KR20120072663A - Power supply - Google Patents

Abstract

PURPOSE: A power supply device is provided to reduce ripples in a low-frequency band of output current by changing power with fly-back and forward methods when switching on and off input power, respectively. CONSTITUTION: An electromagnetic interference filter part(110) filters electromagnetic interference components included in commercial AC power. A rectifier part(120) rectifies and smoothens the power from which the electromagnetic interference components are removed. A power conversion part(130) changes input power into first and second power with fly-back and forward methods, respectively. An output coupling part(140) couples the first and second power from the power conversion part. A control part(150) provides a switching control signal for controlling on and off of a switch based on the voltage level of the first power, the current level of the output power, and detection voltage, which is detected from current flowing in a load. A path providing part(160) provides a circulation path for power according to on and off of the switch.

Description

Power supply unit {POWER SUPPLY}

The present invention relates to a power supply having a low ripple in an output current.

Recently, liquid crystal displays (LCDs) among display devices have been used in various products such as computers, notebooks, and AV devices due to the advantages of small size, slimness, and low power consumption.

Such a liquid crystal display device employs a backlight unit for emitting light necessary for pixels.

The backlight unit may include a plurality of lamps having a bar shape, a power supply circuit for supplying power to the lamps, and supplying driving power for other circuits, and a controller for adjusting the brightness of the lamps by receiving the driving power.

In the meantime, a cold cathode fluorescent lamp (CCFL) is generally used as the lamp. However, the backlight unit employing a light emitting diode as a light source in consideration of processing speed, power consumption, and lifespan. Is emerging.

 The backlight unit adopting such a light emitting diode as a light source essentially adopts a power supply device for supplying driving power for driving the light emitting diode.

The power supply unit rectifies and smoothes the commercial AC power, and then switches the rectified and smoothed power to a predetermined stage power supply, and converts the rectified and smoothed power into a primary stage. A two stage method for performing a power factor correcting operation and then secondly switching the power factor corrected power to a driving power source may be implemented.

The single stage method described above has a problem in that the structure is simple, which is advantageous to low cost, but the low frequency ripple of the 120 Hz band is not easily eliminated among the output currents of the driving power supply. Is easy to remove, but the number of elements and the complexity is expensive, the manufacturing cost is expensive, the power conversion efficiency is reduced by a two-step power conversion process.

It is an object of the present invention to provide a power supply device capable of preventing a reduction in power change efficiency while reducing ripple in a low frequency band in an output current.

In order to achieve the above object, one technical aspect of the present invention comprises at least one switch, and switching the input power to the input power in a fly-back (Fly-Back) voltage level according to the switching A power conversion unit for converting the first power source into a first power source and converting the input power source into a second power source having a voltage level according to the switching; And a control unit for controlling a switching frequency of the first conversion unit based on an output power supply of the output coupling unit.

According to one technical aspect of the present invention, the output coupling unit may supply the driving power to at least one light emitting diode.

According to one technical aspect of the present invention, the control unit controls the switching frequency of the power conversion unit based on the voltage level of the first power supply, the current level of the driving power supply, and the detected voltage detecting the current flowing in the load. By controlling the power conversion of the first power supply, and controlling the switching duty of the power conversion unit may control the power conversion of the second power supply.

According to one technical aspect of the present invention, the control unit includes a first comparator for comparing the current level of the driving power supply with a preset reference current level, and triangular wave generation for generating a triangular wave whose frequency is controlled according to a control signal. A second comparator for comparing a comparison signal of the first comparator with a triangular wave of the triangular wave generator to output a switching control signal for controlling switching of the power converter; a voltage level of the first power source and a preset reference It may include a frequency control unit for comparing the voltage level, calculating the comparison result and the detected voltage to provide a control signal for controlling the frequency of the triangular wave generator.

According to one technical aspect of the present invention, the frequency generator includes a third comparator comparing the voltage level of the driving power supply with a preset reference voltage level, and a square value of the detected voltage and the third comparator. A first operation unit for multiplying the result and a second operation unit for multiplying a preset frequency constant by the operation result of the first operation unit.

According to one technical aspect of the present invention, the power converter is a switch for switching the input power in accordance with the switching control of the controller, and the voltage of the switched power in a flyback method and a forward method according to a predetermined turns ratio The transformer may include a level converting transformer and first and second rectifying diodes rectifying the power converted from the transformer.

According to one technical aspect of the present invention, it may further include a path providing unit for providing a circulation path of the power of the transformer.

According to one technical aspect of the present invention, the transformer has a predetermined winding start point, receives the input power at one end, and is connected to the first primary winding and the other end connected to the switch, and opposite to the first primary winding. Has a winding start point of one end, the first end of which is connected to the path providing portion, the other end of which is connected to primary side ground, and the same winding start point as that of the first primary winding; A first secondary winding receiving power from a first primary winding, and a second secondary winding having a winding start point opposite to the first primary winding and receiving power from the first primary winding when the switch is switched off. can do.

According to one technical aspect of the present invention, the path providing unit has a first diode having a cathode connected to one end of the first primary winding, a cathode connected to an anode of the first diode, and the path of the second primary winding. It may include a second diode having an anode connected to one end, one end connected to the cathode of the second diode, and a capacitor having the other end connected to the primary side ground.

According to one technical aspect of the present invention, the output coupling portion has an cathode connected to the cathode of the first rectifying diode, an output diode having an anode connected to the cathode of the second rectifying diode, and an anode of the output diode. An output capacitor having one end connected to the other end connected to the secondary ground, an inductor having one end connected to the cathode of the output diode, the other end connected to the load, one end connected to the other end of the inductor, and a secondary side ground It may include a stabilizing capacitor having the other end connected.

According to one technical aspect of the present invention, the rectification and smoothing the commercial AC power may further include a rectifying unit for transmitting to the power conversion unit, and filtering the electromagnetic interference contained in the commercial AC power and delivered to the rectifying unit It may further include an electromagnetic interference filter.

According to the present invention, by switching the power to the flyback method and the forward method, respectively, at the time of switching on and off switching the input power source, it is possible to prevent the reduction of the power change efficiency while reducing the ripple of the low frequency band in the output current. There is.

1 is a schematic configuration diagram of a power supply device of the present invention.
2 is a diagram illustrating a path through which power is transmitted in the power supply device of the present invention.
3 is a main operational waveform graph of the power supply of the present invention.
4A to 4C show an operation mode of the power supply of the present invention.
5 is a graph of the input power input to the power supply of the present invention.
6 is a schematic configuration diagram of a control unit employed in the power supply apparatus of the present invention.
7A is an output power ripple graph of a power supply device employing a general single stage method, and FIG. 7B is an output power ripple graph of the power supply device of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

1 is a schematic configuration diagram of a power supply apparatus of the present invention.

Referring to FIG. 1, the power supply device 100 of the present invention may include a power conversion unit 130, an output coupling unit 140, a control unit 150, and a path providing unit 160. The interference filter unit 110 and the rectifier 120 may be further included.

The electromagnetic interference filter unit 110 may filter and transmit the electromagnetic interference component included in the commercial AC power source to the rectifier 120.

The rectifier 120 may rectify and smooth power to which the electromagnetic interference has been removed and transmit the same to the power converter 130.

The power converter 130 switches the input power Vin input from the rectifier 120 to convert the input power Vin into a fly-back and forward method, respectively. And a second power source Vo2.

To this end, the power converter 130 may include a switch Q, a transformer T, and first and second rectifying diodes D1 and D2.

The switch Q may be turned on and off according to the switching control signal of the controller 150 to switch the input power Vin.

The transformer T may include first and second primary windings N _P1 and N _P2 and first and second secondary windings N _S1 and N _S2 .

One end of the first primary winding N _P1 is connected to the rectifier to receive the input power Vin, and the other end is connected to the switch Q to power the secondary winding coupled electromagnetically according to the turn on / off of the switch Q. Can be passed. One end of the second primary winding N _P2 may be connected to the path providing unit 160, and the other end thereof may be connected to the primary side ground. In this case, the winding start points (points shown in the drawing) of the first primary winding N _P1 and the second primary winding N _P2 may be opposite to each other.

One end of the first secondary winding N _S1 may be connected to the anode of the first rectifying diode D1, and the other end thereof may be connected to the output coupling unit 140. Winding start point of the first secondary winding (N _S1) is from a first primary winding (N _P1) may have the same location as the winding start point, whereby the first primary winding (N _P1) in turn turns on a switch (Q) in accordance with the You can regain power. One end of the second secondary winding N _S2 may be connected to the output coupling unit 140, and the other end thereof may be connected to the secondary side ground. The starting point of the winding of the second secondary winding N _S2 may have a position opposite to the starting point of the winding of the first primary winding N _P1 , and thus, when the switch Q is turned off, the first primary winding N _P1 You can get power from).

The first rectifying diode D1 rectifies the power supply from the first secondary winding N _S1 to output the second power supply Vo2, and the second rectifying diode D2 is from the second secondary winding N _S2 . The power source may be rectified to output the first power source Vo1.

The output combiner 140 may combine and output the first power Vo1 and the second power Vo2 from the power converter 130.

To this end, the output coupling unit 140 may include an output diode D3, an output capacitor Clink, an inductor Lo, and a stabilization capacitor Co.

The cathode of the output diode D3 may be connected to the cathode of the first rectifying diode D1, and the anode of the output diode D3 may be connected to the cathode of the second rectifying diode D2. One end of the output capacitor Clink may be connected to the anode of the output diode D3 and the cathode of the second rectifying diode D2, and the other end thereof may be connected to the secondary side ground. One end of the inductor Lo may be connected to the cathode of the output diode D3, and the other end thereof may be connected to the stabilization capacitor Co. One end of the stabilizing capacitor Co may be connected to the other end of the inductor Lo, and the other end of the stabilizing capacitor Co may be connected to the secondary side ground.

The controller 150 turns on the switch Q based on the voltage level of the first power source Vo1, the current Io level of the output power source, and the detection voltage Vi, sense that detects a current flowing in the load as a voltage. And a switching control signal for controlling the turn off. The detailed configuration of the controller 150 will be described later with reference to FIG. 6.

The path provider 160 may provide a circulating path of power by turning on and off the switch Q. FIG.

To this end, the path providing unit 160 may include first and second diodes D4 and D5 and a capacitor C1. The anode of the first diode D4 may be connected to one end of the second primary winding N _P2 , and the cathode of the first diode D4 may be connected to the anode of the second diode D5. The cathode of the second diode D5 may be connected to one end of the first primary winding N _P1 . One end of the capacitor C1 may be connected to the anode of the first diode D4 and the other end may be connected to the primary side ground.

는 입력 전원의 최대값을 나타낸다.
The input power Vin from the rectifier may have a 120 Hz period, as shown in FIG. 5, and the power Vdead charged in the capacitor C1 may be maintained as shown in the graph.

Represents the maximum value of the input power supply.

2 is a view showing a path through which the power of the power supply of the present invention is delivered.

As shown in FIG. 2, the power supply device of the present invention generates a first power source Vo1 and a second power source Vo2 by a flyback method and a forward method, respectively, and combines the outputs of the first power source Vo1 and the second power source Vo2 and transfers the outputs to a load, in particular a light emitting diode. As a result, power conversion efficiency may be high.

(Formula 1)

η ₁ and η ₂ refer to the efficiency of power conversion induced by the first and second secondary windings, respectively, where k can be expressed as Equation 2 below.

(Equation 2)

That is, k may be expressed as a ratio of input power and power of the flyback circuit. As the value of k increases, the synergy effect of the power conversion efficiency decreases, and as the value of k decreases, the power factor decreases. For example, when the voltage level of the output power Vo is 24V, the voltage level of the first power Vo1 is 20V, and the efficiency and the power factor are set to 90%, the power supply of a typical two-stage power supply device is used. Although the conversion efficiency is about 81%, the power conversion efficiency of the present invention can be increased to 88.5%.

Referring to FIG. 2, the first power source Vo1 is output when the switch Q is turned off in the flyback manner as shown by the arrow, and the second power source Vo2 is turned on when the switch Q is turned on in the forward manner. ) May be output. The turn on and off of the switch Q is controlled by a switching control signal from the control unit 150, and in order to perform one of the switch Q to perform the flyback and forward power conversion operations, the first The voltage level of the power source Vo1 may be adjusted by switching frequency control, and the voltage level of the second power source Vo2 may be adjusted by switching duty control.

That is, since the first power source Vo1 may be output when the switch Q is turned off, and the second power source Vo2 may be output when the switch Q is turned on in a forward manner, the turn of the switch Q is turned on. When turned off, the voltage of the first power source Vo1 increases and the voltage of the second power source Vo2 decreases. On the contrary, when the switch Q is turned on, the voltage of the first power source Vo1 decreases. The voltage of the second power source Vo2 is increased.

Therefore, since the output power Vo is the sum of the first power Vo1 and the second power Vo2, the ripples of the output power Vo cancel each other, thereby reducing the ripple component included in the output power Vo.

3 is a graph of the main operation waveform of the power supply of the present invention, Figures 4a to 4c is a view showing the operation mode of the power supply of the present invention.

4A to 4C illustrate an operation in the first mode t0-t1 to the third mode t2-t3 in the operation waveform graph of FIG. 3.

3 and 4A, first, when the switch Q is turned on, since the positive voltage is applied to the winding start point of the transformer T, the first rectifying diode D1 is turned on and the output diode D3 is turned on. (N _S1 / N _P1 ) V _in Since the voltage is applied and the second rectifying diode D2 is applied with the voltage V _O 1+ (N _S2 / N _P1 ) V _in , both the second rectifying diode D2 and the output diode D3 are turned off. A conduction path of electric current like a solid line is formed. The voltage of the input power source Vin is applied across the magnetizing inductor L _m so that the current rises with a slope of V _in / L _m . In addition, since the first rectifying diode D1 is conducted, (N _S1 / N _P1 ) V _in across the inductor Lo. + V _O 1-V _O voltage is applied to ((N _S1 / N _P1 ) V _in The current rises with the slope of + V _O 1 -V _O ) / L _O.

3 and 4B, when the switch Q is turned off, as shown in FIG. 4B, the magnetizing inductor current of the transformer T flows in a direction opposite to the starting point of the winding of the transformer T, so that the second rectifier diode ( D2) and output diode D3 are turned on, and (N _S1 / N _P1 ) V _in voltage is applied to first rectifier diode D1 to turn off to form a conductive path of current as shown in FIG. 4B. do. Since the second rectifying diode D2 is conductive, the voltage across the magnetizing inductor L _m becomes-(N _P1 / N _S2 ) V _O1 , and the current _is- (N _P1 / N _S2 ) V _O1 / L _m It decreases with the slope of. Since the switch Q is turned off, the voltage across the switch V _DS becomes V _in + (N _P1 / N _S2 ) V _O1 , and the current ID2 flowing through the second rectifying diode D2 is-(N _P2 / N _S2 ) decrease with the slope of ² V ₀₁ / L _m . Across the output inductor is applied the voltage V _O -V _O 1 and the current I _Lo decreases with the slope of (V _O -V _O 1) / L _O. When the current I _Lm flowing in the magnetization inductor L _m becomes '0', the second mode t1-t2 ends.

3 and 4A, after the current I _Lm flowing in the magnetization inductor L _m becomes 0, the second rectifying diode D2 is turned off and only the output diode D3 is turned on as shown in FIG. The current I _Lo flowing in _Lo continues to decrease with the slope of (V _O -V _O 1) / L _O , in which the current freewheels.

6 is a schematic configuration diagram of a control unit employed in the power supply apparatus of the present invention.

Referring to FIG. 1 along with FIG. 6, as described above, the power supply apparatus of the present invention converts power in a flyback method and a forward method by sharing one switch in a power conversion method.

Accordingly, the input / output relational expression is as shown in Equation 3 below.

(Formula 3)

At this time, the minimum input voltage becomes Vdead by the capacitor C of the path providing unit 160 as shown in FIG. 5, and the ratio is maximized. Same as

(Equation 4)

Meanwhile, the average current Ip of the current flowing through the magnetizing inductor Lm of the transformer T may be derived as shown in Equation 5 below.

(Formula 5)

The condition for the power factor to be 1 is a case where the input impedance is seen as the resistance component Re, which can be expressed by Equation 6 below.

(Equation 6)

According to Equations 3 and 5, the frequency may be equal to Equation 7 below.

(Equation 7)

Equation 7 described above is a switching frequency control principle of the present invention. The controller 150 may be configured to indirectly follow the resistance component Re of the input impedance by configuring the controller 150 so that the first power source Vo1 follows a preset voltage. .

In order to establish Equation 8 described above, the controller 150 employed in the power supply device 100 of the present invention includes a first comparator 151, a triangle wave generator 152, a second comparator 153, and a frequency. The controller 154 may be included.

The first comparator 151 may compare the current Io level of the driving power supply with a preset reference current Io, ref level and transmit the comparison result to the second comparator 153.

The triangle wave generator 152 may generate a triangle wave whose frequency is controlled according to the provided control signal.

The second comparator 153 may output a switching control signal for controlling the switching of the switch Q by comparing the comparison result of the first comparator 151 with the triangular wave of the triangular wave generator 152. The frequency control information of the switching control signal may satisfy Equation 8 described above.

The frequency controller 154 compares the voltage level of the first power source Vo1 with a preset reference voltage Vo1, ref level, calculates a comparison result, and detects a voltage to control the frequency of the triangular wave generator. Can be provided.

To this end, the frequency controller 154 may include a third comparator 154a, a first calculator 154b, and a second calculator 154c.

The third comparator 154a compares the voltage level of the first power source Vo1 with the voltage levels of the preset reference voltages Vo1 and ref and transmits the comparison result to the first calculator 154b.

The first calculator 154b may multiply the detected detection voltages Vi and sense by the comparison result from the third comparator 154a and the current flowing through the load.

The second calculator 154c multiplies the calculation result of the first calculator 154b by a preset frequency constant K to provide a control signal capable of controlling the frequency of the triangular wave generator 152.

The operation of the frequency controller 154 described above is expressed by Equation 8 below.

Equation 7 described above may be arranged as Equation 8 below.

(Equation 8)

Here, T is the frequency of the triangular wave of the triangular wave generator 152.

It will be described with respect to the switching frequency control of the above-described control unit 150.

The controller 150 controls the voltage of the first power source Vo1 through the switching frequency control of the switch Q. That is, when the voltage of the first power source Vo1 increases and the comparison result Vc1 of the third comparator 154a decreases, the period of the triangular wave generated by the triangular wave generator 152 decreases according to Equation 8 described above. When the frequency of the triangular wave increases, and the voltage of the first power source Vo1 decreases and the comparison result Vc1 of the third comparator 154a increases, the period of the triangular wave increases and the frequency of the triangular wave decreases. Similarly, when the voltage level of the detection voltages Vi and sense is low, the frequency of the triangular wave increases, and when the voltage level of the detection voltages Vi and sense is high, the frequency of the triangle wave decreases.

Accordingly, since the second comparator 153 compares the comparison result of the first comparator 151 with the triangular wave and provides a switching control signal, the current Io flowing through the load increases to increase the first comparator 151. When the comparison result of Vc decreases, the fertilization rate decreases, and the current flowing in the load decreases, so that the comparison result Vc of the first comparator 151 increases the fertilization rate so that the constant current control of the power supplied to the load is achieved. It becomes possible. In particular, when the load is a light emitting diode, it is possible to control the constant current capable of driving the light emitting diode.

7A is an output power ripple graph of a power supply device employing a general single stage method, and FIG. 7B is an output power ripple graph of the power supply device of the present invention.

Referring to FIG. 7A, in the case of a power supply device employing a general single stage method, a large ripple of about 56% occurs in the output current. On the other hand, referring to Figure 7b, it can be seen that the output current ripple of the power supply of the present invention is very small within 5%.

As described above, according to the present invention, when a driving power is supplied to a load, in particular, a light emitting diode, one switch is shared to perform a power conversion operation in a flyback method and a forward method, thereby maintaining a high power conversion efficiency. The low frequency band ripple of the current can be reduced.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the particular forms disclosed. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

100 ... power supply
110. Electromagnetic interference filter
120 ... rectifier
130 ... power conversion unit
140 ... output coupling
150 ... control unit
151.Comparative Part 1
152 ... triangle wave generator
153 Second Comparison Unit
154 ... frequency control
154a ... 3 comparison section
154b ... first calculating unit
154c ... second operation unit
160.Route Provider

Claims (12)

At least one switch, the input power is switched to convert the input power to a first power source having a voltage level according to the switching in a fly-back (Fly-Back) method, the input power is switched in a forward manner A power converting unit converting the second power to a second power having a voltage level according to the method;
An output coupler configured to output a driving power coupled to the load by combining the first power and the second power to the power converter; And
A control unit controlling a switching frequency of the first conversion unit based on an output power of the output coupling unit
Power supply comprising a. The method of claim 1,
And the output coupling unit supplies the driving power to at least one light emitting diode. The method of claim 1,
The control unit controls power conversion of the first power supply by controlling a switching frequency of the power conversion unit based on a voltage level of the first power supply, a current level of the driving power supply, and a detected voltage detecting a current flowing through the load. And controlling the switching duty of the power converter to control power conversion of the second power source. 4. The apparatus of claim 3, wherein the control unit
A first comparing unit comparing a current level of the driving power supply with a preset reference current level;
A triangular wave generator for generating a triangular wave whose frequency is controlled according to a control signal;
A second comparator for comparing a comparison signal of a first comparator and a triangular wave of the triangular wave generator to output a switching control signal for controlling switching of the power converter; And
A frequency controller for comparing a voltage level of the first power supply with a preset reference voltage level, calculating a result of the comparison and the detected voltage, and providing a control signal for controlling the frequency of the triangular wave generator;
Power supply comprising a. The method of claim 4, wherein the frequency generator
A third comparing unit comparing the voltage level of the driving power supply with a preset reference voltage level;
A first calculating unit multiplying a square value of the detection voltage and a comparison result of the third comparing unit; And
A second operation unit which multiplies a calculation result of the first operation unit by a preset frequency constant
Power supply comprising a. The method of claim 1, wherein the power conversion unit
A switch for switching the input power according to the switching control of the controller;
A transformer for voltage level conversion of the switched power supply in a flyback method and a forward method according to a preset turns ratio; And
First and second rectifier diodes respectively rectifying the power converted from the transformer
Power supply comprising a. The method of claim 6,
The power supply device further comprises a path providing unit for providing a circulation path of the power of the transformer. The method of claim 7, wherein the transformer
A first primary winding having a predetermined winding start point, receiving the input power at one end, and having the other end connected to the switch;
A second primary winding having a winding start point opposite to the first primary winding, one end of which is connected to the path providing portion and the other end of which is connected to a primary side ground;
A first secondary winding having the same winding start point as the first primary winding and receiving power from the first primary winding upon switching on of the switch; And
A second secondary winding having a winding start point opposite to the first primary winding and receiving power from the first primary winding upon switching off of the switch;
Power supply comprising a. The method of claim 8, wherein the path providing unit
A first diode having a cathode connected to one end of the first primary winding;
A second diode having a cathode connected to the anode of the first diode and having an anode connected to one end of the second primary winding; And
A capacitor having one end connected to the cathode of the second diode and the other end connected to the primary side ground
Power supply comprising a. The method of claim 6, wherein the output coupling portion
An output diode having a cathode connected to the cathode of the first rectifying diode and an anode connected to the cathode of the second rectifying diode;
An output capacitor having one end connected to an anode of the output diode and the other end connected to a secondary side ground;
An inductor having one end connected to the cathode of the output diode and the other end connected to the load; And
Stabilization capacitor having one end connected to the other end of the inductor and the other end connected to the secondary side ground
Power supply comprising a. The method of claim 1,
And a rectifier for rectifying and smoothing commercial AC power and transferring the same to the power converter. The method of claim 11,
And an electromagnetic interference filter unit for filtering and transmitting the electromagnetic interference included in the commercial AC power to the rectifier.

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