JP3124921B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-D for obtaining a step-down, step-up or step-up / step-down DC voltage source from a DC input.
It relates to a C converter.

[0002]

2. Description of the Related Art Conventionally, DC-DC used in power supplies for electronic circuits, battery chargers, high power factor sine wave input rectifiers, and the like.
The converter shown in FIG. 5 was used. 1 is an input voltage source, 2 is a first switching element that turns on and off at a high frequency, 51 is a smoothing reactor that smoothes the output switched by the first switching element 2, 7
Is a smoothing capacitor, and 9 is a load connected to the output. Reference numeral 52 denotes a free-wheeling diode.

The operation of the DC-DC converter will be described with reference to FIG. Before time to, the first switching element 2 is turned on, and the load current Io flows from the input power supply 1 via the first switching element 2 and the smoothing reactor 51.

As shown in FIG. 6A, when the drive signal is turned off and the switching element 2 is turned off at time to, the current flowing through the first switching element 2 becomes 0 as shown in FIG. Then, the energy of the smoothing reactor 51 flows back to the load 9 via the free-wheeling diode 52 as shown in FIG.

When a driving signal is input at time t1 as shown in FIG. 6A and the first switching element 2 is turned on, the free-wheeling diode 52 is turned off as shown in FIG. 6E. At the same time, as shown in FIG. 6C, the current of the first switching element 2 increases, and the current flows to the load 9 via the smoothing reactor 51. At this time, a large surge current due to the reverse recovery of the free-wheeling diode 52 flows through the first switching element 2 as shown in FIG.

[0006]

When the first switching element 2 is turned off, the first switching element 2 is turned off.
As shown in FIG. 6B, a large dv / dt occurs, the surge voltage of the first switching element 2 increases, and the turn-off loss also increases. Further, when the first switching element 2 is turned on, a large surge current due to the reverse recovery of the free-wheeling diode 52 flows through the first switching element 2, so that the turn-on loss of the first switching element 2 increases. Further, there is a problem that electromagnetic noise generated from the converter due to the surge voltage and current is large. As a result, it is necessary to increase the voltage / current capacity of the switching element, the radiation fins, the noise filter, and the like, so that the efficiency is low.

[0007]

A DC-DC converter according to the present invention comprises a first switching element connected in series to an input voltage source and operating on and off at a high frequency, and a first switching element having an intermediate tap. A smoothing reactor for smoothing an output, a freewheeling diode connected to a winding winding of the smoothing reactor, and a saturable filter provided between the output of the first switching element and the smoothing reactor. A second switching element that is provided between the reactor and the output of the first switching element and the input voltage source, and that turns off and on when the first switching element turns on and off; A first diode and a first capacitor provided in anti-parallel, and a second diode provided in anti-parallel with the second switching element; Is obtained by a series circuit of a de the second capacitor and the first reactor and the third capacitor. Thereby, the first switching element and the second switching element operate with zero voltage switching both when turning on and when turning off. For this reason, switching loss is reduced and dV / dt is also reduced.

Also, a smoothing reactor connected in series to an input voltage source and having an intermediate tap, a saturable reactor connected to the intermediate tap of the smoothing reactor, an output of the saturable reactor and the input voltage source, And a second switching element, which is provided between the output of the saturable reactor and the load, and is turned on and off when the first switching element is turned on and off. A freewheeling diode connected between a winding winding of the smoothing reactor and a load; a first diode, a first capacitor, and a first reactor provided in anti-parallel with the first switching element. And a second circuit provided in anti-parallel with the second switching element. It is obtained by a capacitor. Thereby, the first switching element and the second switching element operate with zero voltage switching both when turning on and when turning off. For this reason, switching loss is reduced and dV / dt is also reduced.

A first switching element connected in series to an input voltage source and operating on and off at a high frequency; a saturable reactor connected to an output of the first switching element; an output of the saturable reactor; A second reactor provided between the output of the first switching element and a load, the second switching element being provided between the output of the first switching element and the load and being turned on / off when the first switching element is turned on / off; A switching element, a freewheeling diode connected between the winding winding of the smoothing reactor and the load, a first diode and a first capacitor provided in anti-parallel with the first switching element. A second diode and a second capacitor, and a first reactor and a third capacitor, which are provided in anti-parallel with the second switching element. It is obtained by a series circuit of the capacitor. Thereby, the first switching element and the second switching element operate with zero voltage switching both when turning on and when turning off. For this reason, switching loss is reduced and dV / dt is also reduced.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a DC-DC converter according to the present invention will be described with reference to FIGS. In FIG. 1, reference numeral 1 denotes an input voltage source, and 2 denotes a self-extinguishing first switching element which operates on and off at a high frequency, and is connected to one end A of the input voltage source 1. 3 is a saturable reactor connected to the output terminal C of the first switching element 2, 4 is a smoothing reactor having a tap P2, and the tap P2 is connected to the output terminal of the saturable reactor 3.
7 is a smoothing capacitor connected to the output terminal P1 of the output winding 5 of the smoothing reactor 4 and the other end of the input voltage source 1, and 9 is a DC
-A load connected to the output of the DC converter.

[0011] Further, 11 is connected between the output terminal C of the first switching element 2 and the other end B of the input voltage source 1,
A self-extinguishing second switching element 12 that operates on and off at a high frequency is a free-wheeling diode connected between the output end of the foot winding 6 of the smoothing reactor 4 and the other end B of the input voltage source 1. , 13 and 14 are a first diode and a first capacitor connected in anti-parallel with the first switching element 2, and 16, 17 are second switching elements 1
A second diode and a second capacitor connected in anti-parallel with the first diode. Reference numerals 21 and 22 denote a first reactor and a third capacitor which are connected in series and connected in a reverse row to the second switching element 11.

As shown in FIGS. 2A and 2B, a drive signal is applied to each of the switching elements 2 and 11, and when the drive signal is switched, the switching elements 2 and 11 are switched.
11 are both off, a short drive signal pause period tda, t
db is provided.

The operation will be described below. Immediately before the time to, a drive signal is input to the first switching element 2 and no drive signal is input to the second switching element 11 as shown in FIGS. 2A and 2B. As shown by the solid line in FIG. 2C, the first switching element 2 is turned on when the voltage across the first switching element 2 is 0,
As shown by the broken line in FIG. 2C, the voltage across the second switching element 11 becomes the voltage E of the input voltage source 1 and is turned off.

When the first switching element 2 is turned on,
Load 9 via input voltage source 1, first switching element 2, saturated saturable reactor 3, and smoothing reactor 4
Current is flowing through Also, an input voltage source 1, a first switching element 2, a first reactor 21, a third capacitor 2
2, the capacitor 17 is charged to the value of the voltage E of the input voltage source 1.

As shown in FIG. 2A, when the drive signal of the first switching element 2 is turned off at time to, the current flowing through the first switching element 2 is reduced to the first capacitor 1
4, the voltage across the capacitor 14, that is, the voltage across the first switching element 2 is as shown in FIG.
As shown by the solid line. Here, if the rise time of the voltage V2 across the first switching element 2 is selected to be longer than the turn-off time of the first switching element 2, the turn-off loss of the first switching element 2 becomes almost zero. .

On the other hand, the charge of the second capacitor 17 is discharged through the saturable reactor 3, the smoothing reactor 4, the load 9, the reactor 21, and the capacitor 22 as shown by a broken line in FIG. There is no loss due to the discharge of the charged charge.

Then, when the electric charge of the second capacitor 17 is discharged and the voltage across the second capacitor 17 becomes 0 at time t1 as shown in FIG. 2C, the second diode 16 is turned on and the first reactor is turned on. The energy stored in the first reactor 21 is released through the third capacitor 22 and the diode 16, and the current shown in FIG.
A current indicated by a broken line in FIG. Further, the smoothing reactor 4 accumulated when the switching element 2 is turned on.
As shown in FIG. 2 (g), the freewheeling diode 12 turns on the freewheeling diode 12, the secondary winding 6 of the smoothing reactor 4, and the output winding 5 as shown in FIG.
Through the load 9. Further, the saturable reactor 3 becomes unsaturated due to a decrease in the flowing current.

At time t2 when the diode 16 is on, a drive signal is input to the switching element 11 as shown in FIG. The current flowing out of the first reactor 21 and flowing through the diode 16 decreases as shown by the broken line in FIG. 2E, and when the current reaches 0, the switching element 11 is turned on and the current flows in the positive direction. The turn-on loss of the switching element 11 is zero. At this time, the capacitor 14 is clamped to the value of the voltage E of the input voltage source 1.

Then, as shown in FIG.
When the driving signal of the switching element 11 is turned off, a current flows from the reactor 21 to the input voltage source 1, the capacitor 14, and the capacitor 17, and the voltage across the capacitor 14 decreases as shown by the solid line in FIG. Capacitor 17
2 rises as shown by the broken line in FIG. Here, if the rise time of the voltage V11 across the capacitor 17 is set to be longer than the turn-off time of the switching element 11, the turn-off loss of the switching element 11 becomes almost zero.

On the other hand, the electric charge charged in the capacitor 14 is fed back to the voltage source 1, and the electric charge of the capacitor 14 is discharged through the voltage source 1, the capacitor 22, and the reactor 21. Also does not occur. Then, when the voltage between both ends of the capacitor 14 becomes 0, the diode 13 is turned on, and as shown in FIG.
1 flows through the diode 13, the voltage source 1, and the capacitor 22, and the saturable reactor 3 as shown in FIG.
As shown in (h), a voltage in the set direction is applied. However, the saturable reactor 3 is in an unsaturated state.

At time t5 when the diode 13 is on, a drive signal is input to the switching element 2 as shown in FIG. Even if the switching element 2 is turned on,
The saturable reactor 3 is still in an unsaturated state, and a load current flows through the load 9 from the smoothing reactor 4 via the freewheeling diode 12 as shown in FIG.

When the magnetic flux level of the saturable reactor 3 rises and reaches saturation at time t6 as shown in FIG. 2B, the free-wheeling diode 12 is turned off,
The load current Io is supplied to the load 9 via the input voltage source 1, the switching element 2, the saturable reactor 3, and the smoothing reactor 4.
Flows to Since the drive signal has already been applied to the switching element 2, the switching element turns on at zero voltage. The current of the reactor 21 includes a saturable reactor 3, a smoothing reactor 4, a load 9, and a capacitor 2.
After flowing down through the switching element 2, the current flows through the switching element 2 from the input voltage source 1.
One cycle ends at 7.

Since the switching element 2 and the second switching element 11 operate at zero voltage switching both at the time of turn-on and at the time of turn-off, the switching loss can be extremely reduced. Further, since dv / dt of the switching element 2 and the auxiliary switching element 11 is also reduced, the generation of electromagnetic noise is suppressed.

Note that the period during which the saturable reactor 3 needs to prevent conduction of the switching element 2 may be sufficiently small with respect to the switching cycle, so that the capacity of the saturable reactor can be reduced. Further, the current ip flowing through the reactor 21 due to the function of the saturable reactor may be sufficiently smaller than the load current Io, so that the current capacity of the reactor 21, the second switching element 11, and the diode 16 is also the current capacity of the switching element 2. Can be made extremely small. Further, although the load current Io and the current ip of the reactor 21 flow through the switching element 2, the current ip of the reactor 21 is sufficiently smaller than the load current Io, so that the current capacity of the switching element is slightly larger than that of the conventional circuit. Only.

When MOSFETs are used for the switching element 2 and the second switching element 11, the capacitors 14 and 17 can use the junction capacitances of the MOSFETs, and the diodes 13 and 16 can be used as the MOS FETs, respectively.
Internal diodes are available. Further, the saturable reactor can realize zero-voltage switching with a small capacity, and the miniaturization and high efficiency of the radiation fin, the noise filter and the like can be obtained.

The output of the converter can be controlled by changing the duty ratio D (DT / T) shown in FIG.
When a low voltage is output, if a MOSFET is used instead of the free-wheeling diode 12, the on-state voltage is reduced and the loss is reduced as compared with the diode.

In the embodiment of FIG. 1, a DC-DC converter for obtaining a step-down DC voltage source has been described. However, an embodiment of a DC-DC converter for obtaining a step-up DC voltage source is shown in FIG. Shown in That is, the smoothing reactor 4 having an intermediate tap connected in series to the input voltage source E, the saturable reactor 3 connected to the intermediate tap P2 of the smoothing reactor 4, the output of the saturable reactor 3, and the input voltage source And a first switching element 2 provided between the output of the saturable reactor 3 and the load.
A second switching element 11 that is turned on and off when the power supply is turned on and off, and a free-wheeling diode 12 that is connected between the foot winding 6 of the smoothing reactor 4 and the load 9.
A first diode 13 and a first capacitor 14 provided in anti-parallel to the first switching element 12 and a series circuit of the first reactor 21 and the third capacitor 22;
A second diode 16 and a second capacitor 17 provided in anti-parallel with the switching element.

The DC-DC converter shown in FIG.
Similar to the DC-DC converter described above, the operation of the second switching element is made to correspond to the first switching element, and the same operation can be performed by performing on / off operation.

Also, a DC for obtaining a step-up / step-down DC voltage source
FIG. 4 shows an embodiment of a DC converter. That is, a first switching element 2 connected in series to the input voltage source E and operating on and off at a high frequency, a saturable reactor 3 connected to an output of the first switching element 2, an output of the saturable reactor 3 and an input A smoothing reactor 4 provided between the output of the first switching element 2 and the load, and a second reactor which is provided between the output of the first switching element 2 and the load and is turned on and off when the first switching element 2 is turned on and off; A switching element 11, a freewheeling diode 12 connected between the winding winding 6 of the smoothing reactor 4 and the load 9, a first diode 13 provided in anti-parallel with the first switching element 12, The first capacitor 14, the second diode 16 and the second capacitor 17 provided in anti-parallel with the second switching element, and the first reactor 2 When and a series circuit of a third capacitor 22.

The DC-DC converter shown in FIG.
Similar to the DC-DC converter described above, the operation of the second switching element is made to correspond to the first switching element, and the same operation can be performed by performing on / off operation.

[0031]

According to the DC-DC converter of the present invention, the switching operation is performed at zero voltage switching both at the time of turn-on and at the time of turn-off, so that the switching loss can be extremely reduced. Also, dv / dt of the switching element
Therefore, generation of electromagnetic noise is suppressed. As a result, the radiation fins and the noise filter can be reduced in size and have a high power factor.

The period during which the additional saturable reactor also needs to prevent conduction of the first switching element is:
Since the switching period may be sufficiently small, the capacity can be reduced. Further, since the current flowing through the reactor 21 can be made sufficiently smaller than the load current,
The second switching element and the first and second diodes can also be made small in capacity.

The first and second switching elements have M
When the OSFET is used, the junction capacitance of the MOSFET can be used for the first and second capacitors, and an internal diode can be used for the diode. Further, the saturable reactor can perform zero voltage switching, and can reduce the size of the radiation fin and the noise filter.

[Brief description of the drawings]

FIG. 1 is a schematic connection diagram of an embodiment of a DC-DC converter of the present invention.

FIG. 2 is a timing chart of each unit in FIG.

FIG. 3 is a schematic connection diagram of another embodiment of the DC-DC converter of the present invention.

FIG. 4 is a schematic connection diagram of another embodiment of the DC-DC converter of the present invention.

FIG. 5 is a schematic connection diagram of a conventional DC-DC converter.

FIG. 6 is a time chart of each unit in FIG. 5;

[Explanation of symbols]

 Reference Signs List 1 input voltage source 2 (first) switching element 3 saturable reactor 4 smoothing reactor 9 load 11 (second) switching element 13 (first) diode 14 (first) capacitor 16 (second) diode 17 (second 2) Capacitor 21 (first) reactor 22 (third) capacitor

Claims (3)

(57) [Claims] 1. A first switching element connected in series to an input voltage source and operating on and off at a high frequency, a smoothing reactor having an intermediate tap for smoothing an output of the first switching element, and a smoothing reactor. A free-wheeling diode connected to the winding of the winding, a saturable reactor provided between the output of the first switching element and the smoothing reactor, the output of the first switching element, A second switching element that is provided between the input voltage source and that is turned on and off when the first switching element is turned on and off, a first diode provided in antiparallel to the first switching element, and a first diode.
A capacitor, a second diode and a second capacitor provided in antiparallel with the second switching element, and a first diode.
D having a series circuit of a reactor and a third capacitor
C-DC converter. 2. A smoothing reactor having an intermediate tap connected in series to an input voltage source, a saturable reactor connected to an intermediate tap of the smoothing reactor, an output of the saturable reactor, and the input voltage source. A first switching element provided between the first switching element and an on / off operation at a high frequency;
A second switching element that is provided between the output of the saturable reactor and the load and that is turned off and on when the first switching element is turned on and off, and between a winding foot winding of the smoothing reactor and the load; A connected freewheeling diode, a series circuit of a first diode and a first capacitor, and a first reactor and a third capacitor provided in antiparallel with the first switching element; A DC-DC converter comprising a second diode and a second capacitor provided in parallel. 3. A first switching element connected in series to an input voltage source and operating on and off at a high frequency, a saturable reactor connected to an output of the first switching element, an output of the saturable reactor, A smoothing reactor having an intermediate tap provided between the input voltage source,
A second switching element that is provided between the output of the first switching element and the load and that is turned on and off when the first switching element is turned on and off, and a winding foot winding of the smoothing reactor and the load. A free-wheeling diode connected therebetween, a first diode and a first capacitor provided in antiparallel with the first switching element, and a second diode provided in antiparallel with the second switching element. DC-DC comprising a second capacitor and a series circuit of a first reactor and a third capacitor
converter.