JP2604302Y2 - Resonant 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 switching regulator, and more particularly to a resonance type DC-DC converter.

[0002]

2. Description of the Related Art FIG. 10 is a circuit diagram showing an example of a conventional resonant DC-DC converter. 10, 1 and 0 are first and second DC power supplies, 2 and 3 are MOS-FETs as first and second switching elements, 4 and 5 are first and second resonance capacitors, 6 Is a transformer, 7 is a resonance reactor, 8 and 9 are rectifier diodes, 12 is a smoothing capacitor, 13 is a load, 14 and 15 are voltage dividing resistors, 16 is a reference voltage source, 17 is an operational amplifier, and 18 and 19 are photocouplers, respectively. Is a light emitting diode and a light receiving transistor, and 20 is a control circuit. The voltages of the first and second DC power supplies are the same. The voltage dividing resistors 14 and 15 constitute a voltage detection circuit, and include a reference voltage source 16 and an operational amplifier 1.
7, the light emitting diode 18 and the light receiving transistor 19 constitute an error amplifier circuit. The control circuit 20 applies a control pulse signal whose pulse width changes according to the terminal voltage of the load 13 to each gate terminal of the first and second MOS-FETs 2 and 3 by providing a certain pause period (dead time). The first and second MOS-FETs 2 and 3 are alternately provided so as to alternately turn on and off.

Next, the operation of the circuit shown in FIG. 10 will be described. The control circuit 20 applies the control pulse signals V _G1 and V _G2 shown in FIGS. 11A and 11B to a certain dead time t.
_D is provided and applied to the gate terminals of the first and second MOS-FETs 2 and 3, respectively.
3 are alternately turned on and off. First MOS-FE
When T2 is turned on, the voltage of the first DC power supply 1 is applied to the primary winding 6a of the transformer 6 through the resonance reactor 7, and a voltage is induced in the first secondary winding 6c. At the same time, energy is stored in the resonance reactor 7.
At this time, a current flows through the path of the rectifier diode 8 and the smoothing capacitor 12 due to the voltage induced in the first secondary winding 6c. At this time showing a waveform of the current I _Q1 flowing through the first MOS-FET2 in FIG. 11 (C). As shown in FIG. 11A, after the time T ₁ has elapsed, the first MOS-FET 2
Is turned off, the energy stored in the resonance reactor 7 is released during the ON period of the first MOS-FET 2. At this time, voltage resonance mainly occurs by the resonance reactor 7 and the first and second resonance capacitors 4 and 5, and the voltage V _Q1 across the first MOS-FET 2 is reduced as shown in FIG.
It rises in a sine wave shape as shown in FIG. As a result,
Since the overlap between the waveform of the voltage V _Q1 shown in FIG. 11 (E) and the waveform of the current I _Q1 shown in FIG. 11 (C) is reduced, the first MO
Zero voltage switching (ZVS) at the ON / OFF transition period of the S-FET 2 becomes possible. Further, the voltage V _Q2 across the second MOS-FET 3 is reduced by the voltage resonance as shown in FIG.
It descends in a sine wave shape as shown in FIG.

A second MOS-FET 3 shown in FIG.
When the voltage V _Q2 across the two terminals reaches 0 V, the second MOS-
When the FET 3 is turned on, the voltage of the second DC power supply 0 is applied to the primary winding 6a of the transformer 6 through the resonance reactor 7 in a polarity opposite to that of the previous case, and the voltage is applied to the second secondary winding 6d. Induced. At the same time, energy is stored in the resonance reactor 7. At this time, the second secondary winding 6d
A current flows through the path of the rectifier diode 9 and the smoothing capacitor 12 by the voltage induced in the rectifier diode 9 and the smoothing capacitor 12. At this time, the second M
The waveform of the current I _Q2 flowing through the OS-FET 3 shown in FIG. 11 (D). As shown in FIG. 11 (B), when the second MOS-FET 3 is turned off after the T ₁ is the time elapsed, the second MO
Energy stored in the resonance reactor 7 is released during the ON period of the S-FET 3. At this time, voltage resonance mainly occurs by the resonance reactor 7 and the first and second resonance capacitors 4 and 5, and the second MOS-FET
The voltage V _Q2 at both ends of S3 rises in a sine wave shape as shown in FIG. As a result, the voltage V _Q2 shown in FIG.
11D and the waveform of the current _IQ2 shown in FIG. 11D are reduced, so that zero voltage switching (ZVS) can be performed during the on / off transition period of the second MOS-FET 3. In addition, the first MOS-FET 2
The voltage V _Q1 across both ends falls in a sine wave shape as shown in FIG. Then, the voltage V _Q1 shown in FIG.
When the voltage reaches V, the first MOS-FET 2 is turned on again.

By repeating the above operation, the first and second
Is converted to another DC voltage.
This DC voltage is further smoothed by the smoothing capacitor 12 and supplied to the load 13. The smoothed DC voltage is divided by the dividing resistors 14 and 15, and the divided voltage is compared with the voltage of the reference voltage source 16 by the operational amplifier 17. The comparison output of the operational amplifier 17 controls the light receiving transistor 19 through the light emitting diode 18 forming a photocoupler. The output of the light receiving transistor 19 is input to the control circuit 20, and the control circuit 20
Controls the pulse width of a control pulse signal to be applied to each gate terminal of the first and second MOS-FETs 2 and 3, thereby keeping the DC voltage supplied to the load 13 constant and stabilizing the output voltage. be able to.

[0006]

By the way, in the resonance type DC-DC converter shown in FIG. 10, when the current flowing through the load 13 decreases, the current flowing through the resonance reactor 7 on the primary side of the transformer 6 also decreases. As a result, energy sufficient to cause voltage resonance cannot be stored in the resonance reactor 7. Therefore, when the load becomes light, as shown in FIGS. 11A and 11B, the pulse widths of the control pulse signals V _G1 and V _G2 become very narrow as compared with the constant voltage operation (T ₁ ? T ₂ ). Since the current flowing through the load 13 decreases, voltage resonance cannot be performed. Thereby, the first and second MOS-FETs 2,
The rising and falling of the waveforms of the voltages V _Q1 and V _Q2 across the terminal 3 are disturbed as shown in FIGS. 11 (E) and 11 (F). Therefore, the switching loss of the first and second MOS-FETs 2 and 3 is increased at the time of light load, and noise is generated. Also, the dead time t _D shown in FIGS. 11A and 11B needs to be kept constant regardless of the load, so that the control pulse signals V _G1 , V _G
Since the frequency of _G2 becomes extremely high, there is a problem that the control range of the frequency of the control pulse signal is actually narrowed.

Accordingly, an object of the present invention is to provide a resonant DC-DC converter capable of reducing the occurrence of switching loss and noise even under a light load.

[0008]

SUMMARY OF THE INVENTION Resonant DC according to the present invention
A DC converter is connected between the primary winding of the transformer and the DC power supply and applies a DC voltage in a first direction to the primary winding; A second switching element connected between the DC power supply and applying a DC voltage in a second direction to the primary winding; and a first switching element connected in parallel with each of the first and second switching elements. It includes a second resonance capacitor, a resonance reactor connected in series with the primary winding, and a rectifying and smoothing circuit connected to the secondary winding of the transformer. In this resonance type DC-DC converter, a circulating current reactor is connected in parallel with the primary winding or the secondary winding, and the circulating current reactor is connected regardless of the magnitude of the load current flowing from the secondary winding to the load. , A resonance current always flows through the resonance reactor, and energy sufficient to cause voltage resonance at a light load is stored in the resonance reactor.

A resonance type D according to another embodiment of the present invention.
The C-DC converter is connected between a primary winding of a transformer and a DC power supply and applies a DC voltage in a first direction to the primary winding, and a primary winding of the transformer. A second switching element that is connected between the power supply and the DC power supply and applies a DC voltage in the second direction to the primary winding;
A first and second resonance capacitor connected in parallel with each of the first and second switching elements;
It includes a resonance reactor connected in series with the next winding, and a rectifying / smoothing circuit connected to the resonance reactor.
In this resonance type DC-DC converter, the secondary winding, the resonance reactor, and the circulating current reactor are connected in a closed circuit.

[0010]

[Function] By constantly flowing a resonance current to the resonance reactor through the circulating current reactor, energy sufficient to cause voltage resonance at a light load can be accumulated in the resonance reactor. Switching loss and noise can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a resonance type DC-DC converter according to the present invention will be described below with reference to FIGS. However, in these drawings, the same portions as those shown in FIGS. 10 and 11 are denoted by the same reference numerals, and description thereof will be omitted.
In the DC-DC converter of the present embodiment, a circulating current reactor 24 is connected in parallel with the primary winding 6a of the transformer 6, as shown in FIG. Other configurations are shown in FIG.
Same as 0.

The operation of the above configuration is as follows. First, the control pulse signal V _G1 and V _G2 shown in FIGS. 2A and 2B are supplied from the control circuit 20 at a certain dead time t _D.
Are provided to the gate terminals of the first and second MOS-FETs 2 and 3, respectively. Thereby, the first and second M
OS-FETs 2 and 3 are alternately turned on and off. When the first MOS-FET 2 is turned on, 1 of the transformer 6
The voltage of the first DC power supply 1 is applied to the next winding 6a and the circulating current reactor 24 through the resonance reactor 7,
A voltage is induced in the first secondary winding 6c. Due to the voltage induced in the first secondary winding 6c, a current flows through the path of the rectifier diode 8 and the smoothing capacitor 12. At the same time, a sufficiently large energy is stored in the resonance reactor 7. At this time showing a waveform of the current I _Q1 flowing through the first MOS-FET2 in FIG. 2 (C). Next, as shown in FIG. 2A, after the time T ₁ has elapsed, the first MOS-FET
When 2 is turned off, the energy stored in the resonance reactor 7 is released during the ON period of the first MOS-FET 2. At this time, mainly the resonance reactor 7 and the first
2 and the second resonance capacitors 4 and 5 cause voltage resonance, and the voltage V _Q1 across the first MOS-FET 2 is
It rises in a sine wave shape as shown in FIG. As a result,
The waveform of the voltage V _Q1 shown in FIG. 2 (E) and the current I _Q shown in FIG.
_Since the overlap with the waveform of _Q1 is reduced, the first MOS-
Zero voltage switching (ZVS) at the on / off transition period of the FET 2 becomes possible. Further, the voltage V _Q2 across the second MOS-FET 3 drops in a sinusoidal manner due to the voltage resonance as shown in FIG.

Subsequently, a second MOS-F shown in FIG.
When the voltage V _Q2 across ET3 reaches 0V, the second M
When the OS-FET 3 is turned on, the voltage of the second DC power supply 0 is applied to the primary winding 6a of the transformer 6 and the circulating current reactor 24 through the resonance reactor 7 in the opposite polarity to the previous one, and the second A voltage is induced in the secondary winding 6d.
A current flows through the path of the rectifier diode 9 and the smoothing capacitor 12 due to the voltage induced in the second secondary winding 6d. At the same time, a sufficiently large energy is stored in the resonance reactor 7. At this time, the second MOS-FE
The waveform of the current I _Q2 flowing through T3 shown in FIG. 2 (D). next,
As shown in FIG. 2 (B), when the second MOS-FET 3 is turned off after the T ₁ is the time elapsed, the second MOS-FET
During the ON period of 3, the energy stored in the resonance reactor 7 is released. At this time, voltage resonance mainly occurs by the resonance reactor 7 and the first and second resonance capacitors 4 and 5, and the voltage V _Q2 across the second MOS-FET 3 is sinusoidal as shown in FIG. It rises in a wavy shape. As a result, the waveform of the voltage V _Q2 shown in FIG.
Since the overlap with the waveform of the current I _Q2 shown in (D) is reduced, zero voltage switching (ZVS) at the on / off transition period of the second MOS-FET 3 becomes possible. Further, the voltage V _Q1 across the first MOS-FET 2 drops in a sinusoidal manner due to the voltage resonance as shown in FIG. Then, when the voltage V _Q1 shown in FIG. 2E reaches 0 V, the first MOS-FET 2 is turned on again.

By repeating the above operation, the first and second
Is converted to another DC voltage.
This DC voltage is further smoothed by the smoothing capacitor 12 and supplied to the load 13. Further, the control circuit 20 controls the pulse width of a control pulse signal to be applied to each gate terminal of the first and second MOS-FETs 2 and 3 according to the DC voltage smoothed by the smoothing capacitor 12. Load 13
The output voltage is stabilized by keeping the DC voltage supplied to the power supply constant.

Next, the case where the load 13 of the circuit of FIG. 1 is light will be described. When load 13 becomes light load, load 1
3 becomes high, and the control signal pulse signal V output from the control circuit 21 as shown in FIGS. 2A and 2B.
_G1, the pulse width of the V _G2 is narrowed narrower (T _1> T _2). At this time, the current flowing through the load 13 decreases, but in this circuit, a constant resonance current always flows through the circulating current reactor 24 regardless of the magnitude of the load current.
Flow through the reactor 7 even when the load is light.
Large enough energy is stored. Therefore, when the first and second MOS-FETs 2 and 3 are turned off at light load, voltage resonance occurs, and the first and second MOS-FETs 2 and 3 are turned off as shown in FIGS. The rising and falling of each of the waveforms of the voltages V _Q1 and V _Q2 at both ends are sinusoidal.

As described above, in the present embodiment, a constant resonance current can always flow through the circulating current reactor 24 to the resonance reactor 7 regardless of the magnitude of the load current. This resonance current is supplied to the circulating current reactor 24.
Can be set freely by arbitrarily selecting the value of the inductance. Therefore, energy required to cause voltage resonance at light load can be sufficiently stored in the resonance reactor 7. For this reason, FIGS. 2E and 2F
As shown in FIG.
-Zero voltage switching (ZVS) is possible in all load ranges because the rising and falling of the waveforms of the voltages V _Q1 and V _Q2 across the FETs ₂ and 3 are not disturbed. Therefore, there is no increase in switching loss of the first and second MOS-FETs 2 and 3 and no generation of noise. Further, since a constant circulating current is formed by the resonance current, it becomes possible to cope with a light load or the like with a relatively wide pulse width of the control pulse signal. For this reason, there is no remarkable rise in frequency due to a load change, and the frequency control range of the control pulse signal can be extremely widened.

The embodiment of the present invention is not limited to the above embodiment, and various modifications are possible. For example, the following (a)-
(g) is a part of the modification. (A) Circulating current reactor 24 in the circuit of FIG.
Are the first and second transformers 6 as shown in the circuit of FIG.
May be connected to both ends of the series circuit of the secondary windings 6a and 6b. (B) Instead of the first and second DC power supplies 1 and 0 in the circuit of FIG. 1, a transformer using a single DC power supply 1 and capacitors 25 and 26 for a half bridge as shown in the circuit of FIG. The primary-side switching circuit of No. 6 may be configured as a half-bridge type. (C) The resonance reactor 7 and the circulating current reactor 24 on the primary side of the transformer 6 in the circuit of FIG.
As shown in the circuit, the resonance reactor 7 having the first and second windings 7a and 7b may be used and provided on the secondary side of the transformer 6 together with the circulating current reactor 24. (D) The switching circuit on the primary side of the transformer 6 in the circuit of FIG. 1 may be configured as a push-pull type as shown in the circuit of FIG. In the circuit of FIG. 6, 6a and 6b
Denotes first and second primary windings. (E) The resonance reactor 7 and the circulating current reactor 24 on the primary side of the transformer 6 in the circuit of FIG.
May be provided on the secondary side of the transformer 6 as shown in FIG. (F) A center tap type rectifying / smoothing circuit composed of rectifier diodes 8, 9 and a smoothing capacitor 12 on the secondary side of the circuit of FIG. 7 is replaced with rectifier diodes 8, 9, capacitors 10, 11 and A voltage doubler rectifying / smoothing circuit including the smoothing capacitor 12 may be used. (G) Further, the capacitors 10 and 1 in the circuit of FIG.
Instead of the rectifier diode 22 shown in FIG.
23 may be connected to form a full-bridge rectifying / smoothing circuit.

[0018]

As described above, in the present invention, the addition of the circulating current reactor allows a constant resonance current to flow regardless of the magnitude of the load current. Therefore, zero voltage switching (ZVS) is performed in all load ranges. Becomes possible.
Therefore, it is possible to reduce switching loss and noise in all load ranges. In addition, since this resonance current is also a constant circulating current, it is possible to realize a relatively wide minimum pulse width of the control pulse signal and suppress a remarkable frequency variation with respect to a load variation. Therefore, the control range of the frequency of the control pulse signal can be extremely widened.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram showing the voltage and current of each part of the circuit of FIG. 1 during constant voltage operation and light load.

FIG. 3 is an electric circuit diagram showing a modification of the circuit of FIG. 1;

FIG. 4 is an electric circuit diagram showing another modification of the circuit of FIG. 1;

FIG. 5 is an electric circuit diagram showing another modification of the circuit of FIG. 1;

6 is an electric circuit diagram showing an example in which the primary-side switching circuit in the circuit of FIG. 1 is a push-pull type.

FIG. 7 is an electric circuit diagram showing a modification of the circuit of FIG. 6;

FIG. 8 is an electric circuit diagram showing a modification of the circuit of FIG. 7;

FIG. 9 is an electric circuit diagram showing a modification of the circuit of FIG. 8;

FIG. 10 is an electric circuit diagram of a conventional resonant DC-DC converter.

FIG. 11 is a waveform chart showing the voltage and current of each part of the circuit of FIG. 10 during constant voltage operation and light load.

[Explanation of symbols]

1, 0. . . First and second DC power supplies, 2, 3,. . . First and second MOS-FETs (switching elements),
4,5. . . First and second resonance capacitors,
6. . . Transformer, 6a, 6b. . . First and second primary windings, 6c, 6d. . . First and second secondary windings,
7. . . Resonance reactor, 7a, 7b. . . First and second windings, 8, 9, 22, 23. . . Rectifier diode,
10,11. . . Capacitor 12. . . 12. smoothing capacitor; . . Load, 14,15. . . Voltage dividing resistor, 1
6. . . Reference voltage source, 17. . . Operational amplifier, 1
8. . . Light emitting diode, 19. . . Light receiving transistor, 20. . . Control circuit, 24. . . Circulating current reactor, 25, 26. . . Half Bridge Capacitor

Claims (2)

(57) [Scope of request for utility model registration] 1. A first switching element connected between a primary winding of a transformer and a DC power supply and for applying a DC voltage in a first direction to the primary winding, and a primary winding of the transformer. A second switching element connected between a line and a DC power supply and for applying a DC voltage in a second direction to the primary winding; and a second switching element connected in parallel with each of the first and second switching elements. A resonance type DC-DC converter comprising first and second resonance capacitors, a resonance reactor connected in series with the primary winding, and a rectifying and smoothing circuit connected to the secondary winding of the transformer. In the DC converter, a circulating current reactor is connected in parallel with the primary winding or the secondary winding, and regardless of a magnitude of a load current flowing from the secondary winding to a load, the circulating current is passed through the circulating current reactor. The resonance current is always It poured into Akutoru, resonant DC, characterized by storing sufficient energy to cause a voltage resonance at light loads the resonant reactor
-DC converter. 2. A first switching element connected between a primary winding of a transformer and a DC power supply for applying a DC voltage in a first direction to the primary winding, and a primary winding of the transformer. A second switching element connected between a line and a DC power supply and for applying a DC voltage in a second direction to the primary winding; and a second switching element connected in parallel with each of the first and second switching elements. Resonance DC-DC comprising: a first and a second resonance capacitor; a resonance reactor connected in series with a secondary winding of the transformer; and a rectifying and smoothing circuit connected to the resonance reactor. A converter, wherein the secondary winding, the resonance reactor, and the circulating current reactor are connected in a closed circuit.
C-DC converter.