JPH0685632B2 - DC / DC converter - Google Patents

Description

The present invention relates to a DC / DC converter that obtains a DC output insulated from a DC power supply by using a high-frequency switching circuit, and in particular to a compact size without lowering conversion efficiency. The present invention relates to a conversion device capable of achieving the conversion.

[Conventional technology]

FIG. 3 is a block diagram of a conventional DC / DC converter device. In the figure, 2 is a high frequency switching circuit, 3 is a transformer, and 4 is
DC / A consisting of high frequency switching circuit 2 and transformer 3
C converter, L ₁ is the leakage inductance of the transformer 3, 5 is
A single-phase bridge rectifier circuit configured by bridge-connecting rectifying diodes 6 to 9 in which RC snubber circuits 10 to 13 in which a resistor R and a capacitor C are connected in series are respectively connected in parallel, and 14 is a smoothing reactor 15 A smoothing circuit including a smoothing capacitor 16 and a load 18 connected between the output terminals 17a and 17b of the smoothing circuit 14.

The high-frequency switching circuit 2 switches the DC voltage of the DC power supply 1 so as to alternately and periodically change a rectangular waveform on the positive side and the negative side with a predetermined rest period τ and a bipolar high-frequency AC. The voltage 2a is output to the primary side of the transformer 3. In addition, the single-phase bridge rectifier circuit 5 includes a transformer 3
The full-wave rectification is performed on the high-frequency AC voltage E ₂ that is the output of the transformer 3 and is connected to the secondary side of the. Further, the smoothing circuit 14 is connected to the single-phase bridge rectifier circuit 5, smoothes the output voltage of the single-phase bridge rectifier circuit 5, and outputs the smoothed DC voltage V to the output terminals 17a and 17b.

Here, the DC / DC converter 19 (hereinafter simply referred to as the converter 19) includes a DC / AC converter 4, a single-phase bridge rectifier circuit 5, and a smoothing circuit 14.

Next, the operation of the converter 19 will be described with reference to the waveform diagram of FIG. In the following description, the diodes 6-9
The voltage of each engraving layer in the above shall be ignored.

When the switching circuit 2 outputs the above-mentioned AC voltage 2a, the secondary side output voltage E ₂ of the transformer 3 has a waveform shown in FIG. Therefore, assuming that the voltage E ₂ becomes positive at time t1, the current I ₁ flows through the path 20 (diode 6 → smooth reactor 15 → load 18 → diode 9) shown by the alternate long and short dash line in the direction of the arrow. Next, when the voltage E ₂ becomes zero at time t2, the current I ₁ flowing in the secondary winding of the transformer 3 due to the buffering action of the smoothing circuit 14 commutates to all the diodes 6 to 9. , The diodes 6 to 9 are connected to the path 20 immediately before the time t2.
The magnitude of the current I ₁ | I ₁ |
During the period up to, ie, the dwell time τ, the conduction current of each diode decreases with time.

When the voltage E ₂ becomes negative at time t3, the path shown by the dotted line
A current I ₂ flows through 21 (diode 8 → smoothing reactor 15 → load 18 → diode 7) in the direction of the arrow. In the following, the current I ₁ flows through the path 20 in the direction of the arrow and the current I ₂ flows through the path 21 in the direction of the arrow, and unless otherwise specified, the diodes 6 and 9 and the diodes 7 and 8 are used. The currents that flow through are simply referred to as current I ₁ and current I ₂ .

At this time, under the influence of the leakage inductance L ₁ of the transformer 3, the current I ₁ decreases at the posted rate of change of E ₂ / L ₁ , and at the same time the current I ₂ rises at the same rate of change. The current I ₁ continues to decrease and eventually becomes zero, and further decreases (increases in the opposite direction). At time t4, the reverse recovery peak value I of the diodes 6 and 9 is increased.
reach rrp. The current I _{1 that} has reached the reverse recovery peak value Irrp decreases the current amount in the field within a short time, and at time t5.
Since I ₁ = 0, the diodes 6 and 9 reversely recover.

Since the current I ₁ changes as described above after the time t3, the current I ₂ changes as shown in the fourth (b) in order to compensate for this temporal change. Thereafter, E ₂ the current I ₁ until zero continues zero at time t6, the current I ₂ is the same change as the current I ₁ between time t1 to t2.

The output of the single-phase bridge rectifier circuit 5 shown in FIG.
The current shown in FIG. 4D is supplied to the load 18 via the smoothing circuit 14.

Next, the DC voltage generated at the terminals 17a and 17b will be described with reference to FIG.

FIG. 4C shows the voltage E with the anodes of the diodes 6 to 9 as reference potentials, and the change over time in the voltage across each of the diodes 6 and 9 is shown by the solid line 23. Dash-dot line 24
It is shown in.

For example, the current I ₁ with time rate of change of the current I ₁ is rapidly reversed at time t4, the smoothing reactor 15, it is not possible to flow the to path through the smoothing capacitor 16 and load 18,
Each of the diodes 6 and 9 may be destroyed by the pulse-like high voltage (E ₂ + ΔE) shown in FIG. This pulsed voltage 22
Appears immediately after time t4, but when the diodes 6 and 9 reversely recover and I ₁ = 0, the rising voltage ΔE of the pulsed voltage 22 disappears and E of the waveform 23 becomes equal to E ₂ .

It is obvious that the waveform 24 has the same shape as the waveform 23, and 25 is the waveform 24 corresponding to the pulsed voltage 22.
Is a pulsed voltage in.

As described above, the diode 6 is operated by the operation of the conversion device 19.
A pulsed voltage is applied to ~ 9, and if this voltage exceeds the allowable value of the diode, the diode will be destroyed. Therefore, to suppress the pulsed voltage below the allowable value, use a series circuit of a resistor and a capacitor. Become a snubber circuit 10 ~ 13
Is connected in parallel with the diode.

[Problems to be solved by the invention]

The snubber circuits 10 to 13 shown in FIG. 3 have the electromagnetic energy (1/2) · Ll generated in the leakage inductor Ll by the reverse recovery current flowing through the diodes 6 to 9 in order to achieve the above-mentioned object.
Since (Irrp) ² is absorbed by the capacitor C, and as a result, the jump voltage ΔE applied to the diodes 6 to 9 is set to be equal to or less than the allowable value (ΔE) a of the voltage,
In this case, the value of C is determined so as to satisfy the expression (1).

(1/2) ・ Ll ・ (Irrp) ² = (1/2) ・ C ・ {(ΔE)
a} ² × 2 (1) Therefore, in the converter 19, it is unavoidable that an energy loss of C · {ΔE) a} ² occurs in the resistor R for each period T shown in FIG. Since the voltage {E ₂ + (ΔE) a} described above is applied to each of the snubber circuits 10 to 13, in FIG. 3, the energy loss Pr shown in (2) at each cycle T is equal to that of the resistance R. It will occur in each.

Pr = C · {E ₂ + (ΔE) a} ² (2) Then, in this case, in general, (ΔE) a << E ₂ , so that a DC / DC converter is used as shown in FIG. When configured, a large power loss Pr will occur. Therefore, in the converter 19, it is necessary to reduce this power loss, but for that purpose, the value of the resistor R must be increased to reduce the charging / discharging current to the capacitor C, so that in the end, the DC / DC converter. 1
9 has a problem that the snubber circuit and hence the conversion device become large in size in an attempt to improve the power conversion efficiency.

An object of the present invention is to guide the energy generated in the above-mentioned leakage inductance to the load of the DC / DC converter without passing through the above-mentioned resistor R, thereby achieving the downsizing of the converter without lowering the conversion efficiency. To do.

In order to solve the above-mentioned problems, according to the present invention, the output voltage of a DC power supply is opened and closed to output a periodic bipolar bipolar pulsed AC voltage to the power supply by insulating it from the power supply. DC / AC conversion unit, a single-phase bridge rectifier circuit that full-wave rectifies the AC voltage, and an output voltage of the single-phase bridge rectifier circuit is smoothed, and the smoothed DC voltage is output between both output terminals. In a DC / DC converter comprising a smoothing circuit, and a DC CD snubber circuit to which the output voltage of the single-phase bridge rectifying circuit is applied, which consists of a diode and a capacitor connected in series to the cathode of the diode, It is connected between the diode and the capacitor of the series CD snubber circuit and the DC voltage output terminal, and is opened and closed in synchronization with the AC voltage to smooth the DC voltage across the capacitor. It shall constitute the DC / DC converter includes a DC chopper circuit to be applied between the two output terminals and.

[Action]

When achieved as described above, the reverse rising voltage in each of the rectifying diodes forming the single-phase bridge rectifying circuit due to the leakage inductance of the transformer, which occurs during the reverse recovery, does not pass through the resistor. Then, the capacitor of the series CD snubber circuit absorbs the energy, and then the energy absorbed by this capacitor is discharged to the output terminal with a small current value through the series chipper circuit and supplied to the load connected to the output terminal. Therefore, it is possible to obtain the DC / DC conversion device in which the power loss generated in the snubber resistance described above is eliminated and the conversion efficiency is not reduced. Further, in this case, since there is no snubber resistance, the conversion device can be downsized.

〔Example〕

FIG. 1 is a block diagram of an embodiment of the present invention. In the figure
Reference numeral 26 is a transformer having a secondary winding 26a and a tertiary winding 26b, and a DC / AC converter 27 is constituted by the transformer 26 and the high frequency switching circuit 2 shown in FIG. . 28 is a single-phase bridge rectifier circuit constructed by connecting diodes 6 to 9 in a bridge, 31 is a series CD snubber circuit consisting of a diode 29 and a capacitor 30 connected in series to the cathode of the diode 29, and a single-phase bridge is provided at both ends. The output voltage of the rectifier circuit 28 is applied and the diode 29 is connected in the opposite direction to the diodes 6-9.

Further, a series circuit of a MOSFET 32 and a smoothing reactor 33 is connected between a connection point of the diode 29 and the capacitor 30 of the series CD snubber circuit 31 and the output terminal 17a. MOSFET 32
A freewheeling diode 35 is connected between a connection point between the smoothing reactor 33 and the output terminal 17b, and a MOSFET 32, the smoothing reactor 33, the freewheeling diode 35, and a drive circuit 34 for the MOSFET 32 form a chopper circuit 36.

The drive circuit 34 of the MOSFET 32 operates by a voltage generated in the tertiary winding 26b of the transformer 26, and outputs a drive signal for opening and closing the MOSFET 32 in synchronization with the AC voltage E _2.
Output to 32. Since the MOSFET 32 opens and closes the voltage across the capacitor 30 of the series CD snubber circuit 31 in synchronization with the AC voltage E ₂ , the chopper circuit 36 applies a smooth DC output voltage to the output terminals 17a and 17b.

Here, the DC / DC converter 37 (hereinafter simply referred to as the converter 37) includes a DC / AC converter 27, a single-phase bridge rectifier circuit 28, a smoothing circuit 14, and a chopper circuit 36.

Next, the operation of the main part of the conversion device 37 will be described with reference to the waveform explanatory diagram of FIG.

Also in the converter 37, since the alternating voltage E ₂ which changes in a pulse shape of periodic bipolar polarity is applied to the single-phase bridge rectifier circuit 28, when E ₂ becomes positive, the diodes 6 and 9 are turned on, and
_{When 2} becomes negative, diodes 7 and 8 are turned on.

Here, when the diodes 6 and 9 are turned on at time t1, a rapidly changing reverse current flows in the diodes 7 and 8 through the leakage inductance L ₁ of the transformer 26. At this time, since the path passing through the smoothing reactor 15, the smoothing capacitor 16 and the load 18 has a large inductance, a rapidly changing current cannot flow and the diodes 7 and 8 reversely recover and at the same time, this current is a direct current snubber circuit 31. Commute to the path through. As a result, each of the diodes 7 and 8 has a fourth
A large pulse voltage in the opposite direction shown in FIGS. 22 and 25 is applied. Such a voltage is supplied to the smoothing circuit 14, but since the inductance of the smoothing reactor 15 is large and the current cannot be increased and the capacitor 30 is charged through the diode 29, the waveform of the output voltage Er of the rectifier circuit 28 is As shown in FIG. 2, when the diodes 6 and 9 are turned off at the time t3, the voltage Er exhibits the same temporal change as that described above.

When the diodes 7 and 8 are turned off at time t1, the voltage Er rises as shown in FIG. 2, so that the capacitor 30 is charged and the voltage Ec of the capacitor 30 rises. Since this voltage is applied to the diodes 6 to 9, if this value exceeds the allowable value of the diode, the diode will be destroyed.

However, the converter 37 includes a diode 29 and a capacitor 30.
The chopper circuit 36 is provided between the output terminal 17a and the connection circuit with the drive circuit 34, and the drive circuit 34 synchronizes with the output voltage of the tertiary winding 26b and outputs the signal for the chopper shown in FIG. Es is output. That is, the MOSFET 32 is configured to be in a conductive state when the signal Es is high and to be in a cutoff state when the signal Es is low.

After time t1, the capacitor 30 is charged via the diode 29, and at the same time as the capacitor voltage Ec rises, the control circuit 34 outputs the “high” chopper signal Es, and the current flows through the MOSFET 32 and the reactor 33 sequentially, and the capacitor 30 The electric charge stored in the load 18 is discharged to the load 18.

Then, at time t10, the voltage Er settles down to E ₂ , and the change over time in the voltage Ec across the capacitor 30 from time t1 to time t10 is as shown in FIG. _2, and at time t10 Ec = E ₂ Become. Further, at time t2, the voltage Er becomes zero and the chopper signal Es becomes low, so that the MOSFET 32 is cut off.
As a result, the current flowing through the reactor 33 circulates in the closed circuit composed of the reactor, the load 18, and the diode 35 and decreases. Therefore, the voltage Ec of the capacitor 30 is after time t2.
The value of E ₂ will continue. It is obvious that the waveform of the voltage Ec after the time t3 is similar to the waveform after the time t1.

In the converter 37, the voltage induced by the inductance Ll is absorbed by the capacitor 30 as described above, and therefore, in this case as well, the reverse voltage applied to each of the diodes 6 to 9 is the same as in the converter 19. To (E ₂ + Δ
It is obvious that the DC / DC converter can be suppressed to E), and the capacitance C _{1 of the} capacitor 30 is set so that the equation (3) is satisfied also in the converter 37. The breakdown of the diodes 6 to 9 is prevented.

C ₁ {Irrp / (ΔE) a} ² · Ll (3) Then, the power loss P generated in the case of FIG. 1 is the diode 29 during the period when the voltage is generated in the secondary winding 26a. , FET3
2, the loss due to the current flowing through the reactor 33 and the reactor 33 when no voltage is generated in the winding 26a,
In this case, the latter current can be suppressed to a very small current by the sum of the loss due to the current flowing through the load 18 and the diode 35. In this case, the former device has a conversion device in the path through which the current flows.
Since there is no resistance R as in 19, the converter 37
The loss P in 2 is extremely smaller than the loss 2Pr in the converter 19. Therefore, if the converter is configured as 37, the resistor R is not required, and therefore the converter can be downsized without lowering the power conversion efficiency.

〔The invention's effect〕

As described above, in the present invention, the output voltage of the DC power supply is opened / closed to output a cyclic bipolar bipolar pulsed AC voltage by insulating it from the DC power supply using a transformer and outputting the DC / A.
A C conversion unit, a single-phase bridge rectifier circuit that full-wave rectifies the AC voltage, and a smoothing circuit that smoothes the output voltage of the single-phase bridge rectifier circuit and outputs the smoothed DC voltage between both output terminals. , A series CD snubber circuit consisting of a diode and a capacitor connected in series to the cathode of the diode, to which the output voltage of the single-phase bridge rectifier circuit is applied, and the voltage across the capacitor is opened and closed in synchronization with the AC voltage. Then, the DC / DC converter was configured so as to include a DC chipper circuit that applies a smooth DC output voltage between both output terminals.

Therefore, when configured as described above, the reverse rising voltage in each of these diodes generated at the time of reverse recovery of each of the rectifying diodes constituting the single-phase bridge rectifying circuit due to the leakage inductance of the transformer,
The capacitor of the series CD snubber circuit is absorbed without passing through the resistor, and then the energy absorbed by this capacitor is discharged to the output terminal with a small current value via the series chipper circuit and connected to the output terminal and supplied to the load. Therefore, it is possible to obtain the DC / DC conversion device in which the power loss generated in the snubber resistance described above is eliminated and the conversion efficiency is not deteriorated. Further, in this case, since there is no snubber resistance, the conversion device can be downsized. Therefore, the present invention has an effect that the conversion device can be miniaturized without lowering the conversion efficiency.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a waveform explanatory diagram of a main part in FIG. 1, FIG. 3 is a configuration diagram of a conventional DC / DC converter, and FIG. It is a wave form explanatory drawing of the principal part in a figure. 1 …… DC power supply, 3,26 …… Transformer, 4,27 …… DC / AC converter, 5,28 …… Single-phase bridge rectifier circuit, 14 …… Smoothing circuit,
15 …… Smoothing reactor, 16 …… Smoothing capacitor, 17a, 17
b …… output terminal, 19,37 …… DC / DC converter, 29 …… diode, 30 …… capacitor, 31 …… serial CD snubber circuit,
36 …… DC chipper circuit, E ₂ …… AC voltage, V …… DC voltage, 10,11,12,13 …… RC snubber circuit.

Claims (1)

[Claims] 1. A DC / AC converter that opens and closes an output voltage of a DC power supply to output a periodic bipolar bipolar pulsed AC voltage while insulating it from the power supply using a transformer, and the AC. A single-phase bridge rectifier circuit for full-wave rectifying the voltage, a smoothing circuit for smoothing the output voltage of the single-phase bridge rectifier circuit and outputting the smoothed DC voltage between both output terminals, a diode and a diode DC consisting of a capacitor connected in series to the cathode and a series CD snubber circuit to which the output voltage of the single-phase bridge rectifier circuit is applied at both ends
In the / DC converter, it is connected between the connection point of the diode and the capacitor of the series CD snubber circuit, and the DC voltage output terminal, by opening and closing in synchronization with the AC voltage, the voltage across the capacitor A DC / DC converter comprising a DC chopper circuit for applying a smooth DC voltage between the output terminals.