JPH08275508A - Voltage step-up dc-dc converter - Google Patents

Abstract

PURPOSE: To suppress the reverse flowing of the current from a smoothing capacitor and to achieve high efficiency of a voltage step-up DC-DC converter circuit using a synchronous commutation technology. CONSTITUTION: When the first MOSFET (M1) is on, the second MOSFET (M2) is made off, and a primary winding 11 of a transformer T1 is conducted. Energy is stored in the transformer T1. Thereafter, the first MOSFET (M1) is turned off, and the second MOSFET (M2) is turned on. The voltage obtained by adding the voltage of a DC power supply 1 and the voltage caused by the counterelectromotive force of the primary winding 11 of the transformer T1 is outputted to a load 14 through the second MOSFET (M2). Furthermore, the gate voltage of the second MOSFET (M2) is formed by a resonance circuit comprising a secondary wiring 12 of the transformer T1, a resonance capacitor C2 and a resistor R1. Thus, the dead time, in which both MOSFETs become the OFF state during the ON period of the first MOSFET (M1) and the second MOSFET (M2), is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter, and more particularly to a step-up DC-DC converter using a synchronous rectification technique.

[0002]

2. Description of the Related Art Conventionally, most step-up DC-DC converters use a diode as a rectifying element to discharge a current to the outside. On the other hand, there is a step-up DC-DC converter that uses a switching element as a rectifying element because of the problems of power loss and heat generation in the diode.

A conventional step-up DC-DC converter using a switching element as a rectifying element will be described below.

FIG. 3 is a block diagram showing the structure of a conventional step-up DC-DC converter. In FIG. 3, 1 is a DC power source, T1 is a transformer, and 11 and 12 are transformers T1.
MO that turns on and off the secondary and secondary windings, M1 and M2 alternately
S-FET, R is a resistor, and C1 is a smoothing capacitor. The positive electrode of the DC power supply 1 is connected to the primary winding 11 of the transformer. On the load side of the primary winding 11, the secondary winding 12, M
The drain of the OS-FET M1 and the source of the MOS-FET M2 are connected, and the drain of the MOS-FET M2 is connected to one end of the smoothing capacitor C1 and the load 14. The secondary winding 12 of the transformer T1 is a MOS-FET via a resistor.
Connected to the gate of M2.

From the control unit 13, the voltage of a predetermined cycle is M
The MOS-FET M1 is applied to the gate of the OS-FET M1, and the MOS-FET M1 is turned on when the voltage is applied, and the drain-source is energized to store energy in the primary winding 11. When the MOS-FET M1 changes from the ON state to the OFF state, a voltage due to the counter electromotive force is generated at both ends of the primary winding 11, and a voltage due to the induced electromotive force is simultaneously generated at both ends of the secondary winding 12. . At this time, MOS-FET
The gate potential of M2 becomes higher than the source potential, and M2
The OS-FET M2 is turned on. Therefore, MOS-F
When the ETM1 is in the OFF state, the voltage obtained by adding the voltage due to the counter electromotive force to the voltage of the DC power supply 1 is the MOS-FET.
It is output to the load 14 via M2 and at the same time the capacitor C1
To charge.

On the contrary, when the MOS-FET M1 is changed from the off state to the on state, a voltage due to an induced electromotive force is generated at both ends of the secondary winding 12, and the gate potential of the MOS-FET M2 is lower than the source potential. And MOS-FET M2
Is turned off. When the MOS-FET M1 is in the ON state, the discharge of the capacitor C1 causes a current to flow in the load 14. As a result, a voltage higher than the voltage of the DC power supply 1 is output to the load 14.

[0007]

However, in the above-mentioned conventional step-up DC-DC converter, the MO
When the S-FET M1 is switched from off to on, the pulse from the control unit 13 turns on the MOS-FET M1 and then turns off the MOS-FET M2. Therefore, from the capacitor C1 to the MOS-FET M2 and MO
There is a problem in controlling the two switching elements (M1, M2) by one control unit 13 due to a decrease in efficiency caused by the current flowing into the negative electrode of the DC power supply 1 through the S-FET M1. Was becoming.

The present invention solves the above-mentioned conventional problems, and an object thereof is to suppress the reverse flow of current from a smoothing capacitor and to improve the efficiency of a step-up DC-DC converter circuit using a synchronous rectification technique.

[0009]

In order to achieve this object, a step-up DC-DC converter according to the present invention comprises a DC power source, a primary winding connected in series to the positive electrode of the DC power source, and the primary winding. A transformer having a secondary winding magnetically coupled to the first winding, a first switching element connected between the primary winding of the transformer and a negative electrode of the DC power supply, and one end connected to a negative electrode of the DC power supply 1. Second smoothing capacitor connected in series between the primary winding of the transformer and the other end of the smoothing capacitor.
Switching element, a resonance capacitor connected between the secondary winding of the transformer and the control terminal of the second switching element, and connected between the control terminal of the second switching element and the negative electrode of the DC power supply. Resistance
And a control unit that applies a voltage of a predetermined cycle to the first switching element.

[0010]

According to the present invention, with the above configuration, the voltage is applied from the control unit to the control terminal of the first switching element at a predetermined cycle, and when the voltage is applied to the control terminal, the first switching element Is turned on,
The drain and source are energized and energy is stored in the primary winding. When the first switching element changes from the ON state to the OFF state, a voltage due to a back electromotive force is generated at both ends of the primary winding, and a voltage due to an induced electromotive force is simultaneously generated at both ends of the secondary winding.

At this time, due to the series resonance of the secondary winding, the resonance capacitor and the resistor, a sinusoidal resonance voltage having the same phase as the voltage due to the induced electromotive force is applied to the control terminal of the second switching element. The second switching element is turned on when the resonance voltage exceeds the sum of the threshold voltage and the output voltage at that time.

Therefore, when the first switching element is in the off state, the voltage obtained by adding the voltage due to the back electromotive force to the voltage of the DC power source is output to the load through the second switching element and simultaneously charges the capacitor. To do. Further, when the first switching element is in the on state, the second switching element is in the off state, and current flows through the load due to discharge of the capacitor. As a result, a voltage higher than the voltage of the DC power supply can be output to the load, and a dead time can be created between the ON times of the first switching element and the second switching element, so that the backflow of the current from the smoothing capacitor is suppressed. You can

Furthermore, since a sinusoidal resonance voltage, rather than a rectangular wave pulse voltage, can be applied to the control terminal, soft switching can be realized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a step-up DC according to an embodiment of the present invention.
2 is a block diagram showing a configuration of a DC converter, and FIG.
FIG. 6 is a diagram showing operation timings of two MOS-FETs. In FIG. 1, 1 is a DC power supply, T1 is a transformer, and 11
Reference numerals 12 and 12 are primary and secondary windings of the transformer T1, M1 and M2 are MOS-FETs which are alternately turned on and off, R1 is a resistor, C2 is a resonance capacitor, and C1 is a smoothing capacitor. The positive electrode of the DC power supply 1 is connected to one ends of the primary winding 11 and the secondary winding 12 of the transformer T1, and the other end of the secondary winding 12 of the transformer T1 is connected to the second end via the resonance capacitor C2. MOS-FET
It is connected to the gate of M2 and the other end of the primary winding 11 of the transformer T1 is connected to the drain of the first MOS-FET M1 and the second M-FET M1.
Connected to the source of OS-FET M2, the control unit 13 is the first
Is connected to the gate of the MOS-FET M1.

The operation of the step-up DC-DC converter of the present embodiment having the above configuration will be described below.

A voltage of a predetermined cycle is applied to the gate of the first MOS-FET M1 from the control unit 13, and when the voltage is applied to the gate, the first MOS-FET M1 is turned on and the drain A transformer T is energized between the sources
Energy is stored in the primary winding 11 of 1. When the first MOS-FET M1 is switched from the ON state to the OFF state, a voltage due to the counter electromotive force is generated across the primary winding 11 of the transformer T1, and at the same time, the secondary winding 12 of the transformer T1 is generated.
A voltage due to the induced electromotive force is generated at both ends of. At this time,
Due to the series resonance of the secondary winding 12 of the transformer T1, the resonance capacitor C2 and the resistor R1, the second MOS-FET M2
A sinusoidal resonance voltage having the same phase as the voltage due to the induced electromotive force is applied to the gate of the. Second MOS-FET M2
Turns on when the resonance voltage exceeds a voltage obtained by adding the threshold voltage and the output voltage. Therefore, the first M
When the OS-FET M1 is in the off state, the voltage obtained by adding the voltage due to the back electromotive force to the voltage of the DC power supply is the second MOS.
-It is output to the load 14 through the FET M2 and simultaneously charges the smoothing capacitor C1. Also, the first MOS-FET
When M1 is on, the second MOS-FET M2 is off and the smoothing capacitor C1 is discharged to load 14
Current flows through.

In FIG. 2, (a) shows the first MOS-F.
The operation timing of ETM1 is shown. Similarly,
(B) shows the operation timing of the second MOS-FET M2. (C) shows a voltage waveform applied to the gate of the second MOS-FET M2. As described above, the inductance component of the secondary winding 12 of the transformer T1, the resonance capacitor C2, and the resistance R1 A resonance voltage waveform due to series resonance is obtained. The first MOS-FET M shown in (a)
The on / off operation of 1 produces the resonance voltage waveform shown in (c). The resonance voltage waveform shown in (c) is the second MOS-F.
During the period in which the output voltage Vd of the ETM2 is equal to or higher than the threshold voltage VT, as shown in FIG.
The S-FET is in the on state, and is in the off state in other periods. Therefore, as can be seen from FIGS. 2A and 2B, the first MOS-FET M1 and the second MOS-FET M1
A dead time in which both MOS-FETs are in the OFF state can be created during the ON period of M2, and the backflow of the current from the smoothing capacitor C1 can be suppressed.

Further, by making the gate voltage of the MOS-FET M2 not a conventional square wave pulse voltage but a sinusoidal resonance voltage, soft switching of the MOS-FET M2 is possible, so that generation of surge voltage is suppressed. Therefore, the generation of noise can be reduced.

As described above, according to the embodiment of the present invention, 2
A transformer is provided to control the operation timing of two MOS-FETs by giving a control signal to one of the two MOS-FETs, and is used as a rectifying element to suppress the reverse current of the current from the smoothing capacitor. MOS-F
By providing a series resonance means for resonating the gate voltage of ET,
This makes it possible to control two MOS-FETs by one control unit, thereby realizing low noise and high efficiency of the circuit.

[0021]

As described above, according to the present invention, when the first switch element is on, the second switch element is off and the primary winding of the transformer is energized to store energy in the transformer. After that, the first switch element is turned off and the second switch element is turned on, and the voltage obtained by adding the voltage of the DC power supply and the voltage due to the counter electromotive force of the primary winding of the transformer is set to the second switch element. Output to the load via. Further, the gate voltage of the second switch element is generated by the resonant circuit including the secondary winding of the transformer, the resonance capacitor, and the resistor, so that the ON period of the first switch element and the second switch element is reduced. Since a dead time in which both switching elements are turned off is created between them, it is possible to suppress the backflow of the current from the smoothing capacitor, which is a problem when operating two switching elements with one control unit. DC-D with low noise and high efficiency using DC
A C converter can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a step-up DC-DC converter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a timing of a switch operation in the embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional step-up DC-DC converter.

[Explanation of symbols]

 1 DC power supply 11 Primary winding 12 Secondary winding 13 Control section 14 Load C1 Smoothing capacitor C2 Resonance capacitor M1, M2 MOS-FET R1 Resonance resistor T1 Transformer VT MOS-FET M2 threshold voltage Vd Output voltage

Claims (1)

[Claims] 1. A transformer having a DC power source, a secondary winding in which a primary winding is connected in series to a positive electrode of the DC power source, and the secondary winding is magnetically coupled to the primary winding; A first switching element connected between the primary winding and the negative electrode of the DC power supply; a smoothing capacitor having one end connected to the negative electrode of the DC power supply 1; a primary winding of the transformer and a smoothing capacitor; A second switching element connected in series between the other ends, a resonance capacitor connected between the secondary winding of the transformer and a control terminal of the second switching element, and the second switching element. Step-up DC-DC including a resistor connected between the control terminal of the switching element and the negative electrode of the DC power supply, and a control unit that applies a voltage of a predetermined cycle to the control terminal of the first switching element Comba Data.