JP5565186B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device, and more particularly to a power conversion device including a snubber circuit suitable for suppressing a surge voltage applied to a semiconductor switching element such as a diode used in a switching power supply or the like.

  2. Description of the Related Art Conventionally, an isolated DC-DC converter that switches an input DC voltage by a semiconductor switching element to generate AC, then boosts or steps down by a transformer, rectifies it, converts it to a different DC voltage, and outputs it. It is known (for example, refer to Patent Document 1).

  FIG. 8 is a schematic configuration diagram illustrating an example of an insulated DC-DC converter (hereinafter referred to as “DC-DC converter”) configured using a MOSFET as a semiconductor switching element that generates alternating current from direct current. In this DC-DC converter, two sets of series circuits in which the source of one of the MOSFETs (Q1 or Q3) and the drain of the other MOSFET (Q2 or Q4) are connected in parallel are connected to the inverter 2 Is configured.

  The on / off control unit 3 turns on the MOSFETs (Q1, Q4) of the inverter 2 and turns off the MOSFETs (Q2, Q3) (first state), and switches the on and off (first state). 2 state) and a state (third state) in which all MOSFETs (Q1 to Q4) are turned off. And the on / off control part 3 switches these 1st-3rd states at high speed, and controls so that a high frequency alternating current (rectangular wave) may be applied to the primary winding W1 of the transformer T. By controlling in this way, a voltage (alternating current) corresponding to the rectangular wave applied to the primary winding W1 is generated in the secondary winding W2 of the transformer T. In order to reduce the size of the transformer T and prevent noise, the frequency of the high-frequency alternating current is generally set to 10 kHz or more in many cases.

  The secondary winding W2 of the transformer T is connected with a rectifier circuit 4 composed of diodes D1, D2, D3, D4 having a short current cutoff time in order to rectify high-frequency alternating current generated in the secondary winding W2. Yes. Since the output of the rectifier circuit 4 is a pulsating current, a smoothing circuit in which a smoothing inductor L and a smoothing capacitor C are connected in series is connected between the output terminals of the rectifying circuit 4. A smoothed DC voltage generated at both ends of the smoothing capacitor C is supplied to the load 5.

  The on / off control unit 3 switches the first to third states at a high speed as described above, and controls the ratio between the on period and the off period of the MOSFETs (Q1 to Q4), thereby applying the direct current applied to the load 5. Adjust the voltage value.

  In the third state, all the MOSFETs (Q1 to Q4) are turned off, and the voltage applied to the primary winding W1 of the transformer T becomes 0V. Even in this third state, the DC-DC converter releases the magnetic energy stored in the smoothing inductor L and continues to supply current to the load 5. A period in which the DC-DC converter is in the third state is defined as a reflux period.

  By the way, when the DC-DC converter shifts from the reflux period to the first state, a reverse voltage is applied to the diodes D2 and D3. At this time, the diodes D2 and D3 perform an operation of cutting off a reverse current, that is, a reverse recovery current in a very short time. The source of this reverse recovery current is a transformer T.

  The path of the reverse recovery current flowing through the transformer T includes the leakage inductance Le of the transformer T and the parasitic capacitances Cp1 to Cp4 of the diodes D1 to D4. The leakage inductance Le and the parasitic capacitances Cp2 and Cp3 form a series resonance circuit. Therefore, when shifting from the return period to the first state, LC resonance occurs due to the electromotive force E2 generated in the secondary winding W2 of the transformer T.

  In this LC resonance, when the initial current of the leakage inductance Le is 0 A and the initial voltages of the parasitic capacitors Cp2 and Cp3 are 0 V, the peak value of the surge voltage generated in the parasitic capacitors Cp2 and Cp3 is the voltage applied to the LC resonance circuit ( Here, it is known to reach twice the electromotive force E2). The peak value of this surge voltage is further increased due to the presence of an initial current (here, reverse recovery current) flowing through the LC resonance circuit. In addition, when shifting to a 2nd state from a recirculation | reflux period, the same surge voltage is applied also to the diodes D1 and D4.

  When the peak value of the surge voltage exceeds the reverse voltage allowed by the element, the diodes D1 to D4 may be damaged. Then, the power converter device provided with the snubber circuit for protecting a switching element from such a surge voltage is known (for example, refer patent documents 2-4).

  For example, the DC-DC converter shown in FIG. 8 is disclosed in Patent Document 4, and the snubber circuit includes a first series circuit in which a capacitor Cs1 and a diode Ds1 are connected in series, and a diode Ds2. The second series circuit includes a Zener diode Dzs connected in series, and the third series circuit includes a diode Ds3 and an inductor Ls connected in series.

  The first series circuit is connected between the output terminals of the rectifier circuit 4. One end of the second series circuit is connected to the series connection point of the capacitor Cs1 and the diode Ds1 of the first series circuit, and the other end is connected to the series connection point of the smoothing inductor L and the smoothing capacitor C of the smoothing circuit. The third series circuit is connected in parallel to the second series circuit.

  In the DC-DC converter having the snubber circuit configured as described above, first, during the return period, a current flows through a path of the capacitor Cs1, the smoothing inductor L, the load 5, the diode Ds1, and the capacitor Cs1, as shown in FIG. Due to this current, the energy stored in the capacitor Cs1 is regenerated in the load 5. Therefore, the capacitor Cs1 is discharged to almost 0V before shifting to the next charging cycle without unnecessary loss.

  Next, when a transition is made from the return period to the first state, the current flowing in the snubber circuit is as follows. First, the secondary winding W2 of the transformer T → diode D1 → capacitor Cs1 → diode Ds3 → inductor. The flow starts from the path of Ls → smoothing capacitor C → diode D4 → secondary winding W2 of transformer T. At this time, the inductor Ls suppresses the peak value of the current that charges the capacitor Cs1.

  Next, the voltage at the series connection point of the capacitor Cs1 and the diode Ds1 of the first series circuit is the Zener voltage Vzs of the Zener diode Dzs and the voltage across the smoothing capacitor C, that is, the output voltage of the DC-DC converter applied to the load 5. When the sum of Eo [Vzs + Eo] is exceeded, in addition to the above path, the current flowing in the snubber circuit is as shown in FIG. 11, the secondary winding W2 of the transformer T → diode D1 → capacitor Cs1 → diode Ds2 → zener. It begins to flow also in the path of the secondary winding W2 of the diode Dzs → smoothing capacitor C → diode D4 → transformer T.

  Thus, even if the diodes D2 and D3 cut off the current, the current of the leakage inductance Le continues to flow through the snubber circuit. As a result, the charging current of the parasitic capacitances Cp2, Cp3 of the diodes D2, D3 is reduced, and the voltage applied to the diodes D2, D3 is lowered.

  Next, the capacitor Cs1 is charged by the current flowing through the snubber circuit, and the voltage Ec across the capacitor Cs1 rises. As a result, a voltage obtained by adding the output voltage Eo of the DC-DC converter and the voltage Ec across the capacitor Cs1 is applied as a reverse voltage to the leakage inductance Le. As a result, the current flowing through the leakage inductance Le decreases.

  As a result, when the diode Ds1 becomes conductive, the current of the inductor Ls flows through the path of inductor Ls → smoothing capacitor C → diode Ds1 → diode Ds3 → inductor Ls as shown in FIG. With this current, the energy stored in the inductor Ls is transferred to the smoothing capacitor C.

  By the way, when shifting from the reflux period to the first state, as described above, LC resonance occurs between the leakage inductance Le of the transformer T and the capacitor Cs1. The peak value Ecp of the voltage Ec generated at both ends of the capacitor Cs1 due to the LC resonance is expressed by the following equation when the influence of the inductor Ls is ignored for simplification.

Ecp = 2 × {E2− (Eo + Vzs)}
For this reason, the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 is expressed by the following equation.

Erp = 2 × {E2− (Eo + Vzs)} + (Eo + Vzs)
= 2 × E2- (Eo + Vzs)
As shown in this equation, in the DC-DC converter shown in FIG. 8, the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 is the voltage [2 × E2 applied when there is no snubber circuit. ].

JP-A 61-106068 JP-A-9-285126 (FIG. 3) Japanese Patent Laid-Open No. 11-98836 (FIG. 8) JP2009-247132A (FIG. 6)

  However, in the conventional snubber circuit described above, the voltage applied to the rectifier circuit 4 may not be suppressed depending on the operating state of the DC-DC converter. Specifically, when the DC-DC converter is started, the on / off control unit 3 starts the on period of the MOSFETs (Q1 to Q4) from zero, gradually lengthens the on period, and the output voltage Eo is rated from 0V. Generally, so-called soft start control is performed in which the voltage is raised to a voltage. When the load 5 is overloaded, the ON period of the MOSFETs (Q1 to Q4) is shortened to near zero to reduce the output voltage Eo so that the output current does not exceed the limit value. Control is performed. Also at this time, the output voltage Eo may be approximately 0V.

In such a case, in the above-described snubber circuit, when the output voltage Eo becomes 0 V, the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 is
Erp = 2 × E2-Vzs
Thus, there is a problem that the effect of suppressing the voltage is reduced.

  Here, it is conceivable to set the Zener voltage Vzs to a high value in order to suppress the peak value of the voltage applied to the diodes D1 to D4 to a low value. However, when the Zener voltage Vzs is increased, the loss generated in the Zener diode Dzs is increased and the device efficiency is lowered. Furthermore, it is necessary to use a Zener diode Dzs having a large heat capacity, and there is a problem that the apparatus becomes large and expensive.

  The present invention is intended to solve the problem of such a conventional power converter, and the peak value of the voltage applied to the diode constituting the rectifier circuit regardless of the value of the output voltage Eo. It aims at realizing the power converter which can control.

In order to achieve the above object, according to a first aspect of the present invention, a rectifier circuit that rectifies and outputs an input voltage, a smoothing inductor and a smoothing capacitor are connected in series, and both ends thereof are connected between output terminals of the rectifier circuit. A power converter comprising a smoothing circuit and a snubber circuit,
The snubber circuit of this power converter is at least
A series circuit in which a first capacitor, a first diode, and a voltage control unit having a control terminal are connected in series, and both ends thereof are connected between output terminals of the rectifier circuit;
A second diode connected between a series connection point of the first capacitor and the first diode of the series circuit and a series connection point of the smoothing inductor and the smoothing capacitor of the smoothing circuit;
One end thereof is connected to the control terminal of the voltage control unit, and the other end is constituted by a voltage command unit connected to a series connection point of the smoothing inductor and the smoothing capacitor,
The voltage command unit is a power conversion device including a predetermined reference power source.

Moreover, 2nd invention is the power converter device which concerns on 1st invention, Comprising:
The voltage command unit, said rectifying circuit and a reference point connection point between the smoothing capacitor and the connection point between the first diode and the voltage control unit and the voltage control point, which may arise in the voltage control point Output the voltage as a command value,
The voltage control unit, as the voltage of the voltage control point is matched against the command value by the voltage command section outputs, and adjusts the voltage of the voltage control point.

Moreover, 3rd invention is the power converter device which concerns on 2nd invention, Comprising:
The voltage command unit uses a voltage obtained by subtracting the voltage of the reference power supply from the voltage of the smoothing capacitor as a command value for the voltage control unit.

Moreover, 4th invention is the power converter device which concerns on 3rd invention, Comprising:
The reference power supply included in the voltage command unit generates a voltage that is substantially the same as the rated output voltage of the power converter as a reference voltage.

Moreover, 5th invention is the power converter device which concerns on 3rd invention, Comprising:
The reference power supply included in the voltage command unit generates a voltage higher than the rated output voltage of the power converter as a reference voltage.

The sixth invention is a power conversion device according to any one of the first to fifth inventions,
The voltage control unit comprises a circuit in which a capacitor and a semiconductor switch element having a control terminal are connected in parallel,
The voltage command unit is composed of a constant voltage element.

  According to the present invention, in a power conversion device that converts an input voltage into a DC voltage, when the diode constituting the rectifier circuit cuts off the reverse recovery current, the voltage Ec of the first capacitor and the smoothing capacitor regardless of the value of the output voltage Eo Therefore, the peak value of the voltage applied to the diodes D1 to D4 constituting the rectifier circuit is effective. Can be suppressed.

The schematic circuit diagram which shows the structure of the DC-DC converter which is one Embodiment of the power converter device which concerns on this invention. The schematic circuit diagram of the DC-DC converter which shows specific embodiment of the snubber circuit shown in FIG. The figure which shows the path | route of the electric current which flows through a snubber circuit during the return period in the DC-DC converter shown in FIG. The figure which shows the path | route through which the charging current of the capacitor | condenser Cs1 flows in the DC-DC converter shown in FIG. The schematic circuit diagram which shows the structure of the DC-DC converter which is other embodiment of the power converter device which concerns on this invention. The schematic circuit diagram which shows the structure of the DC-DC converter which is further another embodiment of the power converter device which concerns on this invention. The schematic circuit diagram which shows the structure of the DC-DC converter which is further another embodiment of the power converter device which concerns on this invention. The schematic circuit diagram which shows the structure of the DC-DC converter which is one Embodiment of the conventional power converter device. The figure which shows the path | route of the electric current which flows through a snubber circuit in the return period in the DC-DC converter shown in FIG. The figure which shows the path | route through which the electric current of the charge of the capacitor | condenser Cs1 flows in the DC-DC converter shown in FIG. The figure which shows the path | route through which the charging current of the capacitor | condenser Cs1 flows in the DC-DC converter shown in FIG. The figure which shows the electric current path which regenerates the energy which the inductor Ls hold | maintains to a load in the DC-DC converter shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. In FIG. 1 to FIG. 7, the same reference numerals are given to components common to the DC-DC converter of FIG. 8 shown as an example of a conventional power converter, and the description thereof is omitted.

The power converter according to the present invention is characterized by a snubber circuit. A schematic circuit diagram of a DC-DC converter according to the present invention is shown in FIG.
The snubber circuit of the DC-DC converter shown in FIG. 1 includes a series circuit in which a capacitor Cs1, a diode Ds1, and a voltage control unit 6 having a control terminal are connected in series, a diode, Ds2, and a voltage command unit 7. Specific connections and functions of the snubber circuit composed of the above components are as follows.

  First, both ends of the series circuit are connected between output terminals of the rectifier circuit 4. Next, the diode Ds2 is connected between the series connection point of the capacitor Cs1 and the diode Ds1, and the series connection point of the smoothing inductor L and the smoothing capacitor C. Furthermore, one end of the voltage command unit 7 is connected to the control terminal of the voltage control unit 6, and at least the other end is connected to the series connection point of the smoothing inductor L and the smoothing capacitor C. Here, a connection point between the rectifier circuit 4 and the smoothing capacitor is a reference point N. As described above, one end of the voltage control unit 6 is also connected to the reference point N.

  Here, the voltage command unit 7 has a reference power source therein, and the reference voltage Vzb is constant regardless of the value of the output voltage Eo of the power converter. The voltage command unit 7 then outputs a voltage [Eo−Vzb] obtained by subtracting the reference voltage Vzb from the output voltage Eo of the power converter. The output of the voltage command unit 7 is a voltage that the voltage control unit 6 should generate at the other end with respect to the reference point N.

  On the other hand, the voltage control unit 6 is configured such that the voltage (the voltage at the other end of the voltage control unit 6 with respect to the reference point N) [−Vs] matches the command voltage [Eo−Vzb] output from the voltage command unit 7. Operate. Therefore, the relationship [−Vs = Eo−Vzb] is established.

  Next, the command voltage output from the voltage command unit 7 is set to a negative voltage of 0 V or less. That is, the reference voltage Vzb in the voltage command unit 7 is set as Vzb ≧ Eo. Thereby, the voltage of the voltage control unit 6 becomes a negative voltage [−Vs] of 0 V or less. Accordingly, during the return period in which the output voltage Er of the rectifier circuit 4 is 0 V, the voltage Ec of the capacitor Cs1 is Vs.

On the other hand, when shifting from the return period to the first state, the electromotive force E2 rises in the secondary winding W2 of the transformer T. At this time, the output voltage Er of the rectifier circuit 4 is an electromotive force E2 generated in the secondary winding W2 of the transformer T. The voltage [Ec + Eo] of the snubber circuit against this is
Ec + Eo = Vs + Eo = Vzb
It becomes.

  From the above, in the DC-DC converter of FIG. 1, the peak value Ecp of the voltage Ec generated at both ends of the capacitor Cs1 due to LC resonance by the leakage inductance Le of the transformer T and the capacitor Cs1 is expressed by the following equation.

Ecp = 2 × (E2-Vzb)
For this reason, the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 is expressed by the following equation.

Erp = Ecp + Vzb = 2 × E2-Vzb
As shown by this equation, the peak value Erp of the voltage applied to the diodes D1 to D4 constituting the rectifier circuit 4 is higher than the voltage [2 × E2] applied when there is no snubber circuit. The reference voltage Vzb can be kept low.

  The reference voltage Vzb in the voltage command unit 7 is constant regardless of the value of the output voltage Eo. Therefore, the DC-DC converter according to the present invention can always exhibit the effect of suppressing the voltage applied to the rectifier circuit 4 regardless of the value of the output voltage Eo.

  Next, FIG. 2 shows an embodiment in which the voltage control unit 6 and the voltage command unit 7 are configured by specific circuits. The operation of the snubber circuit in this embodiment will be described with reference to FIGS.

  In the embodiment shown in FIG. 2, the voltage control unit 6 shown in FIG. 1 is configured by a circuit in which a capacitor Cs2 and a transistor Tr are connected in parallel. Further, the voltage command unit 7 is constituted by a Zener diode Dzb. According to the explanation given in FIG. 1, the voltage of the capacitor Cs2 is Vs, and the voltage of the Zener diode Dzb is Vzb. The other components in FIG. 2 are the same as the components in FIG.

One end of the Zener diode Dzb is connected to the base terminal B of the transistor Tr. Therefore, when the potential [Eo−Vzb] of the base terminal B of the transistor Tr is higher than the potential of the emitter terminal E, the transistor Tr becomes conductive. Due to the conduction of the transistor Tr, the charge of the capacitor Cs2 is discharged through the transistor Tr. At this time, the base current of the transistor Tr flows through the path of the smoothing capacitor C → the Zener diode Dzb → the base terminal B of the transistor Tr → the emitter terminal E of the transistor Tr → the capacitor Cs 2 → the smoothing capacitor C.

When limiting the peak value of the discharge current flowing through the transistor Tr, a resistor for limiting the current may be inserted between the reference point N and the emitter terminal E of the transistor Tr.
On the other hand, when the potential [Eo−Vzb] of the base terminal B is lower than the potential of the emitter terminal E, the transistor Tr becomes non-conductive. When the transistor Tr is off, the capacitor Cs2 is not discharged.

With the above operation of the transistor Tr, the potential of the emitter terminal E of the transistor Tr is always maintained at [−Vs = Eo−Vzb] with respect to the reference point N.
FIG. 3 is a diagram showing a path of a current flowing through the snubber circuit when the DC-DC converter is in the return period in the embodiment shown in FIG. In the return period, the current of the snubber circuit flows through the path of the capacitor Cs1, the smoothing inductor L, the smoothing capacitor C, the capacitor Cs2, the diode Ds1, and the capacitor Cs1. The capacitor Cs2 is charged by this current. However, as described above, the voltage of the capacitor Cs2 is maintained at [−Vs = Eo−Vzb] by the action of the transistor Tr and the Zener diode Dzb.

  FIG. 4 is a diagram illustrating a path of a current that flows in the snubber circuit when shifting from the reflux period to the first state. When the electromotive force E2 rises in the secondary winding W2 of the transformer T, the secondary winding W2 of the transformer T → the diode D1 → the capacitor Cs1 → the diode Ds2 → the smoothing capacitor C → the diode D4 → the secondary of the transformer T. A current flows through the path of the winding W2.

  When this current starts to flow, a reverse voltage is applied to the diodes D2 and D3 that have performed reverse recovery operation. The peak value of this voltage is the peak value Erp of the output voltage Er of the rectifier circuit 4 as in the embodiment shown in FIG. The magnitude is [Erp = 2 × E2-Vzb] regardless of the output voltage Eo of the DC-DC converter.

  The voltage Vzb of the Zener diode Dzb is constant regardless of the value of the output voltage Eo of the DC-DC converter. Therefore, the snubber circuit of the DC-DC converter according to the embodiment shown in FIG. 2 always suppresses the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 regardless of the value of the output voltage Eo. The effect which it does can be demonstrated.

  Next, FIG. 5 is a schematic circuit diagram showing a configuration of a DC-DC converter which is another embodiment of the power conversion device according to the present invention. The difference from the embodiment shown in FIG. 1 is that an inductor Ls is provided in series with the diode Ds2. The inductor Ls functions to suppress the peak value of the current that charges the capacitor Cs1. The functions of the other components are the same as the functions of the components shown in FIG.

  Therefore, also in the embodiment shown in FIG. 5, the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 can be suppressed to [Erp = 2 × E2-Vzb]. Moreover, the peak value Erp is not affected by the output voltage Eo of the DC-DC converter. Therefore, the snubber circuit according to the embodiment shown in FIG. 5 can always exhibit the effect of suppressing the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4.

  Similarly to the embodiment shown in FIG. 2, the voltage control unit 6 shown in FIG. 5 is configured by a circuit in which a capacitor Cs2 and a transistor Tr are connected in parallel, and the voltage command unit 7 is configured by a zener diode Dzb. can do.

  Also in such an embodiment, the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 can be set to [Erp = 2 × E2-Vzb]. Moreover, the peak value Erp is not affected by the output voltage Eo of the DC-DC converter. Therefore, even in the snubber circuit configured as described above, the effect of suppressing the peak value Erp of the voltage applied to the diodes D1 to D4 of the rectifier circuit 4 can always be exhibited.

  Next, FIG. 6 is a schematic circuit diagram showing a DC-DC converter which is another embodiment of the power conversion device according to the present invention. In the DC-DC converter shown in FIG. 6, the transformer T, which is a component of the DC-DC converter shown in FIG. 2, is replaced with a transformer Ta having a center tap on the secondary side. Further, the full-bridge rectifier circuit 4 composed of the diodes D1 to D4 is replaced with a rectifier circuit 4a composed of the diodes D1 and D3.

  Here, the diode D1 of the rectifier circuit 4a is connected to the secondary winding W21 of the transformer Ta, and the diode D3 of the rectifier circuit 4a is connected to the secondary winding W22. One end of the smoothing circuit on the smoothing inductor L side is connected to the connection point between the diodes D1 and D3 of the rectifier circuit 4a, and the smoothing circuit is connected to the series connection point (reference point N) of the secondary windings W21 and W22 of the transformer Ta. One end of the smoothing capacitor C is connected. Further, leakage inductances Le1 and Le2 exist in the secondary winding of the transformer Ta.

  In the DC-DC converter thus configured, a series circuit in which a capacitor Cs1 and a diode Ds1 are connected in series and a circuit in which a capacitor Cs2 and a transistor are connected in parallel are connected in series is connected in parallel with the smoothing circuit. The rectifier circuit 4a is connected between the connection point of the diodes D1 and D3 and the reference point N. The diode Ds2 is connected between the connection point of the capacitor Cs1 and the diode Ds1 and the connection point of the smoothing inductor L and the smoothing capacitor C. Further, a Zener diode Dzb is connected between the base terminal B of the transistor Tr and a connection point between the smoothing inductor L and the smoothing capacitor C.

  By the way, when the electromotive force E21 rises in the secondary winding W21 of the transformer Ta, the snubber circuit includes the secondary winding W21 of the transformer Ta → the diode D1 of the rectifier circuit 4a → the capacitor Cs1 → the smoothing capacitor C → the transformer. A current flows through the path of the Ta secondary winding W21. When the electromotive force E22 rises in the secondary winding W22 of the transformer Ta, the snubber circuit includes a secondary winding W22 of the transformer Ta → the diode D3 of the rectifier circuit 4a → the capacitor Cs1 → the smoothing capacitor C → the transformer. A current flows through the path of the Ta secondary winding W22.

  Therefore, in the embodiment shown in FIG. 6, as in the embodiment shown in FIG. 2, the peak value of the voltage applied to the diodes D1 and D3 of the rectifier circuit 4a by applying the snubber circuit according to the present invention. Erp can always be suppressed to [2 × E21 (E22) −Vzb].

  In the embodiment according to the present invention described above, the transistor Tr is connected in parallel to the capacitor Cs2. However, it is not necessary to connect the transistor Tr in parallel with the capacitor Cs2, and a control terminal such as a MOSFET or IGBT is used. And a switch element that can be switched between a conductive state and a non-conductive state by a signal input to the control terminal.

  In the embodiment described above, the inverter 2 is described as a full bridge, but the inverter 2 may be a half bridge. When the inverter 2 is a half bridge, the power source 1 is divided into two.

  FIG. 7 is a schematic circuit diagram showing a DC-DC converter which is still another embodiment of the power conversion device according to the present invention. The DC-DC converter shown in FIG. 7 is called a one-stone DC-DC converter. The inverter 2 composed of MOSFETs (Q1 to Q4), which are components of the DC-DC converter shown in FIG. 2, is replaced with an inverter 2b composed of MOSFET (Q1). Further, the full-bridge rectifier circuit 4 composed of diodes D1 to D4 is replaced with a rectifier circuit 4b composed of diodes D1 and D3.

  Here, one end of the primary winding of the transformer T is connected to one end of the DC power source 1, and the other end is connected to the other end of the DC power source 1 through a MOSFET (Q1). The rectifier circuit 4b is composed of a series circuit of a diode D1 and a diode D3, and is connected to the secondary winding W2 of the transformer T. A leakage inductance Le exists in the secondary winding W2 of the transformer T. A smoothing circuit composed of a series circuit of a smoothing inductor L and a smoothing capacitor C is connected to both ends of the diode D3 of the rectifier circuit 4b. The load 5 is connected to both ends of the smoothing capacitor C of the smoothing circuit.

  In addition, a series circuit in which a capacitor Cs1 and a diode Ds1 are connected in series and a circuit in which a capacitor Cs2 and a transistor are connected in parallel is connected in series is connected in parallel to the smoothing circuit, at both ends of the diode D3 of the rectifier circuit 4b. Connected. Furthermore, the diode Ds2 is connected between the connection point of the capacitor Cs1 and the diode Ds1, and the connection point of the smoothing inductor L and the smoothing capacitor C. Further, a Zener diode Dzb is connected between the base terminal B of the transistor Tr and a connection point between the smoothing inductor L and the smoothing capacitor C.

  In the DC-DC converter configured as described above, when an electromotive force E2 is generated in the secondary winding W2 of the transformer T, the current charging the capacitor Cs1 is changed to the secondary winding W2 of the transformer T → the diode D1 → It flows through the path of the secondary winding W2 of the capacitor Cs1 → smoothing capacitor C → transformer T.

  Therefore, also in the embodiment shown in FIG. 7, the peak value Erp of the voltage applied to the diode D3 of the rectifier circuit 4b is obtained by applying the snubber circuit according to the present invention as in the embodiment shown in FIG. [2 × E2-Vzb] can be suppressed.

  The above-described embodiment of the power conversion device according to the present invention relates to a DC-DC converter that outputs a positive voltage. However, the present invention relates to power such as a DC-DC converter that outputs a negative voltage. The present invention can also be applied to a conversion device.

  Furthermore, the power conversion device according to the present invention is not limited to the above embodiment, and can be applied to a device that suppresses a surge voltage applied to a semiconductor element such as a diode due to leakage inductance. .

  DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2, 2b ... Inverter, 3 ... On-off control part, 4, 4a, 4b ... Rectifier circuit, 5 ... Load, 6 ... Voltage control part, 7 * ..Voltage command section, C ... smoothing capacitor, Cp1-Cp4 ... parasitic capacitance, Cs1, Cs2 ... capacitor, D1-D4 ... diode, Ds1, Ds2 ... diode, Dzb, Dzs ..Zener diode, L ... smooth inductor, Le ... leakage inductance, Ls ... inductor, Q1-Q4 ... MOSFET, T, Ta ... transformer, Tr ... transistor

Claims (6)

A rectifier circuit that rectifies and outputs an input voltage; and
A smoothing circuit in which a smoothing inductor and a smoothing capacitor are connected in series, and both ends thereof are connected between output terminals of the rectifier circuit;
Snubber circuit,
A power conversion device comprising:
The snubber circuit includes a series circuit in which at least a first capacitor, a first diode, and a voltage control unit having a control terminal are connected in series, and both ends thereof are connected between output terminals of the rectifier circuit;
A second diode connected between a series connection point of the first capacitor and the first diode of the series circuit and a series connection point of the smoothing inductor and the smoothing capacitor of the smoothing circuit;
One end of the voltage control unit is connected to the control terminal of the voltage control unit, and the other end is connected to the series connection point of the smoothing inductor and the smoothing capacitor.
Consists of
The voltage conversion unit includes a reference power supply. The voltage command unit, said rectifying circuit and a reference point connection point between the smoothing capacitor and the connection point between the first diode and the voltage control unit and the voltage control point, which may arise in the voltage control point Output the voltage as a command value,
The voltage control unit, as the voltage of the voltage control point with respect to the command value of the voltage command unit outputs match, according to claim 1, wherein adjusting the voltage of the voltage control point Power conversion device. The voltage command unit, a power converter according to the voltage obtained by subtracting a voltage of the reference power from the voltage of the smoothing capacitor to claim 2, characterized in that the command value to the voltage control unit.   4. The power converter according to claim 3, wherein the reference power source included in the voltage command unit generates a voltage that is substantially the same as a rated output voltage of the power converter as a reference voltage. 5.   The power conversion device according to claim 3, wherein the reference power supply included in the voltage command unit generates a voltage higher than a rated output voltage of the power conversion device as a reference voltage. The voltage control unit comprises a circuit in which a capacitor and a semiconductor switch element having a control terminal are connected in parallel,
The power converter according to any one of claims 1 to 5, wherein the voltage command unit includes a constant voltage element.