KR20040011042A - Dc/dc soft switching converter - Google Patents

Abstract

PURPOSE: A DC/DC soft switching converter is provided to reduce switching losses and achieve improved operating efficiency, while reducing the volume of the system. CONSTITUTION: A DC/DC soft switching converter comprises a transformer(Tr) including a primary coil(L1) having a magnetizing inductance component and a leakage inductance component and secondary coils(L2,L3) coupled to the primary coil; a first switch(Q1) and a second switch(Q2) connected in parallel with the primary coil; a first diode(DQ1) and a second diode(DQ2) connected in parallel to the ends of the first switch and the second switch, respectively; a first capacitor(CQ1) and a second capacitor(CQ2) connected in parallel to the ends of the first switch and the second switch; a third capacitor(C3) connected in serial to the second switch; a fourth capacitor(C4) connected in serial to the primary coil; and an inductor connected to the ends of the first switch, the second switch and the primary coil, wherein the inductor applies the DC voltage input from the DC power to the first switch, the second switch and the primary coil.

Description

DC / DC Soft Switching Converters {DC / DC SOFT SWITCHING CONVERTER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter for varying the output of a DC voltage, and more particularly, to a DC / DC soft switching converter used for a switching mode power supply (SMPS).

Switching Mode Power Supply (SMPS) is widely used as a DC stabilized power supply for electronic and communication equipment such as electronic calculators, electronic exchangers and OA equipment. SMPS is a stabilizing power supply having a great advantage in efficiency, miniaturization and weight reduction compared to the conventional stabilizing power supply by controlling the flow of power using the switching process of the semiconductor device.

However, in such electronic and communication devices, the system part is rapidly miniaturized and lightened due to the development of semiconductor integrated circuits, while the power supply part is limited in miniaturization and light weight due to the presence of inductors and capacitors, which are energy storage elements. Will be. Therefore, in order to reduce the size and weight of electronic and communication equipment, the size and weight of SMPS are relatively large.

SMPS can be divided into AC / DC type that converts AC voltage into DC voltage and DC / DC type that converts DC voltage into DC voltage, which can be divided into insulation type and non-insulation type. Non-insulated types include step-down type (buck type or step-down type), step-up type (boost type or step-up type), and step-up type (buck-boost type) .Insulated type mainly uses transformer and step-down type (buck) -Boost type, Flyback, RCC, and Force type, Forward, Half Bridge, Full Bridge, Push-Pull. These are usually referred to as Switched Mode Power Supplies (SMPS) because they control power by controlling the ON time of the switch.

As described above, in order to reduce the size and weight of the SMPS, by increasing the switching frequency of the SMPS, it is possible to reduce the size and weight of transformers, inductors, and capacitors, which occupy a large proportion in volume and weight. This significantly reduces size and weight compared to other types of linear power supplies in its class. In addition, SMPS has become mainstream in the power supply sector due to its simple control characteristics.

However, the disadvantage of SMPS is that the voltage and current are overlapped due to the interruption of voltage or current on / off, so the loss caused by the switch (mainly in the form of heat) increases in proportion to the switching frequency and the current or the magnitude of the applied voltage. Is that. This is a factor that limits the increase in the switching frequency of the SMPS. In addition, there is a disadvantage in that EMI noise is increased compared to other types of linear power supply.

In order to overcome this disadvantage, a method of zeroing the voltage or current at the time of switching on and off has been proposed. At this time, the case of controlling the voltage to be zero is called zero voltage switching (ZVS) and the case of controlling the current to be zero is called zero current switching (ZCS). Soft Switching). In addition, a power supply device designed to reduce switching losses and increase efficiency by such soft switching is called a soft switching converter in a broad sense.

However, in the conventional soft switching converter, the efficiency of the converter is reduced by the loss in the switch due to the overlap of the voltage and the current as described above, and the current of the primary coil and the secondary coil of the transformer becomes a square wave. Therefore, the noise of the secondary coil diode is bad.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a DC / DC soft switching converter capable of reducing switching loss and increasing operating efficiency and frequency.

There are various types of switches used in SMPS, but mainly FET (Field Effect Transistor) is used. Inside the FET, parasitic capacitances and parasitic diodes are inherent in manufacturing techniques. Another object of the present invention is to provide a DC / DC soft switching converter capable of performing soft switching in a more efficient structure by controlling switching operation using parasitic capacitance and LC resonance caused by leakage inductance component of the transformer and parasitic diode. To provide.

1 is a circuit diagram of a soft switching converter according to the present invention;

FIG. 2 is a graph showing waveforms of voltage and current at each part of FIG. 1, and

3A to 3F are circuit diagrams illustrating a flow of current according to a switching state in each mode of FIG. 1.

Explanation of symbols on the main parts of the drawings

V _i : Input DC Power L _in : Input Inductor

Q ₁ , Q ₂ : First and second switches D _Q1 , D _Q2 : Inverse parallel diode

C _Q1 , C _Q2 : Parasitic Capacitors C ₃ , C ₄ : Capacitors

T _r : Transformer L ₁ : Primary Coil

L ₂ , L ₃ : Secondary coil L _m : Magnetized inductance component

L ₄ : Leakage inductance component

A soft switching converter according to the present invention for achieving the above object, a transformer having a primary coil having a magnetizing inductance component and a leakage inductance component, and a secondary coil coupled to the primary coil; First and second switches connected in parallel with respect to the primary coils, respectively; First and second diodes connected in parallel to both ends of each of the first switch and the second switch; A first capacitor and a second capacitor connected in parallel to both ends of the first switch and the second switch; A third capacitor connected in series with the second switch; A fourth capacitor connected in series with the primary coil; And an inductor commonly connected to one end of the first switch, the second switch, and the primary coil to apply a DC voltage input from a DC power source to the first switch, the second switch, and the primary coil. Characterized in that it comprises a.

The first switch and / or the second switch may be made of a semiconductor device such as an insulated gate type FET, and in this case, the first diode and / or the second diode may be anti-parallel parasitic of the FET. Preferably, the diode component and the first capacitor and / or the second capacitor are implemented by the parasitic capacitance component of the FET.

In addition, the soft switching converter according to the present invention is implemented as a full-wave rectification circuit and the like has a rectifying circuit unit for rectifying the AC voltage of the secondary coil. A low pass filter composed of an inductor and a capacitor is installed at the output terminal of the full-wave rectifier circuit, and serves to remove energy and to supply energy to the output side.

According to the invention, soft switching without switching losses is performed. In addition, switching loss can be further reduced by controlling the switching operation using the parasitic capacitance and the resonance caused by the leakage inductance component of the transformer and the parasitic diode. This reduction in switching losses can increase the switching frequency, thereby reducing the size of the transformer, inductor, capacitors, etc., thereby reducing the volume of the entire system.

In addition, according to the present invention, the primary side current of the transformer is transmitted as a triangular wave instead of a square wave. Accordingly, the primary side voltage and the secondary side voltage are reduced in ripple, thereby reducing EMI noise. Thus, the efficiency of the entire system is increased.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a circuit diagram of a DC / DC soft switching converter according to the present invention.

The DC / DC soft switching converter according to the present invention includes a transformer T _r , a first switch Q ₁ , a second switch Q ₂ , a capacitor C ₃ , C ₄ , an input inductor Lin, and The rectifier circuit part is provided.

A transformer (T _r) has a primary coil (L _1), and the primary coil (L ₁₎ magnetically to the secondary coil, which is coupled to (L _2, L ₃₎ on. The primary coil L ₁ has a magnetizing inductance component L _m and a leakage inductance component L ₄ . The capacitor C ₄ is connected in series to the primary coil L ₁ .

The upper end of the first switch Q ₁ is connected to the primary coil L ₁ , and the lower end is connected to the ground terminal, whereby the first switch Q ₁ is connected to the primary coil L ₁ and the capacitor. Connected in parallel for (C ₄ ).

An upper end of the second switch Q ₂ is connected to the primary coil L ₁ , and a capacitor C ₃ is connected to the lower end of the second switch Q ₂ . The second switch Q ₂ and the capacitor C ₃ connected in series are connected in parallel to the primary coil L ₁ and the capacitor C ₄ connected in series.

The first switch Q ₁ and the second switch Q _{2 are} formed of an insulated gate FET as shown in FIG. 1, and more specifically, an N-channel enhancement type metal MOS FET (N-channel enhancement type metal). -oxide-semiconductor field effect transistor). The source of the first switch Q ₁ is connected to the ground terminal, the source of the second switch Q ₂ is connected to the input inductor L _in , and the drain is connected to the capacitor C ₃ .

The first switch Q ₁ and the second switch Q ₂ have antiparallel diodes D _Q1 and D _Q2 , which are parasitic diode components, and parasitic capacitors C _Q1 and C _Q2, respectively. Accordingly, the first switch Q ₁ and the second switch Q ₂ are equivalently connected with the diodes D _Q1 and D _Q2 and the capacitors C _Q1 and C _Q2 in parallel to each gate. It is modeled as a switch that performs switching operation by input voltage.

The input inductor L _in is commonly connected to an upper end of the first switch Q ₁ , the second switch Q ₂ , and the primary coil L ₁ . Direct-current voltage input from the DC power source (V _i) is applied to the input inductor (L _in) through a first switch (Q _1), second switch (Q ₂₎ and the primary coil (L _1).

Rectification circuit is composed basically of two coil parts (L _2, L ₃₎ of the secondary coils divided into (L _2, L ₃₎ and a diode full-wave rectification circuit (Full wave rectifier) by (D _3, D ₄₎ It is. The output terminal of the full-wave rectification circuit is supplied with the output inductor (L _o), a smoothing capacitor (C _o) and is connected to a smoothing capacitor (C _o) load (R _o) is the output as an output voltage (V _o) of the. As a result, the AC voltages of the secondary coils L ₂ and L ₃ are rectified, smoothed, and supplied to the load _Ro .

In the circuit of FIG. 1, the first switch Q ₁ and the input inductor L _{in become} an input side circuit of the converter, and the second switch Q ₂ and the capacitor C ₃ constitute an active clamp circuit. .

A capacitor (C ₄₎ is formed to have a larger capacity operates in a voltage source which supplies energy to the output side to have the same voltage as the input voltage (V _i), the first switch (Q ₁₎ is conductive.

FIG. 2 is a graph showing waveforms at respective parts in order to theoretically explain the operation of the converter according to the present invention shown in FIG. 1. To interpret this circuit, the following assumptions are made:

i) The first switch Q ₁ operates at the rate D, the second switch Q ₂ operates at the rate 1-D, and the dead time is ignored when the switches Q ₁ and Q ₂ operate. do.

ii) The magnetizing inductance (L _m ) and the leakage inductance (L ₄ ) of the transformer are both analyzed by moving them to the primary coil (L ₁ ) side of the transformer (T _r ).

iii) The secondary side of transformer T _r has the same turns ratio of n: 1 relative to the primary side, respectively.

iv) The losses of all circuit elements are ignored.

The meaning of each symbol in FIG. 2 is as follows.

A driving voltage as a source voltage of the first switch (Q ₁₎ and the second switch (Q _2), - a first switch (Q ₁₎ and the second gate of the switch _{(Q 2): V GS1,} V GS2

V _DS1 , V _DS2 : voltages at both ends of the first switch Q ₁ and the second switch Q ₂ ,

i _Q1 , i _Q2 : current flowing through the first switch Q ₁ and the second switch Q ₂ ,

i _L4 : Current flowing through the leakage inductance (L ₄ ),

i _D3 , i _D4 : current flowing through diode (D ₃ ) and diode (D ₄ ),

i _in : Current flowing through the input power (V _i ),

V _C3 , V _C4 , V _L1 : voltage across capacitor C ₃ , capacitor C ₄ , and primary coil L ₁ .

The operation of the converter according to the present invention will be described first as follows.

In the converter of FIG. 1, two switches Q ₁ and Q ₂ alternately turn on / off an input power and convert an input power to an output. A first switch in the interval (Q ₁₎ is on the energy that was charged in the capacitor (C ₄₎ in the previous period is transmitted as an output, a second switch in the period in which (Q ₂₎ is turned on energy from the input power source (V _i) Is passed to the output.

In addition, in the dead-time section, in which the two switches Q ₁ and Q ₂ are turned off at the same time, the inductance component including the magnetizing inductance L _m and the parasitic capacitance C of the switches Q ₁ and Q ₂ . by the resonance between the _Q1, C _Q2) is made zero-voltage switching operation.

Hereinafter, the operation of the converter according to the present invention as described above will be described in more detail with respect to each mode.

In the present invention, the input inductor (L _in ), the capacitor (C ₃ ), the capacitor (C ₄ ) are all composed of a device having a relatively large capacitance. Accordingly, the current i _in flowing through the input inductor L _in approximates a constant current, and the voltage V _C3 of the capacitor C ₃ and the voltage V _C4 of the capacitor C ₄ approximate a constant voltage. Shall be.

3 (a) to 3 (f) show equivalent circuits in modes 1 to 6, respectively. The operation in each mode will be described in detail as follows.

1) Mode 1 (t ₁ ~ t ₂ ): Q ₁ turn off, Q ₂ off

In mode 1, the first switch Q ₁ is turned off and the second switch Q ₂ maintains the off state, which is the state in the previous mode.

When the first switch Q ₁ is turned off at time t ₁ , the capacitor is instantaneously caused by the resonance of the magnetizing inductance L _m , the leakage inductance L ₄ , and the parasitic capacitances C _Q1 and C _Q2 . C _Q1 is charged and capacitor C _Q2 is discharged. At the time when charging and discharging is completed, the voltage V _DS1 across the capacitor C _Q1 becomes V _i / (1-D) and the voltage V _DS2 across the capacitor C _Q2 becomes zero voltage. .

A capacitor (C _Q2) after the discharge is complete, the magnetizing inductance (L _m) and the leakage inductance (L _m) is still the anti-parallel diode (D _Q2 of the current (i _Q2) of the second switch (Q ₂₎ by the extra energy of the ), V _DS2 remains at zero voltage.

On the output side, the output inductor L _o is a reflux period in which energy is released to the output side. The diodes D ₃ and D ₄ form a reflux path to flow i _D3 and i _D4 .

2) Mode 2 (t ₂ ~ t ₃ ): Q ₁ off, Q ₂ turn on

In mode 2, the first switch Q ₁ maintains the off state, which is the state in the previous mode, and the second switch Q ₂ is turned on.

Even when the second switch Q ₂ is turned on at the time t ₂ , the antiparallel diode D _Q2 of the second switch Q ₂ continues to conduct, so that the V _DS2 becomes a zero voltage state, and thus the zero voltage turn-on is still performed. No current flows through the channel of the switch Q ₂ . On the output side, reflux is maintained during this time period, but i _D3 becomes zero at the end point t ₃ of this time period, and the reflux is terminated as the diode D ₃ is current.

3) Mode 3 (t ₃ ~ t ₄ ): Q ₁ off, Q ₂ on

In mode 3, the first switch Q ₁ and the second switch Q ₂ maintain the off state and the on state, which are the states of the previous mode, respectively.

The period of time a second switch (Q ₂₎ in the doedaga conduction duration of a period of time while the anti-parallel diode (D _Q2) begins to the channel of the second switch (Q ₂₎ the polarity of the current bakkwimyeonseo conductive for liver.

On the other hand, only the diode D ₄ is turned on at the output side, and the output inductor L _o accumulates energy. At this time, energy is supplied from the input side.

4) Mode 4 (t ₄ ~ t ₅ ): Q ₁ off, Q ₂ turn off

In mode 4, the first switch Q ₁ maintains the off state, which is the state in the previous mode, and the second switch Q ₂ is turned off.

When the second switch Q ₂ is turned off at time t ₄ , the capacitor C _{Q1 is} instantaneously caused by the resonance of the magnetizing inductance L _m , the leakage inductance L ₄ , and the parasitic capacitances C _Q1 and C _Q2 . ) Is discharged and the capacitor C _Q2 is charged. At the time when charging and discharging is completed, the voltage V _DS1 across the capacitor C _Q1 becomes zero and the voltage V _DS2 across the capacitor C _Q2 becomes the voltage of the capacitor C ₃ . V _C3 ) (= V _i / (1-D))

A capacitor (C _Q1) after the discharge is complete, the magnetizing inductance (L _m) and the leakage inductance (L ₄₎ of the continuing antiparallel diode (D _Q1 current (i _Q1) of the first switch (Q ₁₎ by the extra energy of the ), V _DS1 maintains the zero voltage state.

The output side is a reflux period in which the output inductor L _o releases the energy accumulated in the mode 3 to the output side, and the diodes D ₃ and D ₄ form a reflux path to flow i _D3 and i _D4 .

5) Mode 5 (t ₅ ~ t ₆ ): Q ₁ turn on, Q ₂ off

In mode 5, the first switch Q ₁ is turned on and the second switch Q ₂ maintains the off state, which is the state in the previous mode.

By turning on the first switch Q ₁ at time t ₅ , zero-voltage turn-on is performed and current flowing through the anti-parallel diode D _Q1 flows to the channel of the first switch Q ₁ . On the output side, reflux is maintained during this time period, but i _D4 becomes zero at the end point t ₆ of this time period, and the reflux is terminated as the diode D ₄ is current.

6) Mode 6 (t ₆ ~ t ₇ ): Q ₁ on, Q ₂ off

In mode 6, the first switch Q ₁ and the second switch Q ₂ maintain the on state and the off state, respectively, which are the states in the previous mode.

On the output side, only the diode D ₃ is turned on so that the output inductor L _o accumulates energy. At this time, energy is supplied from the capacitor C ₄ .

As described above, the operation of Modes 1 to 6 is repeated, so that soft switching is performed.

On the other hand, the output inductor (L _o ) and the capacitor (C ₄ ) connected to the output terminal of the full-wave rectifier circuit functions as a low pass filter (Low Pass Filter). As a result, noise of the voltage output from the full-wave rectifying circuit is removed. In addition, as described above, the output inductor _LO serves to supply the stored energy to the output side during the dead time of the output to the full-wave rectifying circuit.

In the above embodiment, a DC / DC soft switching converter is used as a step-down converter, but the soft switching converter according to the present invention can be used in step-down type as well as step-up type. This may be implemented by changing the turns ratio of the primary coil L ₁ and the secondary coils L ₂ and L ₃ of the transformer T _r .

According to the present invention, as shown in Figure 2, the alternating state of the switching state of the first switch (Q ₁ ) and the second switch (Q ₂ ) (that is, the voltage change of V _GS1 and V _GS2 ) zero voltage Since it is performed in the in state (i.e., when V _L1 is zero voltage), soft switching without switching loss, which is a loss occurring in the switch due to superposition of voltage and current, is performed.

In addition, switching loss is controlled by using the parasitic capacitances C _Q1 and C _Q2 and the resonance caused by the leakage inductance L ₄ of the transformer T _r , and the switching operation by using the parasitic diodes D _Q1 and D _Q2 . Can be reduced. This reduction in switching losses can increase the switching frequency, thereby reducing the size of the transformer, inductor, capacitors, etc., thereby reducing the volume of the entire system.

In addition, according to the present invention, as shown in FIG. 2, the primary side current of the transformer T _r is transmitted as a triangular wave instead of a square wave, so that the primary side voltage and the secondary side voltage have less ripple. EMI noise is reduced. Thus, the efficiency of the entire system is increased.

Although the above has been illustrated and described with respect to the preferred embodiment of the present invention, the present invention is not limited to the above-described specific embodiment, and those skilled in the art, various modifications that do not depart from the gist of the present invention. Of course, such modifications will fall within the claims of the present invention.

Claims (8)

A transformer having a primary coil having a magnetizing inductance component and a leakage inductance component, and a secondary coil coupled to the primary coil; First and second switches connected in parallel with respect to the primary coils, respectively; First and second diodes connected in parallel to both ends of each of the first switch and the second switch; A first capacitor and a second capacitor connected in parallel to both ends of the first switch and the second switch; A third capacitor connected in series with the second switch; A fourth capacitor connected in series with the primary coil; And An inductor commonly connected to one end of the first switch, the second switch, and the primary coil to apply a DC voltage input from a DC power source to the first switch, the second switch, and the primary coil; Soft switching converter comprising a. The method of claim 1, And the first switch and / or the second switch are made of a semiconductor device. The method of claim 2, And the first switch and / or the second switch is an insulated gate type FET. The method of claim 3, wherein Said first diode and / or said second diode being implemented by an anti-parallel parasitic diode component of said FET. The method according to claim 3 or 4, And said first capacitor and / or said second capacitor are implemented by parasitic capacitance components of said FET. The method of claim 1, Soft rectifying circuit further comprises a rectifier circuit for rectifying the AC voltage of the secondary coil. The method of claim 6, And the rectifier circuit part is a full wave rectifier circuit. The method according to claim 6 or 7, And a low pass filter connected to an output of the rectifier circuit.