KR100815567B1 - Power factor correction circuit using snubber circuit - Google Patents

Abstract

A power factor correction circuit using a snubber circuit is provided to reduce the complexity of the circuit by using diodes of small capacity to reduce average current flowing on each diode. A power factor correction circuit includes a converter unit(51) and a turn-on snubber circuit unit(52). The converter unit has a first inductor(Lm) connected between a power input stage and a load, an output diode(Do) connected between the first inductor and the load, an output capacitor(Co) connected to the load in parallel, and a switching device(M) connected in parallel to power applied from the power input stage. The turn-on snubber circuit unit is connected to the converter unit to reduce turn-on switching loss of the switching device. The turn-on snubber circuit unit has a second inductor(Ls) having one end connected to the first inductor, a first capacitor(Cs1) having one end connected to the second inductor and the other end connected to an anode of the output diode, a first diode(Ds1) having an anode connected to the second inductor and a cathode connected to the anode of the output diode, and a second diode(Ds2) having an anode connected to the first inductor and a cathode connected to the cathode of the first diode.

Description

Power factor correction circuit using snubber circuit {POWER FACTOR CORRECTION CIRCUIT USING SNUBBER CIRCUIT}

1 is a view showing a power system of a general power conversion circuit;

2 is a circuit diagram of a power factor improvement circuit according to the prior art;

3 is a diagram illustrating switching losses generated when a switching element is turned on;

4A is a view showing reverse recovery characteristics of an output diode;

4B is a diagram showing a short circuit path at the time of switching on,

5 is a circuit diagram of a power factor improvement circuit using a snubber circuit according to the present invention;

6A to 6E are diagrams showing a current flow for each operation mode of the present invention in a solid line;

7 is a main waveform diagram according to each operation mode of the present invention;

8 is a diagram conceptually showing a switching current waveform when a turn-on snubber circuit is added and turn-on switching loss at that time;

9A to 9C are circuit diagrams of a power factor improvement circuit of the present invention including a turn-off snubber circuit unit;

10 is a diagram conceptually showing a switching current waveform when a turn-off snubber circuit portion is added and a turn-off switching loss at that time.

* Description of Major Symbols in Drawings *

51 converter 52 turn-on snubber circuit

53: turn-off snubber circuit portion M: switching element

Do: Output Diode Co: Output Capacitor

Lm: first inductor Ls: second inductor

La: third inductor D _s1 : first diode

D _s2 : second diode D _s3 : third diode

C _s1 : first capacitor C _s2 : second capacitor

C _s3 : third capacitor R: resistance

The present invention relates to a power factor improvement circuit using a snubber circuit, and more particularly, to a power factor improvement circuit for reducing switching loss and improving the reverse recovery characteristic of a diode by using a snubber circuit to have improved efficiency. .

Conventional power supplies have used simple full bridge rectifiers and large capacity electrolytic capacitors to obtain DC voltages from commercial AC voltages, but currently have strong regulations to solve problems caused by harmonic currents on commercial lines. have.

Therefore, the power system of the general power conversion circuit is composed of a power factor improving stage 11 and a DC power conversion stage 12, as shown in Figure 1, the power factor improving stage 11 performs the AC / DC conversion function It consists of a rectifier (11a) and a PFC stage (11b) that performs a power factor correction (PFC) function to generate a DC voltage of about 400V, which is required by the load in the DC power conversion stage 12 As a specification, DC / DC power conversion is performed.

Until recently, various technologies for improving power factor have been researched and developed. As a topology for PFC, boost converters, which are known for their excellent characteristics and reliability, are mainly used. However, high efficiency and high reliability of the boost converter that improves power factor requires high switching frequency operation to reduce harmonics and input / output filter sizes, and thus soft switching techniques to reduce the switching stress and loss. There is a need.

Until now, many literatures have proposed such a circuit technique, and a typical method is to use a snubber circuit.

2 is a circuit diagram of a power factor improvement circuit according to the related art, and shows a boost converter mainly used as a PFC converter.

Referring to the operation of the circuit of FIG. 2, the energy storage mode and the energy delivery mode may be classified into two types.

In the energy storage mode, the switching element M conducts, and when the switching element M conducts, all of the input voltage Vin is applied to the inductor L to store energy in the form of a current.

Afterwards, in the energy transfer mode, the switching element M is cut off. When the switching element M is cut off, both the energy stored in the inductor L and the input side energy are transferred to the load terminal through the output diode D, and the input voltage Vin is applied. A larger output voltage (V _o ) is produced.

However, in the power factor improvement circuit according to the prior art, a large switching loss occurs when the switching element M is turned on due to the actual characteristics of the circuit element and parasitic components present in the circuit. Due to the reverse recovery characteristic of D), there is a problem that the circuit is short-circuited momentarily.

FIG. 3 is a diagram illustrating switching losses generated when the switching element is turned on. FIG. 4A is a diagram illustrating reverse recovery characteristics of the output diode D, and FIG. 4B is a short circuit when the switching element M is turned on. As a diagram illustrating a path, the above-mentioned problem will be briefly described with reference to FIGS. 3, 4A, and 4B.

First, as shown in FIG. 3, when the switching device M is turned on, an area where the switching voltage v _ds and the current i _ds cross each other is generated. As a result, switching loss and Noise is generated.

This is especially proportional to the operating frequency of the power supply, so this increase in frequency leads to an increase in losses and noise, resulting in reduced efficiency and switch heating. This is especially true for high speed switching operations.

On the other hand, in order for the circuit of FIG. 2 to switch to the energy storage mode in the state of the energy transfer mode in which the output diode D is conducting, the output diode D is the output voltage D at the moment when the switching element M is turned on. It should be reverse biased by V _O ) but not instantaneously blocked due to diode reverse recovery characteristics, and current i _D flows in the reverse direction as shown in FIG. 4A, resulting in a short circuit path as shown in FIG. 4B. path) is formed. This results in severe surge current in each device, which can generate heat, permanent burnout, and severe electro-magnetic interference (EMI).

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problems, and an object thereof is to provide a power factor improvement circuit for reducing switching loss by using a snubber circuit and improving the reverse recovery characteristic of a diode to have improved efficiency.

The objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a power factor improvement circuit including a first inductor connected between a power input terminal and a load, an output diode connected between the first inductor and a load, an output capacitor connected in parallel to the load, and the A converter including a switching element connected in parallel to a power applied from a power input, and converting the power applied from the power input to a voltage having a corresponding DC level; And a turn-on snubber circuit portion connected to the converter portion to reduce turn-on switching loss of the switching element.

The turn-on snubber circuit unit includes: a second inductor having one end connected to the first inductor; a first capacitor having one end connected to the second inductor and the other end connected to an anode of the output diode; and the first capacitor A first diode connected in parallel, an anode connected to the second inductor, a cathode connected to the anode of the output diode, an anode connected to the first inductor, and a cathode connected to the cathode of the first diode. It characterized in that it comprises a second diode connected.

In this case, the present invention may further include a turn-off snubber circuit unit connected to the converter unit to reduce turn-off switching loss of the switching element.

In this case, the turn-off snubber circuit unit may be implemented as an RC snubber including a resistor having one end connected to a switching element and a second end connected to a ground and a second capacitor connected in parallel with the resistance.

It can also be implemented as an RCD snubber comprising a third diode whose anode is connected to one end of the switching element, a cathode of which is connected to one end of the third diode, a resistor having one end grounded, and a third capacitor connected in parallel with the resistance. .

In addition, the present invention may further include a third inductor between the first inductor and the second inductor.

In this case, the third inductor may be formed as an auxiliary winding of the first inductor.

Meanwhile, the first and second diodes and the third diode may be implemented as fast recovery diodes.

The above objects, features, and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be.

In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a circuit diagram of a power factor improving circuit using a snubber circuit according to the present invention. As shown in FIG. 5, the power factor improving circuit according to the present invention includes a converter unit 51 and a turn-on snubber circuit unit 52. It is included.

Here, the converter unit 51 includes a first inductor Lm, an output diode Do, an output capacitor Co, and a switching element M. The power source Vin input from the power input terminal is directly connected to the DC. It converts and outputs the voltage (Vo) of the level.

At this time, the first inductor Lm is connected between the power input terminal and the load, and the output diode Do is connected between the first inductor Lm and the load.

In addition, the output capacitor Co is connected in parallel with the load, and the switching element M is connected in parallel with the input power source Vin.

In this case, the switching device M uses an active device. Since the active element M includes a gate, a source, and a drain, the magnitude and direction of the current flowing from the drain to the source or vice versa is determined according to the magnitude and polarity of the voltage applied between the gate and the source. Have

Such active devices include bipolar junction transistors (BJTs), junction field effect transistors (JFETs), metal oxide semiconductor field effect transistors (MOSFETs), and metal semiconductor field effect transistors (MESFETs).

On the other hand, the turn-on snubber circuit 52 is connected to the converter 51 to reduce the turn-on switching loss of the switching element (M), the first capacitor (C _s1 ), the second inductor (Ls), the first and the first Two diodes (D _s1 , D _s2 ).

At this time, one end of the second inductor Ls is connected to the first inductor Lm, and the first capacitor C _s1 is connected to the second inductor Ls and one end thereof, and the other end thereof is the output diode Do. Is connected to the anode.

In addition, the first diode D _s1 is connected in parallel with the first capacitor C _s1 , an anode is connected with the second inductor Ls, and a cathode is connected with the anode of the output diode Do.

In addition, the second diode D _s2 has an anode connected to the second inductor Ls and a cathode connected to the cathode of the first diode D _s1 .

At this time, the diodes D s _{1 and} D s ₂ that may be used in the turn-on snubber circuit unit 52 may preferably use a device having a smaller capacity than that of the output diode Do. This is because the loss of conduction can be reduced by reducing the average current flowing through the circuit, and the complexity of the circuit configuration can be reduced.

In addition, the first and second diodes (D _s1,, D _s2) is a fast recovery diode it is preferable to use the (fast recovery diode), which high-speed restore the first and second diodes (D _s1,, D _s2) When the diode is used for a very short time, the carrier accumulation effect is small, which is suitable for high speed operation.

On the other hand, since some of the inductor component (L) is used in the present invention, the power factor may be improved by using the resonance characteristic, but the first inductor Lm and the second inductor may be used to enhance the resonance characteristic. A third inductor La may be added between Ls, and in this case, the third inductor La may be formed as an auxiliary winding of the first inductor Lm.

Hereinafter, the operation process of the present invention will be described for each mode with reference to FIGS. 5 to 7.

6A to 6E are diagrams showing a current flow for each operation mode of the present invention in solid line, and FIG. 7 shows a main waveform diagram according to each operation mode of the present invention.

Mode 1 (t ₀ to t ₁ )

6A is a diagram illustrating a current flow in mode 1, _in which energy is stored in the first inductor L _m from the input power supply V _{in with} the switching element M of the converter unit 51 turned on. It is a section. In this case, when the third inductor La is formed by the auxiliary winding of the first inductor L _m , a voltage having a size of V _in / N (where N is the winding ratio) is applied to the third inductor La, whereby a third inductor ( La) _-second diode (D _s2 ) -second inductor (Ls) -first capacitor (C _s1 ) to form a closed loop, which transfers energy to the first capacitor (C _s1 ). Done.

At this time, the voltage V _Cs1 across the first capacitor C _s1 increases until the current i _Ds2 flowing through the second diode D _s2 is half-period resonance, at which point the half-cycle resonance ends. Mode 1 ends.

Mode 2 (t ₁ to t ₂ )

6B is a diagram illustrating a current flow in mode 2, in which the switching element M is continuously turned on, and the current i _Lm flowing into the first inductor L _m is the switching element M. It is equal to the current (i _Ds ) flowing in, and the load is supplied with power from the output capacitor (C _o ).

Mode 3 (t ₂ to t ₃ )

FIG. 6C is a diagram illustrating a current flow in mode 3, in which power starts to be delivered to the load when the switching element M is turned off, and the current i _Lm of the first inductor L _m is equal to the second. The diode D _s2 and the second inductor L _s are distributed and flowed.

At this time, the voltage V _Cs1 across the first capacitor C _s1 charged in the mode 1 begins to decrease, and the mode 3 ends when the current i _Ds2 flowing to the second diode D _s2 falls to zero.

Mode 4 (t ₃ to t ₄ )

FIG. 6D is a diagram illustrating a current flow in mode 4, which starts from a point where the current i _Ls of the second inductor L _s is equal to the current i _Lm of the first inductor L _m . It continues until the voltage charged in the first capacitor C _s1 drops to zero voltage.

Mode 5 (t ₄ to t ₅ )

Figure 6e is a diagram showing the current flow in mode 5, the mode when the both-end voltage (V _Cs1) of the capacitor (C _s1) in the mode 4, the fall to zero voltage, the first capacitor (C _s1) and connected in parallel The first diode D _s1 is turned on, thereby forming a current loop of L _m -L _s -D _s1 -D _o to transfer the input side energy to the output side.

The five operation modes described above are based on one cycle and are continuously repeated.

As such, by implementing the present invention using the turn-on snubber circuit unit 52, the present invention has the advantage of reducing switching loss and improving the reverse recovery characteristics of the diode. same.

First, FIG. 8 conceptually illustrates a switching current waveform when a turn-on snubber circuit portion is added and a turn-on switching loss at that time. As shown in FIG. 8, a switching current waveform when no turn-on snubber circuit portion is added. Since the rising slope of (indicated by the dotted line) is large, the area where the voltage V _Ds across the switching element and the current i _Ds cross each other becomes large, and thus the turn-on switching loss is very large.

However, when the turn-on snubber circuit portion is added to lower the inclination of the switching current i _Ds , as shown in FIG. 8, a region where the voltage V _Ds across the switching element and the current i _Ds cross each other is small. As a result, the turn-on switching losses can be greatly reduced.

Therefore, in the present invention, the turn-on snubber circuit portion 52 on the conduction path during the turn-on of the switching element M, in particular a second inductor Ls, is added to lower the inclination of the switching current i _Ds . This has the advantage of reducing switching losses incurred.

In addition, as mentioned above, in the conventional power factor improvement circuit, when the output diode having a large current flows off momentarily, a short circuit occurs due to the diode reverse recovery characteristic, so that the current flowing when the output diode is turned off gradually decreases. This is usually called diode zero current switching.

Therefore, the present invention is connected to the turn-on snubber circuit portion, in particular a separate second inductor (Ls) in series with the output diode to suppress the sudden change of the diode current, heat generation, permanent burnout that can be caused by a short circuit situation It also has the advantage of solving problems such as EMI.

In addition, the turn-on snubber circuit portion 52 of the present invention eliminates the need for an additional control circuit for the active switching element by using a snubber circuit that does not require a separate switching element. Not only this, but the circuit can be made up of only a small passive element, so that the circuit can be implemented more simply.

On the other hand, the present invention may further include a turn-off snubber circuit portion to reduce the turn-off loss of the switching element (M), Figure 9a to 9c is a power factor improvement of the present invention including such a turn-off snubber circuit portion The circuit is shown.

As shown in FIG. 9A, the turn-off snubber circuit unit 53 may be connected to the switching element M of the converter unit to reduce turn-off switching loss, and may be implemented as an RC snubber as shown in FIG. 9B. It can also be implemented as an RCD snubber, as in 9c.

The turn-off snubber circuit part 53 of FIG. 9B is implemented as an RC snubber, and a resistor R having one end connected to the switching element M and the other end grounded is connected in parallel with the resistor R. It consists of two capacitors C _s2 .

Further, the turn-off snubber circuit 53 of Figure 9c is that implemented as RCD snubber, and the third diode (D _s3) which anode is connected to one end of the switching element (M), a third diode (D _s3) And a third capacitor (C _s2 ) connected in parallel with the resistor (R) and a resistor (R) whose one end is connected and the other end is grounded.

At this time, the third diode (D _s3) may use a high-speed recovery diode suitable for high speed operation as in the first and second diodes (D _s1, D _s2).

However, the turn-off snubber circuit 53 is not limited to an RC snubber or an RCD snubber, and may be implemented as any snubber capable of reducing turn-off switching loss.

The present invention can also have the advantage of reducing the turn-off switching loss by adding the turn-off snubber circuit portion 53, which will be described in detail as follows.

First, FIG. 10 is a diagram conceptually illustrating a switching current waveform and a turn-off switching loss at the time of adding a turn-off snubber circuit. When the turn-off snubber circuit is not added, as shown in FIG. 10. Since the rising slope of the switching voltage waveform (indicated by the dotted line) is large, the area where the voltage V _Ds across the switching element and the current i _Ds cross each other becomes large, and thus the turn-off switching loss is very large.

However, in the case of lowering the slope of the switching voltage V _Ds by adding a turn-off snubber circuit, as shown in FIG. 10, a region where the voltage V _Ds across the switching element and the current i _Ds cross each other is small. As a result, the turn-off switching loss can be greatly reduced.

Therefore, the present invention has the advantage of improving switching loss and heat generation by lowering the pre-switching voltage slope during turn-off of the switching element through the turn-off snubber circuit.

In addition, according to the present invention, a voltage that may be instantaneously generated as shown in FIG. 10 by the turn-on delay time of the second diode D _s2 and the output diode Do through the turn-off snubber circuit 53. By removing the voltage spike, the voltage across the switching element V _DS at the switching element turn-off is more smoothly clamped to the output voltage.

In particular, the number of power diodes used in the power factor improvement circuit is the same or less than that of the conventional lossless snubber, and the voltage stress of the diode Ds1 connected in parallel with the capacitor Cs1 having the low voltage is several times higher than that of the conventional lossless snubber. It is possible to use inexpensive and high-performance diode because it is low.

One preferred embodiment of the present invention described above is disclosed for the purpose of illustration, various substitutions, modifications and Modifications may be made and such substitutions, changes and the like should be regarded as belonging to the following claims.

As described above, the power factor improvement circuit using the snubber circuit according to the present invention has the effect of reducing switching loss and improving the reverse recovery characteristics of the diode by using the snubber circuit, thereby improving efficiency.

In addition, the use of a snubber circuit that does not require a separate switching element eliminates the need for an additional control circuit for the active switching element, so that there is no additional loss or circuit effect caused by this, and the circuit is only required with a small passive element. It can be configured, which has the effect of making the circuit simpler.

In addition, the number of power diodes used in the power factor improvement circuit is the same or smaller than that of the conventional lossless snubber, and the voltage stress of the diode Ds1 connected in parallel with the capacitor Cs1 having the low voltage is several times higher than that of the conventional lossless snubber. Since this is low, it is possible to use a low cost and excellent diode.

Claims (8)

A first inductor connected between the power input terminal and the load, an output diode connected between the first inductor and the load, an output capacitor connected in parallel to the load, and a switching element connected in parallel to a power applied from the power input terminal, A converter unit converting the power applied from the power input terminal into a voltage having a DC level; And  And a turn-on snubber circuit portion connected to the converter portion to reduce turn-on switching loss of the switching element. The turn-on snubber circuit unit, A second inductor connected to the first inductor and one end thereof; A first capacitor having one end connected to the second inductor and the other end connected to an anode of the output diode; A first diode connected in parallel to the first capacitor, an anode connected to the second inductor, and a cathode connected to the anode of the output diode; And an anode connected to the first inductor and a cathode connected to the cathode of the first diode. The method of claim 1, And a turn-off snubber circuit unit connected to the converter unit to reduce turn-off switching loss of the switching element. The method of claim 2, wherein the turn off snubber circuit portion, One end of which is connected to the switching element and the other end of which is grounded, A power factor improvement circuit using a snubber circuit, characterized in that the RC snubber including a second capacitor connected in parallel with the resistor. The method of claim 2, wherein the turn off snubber circuit portion, A third diode having an anode connected to one end of the switching element, A resistor connected to the cathode of the third diode and one end thereof and grounded at the other end thereof; A power factor improvement circuit using the snubber circuit, characterized in that the RCD snubber including a third capacitor connected in parallel with the resistor. The method according to any one of claims 1 to 4, A power factor improvement circuit using a snubber circuit further comprises a third inductor between the first inductor and the second inductor. The method of claim 5, wherein the third inductor, The power factor improvement circuit using the snubber circuit, characterized in that formed by the auxiliary winding of the first inductor. The method according to any one of claims 1 to 3, The first and second diodes power factor improvement circuit using a snubber circuit, characterized in that the fast recovery diode (fast recovery diode). The method of claim 4, wherein The third diode is a power factor recovery circuit using a snubber circuit, characterized in that the fast recovery diode (fast recovery diode).

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