JPH06311743A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To make it possible to convert input to output and reversely convert output to input, by using a control circuit for turning on and off a pair of first and third switching elements and a pair of second and fourth switching elements alternately and converting a voltage into a different level from a DC power supply. CONSTITUTION:A control circuit 34 is used for turning on and off a pair of MOSFETs 21 and 30 and a pair of MOSFETs 22 and 31 alternately with a given interruption in between. Then, the MOSFETs 21, 22, 30 and 21 have each sine-wave drain current, and each rise and fall waveform of a voltage between drain and source becomes a part of sine wave. In this way, a harmonic factor is reduced and switching noises are lowered. An overlapped current waveform with a voltage waveform is also reduced so that zero-current and zero-voltage switching is realized with a small loss in switching. Moreover, since a converted DC voltage is different from a DC power supply, input/output two-way conversion can be carried out in operation.

Description

Detailed Description of the Invention

The present invention relates to a DC-DC converter,
In particular, the present invention relates to a DC-DC converter capable of reducing switching noise and switching loss and capable of bidirectional operation.

[0002]

2. Description of the Related Art In a power supply circuit of an electronic device or the like, a DC voltage different from the voltage of a DC power supply may be required.
In this case, a DC-DC converter is generally used. In the conventional DC-DC converter shown in FIG. 6, the main switching element 3 and the diode 2 are connected in series at both ends of the primary winding of the transformer 4, and the intermediate point of the primary winding of the transformer 4 and the main switching element. 3 is connected to the connection point of the diode 2 and the DC power source 1 is connected to the secondary winding of the transformer 4 and a rectifying circuit including the rectifying diodes 5 and 6 and a smoothing circuit including the smoothing reactor 7 and the smoothing capacitor 8 are connected. The load 9 is connected through the load. The DC-DC converter is a so-called forward type converter, and the main switching element 3 is turned on / off by a rectangular wave to convert the DC voltage of the DC power supply 1 into a rectangular wave AC voltage, which is stepped up or down by the transformer 4. After that, a rectangular wave AC voltage is converted into a pulsating voltage by a rectifying circuit including rectifying diodes 5 and 6, and a ripple circuit of the pulsating voltage is removed by a smoothing circuit including a smoothing reactor 7 and a smoothing capacitor 8 to boost or The reduced DC voltage is supplied to the load 9. DC-
FIG. 8 shows a conventional uninterruptible power supply device as an application example of the DC converter. The uninterruptible power supply system of FIG.
The DC-DC converter 13 supplies the necessary DC voltage to the load 9, and the changeover switches 14 and 15 are connected to the a and a'sides to operate the charging DC-DC converter 16 at all times. The battery 17 is maintained in a fully charged state. Further, when the commercial power source 10 is out of power, the changeover switches 14 and 15 are changed over to the b and b ′ sides to operate the discharge DC-DC converter 18, and the battery 17
Of the DC power to the smoothing circuit 12, and the DC-DC converter 13 continues to supply the DC voltage required to the load 9. DC-D used in the uninterruptible power supply system of FIG.
As the C converters 13, 16 and 18, a flyback type DC-DC converter as shown in FIG. 7 may be used instead of the forward type DC-DC converter shown in FIG.

[0003]

By the way, in the DC-DC converters shown in FIGS. 6 and 7, the main switching element 3 is used.
Is operated with a rectangular wave, there is a lot of switching noise, and since the current waveform and the voltage waveform of the main switching element 3 often overlap, there is a drawback that switching loss increases. In particular, the flyback type DC-D of FIG.
In the C converter, since the switching current of the main switching element 3 has a triangular waveform, the forward type D shown in FIG.
The switching loss is larger than that of the C-DC converter. Further, in the DC-DC converters of FIGS. 6 and 7, since the input side and the output side are uniquely determined by the rectifying diodes 5 and 6, reverse operation from the output side to the input side is impossible. Therefore, when the DC-DC converters of FIGS. 6 and 7 are used in the uninterruptible power supply device shown in FIG. 8, for example, charging and discharging DC-DC converters 16 and 18 for charging and discharging the battery 17 are used. Needed. In addition, the changeover switch 1 is used to change over these operations.
I also needed 4, 15. Therefore, the uninterruptible power supply has a drawback that the device configuration is complicated and maintenance and inspection are complicated.

In view of this, the present invention is a DC capable of reducing switching noise and switching loss and capable of bidirectional operation.
-To provide a DC converter.

[0005]

DC-DC according to the present invention
The converter has a first and a second terminal across a DC power source or a load.
Connecting a series circuit of switching elements, and connecting a series circuit of first and second voltage dividing capacitors in parallel with the series circuit, connecting points of the first and second switching elements and the first and second switching elements. A series circuit of a primary winding of the transformer and a resonance reactor is connected between the connection point of the voltage dividing capacitor of No. 2 and the third and fourth ends of the secondary winding of the transformer.
Connecting a series circuit of switching elements, and connecting a load or a DC power supply between a connection point of the third and fourth switching elements and an intermediate point of the secondary winding, and connecting the load or the DC power supply. The smoothing capacitor is connected in parallel, and the first
A control circuit for providing a control signal to each of the control terminals of the fourth switching element is provided, and the control circuit alternately turns on the first and third switching elements and the second and fourth switching elements. -It is turned off to convert into a DC voltage of a level different from the voltage of the DC power supply.
In the embodiment of the present invention, first and second resonance capacitors are respectively connected in parallel with the first and second switching elements, and third and fourth resonance elements are connected in parallel with the third and fourth switching elements. The resonance capacitors of the
The first and second rectifying elements are connected in parallel with the second and second voltage dividing capacitors, respectively. The transformer may also function as the resonance reactor.

[0006]

The waveform of the switching current flowing through each switching element when each switching element is in an on-state has a sinusoidal waveform due to the series resonance of each voltage dividing capacitor and the resonance reactor. Further, the switching voltage waveform applied to each switching element when each switching element is in the off state has a rising and a falling part of a sine wave due to series resonance of each resonance capacitor and each winding of the transformer. Therefore, switching noise can be reduced.
Moreover, since there is little overlap between the current waveform and the voltage waveform of each switching element, the switching loss can be reduced. In addition, since the control circuit alternately turns on and off the first and third switching elements and the second and fourth switching elements to convert into a DC voltage of a level different from the voltage of the DC power supply, A reverse operation of converting a DC voltage from the output (load) side to the input (DC power supply) side is also possible, and bidirectional operation is possible.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a DC-DC converter according to the present invention will be described below with reference to FIGS. However, in FIGS. 1 and 3 to 5, parts that are substantially the same as the parts shown in FIGS. 6 to 8 are given the same reference numerals, and descriptions thereof will be omitted. As shown in FIG. 1, the DC-DC converter of the present embodiment is
A series circuit of first and second MOS-FETs 21 and 22 as first and second switching elements is connected to both ends of the DC power supply 1, and the first and second MOS-FETs 21 and
A series circuit of the first and second voltage dividing capacitors 23 and 24 is connected in parallel with the series circuit of 22, and the first and second M
First and second resonance capacitors 25 and 26 are connected in parallel with the OS-FETs 21 and 22, respectively. Each MOS
-Connection points of FETs 21 and 22 and each voltage dividing capacitor 2
The primary winding 4 of the transformer 4 is connected between the connection point of 3 and 24.
A series circuit of a and the resonance reactor 27 is connected. Further, the first voltage dividing capacitors 23 and 24 are connected in parallel with each other.
Further, the first and second diodes 28 and 29 as the second rectifying element are connected to each other. The first and second diodes 28 and 29 are the first and second voltage dividing capacitors 2
This is to prevent reverse charging of Nos. 3 and 24. At both ends of the secondary winding 4b of the transformer 4, third and fourth MOS-FETs 30 as third and fourth switching elements,
31 series circuits are connected to each MOS-FET 30, 3
A load 9 is connected between the connection point of 1 and the intermediate tap of the secondary winding 4b, and a smoothing capacitor 8 is connected in parallel with the load 9. In addition, the third and fourth MOS-FET3
Third and fourth resonance capacitors 3 in parallel with 0 and 31
2, 33 are connected to each other. First to fourth MOS-
Each of the gate terminals of the FETs 21, 22, 30, 31 has M
A control circuit 34 for giving a control signal is connected to the gate terminals of the OS-FETs 21, 22, 30, 31. Each M
By applying a control signal to the gate terminals of the OS-FETs 21, 22, 30, 31, each MOS-FET 21,
22, 30, 31 can be turned on and off. Therefore, the control circuit 34 controls the first and third MOs.
S-FETs 21, 30 and second and fourth MOS-FETs 2
It is possible to alternately turn on and off 2 and 31 to convert into a DC voltage of a level different from the voltage of the DC power supply 1.

In the above configuration, the control signal voltage V _{GS 1} -V shown in FIGS. 2A to 2D is supplied from the control circuit 34 to the gate terminals of the first to fourth MOS-FETs 21, 22, 30, 31 respectively. V _GS4 is applied with a certain rest period to apply the first and third MOS-FETs 21 and 30 and the second and fourth MO-FETs.
The S-FETs 22 and 31 are alternately turned on and off. When the first and third MOS-FETs 21 and 30 are in the ON state and the second and fourth MOS-FETs 22 and 31 are in the OFF state, the first portion charged with a voltage half the voltage of the DC power supply 1 is charged. Energy is released from the pressure capacitor 23, and the first MOS-FET 21 and the resonance reactor 2
7. A current flows in the path of the primary winding 4a of the transformer 4.
The current at this time becomes a sine wave due to the series resonance of the first voltage dividing capacitor 23 and the resonance reactor 27. At the same time, a triangular wave having an upward slope is slightly superimposed as the exciting current of the transformer 4, so that the first MOS-FET 2
The drain current I _DS1 of No. 1 has a waveform as shown in FIG. Further, since the resonance current flows through the third MOS-FET 30 on the secondary side of the transformer 4, the third MOS-
The waveform of the drain current I _DS3 of the FET 30 is a half-cycle waveform of a sine wave as shown in FIG.

First and third MOS-FETs 21 and 30
Turns off, the primary and secondary windings 4 of the transformer 4
The energy accumulated in a and 4b is released, and the first diode 28, the first resonance capacitor 25, the resonance reactor 27, the path of the primary winding 4a, and the second winding are provided on the primary side of the transformer 4. A current flows in the path of the voltage dividing capacitor 24, the second resonance capacitor 26, the resonance reactor 27, and the primary winding 4a to generate a voltage across the primary winding 4a. In addition, current also flows on the secondary side of the transformer 4 and the secondary winding 4b.
A voltage develops across the At this time, series resonance occurs due to the first to fourth resonance capacitors 25, 26, 32, 33 and the windings 4a, 4b of the transformer 4, so that the first and third resonances are generated.
Drain-source voltages V _DS1 and V _{DS 3} of the MOS-FETs 21 and ₃₀ and the second and fourth MOS-FETs 22 and _{3 of}
The waveforms of the drain-source voltages V _DS2 and V _DS4 of No. 1 are the rising edges of the voltage waveforms as shown in FIGS. 2 (E) and 2 (F).
The waveform has a 1/4 cycle of a sine wave in the falling portion.

First and third MOS-FETs 21, 30
Drain-source voltage V _DS1 , V _DS3 of the second and fourth
The respective peak values of the drain-source voltages V _DS2 and V _DS4 of the MOS-FETs 22 and 31 are proportional to the voltage of the DC power supply 1. Further, as shown in each of FIGS. 2 (G), (H), (J), and (K), the first to fourth MOS-FETs 21, 22, 3,
The peak value of each of the drain currents I _{DS1 to} I _DS4 of 0 and 31 changes in proportion to the current I _O flowing through the load 9 shown in FIG.

As described above, in this embodiment, each MOS-F is
Drain currents I _{DS1 to} I of ET21, 22, 30, 31
Each waveform of _DS4 becomes sinusoidal, each MOS-FET21,
22, 30, 31 drain-source voltage V _{DS1 to} V
The rising and falling _edges of each _DS4 waveform become part of the sine wave. Therefore, harmonic components that cause noise are reduced, and switching noise can be reduced.
Further, since the current waveform and the voltage waveform of each of the MOS-FETs 21, 22, 30, 31 do not overlap each other, zero current and zero voltage switching (ZCS, ZVS) can be achieved, and the switching loss can be reduced. Further, although the third and fourth MOS-FETs 30 and 31 were conventionally composed of diodes in many cases, since the MOS-FET generally has a smaller forward voltage drop and consumes less power than the diode, the conversion efficiency is low. It becomes possible to raise. Further, the control circuit 34 causes the first and third MOS-
FETs 21, 30 and second and fourth MOS-FET2
Since 2 and 31 are alternately turned on and off to convert to a DC voltage of a level different from the voltage of the DC power supply 1, for example, the connection positions of the DC power supply 1 and the load 9 are exchanged, and the output (load 9) side A reverse operation in which a DC voltage is converted from the input to the input (DC power supply 1) side is also possible. That is, from the control circuit 34 to the first to fourth MOS-FETs 21, 22, 30, 31.
As long as the control signals shown in FIGS. 2 (A) to 2 (D) are applied to the gate terminals of, respectively, due to the voltage difference between the input side and the output side,
The circuit of FIG. 1 simply operates from the higher voltage side to the lower voltage side. It goes without saying that the output voltage of the circuit of FIG. 1 is determined by the turn ratio of the primary and secondary windings 4a and 4b of the transformer 4. Therefore, a DC that is capable of bidirectional operation
-A DC converter can be obtained.

The DC-DC converter of the present invention can be effectively used for an uninterruptible power supply, for example. FIG. 3 shows D of the present invention.
An uninterruptible power supply using a C-DC converter is shown.
The uninterruptible power supply of FIG. 3 is a DC-DC converter 16 for charging and discharging of the conventional uninterruptible power supply shown in FIG.
Instead of 8, the DC-DC converter 19 of the present invention is inserted. That is, since the DC-DC converter 19 of the present invention is capable of bidirectional operation, normally, the AC of the commercial power source 10 is rectified and smoothed by the rectifying circuit 11 and the smoothing circuit 12, and the DC-DC converter 13 applies the load 9 to the load 9. In addition to supplying the necessary DC voltage, the DC-DC converter 19 also supplies the DC voltage to the battery 17 to supply the battery 1
7 in a fully charged state, the DC voltage of the battery 17 is sent to the smoothing circuit 12 by the DC-DC converter 19 when the commercial power supply 10 is out of power, and the DC voltage required for the load 9 is supplied by the DC-DC converter 13. You can continue to supply. Therefore, the two DC-DC converters 16 and 18 for charging / discharging the battery 17, which are conventionally required, can be integrated into one. Also, two DC-DC converters 1
Changeover switch 14 for changing over the operations of 6 and 18,
Since 15 is also unnecessary, the device configuration of the uninterruptible power supply can be simplified, and labor saving such as maintenance and inspection can be achieved.

Next, FIG. 4 shows an example in which the DC-DC converter of the above embodiment is of the self-excited oscillation type. DC-D in FIG.
The C converter has the first and second M converters in the circuit of FIG.
First and second starting resistors 35 and 36 are connected between the gate and drain terminals of the OS-FETs 21 and 22, respectively, and the third and fourth MOS-FETs 30 and 3 are connected.
The third and fourth starting resistors 37 and 38 are respectively connected between the gate terminal and the drain terminal of each of the control circuit 34, and the control circuit 34 includes a saturable transformer 39 and capacitors 40 to 43.
The zener diodes 44 to 51 and the current limiting resistor 52 are used.

In the circuit of FIG. 4, when a DC voltage is supplied from the DC power supply 1, the first and second starting resistors 35,
A current flows through any one of the first and second MOS-Fs 36
Either ET21 or ET22 is turned on and the transformer 4
A voltage is generated in the primary winding 4a. This voltage is also applied to the winding 39a of the saturable transformer 39, and each winding 39b-3
An induced voltage is generated in 9e. When the first MOS-FET 21 is turned on, the first and third MOS-FETs 21,
A positive voltage is generated between the gate and the source of the MOS transistor 30, and the MOS-FETs 21 and 30 are simultaneously turned on by the positive feedback action, so that the second and fourth MOS-FETs 22 and 3 are connected.
A reverse voltage is generated between each gate and source of 1
The OS-FETs 22 and 31 are reverse-biased and at the same time hold the off state. Further, when the second MOS-FET 22 is turned on, the second and fourth MOS-FETs 22 and 31 are
Are simultaneously turned on by the positive feedback action, and the first and third MOS-FETs 21 and 30 are reverse-biased and simultaneously held off. When the ON state is maintained for a certain period of time, the magnetic flux of the saturable transformer 39 is saturated and the positive feedback disappears, and all the first to fourth MOS-FETs 21, 22, 30, 31 are turned off. At this time, each winding 4 of the transformer 4
Resonance voltage is generated in a and 4b, and after a lapse of a predetermined time, the polarities of the windings 39a to 39e of the transformer 4 are inverted and the saturable transformer 39 is released from the saturated state.
A reverse voltage is generated at. As a result, all MOS-
Two MOS-FETs that were already in the off state before the FETs were turned off were simultaneously turned on by the positive feedback effect, and two MOS-FETs that were in the on state before all the MOS-FETs were turned off. The FET is reverse biased and at the same time maintains the off state. After that, by repeating the above operation, the first and third MOS-FETs 21 and the second and fourth MOS-FETs 22 and 31 are alternately turned on and off. When the DC power supply 1 is provided on the load 9 side and the load 9 is provided on the DC power supply 1 side, the third and fourth MOS-Fs are connected by the third and fourth starting resistors 37 and 38.
Either ET30 or 31 is turned on, and the transformer 4
A voltage is generated in the secondary winding 4b and a voltage is induced in the primary winding 4a. After that, substantially the same operation as described above is repeated, and the first and third MOS-FETs 21 and the second and fourth MOS-FETs 21 are connected.
The MOS-FETs 22 and 31 are alternately turned on and off.

As described above, in the embodiment shown in FIG. 4, the first to the fourth MOS-38 are provided by the first to the fourth starting resistors 35 to 38.
One of the FETs 21, 22, 30, 31 is turned on and activated, and the saturation characteristic of the saturable transformer 39 is used to turn on / off the first to fourth MOS-FETs 21, 22, 30, 31. Since it is maintained, it is possible to freely start from the side having the voltage source from either the primary side or the secondary side of the transformer 4 without requiring a special auxiliary circuit (for example, a starting circuit, an oscillation circuit, etc.). . Further, in the circuit of FIG. 4, if the third and fourth starting resistors 37 and 38 are omitted, it is possible to start only from the primary side of the transformer 4, and the first and second starting resistors 35, If 36 is omitted, it can be started only from the secondary side of the transformer 4. That is, it is possible to easily limit the direction of activation depending on which side the activation resistor is added.

The DC-DC converter of the embodiment shown in FIG.
Like the embodiment of FIG. 1, it can be effectively used for the uninterruptible power supply device shown in FIG. For example, if the battery 17 (FIG. 3) is connected instead of the load 9 in FIG. 4 and the third and fourth starting resistors 37 and 38 are omitted, the circuit of FIG. 4 is shown in FIG. When it is used as the DC-DC converter 19 of the above, it can be started only from the commercial power supply 10 side without starting from the battery 17 side.
The energy of the battery 17 can be supplied to the load 9 (FIG. 3) in case of power failure.

The embodiment of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made. For example, in the above embodiment, MOS-FETs are used as the first to fourth switching elements.
However, other switching elements such as a junction field effect transistor (J-FET), a bipolar transistor, and an SCR (reverse blocking three-terminal thyristor) may be used. Further, the resonance reactor 27 of the above-described embodiment may also serve as the transformer 4 (for example, the leakage inductance of the transformer 4 is used as the resonance reactor 27). The first to fourth resonance capacitors may use the parasitic capacitance of MOS-FET. Further, the first and second diodes 28 and 29 and the third and fourth resonance capacitors 32 and 33 may be omitted. Further, as shown in FIG. 5, a starting circuit 53 may be connected between one end of the DC power supply 1 and the control circuit 34 in the circuit of the embodiment of FIG. 1 to form a separately excited DC-DC converter.

[0018]

As described above, according to the present invention, since a part of the current waveform and the voltage waveform of each switching element has a sine wave shape, the harmonic components that cause noise are reduced,
Switching noise can be reduced. Further, since there is little overlap between the current waveform and the voltage waveform of each switching element, zero current and zero voltage switching (ZCS,
ZVS) is achieved and switching loss can be reduced. Therefore, since the heat generation amount of each switching element can be reduced, it is possible to reduce the size of the fins for heat radiation and the like to reduce the size of the device. Further, since bidirectional operation is possible, when used as a DC-DC converter for charging and discharging a backup battery of an uninterruptible power supply, for example, two DC-DC converters required conventionally are combined into one. can do. Therefore, a changeover switch and a changeover circuit for changing over the operation of the two DC-DC converters are not required, so that it is possible to simplify the device configuration of the uninterruptible power supply and save labor such as maintenance and inspection. Becomes

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a DC-DC converter showing an embodiment of the present invention.

2 is a diagram illustrating a gate-source voltage and a drain-source voltage of each MOS-FET in FIG. 1 and each MOS-FE;
Waveform diagram showing the current and load current flowing through T

FIG. 3 is a block diagram showing an example in which the DC-DC converter of the present invention is applied to an uninterruptible power supply.

FIG. 4 is an electric circuit diagram showing an example in which the DC-DC converter of FIG. 1 is a self-excited oscillation type.

FIG. 5 is an electric circuit diagram showing an example in which the DC-DC converter of FIG. 1 is separately excited.

FIG. 6 is an electric circuit diagram showing a conventional example of a DC-DC converter.

FIG. 7 is an electric circuit diagram showing another conventional example of a DC-DC converter.

FIG. 8 is a block diagram showing a conventional uninterruptible power supply device.

[Explanation of symbols] 1. ． ． DC power supply, 4. ． ． Transformer, 4a. ． ． Primary winding, 4b. ． ． Secondary winding, 8. ． ． Smoothing capacitor,
9. ． ． Load, 21, 22, 30, 31 ,. ． ． First to fourth MOS-FETs (first to fourth switching elements), 23, 24. ． ． First and second voltage dividing capacitors 25, 26, 32, 33. ． ． First to fourth resonance capacitors, 27. ． ． Reactor, 28, 29. ． ．
First and second diodes (first and second rectifying elements), 34. ． ． Control circuit 35-38. ． ． First to fourth starting resistors, 39. ． ． Saturable transformer, 40-4
3. ． ． Capacitors, 44-51. ． ． Zener diode, 52. ． ． Current limiting resistor, 53. ． ． Start circuit

Claims (5)

[Claims] 1. A first and second device at both ends of a DC power supply or a load.
Connecting a series circuit of switching elements, and connecting a series circuit of first and second voltage dividing capacitors in parallel with the series circuit, connecting points of the first and second switching elements and the first and second switching elements. A series circuit of a primary winding of the transformer and a resonance reactor is connected between the connection point of the voltage dividing capacitor of No. 2 and the third and fourth ends of the secondary winding of the transformer.
Connecting a series circuit of switching elements, and connecting a load or a DC power supply between a connection point of the third and fourth switching elements and an intermediate point of the secondary winding, and connecting the load or the DC power supply. The smoothing capacitor is connected in parallel, and the first
A control circuit for providing a control signal to each of the control terminals of the fourth switching element is provided, and the control circuit alternately turns on the first and third switching elements and the second and fourth switching elements. A DC-DC converter which is turned off to convert into a DC voltage of a level different from the voltage of the DC power supply. 2. The DC-DC converter according to claim 1, wherein the first and second resonance capacitors are connected in parallel with the first and second switching elements, respectively. 3. The DC-DC converter according to claim 1, wherein the third and fourth switching capacitors are connected in parallel to the third and fourth switching elements, respectively. . 4. The DC-DC according to claim 1, wherein the first and second rectifying elements are connected in parallel with the first and second voltage dividing capacitors, respectively. Converter. 5. The DC-DC converter according to any one of claims 1 to 4, wherein the transformer also serves as the resonance reactor. [0001]