# Patent

## Title
Power factor correction circuit with active snubber and power supply including the same

## Abstract

There are provided a power factor correction circuit and a power supply including the same, the power factor correction circuit including a main switch adjusting a phase difference between a current and a voltage of input power, a main inductor storing or discharging the power according to switching of the main switch, a snubber circuit unit including a snubber switch forming a transfer path for surplus power present before the main switch is turned on and a snubber inductor adjusting an amount of a current applied to the snubber switch, and a reduction circuit unit reducing excessive power imposed on the snubber switch by varying inductance of the snubber inductor.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority of Korean Patent Application No. 10-2012-0143966 filed on Dec. 11, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power factor correction circuit and a power supply including the same.
2. Description of the Related Art
Recently, the governments of many countries have recommended the efficient use of energy according to energy efficiency policies, and in particular, the implementation of efficient energy usage in electronic products and home appliances is widely recommended.
In efficiently using energy according to such a governmental recommendation, a correction circuit for implementing efficient energy usage is largely applied to a power supply device that supplies power to electronic products, home appliances, and the like.
A power factor correction circuit is an example of the correction circuit. The power factor correction circuit is a circuit that switches input power to adjust a phase difference (power factor) between a current and a voltage of the input power in such a manner that power is effectively transferred to a rear stage.
However, when this power factor correction circuit performs a switching operation in order to adjust the phase difference of the input power, a peak voltage may be generated, such that a switching element may be damaged and switching loss may occur.
Patent Document 1, the following related art document, relates to a power factor improvement circuit for improving a power factor using energy accumulated in an inductor of a snubber circuit unit, but does not disclose a technical point for decreasing a spike voltage generated during switching.
RELATED ART DOCUMENT
(Patent Document 1) US Patent Laid-Open Publication No. 2011/0199066
SUMMARY OF THE INVENTION
An aspect of the present invention provides a power factor correction circuit capable of decreasing a peak voltage generated at the time at which a snubber switch providing a zero-voltage turn-on condition to a main switch switching input power to improve a power factor thereof is turned off, and a power supply including the same.
According to an aspect of the present invention, there is provided a power factor correction circuit, including: a main switch adjusting a phase difference between a current and a voltage of input power; a main inductor storing or discharging the power according to switching of the main switch; a snubber circuit unit including a snubber switch forming a transfer path for surplus power present before the main switch is turned on and a snubber inductor adjusting an amount of a current applied to the snubber switch; and a reduction circuit unit reducing excessive power imposed on the snubber switch by varying inductance of the snubber inductor.
The reduction circuit unit may include: an auxiliary inductor inductively coupled to the snubber inductor; a direct current (DC) power source supplying the power to the auxiliary inductor; a variable resistor adjusting an amount of a current supplied to the auxiliary inductor by the DC power source; and an auxiliary switch supplying or blocking the power supplied from the DC power source.
The snubber switch may be turned on for a preset first time, and the main switch may be turned on after a preset first delay time has elapsed from a time at which the snubber switch is turned on.
The first time may be longer than the first delay time.
The snubber switch may be turned on for a preset first time, and the auxiliary switch may be turned on after a preset second delay time has elapsed from a time at which the snubber switch is turned on and maintained in a turned on state for a preset second time.
A sum of the second time and the second delay time may be longer than the first time.
The power factor correction circuit may further include a reverse current preventing diode preventing a reverse current of the main switch.
The power factor correction circuit may further include a diode providing a transfer path for the power released from the main inductor according to the switching of the main switch.
The power factor correction circuit may further include a capacitor stabilizing the power transferred from the diode.
The power factor correction circuit may further include a controller providing switching control signals controlling switching operations of the main switch, the snubber switch, and the auxiliary switch.
The input power may be rectified power.
The main switch, the snubber switch, and the auxiliary switch may include at least one of an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field-effect transistor (MOS-FET) and a bipolar junction transistor (BJT).
According to another aspect of the present invention, there is provided a power supply, including: a power factor correction circuit including a main switch adjusting a phase difference between a current and a voltage of input power; a main inductor storing or discharging the power according to switching of the main switch; a snubber circuit unit including a snubber switch forming a transfer path for surplus power present before the main switch is turned on and a snubber inductor adjusting an amount of a current applied to the snubber switch; and a reduction circuit unit reducing excessive power imposed on the snubber switch by varying inductance of the snubber inductor; a power converting unit switching the power from the power factor correction circuit to convert the power into power having a preset level; and a switching controlling unit controlling the switching of the power performed by the power converting unit.
The reduction circuit unit may include: an auxiliary inductor inductively coupled to the snubber inductor; a direct current (DC) power source supplying the power to the auxiliary inductor; a variable resistor adjusting an amount of a current supplied to the auxiliary inductor by the DC power source; and an auxiliary switch supplying or blocking the power supplied from the DC power source.
The snubber switch may be turned on for a preset first time, and the main switch may be turned on after a preset first delay time has elapsed from a time at which the snubber switch is turned on.
The first time may be longer than the first delay time.
The snubber switch may be turned on for a preset first time, and the auxiliary switch may be turned on after a preset second delay time has elapsed from a time at which the snubber switch is turned on and maintained in a turned on state for a preset second time.
A sum of the second time and the second delay time may be longer than the first time.
The power factor correction circuit may further include a reverse current preventing diode preventing a reverse current of the main switch.
The power factor correction circuit may further include a diode providing a transfer path for the power released from the main inductor according to the switching of the main switch.
The power factor correction circuit may further include a capacitor stabilizing the power transferred from the diode.
The power factor correction circuit may further include a controller providing switching control signals controlling switching operations of the main switch, the snubber switch, and the auxiliary switch.
The power supply may further include a rectifying unit transferring the input power generated by rectifying alternating current (AC) power to the power factor correction circuit.
The main switch, the snubber switch, and the auxiliary switch may include at least one of an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field-effect transistor (MOS-FET) and a bipolar junction transistor (BJT).



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIGS. 1 and 2 are circuit views schematically showing a power factor correction circuit according to an embodiment of the present invention;
FIG. 3 is a graph illustrating switching control signals of a main switch, a snubber switch, and an auxiliary switch employed in the power factor correction circuit according to the embodiment of the present invention;
FIGS. 4A and 4B are graphs respectively showing voltage generated across the snubber switch employed in the power factor correction circuit according to the embodiment of the present invention; and
FIG. 5 is a view schematically showing a configuration of a power supply including a power factor correction circuit according to an embodiment of the present invention.



DETAILED DESCRIPTION OF THE EMBODIMENTS
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements.
FIGS. 1 and 2 are circuit views schematically showing a power factor correction circuit 100 according to an embodiment of the present invention.
Referring to FIG. 1, the power factor correction circuit 100 according to the embodiment of the present invention may include a main inductor L, a main switch S, a snubber circuit unit 110, and a reduction circuit unit 120, and may further include a diode D, a capacitor C, a reverse current preventing diode DR, and a controller 130.
The main switch S may perform a switching operation to adjust a phase difference between a voltage and a current of input power input from an input terminal IN. Here, the input power may be rectified power.
The reverse current preventing diode DR may prevent a reverse current of the main switch S by providing a bypass path from an anode to a cathode of the reverse current preventing diode DR, when the reverse current is applied to the main switch S. When the main switch S is configured of a transistor, the reverse current preventing diode DR may be a diode formed in a body of the transistor. However, the reverse current preventing diode DR is not limited thereto and may be a separate diode.
The main inductor L may be disposed between the input terminal IN receiving the input power and the main switch S to thereby store or release the power according to the switching operation of the main switch S and the diode D may provide a transfer path for the power released from the main inductor L according to the switching operation of the main switch S. In addition, the capacitor C may be connected to an output terminal OUT in parallel to thereby stabilize the power output from the diode D.
The snubber circuit unit 110 may include a snubber switch Sn connected to the main switch in parallel and a snubber inductor Ln provided between the snubber switch Sn and the main switch S to adjust an amount of a current flowing in the snubber switch Sn.
The reduction circuit unit 120 may include an auxiliary inductor La inductively coupled to the snubber inductor Ln, a direct current (DC) power source Va supplying the power to the auxiliary inductor La, a variable resistor Ra adjusting an amount of a current supplied to the auxiliary inductor La by the DC power source Va, and an auxiliary switch Sa supplying or blocking the power supplied from the DC power source Va.
The controller 130 may generate switching control signals G, Gn, and Ga controlling switching operations of the main switch S, the snubber switch Sn, and the auxiliary switch Sa.
The main switch S, the snubber switch Sn, and the auxiliary switch Sa according to the embodiment of the present invention may be configured of one of an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field-effect transistor (MOS-FET) and a bipolar junction transistor (BJT). Referring to FIG. 2, although FIG. 2 shows an example in which the main switch S, the snubber switch Sn, and the auxiliary switch Sa are configured of the BJTs, the present invention is not limited thereto.
FIG. 3 is a graph illustrating switching control signals of the main switch S, the snubber switch Sn, and the auxiliary switch Sa employed in the power factor correction circuit 100 according to the embodiment of the present invention. In the case in which the switching control signals G, Gn, and Ga are at high levels, the main switch S, the snubber switch Sn, and the auxiliary switch Sa are turned on and in the case in which the switching control signals G, Gn, and Ga are at low levels, the main switch S, the snubber switch Sn, and the auxiliary switch Sa are turned off.
The main switch S of the power factor correction circuit 100 according to the embodiment of the present invention may perform the switching operation to adjust the phase difference between the voltage and the current of the input power, thereby improving the power factor of the input power. In this case, the snubber switch Sn may bypass surplus power remaining during on and off switching of the main switch S to a ground, whereby a zero-voltage switching condition may be provided to the main switch S. Therefore, switching loss of the main switch S may be removed.
As shown in FIG. 3, the snubber switch Sn is turned on earlier than the main switch S by a first delay time TD1, thereby forming a transfer path for the surplus power. Here, the snubber switch Sn may be turned on for a first time T1. In this case, the first time T1 is set to be longer than the first delay time TD1, such that the snubber switch Sn may be turned off before the main switch S is turned off.
Meanwhile, when the snubber switch Sn is turned on, in order to prevent the current having a high current level from being applied to the snubber switch Sn, the snubber inductor Ln is provided between the snubber switch Sn and the main switch S. In this configuration, when the snubber switch Sn is turned off, since a path through which the current flowing in the snubber inductor Ln is conducted is not present, a peak voltage is generated across the snubber switch Sn, whereby damage to the snubber switch Sn and switching loss thereof may occur.
FIGS. 4A and 4B are graphs respectively showing voltage generated across the snubber switch Sn employed in the power factor correction circuit according to the embodiment of the present invention. FIG. 4A is a graph showing the voltage generated across the snubber switch Sn when the path through which the current flowing in the snubber inductor Ln is conducted is not present, during the turning off of the snubber switch Sn.
Before the first time t1, the snubber switch Sn may be turned off, such that a high voltage is generated across the snubber switch Sn. Thereafter, at the first time t1, the snubber switch Sn is turned on, such that a low voltage is generated across the snubber switch Sn. However, at a time t2, when the snubber switch Sn is turned on, since the path through which the current flowing in the snubber inductor Ln is conducted is not present, a high peak voltage is generated.
In order to reduce the peak voltage, referring to FIG. 1, the power factor correction circuit may employ the reduction circuit unit 120. The reduction circuit unit may vary inductance of the snubber inductor to remove excessive power imposed on the snubber switch, that is, the peak voltage.
As described above, referring to FIG. 1, the reduction circuit unit 120 may include the auxiliary inductor La inductively coupled to the snubber inductor Ln, the direct current (DC) power source Va supplying the power to the auxiliary inductor La, the variable resistor Ra adjusting an amount of the current supplied to the auxiliary inductor La by the DC power source Va, and the auxiliary switch Sa supplying or blocking the power supplied from the DC power source Va.
Referring back to FIG. 3, the auxiliary switch Sa may be turned on after a preset second delay time TD2 has elapsed from a time at which the snubber switch Sn is turned on, and maintained in a turned on state for a preset second time T2. In this case, the sum of the second time T2 and the second delay time TD2 is set to be longer than the first time T1, whereby the auxiliary switch Sa may be turned off after the snubber switch Sn is turned off. In addition, the second delay time TD2 may be set to be longer than the first delay time TD1.
In the case in which the auxiliary switch Sa is turned off, since the reduction circuit unit 120 is in an electrically turned off state, the reduction circuit unit 120 does not affect the snubber circuit unit 110, such that the snubber inductor Ln may maintain a normal inductance. Therefore, the snubber circuit unit 110 may remove the switching loss of the main switch S by providing the zero-voltage turn-on condition to the main switch S.
However, in the case in which the auxiliary switch Sa is turned on unlike the above, the DC power source Va supplies the power to the auxiliary inductor La inductively coupled to the snubber inductor Ln, thereby affecting the inductance of the snubber inductor Ln. That is, the auxiliary inductor La supplied with direct current (DC) generated by the DC power source Va may decrease the inductance of the snubber inductor Ln by saturating magnetic flux of a core included in the snubber inductor Ln and may ideally decrease an inductance value of the snubber inductor Ln to zero “0”. Therefore, the reduction circuit unit 120 may decrease the inductance of the snubber inductor Ln. As the inductance of the snubber inductor Ln is decreased, such that the peak voltage generated across the snubber switch Sn during the turning off of the snubber switch Sn may be removed.
The auxiliary resistor Ra may be varied by settings, and in the case, the amount of the current supplied to the auxiliary inductor La by the DC power source Va is determined by varying resistance in the auxiliary resistor Ra. This may affect in determining the saturation magnetic flux of the core included in the snubber inductor Ln.
In summary, the power factor correction circuit according to the embodiment of the present invention may significantly improve power factor efficiency and electromagnetic interference (EMI) noise level by removing the switching loss generated when the main switch S is turned on and the snubber switch Sn is turned off.
FIG. 4B is a graph showing the case in which the peak voltage generated across the snubber switch Sn during the turning off of the snubber switch Sn is removed using the reduction circuit unit 120 of the power factor correction circuit according to the embodiment of the present invention. Comparing FIGS. 4A and 4B, it may be appreciated that the peak voltage is reduced at the time t2.
FIG. 5 is a view schematically showing a configuration of a power supply including the power factor correction circuit 100 according to the embodiment of the present invention.
Referring to FIG. 5, the power supply may include the power factor correction circuit 100, a power converting unit 200, a switching controlling unit 300, and a rectifying unit 400.
The power factor correction circuit 100 of FIG. 5 is the same as the power factor correction circuit 100 shown in FIG. 1. Therefore, a detailed description thereof will be omitted.
The power converting unit 200 may switches direct current (DC) power from the power factor correction circuit to convert the DC power into DC power having a preset voltage level and then supply the converted DC power to a load, the switching controlling unit 300 may control the switching of the power converting unit 200 according to a voltage or current level of the output DC power, and the rectifying unit 400 may transfer the input power generated by rectifying alternating current (AC) power to the power factor correction circuit 100.
As set forth above, according to the embodiment of the present invention, the zero-voltage turn-on condition is provided to the main switch switching the input power to improve the power factor thereof, whereby damage to the main switch may be prevented and switching loss thereof can be decreased.
In addition, the inductance of the snubber inductor connected to the snubber switch providing the zero-voltage turn-on condition to the main switch is decreased, such that the peak voltage can removed, whereby damage to the snubber switch can be prevented.
While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

## Claims

1. A power factor correction circuit, comprising:
a main switch adjusting a phase difference between a current and a voltage of input power;
a main inductor storing or discharging the power according to switching of the main switch;
a snubber circuit unit including a snubber switch forming a transfer path for surplus power present before the main switch is turned on and a snubber inductor adjusting an amount of a current applied to the snubber switch; and
a reduction circuit unit reducing excessive power imposed on the snubber switch by varying inductance of the snubber inductor,
wherein the reduction circuit unit includes;
an auxiliary inductor inductively coupled to the snubber inductor;
a direct current (DC) power source supplying the power to the auxiliary inductor;
a variable resistor adjusting an amount of a current supplied to the auxiliary inductor by the DC power source; and
an auxiliary switch supplying or blocking the power supplied from the DC power source.

2. The power factor correction circuit of claim 1, wherein the snubber switch is turned on for a preset first time, and the main switch is turned on after a preset first delay time has elapsed from a time at which the snubber switch is turned on.

3. The power factor correction circuit of claim 2, wherein the preset first time is longer than the preset first delay time.

4. The power factor correction circuit of claim 1, wherein the snubber switch is turned on for a preset first time, and the auxiliary switch is turned on after a preset second delay time has elapsed from a time at which the snubber switch is turned on and maintained in a turned on state for a preset second time.

5. The power factor correction circuit of claim 4, wherein a sum of the preset second time and the preset second delay time is longer than the preset first time.

6. The power factor correction circuit of claim 1, further comprising a reverse current preventing diode preventing a reverse current of the main switch.

7. The power factor correction circuit of claim 1, further comprising a diode providing a transfer path for the power released from the main inductor according to the switching of the main switch.

8. The power factor correction circuit of claim 7, further comprising a capacitor stabilizing the power transferred from the diode.

9. The power factor correction circuit of claim 1, further comprising a controller providing switching control signals controlling switching operations of the main switch, the snubber switch, and the auxiliary switch.

10. The power factor correction circuit of claim 1, wherein the input power is rectified power.

11. The power factor correction circuit of claim 1, wherein the main switch, the snubber switch, and the auxiliary switch include at least one of an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field-effect transistor (MOS-FET) and a bipolar junction transistor (BJT).

12. A power supply, comprising:
a power factor correction circuit including a main switch adjusting a phase difference between a current and a voltage of input power; a main inductor storing or discharging the power according to switching of the main switch; a snubber circuit unit including a snubber switch forming a transfer path for surplus power present before the main switch is turned on and a snubber inductor adjusting an amount of a current applied to the snubber switch; and a reduction circuit unit reducing excessive power imposed on the snubber switch by varying inductance of the snubber inductor;
a power converting unit switching the power from the power factor correction circuit to convert the power into power having a preset level; and
a switching controlling unit controlling the switching of the power performed by the power converting unit,
wherein the reduction circuit unit includes;
an auxiliary inductor inductively coupled to the snubber inductor,
a direct current (DC) power source supplying the power to the auxiliary inductor;
a variable resistor adjusting an amount of a current supplied to the auxiliary inductor by the DC power source; and
an auxiliary switch supplying or blocking the power supplied from the DC power source.

13. The power supply of claim 12, wherein the snubber switch is turned on for a preset first time, and the main switch is turned on after a preset first delay time has elapsed from a time at which the snubber switch is turned on.

14. The power supply of claim 13, wherein the preset first time is longer than the preset first delay time.

15. The power supply of claim 12, wherein the snubber switch is turned on for a preset first time, and the auxiliary switch is turned on after a preset second delay time has elapsed from a time at which the snubber switch is turned on and maintained in a turned on state for a preset second time.

16. The power supply of claim 15, wherein a sum of the preset second time and the preset second delay time is longer than the preset first time.

17. The power supply of claim 12, wherein the power factor correction circuit further includes a reverse current preventing diode preventing a reverse current of the main switch.

18. The power supply of claim 12, wherein the power factor correction circuit further includes a diode providing a transfer path for the power released from the main inductor according to the switching of the main switch.

19. The power supply of claim 18, wherein the power factor correction circuit further includes a capacitor stabilizing the power transferred from the diode.

20. The power supply of claim 12, wherein the power factor correction circuit further includes a controller providing switching control signals controlling switching operations of the main switch, the snubber switch, and the auxiliary switch.

21. The power supply of claim 12, further comprising a rectifying unit transferring the input power generated by rectifying alternating current (AC) power to the power factor correction circuit.

22. The power supply of claim 12, wherein the main switch, the snubber switch, and the auxiliary switch include at least one of an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field-effect transistor (MOS-FET) and a bipolar junction transistor (BJT).