KR100207020B1 - A snubber circuit for being no loss and to improve circuit for input-factor of a dc/dc converter - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lossless snubber circuit for soft switching a switching element in a DC / DC converter in a conventional single or two switch type converter, and to an input power factor improving circuit of a DC / DC converter to which the circuit is applied. In addition to the components of the two-switch forward DC / DC converter, the first switch S ₁ is connected in series between the first snubber capacitor C20, the first snubber diode D21 and the snubber. An inductor L20 and a current diode D20 connected to the second switch S ₂ at a contact point of the first snubber capacitor C20 and the first snubber diode D21. Primary side snubber circuit 200; A second snubber capacitor C10 and a second snubber diode D11 and the second snubber capacitor C10 and the second snubber diode D11 connected in series across the secondary side of the transformer Tr; A secondary snubber circuit (100) consisting of a second snubber diode (D10) connected to a rear end of the smoothing inductor (L _f ) at a contact of; AC filter 310 for filtering the input AC power, bridge diode 320 for rectifying and outputting the filtered AC power, reflux diode D ₁ and first switch S _{1 in} the bridge diode 320. An input power factor improvement circuit 300 including a boost inductor L330 connected to a contact of the power factor; It is configured to further include, to eliminate switching losses and parasitic vibration to reduce the generation of electromagnetic waves, to eliminate the harmonic interference caused by the waveform distortion of the input current is very excellent invention that can increase the power transmission efficiency.

Description

Lossless Snubber Circuit and Input Power Factor Correction Circuit for Soft Switching of DC / DC Converters

The present invention relates to a lossless snubber circuit for soft switching of a DC / DC converter and an input power factor improvement circuit of a DC / DC converter to which the circuit is applied, and more particularly, in a single or two switch type converter, Soft-switching switching elements in the DC / DC converter using lossless snubbers to eliminate switching losses that occur during turn-on or turn-off and due to reverse recovery characteristics of the output diodes In addition to the soft switching of the output rectifier diode, the DC / DC converter can reduce EMI (Electro Magnetic Interference) due to reverse recovery loss and parasitic vibration of the diode, especially the software of the forward DC / DC converter. Lossless snubber circuit for switching and converter using boost current as input power As a simple circuit, the present invention relates to an input power factor improvement circuit of a DC / DC converter that can improve the power factor of input power and improve power usage and transmission efficiency.

FIG. 1 shows a basic configuration circuit of a conventional two-switch forward converter which performs a DC / DC converter function by hard-switching, and a high frequency transformer for inducing power applied intermittently to the secondary side. (Tr); First and second switches S ₁ and S ₂ for intermittently applying the supplied DC power to the primary side of the transformer Tr; A freewheeling diode D ₁ connected in a reverse direction between the first switch S ₁ and a power source; A reflux diode (D ₂ ) connected in a reverse direction between the second switch (S ₂ ) and ground; An output rectifier diode (D ₃ , D ₄ ) for rectifying the current induced on the secondary side of the transformer (Tr); And an output filter (L _f , Co) for smoothing the output current. It consists of the main components of the.

FIG. 2 illustrates a basic operation waveform diagram of the hard switching two-switch forward DC / DC converter configured as described above, and the basic operation of the forward converter of FIG. 1 will be described with reference to the waveform diagram.

First, when the first and second switches S ₁ and S ₂ are simultaneously turned on at a time t ₁ , a DC input voltage Vin is applied to the primary winding (winding: N ₁ ) of the high frequency transformer Tr. As a result, the secondary winding (winding: N ₂ ) generates a voltage of (N ₂ / N ₁ ) Vin. The voltage generated in the secondary winding is rectified through the output rectifying diode D ₃ or D ₄ and smoothed by the output filters L _f and Co to be supplied to the load.

At the time t ₂ while the power is being supplied to the load as described above, the first and second switches S ₁ and S ₂ are turned off, and the leakage inductance and the excitation energy of the high frequency transformer Tr are refluxed. Through the diodes (D ₁ , D ₂ ) it is returned to the input DC power Vin. At this time, the voltage of the primary winding of the high frequency transformer (Tr) is clamped to the input DC voltage Vin by the reflux diodes (D ₁ , D ₂ ), so that the first and second switches (S ₁ , S ₂₎ The voltage across both ends is also Vin.

However, in the DC / DC converter operating as described above, the first and second switches of the first and second switches by the parasitic capacitance (Cp) and the wiring inductance in the _{(S 1, S 2) (} S 1, S ₂ ) exhibits a high impedance at time t ₂ when the switch is turned off, and thus an impedance of the switches S ₁ and S ₂ at time t ₂ when the first and second switches S ₁ and S ₂ turn off. Is abruptly changed to generate a surge voltage according to the switching as shown in the V _S1 graph of FIG. Surge voltage generated in this manner, the switch is to impose a high voltage stress to (S _1, S ₂₎ shorten the service life of the switch (S _1, S _2), also the switches (S _1, S ₂₎ The tail current flowing for a short time after turning off causes switching power loss.

In addition, when the first and second switches S ₁ and S ₂ are turned off at a time t ₂ , a reverse voltage is rapidly applied to the output rectifying diode D ₃ , whereby the high frequency transformer Tr and the output a rectifier diode (D ₃₎ is that the parasitic oscillation and the surge voltage caused by a parasitic capacitance (Cp) is applied severe voltage stress on the output rectifying diode (D ₃₎ Thus the output rectifying diode (D ₃₎ the destruction of the In addition, the noise may be generated in the output DC voltage to reduce the quality of the output power. Such a phenomenon may occur when the first and second switches S ₁ and S ₂ are turned on. _The same occurs in the output rectifier diode D _{4 to} which the reverse voltage is rapidly applied at _one time point.

In order to suppress the occurrence of surge voltage and parasitic vibration due to the switching as described above, the primary side main switching unit S ₁ , S ₂ and D ₁ , D _{2 of} the high frequency transformer Tr and the output rectifying diode of the secondary side capacitor (RC) or a resistor-capacitor - (D _3, D ₄₎ resistance to the diode (RCD), but this method of applying a snubber circuit proposed consisting of, this method the switch (S _1, S ₂₎ of the Since the energy accumulated in each snubber capacitor during turn-on and turn-off is consumed by discharging through the snubber resistor, the higher the switching frequency and the higher the input voltage, the larger the switching loss occurs. There is still a problem.

Also, in the single switch forward DC / DC converter having the circuit configuration as shown in FIG. ₃ , the parasitic capacitance Cp, the wiring inductance of the switch S ₁ and the diodes D ₁ , D ₃ , D ₄ , and the high frequency transformer ( Tr due to leakage inductance, the switch (in the switching element during the turn-on and turn-off of the _{s 1) (s 1, D} 1, D 3, when applied to a rapid voltage change at both ends of the D ₄₎ of the switch in), ( S ₁ ) and the diodes D ₁ , D ₃ , and D ₄ have a problem in that a surge voltage and a switching loss occur.

In addition, in the conventional DC / DC converter using an AC voltage as a direct power source, as shown in FIG. 4, only the diode rectifier 30 is used for the AC input to charge energy in the input capacitor Cin, thereby providing a direct current. Used as a power source.

However, in the case of generating and using the DC power supply by the above method, the AC input current Iac is transferred to the capacitor CIN only when the AC input voltage Vac is greater than the voltage Vin of the input capacitor CIN. Therefore, as shown in FIG. 5, the input AC current waveform appears as a pulse-shaped distorted angular shape. The harmonic current in the distorted waveform thus causes harmonic disturbances to other power supplies and power supplies. As a result, IEC-555 and power supply specifications in many countries require that the harmonic content of the input supply current of the power supply be limited below a specified level. In order to satisfy these standards, a method of adding a power factor correction circuit (PFC) installed at the front end of a DC / DC converter to a switching power supply has been proposed and currently used.

However, the above method has good electrical characteristics, but the size and cost of the power supply device are greatly increased due to the addition of a power factor correction circuit. In order to solve this problem, efforts are being made to reduce the size to an acceptable range and to reduce costs, thereby integrating the power factor correction circuit and the isolated DC / DC conversion into a single power stage. Attempts have been made to turn on and off switching elements (transistors, diodes, etc.), such as parasitic vibrations between the leakage inductance of high-frequency transformers and parasitic capacitances of switching elements, and increased switching losses due to surge voltages. Due to the shortcomings, the integration attempt is not effective.

Accordingly, an object of the present invention is to provide a lossless snubber circuit that does not consume power while enabling soft switching of a rectifier of a secondary side of a forward DC / DC converter. will be.

It is also an object of the present invention to provide a lossless snubber circuit that does not consume power while enabling soft switching of primary switching elements of a single or two switch type DC / DC converter.

It is also an object of the present invention to provide an input power factor improvement circuit for suppressing waveform distortion of an input AC power to improve a power factor of an AC input in a DC / DC converter using AC power directly as a power source. Another object of the present invention is to provide an input power factor improvement circuit applicable to a single switch type DC / DC converter.

1 is a circuit diagram of a conventional hard-switching two-switch forward DC / DC converter,

2 is an operation waveform diagram of each part of a conventional hard switching two-switch forward DC / DC converter,

3 is a circuit diagram of a conventional hard switching single switch forward DC / DC converter,

4 is a circuit diagram of a conventional two-switch forward DC / DC converter using an AC input power using only a diode rectifier.

5 is an operating waveform diagram of an input voltage and a current and an input capacitor voltage according to input power usage of the forward DC / DC converter of FIG.

6 is a circuit diagram in which a lossless snubber circuit according to the present invention is applied to both the primary side and the secondary side of a forward-type DC / DC converter of a two-switch type,

FIG. 7 is a waveform diagram of each part generated when the forward DC / DC converter of FIG. 6 is operated.

FIG. 8 is a current flow diagram illustrating six types of current flows of the forward DC / DC converter of FIG. 6 according to each operation mode.

9 is a circuit diagram in which the lossless snubber circuit according to the present invention is applied only to the secondary side of a two-switch forward DC / DC converter.

10 is a circuit diagram of a single switch type forward DC / DC converter in which a lossless snubber circuit according to the present invention is applied to both the primary side and the secondary side.

11 is a circuit diagram in which the lossless snubber circuit according to the present invention is applied only to the secondary side of a single switch type forward DC / DC converter.

12 is a circuit diagram of a two-switch forward DC / DC converter in which a lossless snubber circuit and an input power factor improvement circuit according to the present invention are applied to both the primary side, the secondary side, and the AC input terminal,

FIG. 13 is a waveform diagram of each part generated when the forward DC / DC converter of FIG. 12 is operated.

FIG. 14 is a current flow diagram illustrating six types of current flows of the forward DC / DC converter of FIG. 12 according to each operation mode.

FIG. 15 is a waveform diagram illustrating a process in which an input alternating current is transmitted without waveform distortion in accordance with an application of an input power factor correction circuit according to the present invention. FIG. B is an enlarged waveform of 'A' section of a diagram in detail. Degree,

FIG. 16 is a circuit diagram of a single switch type forward DC / DC converter in which a lossless snubber circuit and an input power factor improvement circuit according to the present invention are applied to both the primary side, the secondary side, and the single-phase AC input terminal.

FIG. 17 is a circuit diagram of a two-switch forward DC / DC converter in which a lossless snubber circuit and an input power factor improvement circuit according to the present invention are applied to both the primary side, the secondary side, and a commercial three-phase AC input stage.

FIG. 18 is a circuit diagram of a single switch type forward DC / DC converter in which a lossless snubber circuit and an input power factor improvement circuit according to the present invention are applied to both the primary side, the secondary side, and a commercial three-phase AC input terminal.

* Explanation of symbols for main parts of the drawings

30, 320: bridge rectification diodes 100, 200: snutter circuit according to the present invention

300: input power factor improvement circuit according to the present invention

310: AC filter C10, C20: snubber capacitor

Cin: Input Capacitor Co: Output Capacitor

Cp: Key Capacitance D10, D11, D12: Snubber Diode

D ₁ , D ₂ : free-wheel diode D20: current diode

D331, D332: input diode D _3, D _4: the output rectifying diode

L20: Snubber inductor L330: Boost inductor

L _f : Smoothing inductor S ₁ , S ₂ : Switch

Tr: High Frequency Transformer

A lossless snubber circuit for soft switching of a DC / DC converter according to the present invention for achieving the above object, in the forward DC / DC converter, a capacitive element; A first rectifying element; And a second rectifying element; The capacitive element, the first rectifying element and the second rectifying element are Y-connected, and the other terminal is connected to the non-grounded terminal, the load terminal, and the ground of the secondary side of each transformer, wherein the first rectifying element is The current is arranged to flow toward the load, and the second rectifier is characterized in that the current is arranged to flow to the Y-connection point is connected.

In addition, the lossless snubber circuit for soft switching of the DC / DC converter according to the present invention, a DC / DC converter comprising a switch connected between one end of the primary side of the transformer and the ground, Capacitive transfer element; A first rectifying element; And a second rectifying element and an inductive element connected in series to form a reverse charging path of the capacitive element. It comprises a, wherein the capacitive element, the first rectifying element and the reverse charging cell to form a Y-connection, the other terminal is the non-grounded terminal of the switch, the other end and the ground terminal of the primary side of the transformer connected to the switch, respectively And the first rectifying element is arranged such that current flows out of the Y-junction.

In addition, an AC input stage input power factor improvement circuit of the DC / DC converter according to the present invention includes a capacitor connected between one end of the primary side of the transformer and ground; An input capacitor supplying power to the transformer; A DC / DC converter comprising: rectification means for rectifying an input AC power; And an inductive element connected between the current output terminal of the rectifying means and the ungrounded terminal of the switch. AC filter means for filtering the AC power input and configured to include and output to the rectifying means; The input power factor improvement circuit of the DC / DC converter according to the present invention is disposed in a direction in which current flows toward the transformer, and is connected to each end of the inductive element and the transformer primary side, respectively. Two rectifying elements; There is another feature that is configured to include more.

In the secondary side lossless snubber circuit in the forward converter for soft switching of the DC / DC converter according to the present invention configured as described above, the reverse charge is performed when the primary switch applies a voltage to the transformer. Capacitive element is forward-charged through the first rectifying element, so that a gentle reverse voltage is applied to the output rectifier diode of the secondary side arranged in the reverse direction, the forward-charged when the switch of the primary side is turned off The capacitive element starts to discharge through the second rectifier element and is slowly reversely charged, so that a gentle reverse voltage is applied to the output rectifier diode disposed in the forward direction of the secondary side, so that a sudden change in impedance is not generated. .

Further, in the lossless snubber circuit on the primary side for soft switching of the DC / DC converter according to the present invention configured as described above, the capacitive element, which is already charged when the switch is turned on, is induced with the second rectifying element. Slow charging is performed through the element, so that a gentle current is applied to the switch in the zero current state, and when the switch is turned off, the charged capacitive element is discharged in the reverse direction through the first rectifying element. By slowly starting forward charging is performed, the switch is gradually applied to the zero voltage switching, the sudden impedance change effect due to parasitic capacitance in the switch does not occur.

In addition, in the input power factor improvement circuit of the DC / DC converter according to the present invention configured as described above, when the switch is turned on, the current rectified by the rectifying means flows into the switch through the inductive element and gradually increases to flow. When the switch is turned off, the current flowing through the inductive element is gradually reduced through a diode connected between the input capacitors and is charged into the input capacitors, thereby increasing the frequency of the input power according to the high speed switch frequency of the switch. Since all pulse-modulated triangular wave power serving as fundamental waves flows into the input capacitor, distortion of the input waveform does not occur.

Hereinafter, the configuration and operation of an embodiment of a lossless snubber circuit for soft switching of a DC / DC converter according to the present invention will be described in detail by applying to a two-switch forward DC / DC converter.

FIG. 6 is a circuit diagram of a forward-switched DC / DC converter of a two-switched dust cut-off snubber circuit according to the present invention applied to both the primary side and the secondary side, and induces a high frequency transformer for inducing a voltage applied to the primary side to the secondary side. (Tr); First and second switches S ₁ and S ₂ intermittently applying a DC power supply to the primary side of the transformer Tr; Reflux diodes D ₁ and D ₂ connected in a reverse direction between the first switch S ₁ and the power supply terminal and the second switch S ₂ and ground; First and second output rectifying diodes D ₃ and D ₄ for rectifying the current induced at the secondary side of the transformer Tr into a forward output current; A smoothing inductor L _f and an output capacitor Co for smoothing the output rectified current; In addition to the components of the conventional two-switched forward DC / DC converter, the first snubber capacitor C20 and the first snubber diode connected in series between both ends of the first switch S ₁ . D21 and snubber inductor L20; The primary side switch includes a commutation diode D20 connected to the second switch S ₂ at a contact point of the first snubber capacitor C20 and the first snubber diode D21. Nuber circuit 200; A second snubber capacitor C10 and a second snubber diode D11 and the second snubber capacitor C10 and the second snubber diode connected in series to both ends of the secondary side of the transformer Tr; A secondary snubber circuit (100) consisting of a third snubber diode (D10) connected to a rear end of the smoothing inductor (L _f ) at a contact of D11); It is configured to include.

FIG. 7 shows waveforms of the main part generated during the switching operation of the two-switch forward DC / DC converter of FIG. 6, and the time points at which each waveform is switched (t ₀ , t ₁ , t ₂ , t _3). , t ₄ , t ₅ , and t ₆ ) can be classified into six operation modes because a change occurs in the operation of the converter. FIG. 8 shows the forward DC / DC converter of FIG. 6 according to each operation mode, in which a portion indicated by a thick line on the circuit shows that current flows along the path in each corresponding mode.

Hereinafter, the operation of the forward DC / DC converter to which the snubber circuits 100 and 200 according to the present invention are applied to both the primary side and the secondary side is performed according to the waveforms of FIG. 7 and the modes of FIG. It will be described in detail with reference to the circuit diagram. For the description of the initial operation mode (mode 0), the voltage V _C20 at both ends of the first snubber capacitor _C20 is charged to the input voltage Vin, and the voltage V _C10 at both ends of the second snubber capacitor C10 on the secondary side is It is assumed that the secondary voltage of the high frequency transformer Tr is charged with the negative voltage (-V _t2 ). This assumption is a condition that the forward DC / DC converter of FIG. 7 is obtained by itself due to the characteristics of the circuit when a certain period of time passes in the initial operation. The following description will reveal that the above assumption is merely for convenience of explanation.

[Mode 0 (t ₀ ~ t ₁ )]

This mode starts when the first and second switches S ₁ and S ₂ are turned on in the zero current state, and the current flow at the start of this mode is as shown in FIG. When the first and second switches S ₁ and S ₂ are turned on, a DC input voltage Vin is applied to the primary side of the high frequency transformer Tr, and thus the current I _t1 flowing to the primary side of the transformer Tr. And a sum current of the discharge current I ₂₀₀ of the first snubber capacitor C20, which has already been charged to the input voltage Vin, flowing along the path formed by the first switch S ₁ , is generated by the first switch S _1. Flows through). After the first snubber capacitor C20 continues to discharge and the voltage V _{C20 at} both ends thereof becomes 0, the accumulated energy according to the current flowing through the first snubber diode D21 to the snubber inductor L20 is accumulated. Starts charging to the negative voltage (-Vin) of the input voltage Vin.

On the other hand, the voltage induced on the secondary side of the high frequency transformer (Tr) is instantaneously through the first output rectifying diode (D ₃ ) at the moment the first and second switches (S ₁ , S ₂ ) are turned on. The output through the low impedance path provided by the second snubber capacitor C10 and the third snubber diode D10, which is not applied to the second output rectifier diode D ₄ and is back charged to −V ₁₂ . The secondary current I _t1 / n (n = N ₂ / N ₁ ) flows through the capacitor Co. As the second snubber capacitor C10 begins to slowly charge to V _t2 , the second output rectifier diode D ₄ is in a conductive state in which a circulating current is flowing in a previous operation mode (see operation mode 5 described later). in it is gradually switched to cut-off state, and the current flowing through the first output rectifier diode (D ₃₎ during the filling of the second snubber capacitor (C10), while linearly increasing the first output rectifier diode (D ₃₎ While the current flowing through the linearly increases, the first output rectifier diode D ₃ is gradually switched from the interruption state to the conduction state, so that the zero current and the zero voltage switching are performed at the start of the state transition. The second snubber capacitor C10 is overcharged to 2 V _{t2 which} is twice the voltage of the secondary side during the charging process, and then returns to V _t2 .

This mode ends when the voltage of the first snubber capacitor C20 is reversely charged from the input voltage Vin to -Vin and the next operation mode proceeds.

[Mode 1 (t ₁ to t ₂ )]

This mode is a powering mode, in which input power is transferred to the load on the secondary side of the high frequency transformer Tr through the first and second switches S ₁ and S ₂ , and FIG. To form a current flow such as This mode is a state in which both resonance of the first snubber capacitor C20 and the second snubber capacitor C10 stopped in mode 0 is stopped. In particular, -Vin reversely charged to the first snubber capacitor C20. Since the voltage is connected to the input voltage Vin through the current diode D20 and is coincident, the discharge path is not formed and is maintained until the next operation mode is started in the reversely charged state.

[Mode 2 (t ₂ ~ t ₃ )]

This mode is started when the first and second switches S ₁ and S ₂ are turned off according to a defined duty ratio. First, when the first and second switches S ₁ and S ₂ are turned off, the first snubber capacitor C20, which has reversed negative input voltage -Vin, becomes the current diode D20. And reverse discharge through a loop formed by the primary winding of the high frequency transformer (Tr). During this reverse discharge said first snubber capacitor (C20) positive, because the potential is to be applied as a reverse voltage to said reflux diode (D ₂₎ through the commutation diode (D20) of the freewheeling diode (D ₂₎ is non-conducting I can't. Therefore, as in the conventional switching, the first and _second reflux diodes D ₁ and D ₂ are electrically conducted by the reflux current at the time of turning off the first and second switches S ₁ and S ₂ . Unlike the sudden input voltage Vin being applied to the two switches S ₁ and S ₂ , the voltage is gently applied according to the reverse discharge speed (charge rate) of the first snubber capacitor C 20, thereby providing the first voltage. And at the time of turning off the second switch (S ₁ , S ₂ ) will be made in the zero voltage state. The positive voltage of the first snubber capacitor C20 continues to reverse discharge along the same current path as that of the primary side in FIG.

On the other hand, the value of I _t1 / n flowing on the secondary side becomes 0, and the first output is applied to a path in which energy charged at V _t2 in the second snubber capacitor C10 is formed in (c) of FIG. 8. The discharge starts through the rectifying diode D ₃ and supplies the load current I _O which flows uniformly by the smoothing filters L _f and Co.

[Mode 3 (t ₃ to t ₄ )]

During the discharge of the second snubber capacitor C10, when the voltage across both ends becomes zero, the voltage applied in the forward direction to the first output rectifying diode D ₃ becomes zero, so that the current flows from the conduction state to the blocking state. The current I _D3 goes to zero and this mode starts. The load current Io constantly flowing toward the load by the leveling inductor L _f , in which the first output rectifying diode D ₃ is blocked, begins to flow through the second output rectifying diode D ₄ . The second snubber capacitor C10 discharged to 0 may be caused by the polarity inversion of the secondary voltage of the high frequency transformer Tr according to the polarity inversion of the primary voltage of the high frequency transformer Tr. Charging proceeds to -V _t2 in the reverse direction through the leakage inductance of N.), and a reverse voltage V _D3 is gently applied to the first output rectifying diode D ₃ in accordance with the charging rate. On the secondary side of the transformer Tr current flows during this mode in accordance with two current loops as shown in (d) of FIG.

On the other hand, during this mode, the first snubber capacitor C20 reverses discharge and continues charging until the voltage across both ends becomes input voltage Vin along the same current path as in Mode 2 even after the voltage across both ends becomes zero. do.

[Mode 4 (t ₄ to t ₅ )]

This mode starts when the first snubber capacitor C20 continues to charge and the voltage across both ends is equal to the input voltage Vin. When the first snubber capacitor C20 is charged to the input voltage Vin, The flow of the current I _{t1 to} the first snubber capacitor C20 is stopped and the reflux diodes D ₁ and D ₂ are turned on so that the energy accumulated in the leakage inductance of the high frequency transformer Tr and the excitation Energy is reduced as it returns to the input power source.

On the other hand, the current flow is interrupted to the second snubber capacitor C10 that has already been reversely charged to the voltage of -V _t2 by the reverse charging process before entering this mode, and only the load current Io is outputted to the second output. It is refluxed through the rectifying diode D ₄ .

[Mode 5 (t ₅ to t ₆ )]

When both the energy accumulated in the leakage inductor of the high frequency transformer Tr and the excitation energy return to the input power source, that is, the reflux current I _D1 through the freewheeling diodes D ₁ and D ₂ and the high frequency transformer Tr. When) becomes 0, this mode starts.

When the reflux current is zero, the primary and secondary voltages of the high frequency transformer Tr, which have been held in reverse directions on the primary and secondary sides of the high frequency transformer Tr, are linearly reduced by the reflux current. To start. At this time, the voltage V _t2 charged in the second snubber capacitor C10 starts to discharge through the third snubber diode D10 and the output capacitor Co, stays at the output voltage Vout, and the first voltage. The voltage V _D3 at both ends of the output rectifying diode D ₃ also decreases linearly. During this mode, only the load current Io is refluxed through the second output rectifying diode D ₄ as shown in (f) of FIG.

In such a state, the first and second switches (S _1, S _2), the mode 0, there is to be repeated when the turn-on, the first and second switches (S _1, S _2), the zero current point which is turned on Switching is performed as described in mode 0.

In the forward DC / DC converter in which the lossless snubber circuit according to the present invention is applied to both the primary side and the secondary side according to the six divided operation modes described so far, the first and Soft switching and state switching of the second switches S ₁ and S ₂ and the first and second output rectifying diodes D ₃ and D ₄ are performed.

The lossless snubber circuit 200 on the primary side of the lossless snubber circuits 100 and 200 for soft switching of the DC / DC converter according to the present invention is not limited to the circuit configuration on the secondary side, that is, the smoothing inductor. It can be applied to soft switching of a primary switch of a circuit such as a flyback DC / DC connector without (L _f ), and the operation of the primary side at this time is the same as the operation process described above. In addition, as shown in FIG. 9, the lossless snubber circuit 100 on the secondary side is also installed only on the secondary side regardless of whether the lossless snubber circuit 20 is applied to the primary side. The state of the two output rectifier diodes (D ₃ , D ₄ ) can be switched, and the operation at this time is the operation of the lossless snubber circuit 200 on the primary side in FIGS. 7 and 8. Same as excluded.

10 and 11 show another embodiment in which a lossless snubber circuit for soft switching of a DC / DC converter according to the present invention is applied to a single switch type forward DC / DC converter, and FIG. 10 is shown on both the primary side and the secondary side. A lossless snubber circuit is applied, and FIG. 11 is a lossless snubber circuit applied only to the secondary side.

The circuit connection in the case of being applied to a single-switch forward DC / DC converter has the same configuration on the secondary side as shown in FIGS. 10 and 11, except that the primary (current) diode D20 on the primary side is Only those connected in the reverse direction to the power input terminal are different, and each operation mode and operation waveform, and the current paths according to the operation mode are substantially the same as those of FIG. 7 and FIG. It has almost the same operating characteristics as the star circuit.

12 is a two-switch forward DC / DC method in which an input power factor improvement circuit of a DC / DC converter using an AC input according to the present invention is applied to a lossless snubber circuit for soft switching of the DC / DC converter according to the present invention. As a circuit diagram of a converter, an AC filter 310 in which switching frequency components filter noise from an input AC power; A bridge diode 320 for rectifying and outputting the filtered AC power; A boost inductor (L330) connected to the flyback diode (D ₁ ) and the switch (S ₁ ) at the bridge diode (320); The input power factor improvement circuit 300 is configured to further include.

13 and 14 show the waveforms and current flows of the main parts of the forward DC / DC converter of FIG. 12, respectively. FIG. 13 shows the current components flowing through the boost inductor L330. Except for the addition of the waveforms of I _I , ₃₃₀ ), the waveforms of all parts are the same as those of FIG. 7, which is the waveform diagram of the main part of the forward DC / DC converter of FIG. 6, and each circuit diagram showing the current flow of FIG. While the switches S ₁ and S ₂ are turned on (during mode 0 and mode 1), an input current flows through the switch S ₁ and the boost inductor L330 located at the rear end of the bridge diode 320. ) And energy stored in the boost inductor L330 from the turn-off of the switches S ₁ and S ₂ (after Mode 2) is inputted through the freewheeling diode D ₁ . Excluding the current flow into and out of Cin), Flow chart and is the same in a one-to-one basis.

(A) and (b) of FIG. 15 are waveforms showing a process in which an AC current is transmitted to the input capacitor Cin without distortion by the boosting inductor L330, and (b) shows the boosting inductor ( In order to show the relationship between the voltage V _{L330 of L330} in detail, the waveform diagram 'A' of FIG. (B) of FIG. 15 is a waveform diagram for theoretically explaining the current inflow due to the boost. The waveform is slightly different from the actual waveform. Particularly, in the actual waveform, the width of each voltage waveform of the boost inductor L330 is different. The pulse widths appear differently so that. Hereinafter, referring to FIGS. 13, 14, and 15, an operation of introducing an input AC current into the input capacitor Cin without distortion in the forward DC / DC converter of FIG. 12 will be described in detail.

While the switches S ₁ and S ₂ are turned on and in mode 0 and mode 1, the energy accumulated in the input capacitor Cin, as shown in (a) and (b) of FIG. S ₂ ), the current flows through the primary side of the transformer Tr and the switch S ₁ to supply energy to the secondary side, while the current rectified by the bridge diode 320 is the boost inductor L330. Through the switch (S ₁ ) to flow through. At this time, both ends of the boosting inductor L330 are positively applied to the bridge diode 320 so that all of the AC voltages are applied. Since the applied AC voltage is almost constant in a short time, the boosting inductor ( The current I _L330 flowing in _L330 increases linearly (the 'a' section of the fifteenth (b)), and energy is accumulated in the boosting inductor L330 while the current increases. When the switches S ₁ and S ₂ are turned off in mode 2, the voltages at both ends of the boosting inductor L330 are inverted while the inverted voltages are output voltage of the bridge diode 320 at the inversion time. In addition to the rectified Vac, it is transferred to the input capacitor Cin. (Section b of the fifteenth (b)) The magnitude of the inversion voltage of the boost inductor L330 at this time is the input capacitor ( The difference between the voltage of Cin and the rectified input voltage (Vac) is such that the flyback diode (D ₁ ) is conducted so that the energy accumulated in the boosting inductor (L330) flows into the input capacitor (Cin). The current flowing through the boost inductor L330 decreases linearly while being charged. When the difference between the input capacitor (Cin) and the rectified input voltage (Vac) at the front of the inversion time of the boosting inductor (L330) is large, the magnitude of the inverted voltage is also increased, the speed at which energy flows into the input capacitor (Cin) If the fast voltage is small and the difference between the positive voltages is small, the speed at which energy is introduced into the input capacitor Cin is relatively slow.

According to the above process, as shown in (a) of FIG. 15, the current flowing into the input capacitor (Cin) is a triangular wave pulse having the waveform of the input current (Iac) as a fundamental wave, so the input current (Iac) is introduced. Distortion does not occur in the waveform of, and therefore, it becomes a clean sine wave.

The input power factor improvement circuit may be applied to a single switch type DC / DC converter, and at this time, as shown in FIG. 16, both ends of the primary coils of the boost inductor L330 and the high frequency transformer Tr. The input diodes D331 and D332 are arranged in the direction in which the current flows from the boost inductor L330 and are inserted and connected to each other, and the input currents Iac flow into the input capacitor Cin. The charging process is as described above.

In addition, the input power factor improvement circuit as described above can be applied not only to the single phase input power but also to the three phases as shown in FIGS. 17 and 18, as well as the AC filter 310 at this time. The filter circuit is installed in each phase, and the bridge diode 320 differs only in that two diodes that flow out and flow in each phase are installed, and the incoming alternating current Iac is converted into the input capacitor Cin. The operation and function of the boosting inductor L330 for inflow and charging are the same as in the single phase.

The lossless snubber circuit for soft switching of the DC / DC converter according to the present invention, which is configured and acts as described above, is applied to various DC / DC converters so that the switching elements in the converter achieve soft switching without consuming power by itself. To reduce switching losses, and especially to forward DC / DC converters, to reduce the reverse recovery losses and parasitic vibrations of the secondary output diodes, thereby improving the quality of the output current and voltage. In addition, in the case where a simple circuit input power factor improvement circuit composed of a small size and low cost according to the present invention is installed in addition to a DC / DC converter for soft switching, the input AC current is applied without waveform distortion. Into the DC / DC converter, and thus different by harmonic content caused by waveform distortion. It is a very useful, economical and excellent invention which has the effect of eliminating harmonic interference to a power supply device and a power supply, and improving the power transmission efficiency of electric power.

Claims (5)

A forward DC / DC converter, comprising: a capacitive element and a first rectifying element; And a second rectifying element; It comprises a, wherein the capacitive element, the first rectifying element and the second rectifying element is Y-connected, the capacitive element is connected to the secondary non-grounded terminal of the transformer, the first rectifying element so that current flows toward the load A lossless snubber circuit for soft switching of a DC / DC converter, the second rectifying element being arranged to be connected to a load terminal and arranged to flow current to the Y-connection point. A DC / DC converter comprising a switch connected between one end of a primary side of a transformer and a ground, comprising: a capacitive element; A reverse charge battery path comprising a first rectifying device, and a second rectifying device and an inductive device connected in series to form a reverse charging path of the capacitive device; It is configured to include, wherein the capacitive element, the first rectifying element and the reverse charging cell to the Y-connection, the capacitive element is connected to the non-grounded terminal of the switch, the first rectifying element is the current of the Y-connection point Lossless snubber circuit for soft switching of the DC / DC converter is arranged to flow out of the switch is connected to the other end of the primary side of the transformer is connected to the switch, the reverse battery is connected to the ground. A switch connected between one end of the primary side of the transformer and ground; And an input capacitor supplying power to the transformer; A DC / DC converter to which the lossless circuit of claim 2 is applied, comprising: rectification means for rectifying an input AC power; And an inductive element connected between the current output terminal of the rectifying means and the ungrounded terminal of the switch. Input power factor improvement circuit of the DC / DC converter, including. 4. The filter according to claim 3, further comprising: an AC filter means for filtering input AC power to input only electric power of a specific frequency to the current means; The input power factor improvement circuit of the DC / DC converter further comprises. 5. The apparatus of claim 3 or 4, further comprising: a first rectifying element disposed between the inductive element and the non-grounded end of the switch so that a current flows through the switch; And a second rectifying element disposed at the other end of the primary end of the transformer to which the inductive element and the switch are connected such that a current flows to the input capacitor. The input power factor improvement circuit of the DC / DC converter further comprises.

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