the snubber switching element driving unit 32 as shown in FIG. 2E during the dead time period when all of the first to fourth main switching elements 111 to 141 are turned off. When 225 is turned on, a current path from the connection point A to the LC filter circuit 23 is formed. As a result, the energy caused by the spike voltage stored in the first capacitor 226 is released from the first capacitor 226, and the reactor included in the snubber switching element 225, the third diode 224, and the LC filter circuit 23. 24, etc., and supplied to the load 26 (see FIG. 2 (j)). As a result, the charging voltage of the first capacitor 226 decreases.

When the snubber switching element 225 is turned on and the first capacitor 226 is discharged, the charging voltage of the capacitor 226 decreases. Therefore, in order to make the capacitor 226 function as a constant voltage source, the energy corresponding to the spike voltage is used. only there is a need to be released from the first capacitor 226, would otherwise, certain on-time t ₄ of snubber switching element 225 needs to be accurately controlled. However, as described above, if the capacitance of the first capacitor 226 is sufficiently larger than the capacitance of the second capacitor 229, both ends of the first capacitor 226 can be obtained even when the snubber switching element 225 is turned on. Since the voltage decrease rate is small, even if the on-time t ₄ of the snubber switching element 225 is determined to be somewhat rough, the voltage across the first capacitor 226 can be considered to be substantially constant. Therefore, the accuracy of the on-time t ₄ of the snubber switching element 225 may be low.

  FIG. 3B is an actual measurement waveform of the anode-cathode voltage of the diode in the rectifier circuit 21 in the DC-DC converter device of the present embodiment. As apparent from comparison with the actually measured waveform observed when the snubber circuit 22 shown in FIG. 3A is not used, the amplitude of the surge voltage is suppressed to about ¼ to ３.

  As described above, in the DC-DC converter device of the present embodiment, the voltage held in the first capacitor 226 can be used as a reference for clamping, and spike voltages exceeding the voltage can be suppressed. Thereby, the surge voltage can be accurately suppressed. Even when the output voltage is lowered to around 0 V according to the load 26, there is no element that causes a loss due to the difference between the charging voltage of the first capacitor 226 and the output voltage. Therefore, a wide variable range of the output voltage can be ensured, so that various loads 26 can be handled.

In the DC-DC converter device of the above embodiment, as shown in FIG. 2, the snubber switching element 225 is turned on for a predetermined time t ₄ once in one cycle (in this example, the frequency of 80 kHz). Although the excess energy charged to 226 is being released, this need not necessarily be done once per cycle. Therefore, for example, the snubber switching element 225 is turned on based on a signal obtained by dividing a signal for determining a cycle for turning on / off the main switching elements 111 to 141 (for example, 1/2 division or 1/4 division). The timing may be determined. Thus, even if the cycle for turning on / off the main switching elements 111 to 141 is 80 kHz, the cycle for turning on the snubber switching element 225 is 40 kHz or 20 kHz.

As described above, when the cycle for turning on the snubber switching element 225 is extended, the amount of energy to be released increases by one energy release, and therefore, the ON time t ₄ may be lengthened accordingly. If the on-time t ₄ is too short, it may be difficult to accurately control the on-time. However, if the on-time is extended by extending the energy release cycle, the on-time can be accurately controlled.

  Moreover, the said Example is only an example of this invention, Even if it changes suitably, amends, and is added in the range of the meaning of this invention, it is naturally included in the claim of this application.

DESCRIPTION OF SYMBOLS 1 ... Primary side circuit 10 ... DC power supply 111, 121, 131, 141 ... Main switching element 112, 122, 132, 142 ... Clamp diode 20 ... Transformer 201 ... Primary winding 202 ... Secondary winding 2 ... Secondary side circuit 21 ... Rectifier circuits 211, 212, 213, 214, 221, 222, 224, 228 ... Diode 22 ... Snubber circuit 223, 227 ... Resistor 225 ... Snubber switching elements 226, 229, 25 ... Capacitor 23 ... LC filter circuit 24 ... Reactor 26 ... Load 30 ... Drive control unit 31 ... Main switching element driving unit 32 ... Snubber switching element driving unit

Claims (2)

A current including a DC power supply, a transformer having a primary winding and a secondary winding, and a plurality of main switching elements, switching a DC current supplied from the DC power supply and alternately inverting the primary winding of the transformer A DC-DC converter device comprising: a switching circuit for supplying AC power; and converting the AC power induced in the secondary winding by the current flowing in the primary winding of the transformer to DC and supplying the load to a load.
a) a rectifying circuit including a plurality of rectifying diodes connected to the secondary winding of the transformer;
b) a smoothing circuit including a reactor and a capacitor connected to the output terminal of the rectifier circuit;
c) a snubber circuit interposed between the rectifier circuit and the smoothing circuit and connected in parallel to the rectifier circuit;
d) A drive control unit that turns on and off the main switching element and a snubber switching element described later, converts the AC power induced in the secondary winding of the transformer into a DC by the rectifier circuit, and supplies the AC power to the load When,
With
The snubber circuit includes a first series circuit in which a third diode connected in the reverse direction, a snubber switching element and a first capacitor are connected in series, and a forward connection connected in parallel to the rectifier circuit. A second series circuit in which a fourth diode and a second capacitor are connected in series; a connection point A between the first capacitor in the first series circuit and the snubber switching element; A first resistor connected between a second capacitor in the series circuit of 2 and a connection point B of the fourth diode, an anode connected to both ends of the secondary winding, and a cathode Each including a first and a second diode connected to the connection point A via a common second resistor,
The drive control unit charges the first capacitor through the first resistor by charging energy of the second capacitor after charging the second capacitor through the fourth diode, The charging energy stored in the capacitor is controlled such that when the plurality of main switching elements are in an off state, the snubber switching element is turned on for a predetermined period and discharged to the load through the third diode. A DC-DC converter device. The DC-DC converter device according to claim 1,
The drive control unit turns on the snubber switching element every time a plurality of cycles for turning on and off the plurality of main switching elements are executed.

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