JPH11187657A - Resonant type dc-to-dc converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a size smaller by generating a current with its phase shifted by 180 degrees, based on a resonance voltage of a resonant circuit formed at a secondary side of a transformer, adding it, and supplying it to a load. SOLUTION: Switches 1, 2 of a resonant type DC-to-DC converter circuit are turned on alternately with dead time included by a pulse signal from a switching pulse generation circuit, and zero voltage switching is conducted during the dead time. Trapezoidal current corresponding to the voltage developed across the switch 1 is applied to the primary side of a transformer 5, converted into a prescribed voltage VS and becomes the input voltage of a resonant circuit constituted of an inductor 6 and capacitors 7, 8. On the other hand, current flows through inductors 11, 12 based on the voltage developed across the capacitor 8, therefore added current flows through a load resistor 14. The phase in the current flowing through the inductors 11, 12 is shifted by 180 degrees, therefore, current ripple is cancelled so that the inductors 11, 12 can be made small. It is thus possible to be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonant DC-DC converter circuit which can be used with a fixed switching frequency, and more particularly to a resonant DC-D converter which can be reduced in size.
It relates to a C converter circuit.

[0002]

2. Description of the Related Art Switching power supplies are widely used in electronic equipment such as information equipment and communication equipment as high-efficiency, compact and lightweight power supplies. Switching power supplies used in these electronic devices are required to have higher efficiency, smaller size, lighter weight, and lower noise. To meet such demands, various resonant converters used for switching power supplies have been proposed. However, it is generally difficult to adjust the voltage while keeping the switching frequency fixed, and the resonant converter is used with a variable frequency.
Changing the switching frequency fluctuates the spectrum of noise generated by opening and closing the switch, and as a result, noise countermeasures become difficult. In addition, since magnetic components and capacitors that determine the size of the converter must be selected based on the lowest frequency, there is a limit to downsizing.

As a resonant converter capable of solving such a drawback, a converter capable of adjusting a voltage while fixing a frequency has been devised. For example, there is a converter described in Japanese Patent Application Laid-Open No. 9-93922. FIG.
FIG. 1 is a circuit diagram showing a configuration of a resonance type DC-DC converter circuit described in Japanese Unexamined Patent Application Publication No. H10-115,004. This resonance type DC-DC converter circuit comprises a main switching FET 1 (switch 1), a capacitor 3 and an auxiliary switching FET.
2 (switch 2) and a parallel connection of an inductor 15 and a clamp circuit connected between the DC voltage source 4 and the main switching switch 1;
And a capacitor 7, a series resonance circuit connected to the clamp circuit, a transformer 16 having a primary side connected to the series resonance circuit, and a full-wave rectification circuit including diodes 17 and 18 connected to the secondary side of the transformer 16. It includes a smoothing capacitor 13 and a load resistor 14 connected between the output of the wave rectifier circuit and the center tap of the transformer 16.

In the resonance type DC-DC converter circuit having such a configuration, as shown in FIG. 4, switches 1 and 2 are interleaved with a dead time by a pulse signal from a switching pulse generation circuit (not shown). Turn on alternately. Due to the presence of the clamp circuit, a voltage Vds1 which is substantially proportional to the pulse width of the pulse signal is generated at both ends of the main switching switch 1. That is, PWM control is possible at a constant frequency. As a result, a noise-reducing DC-D that facilitates noise countermeasures and can be downsized.
A C converter circuit has been obtained. In FIG. 4, S1 indicates the on / off state of the switch 1, and S2 indicates the on / off state of the switch 2. VLA indicates a voltage across the inductor 15, and iLA indicates a current flowing through the inductor 15. In addition, (1 / (1-
D)) D in Vin represents the duty ratio of the PWM signal for turning on and off the switches 1 and 2, and Vin represents the voltage of the DC voltage source 4.

[0005]

However, in a resonance type DC-DC converter circuit using an active clamp + center tap type rectifier circuit as shown in FIG. 3, as shown in FIG. The current iLA superimposed with the DC flows. Therefore, the inductor 15 must have a large shape. As a result, there is a problem that a limit is imposed on miniaturization of the resonance type DC-DC converter circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and is a resonance type DC-DC converter circuit capable of performing PWM control at a constant frequency, in which the size can be further reduced. An object of the present invention is to provide a resonance type DC-DC converter circuit.

[0007]

SUMMARY OF THE INVENTION Resonant DC according to the present invention
A DC converter circuit, wherein the resonance circuit is provided on the secondary side of the transformer, and is 180 ° based on the resonance voltage of the resonance circuit;
It has a current doubler that generates currents out of phase, adds the currents, and supplies them to a load. Also,
A clamp circuit composed of a series connection of a capacitor and an auxiliary switch element is connected to the main switch element, and the main switch element and the auxiliary switch element are turned on alternately with a dead time therebetween. The resonance circuit includes a series connection of an inductor and one capacitor, and the other capacitor. The current doubler is configured to apply a voltage across the other capacitor in the resonance circuit.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a resonance type DC according to the present invention.
FIG. 3 is a circuit diagram illustrating an embodiment of a DC converter circuit. As shown in the figure, this resonance type DC-DC converter circuit includes a main switching FET 1 (switch 1),
A clamp circuit connected in series between a capacitor 3 and an auxiliary switching FET 2 (switch 2), connected between a DC voltage source 4 and a switch 1, and a transformer (no center tap) connected on the primary side to the clamp circuit
5, a series-parallel resonance circuit comprising an inductor 6 and capacitors 7 and 8 connected to the secondary side of a transformer 16, diodes 9 and 10 for rectifying resonance voltages at both ends of the capacitor 8, and current doublers comprising inductors 11 and 12 , A smoothing capacitor 13, and a load resistor 14.

Next, the operation will be described. FIG. 2 (A)
FIG. 2B is a circuit diagram showing a current doubler portion, and FIG.
3 is a waveform chart showing a waveform example of each unit. In FIG. 2B, S1 indicates the on / off state of the switch 1, and S2 indicates the on / off state of the switch 2. Vds1 indicates the voltage across the switch 1, and VS indicates the voltage on the secondary side of the transformer 5. VCp indicates a voltage across the capacitor 8.
Further, iL01 indicates a current flowing through one inductor 11 in the current doubler, and iL02 indicates a current flowing through the other inductor 12 in the current doubler. And io indicates the current supplied to the load. Note that FIG.
D at (1 / (1-D)) Vin described in (B)
Represents the duty ratio of the PWM signal for turning on and off the switches 1 and 2, and Vin represents the voltage of the DC voltage source 4.

[0010] As shown in FIG.
Are alternately turned on with a dead time therebetween by a pulse signal from a switching pulse generation circuit (not shown). During the dead time of each switch 1 and 2, the transformer 5
The output capacitance is charged and discharged through the parasitic diode by the excitation current on the primary side. Therefore, zero voltage switching is performed.

A trapezoidal voltage corresponding to the voltage Vds1 across the switch 1 is applied to the primary side of the transformer 5. This voltage is
The voltage is converted to a predetermined voltage VS by the transformer 5. This voltage becomes the input voltage of the resonance circuit including the inductor 6 and the capacitors 7 and 8. By this resonance circuit, the voltage Vcp across the capacitor 8 becomes sinusoidal as shown in FIG.

An inductor 1 constituting a current doubler
The currents iL01 and iL02 as shown in FIG. 2B flow through the capacitors 1 and 12 based on the voltage VCp across the capacitor 8. Consequently, the current io resulting from the addition flows through the load resistor 14. . As shown in FIG. 2B, currents iL01 and iL02 flowing through inductors 11 and 12 are 180 °
Because of the phase shift, the current ripple is cancelled. Therefore, the inductors 11 and 12 can be small.

If the magnetic coupling is suppressed, the inductor 1
1 and 12 can be realized by one core, and in that case, the shape of the converter circuit can be further reduced. Although a capacitor 8 is added to the circuit shown in FIG. 3, the capacitor 8 is used for resonance, and may be as small as several hundred pF. Further, FIG.
In the circuit shown in (1), a center tap on the transformer secondary side is not required, and the shape of the transformer 5 can be reduced.

Note that Japanese Patent Application Laid-Open No. 9-93922 discloses that
A converter circuit using a full-wave rectifier circuit with a transformer without a center tap and a diode bridge is also described.However, according to this circuit, the current ripple is reduced by the current doubler and the diode forward drop There is an advantage that the voltage is halved and the efficiency decrease at the time of low voltage output is small.

[0015]

As described above, according to the present invention, the resonance type DC-DC converter circuit is used to convert the current 180 ° out of phase based on the resonance voltage of the resonance circuit provided on the secondary side of the transformer. Since a current doubler is provided for generating and adding the currents and supplying the current to the load, the conventional P
The magnetic components can be reduced or downsized only by adding a small inductor and a capacitor to the resonance type DC-DC converter circuit capable of WM control, and there is an effect that the size can be further reduced as a whole.

[Brief description of the drawings]

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

FIG. 2A is a circuit diagram showing a current doubler portion, and FIG. 2B is a waveform diagram showing waveforms of respective portions of a DC-DC converter circuit.

FIG. 3 is a circuit diagram showing a conventional resonance type DC-DC converter circuit.

FIG. 4 is a waveform chart showing waveforms at various parts of the DC-DC converter circuit shown in FIG. 3;

[Explanation of symbols]

 1, 2 switch 3 capacitor 4 DC voltage source 5 transformer 6 inductor 7, 8 capacitor 9, 10 diode 11, 12 capacitor 13 smoothing capacitor 14 load resistance

Claims (3)

[Claims] A main switch element for switching a DC voltage from a DC voltage source and supplying the switched DC voltage to a primary side of a transformer;
A rectifier circuit for rectifying and outputting a secondary-side output of a transformer, wherein the resonance-type DC-DC converter circuit includes a resonance circuit, wherein the resonance circuit is provided on a secondary side of the transformer; A resonance type DC having a current doubler that generates currents 180 ° out of phase based on a resonance voltage of a resonance circuit, and adds the currents and supplies the currents to a load.
A DC converter circuit. 2. A clamp circuit comprising a series connection of a capacitor and an auxiliary switch element is connected to a main switch element, and the main switch element and the auxiliary switch element are turned on alternately with a dead time therebetween. Resonant DC
A DC converter circuit. 3. The resonance circuit includes a series connection of an inductor and one capacitor, and the other capacitor, and a voltage between both ends of the other capacitor in the resonance circuit is applied to the current doubler. The described resonance type D
C-DC converter circuit.