KR20240024157A - Full Bridge DC-DC Converter Having Soft-Switching Circuit Under Entire Load Condition - Google Patents

Abstract

The present invention relates to a full-bridge converter equipped with a full-load soft switching circuit that can reduce hard switching noise at full load.
The present invention includes at least one soft switching circuit connected between an input power source and a full bridge circuit, wherein the soft switching circuit consists only of passive elements that do not require a separate driving power source, so that the primary side current of the transformer is insufficient for no-load or It is characterized in that hard switching of the first to fourth switches is prevented under low load conditions.

Description

Full Bridge Converter Having Soft-Switching Circuit Under Entire Load Condition}

The present invention relates to a full-bridge converter equipped with a full-load soft switching circuit that can reduce hard switching noise at full load.

A full bridge DC-DC converter uses the parasitic capacitor of the switch element provided in the primary side full bridge circuit and the leakage inductance of the transformer to perform zero voltage switching (ZVS), that is, soft switching, of the primary side switch. Because this is possible, it has high efficiency and is applied to welders, electric vehicles, etc., which require high-efficiency power conversion through high-speed switching operations.

As shown in Figure 1, the full-bridge converter is an insulated converter in which the primary and secondary circuits are electrically isolated around the transformer 11. The primary side uses a full bridge structure, and the secondary side uses a center tap structure. High current can be generated at low output voltage. The energy generated in the converter's power circuit is transferred from the primary side of the transformer (11) to the secondary side and supplied to the load, and depending on the size of the energy consumed by the load, it is transmitted from the converter's power circuit to the primary side of the transformer (11). The size of the current is determined, and this current can be divided according to the energy circulation operation and energy transfer operation of the converter. When switching from energy circulation to energy transfer operation, energy is stored in the leakage inductance of the transformer, and when switching from energy transfer to energy circulation operation, the leakage inductance (L _lkg1 ) of the transformer (11) and the secondary side of the transformer (11) are stored. Energy is stored in the output inductor (L _o1 ).

In order for zero voltage switching of the converter's switches (Q ₁ , Q ₂ , Q ₃ , Q ₄ ; for example, MOSFET) to occur, energy is consumed on the secondary side of the transformer 11, which causes the primary side of the transformer 11 Current must flow in the circuit, and if sufficient current is not generated in the primary circuit, it is difficult to form a zero-voltage switching condition. Compared to the case of switching from energy transfer to energy circulation operation, it is more difficult to form a zero voltage switching condition when switching from energy circulation to energy transfer operation.

In addition, regardless of energy circulation and energy transfer operations, under low load or no-load conditions, the current flowing in the primary circuit of the transformer 11 is small, so the switch element (MOSFET) of the primary circuit of the transformer 11 is used for zero voltage switching. Energy is inevitably insufficient, resulting in hard switching operation for the switch element. This causes hard switching noise.

In the past, in order to deal with hard switching noise, a technique was used to inject energy to artificially create a zero voltage switching condition by adding an auxiliary power source to the full bridge circuit of the converter. However, when applying auxiliary power to control the primary circuit of the transformer, not only does the circuit area and manufacturing cost increase, but an additional controller is required to control the auxiliary power. Additionally, conventional methods have been used to adjust the inductance of the primary side of the transformer so that zero voltage switching conditions can be easily formed.

[Patent Document 1] discloses a full-bridge converter that can operate properly under a wide range of load conditions, including no-load conditions. In this document, an auxiliary circuit (2) including an auxiliary transformer is used, and the auxiliary circuit (2) includes an auxiliary transformer (T _A ) and two diodes (D _A1 , D _A2 ) on the primary side of the peripheral summation (T _M ). The added auxiliary transformer (T _A ) is a coupled inductor with a transformer structure. Since the inductance of the coupled inductor affects the flow of primary current, independent circuit design is impossible, and the auxiliary There is a problem that it is difficult to optimize the design of the converter because the characteristics of the transformer must be considered.

[Patent Document 1] Korean Patent No. 10-0352804 (registered on September 2, 2002)

[Non-patent Document 1] Kwang-Hwa Liu and Fred C. Y. Lee, "Zero-Voltage Switching Technique in DC/DC Converters, "IEEE Trans. Power Electron., vol. 5, no. 3, pp. 293-304, July 1990. [Non-patent Document 2] Oliver D. Patterson and Deepakraj M. Divan, "Pseudo-Resonant Full Bridge DC/DC Converter," IEEE Trans. Power Electron., vol. 6, no. 4, pp. 671-678, Oct. 1991.

The purpose of the present invention, designed to solve the above problems, is to reduce hard switching noise by adding a soft switching circuit composed of passive elements to the full bridge circuit, and the soft switching circuit does not require an auxiliary power source and reduces the flow of current on the primary side of the transformer. The goal is to provide a full-bridge converter with a full-load soft switching circuit that facilitates optimal design of the converter because it does not affect the

A full bridge converter equipped with a full-load soft switching circuit according to the present invention to achieve the above object includes an input power source; A transformer with a primary winding, a secondary winding, and a leakage inductance; a full bridge circuit connected to the primary side of the transformer; At least one soft switching circuit connected between the input power and the full bridge circuit, wherein the full bridge circuit includes first and second switches coupled in series at the first node, and a third switch coupled in series at the second node. and a fourth switch, wherein the first and second switches are connected in parallel to the input power source, the third and fourth switches are connected in parallel to the input power source, and each of the first and second nodes is It is electrically coupled to the primary winding of the transformer, and one soft switching circuit is connected in parallel between a half bridge composed of the first and second switches and the input power supply, and simultaneously connected to the third and fourth switches. Another soft switching circuit is connected in parallel between the other configured half bridge and the input power supply, and the soft switching circuit consists only of passive elements that do not require a separate driving power source, so that the primary current of the transformer is insufficient. It is characterized in that hard switching of the first to fourth switches is prevented under no-load or low-load conditions.

Additionally, the soft switching circuit is characterized by being composed of a pair of resonance capacitors, a pair of diodes, and a resonance inductor.

In addition, the soft switching circuit charges the parasitic capacitor of at least one of the first to fourth switches and discharges the parasitic capacitor of the other switch in the dead time period of the converter to reduce the zero voltage of the other switch. It is characterized by creating a switching condition.

In addition, the resonance period is set to store the energy required for zero voltage switching in the dead time period in the resonance inductor, and the resonance period is determined by a pair of resonance capacitors and a resonance inductor and is set to be greater than the dead time time. It is characterized by

In the present invention, by adding a soft switching circuit to the transformer primary circuit, zero voltage switching operation is stably achieved at full load (from no load to full load), and the soft switching circuit does not require auxiliary power and supports the flow of transformer primary current. Since there is no influence, optimal design of the converter is easy.

1 is a circuit diagram of a conventional full bridge converter,
Figure 2 is a circuit diagram of a full-bridge converter with a full-load soft switching circuit according to an embodiment of the present invention;
Figure 3 is a timing chart of one cycle of operation for the full bridge converter of Figure 2;
Figure 4 is a timing chart of one cycle of operation for a half bridge constituting the full bridge converter of Figure 2;
Figure 5 is a circuit diagram showing mode 0 operation of a full bridge converter according to an embodiment;
Figure 6 is a circuit diagram showing mode 1 operation of a full bridge converter according to an embodiment;
7 is a circuit diagram showing mode 2 operation of a full bridge converter according to an embodiment;
8 is a circuit diagram showing mode 3 operation of a full bridge converter according to an embodiment;
9 is a circuit diagram showing mode 4 operation of a full bridge converter according to an embodiment;
10 is a circuit diagram showing mode 5 operation of a full bridge converter according to an embodiment;
11 and 12 are equivalent circuit diagrams for simulating a full bridge converter according to an embodiment;
13 is an operating waveform of a full bridge converter under full load conditions according to an embodiment;
14 is an operating waveform of a full bridge converter under no-load conditions according to an embodiment;
15 is an experimental waveform of a full bridge converter under full load conditions according to an embodiment,
Figure 16 is an experimental waveform of a full bridge converter under low load conditions according to an embodiment.

Hereinafter, the present invention will be explained by explaining embodiments of the present invention with reference to the attached drawings. The same reference numerals in each drawing indicate the same member. Additionally, in describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. Additionally, when a part "includes" a certain component, this means that it may further include other components rather than excluding other components, unless specifically stated to the contrary.

As shown in Figure 2, the full-bridge converter equipped with a full-load soft switching circuit according to the present invention applies a full bridge structure on the primary side of the transformer 11 and a center tap structure on the secondary side to generate high current at low output voltage. occurs. The primary full bridge circuit includes four switches (Q ₁ , Q ₂ , Q ₃ , Q ₄ ), that is, two half bridges are connected in parallel. One half bridge consists of two switches (Q ₁ , Q ₂ ) connected in series, and the other half bridge consists of two switches (Q ₃ , Q ₄ ) connected in series.

The full bridge circuit includes a first switch (Q ₁ ) and a second switch (Q ₂ ) coupled in series at the first node (N1), a third switch (Q ₃ ) coupled in series at the second node (N2), and It includes a fourth switch (Q ₄ ). The transformer 11 has a primary winding, a secondary winding, and a parasitic leakage inductance (L _lkg1 ) naturally formed from the winding structure of the transformer.

Each switch (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) is a semiconductor device with a parasitic capacitor placed in parallel with the switch's conducting terminals (e.g., source and drain for MOSFETs, emitter and collector for BJTs and IGBTs). It may include switching elements (e.g., MOSFET, BJT, IGBT, etc.) and may have similarly arranged parasitic conductive diodes.

The series connection of the first and second switches (Q ₁ , Q ₂ ) is connected in parallel to the input power (V _in ), and the series connection of the third and fourth switches (Q ₃ , Q ₄ ) is connected in parallel to the input power (V _in ) is connected in parallel. Each of the first and second nodes N1 and N2 is electrically coupled to the terminal of the primary winding of the transformer 11.

If there is not enough current flowing through the primary side of the transformer at no load or low load, the parasitic capacitor of the switch (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) may be turned on according to the control signal of the gate signal while being charged. . The turn-on switch generates power loss when charging or discharging the energy stored in the parasitic capacitor, and in addition, it resonates by combining with the parasitic inductance component present in the full bridge circuit. Noise at the resonant frequency may be generated by the leakage inductance and parasitic capacitor of a hard switching switch. If noise much greater than the withstand voltage of the switch is generated, permanent damage to the switch may occur. This hard switching noise may cause interference in surrounding sensing circuits, and the hard switching noise may also affect the gate driving circuit (not shown) that controls the switches (Q ₁ , Q ₂ , Q ₃ , Q ₄ ). do. Therefore, it is important to reduce hard switching noise in order to operate stably at full load from no load to full load.

In the embodiment, a soft switching circuit 10 is added to the full bridge circuit to supply current to each of the switches Q ₁ , Q ₂ , Q ₃ , and Q ₄ to form a zero-voltage switching condition. The full bridge includes a pair of half bridges with a symmetrical structure, and each half bridge includes a pair of switches (Q ₁ , Q ₂ ) (Q ₃ , Q ₄ ) connected in series. A soft switching circuit 10 to reduce hard switching noise is connected in parallel to each half bridge. The soft switching circuit 10 can be composed of only passive elements (diodes, capacitors, and inductors) that do not require a separate driving power source. One soft switching circuit 10 includes a pair of diodes (D ₁ , D ₂ ) connected in series, a pair of resonance capacitors (C ₁ , C ₂ ), and a resonance inductor (L _a ) connected in series, and the other One soft switching circuit 10 includes a pair of diodes (D ₃ , D ₄ ) connected in series, a pair of resonance capacitors (C ₃ , C ₄ ) connected in series, and a resonance inductor (L _b ).

The resonance inductor (L _a ) (L _b ) of the soft switching circuit 10 is an inductor for high-frequency switching direct current so as not to saturate during energy circulation. The current size of the resonant inductor (L _a ) (L _b ) is determined by the resonant capacitors (C ₁ , C _{2 ,} C ₃ , C ₄ ), the input power (V _in ), and the charging time. The resonant inductor (L _a ) (L _b ) supplies current in the dead time section of the power circuit to charge or discharge the parasitic capacitor of the switch (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) to form a zero-voltage switching condition. Do what you are told to do. In the remaining sections except for the dead time section, the current stored in the resonant inductor (L _a ) (L _b ) operates as a forward or reverse current source.

In the embodiment, a zero voltage switching condition may be formed through the switching operation of the soft switching circuit 10 and the switches Q ₁ , Q ₂ , Q ₃ , and Q ₄ . Therefore, the current flows constantly through the resonance inductor (L _a ) (L _b ), causing some conduction loss in the diode or switch in the path through which the resonance current flows. However, the inductor energy required for zero-voltage switching of the switch can be stored with a small resonance current if the resonance inductor (L _a ) (L _b ) is designed sufficiently large. Therefore, even if current flows continuously through the resonant inductor (L _a ) (L _b ), the current stress and conduction loss on the circuit can be designed to be small.

In the soft switching circuit 10, the resonance inductor L _a (L _b ) resonates with the parasitic capacitor of the switch in the dead time section of the switches Q ₁ , Q ₂ , Q ₃ , and Q ₄ forming a full bridge.

The resonant inductor (L _a ) (L _b ) stores energy by alternating the direction of the current whenever a dead time section begins and operates as a current source in the remaining operation sections (energy transfer section and energy circulation section). At this time, energy is stored in each resonance inductor (L _a , L _b ) by resonance of the resonance capacitors (C ₁ , C _2, C ₃ , C ₄ ) and the resonance inductors (L _a , L _b ). Energy is stored during one quarter of the resonance period. In the dead time section where the energy circulation section ends, the resonance period is set to store the energy required for zero voltage switching in the resonance inductor, that is, the resonance capacitors (C ₁ , C _{2 ,} C ₃ , C ₄ ) and the resonance inductor (L _a , L _b ) must be greater than the dead time.

Referring to Figure 3, the operation timing chart corresponding to one cycle of the full bridge converter controlled by the zero voltage switching pulse width modulation method (ZVS PWM) is from mode 0 section (M ₀ ) to mode 9 section (M ₉ ). It consists of 10 sections. For reference, FIG. 4 is an operation timing chart of one cycle for a half bridge including first and second switches (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) in relation to the operation timing chart of FIG. 3 . The operations of the first and second switches (Q ₁ , Q ₂ ) performed in half of one cycle are replaced by the operations of the third and fourth switches (Q ₃ , Q ₄ ) in the other half and repeated in the same pattern.

Below, the mode 0 section (M ₀ ) corresponding to half of one cycle, the mode 4 section (M ₄ ), and the mode 5 section (M ₅ ) where the remaining half begins will be described.

Referring to FIG. 5, the mode 0 section (M ₀ ) is from time t ₀ to time t ₁ . In the mode 0 section (M ₀ ), since the energy circulation of the previous cycle is maintained, the primary current of the transformer 11 circulates in the reverse direction through the second and fourth switches (Q ₂ , Q ₄ ) that are turned on. At this time, the soft switching circuit 10 operates as a current source. If the switching frequency is very high, the resonant inductor L _a (L _b ) of the soft switching circuit 10 operates as a current source by the energy stored in the inductor for nanoseconds (nsec). For example, when the polarity of the voltage applied to the resonance inductor (L _a ) changes, the direction of the current (i _La ) in the resonance inductor (L _a ) changes to the opposite direction and energy is stored, and the energy stored in the resonance inductor (L _a ) changes to the opposite direction. It operates as a current source. In the mode 0 section (M ₀ ), current is supplied to the second switch (Q ₂ ) through the diode (D ₂ ).

The mode 0 section (M ₀ ) performs an energy circulation operation. Since the primary current of the transformer 11 is direct current, magnetic coupling does not occur in the transformer 11, so energy is not transferred to the secondary side of the transformer 11. . The energy stored in the output inductor (L _o ) causes current to flow in the secondary side of the transformer (11), and the amount of current gradually decreases as energy is consumed in the output side load (R _L ).

Referring to FIG. 6, mode 1 section (M ₁ ) is from time t ₁ to time t ₂ and is a dead time section in which both the first and second switches (Q ₁ ) (Q ₂ ) are turned off.

As the second switch (Q ₂ ) is turned off, the parasitic capacitor voltage (V _ds2 ) of the second switch (Q ₂ ) is charged and the parasitic capacitor voltage (V _ds1 ) of the first switch (Q ₁ ) is discharged. It is stabilized at a voltage (V _in /2) corresponding to half of the input voltage. If sufficient energy is stored in the leakage inductance (L _1kg1 ) of the transformer (11), the parasitic capacitor of the second switch (Q ₂ ) continues to It is charged and increases to the input voltage (V _in ). Here, the parasitic capacitor of the first switch (Q ₁ ) is discharged to 0 voltage, which becomes the zero voltage condition of the first switch (Q ₁ ). If the primary current of the transformer 11 is insufficient and the zero voltage condition of the first switch (Q ₁ ) does not occur only with the leakage inductance (L _{1 kg 1} ) of the transformer 11, the resonance inductor (L) of the soft switching circuit 10 The energy stored in _a ) additionally charges the parasitic capacitor of the second switch (Q ₂ ) to generate a zero voltage condition of the first switch (Q ₁ ). _For example, when the primary current of the transformer 11 is insufficient at no load or _low load, the second switch ( The charging operation for the parasitic capacitor of Q ₂ ) is continued so that the first switch (Q ₁ ) can be discharged to 0 voltage.

Referring to FIG. 7, the mode 2 section (M ₂ ) is from time t ₂ to time t ₃ .

As the first switch (Q ₁ ), which met the zero voltage switching condition in the previous mode 1 section (M ₁ ), is turned on, the primary current of the transformer 11 begins to increase in the forward direction in the mode 2 section (M ₂ ). Thus, energy is supplied to the transformer 11. Since the parasitic capacitor of the first switch (Q ₁ ) has already reached a zero voltage condition in the mode 1 section (M ₁ ), the first switch (Q ₁ ) conducts without turn-on switching loss in the mode 2 section (M ₂ ). When the first switch (Q1) is turned on, the resonance inductor (L _a ) of the soft switching circuit 10 resonates with the resonance capacitor (C ₂ ) and is charged by the forward current, and the inductor current (I _La ) and the capacitor voltage (V _C2 ) starts to increase.

Referring to FIG. 8, the mode 3 section (M ₃ ) is from time t ₃ to time t ₄ .

In the mode 3 section (M ₃ ), when the first switch (Q ₁ ) is turned on, the current on the primary side of the transformer 11 flows in the forward direction and energy is transferred to the secondary side of the transformer 11. When charging of the resonance capacitor (C ₂ ) is completed, the current (I _La ) of the resonance inductor (L _a ) flows to the input power (V _in ) through the diode (D ₁ ). The primary current of the transformer 11 is determined by the turns ratio of the primary and secondary sides of the transformer 11, the output inductor (L _o ) of the secondary side, the output voltage, and the load resistance.

Referring to FIG. 9, the mode 4 section (M ₄ ) is from time t ₄ to time t ₅ .

In the mode 4 section (M ₄ ), the first switch (Q ₁ ) is turned off. The mode 4 section (M ₄ ) is a dead time section in which both the first and second switches (Q ₁ ) (Q ₂ ) are turned off. Since the turn-off time of the first and second switches (Q ₁ ) (Q ₂ ) is a very short time, energy is transferred from the primary side of the transformer 11 to the secondary side.

When the first switch (Q ₁ ) is turned off, the current (I _La ) of the resonance inductor (L _a ) of the soft switching circuit 10 flows in the forward direction and charges the parasitic capacitor of the turned-off first switch (Q ₁ ). . At this time, the parasitic capacitor of the turned-off second switch (Q ₂ ) is discharged. Here, the parasitic capacitor of the second switch (Q ₂ ) discharges to 0 voltage, which becomes the zero voltage condition of the second switch (Q ₂ ).

Referring to FIG. 10, the mode 5 section (M ₅ ) is from time t ₅ to time t ₆ .

In the mode 5 section (M ₅ ), the second switch (Q ₂ ) is turned on and the primary current of the transformer 11 circulates through the second and fourth switches (Q ₂ ) (Q ₄ ). In the mode 5 section (M ₅ ), the primary current of the transformer 11 is direct current, so magnetic coupling does not occur in the transformer 11, so energy is not transferred from the primary side of the transformer 11 to the secondary side. The current in the output inductor (L _o ) circulates in the secondary circuit of the transformer (11).

When the second switch (Q ₂ ) is turned on, the resonance capacitor (C ₂ ) of the soft switching circuit 10 charges energy to the resonance inductor (L _a ). The voltage of the resonance capacitor (C ₂ ) is discharged to 0 voltage. The current (I _La ) of the resonant inductor (L _a ) flows in the reverse direction and passes through the diode (D ₂ ) and the second switch (Q ₂ ). The current (I _La ) of the resonant inductor (L _a ) operates as a current source from the mode 6 section (M ₆ ) to the mode 9 section (M ₉ ).

In this way, the soft switching circuit 10 stores the energy generated by resonance of the resonance capacitor and the resonance inductor of the soft switching circuit 10 in the resonance inductor during the time spanning from the start of each dead time section to the energy transfer section and the energy circulation section. . Regardless of the presence or absence of current on the primary side of the transformer 11, the resonant inductor of the soft switching circuit supplies the stored energy to the switch to generate a zero voltage switching condition.

Figures 11 and 12 are equivalent circuit diagrams for simulated actual cases of the soft switching circuit, Figure 13 is the operating waveform of the soft switching circuit under full load conditions, and Figure 14 is the operating waveform of the soft switching circuit under no load conditions.

If the primary current (I _p1 ) is sufficiently large, the zero voltage switching operation of the third and fourth switches (Q 3 , Q ₄ ) among the first to fourth switches (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) is smooth _. The first and second switches (Q ₁ , Q ₂ ) must perform a zero-voltage switching operation with a current of leakage inductance (L _{1 kg 1} ). If the zero voltage switching operation for the first and second switches (Q ₁ , Q ₂ ) does not occur at low load, hard switching noise increases and power conversion efficiency decreases. In the embodiment, a soft switching circuit 10 is connected in parallel to a pair of switches (Q ₁ , Q ₂ ) connected in series and another pair of switches (Q ₃ , Q ₄ ) connected in series, respectively, and Zero voltage switching operation for switches (Q ₁ , Q ₂ ) (Q ₃ , Q ₄ ) connected in series is performed smoothly.

Referring to FIG. 13, since there is a load on the secondary side of the transformer 11, a current flows through the primary side of the transformer 11 and the soft switching circuit 10, that is, it resonates with the primary current (I _p1 ; ①). The current (I _La ;②) of the inductor (L _a ) increases. At this time, the voltage (V _sw1 ) of the first switch (Q ₁ ) of the soft switching circuit 10 is converted to a low state (③), thereby satisfying the zero voltage switching condition. The first switch (Q ₁ ) for which the zero voltage switching condition is met is turned on by the gate signal (G1) (④). Since the turn-on operation is performed on the first switch (Q ₁ ) under zero voltage switching conditions, conduction loss can be reduced.

Referring to FIG. 14, under no-load conditions, the primary current (I _p1 ; ⑤) of the transformer 11 depends on the current (I _La ; ⑥) of the resonant inductor (L _a ) because only a small magnetization current flows. 1 The voltage (V _sw1 ) of the switch (Q ₁ ) switches to the low state (⑦), and the first switch (Q ₁ ) that has met the zero voltage switching condition is turned on by the gate signal (G1) (⑧). . In this way, at no load or low load, the primary current of the transformer 11 is greatly reduced, so hard switching operation can be performed in all switches (Q ₁ , Q ₂ , Q ₃ , Q ₄ ), but the soft switching circuit (10) of the embodiment ), hard switching noise can be prevented by forming the zero voltage switching conditions of the switch.

Figure 15 is an operating waveform tested under full load conditions at an output voltage of 50V and an output current of 200A, and Figure 16 is an operating waveform tested at an output voltage of 50V and an output current of 200A under low load conditions. Here, channel 1 (CH1) is the voltage of the first switch (Q ₁ ), channel 2 (CH2) is the gate signal (G1) of the first switch (Q ₁ ), and channel 3 (CH3) is the resonance inductor (L _a ). The current (I _La ), channel 4 (CH4) is the voltage (Vc ₂ ) of the resonance capacitor (C ₂ ).

Referring to FIG. 15, under full load conditions, at the point (②) when the gate signal (G1) of the first switch (Q ₁ ) becomes high, the first switch (Q ₁ ) is turned off (①), and the resonance inductor (L _a As the current (I _La ) flows into the resonance capacitor (C ₂ ), the current (③, I _La ) of the resonance inductor (L _a ) and the voltage (④, Vc ₂ ) of the resonance capacitor (C ₂ ) rise. Save energy. In addition, at the point in time (⑤) when the gate signal (G1) of the first switch (Q ₁ ) becomes low, the first switch (Q ₁ ) is turned on (⑥), and the current (I _La ) of the resonance inductor (L _a ) The current (③, I _La ) of the resonance inductor (L _a ) and the voltage (④, Vc ₂ ) of the resonance capacitor (C ₂ ) flow through the first switch (Q ₁ ) via the resonance capacitor (C ₂ ). descends. This confirms that the resonant inductor and resonant capacitor of the soft switching circuit can suppress hard switching noise that may occur in the switch by absorbing or emitting energy.

Referring to FIG. 16, under no-load conditions, at the point (②) when the gate signal (G1) of the first switch (Q ₁ ) becomes high, the first switch (Q ₁ ) is turned off (①), and the resonance inductor (L _a As the current (I _La ) flows into the resonance capacitor (C ₂ ), the current (③, I _La ) of the resonance inductor (L _a ) and the voltage (④, Vc ₂ ) of the resonance capacitor (C ₂ ) rise. Save energy. Afterwards, at the point when the gate signal (G1) of the first switch (Q ₁ ) is lowered and the first switch (Q ₁ ) is turned on, the current (I _La ) of the resonance inductor (L _a ) passes through the resonance capacitor (C ₂ ). Accordingly, as the flow flows through the first switch (Q ₁ ), the current (I _La ) of the resonance inductor (L _a ) and the voltage (Vc ₂ ) of the resonance capacitor (C ₂ ) decrease.

In this embodiment, the full bridge converter can suppress hard switching noise that may occur in the switch by absorbing or emitting energy by the resonant inductor and resonant capacitor of the added soft switching circuit at full load (full load to no load). can confirm.

The description of the present invention described above is for illustrative purposes, and those skilled in the art will understand that the present invention can be easily modified into other specific forms without changing the technical idea or essential features of the present invention. will be.

10: soft switching circuit
11: transformer

Claims (4)

input power;
A transformer with a primary winding, a secondary winding, and a leakage inductance;
a full bridge circuit connected to the primary side of the transformer;
At least one soft switching circuit connected between the input power source and the full bridge circuit,
The full bridge circuit includes first and second switches coupled in series at a first node, and third and fourth switches coupled in series at a second node, wherein the first and second switches are connected to the input power. connected in parallel, wherein the third and fourth switches are connected in parallel to the input power source, and each of the first and second nodes is electrically coupled to the primary winding of the transformer,
One soft switching circuit is connected in parallel between one half bridge composed of the first and second switches and the input power supply, and simultaneously between the other half bridge composed of the third and fourth switches and the input power supply. Another of the soft switching circuits is connected in parallel,
The soft switching circuit consists only of passive elements that do not require a separate driving power source, and prevents hard switching of the first to fourth switches under no-load or low-load conditions when the primary side current of the transformer is insufficient. Full bridge converter with full-load soft switching circuitry. According to paragraph 1,
A full bridge converter with a full-load soft switching circuit, characterized in that the soft switching circuit consists of a pair of resonant capacitors, a pair of diodes, and a resonant inductor. According to paragraph 2,
The soft switching circuit charges the parasitic capacitor of at least one of the first to fourth switches in the dead time period of the converter and discharges the parasitic capacitor of the other switch to set the zero voltage switching condition of the other switch. A full-bridge converter with a full-load soft switching circuit that generates. According to paragraph 3,
In the dead time section, the resonance period is set to store the energy required for zero voltage switching in the resonance inductor,
A full bridge converter with a full-load soft switching circuit, characterized in that the resonance period is determined by a pair of resonance capacitors and a resonance inductor and is set to be greater than the dead time time.